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  • ddc:550.78
  • ddc:551.22
  • ddc:551.9
  • English  (148)
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  • 2020-2024  (101)
  • 2020-2023  (47)
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  • 1
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    Nitrogen and Phosphorus Control Soil Methane Uptake in Tropical Montane Forests (2021)
    Details
    Publication Date: 2022-04-04
    Description: Tropical forests contribute about one third to global annual CH4 uptake by soils. Understanding the factors that control the soil‐atmosphere exchange of CH4 at a large scale is a critical step to improve the CH4 flux estimate for tropical soils, which is presently poorly constrained. Since tropical forest degradation often involves shifts in nutrient availabilities, it is critical to evaluate how this will affect soil CH4 flux. Here, we report how nitrogen (N; 50 kg N ha−1 yr−1), phosphorus (P; 10 kg P ha−1 yr−1), and combined N + P additions affect soil CH4 fluxes across an elevation gradient of tropical montane forests. We measured soil CH4 fluxes in a nutrient application experiment at different elevations over a period of 5 years. Nutrient additions increased soil CH4 uptake after 4–5 years of treatment but effects were not uniform across elevations. At 1,000 m, where total soil P was high, we detected mainly N limitation of soil CH4 uptake. At 2,000 m, where total soil P was low, a strong P limitation of soil CH4 uptake was observed. At 3,000 m, where total P was low in the organic layer but high in mineral soil, we found N limitation of soil CH4 uptake. Our results show that projected increases of N and P depositions may increase soil CH4 uptake in tropical montane forests but the direction, magnitude, and timing of the effects will depend on forests' nutrient status and plant‐microbial competition for N and P.
    Description: Plain Language Summary: CH4 is a potent greenhouse gas that contributes to global warming. Tropical forests are a natural sink of CH4 but increasing nutrient depositions due to industrialization may alter the sink strength of tropical forests. Our results show that projected increases of nitrogen and phosphorus depositions may increase soil CH4 uptake in tropical montane forests but the direction, magnitude, and timing of the effects will depend on forests' nutrients and plant‐microbial competition.
    Description: Key Points: Projected increases in nitrogen and phosphorus depositions in the tropics will stimulate soil methane uptake in tropical montane forests. The direction, magnitude, and timing of nutrient deposition effects on soil methane uptake will depend on forests' nutrient status. Nutrient limitations on ecosystem processes have to be investigated in actual field conditions.
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.25625/XLNKNK
    Keywords: ddc:551.9 ; ddc:631.41
    Language: English
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  • 2
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    Iron Exports From Catchments Are Constrained by Redox Status and Topography (2022)
    Details
    Publication Date: 2022-04-04
    Description: Fe(III) hydroxides stabilize organic carbon (OC) and P in soils. Observations of rising stream Fe concentrations are controversially posited to result from a flushing of iron‐rich deeper soil layers or a decrease of competing electron acceptors inhibiting Fe reduction (NO3− $\mathrm{N}{{\mathrm{O}}_{3}}^{-}$ and SO42− $\mathrm{S}{{\mathrm{O}}_{4}}^{2-}$). Here, we argue that catchment topography constrains the release of Fe, OC, and P to streams. We therefore incubated organic topsoil and mineral subsoil and modified the availability of NO3− $\mathrm{N}{{\mathrm{O}}_{3}}^{-}$. We found that Fe leaching was highest in topsoil. Fe, OC, and P released at quantities proportional to their ratios in the source soil. Supply of NO3− $\mathrm{N}{{\mathrm{O}}_{3}}^{-}$ reduced Fe leaching to 18% and increased pore water OC:Fe and P:Fe ratios. Subsoil, however, was an insignificant Fe source (〈0.5%). Here, the leached quantities of Fe, OC and P were highly disproportionate to the soil source with an excess of released OC and P. We tested if experimental findings scale up using data from 88 German catchments representing gradients in NO3− $\mathrm{N}{{\mathrm{O}}_{3}}^{-}$ concentration and topography. Average stream Fe concentrations increased with decreasing NO3− $\mathrm{N}{{\mathrm{O}}_{3}}^{-}$ and were high in catchments with shallow topography where high groundwater levels support reductive processes and topsoils are hydrologically connected to streams; but Fe concentrations were low in catchments with steep topography where flow occurs primarily through subsoils. OC:Fe and P:Fe ratios in the streams similarly varied by NO3− $\mathrm{N}{{\mathrm{O}}_{3}}^{-}$ and topography. This corroborates the findings from the laboratory experiment and suggests that catchment topography and competing electron acceptors constrain the formation of Fe‐reducing conditions and control the release of Fe, OC, and P to streams.
    Description: Plain Language Summary: Iron is the second most abundant metal in the crust; its cycle is tightly connected to those of carbon, oxygen, and sulfur. The oxidized form (FeIII) is almost insoluble, but Fe can be mobilized by complexation or microbial Fe reduction. Both processes depend on availability of organic C. We found that Fe concentrations in streams were constrained by the topography of catchments and NO3− $\mathrm{N}{{\mathrm{O}}_{3}}^{-}$ abundance. Shallower catchments are characterized by higher groundwater tables connecting the organic topsoils efficiently to streams. NO3− $\mathrm{N}{{\mathrm{O}}_{3}}^{-}$ suppresses Fe reduction as a competing electron acceptor to Fe. We conclude that trends in soil wetness or atmospheric N deposition can change the stability of Fe and thus the release of PO43− $\mathrm{P}{{\mathrm{O}}_{4}}^{3-}$ and harmful metals to surface waters.
    Description: Key Points: Organic topsoils leach substantial amounts of Fe when incubated in the absence of NO3, a competing electron acceptor that inhibits Fe reduction. Shallow catchments with fluvially coupled topsoils and low NO3 availability release 200 fold more Fe than steep ones with high NO3 abundance. Catchment topography and NO3 availability explain 62%–64% of the variability of Fe concentration and OC:Fe and P:Fe ratios across 88 streams.
    Description: EFRE‐Europe
    Description: https://doi.org/10.4211/hs.43601618877945c5a46b715aa98db729
    Keywords: ddc:551.9
    Language: English
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  • 3
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    Water Isotopic Signature of Surface Snow Metamorphism in Antarctica (2021)
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    Publication Date: 2022-04-01
    Description: Water isotope ratios of ice cores are a key source of information on past temperatures. Through fractionation within the hydrological cycle, temperature is imprinted in the water isotopic composition of snowfalls. However, this signal of climatic interest is modified after deposition when snow remains at the surface exposed to the atmosphere. Comparing time series of surface snow isotopic composition at Dome C with satellite observations of surface snow metamorphism, we found that long summer periods without precipitation favor surface snow metamorphism altering the surface snow isotopic composition. Using excess parameters (combining D,17O, and 18O fractions) allow the identification of this alteration caused by sublimation and condensation of surface hoar. The combined measurement of all three isotopic compositions could help identifying ice core sections influenced by snow metamorphism in sites with very low snow accumulation.
    Description: Plain Language Summary: Water isotopes in ice core records are often used to reconstruct past climate temperature variations. Classically, the temperature signal is thought to be imprinted in water isotopes of precipitation, and then archived in the ice core as it falls, and in cold areas of Antarctica, piles up for very long period. Here, we show that the surface snow isotopic composition varies in between precipitation events, suggesting that there might be more than one contribution to the isotopic signal in ice core records. This is particularly important for low accumulation sites, where the snow at the surface remains exposed for very long time periods. The combined use of several isotopic ratios in surface snow helps us disentangle the processes that create this signal.
    Description: Key Points: During summer without precipitation, intense snow metamorphism shows a strong water isotopic signature. During summer without precipitation, intense snow metamorphism shows a strong water isotopic signature. The d‐excess and 17O‐excess of the snow is a proxy of snow metamorphism for low accumulation regions.
    Description: FP7 Ideas: European Research Council (FP7 Ideas) http://dx.doi.org/10.13039/100011199
    Description: Foundation Prince Albert of Monaco
    Description: Alexander von Humboldt‐Stiftung (Humboldt‐Stiftung) http://dx.doi.org/10.13039/100005156
    Description: DFG project CLIMAIC
    Description: https://doi.pangaea.de/10.1594/PANGAEA.934273
    Keywords: ddc:551.31 ; ddc:551.9
    Language: English
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  • 4
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    Impacts of Drying and Rewetting on the Radiocarbon Signature of Respired CO2 and Implications for Incubating Archived Soils (2021)
    Details
    Publication Date: 2022-04-01
    Description: The radiocarbon signature of respired CO2 (∆14C‐CO2) measured in laboratory soil incubations integrates contributions from soil carbon pools with a wide range of ages, making it a powerful model constraint. Incubating archived soils enriched by “bomb‐C” from mid‐20th century nuclear weapons testing would be even more powerful as it would enable us to trace this pulse over time. However, air‐drying and subsequent rewetting of archived soils, as well as storage duration, may alter the relative contribution to respiration from soil carbon pools with different cycling rates. We designed three experiments to assess air‐drying and rewetting effects on ∆14C‐CO2 with constant storage duration (Experiment 1), without storage (Experiment 2), and with variable storage duration (Experiment 3). We found that air‐drying and rewetting led to small but significant (α 〈 0.05) shifts in ∆14C‐CO2 relative to undried controls in all experiments, with grassland soils responding more strongly than forest soils. Storage duration (4–14 y) did not have a substantial effect. Mean differences (95% CIs) for experiments 1, 2, and 3 were: 23.3‰ (±6.6), 19.6‰ (±10.3), and 29.3‰ (±29.1) for grassland soils, versus −11.6‰ (±4.1), 12.7‰ (±8.5), and −24.2‰ (±13.2) for forest soils. Our results indicate that air‐drying and rewetting soils mobilizes a slightly older pool of carbon that would otherwise be inaccessible to microbes, an effect that persists throughout the incubation. However, as the bias in ∆14C‐CO2 from air‐drying and rewetting is small, measuring ∆14C‐CO2 in incubations of archived soils appears to be a promising technique for constraining soil carbon models.
    Description: Plain Language Summary: Soils play a key role in the global carbon cycle by sequestering carbon from the atmosphere for decades to millennia. However, it is unclear if they will continue to do so as the climate changes. Microbial decomposition of soil organic matter returns carbon back to the atmosphere, and radiocarbon dating of this returning CO2 (∆14C‐CO2) can be used to quantify how long carbon is stored in ecosystems. Incubating archived soils could provide unique insight into soil carbon sequestration potential by quantifying the change in ∆14C‐CO2 over time. However, air‐drying, duration of archiving, and subsequent rewetting of soils may bias estimates of sequestration potential by altering the balance of younger versus older carbon leaving the soil. We compared ∆14C‐CO2 from soils incubated with and without air‐drying and archiving, and found that the air‐dried soils appeared to release slightly older carbon than soils that had never been air‐dried. The amount of time the soils were archived did not have an effect. Since the bias from air‐drying and rewetting was small, incubating archived soils appears to be a promising technique for improving our ability to model soil carbon cycling under global climate change.
    Description: Key Points: ∆14C of CO2 measured in incubations of archived soils provides additional constraints for soil carbon models. Air‐drying and rewetting soils shifted the ∆14C of respired CO2 by 10‰–20‰ independent of the duration of storage. Differences in direction and magnitude of ∆14C‐CO2 shifts between forests and grasslands depended on sampling year and system C dynamics.
    Description: EC, H2020, H2020 Priority Excellent Science, H2020 European Research Council (ERC) http://dx.doi.org/10.13039/100010663
    Description: https://doi.org/10.5281/zenodo.4959705
    Keywords: ddc:551.9 ; ddc:631.41 ; ddc:550.724
    Language: English
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  • 5
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    Do tree species affect decadal changes in soil organic carbon and total nitrogen stocks in Danish common garden experiments? (2021)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2022-04-01
    Description: Temperate forest soils are often considered as an important sink for atmospheric carbon (C), thereby buffering anthropogenic CO2 emissions. However, the effect of tree species composition on the magnitude of this sink is unclear. We resampled a tree species common garden experiment (six sites) a decade after initial sampling to evaluate whether forest floor (FF) and topsoil organic carbon (Corg) and total nitrogen (Nt) stocks changed in dependence of tree species (Norway spruce—Picea abies L., European beech—Fagus sylvatica L., pedunculate oak—Quercus robur L., sycamore maple—Acer pseudoplatanus L., European ash—Fraxinus excelsior L. and small‐leaved lime—Tilia cordata L.). Two groups of species were identified in terms of Corg and Nt distribution: (1) Spruce with high Corg and Nt stocks in the FF developed as a mor humus layer which tended to have smaller Corg and Nt stocks and a wider Corg:Nt ratio in the mineral topsoil, and (2) the broadleaved species, of which ash and maple distinguished most clearly from spruce by very low Corg and Nt stocks in the FF developed as mull humus layer, had greater Corg and Nt stocks, and narrow Corg:Nt ratios in the mineral topsoil. Over 11 years, FF Corg and Nt stocks increased most under spruce, while small decreases in bulk mineral soil (esp. in 0–15 cm and 0–30 cm depth) Corg and Nt stocks dominated irrespective of species. Observed decadal changes were associated with site‐related and tree species‐mediated soil properties in a way that hinted towards short‐term accumulation and mineralisation dynamics of easily available organic substances. We found no indication for Corg stabilisation. However, results indicated increasing Nt stabilisation with increasing biomass of burrowing earthworms, which were highest under ash, lime and maple and lowest under spruce. Highlights We studied if tree species differences in topsoil Corg and Nt stocks substantiate after a decade. The study is unique in its repeated soil sampling in a multisite common garden experiment. Forest floors increased under spruce, but topsoil stocks decreased irrespective of species. Changes were of short‐term nature. Nitrogen was most stable under arbuscular mycorrhizal species.
    Description: Deutsche Forschungsgemeinschaff (DFG)
    Keywords: ddc:551.9 ; ddc:631.41
    Language: English
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  • 6
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    Assessing the robustness of carbonate‐associated sulfate during hydrothermal dolomitization of the Latemar platform, Italy (2021)
    Details
    Publication Date: 2022-03-30
    Description: Carbonate‐associated sulfate (CAS) is an important proxy for reconstructing marine sulfur cycling throughout Earth's history. In order to assess the impact of carbonate neomorphism on δ34SCAS data, a mineralogical‐spatial transect from early diagenetic limestone into low‐temperature hydrothermal dolostone was analyzed in the middle Triassic Latemar platform interior, northern Italy. This study addresses the yet unconstrained question whether hydrothermal dolostone preserves a marine δ34SCAS signature and, hence, might represent an archive for past seawater sulfate. In this study, δ34SCAS values were measured in low‐temperature hydrothermal dolostone and compared with data from their corresponding precursor limestone. Results shown here reveal that δ34SCAS values for dolostone and precursor limestone are indistinguishable. This points to a rock‐buffered middle Triassic marine δ34S signature not affected by hydrothermal alteration. Hence, hydrothermal dolostone represents, under favorable conditions, an archive for unraveling past marine sulfur cycling.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551.9 ; ddc:552
    Language: English
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  • 7
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    Formation of chondrule analogs aboard the International Space Station (2021)
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    Publication Date: 2022-03-30
    Description: Chondrules are thought to play a crucial role in planet formation, but the mechanisms leading to their formation are still a matter of unresolved discussion. So far, experiments designed to understand chondrule formation conditions have been carried out only under the influence of terrestrial gravity. In order to introduce more realistic conditions, we developed a chondrule formation experiment, which was carried out at long‐term microgravity aboard the International Space Station. In this experiment, freely levitating forsterite (Mg2SiO4) dust particles were exposed to electric arc discharges, thus simulating chondrule formation via nebular lightning. The arc discharges were able to melt single dust particles completely, which then crystallized with very high cooling rates of 〉105 K h−1. The crystals in the spherules show a crystallographic preferred orientation of the [010] axes perpendicular to the spherule surface, similar to the preferred orientation observed in some natural chondrules. This microstructure is probably the result of crystallization under microgravity conditions. Furthermore, the spherules interacted with the surrounding gas during crystallization. We show that this type of experiment is able to form spherules, which show some similarities with the morphology of chondrules despite very short heating pulses and high cooling rates.
    Description: Carl Zeiss Meditec AG http://dx.doi.org/10.13039/501100002806
    Description: BIOVIA Science Ambassador program
    Description: Bundesministerium für Wirtschaft und Energie http://dx.doi.org/10.13039/501100006360
    Description: Deutsches Zentrum für Luft‐ und Raumfahrt http://dx.doi.org/10.13039/501100002946
    Description: NanoRacks LLC
    Description: DreamUp
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Dr. Rolf M. Schwiete Stiftung
    Keywords: ddc:549 ; ddc:550.78
    Language: English
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  • 8
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    Increased petrogenic and biospheric organic carbon burial in sub‐Antarctic fjord sediments in response to recent glacier retreat (2021)
    John Wiley & Sons, Inc. | Hoboken, USA
    Details
    Publication Date: 2022-03-30
    Description: Fjords are recognized as hotspots of organic carbon (OC) burial in the coastal ocean. In fjords with glaciated catchments, glacier discharge carries large amounts of suspended matter. This sedimentary load includes OC from bedrock and terrigenous sources (modern vegetation, peat, soil deposits), which is either buried in the fjord or remineralized during export, acting as a potential source of CO2 to the atmosphere. In sub‐Antarctic South Georgia, fjord‐terminating glaciers have been retreating during the past decades, likely as a response to changing climate conditions. We determine sources of OC in surface sediments of Cumberland Bay, South Georgia, using lipid biomarkers and the bulk 14C isotopic composition, and quantify OC burial at present and for the time period of documented glacier retreat (between 1958 and 2017). Petrogenic OC is the dominant type of OC in proximity to the present‐day calving fronts (60.4 ± 1.4% to 73.8 ± 2.6%) and decreases to 14.0 ± 2.7% outside the fjord, indicating that petrogenic OC is effectively buried in the fjord. Beside of marine OC, terrigenous OC comprises 2.7 ± 0.5% to 7.9 ± 5.9% and is mostly derived from modern plants and Holocene peat and soil deposits that are eroded along the flanks of the fjord, rather than released by the retreating fjord glaciers. We estimate that the retreat of tidewater glaciers between 1958 and 2017 led to an increase in petrogenic carbon accumulation of 22% in Cumberland West Bay and 6.5% in Cumberland East Bay, suggesting that successive glacier retreat does not only release petrogenic OC into the fjord, but also increases the capacity of OC burial.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:552 ; ddc:551.9
    Language: English
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  • 9
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    Past and Future Climate Variability Uncertainties in the Global Carbon Budget Using the MPI Grand Ensemble (2021)
    Details
    Publication Date: 2022-03-25
    Description: Quantifying the anthropogenic fluxes of CO2 is important to understand the evolution of carbon sink capacities, on which the required strength of our mitigation efforts directly depends. For the historical period, the global carbon budget (GCB) can be compiled from observations and model simulations as is done annually in the Global Carbon Project's (GCP) carbon budgets. However, the historical budget only considers a single realization of the Earth system and cannot account for internal climate variability. Understanding the distribution of internal climate variability is critical for predicting the future carbon budget terms and uncertainties. We present here a decomposition of the GCB for the historical period and the RCP4.5 scenario using single‐model large ensemble simulations from the Max Planck Institute Grand Ensemble (MPI‐GE) to capture internal variability. We calculate uncertainty ranges for the natural sinks and anthropogenic emissions that arise from internal climate variability, and by using this distribution, we investigate the likelihood of historical fluxes with respect to plausible climate states. Our results show these likelihoods have substantial fluctuations due to internal variability, which are partially related to El Niño‐Southern Oscillation (ENSO). We find that the largest internal variability in the MPI‐GE stems from the natural land sink and its increasing carbon stocks over time. The allowable fossil fuel emissions consistent with 3 C warming may be between 9 and 18 Pg C yr−1. The MPI‐GE is generally consistent with GCP's global budgets with the notable exception of land‐use change emissions in recent decades, highlighting that human action is inconsistent with climate mitigation goals.
    Description: Key Points: We use a single‐model large ensemble to estimate uncertainties from internal climate variability in the global carbon budget. The land sink accounts for most internal climate uncertainty which may permit 9–18 Pg C yr−1 in allowable emissions by 2050 (for 3°C warming).
    Description: European Union's Horizon 2020
    Keywords: ddc:551.9 ; ddc:551.6
    Language: English
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  • 10
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    Slow Slip Triggers the 2018 Mw 6.9 Zakynthos Earthquake Within the Weakly Locked Hellenic Subduction System, Greece (2021)
    Details
    Publication Date: 2022-03-25
    Description: Slow slip events (SSEs) at subduction zones can precede large‐magnitude earthquakes and may serve as precursor indicators, but the triggering of earthquakes by slow slip remains insufficiently understood. Here, we combine geodetic, Coulomb wedge and Coulomb failure‐stress models with seismological data to explore the potential causal relationship between two SSEs and the 2018 Mw 6.9 Zakynthos Earthquake within the Hellenic Subduction System. We show that both SSEs released up to 10 mm of aseismic slip on the plate‐interface and were accompanied by an increase in upper‐plate seismicity rate. While the first SSE in late 2014 generated only mild Coulomb failure stress changes (≤3 kPa), that were nevertheless sufficient to destabilize faults of various kinematics in the overriding plate, the second SSE in 2018 caused stress changes up to 25 kPa prior to the mainshock. Collectively, these stress changes affected a highly overpressured and mechanically weak forearc, whose state of stress fluctuated between horizontal deviatoric compression and tension during the years preceding the Zakynthos Earthquake. We conclude that this configuration facilitated episodes of aseismic and seismic deformation that ultimately triggered the Zakynthos Earthquake.
    Description: Key Points: Two slow‐slip events (each ≤10 mm) on the plate‐interface of the western Hellenic subduction system are explored. Stress perturbations due to slow‐slip promoted failure of upper‐plate faults and triggered the 2018 Mw 6.9 Zakynthos Earthquake. The forearc is mechanically weak and small friction changes on the megathrust with time, may reverse the stress‐state in the upper‐plate.
    Keywords: ddc:551.22
    Language: English
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  • 11
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    The Spectrum of Slip Behaviors of a Granular Fault Gouge Analogue Governed by Rate and State Friction (2021)
    Details
    Publication Date: 2022-03-25
    Description: Currently, it is unknown how seismic and aseismic slip influences the recurrence and magnitude of earthquakes. Modern seismic hazard assessment is therefore based on statistics combined with numerical simulations of fault slip and stress transfer. To improve the underlying statistical models we conduct low velocity shear experiments with glass micro‐beads as fault gouge analogue at confining stresses of 5–20 kPa. As a result, we show that characteristic slip events emerge, ranging from fast and large slip to small scale oscillating creep and stable sliding. In particular, we observe small scale slip events that occur immediately before large scale slip events for a specific set of experiments. Similar to natural faults we find a separation of scales by several orders of magnitude for slow events and fast events. Enhanced creep and transient dilatational events pinpoint that the granular analogue is close to failure. From slide‐hold‐slide tests, we find that the rate‐and‐state properties are in the same range as estimates for natural faults and fault rocks. The fault shows velocity weakening characteristics with a reduction of frictional strength between 0.8% and 1.3% per e‐fold increase in sliding velocity. Furthermore, the slip modes that are observed in the normal shear experiments are in good agreement with analytical solutions. Our findings highlight the influence of micromechanical processes on macroscopic fault behavior. The comprehensive data set associated with this study can act as a benchmark for numerical simulations and improve the understanding of observations of natural faults.
    Description: Plain Language Summary: Earthquakes occur when two continental plates slide past each other. The motion is concentrated at the interface of the two plates which is called a fault. In many cases the fault is filled with granular material, called gouge, that supports the pressure between the plates. Therefore, the properties of this gouge determine how fast and how large an earthquake can be. It also has an influence on the time between earthquakes. In our study, we examine a simplified version of a fault gouge in a simple small‐scale model. Instead of rock material we use glass beads and measure how different conditions affect the motion of the model. We find that our model reproduces features of fault gouge because it shows similar behavior. When there is no motion our model fault becomes stronger with a rate equal to fault gouge. Also, the type of strengthening is analogous to fault gouge. During slip, the glass beads become weaker as the slip velocity increases in a similar manner as in natural faults. These results improve the understanding of computer simulations and natural observations.
    Description: Key Points: Slip modes in granular gouge are akin to natural fault slip. Glass beads are a suitable granular analogue for fault gouge and show rate‐and‐state dependent friction. Enhanced creep and small scale events are signals for imminent failure and indicate fault criticality.
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Description: 亥姆霍兹联合会致力, Helmholtz‐Zentrum Potsdam ‐ Deutsches GeoForschungsZentrum GFZ (GFZ) http://dx.doi.org/10.13039/501100010956
    Keywords: ddc:550.78
    Language: English
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  • 12
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    Age Uncertainty in Recurrence Analysis of Paleoseismic Records (2021)
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    Publication Date: 2022-03-24
    Description: Determining the aperiodicity of large earthquake recurrences is key to forecast future rupture behavior. Aperiodicity is classically expressed as the coefficient of variation of recurrence intervals, though the recent trend to express it as burstiness is more intuitive and avoids minor inaccuracies. Due to the underestimation of burstiness in records with a low number of recurrence intervals, the paradigm is to obtain long paleoseismic records with many events. Here, we present a suite of synthetic paleoseismic records designed around the Weibull and inverse Gaussian distributions that demonstrate that age uncertainty relative to the mean recurrence interval causes overestimation of burstiness. The effects of overestimation and underestimation interact and give complex results for accurate estimates of aperiodicity. Furthermore, we show that the way recurrence intervals are sampled from a paleoseismic record can have strong influences on the resulting statistic and its implication for probabilistic seismic hazard assessment. Comparing values of burstiness between paleoseismic records should therefore be done with caution.
    Description: Plain Language Summary: To forecast future earthquake activity, paleoseismologists aim to have many events in a single sedimentary record to estimate the periodicity of an earthquake sequence with as little uncertainty as possible. This focus on the number of events is not wrong, but event age uncertainty is another—often neglected and not yet described—source of uncertainty that can interfere in estimating periodicity correctly. In this study, we show in what way and by how much event age uncertainty affects the uncertainty in periodicity. We create a model of many different artificial earthquake sequences. For our model setup, we choose: (1) two types of patterns; (2) six degrees of periodicity; (3) 10 different levels of event age uncertainty; and (4) a wide range of number of events (from 4 to 101 events). Then we create 50,000 earthquake sequences for each unique combination within this spectrum and analyze the variability in periodicity. We find that low number of events underestimates periodicity and high age uncertainty overestimates periodicity. Having many events in a record is more important, if the earthquake sequence is not periodic. Having accurately dated events is more important, if the earthquake sequence is periodic.
    Description: Key Points: Low number of recurrence intervals in paleoseismic records underestimates aperiodicity. High age uncertainty relative to the mean recurrence interval in paleoseismic records overestimates aperiodicity. For calculating coefficient of variation and burstiness it matters how recurrence intervals are sampled from records.
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551.22
    Language: English
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  • 13
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    Last Glacial central Mediterranean hydrology inferred from Lake Trasimeno’s (Italy) calcium carbonate geochemistry (2021)
    Details
    Publication Date: 2022-03-24
    Description: There is still a paucity of hydrological data explaining the relationship between (rapid, millennial‐scale) climate forcing and Mediterranean rainfall since the Last Glacial. We show that distinct lake‐level fluctuations at Lake Trasimeno (Italy) are associated with changing aridity in the central Mediterranean during the last ~47 800 years. The lake‐level fluctuations are reconstructed based on carbonate mineral content and carbonate mineral species, as well as the stable oxygen and carbon isotope (δ18O and δ13C) geochemistry of endogenic carbonates. Low lake levels are linked to high carbonate, Mg‐calcite and aragonite contents, and high δ18O and δ13C values. Inferred hydrological changes are linked to glacial–interglacial and, tentatively within the limitations of our chronology, to millennial‐scale climate variability as well as the intensity of the Atlantic Meridional Overturning Circulation (AMOC). Prior to the Last Glacial Maximum (LGM), during intervals equivalent to Marine Isotope Stage 3 (MIS 3), a stronger AMOC associated with Greenland interstadial periods (Dansgaard/Oeschger (D/O) warm periods) and stronger Asian monsoon probably coincide with increased precipitation in central Italy as inferred from high lake levels at Lake Trasimeno. Periods of weak AMOC intensity such as during Greenland stadials (D/O cold periods), during Heinrich events, and weak Asian monsoons are correlated with lake level lowstands, which imply relatively dry conditions in central Italy. Lake Trasimeno’s water level during the LGM and the Lateglacial (MIS 2) is relatively stable, with recorded changes showing distinct similarities to orbital configurations. Although muted, high latitude climate forcing is still evident in the data during peak glacial conditions. The transition from D/O‐like hydrological variability at Lake Trasimeno during MIS 3 to orbitally controlled fluctuations during the Lateglacial to Holocene transition coincides with an increasing amplitude in local winter and summer insolation, probably indicating increasing seasonality and a larger temperature gradient between low‐ and high‐latitude settings.
    Description: Deutscher Akademischer Austauschdienst http://dx.doi.org/10.13039/501100001655
    Keywords: ddc:551.9
    Language: English
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    Detrital apatite geochemistry and thermochronology from the Oligocene/Miocene Alpine foreland record the early exhumation of the Tauern Window (2021)
    Details
    Publication Date: 2022-03-24
    Description: The early exhumation history of the Tauern Window in the European Eastern Alps and its surface expression is poorly dated and quantified, partly because thermochronological and provenance information are sparse from the Upper Austrian Northern Alpine Foreland Basin. For the first time, we combine a single‐grain double‐dating approach (Apatite Fission Track and U‐Pb dating) with trace‐element geochemistry analysis on the same apatites to reconstruct the provenance and exhumation history of the late Oligocene/early Miocene Eastern Alps. The results from 22 samples from the Chattian to Burdigalian sedimentary infill of the Upper Austrian Northern Alpine Foreland Basin were integrated with a 3D seismic‐reflection data set and published stratigraphic reports. Our highly discriminative data set indicates an increasing proportion of apatites (from 6% to 23%) with Sr/Y values 〈0.1 up‐section and an increasing amount of apatites (from 24% to 38%) containing 〉1,000 ppm light rare‐earth elements from Chattian to Burdigalian time. The number of U‐Pb ages with acceptable uncertainties increases from 40% to 59% up‐section, with mostly late Variscan/Permian ages, while an increasing number of grains (10%–27%) have Eocene or younger apatite fission track cooling ages. The changes in the apatite trace‐element geochemistry and U‐Pb data mirror increased sediment input from an ≥upper amphibolite‐facies metamorphic source of late Variscan/Permian age – probably the Ötztal‐Bundschuh nappe system – accompanied by increasing exhumation rates indicated by decreasing apatite fission track lag times. We attribute these changes to the surface response to upright folding and doming in the Penninic units of the future Tauern Window starting at 29–27 Ma. This early period of exhumation (0.3–0.6 mm/a) is triggered by early Adriatic indentation along the Giudicarie Fault System.
    Description: Science Foundation Ireland http://dx.doi.org/10.13039/501100001602
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551.701 ; ddc:551.9
    Language: English
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    Tephra Deposition and Bonding With Reactive Oxides Enhances Burial of Organic Carbon in the Bering Sea (2021)
    Details
    Publication Date: 2022-03-24
    Description: Preservation of organic carbon (OC) in marine sediments exerts a major control on the cycling of carbon in the Earth system. In these marine environments, OC preservation may be enhanced by diagenetic reactions in locations where deposition of fragmental volcanic material called tephra occurs. While the mechanisms by which this process occurs are well understood, site‐specific studies of this process are limited. Here, we report a study of sediments from the Bering Sea (IODP Site U1339D) to investigate the effects of marine tephra deposition on carbon cycling during the Pleistocene and Holocene. Our results suggest that tephra layers are loci of OC burial with distinct δ13C values, and that this process is primarily linked to bonding of OC with reactive metals, accounting for ∼80% of all OC within tephra layers. In addition, distribution of reactive metals from the tephra into non‐volcanic sediments above and below the tephra layers enhances OC preservation in these sediments, with ∼33% of OC bound to reactive phases. Importantly, OC‐Fe coupling is evident in sediments 〉700,000 years old. Thus, these interactions may help explain the observed preservation of OC in ancient marine sediments.
    Description: Plain Language Summary: The burial of organic carbon (OC) in marine sediments is one of the major carbon sinks on Earth, meaning that it removes carbon dioxide from the ocean‐atmosphere system. However, the speed at which burial occurs varies across the globe, and is dependent on a range of factors, from the amount of nutrients in the water column, to the type of sediment. Despite evidence suggesting that when tephra is deposited to the seafloor carbon burial is enhanced, very little work has been done to investigate this process. We have therefore analyzed sediments from the Bering Sea, where volcanoes from the Aleutian Islands and Kamchatka regularly deposit tephra in the ocean. We found that OC burial is indeed associated with ash deposition, and importantly, that OC is preserved in the ash layers themselves. We show here that this carbon is preserved effectively because of chemical reactions between the OC and reactive iron, which is released by the ash, creating conditions which preserve carbon for hundreds of thousands of years.
    Description: Key Points: Tephra layers are loci of marine organic carbon (OC) burial with distinct carbon isotopic compositions. Preservation primarily linked to association of OC with reactive iron phases, accounting for ∼80% of all OC in tephra layers. OC‐reactive Fe coupling is observed in sediments 〉700,000 years old, indicating long‐term persistence of these complexes.
    Description: NERC
    Keywords: ddc:551.9
    Language: English
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    Effects of CO2 and Ocean Mixing on Miocene and Pliocene Temperature Gradients (2022)
    Details
    Publication Date: 2022-03-28
    Description: Cenozoic climate changes have been linked to tectonic activity and variations in atmospheric CO2 concentrations. Here, we present Miocene and Pliocene sensitivity experiments performed with the climate model COSMOS. The experiments contain changes with respect to paleogeography, ocean gateway configuration, and atmospheric CO2 concentrations, as well as a range of vertical mixing coefficients in the ocean. For the mid‐Miocene, we show that the impact of ocean mixing on surface temperature is comparable to the effect of the possible range in reconstructed CO2 concentrations. In combination with stronger vertical mixing, relatively moderate CO2 concentrations of 450 ppmv enable global‐mean surface, deep‐water, and meridional temperature characteristics representative of mid‐Miocene Climatic Optimum (MMCO) reconstructions. The Miocene climate shows a reduced meridional temperature gradient and reduced seasonality. In the case of enhanced mixing, surface and deep ocean temperatures show significant warming of up to 5–10°C and an Arctic temperature anomaly of 〉12°C. In the Pliocene simulations, the impact of vertical mixing and CO2 is less important for the deep ocean, which we interpret as a different sensitivity dependence on the background state and mixed layer dynamics. We find a significant reduction in surface albedo and effective emissivity for either a high level of atmospheric CO2 or increased vertical mixing. Our mixing sensitivity experiments provide a warm deep ocean via ocean heat uptake. We propose that the mixing hypothesis can be tested by reconstructions of the thermocline and seasonal paleoclimate data indicating a lower seasonality relative to today.
    Description: Plain Language Summary: Cenozoic climate changes have been associated with tectonic changes and altered atmospheric CO2 concentrations. Here, we present Miocene and Pliocene computer simulations where we changed paleogeography, ocean gateways, and atmospheric CO2 concentrations as well as vertical mixing in the ocean. We show that the effect of ocean mixing on temperature is comparable to the respective effect of a possible range of CO2 concentrations. In combination with stronger vertical mixing, relatively moderate CO2 concentrations of 450 ppmv allow surface and deep‐water temperatures representative for reconstructions of the climate optimum of the mid‐Miocene. In the Pliocene simulations, the influence of vertical mixing and CO2 is less important than in the Miocene. We provide a possible mechanism of ocean heat absorption, albedo, and emissivity changes including a deeper oceanic mixing layer and a lower seasonality in the Miocene compared to today.
    Description: Key Points: Miocene experiment with standard mixing and atmospheric CO2 of 600 ppm captures large‐scale temperature characteristics of the mid‐Miocene. With enhanced ocean mixing the temperature characteristics and meridional temperature gradient can be reproduced with a CO2 level of 450 ppm. Miocene shows a strong warming at polar latitudes and reduced seasonality, vertical mixing, and CO2 are less important for the Pliocene.
    Description: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) http://dx.doi.org/10.13039/501100003207
    Description: Helmholtz Association (亥姆霍兹联合会致力) http://dx.doi.org/10.13039/501100009318
    Description: Helmholtz Climate Initiative RE‐KLIM
    Keywords: ddc:550.78
    Language: English
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    Chemical Evolution of the Exceptional Arctic Stratospheric Winter 2019/2020 Compared to Previous Arctic and Antarctic Winters (2021)
    Details
    Publication Date: 2022-03-28
    Description: The winter 2019/2020 showed the lowest ozone mixing ratios ever observed in the Arctic winter stratosphere. It was the coldest Arctic stratospheric winter on record and was characterized by an unusually strong and long‐lasting polar vortex. We study the chemical evolution and ozone depletion in the winter 2019/2020 using the global Chemistry and Transport Model ATLAS. We examine whether the chemical processes in 2019/2020 are more characteristic of typical conditions in Antarctic winters or in average Arctic winters. Model runs for the winter 2019/2020 are compared to simulations of the Arctic winters 2004/2005, 2009/2010, and 2010/2011 and of the Antarctic winters 2006 and 2011, to assess differences in chemical evolution in winters with different meteorological conditions. In some respects, the winter 2019/2020 (and also the winter 2010/2011) was a hybrid between Arctic and Antarctic conditions, for example, with respect to the fraction of chlorine deactivation into HCl versus ClONO2, the amount of denitrification, and the importance of the heterogeneous HOCl + HCl reaction for chlorine activation. The pronounced ozone minimum of less than 0.2 ppm at about 450 K potential temperature that was observed in about 20% of the polar vortex area in 2019/2020 was caused by exceptionally long periods in the history of these air masses with low temperatures in sunlight. Based on a simple extrapolation of observed loss rates, only an additional 21–46 h spent below the upper temperature limit for polar stratospheric cloud formation and in sunlight would have been necessary to reduce ozone to near zero values (0.05 ppm) in these parts of the vortex.
    Description: Key Points: The Arctic stratospheric winter 2019/2020 showed the lowest ozone mixing ratios ever observed and was one of the coldest on record. Chemical evolution of the Arctic winter 2019/2020 was a hybrid between typical Arctic and typical Antarctic conditions. Only an additional 21–46 h below PSC temperatures and in sunlight would have been necessary to reduce ozone to near zero locally.
    Description: International Multidisciplinary Drifting Observatory for the Study of the Arctic Climate (MOSAiC)
    Keywords: ddc:551.5 ; ddc:551.9
    Language: English
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    Spatio‐Temporal Evolution of Earthquake Static Stress Drop Values in the 2016–2017 Central Italy Seismic Sequence (2021)
    Details
    Publication Date: 2022-03-29
    Description: The static stress drop of an earthquake is an indicator of the stress state of a specific fault before rupture initiation. The stress state is primarily controlled by the ambient stress field, fault strength, fault complexity, and the presence of fluids. This study aims to investigate the spatio‐temporal distribution of static stress drop values of the 2016–2017 multi‐fault rupture seismic sequence in central Italy, which includes three earthquakes with Mw ≥ 5.9 (Amatrice, Visso, and Norcia earthquakes), and over 95,000 aftershocks (M 0.5–6.5). We estimate stress drop values using a circular crack model with corner frequency and seismic moment estimates from single‐spectra fitting, a cluster‐event method, and spectral‐ratio fitting. The temporal distribution of stress drop values shows an apparent increase of stress drop following a large earthquake (Mw ≥ 5.9). The spatial distribution shows comparably high stress drop values for early aftershocks surrounding the mainshock rupture area. High stress drop events correlate with fault complexity, such as fault intersections at depth and reactivated thrust fronts. We observe a constant stress drop for Mw ≥ ∼3, in contrast to previous studies. Instrument response and signal‐to‐noise bandwidth limitations likely govern the observed decrease in stress drop with decreasing magnitude for events with Mw ≤ 3. The spatio‐temporal distribution of stress drop values in a complex seismic sequence could support a more complete understanding of the earthquake rupture process and the evolution of seismic sequences. It could also highlight areas where stress loading is focused, which would have implications for short and intermediate term seismic hazard estimates.
    Description: Plain Language Summary: The ongoing earthquake sequence that began in 2016 in central Italy has produced a significant physical imprint on the earth's surface from the rupture of the three largest events, and has changed the state of stress within the crust. The earthquakes release stored stress in some regions, which can be measured indirectly by the waveforms recorded on seismometers (seismograms), and increase stress in others. Here we analyze seismograms, including those of numerous small earthquakes, to estimate source properties such as the physical size of the rupture surface and the corresponding fault slip. Source properties relate to the amount of stress released by an earthquake and are relevant to learning about the fault rupture process and the redistribution of stress during the evolution of a seismic sequence. We use a combination of approaches to find that the occurrence of large earthquakes leads to a temporal increase of stress in the vicinity of the ruptured fault, and that high stress release correlates with places where faults intersect in the subsurface. Our findings provide a more comprehensive picture of the complex seismic sequence and highlight areas that could influence short and intermediate term seismic hazard estimates.
    Description: Key Points: The AVN seismic sequence shows significant spatio‐temporal variations in stress drop values. Higher stress drop values correlate with increasing fault complexity and stress field heterogeneity. Instrument response and signal‐to‐noise limitations likely govern stress drop scaling for events with for M 〈 ∼3.
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551.22
    Language: English
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    Probability Distributions of Radiocarbon in Open Linear Compartmental Systems at Steady‐State (2022)
    Details
    Publication Date: 2022-06-26
    Description: Radiocarbon (14C) is commonly used as a tracer of the carbon cycle to determine how fast carbon moves between different reservoirs such as plants, soils, rivers, or oceans. However such studies mostly emphasize the mean value (as Δ14C) of an unknown probability distribution. We introduce a novel algorithm to compute Δ14C distributions from knowledge of the age distribution of carbon in linear compartmental systems at steady‐state. Our results demonstrate that the shape of the distributions might differ according to the speed of cycling of ecosystem compartments and their connectivity within the system, and might contain multiple peaks and long tails. The distributions are also sensitive to the variations of Δ14C in the atmosphere over time, as influenced by the counteracting anthropogenic effects of fossil‐fuel emissions (14C‐free) and nuclear weapons testing (excess 14C). Lastly, we discuss insights that such distributions can offer for sampling and design of experiments aiming to capture the precise variance of Δ14C values present in the multi‐compartmental ecosystems.
    Description: Plain Language Summary: Radiocarbon (14C) is a radioactive isotope of carbon prominent in environmental sciences for tracing the dynamics of ecosystems, especially as recent changes in atmospheric radiocarbon allow tracking excess 14C created by nuclear weapons testing in the atmosphere on timescales shorter than what can be determined using radioactive decay. For climate change mitigation, a crucial uncertainty is the time carbon captured through photosynthesis spends in ecosystems before being released. For this purpose, radiocarbon can be valuable as a biological tracer; however, it is necessary to accurately link the real age of carbon and its radiocarbon age, as they usually differ. Forests and soils are open systems, connecting components with intrinsically different cycling timescales, so that the mean age comes from an age distribution that is usually unknown. Here, we developed an algorithm to compute the 14C contents for models consisting of multiple interconnected carbon pools. Our approach offers more accurate estimations of the mean 14C content of the system and computations of the distribution of 14C within the system at different points in time. Results obtained from this method can provide additional insights on the dynamics of the carbon cycle in multiple compartments, and can help to better interpret observations.
    Description: Key Points: Probability distributions of radiocarbon in ecosystem compartments can be derived from carbon age distributions. The shape of these distributions vary according to the speed of carbon cycling and the year of observation. Probability distributions of radiocarbon provide insights to study carbon dynamics and to interpret radiocarbon data.
    Description: Bundesministerium für Bildung und Forschung (BMBF) http://dx.doi.org/10.13039/501100002347
    Description: Max‐Planck‐Gesellschaft (MPG) http://dx.doi.org/10.13039/501100004189
    Description: https://doi.org/10.5281/zenodo.6373329
    Keywords: ddc:551.9
    Language: English
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    Multi‐Band Raman Analysis of Radiation Damage in Zircon for Thermochronology: Partial Annealing and Mixed Signals (2022)
    Details
    Publication Date: 2022-06-24
    Description: Four zircon Raman bands were previously calibrated to give consistent estimates of the accumulated self‐irradiation α‐dose in unannealed volcanic samples. Partial annealing of radiation damage produces inconsistent values because of differences in the relative annealing sensitivities. The damage estimates based on the external rotation band (DER) at ∼356 cm−1 and that based on the ν2(SiO4) band (D2) at ∼438 cm−1 are the most and least sensitive to damage annealing. The D2/DER‐ratio thus provides a numerical estimate of the extent of geologic annealing that a zircon sample has experienced. This ratio characterizes the thermal history of a zircon sample but also its state of radiation damage during the course of its geologic history, and thus the manner in which this state influences other thermochronologic methods. Meaningful interpretation of the zircon Raman age requires that the spectra are free of measurement artifacts. The major artifacts result from micrometer‐scale gradients of the damage densities within a zircon grain due to uranium and thorium zoning. The micrometer‐sized sampled volume may span different densities, producing overlapping spectra, causing apparent peak broadening, overestimated damage densities, and zircon Raman ages. The D3/D2‐ratio of the damage densities calculated from the ν3(SiO4) and ν2(SiO4) bands, most and least affected by overlap, is an efficient indicator of a meaningless signal. It reveals overlap in annealed and unannealed samples, because the used bands have similar responses to annealing. Multi‐band Raman maps can be converted to damage‐ratio maps for screening zircon mounts, and selecting spots for thermochronologic investigations.
    Description: Plain Language Summary: Radioactive processes cause damage to the lattice of zircon crystals. This damage can be measured with a Raman instrument. Such measurements are important for methods determining the ages and thermal histories of zircon grains in rocks. Thus, the Raman measurements must be reliable and meaningful. This work proposes tools for detecting effects that hinder the interpretation of zircon Raman data. These effects are mixed signals and loss of damage due to exposure to elevated temperatures in the geologic environment. Zircon Raman spectra have different bands that respond differently to mixed signals and temperature. The ratio of the damage estimates from the least and most temperature‐sensitive bands thus indicates partial annealing. Raman spectra of zoned zircons often straddle areas with different lattice damage. Their overlapping signals cause artificial band broadening, and a damage overestimation. The ratio of the damage estimated from the least and the most affected bands identifies mixed signals and allows to reject unsuitable samples. The damage ratios can also be plotted in maps for damage screening and for selecting optimal spots for measurements.
    Description: Key Points: Annealing and inhomogeneous damage are two main factors hindering radiation‐damage estimation for zircon Raman dating. Comparison of internal and external Raman bandwidths allows to detect partial annealing of radiation damage in zircon. Comparison of internal Raman bandwidths allows to detect artifactual broadening in zoned zircon.
    Description: Studienstiftung des Deutschen Volkes (Studienstiftung) http://dx.doi.org/10.13039/501100004350
    Description: http://dx.doi.org/10.25532/OPARA-155
    Keywords: ddc:549 ; ddc:551.9
    Language: English
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    Electrochemical Properties of Peat Particulate Organic Matter on a Global Scale: Relation to Peat Chemistry and Degree of Decomposition (2022)
    Details
    Publication Date: 2022-06-22
    Description: Methane production in peatlands is controlled by the availability of electron acceptors for microbial respiration, including peat dissolved organic matter (DOM) and particulate organic matter (POM). Despite the much larger mass of POM in peat, knowledge on the ranges of its electron transfer capacities—electron accepting capacity (EAC), and electron donating capacity (EDC)—is scarce in comparison to DOM and humic and fulvic acids. Moreover, it is unclear how peat POM chemistry and decomposition relate to its EAC and EDC. To address these knowledge gaps, we compiled peat samples with varying carbon contents from mid to high latitude peatlands and analyzed their EACPOM and EDCPOM, element ratios, decomposition indicators, and relative amounts of molecular structures as derived from mid infrared spectra. Peat EACPOM and EDCPOM are smaller (per gram carbon) than EAC and EDC of DOM and terrestrial and aquatic humic and fulvic acids and are highly variable within and between sites. Both are small in highly decomposed peat, unless it has larger amounts of quinones and phenols. Element ratio‐based models failed to predict EACPOM and EDCPOM, while mid infrared spectra‐based models can predict peat EACPOM to a large extent, but not EDCPOM. We suggest a conceptual model that describes how vegetation chemistry and decomposition control polymeric phenol and quinone contents as drivers of peat EDCPOM and EACPOM. The conceptual model implies that we need mechanistic models or spatially resolved measurements to understand the variability in peat EDCPOM and EACPOM and thus its role in controlling methane formation.
    Description: Plain Language Summary: Peatlands accumulated large amounts of carbon via photosynthesis and slow decomposition of senesced plant material. Microorganisms within the peat form methane. For this reason, peatlands are important global sources of the greenhouse gas methane and therefore can contribute to climate change. In order to produce methane, the microorganisms have to transfer electrons between compounds in respiration processes. Only recently, it has been found that the peat itself can reversibly transfer electrons and that its capacities to reversibly accept electron accepting capacity (EAC) and reversibly donate electron donating capacity (EDC) electrons are large. We investigated which conditions favor large or small EAC and EDC of peat so that we can better explain methane formation. We argue that vegetation and decomposition control the amount of phenols and quinones—molecules in the peat that presumably are responsible for most of the peat's EAC and EDC. The EAC and EDC probably are largest for peat formed from vegetation rich in quinones and phenols, such as shrubs, and smaller for other vegetation types, for example, certain mosses. Intense decomposition may reduce both the EAC and EDC.
    Description: Key Points: Peat particulate organic matter electron accepting and donating capacities per grams of carbon are smaller than for humic and fulvic acids. Both capacities are small in highly decomposed peat, unless it has larger amounts of quinones and phenols. We explain these patterns with parent vegetation chemistry and conditions during decomposition.
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Description: CAS | Youth Innovation Promotion Association (YIPA) http://dx.doi.org/10.13039/501100012492
    Description: https://github.com/henningte/redoxpeat
    Keywords: ddc:551.9
    Language: English
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    Rupture Heterogeneity and Directivity Effects in Back‐Projection Analysis (2022)
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    Publication Date: 2022-06-21
    Description: The back projection method is a tremendously powerful technique for investigating the time dependent earthquake source, but its physical interpretation is elusive. We investigate how earthquake rupture heterogeneity and directivity can affect back‐projection results (imaged location and beam power) using synthetic earthquake models. Rather than attempting to model the dynamics of any specific real earthquake, we use idealized kinematic rupture models, with constant or varying rupture velocity, peak slip rate, and fault‐local strike orientation along unilateral or bilateral rupturing faults, and perform back‐projection with the resultant synthetic seismograms. Our experiments show back‐projection can track only heterogeneous rupture processes; homogeneous rupture is not resolved in our synthetic experiments. The amplitude of beam power does not necessarily correlate with the amplitude of any specific rupture parameter (e.g., slip rate or rupture velocity) at the back‐projected location. Rather, it depends on the spatial heterogeneity around the back‐projected rupture front, and is affected by the rupture directivity. A shorter characteristic wavelength of the source heterogeneity or rupture directivity toward the array results in strong beam power in higher frequency. We derive an equation based on Doppler theory to relate the wavelength of heterogeneity with synthetic seismogram frequency. This theoretical relation can explain the frequency‐ and array‐dependent back‐projection results not only in our synthetic experiments but also to analyze the 2019 M7.6 bilaterally rupturing New Ireland earthquake. Our study provides a novel perspective to physically interpret back‐projection results and to retrieve information about earthquake rupture characteristics.
    Description: Plain Language Summary: With the deployment of continental scale seismic arrays, seismologists can quickly locate the high‐frequency seismic radiation sources and track the earthquake rupture propagation using a technique called back‐projection. It is a signal beamforming technique application in seismology, and similar applications can be found in fields such as radar, wireless communication, and radio astronomy. Recent studies have proposed multiple advancements in improving the back‐projection location. However, the physical interpretation of the amplitude of stacked high‐frequency source radiations, which is commonly referred to as beam power, is still challenging since the analysis is not based on a forward model. In this article, we conduct a set of synthetic experiments to investigate the physical significance of back‐projection beam power. We find that beam power is mainly controlled by the spatial heterogeneity wavelength near the rupture front, rupture directivity, and the seismogram frequency. It is in contrast with some previous studies that link the beam power to the maximum slip rate (acceleration) amplitude near the rupture front. Based on the results, we develop a novel theoretical framework that can quantitatively interpret the frequency‐ and array‐dependent back‐projection results not only in our synthetic experiments, but also the 2019 bilateral rupture M7.6 New Ireland earthquake.
    Description: Key Points: We use kinematic forward models to investigate the relation between back‐projection beam location, power and earthquake source properties. Frequency‐dependent back‐projection peak beam power depends on the spatial heterogeneity near the rupture front, and rupture directivity. We develop a novel framework to analyze frequency‐ and array‐dependent back‐projection results, including the 2019 M7.6 New Ireland Event.
    Description: European Union's Horizon 2020 (ChEESE)
    Description: European Research Council (ERC)
    Description: German Research Foundation (DGF)
    Description: KAUST‐CRG
    Description: Leon and Joann V.C. Knopoff
    Description: NSF EAR
    Description: https://doi.org/10.7914/SN/AK
    Description: https://doi.org/10.7914/SN/AT
    Description: https://doi.org/10.7914/SN/AV
    Description: https://doi.org/10.7914/SN/BW
    Description: https://doi.org/10.7914/SN/CC
    Description: https://doi.org/10.7914/SN/CI
    Description: https://doi.org/10.7914/SN/CN
    Description: https://doi.org/10.7914/SN/II
    Description: https://doi.org/10.7914/SN/IU
    Description: https://doi.org/10.7914/SN/TA
    Description: https://doi.org/10.7914/SN/UW
    Keywords: ddc:551.22
    Language: English
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    Thermolab: A Thermodynamics Laboratory for Nonlinear Transport Processes in Open Systems (2022)
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    Publication Date: 2022-06-28
    Description: We developed a numerical thermodynamics laboratory called “Thermolab” to study the effects of the thermodynamic behavior of nonideal solution models on reactive transport processes in open systems. The equations of the state of internally consistent thermodynamic data sets are implemented in MATLAB functions and form the basis for calculating Gibbs energy. A linear algebraic approach is used in Thermolab to compute Gibbs energy of mixing for multicomponent phases to study the impact of the nonideality of solution models on transport processes. The Gibbs energies are benchmarked with experimental data, phase diagrams, and other thermodynamic software. Constrained Gibbs minimization is exemplified with MATLAB codes and iterative refinement of composition of mixtures may be used to increase precision and accuracy. All needed transport variables such as densities, phase compositions, and chemical potentials are obtained from Gibbs energy of the stable phases after the minimization in Thermolab. We demonstrate the use of precomputed local equilibrium data obtained with Thermolab in reactive transport models. In reactive fluid flow the shape and the velocity of the reaction front vary depending on the nonlinearity of the partitioning of a component in fluid and solid. We argue that nonideality of solution models has to be taken into account and further explored in reactive transport models. Thermolab Gibbs energies can be used in Cahn‐Hilliard models for nonlinear diffusion and phase growth. This presents a transient process toward equilibrium and avoids computational problems arising during precomputing of equilibrium data.
    Description: Plain Language Summary: The behavior of Earth materials, rocks, minerals, melts, fluids, and gases is important to predict physical processes in the Earth with computer models. The purpose of this is to study how the changes of variables such as fluid and solid composition influence the diffusion, fluid flow, and reaction in rocks. Here, we present a set of computer codes, called Thermolab, to calculate important physical properties such as density and chemical composition of solids, fluids, and melts in chemical equilibrium. The calculations are based on the Gibbs energy that exists for every material. We use computer codes, written in MATLAB/OCTAVE language, to show how this Gibbs energy is calculated and used to compute chemical equilibrium and find the physical properties such as density and chemical composition. We discuss techniques for accurate calculation of chemical equilibrium and physical properties in real rocks. Finally, we use Thermolab to formulate a computer model of fluids reacting with rocks. We find that chemical composition of the fluid and rock strongly affects the speed and shape of the boundary between reacted and unreacted rock. Thermolab can be used in phase growth models to investigate the way in which rocks develop toward equilibrium.
    Description: Key Points: Thermolab: a set of MATLAB codes is presented to perform equilibrium and nonequilibrium thermodynamic calculations. Local thermodynamic equilibrium is used to study effects of nonideality of solution models on nonlinear transport processes. Nonlinear diffusion processes are investigated with Thermolab providing a transient natural physical process toward equilibrium.
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Description: Russian Ministry of Science and Higher Education
    Description: https://hansjcv.github.io/Thermolab/
    Description: https://doi.org/10.5281/zenodo.6383253
    Keywords: ddc:551.9 ; ddc:541.36
    Language: English
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    Toward Reconciling Radiocarbon Production Rates With Carbon Cycle Changes of the Last 55,000 Years (2022)
    Details
    Publication Date: 2022-06-28
    Description: Since it is currently not understood how changes in 14C production rate (Q), and in the carbon cycle, can be combined to explain the reconstructed atmospheric Δ14C record, we discuss possible reasons for this knowledge gap. Reviewing the literature, we exclude that changes in the content of atoms in the atmosphere, which produce cosmogenic 14C after being hit by galactic cosmic rays, might be responsible for parts of the observed differences. When combining Q with carbon cycle changes, one needs to understand the changes in the atmospheric 14C inventory, which are partially counterintuitive. For example, during the Last Glacial Maximum, Δ14C was ∼400‰ higher compared with preindustrial times, but the 14C inventory was 10% smaller. Some pronounced changes in atmospheric Δ14C do not correspond to any significant changes in the atmospheric 14C inventory, since CO2 was changing simultaneously. Using two conceptually different models (BICYCLE‐SE and LSG‐OGCM), we derive hypothetical Qs by forcing the models with identical atmospheric CO2 and Δ14C data. Results are compared with the most recent data‐based estimates of Q derived from cosmogenic isotopes. Millennial‐scale climate change connected to the bipolar seesaw is missing in the applied models, which might explain some, but probably not all, of the apparent model‐data disagreement in Q. Furthermore, Q based on either data from marine sediments or ice cores contains offsets, suggesting an interpretation deficit in the current data‐based approaches.
    Description: Key Points: No important change found in the level of precursor material, which produces cosmogenic radiocarbon after being hit by galactic cosmic rays. Transient changes in the bipolar seesaw are needed in applied carbon cycle models to improve interpretation of the radiocarbon cycle. Sediment core‐ and ice core‐based radiocarbon production rates differ systematically, suggesting missing processes.
    Description: Bundesministerium für Bildung und Forschung (BMBF) http://dx.doi.org/10.13039/501100002347
    Description: Swedish Research Concil
    Description: Helmholtz Association (亥姆霍兹联合会致力) http://dx.doi.org/10.13039/501100009318
    Description: https://doi.org/10.1594/PANGAEA.871273
    Description: https://www.ncdc.noaa.gov/paleo-search/study/31772
    Description: https://doi.org/10.1594/PANGAEA.914500
    Description: https://www.iceandclimate.nbi.ku.dk/data/
    Description: https://doi.org/10.1594/PANGAEA.932965
    Keywords: ddc:551.9
    Language: English
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    Precipitation and Lake Water Evaporation Recorded by Terrestrial and Aquatic n‐Alkane δ2H Isotopes in Lake Khar Nuur, Mongolia (2022)
    Details
    Publication Date: 2022-06-28
    Description: The compound‐specific hydrogen isotopic composition (δ2H) of n‐alkanes is a valuable proxy to investigate hydrological conditions in lake sediments. While terrestrial n‐alkanes reflect the isotopic signal of the local precipitation, aquatic n‐alkanes incorporate the isotopic signal of the lake's water, which can be strongly modulated by evaporative enrichment. So far, the spatial distribution of the terrestrial and aquatic δ2H signal within lakes have not systematically been investigated. Here, we present compound‐specific δ2H results of terrestrial (δ2HC31) and aquatic (δ2HC23) n‐alkanes of surface sediment samples from Lake Khar Nuur, a semi‐arid and high‐altitude lake in the Mongolian Altai, and additionally investigate the δ2H signal of topsoils from the catchment. Our results show that the majority of the n‐alkane δ2H values from the catchment topsoils correspond well with modeled local growing season precipitation (JJAS). However, few samples in the northern catchment show more positive δ2H values possibly due to increased evapo(transpi)ration by southward exposition and shallower soils there. The only small variability of δ2HC31 in the surface sediments is in the range of most topsoils δ2H from the catchment, and thus, well reflects local growing season precipitation. δ2HC23 in surface sediment samples from the central and deepest parts of the lake, that is, the lake's sediment accumulation zones, shows distinctly more positive δ2HC23 values due to evaporative lake water enrichment. Consequently, Δaq‐terr, which is the isotopic offset between δ2HC23 and δ2HC31, indicates distinct lake water enrichment in the lake's accumulation zones and is a valuable proxy to investigate past hydrological changes.
    Description: Key Points: The hydrogen isotopic composition of terrestrial C31 n‐alkanes reflects the local growing season precipitation at Lake Khar Nuur. Aquatic C23 n‐alkanes incorporate the isotopic signal of the lake's water, which is strongly modulated by evaporative enrichment. The isotopic offset between C23 and C31 is a valuable proxy for evaporation in the lake and past hydrological changes in the catchment.
    Description: https://doi.pangaea.de/10.1594/PANGAEA.940115
    Keywords: ddc:551.9
    Language: English
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    Formation of fused aggregates under long‐term microgravity conditions aboard the ISS with implications for early solar system particle aggregation (2022)
    Koch, Tamara E. ; Spahr, Dominik ; Tkalcec, Beverley J. ; [et al.]
    Details
    Publication Date: 2022-10-13
    Description: In order to gain further insights into early solar system aggregation processes, we carried out an experiment on board the International Space Station, which allowed us to study the behavior of dust particles exposed to electric arc discharges under long‐term microgravity. The experiment led to the formation of robust, elongated, fluffy aggregates, which were studied by scanning electron microscopy, electron backscatter diffraction, and synchrotron micro‐computed tomography. The morphologies of these aggregates strongly resemble the typical shapes of fractal fluffy‐type calcium‐aluminum‐rich inclusions (CAIs). We conclude that a small amount of melting could have supplied the required stability for such fractal structures to have survived transportation and aggregation to and compaction within planetesimals. Other aggregates produced in our experiment have a massy morphology and contain relict grains, likely resulting from the collision of grains with different degrees of melting, also observed in some natural CAIs. Some particles are surrounded by igneous rims, which remind in thickness and crystal orientation of Wark–Lovering rims; another aggregate shows similarities to disk‐shaped CAIs. These results imply that a (flash‐)heating event with subsequent aggregation could have been involved in the formation of different morphological CAI characteristics.
    Description: BIOVIA
    Description: Nordlicht GmbH
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Bundesministerium für Wirtschaft und Energie http://dx.doi.org/10.13039/501100006360
    Description: NanoRacks LLC
    Description: Dr. Rolf M. Schwiete Stiftung http://dx.doi.org/10.13039/501100020027
    Description: Deutsches Zentrum für Luft‐ und Raumfahrt http://dx.doi.org/10.13039/501100002946
    Description: DreamUp
    Description: Carl Zeiss Meditec AG http://dx.doi.org/10.13039/501100002806
    Keywords: ddc:550.78
    Language: English
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    Microbially promoted calcite precipitation in the pelagic redoxcline: Elucidating the formation of the turbid layer (2022)
    Details
    Publication Date: 2022-10-12
    Description: Large bell‐shaped calcite formations called “Hells Bells” were discovered underwater in the stratified cenote El Zapote on the Yucatán Peninsula, Mexico. Together with these extraordinary speleothems, divers found a white, cloudy turbid layer into which some Hells Bells partially extend. Here, we address the central question if the formation of the turbid layer could be based on microbial activity, more specifically, on microbially induced calcite precipitation. Metagenomic and metatranscriptomic profiling of the microbial community in the turbid layer, which overlaps with the pelagic redoxcline in the cenote, revealed chemolithoautotrophic Hydrogenophilales and unclassified β‐Proteobacteria as the metabolic key players. Bioinformatic and hydrogeochemical data suggest chemolithoautotrophic oxidation of sulfide to zero‐valent sulfur catalyzed by denitrifying organisms due to oxygen deficiency. Incomplete sulfide oxidation via nitrate reduction and chemolithoautotrophy are both proton‐consuming processes, which increase the pH in the redoxcline favoring authigenic calcite precipitation and may contribute to Hells Bells growth. The observed mechanism of microbially induced calcite precipitation is potentially applicable to many other stagnant sulfate‐rich water bodies.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: CONACYT‐FONCICYT‐DADC
    Description: https://doi.org/10.11588/data/TMYLWS
    Description: https://doi.org/10.11588/data/GYLDH5
    Keywords: ddc:551.9
    Language: English
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    Geostandards and Geoanalytical Research Bibliographic Review 2020 (2022)
    Weis, Ulrike ; Stoll, Brigitte ; Förster, Michael W. ; [et al.]
    Details
    Publication Date: 2022-10-19
    Description: Key Points: Literature review of 7200 geoanalytical publications for the year 2020. 628 selected articles with summaries of target analytes, relevant reference materials and producers. Selected publications include data obtained by new analytical developments and improved analytical protocols for established RMs, and identifies recently developed RMs for specific scientific topics. image
    Description: This bibliographic review gives an overview of scientific publications in 2020 that contribute important data for geoanalytical reference materials (RMs).
    Keywords: ddc:551.9
    Language: English
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    A Triad Photoanode for Visible Light‐Driven Water Oxidation via Immobilization of Molecular Polyoxometalate on Polymeric Carbon Nitride (2022)
    Details
    Publication Date: 2022-08-04
    Description: Due to their availability, low cost, nontoxicity, and tunability, polymeric carbon nitrides (CNx) represent one of the most attractive materials classes for the development of fully sustainable photo(electro)catalytic systems for solar‐driven water splitting. However, the development of CNx‐based photoanodes for visible light‐driven water oxidation to dioxygen is rather challenging, particularly due to issues related to photoelectrode stability and effective coupling of the light absorber with water oxidation catalysts. Herein, a triadic photoanode comprising a porous TiO2 electron collector scaffold sensitized by CNx coupled to a molecular cobalt polyoxometalate (CoPOM = [Co4(H2O)2(PW9O34)2]10) catalyst is reported. Complete water oxidation to dioxygen under visible (λ 〉 420 nm) light irradiation is demonstrated, with photocurrents down to relatively low bias potentials (0.2 V vs RHE). Furthermore, polyethyleneimine (PEI), a cationic polymer is shown to act as an effective and non‐sacrificial electrostatic linker for immobilization of the anionic CoPOM onto the negatively charged surface of CNx. The optimized deposition of CoPOM using the PEI linker translates directly into improved efficiency of the transfer of photogenerated holes to water molecules and to enhanced oxygen evolution. This work thus provides important design rules for effective immobilization of POM‐based catalysts into soft‐matter photoelectrocatalytic architectures for light‐driven water oxidation.
    Description: A triadic photoanode comprised of a porous TiO2 electron collector scaffold sensitized by polymeric carbon nitride and coupled to a molecular cobalt polyoxometalate (CoPOM) catalyst exhibits visible (λ 〉 420 nm) light‐driven water oxidation to dioxygen. The beneficial role of the cationic polyethyleneimine polymer as an effective electrostatic linker for immobilization of CoPOM onto carbon nitride is highlighted.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Vector Stiftung http://dx.doi.org/10.13039/501100013912
    Keywords: ddc:551.9
    Language: English
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    Inspecting the Reliability of Geochemical Facies Identified for the Waterworks' Capture Zone in Germany (2022)
    Blackwell Publishing Ltd | Malden, US
    Details
    Publication Date: 2022-09-27
    Description: Little research attention has been given to validating clusters obtained from the groundwater geochemistry of the waterworks' capture zone with a prevailing lake‐groundwater exchange. To address this knowledge gap, we proposed a new scheme whereby Gaussian finite mixture modeling (GFMM) and Spike‐and‐Slab Bayesian (SSB) algorithms were utilized to cluster the groundwater geochemistry while quantifying the probability of the resulting cluster membership against each other. We applied GFMM and SSB to 13 geochemical parameters collected during different sampling periods at 13 observation points across the Barnim Highlands plateau located in the northeast of Berlin, Germany; this included 10 observation wells, two lakes, and a gallery of drinking production wells. The cluster analysis of GFMM yielded nine clusters, either with a probability ≥0.8, while the SSB produced three hierarchical clusters with a probability of cluster membership varying from 〈0.2 to 〉0.8. The findings demonstrated that the clustering results of GFMM were in good agreement with the classification as per the principal component analysis and Piper diagram. By superimposing the parameter clustering onto the observation clustering, we could identify discrepancies that exist among the parameters of a certain cluster. This enables the identification of different factors that may control the geochemistry of a certain cluster, although parameters of that cluster share a strong similarity. The GFMM results have shown that from 2002, there has been active groundwater inflow from the lakes towards the capture zone. This means that it is necessary to adopt appropriate measures to reverse the inflow towards the lakes.
    Description: Article impact statement: The probability of cluster membership quantified using an algorithm should be validated against another probabilistic‐based classifier.
    Description: Federal Ministry of Education and Research http://dx.doi.org/10.13039/501100002347
    Keywords: ddc:551.9 ; ddc:551.49
    Language: English
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    Analytical Artefacts Preclude Reliable Isotope Ratio Measurement of Internal Water in Coral Skeletons (2022)
    de Graaf, Stefan ; Vonhof, Hubert B. ; Reijmer, John J. G. ; [et al.]
    Details
    Publication Date: 2022-10-01
    Description: Internal water in cold‐water and tropical coral skeletons was extracted and measured for its oxygen and hydrogen isotope ratios. Water was extracted by crushing pieces of coral hard tissue in a percussion device connected to either a cavity ring‐down spectroscopy (CRDS) system or an isotope ratio mass spectrometry (IRMS) system. Despite most samples yielding sufficient water, each analytical system produces distinct isotope patterns. Experiments show that several characteristics specific to biominerals give rise to discrepancies and analytical artefacts that preclude the acquisition of reproducible isotope data. The main complication is that internal water in biogenic carbonates is distributed in an open interconnected micro‐network that readily exchanges with external water and potentially facilitates interaction with hydration water in the finely dispersed organic matrix in the coral skeleton. Furthermore, only an isotopically fractionated part of the internal water is released from the coral skeletons upon crushing. Altogether, isotope ratio measurement of internal water in corals with bulk crushing techniques does not give primary fluid isotope ratios useful for (palaeo‐)environmental or microbiological studies. As the resulting isotope patterns can show systematic behaviour per technique, isotope data may be erroneously interpreted to reflect the original calcifying fluid when using only a single technique to isotopically characterise internal fluids in coral skeletons.
    Description: Key Points: Free water trapped inside coral skeletons was extracted and isotopically analyzed on two commonly used techniques for fluid inclusion isotope analysis. Measured oxygen and hydrogen isotope ratios do not reproduce between the techniques due to several analytical artefacts. The water extracted from coral skeletons is not of primary origin.
    Description: Nederlandse Organisatie voor Wetenschappelijk Onderzoek http://dx.doi.org/10.13039/501100003246
    Description: Western Indian Ocean Marine Science Association http://dx.doi.org/10.13039/501100009106
    Keywords: ddc:551.9
    Language: English
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    Benthic Carbon Remineralization and Iron Cycling in Relation to Sea Ice Cover Along the Eastern Continental Shelf of the Antarctic Peninsula (2022)
    Details
    Publication Date: 2022-10-04
    Description: Rapid and profound climatic and environmental changes have been predicted for the Antarctic Peninsula with so far unknown impact on the biogeochemistry of the continental shelves. In this study, we investigate benthic carbon sedimentation, remineralization and iron cycling using sediment cores retrieved on a 400 mile transect with contrasting sea ice conditions along the eastern shelf of the Antarctic Peninsula. Sediments at comparable water depths of 330–450 m showed sedimentation and remineralization rates of organic carbon, ranging from 2.5 to 13 and 1.8–7.2 mmol C m−2 d−1, respectively. Both rates were positively correlated with the occurrence of marginal sea ice conditions (5%–35% ice cover) along the transect, suggesting a favorable influence of the corresponding light regime and water column stratification on algae growth and sedimentation rates. From south to north, the burial efficiency of organic carbon decreased from 58% to 27%, while bottom water temperatures increased from −1.9 to −0.1°C. Net iron reduction rates, as estimated from pore‐water profiles of dissolved iron, were significantly correlated with carbon degradation rates and contributed 0.7%–1.2% to the total organic carbon remineralization. Tightly coupled phosphate‐iron recycling was indicated by significant covariation of dissolved iron and phosphate concentrations, which almost consistently exhibited P/Fe flux ratios of 0.26. Iron efflux into bottom waters of 0.6–4.5 μmol Fe m−2 d−1 was estimated from an empirical model. Despite the deep shelf waters, a clear bentho‐pelagic coupling is indicated, shaped by the extent and duration of marginal sea ice conditions during summer, and likely to be affected by future climate change.
    Description: Plain Language Summary: The seafloor of the shallow shelf seas plays a significant role in the recycling of organic carbon and acts as a nutrient source for algae growth in the upper water layers. In Antarctic waters, the change in sea ice cover has a great impact on the growth of algae and the subsequent sinking of organic carbon to the seafloor. With global warming, profound changes in sea ice cover are expected for the Antarctic Peninsula. To better understand its imprint on the seafloor, we collected sediment samples from different locations along the eastern shelf of the Antarctic Peninsula and measured how changes in sea ice cover influence the accumulation and recycling of organic carbon. We found that moderate sea ice cover of 5%–35% increases the amount of organic carbon received by the seafloor and that the fraction that is buried in the sediments decreases from south (58%) to north (27%). We further measured that more iron, an important micro‐nutrient for algae growth, can be released from the seafloor the more organic carbon accumulates. Thus, sea ice conditions determine the organic carbon accumulation, turnover, and nutrient release at the seafloor, which are likely to be affected by future climate change.
    Description: Key Points: Antarctic shelf sediments underlying marginal sea ice cover exhibit high sedimentation and remineralization rates of organic carbon. A high degree of sedimentary Fe‐recycling is found which scales with organic carbon remineralization rates. Coupling between P and Fe recycling is observed with a constant P/Fe flux ratio of 0.26 for sediments with high Fe and P recycling rates.
    Description: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research http://dx.doi.org/10.13039/501100003207
    Description: https://doi.org/10.1594/PANGAEA.942455
    Keywords: ddc:551.9
    Language: English
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    Arctic – Atlantic Exchange of the Dissolved Micronutrients Iron, Manganese, Cobalt, Nickel, Copper and Zinc With a Focus on Fram Strait (2022)
    Details
    Publication Date: 2022-10-04
    Description: The Arctic Ocean is considered a source of micronutrients to the Nordic Seas and the North Atlantic Ocean through the gateway of Fram Strait (FS). However, there is a paucity of trace element data from across the Arctic Ocean gateways, and so it remains unclear how Arctic and North Atlantic exchange shapes micronutrient availability in the two ocean basins. In 2015 and 2016, GEOTRACES cruises sampled the Barents Sea Opening (GN04, 2015) and FS (GN05, 2016) for dissolved iron (dFe), manganese (dMn), cobalt (dCo), nickel (dNi), copper (dCu) and zinc (dZn). Together with the most recent synopsis of Arctic‐Atlantic volume fluxes, the observed trace element distributions suggest that FS is the most important gateway for Arctic‐Atlantic dissolved micronutrient exchange as a consequence of Intermediate and Deep Water transport. Combining fluxes from FS and the Barents Sea Opening with estimates for Davis Strait (GN02, 2015) suggests an annual net southward flux of 2.7 ± 2.4 Gg·a−1 dFe, 0.3 ± 0.3 Gg·a−1 dCo, 15.0 ± 12.5 Gg·a−1 dNi and 14.2 ± 6.9 Gg·a−1 dCu from the Arctic toward the North Atlantic Ocean. Arctic‐Atlantic exchange of dMn and dZn were more balanced, with a net southbound flux of 2.8 ± 4.7 Gg·a−1 dMn and a net northbound flux of 3.0 ± 7.3 Gg·a−1 dZn. Our results suggest that ongoing changes to shelf inputs and sea ice dynamics in the Arctic, especially in Siberian shelf regions, affect micronutrient availability in FS and the high latitude North Atlantic Ocean.
    Description: Plain Language Summary: Recent studies have proposed that the Arctic Ocean is a source of micronutrients such as dissolved iron (dFe), manganese (dMn), cobalt (dCo), nickel (dNi), copper (dCu) and zinc (dZn) to the North Atlantic Ocean. However, data at the Arctic Ocean gateways including Fram Strait and the Barents Sea Opening have been missing to date and so the extent of Arctic micronutrient transport toward the Atlantic Ocean remains unquantified. Here, we show that Fram Strait is the most important gateway for Arctic‐Atlantic micronutrient exchange which is a result of deep water transport at depths 〉500 m. Combined with a flux estimate for Davis Strait, this study suggests that the Arctic Ocean is a net source of dFe, dNi and dCu, and possibly also dCo, toward the North Atlantic Ocean. Arctic‐Atlantic dMn and dZn exchange seems more balanced. Properties in the East Greenland Current showed substantial similarities to observations in the upstream Central Arctic Ocean, indicating that Fram Strait may export micronutrients from Siberian riverine discharge and shelf sediments 〉3,000 km away. Increasing Arctic river discharge, permafrost thaw and coastal erosion, all consequences of ongoing climate change, may therefore alter future Arctic Ocean micronutrient transport to the North Atlantic Ocean.
    Description: Key Points: Fram Strait is the major gateway for Arctic‐Atlantic exchange of the dissolved micronutrients Fe, Mn, Co, Ni, Cu and Zn. The Arctic is a net source of dissolved Fe, Co, Ni and Cu to the Nordic Seas and toward the North Atlantic; Mn and Zn exchange are balanced. Waters of the Central Arctic Ocean, including the Transpolar Drift, are the main drivers of gross Arctic micronutrient export.
    Description: German Research Foundation
    Description: Netherlands Organization for Scientific Research
    Description: https://doi.pangaea.de/10.1594/PANGAEA.859558
    Description: https://doi.pangaea.de/10.1594/PANGAEA.871030
    Description: https://doi.pangaea.de/10.1594/PANGAEA.868396
    Description: https://doi.pangaea.de/10.1594/PANGAEA.905347
    Description: https://dataportal.nioz.nl/doi/10.25850/nioz/7b.b.jc
    Description: https://doi.pangaea.de/10.1594/PANGAEA.933431
    Description: https://www.bco-dmo.org/dataset/718440
    Description: https://doi.org/10.1594/PANGAEA.936029
    Description: https://doi.org/10.1594/PANGAEA.936027
    Description: https://doi.pangaea.de/10.1594/PANGAEA.927429
    Keywords: ddc:551.9
    Language: English
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    Strain Signals Governed by Frictional‐Elastoplastic Interaction of the Upper Plate and Shallow Subduction Megathrust Interface Over Seismic Cycles (2022)
    Details
    Publication Date: 2022-10-06
    Description: The behavior of the shallow portion of the subduction zone, which generates the largest earthquakes and devastating tsunamis, is still insufficiently constrained. Monitoring only a fraction of a single megathrust earthquake cycle and the offshore location of the source of these earthquakes are the foremost reasons for the insufficient understanding. The frictional‐elastoplastic interaction between the megathrust interface and its overlying wedge causes variable surface strain signals such that the wedge strain patterns may reveal the mechanical state of the interface. To contribute to this understanding, we employ Seismotectonic Scale Modeling and simplify elastoplastic megathrust subduction to generate hundreds of analog seismic cycles at a laboratory scale and monitor the surface strain signals over the model's forearc across high to low temporal resolutions. We establish two compressional and critical wedge configurations to explore the mechanical and kinematic interaction between the shallow wedge and the interface. Our results demonstrate that this interaction can partition the wedge into different segments such that the anelastic extensional segment overlays the seismogenic zone at depth. Moreover, the different segments of the wedge may switch their state from compression/extension to extension/compression domains. We highlight that a more segmented upper plate represents megathrust subduction that generates more characteristic and periodic events. Additionally, the strain time series reveals that the strain state may remain quasi‐stable over a few seismic cycles in the coastal zone and then switch to the opposite mode. These observations are crucial for evaluating earthquake‐related morphotectonic markers and short‐term interseismic time series of the coastal regions.
    Description: Key Points: Analog earthquake cycle experiments provide observations to evaluate the surface strain signals from the shallow megathrust. The extensional segment of the forearc overlays the seismogenic zone at depth. The strain state may remain quasi‐stable over a few seismic cycles in the coastal zone.
    Description: SUBITOP Marie Sklodowska‐Curie Action project from the European Union's EU Framework Programme
    Description: Deutsche Forschungsgemeinschaft (CRC 1114) “Scaling Cascades in Complex Systems”
    Description: https://doi.org/10.5880/fidgeo.2022.015
    Keywords: ddc:551.8 ; ddc:550.78
    Language: English
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    Historical Earthquakes, Paleoseismology, Neotectonics and Seismic Hazard: New Insights and Suggested Procedures (2020)
    Deutsche Gesellschaft für Erdbebeningenieurwesen und Baudynamik (DGEB) e.V. | Kiel
    Details
    Publication Date: 2022-07-13
    Description: This publication developed from the 5th International Colloquium on “Historical Earthquakes, Paleoseismology, Neotectonics and Seismic Hazard” which was held from 11 to 13 October 2017 at the Federal Institute for Geosciences and Natural Resources (BGR) in Hannover, Germany. In this colloquium, 75 experts from 17 countries presented and discussed recent results, ongoing studies and planned projects on the topics historical earthquakes, macroseismology, archeoseismology, paleoseismology, earthquake catalogues and databases, active faults, seismotectonics, neotectonics, and seismic hazard assessment.
    Description: Deutsche Gesellschaft für Erdbebeningenieurwesen und Baudynamik
    Description: 〈b〉Introduction: Historical Earthquakes, Paleoseismology, Neotectonics and Seismic Hazard: New Insights and Suggested Procedures〈/b〉 〈br〉 〈i〉Diethelm Kaiser〈/i〉 〈br〉 〈a href="https://doi.org/10.23689/fidgeo-3868"〉 DOI: https://doi.org/10.23689/fidgeo-3868〈/a〉〈br〉 〈br〉〈/br〉 〈b〉Best practice of macroseismic intensity assessment applied to the earthquake catalogue of southwestern Germany〈/b〉 〈br〉 〈i〉 Wolfgang Brüstle, Uwe Braumann, Silke Hock and Fee-Alexandra Rodler 〈/i〉〈br〉 〈a href="https://doi.org/10.23689/fidgeo-3864"〉 DOI:https://doi.org/10.23689/fidgeo-3864〈/a〉〈br〉 〈br〉〈/br〉 〈b〉The earthquake of September 3, 1770 near Alfhausen (Lower Saxony, Germany): a real, doubtful, or a fake event? 〈/b〉 〈br〉 〈i〉Günter Leydecker and Klaus Lehmann 〈/i〉 〈br〉〈a href="https://doi.org/10.23689/fidgeo-3865"〉 DOI: https://doi.org/10.23689/fidgeo-3865〈/a〉〈br〉 〈br〉〈/br〉 〈b〉How well does known seismicity between the Lower Rhine Graben and southern North Sea reflect future earthquake activity? 〈/b〉 〈br〉 〈i〉Thierry Camelbeeck, Kris Vanneste, Koen Verbeeck, David Garcia-Moreno, Koen Van Noten and Thomas Lecocq 〈/i〉 〈br〉〈a href="https://doi.org/10.23689/fidgeo-3866"〉 DOI: https://doi.org/10.23689/fidgeo-3866〈/a〉〈br〉 〈br〉〈/br〉 〈b〉The Paleoseismic Database of Germany and Adjacent Regions PalSeisDB v1.0〈/b〉〈br〉 〈i〉Jochen Hürtgen, Klaus Reicherter, Thomas Spies, Claudia Geisler and Jörg Schlittenhardt 〈/i〉 〈br〉〈a href="https://doi.org/10.23689/fidgeo-3867"〉 DOI: https://doi.org/10.23689/fidgeo-3867〈/a〉〈br〉
    Description: research
    Keywords: ddc:551.22 ; ddc:554.3 ; ddc:550
    Language: English
    Type: doc-type:book
    Format: 135
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    Seismic Velocity Recovery in the Subsurface: Transient Damage and Groundwater Drainage Following the 2015 Gorkha Earthquake, Nepal (2022)
    Details
    Publication Date: 2022-09-22
    Description: Shallow earthquakes frequently disturb the hydrological and mechanical state of the subsurface, with consequences for hazard and water management. Transient post‐seismic hydrological behavior has been widely reported, suggesting that the recovery of material properties (relaxation) following ground shaking may impact groundwater fluctuations. However, the monitoring of seismic velocity variations associated with earthquake damage and hydrological variations are often done assuming that both effects are independent. In a field site prone to highly variable hydrological conditions, we disentangle the different forcing of the relative seismic velocity variations δv retrieved from a small dense seismic array in Nepal in the aftermath of the 2015 Mw 7.8 Gorkha earthquake. We successfully model transient damage effects by introducing a universal relaxation function that contains a unique maximum relaxation timescale for the main shock and the aftershocks, independent of the ground shaking levels. Next, we remove the modeled velocity from the raw data and test whether the corresponding residuals agree with a background hydrological behavior we inferred from a previously calibrated groundwater model. The fitting of the δv data with this model is improved when we introduce transient hydrological properties in the phase immediately following the main shock. This transient behavior, interpreted as an enhanced permeability in the shallow subsurface, lasts for ∼6 months and is shorter than the damage relaxation (∼1 yr). Thus, we demonstrate the capability of seismic interferometry to deconvolve transient hydrological properties after earthquakes from non‐linear mechanical recovery.
    Description: Plain Language Summary: Earthquake ground shaking damage the rocks in the subsurface of the Earth, altering their strength and their permeability. After the main shock, the rock properties slowly return to their pre‐earthquake state, but the duration of this recovery is poorly constrained. One way to investigate these time‐dependent changes is through the monitoring of seismic velocity inferred from ambient ground vibration recorded at seismic stations. Here, we constrain the evolution of seismic velocity following the large 2015 Mw 7.8 Gorkha earthquake in Nepal, in a field site characterized by seasonal groundwater fluctuations. We find that the velocity recoveries after the main shock and the aftershocks can be modeled with the same recovery timescale, independently from the initial shaking intensity. This suggests that earthquakes of different sizes activate the same geological structures and mechanisms during the recovery phase. Thanks to the unique hydrological setting of our field site and a model that links seismic velocity and groundwater level, we also show that this change of rock properties after the main shock is accompanied by a transient change in hydrological properties, an observation inferred for the first time with seismic measurement.
    Description: Key Points: We estimate a recovery time scale (〈1 yr) in seismic velocity changes after the Gorkha earthquake using ambient noise correlations. Velocity recoveries are modeled with relaxation functions characterized by a constant maximum relaxation timescale that is peak ground velocity‐independent. We highlight a transient enhanced permeability from the velocity changes in the first ∼6 months following the main shock.
    Description: GFZ HART program
    Description: https://doi.org/10.5880/GFZ.4.6.2021.002
    Description: https://doi.org/10.14470/KA7560056170
    Keywords: ddc:551.22
    Language: English
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    Growth of microaerophilic Fe(II)‐oxidizing bacteria using Fe(II) produced by Fe(III) photoreduction (2022)
    Details
    Publication Date: 2022-06-17
    Description: Iron(II) (Fe(II)) can be formed by abiotic Fe(III) photoreduction, particularly when Fe(III) is organically complexed. Light‐influenced environments often overlap or even coincide with oxic or microoxic geochemical conditions, for example, in sediments. So far, it is unknown whether microaerophilic Fe(II)‐oxidizing bacteria are able to use the Fe(II) produced by Fe(III) photoreduction as electron donor. Here, we present an adaption of the established agar‐stabilized gradient tube approach in comparison with liquid cultures for the cultivation of microaerophilic Fe(II)‐oxidizing microorganisms by using a ferrihydrite‐citrate mixture undergoing Fe(III) photoreduction as Fe(II) source. We quantified oxygen and Fe(II) gradients with amperometric and voltammetric microelectrodes and evaluated microbial growth by qPCR of 16S rRNA genes. We showed that gradients of dissolved Fe(II) (maximum Fe(II) concentration of 1.25 mM) formed in the gradient tubes when incubated in blue or UV light (400–530 nm or 350–400 nm). Various microaerophilic Fe(II)‐oxidizing bacteria (Curvibacter sp. and Gallionella sp.) grew by oxidizing Fe(II) that was produced in situ by Fe(III) photoreduction. Best growth for these species, based on highest gene copy numbers, was observed in incubations using UV light in both liquid culture and gradient tubes containing 8 mM ferrihydrite‐citrate mixtures (1:1), due to continuous light‐induced Fe(II) formation. Microaerophilic Fe(II)‐oxidizing bacteria contributed up to 40% to the overall Fe(II) oxidation within 24 h of incubation in UV light. Our results highlight the potential importance of Fe(III) photoreduction as a source of Fe(II) for Fe(II)‐oxidizing bacteria by providing Fe(II) in illuminated environments, even under microoxic conditions.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Ministerium für Wissenschaft, Forschung und Kunst Baden‐Württemberg http://dx.doi.org/10.13039/501100003542
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Keywords: ddc:579.317 ; ddc:551.9
    Language: English
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    Simulated Future Trends in Marine Nitrogen Fixation Are Sensitive to Model Iron Implementation (2022)
    Details
    Publication Date: 2022-06-17
    Description: Biological nitrogen fixation is an important oceanic nitrogen source, potentially stabilizing marine fertility in an increasingly stratified and nutrient‐depleted ocean. Iron limitation of low latitude primary producers has been previously demonstrated to affect simulated regional ecosystem responses to climate warming or nitrogen cycle perturbation. Here we use three biogeochemical models that vary in their representation of the iron cycle to estimate change in the marine nitrogen cycle under a high CO2 emissions future scenario (RCP8.5). The first model neglects explicit iron effects on biology (NoFe), the second utilizes prescribed, seasonally cyclic iron concentrations and associated limitation factors (FeMask), and the third contains a fully dynamic iron cycle (FeDyn). Models were calibrated using observed fields to produce near‐equivalent nutrient and oxygen fits, with productivity ranging from 49 to 75 Pg C yr−1. Global marine nitrogen fixation increases by 71.1% with respect to the preindustrial value by the year 2100 in NoFe, while it remains stable (0.7% decrease in FeMask and 0.3% increase in FeDyn) in explicit iron models. The mitigation of global nitrogen fixation trend in the models that include a representation of iron originates in the Eastern boundary upwelling zones, where the bottom‐up control of iron limitation reduces export production with warming, which shrinks the oxygen deficient volume, and reduces denitrification. Warming‐induced trends in the oxygen deficient volume in the upwelling zones have a cascading effect on the global nitrogen cycle, just as they have previously been shown to affect tropical net primary production.
    Description: Plain Language Summary: Phytoplankton need nutrients to grow. Two of those nutrients are nitrogen and iron. Climate change projections suggest that in the future there could be less nitrogen supplied to the surface ocean, which might reduce phytoplankton growth. Less phytoplankton growth could impact a wide range of ocean services, like fishing and fossil carbon draw‐down. However, some phytoplankton have the ability to add “new” nitrogen to the surface ocean directly from the atmosphere. In this study, we explore how this biological fixation of new nitrogen might change into the future using three models. These models differ in how iron is represented, but all do equally well in representing the observed nutrient and oxygen distribution. Biological nitrogen fixation slightly decreases with climate change in the very complex iron model and the moderately complex iron model, but it increases strongly (by more than 70% by the year 2100) in the model that does not include iron effects on biology. Our study addresses the importance of iron models and how they can change our view of how the ocean responds to climate change.
    Description: Key Points: Models performing similarly with respect to global NO3, PO4, and O2 distributions yield diverse responses in marine N2 fixation to warming. Marine N2 fixation trends are sensitive to whether iron limits primary production in upwelling regions, for example, the Eastern Tropical Pacific.
    Description: Helmholtz Research School for Ocean System Science and Technology
    Description: New Zealand Ministry of Business, Innovation and Employment
    Description: https://data.geomar.de/downloads/20.500.12085/673e7de0-20ab-4dd3-afe9-c4bfb00b1faf/
    Keywords: ddc:551.9
    Language: English
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    The Effect of Land Use Classification on the Gas‐Phase and Particle Composition of the Troposphere: Tree Species Versus Forest Type Information (2022)
    Details
    Publication Date: 2022-06-17
    Description: Relationships between vegetation and air quality are intricate and still not fully understood. For regional air quality assessments, a better understanding of the diverse feedback mechanisms is crucial. The present article investigates the impact of land use data set detailedness on air quality predictions. Therefore, two different land use data sets were applied for simulations with COSMO‐MUSCAT for Germany in May 2014. One data set includes detailed information about tree species while the second one obtains generalized widely applied land use classes including mixed and coniferous forests. Moreover, we examined the role of agricultural NO soil emissions, agricultural biomass density enhancements, and model resolution. For a more comprehensive implementation of the secondary organic aerosol (SOA) formation, the SOA module was extended considering additional biogenic volatile organic compound (BVOC) precursor groups from isoprene, α‐pinene, limonene, and sesquiterpene oxidations. The model studies showed substantial differences in BVOC emission patterns between the two land use data sets. The application of detailed tree species information leads to complex BVOC emission patterns with high emission spots. In contrast, coarser forest information lead to standardized comprehensive emissions which result in 50% higher BVOC emissions. These differences affect both the atmospheric oxidizing potential and the production rates of SOA precursors. Land use induced regional differences (tree species minus forest information) in NOx (±2.5%), ozone (−2.5%), OH (±50%), NO3 radical (+70%) concentrations, and SOA (−60%) mass are modeled. Overall, the simulations demonstrate that detailed land use information, extended organic chemistry treatment, and high spatial resolution are mandatory for air quality assessments.
    Description: Plain Language Summary: Trees are associated with being the lungs of the atmosphere as they filter out harmful substances from the air, they store CO2, and produce oxygen via photosynthesis. Other by‐products of photosynthesis are biogenic volatile organic compounds (BVOCs). BVOCs are chemical substances with a high vapor pressure already at room temperatures, so they quickly evaporate from the leaves into the surrounding air and are responsible for the characteristic forest smell. The amount and composition of BVOC emissions strongly depend on the tree species. Every plant has its own distinct emission properties. The chemical degradation of BVOCs impacts the chemical composition of the troposphere and is connected to ground level ozone production and the formation of secondary organic aerosols (SOA), contributing substantially to particulate matter (PM). On a global scale, standardized BVOC emission information on forest levels are often used, but for regional air quality assessments detailed plant specific information is crucial, but still often lacking. Therefore, two different land use data sets were applied in the present study to investigate the impact of standardized forest versus detailed tree‐species information for Germany in May 2014. The study reveals changes in NOx (±2.5%), ozone (−2.5%), OH (±50%), NO3 radical (+70%), and SOA (−60%) concentrations.
    Description: Key Points: Detail of land use data sets crucial for biogenic volatile organic compound emission strength and composition. Composition and concentration variation of these organic compounds induce changes in regional air quality predictions. Detailed land use information, extended organic matter treatment, and high‐resolution simulations are mandatory for air quality assessments.
    Description: Deutsche Bundesstiftung Umwelt (DBU) http://dx.doi.org/10.13039/100007636
    Description: https://doi.org/10.5281/zenodo.4783106
    Description: http://ebas.nilu.no/
    Keywords: ddc:551.5 ; ddc:551.9
    Language: English
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    Effects of the Hydrous Domain in the Mantle Wedge on Magma Formation and Mixing at the Northeast Lau Spreading Center, SW Pacific (2022)
    Details
    Publication Date: 2022-08-09
    Description: Abundant volcanic activity occurs in the back‐arc region of the northern Tofua island arc where the Northeast Lau Spreading Center (NELSC) propagates southwards into older crust causing the formation of numerous seamounts at the propagating rift tip. An off‐axis volcanic diagonal ridge (DR) occurs at the eastern flank of the NELSC, linking the large rear‐arc volcano Niuatahi with the NELSC. New geochemical data from the NELSC, the southern propagator seamounts, and DR reveal that the NELSC lavas are tholeiitic basalts whereas the rear‐arc volcanoes typically erupt lavas with boninitic composition. The sharp geochemical boundary probably reflects the viscosity contrast between off‐axis hydrous harzburgitic mantle and dry fertile mantle beneath the NELSC. The new data do not indicate an inflow of Samoa plume mantle into the NELSC, confirming previously published He isotope data. The NELSC magmas form by mixing of an enriched and a depleted Indian Ocean‐type upper mantle end‐member implying a highly heterogeneous upper mantle composition in this area. Most NELSC lavas are little affected by a slab component implying that melting is adiabatic beneath the spreading center. The DR lavas show the influence of a component from the subducted Louisville Seamount Chain, which was previously thought to be restricted to the nearby arc volcanoes Niuatoputapu and Tafahi. This signature is rarely detected along the NELSC implying little mixing of melts from the low‐viscosity hydrous portion of the mantle wedge beneath the rear‐arc volcanoes into the melting region of the dry mantle beneath the NELSC.
    Description: Plain Language Summary: Volcanic activity is abundant at subduction zones and the chemical analysis of the erupted rocks allows to determine the material transport in the Earth's mantle. The Northeast Lau Spreading Center (NELSC) forms by extension and volcanism behind the northern Tofua island arc. Several large volcanic structures occur east of the NELSC and the lavas of these off‐axis volcanoes are chemically and isotopically distinct implying little mixing with the magmas of the NELSC. The differences suggest decompression melting of relatively dry mantle beneath the NELSC whereas the off‐axis volcanoes reflect melting of water‐rich mantle affected by fluids from the subducting Pacific Plate. The sharp geochemical boundary between the NELSC and off‐axis volcanoes is probably due to a large viscosity contrast between hydrous harzburgitic mantle and dry fertile mantle. Element and isotope ratios indicate that the NELSC magmas form by mixing of enriched and depleted portions of the upper mantle, and we do not find evidence for inflow of the Samoa deep mantle plume from the north. Some of the off‐axis lavas contain a component from a volcanic chain that was subducted some 4 million years ago and that was previously only known in two volcanoes of the Tofua island arc.
    Description: Key Points: Variably enriched mantle sources melt beneath the Northeast Lau Spreading Center (NELSC) but there is no evidence for Samoa mantle plume inflow. Relatively dry fertile mantle beneath NELSC causes sharp geochemical boundary with hydrous harzburgitic North Tonga mantle wedge. Subducted Louisville Seamount Chain material affects rear‐arc volcanism.
    Description: Bundesministerium für Bildung und Forschung (BMBF) http://dx.doi.org/10.13039/501100002347
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551.21 ; ddc:551.116 ; ddc:551.9
    Language: English
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    Collisional mixing between inner and outer solar system planetesimals inferred from the Nedagolla iron meteorite (2021)
    Details
    Publication Date: 2022-07-28
    Description: The ungrouped iron meteorite Nedagolla is the first meteorite with bulk Mo, Ru, and Ni isotopic compositions that are intermediate between those of the noncarbonaceous (NC) and carbonaceous (CC) meteorite reservoirs. The Hf‐W chronology of Nedagolla indicates that this mixed NC–CC isotopic composition was established relatively late, more than 7 Myr after solar system formation. The mixed NC–CC isotopic composition is consistent with the chemical composition of Nedagolla, which combines signatures of metal segregation under more oxidizing conditions (relative depletions in Mo and W), characteristic for CC bodies, and more reducing conditions (high Si and Cr contents), characteristic for some NC bodies, in a single sample. These data combined suggest that Nedagolla formed as the result of collisional mixing of NC and CC core material, which partially re‐equilibrated with silicate mantle material that predominantly derives from the NC body. These mixing processes might have occurred during a hit‐and‐run collision between two differentiated bodies, which also provides a possible pathway for Nedagolla's extreme volatile element depletion. As such, Nedagolla provides the first isotopic evidence for early collisional mixing of NC and CC bodies that is expected as a result of Jupiter's growth.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551.9 ; ddc:549.112
    Language: English
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    Pore Space Topology Controls Ultrasonic Waveforms in Dry Volcanic Rocks (2022)
    Details
    Publication Date: 2022-12-06
    Description: Pore space controls the mechanical and transport properties of rocks. At the laboratory scale, seismic modeling is usually performed in relatively homogeneous settings, and the influence of the pore space on the recorded wavefields is determined by rock‐fluid interactions. Understanding this influence in dry rocks is instrumental for assessing the impact of pore topology on waves propagating in heterogeneous environments, such as volcanoes. Here, we simulated the propagation of shear waves as a function of pore space parameters in computational models built as proxies for volcanic rocks. The spectral‐element simulations provide results comparable with ultrasonic experiments, and the outcome shows that the size, shape, volume, and location of pores impact amplitudes and phases. These variations intensify in waveform coda after multiple scattering. Our results confirm that pore topology is one of the primary regulators of the propagation of elastic waves in dry rocks regardless of porosity.
    Description: Plain Language Summary: Pores control the non‐elastic behavior and, in general, the petrophysical and mechanical properties of rocks. Such properties are essential to assess potential resources such as aquifers and reservoirs or hazards posed by earthquakes, volcanoes, and constructions. The factors controlling the elasticity of rocks are texture, pore space and the fluids filling the pores. While volcanoes represent a key target for rock characterization, measuring and modeling these factors in volcanic rocks remains challenging due to their intrinsic heterogeneities. In this study, we analyzed how pore space parameters influence the overall elastic properties of rocks by changing one parameter at a time. We created synthetic samples and performed computational simulations that show the individual contribution of the amount, size, location, and shape on waveform phases and amplitudes. The findings demonstrate that we can constrain the pore space in heterogeneous rocks in simple but realistic scenarios. Our results are the first step to provide computationaly‐driven forward models of seismic signals in heterogeneous volcanic media, necessary to predict the responses of volcanic rocks to stress.
    Description: Key Points: Computational modeling quantifies the influence of pore space topology on S‐wave propagation in volcanic rocks. Amount, size and location of pores impact ultrasonic wave propagation in dry rocks independently of porosity. Path effects dominate the waveforms and depend on the location of the pores.
    Description: https://doi.org/10.17632/b5p54xtvv9.3
    Keywords: ddc:550.78 ; volcanic rocks ; pore space topology ; S-wave propagation ; computational modeling
    Language: English
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    Direct Evidence of a Slow‐Slip Transient Modulating the Spatiotemporal and Frequency‐Magnitude Earthquake Distribution: Insights From the Armutlu Peninsula, Northwestern Turkey (2022)
    Bocchini, G. M. ; Martínez‐Garzón, P. ; Verdecchia, A. ; [et al.]
    Details
    Publication Date: 2022-12-05
    Description: Earthquakes and slow‐slip events interact, however, detailed studies investigating their interplay are still limited. We generate the highest resolution microseismicity catalog to date for the northern Armutlu Peninsula in a ∼1‐year period to perform a detailed seismicity distribution analysis and correlate the results with a local, geodetically observed slow‐slip transient within the same period. Seismicity shows a transition of cluster‐type behavior from swarm‐like to burst‐like, accompanied by an increasing relative proportion of clustered (non‐Poissonian) relative to background (Poissonian) seismicity and gradually decreasing b‐value as the geodetically observed slow‐slip transient ends. The observed slow‐slip transient decay correlates with gradually increasing effective‐stress‐drop values. The observed correlation between the b‐value and geodetic transient highlights the influence of aseismic deformation on seismic deformation and the impact of slow‐slip transients on local seismic hazard.
    Description: Plain Language Summary: Seismic and aseismic slip on faults can change the stress state in the crust and affect the recurrence time of earthquakes. Observations of how earthquakes and aseismic fault slip influence each other are limited because of the dearth of synchronous high‐resolution seismological and geodetic data. Here we use high‐resolution earthquake data in the northern Armutlu Peninsula along the Marmara seismic gap of the North Anatolian Fault (Turkey) to correlate the earthquake distribution with a local slow‐slip transient that occurred in the same period. We find that the slow‐slip transient modulates the spatiotemporal and frequency‐magnitude evolution of earthquakes, which highlights the influence of slow fault creep on fast fault slip. Our study demonstrates the importance of considering slow‐slip transients for seismic hazard assessment.
    Description: Key Points: Seismicity analysis suggests that both external and internal forcing drive deformation in the Armutlu Peninsula. Temporal correlation between a slow‐slip transient and seismic b‐value highlights interactions between aseismic and seismic deformation. Slow‐slip transients modulate the frequency‐magnitude and spatiotemporal earthquake distribution.
    Description: VW momentum grant
    Description: Helmotz Association Young Investigator Group http://dx.doi.org/10.13039/501100009318
    Description: Helmholtz‐Zentrum Potsdam—Deutsches GeoForschungs Zentrum GFZ, GIPP http://dx.doi.org/10.13039/501100010956
    Keywords: ddc:551.22 ; microseismicity ; enhanced catalog ; near‐fault monitoring ; seismic‐aseismic deformation ; slow‐slip transient
    Language: English
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    Chemical Geodynamics Insights From a Machine Learning Approach (2022)
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    Publication Date: 2022-12-07
    Description: The radiogenic isotope heterogeneity of oceanic basalts is often assessed using 2D isotope ratio diagrams. But because the underlying data are at least six dimensional (87Sr/86Sr, 143Nd/144Nd, 176Hf/177Hf, and 208,207,206Pb/204Pb), it is important to examine isotopic affinities in multi‐dimensional data space. Here, we apply t‐distributed stochastic neighbor embedding (t‐SNE), a multi‐variate statistical data analysis technique, to a recent compilation of radiogenic isotope data of mid ocean ridge (MORB) and ocean island basalts (OIB). The t‐SNE results show that the apparent overlap of MORB‐OIB data trends in 2‐3D isotope ratios diagrams does not exist in multi‐dimensional isotope data space, revealing that there is no discrete “component” that is common to most MORB‐OIB mantle sources on a global scale. Rather, MORB‐OIB sample stochastically distributed small‐scale isotopic heterogeneities. Yet, oceanic basalts with the same isotopic affinity, as identified by t‐SNE, delineate several globally distributed regional domains. In the regional geodynamic context, the isotopic affinity of MORB and OIB is caused by capturing of actively upwelling mantle by adjacent ridges, and thus melting of mantle with similar origin in on, near, and off‐ridge settings. Moreover, within a given isotopic domain, subsidiary upwellings rising from a common deep mantle root often feed OIB volcanism over large surface areas. Overall, the t‐SNE results define a fundamentally new basis for relating isotopic variations in oceanic basalts to mantle geodynamics, and may launch a 21st century era of “chemical geodynamics.”
    Description: Plain Language Summary: The isotopic heterogeneity of basalts erupted at mid ocean ridges (MORB) and ocean islands (OIB) reflects the chemical evolution of Earth's mantle. The visual inspection of various 2D isotope ratio diagrams has fueled a four decade‐long discussion whether basalt heterogeneity reflects melting of only a small number of mantle components, and in particular, whether the apparent overlap of local data trends in global 2D isotope ratio diagrams indicates that melting of a common mantle component contributes to most MORB‐OIB. Here, we use multi‐variate statistical data analysis to show that the apparent overlap of MORB‐OIB data trends in 2D isotope ratio diagrams does not exist in multi‐dimensional isotope data space. Our finding invalidates any inference made for mantle compositional evolution based on the previously proposed existence of a common mantle component, its potential nature or distribution within the mantle. Rather, global MORB‐OIB sample small‐scale isotopic heterogeneities that are distributed stochastically in the Earth's mantle. Yet, MORB‐OIB with the same isotopic affinity, as identified by our multi‐variate data analysis, delineate several globally distributed regional domains. Within the regional geodynamic context, this discovery forms a fundamentally new basis for relating isotopic variations in MORB‐OIB to mantle geodynamics.
    Description: Key Points: Multi‐variate statistical data analysis (t‐distributed stochastic neighbor embedding) identifies global Sr‐Nd‐Hf‐Pb isotopic affinities of oceanic basalts. There is no “common mantle component;” rather, global mid ocean ridge‐ocean island basalts sample stochastically distributed small‐scale isotopic heterogeneities. Globally distributed regional domains of isotopically alike oceanic lavas define a new basis for relating isotopic variations to geodynamics.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung http://dx.doi.org/10.13039/501100001711
    Description: DAAD, German Academic Exchange Service
    Description: https://doi.org/10.25625/0SVW6S
    Description: https://doi.org/10.25625/BQENGN
    Keywords: ddc:551.9 ; mantle heterogeneity ; MORB ; OIB ; geodynamics ; t‐SNE ; radiogenic isotopes ; machine learning
    Language: English
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    Scaling Laws in Aeolian Sand Transport Under Low Sand Availability (2022)
    Details
    Publication Date: 2022-11-01
    Description: The transport of sand by wind shapes the Earth's surface and constitutes one major factor for the emission of dust aerosols. The accurate modeling of wind‐blown sand transport is thus important to achieve reliable climate simulations and to make predictions about the propagation of desertification. Previous models of wind‐blown sand were designed to compute sand transport rates over a thick sand layer, such as the surface of large, active sand dunes. However, natural soils encompass a broad range of low sand availability conditions, such as crusted or bare soils. It has been a long‐standing open question how wind‐blown sand transport rates respond to wind velocity when the bare ground is covered by a thin layer of sand. Here we calculate the trajectories of wind‐blown sand grains and find that sand transport rates increase faster with wind speed under low sand availability conditions than over sand dunes. The reason for this behavior is elucidated in our simulations: The hopping sand grains fly higher the less sand is covering the hard surface. We obtain mathematical expressions for the sand transport rates as a function of the thickness of sand covering the bare soil, which will be important to improve climate models.
    Description: Key Points: We introduce a particle‐based model in investigating Aeolian (wind‐blown) sand transport when the sand cover on the soil is sparse. The scaling of the Aeolian transport rate with the wind shear velocity has a dependency on the sand cover thickness. There is an anomaly in the functional dependence of the transport rate on the sand cover thickness, depending on the rigid ground roughness.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.6084/m9.figshare.19469501
    Keywords: ddc:550.78
    Language: English
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    Magmatic Activity and Dynamics of Melt Supply of Volcanic Centers of Ultraslow Spreading Ridges: Hints From Local Earthquake Tomography at the Knipovich Ridge (2022)
    Details
    Publication Date: 2023-01-19
    Description: Along ultraslow spreading ridges melt is distributed unequally, but melt focusing guides melt away from amagmatic segments toward volcanic centers. An interplay of tectonism and magmatism is thought to control melt ascent, but the detailed process of melt extraction is not yet understood. We present a detailed image of the seismic velocity structure of the Logachev volcanic center and adjacent region along the Knipovich Ridge. With travel times of P‐ and S‐waves of 3,959 earthquakes we performed a local earthquake tomography. We simultaneously inverted for source locations, velocity structure and the Vp/Vs‐ratio. An extensive low velocity anomaly coincident with high Vp/Vs‐ratios 〉1.9 lies underneath the volcanic center at depths of 10 km below sea level in an aseismic area. More shallow, tightly clustered earthquake swarms connect the anomaly to a shallow anomaly with high Vp/Vs‐ratio beneath the basaltic seafloor. We consider the deep low‐velocity anomaly to represent an area of partial melt from which melts ascent vertically to the surface and northwards into the adjacent segment. By comparing tomographic studies of the Logachev and Southwest Indian Ridge Segment‐8 volcano we conclude that volcanic centers of ultraslow spreading ridges host spatially confined, circular partial melt areas below 10 km depth, in contrast to the shallow extended melt lenses along fast spreading ridges. Lateral feeding over distances of 35 km is possible at orthogonal spreading segments, but limited at the obliquely spreading Knipovich Ridge.
    Description: Plain Language Summary: Mid‐ocean ridges mark the tectonic plate boundaries, where the plates drift apart. Fresh magma rises into the gap and builds new seafloor. The slower the plates drift apart, the less magma is present underneath the ridge. At very slow spreading ridges there is not enough magma to build new seafloor along the entire length of the ridge. Rather, melt is guided toward individual volcanic centers spaced at about 100 km, where melt accumulates and ascents. In our study we try to find melt storage areas and ascent paths of such a volcanic center. With velocities of different seismic wave types from earthquakes we map the velocity structure of the area underneath the major Logachev volcanic center. Lower velocities indicate an area partly including melt at depths of more than 10 km, far deeper than at mid‐ocean ridges with sufficient melt supply. From the deep magma reservoir, many earthquake swarms map the long ascent path of melt to the surface. The interplay of magmatic and tectonic activity is important here. In a comparison with results from another volcanic center, we find that lateral magma feeding is possible in orthogonal spreading, but limited in oblique spreading, as at the Knipovich Ridge.
    Description: Key Points: Active volcanic centers at ultraslow spreading ridges host deeper and more confined partial melt areas than faster spreading ridges. Earthquake swarms delineate melt ascent paths from the partial melt area to the surface. Lateral feeding at shallow depths into subordinate segments is prevented by ridge obliquity.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551.22 ; ultraslow spreading ; Knipovich Ridge ; local earthquake tomography ; seismicity ; mid‐ocean ridge ; partial melt area
    Language: English
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    Locally Resolved Stress‐State in Samples During Experimental Deformation: Insights Into the Effect of Stress on Mineral Reactions (2022)
    Details
    Publication Date: 2023-01-20
    Description: Understanding conditions in the Earth's interior requires data derived from laboratory experiments. Such experiments provide important insights into the conditions under which mineral reactions take place as well as processes that control the localization of deformation in the deep Earth. We performed Griggs‐type general shear experiments in combination with numerical models, based on continuum mechanics, to quantify the effect of evolving sample geometry of the experimental assembly. The investigated system is constituted by CaCO3 and the experimental conditions are near the calcite‐aragonite phase transition. All experimental samples show a heterogeneous distribution of the two CaCO3 polymorphs after deformation. This distribution is interpreted to result from local stress variations. These variations are in agreement with the observed phase‐transition patterns and grain‐size gradients across the experimental sample. The comparison of the mechanical models with the sample provides insights into the distribution of local mechanical parameters during deformation. Our results show that, despite the use of homogeneous sample material (here calcite), stress variations develop due to the experimental geometry. The comparison of experiments and numerical models indicates that aragonite formation is primarily controlled by the spatial distribution of mechanical parameters. Furthermore, we monitor the maximum pressure and σ1 that is experienced in every part of our model domain for a given amount of time. We document that local pressure (mean stress) values are responsible for the transformation. Therefore, if the role of stress as a thermodynamic potential is investigated in similar experiments, an accurate description of the state of stress is required.
    Description: Plain Language Summary: To understand processes in the Earth's interior, we can simulate the extreme conditions via laboratory experiments by compressing and heating millimeter‐sized samples. Such experiments provide important insights into mineral reactions and processes that control deformation in the Earth. We performed rock deformation experiments close to calcite‐aragonite phase (CaCO3) transition. Deforming the sample leads to stress variations due to the experimental geometry. These variations are documented by locally occurring phase transition and variation in the grain‐size. We performed computer simulations of the deforming sample to quantify, for the first time, the effect of sample geometry on the distribution of mechanical variables, such as stress, pressure, or deformation, inside the sample. The new findings document that any mechanical variable cannot be treated as homogeneous within the sample because the variations can be significant. Deforming the sample leads to stress concentrations. By comparing the experimental observations and simulation results, we show that locally high pressure triggers the phase transition to aragonite, the high‐pressure polymorph. This has important consequences for further thermodynamic interpretations of systems under stress, where the role of deformation, pressure, or maximum principal stress on mineral reactions is investigated.
    Description: Key Points: Heterogeneous stress distribution in deformation experiments is investigated by numerical models, locally resolving mechanical variables. Resolving the mechanical variables in experiments suggests a link between local pressure (mean stress) variations and phase transition. Thermodynamic interpretations of deformed samples require a detailed understanding of local mechanical parameters.
    Description: ETH Zürich Foundation http://dx.doi.org/10.13039/501100012652
    Description: https://doi.org/10.5281/zenodo.6974768
    Keywords: ddc:550.78 ; deformation experiments ; numerical modeling ; phase transition ; rock deformation ; localization ; stress variations
    Language: English
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    Constraints on the pre-eruptive magmatic history of the Quaternary Laacher See volcano (Germany) (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-21
    Description: Ba zonation patterns in sanidine phenocrysts from mafic and intermediate phonolite and crystal-rich cumulates from the Laacher See volcano (12.9 ka) in western Germany document diffusion times suggestive of periodic recharge events throughout the magma reservoir’s entire lifespan of ~ 24 ky. Phenocrysts analysed from samples that formed late at the base of the compositionally zoned magma reservoir by mixing and mingling between a resident phonolite magma and recharging basanite show resorption and thin (2–10 μm) late-stage Ba-rich overgrowth. Short diffusion profiles across these boundaries give diffusion times of ~ 1.5–3 years at most, which are interpreted to be the maximum duration between the most recent recharge by the basanite and eruption. The lack of such late overgrowth in samples from other parts of the phonolite reservoir suggests that effect of this mixing and mingling was limited to the crystal-rich base. Sanidines in the cumulates, by contrast, are generally devoid of zoned crystals. Only rare cumulate crystals with resorbed outer boundaries and very thin overgrowths (a few microns) with very sharp compositional changes imply the remobilization of cumulates only months before eruption. Based on the diffusion timescales and storage temperatures obtained in a previous study, we present a genetic model for the conditions and timing of storage and (re-)activation of the magma system prior to the eruption of Laacher See, which is the largest volcanic event in Central Europe since the last glaciation.
    Description: Deutscher Akademischer Austauschdienst http://dx.doi.org/10.13039/501100001655
    Keywords: ddc:551.9 ; Laacher see ; Diffusion chronometry ; Barium ; BSE images ; Magma storage
    Language: English
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    Fingerprinting Kinetic Isotope Effects and Diagenetic Exchange Reactions Using Fluid Inclusion and Dual‐Clumped Isotope Analysis (2023)
    Details
    Publication Date: 2023-06-19
    Description: Geochemical analyses of carbonate minerals yield multiple parameters which can be used to estimate the temperature and water composition at which they formed. Analysis of fluid trapped in minerals is a potentially powerful tool to reconstruct paleotemperatures as well as diagenetic and hydrothermal processes, as these could represent the parent fluid. Internal fluids play important roles during the alteration of carbonate fossils, lowering energetic barriers associated with resetting of clumped isotopes, as well as mediating the transport of elements during diagenesis. Here, we explore the behavior of the ∆47–∆48 “dual‐clumped” isotope thermometer during fluid‐carbonate interaction and demonstrate that it is highly sensitive to the water/carbonate ratio, behaving as a linear system in “rock buffered” alteration, and as a decoupled system in water‐dominated systems due to non‐linear mixing effects in ∆48. Dry heating experiments show that the extrapolated “heated” end‐member is indistinguishable from the predicted ∆47 and ∆48 value expected for the experimental temperature. Furthermore, we evaluate two common laboratory sampling methods for their ability to thermally alter samples. We find that the temperature of the commonly used crushing cells used to vapourize water for fluid inclusion δ18O analyses is insufficient to cause fluid‐carbonate oxygen isotope exchange, demonstrating its suitability for analyses of fluid inclusions in carbonates. We also find that belemnites sampled with a hand‐drill yield significantly warmer paleotemperatures than those sampled with mortar and pestle. We conclude that thermally‐driven internal fluid‐carbonate exchange occurs indistinguishably from isotopic equilibrium, limited by the extent to which internal water and carbonate can react.
    Description: Plain Language Summary: Carbonate minerals contain multiple, independent, chemical and isotopic parameters which can be used to calculate the temperature at which the mineral formed. If these proxies agree with one another, it has been confidently assumed that the temperature is indeed genuine. Here, we investigate three such parameters and show how they record kinetic processes during mineral formation, as well as thermally‐driven processes which may alter a climate record. We find that this method could potentially be used to study the kinetic factors at play during biomineralization, even if the “true” temperature is unknown. We also find that some thermal processes result in all three parameters agreeing with one another. Because thermal alteration poses a potential dilemma for climate researchers, we investigate two common laboratory preparation techniques that involve heating a sample before analysis: drilling and heating sample for fluid inclusion analysis. We find that the heat of a drill is sufficient to facilitate these reactions, and potentially imparts a warm bias onto paleotemperatures, however the apparatus used for analyzing fluid inclusions does not appear to significantly alter the material. We conclude our approach using fluid inclusion analysis and dual‐clumped isotopes has the potential to resolve many ambiguities in interpreting climate records.
    Description: Key Points: We explore the behavior of dual‐clumped and fluid‐inclusion isotope paleothermometers during thermal alteration. Different conditions during diagenesis may result in discrepant paleotemperature estimates, which may be used to identify altered records. Hand‐drilling belemnites produces sufficient heat to reset paleotemperatures, but the heat during analysis of fluid inclusions does not.
    Description: DFG
    Description: https://doi.org/10.5281/zenodo.7565557
    Keywords: ddc:551.9 ; diagenesis ; clumped isotopes ; fluid inclusions ; numerical modeling
    Language: English
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    The linkage of 13C and 15N soil depth gradients with C:N and O:C stoichiometry reveals tree species effects on organic matter turnover in soil (2020)
    Springer International Publishing
    Details
    Publication Date: 2023-06-19
    Description: The knowledge of tree species dependent turnover of soil organic matter (SOM) is limited, yet required to understand the carbon sequestration function of forest soil. We combined investigations of 13C and 15N and its relationship to elemental stoichiometry along soil depth gradients in 35-year old monocultural stands of Douglas fir (Pseudotsuga menziesii), black pine (Pinus nigra), European beech (Fagus sylvatica) and red oak (Quercus rubra) growing on a uniform post-mining soil. We investigated the natural abundance of 13C and 15N and the carbon:nitrogen (C:N) and oxygen:carbon (O:C) stoichiometry of litterfall and fine roots as well as SOM in the forest floor and mineral soil. Tree species had a significant effect on SOM δ13C and δ15N reflecting significantly different signatures of litterfall and root inputs. Throughout the soil profile, δ13C and δ15N were significantly related to the C:N and O:C ratio which indicates that isotope enrichment with soil depth is linked to the turnover of organic matter (OM). Significantly higher turnover of OM in soils under deciduous tree species depended to 46% on the quality of litterfall and root inputs (N content, C:N, O:C ratio), and the initial isotopic signatures of litterfall. Hence, SOM composition and turnover also depends on additional—presumably microbial driven—factors. The enrichment of 15N with soil depth was generally linked to 13C. In soils under pine, however, with limited N and C availability, the enrichment of 15N was decoupled from 13C. This suggests that transformation pathways depend on litter quality of tree species.
    Description: Universität Trier (3163)
    Keywords: ddc:550.78 ; Stable isotopes ; Microbial turnover ; Litter ; Roots ; Common garden experiment ; Recultivated forest soil
    Language: English
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    Fate and stability of dissolved organic carbon in topsoils and subsoils under beech forests (2020)
    Kalks, Fabian ; Liebmann, Patrick ; Wordell-Dietrich, Patrick ; [et al.]
    Springer International Publishing
    Details
    Publication Date: 2023-06-19
    Description: Dissolved organic carbon (DOC) from Oa horizons has been proposed to be an important contributor for subsoil organic carbon stocks. We investigated the fate of DOC by directly injecting a DOC solution from 13C labelled litter into three soil depths at beech forest sites. Fate of injected DOC was quantified with deep drilling soil cores down to 2 m depth, 3 and 17 months after the injection. 27 ± 26% of the injected DOC was retained after 3 months and 17 ± 22% after 17 months. Retained DOC was to 70% found in the first 10 cm below the injection depth and on average higher in the topsoil than in the subsoil. After 17 months DOC in the topsoil was largely lost (− 19%) while DOC in the subsoil did not change much (− 4.4%). Data indicated a high stabilisation of injected DOC in the subsoils with no differences between the sites. Potential mineralisation as revealed by incubation experiments however, was not different between DOC injected in topsoil or subsoils underlining the importance of environmental factors in the subsoil for DOC stabilisation compared to topsoil. We conclude that stability of DOC in subsoil is primary driven by its spatial inaccessibility for microorganisms after matrix flow while site specific properties did not significantly affect stabilisation. Instead, a more fine-textured site promotes the vertical transport of DOC due to a higher abundance of preferential flow paths.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:550.78 ; Forest subsoils ; Cascade model ; Incubation experiment ; 13C ; Field experiment
    Language: English
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    Biogeochemical cycling of phosphorus in subsoils of temperate forest ecosystems (2020)
    Springer International Publishing
    Details
    Publication Date: 2023-06-19
    Description: Tree roots penetrate the soil to several meters depth, but the role of subsoils for the supply of nutrient elements such as phosphorus (P) to the trees is poorly understood. Here, we tested the hypothesis that increased P deficiency in the topsoil results in an increased microbial recycling of P from the forest subsoil. We sampled soils from four German temperate forest sites representing a gradient in total P stocks. We analyzed the oxygen isotopic composition of HCl-extractable phosphate (δ18OP) and identified differences in P speciation with increasing soil depth using X-ray absorption near-edge structure (XANES) spectroscopy. We further determined microbial oxygen demand with and without nutrient supply at different soil depths to analyse nutrient limitation of microbial growth and used nanoscale secondary ion mass spectrometry (NanoSIMS) to visualize spatial P gradients in the rhizosphere. We found that δ18OP values in the topsoil of all sites were close to the isotopic signal imparted by biological cycling when oxygen isotopes in phosphate are exchanged by enzymatic activity. However, with increasing soil depth and increasing HCl-P concentrations, δ18Ο values continuously decreased towards values expected for primary minerals in parent material at depths below 60 cm at sites with high subsoil P stocks and below more than 2 m at sites with low subsoil P stocks, respectively. For these depths, XANES spectra also indicated the presence of apatite. NanoSIMS images showed an enrichment of P in the rhizosphere in the topsoil of a site with high P stocks, while this P enrichment was absent at a site with low P stocks and in both subsoils. Addition of C, N and P alone or in combination revealed that microbial activity in subsoils of sites with low P stocks was mostly P limited, whereas sites with high P stocks indicated N limitation or N and P co-limitation. We conclude that subsoil P resources are recycled by trees and soil microorganisms. With continued weathering of the bedrock and mobilisation of P from the weathered rocks, P cycling will proceed to greater depths, especially at sites characterised by P limitation.
    Description: Rheinische Friedrich-Wilhelms-Universität Bonn (1040)
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Rheinische Friedrich-Wilhelms-Universität Bonn (1040)
    Keywords: ddc:551.9 ; Oxygen isotopes ; Phosphate ; NanoSIMS ; XANES ; Microbial P cycling ; Soil
    Language: English
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    GIS-based multicriteria evaluation for earthquake response: a case study of expert opinion in Vancouver, Canada (2020)
    Springer Netherlands
    Details
    Publication Date: 2023-06-19
    Description: GIS-based multicriteria evaluation (MCE) provides a framework for analysing complex decision problems by quantifying variables of interest to score potential locations according to their suitability. In the context of earthquake preparedness and post-disaster response, MCE has relied mainly on uninformed or non-expert stakeholders to identify high-risk zones, prioritise areas for response, or highlight vulnerable populations. In this study, we compare uninformed, informed non-expert, and expert stakeholders’ responses in MCE modelling for earthquake response planning in Vancouver, Canada. Using medium- to low-complexity MCE models, we highlight similarities and differences in the importance of infrastructural and socioeconomic variables, emergency services, and liquefaction potential between a non-weighted MCE, a medium-complexity informed non-expert MCE, and a low-complexity MCE informed by 35 local earthquake planning and response experts from governmental and non-governmental organisations. Differences in the observed results underscore the importance of accessible, expert-informed approaches for prioritising locations for earthquake response planning and for the efficient and geographically precise allocation of resources.
    Description: Friedrich-Alexander-Universität Erlangen-Nürnberg (1041)
    Keywords: ddc:551.22 ; Multicriteria evaluation ; Earthquake ; Disaster response ; Natural hazards ; Expert knowledge ; Participatory mapping
    Language: English
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    Performance of the International Monitoring System Seismic Network Based on Ambient Seismic Noise Measurements (2021)
    Springer International Publishing
    Details
    Publication Date: 2023-06-20
    Description: All nuclear explosions are banned by the Comprehensive Nuclear-Test-Ban Treaty. In the context of the treaty a verification regime was put into place to detect, locate, and characterize nuclear explosions at any time, by anyone and everywhere on the Earth. The International Monitoring System, which plays a key role in the verification regime, was set up by the Preparatory Commission of the Comprehensive Nuclear-Test-Ban Treaty Organization. Out of the several different monitoring techniques applied in the International Monitoring System the seismic waveform approach is the most effective and reliable technology for monitoring nuclear explosions underground. This study introduces a deterministic method of threshold monitoring that allows to asses a lower body wave magnitude limit of a potential seismic event in a certain geographical region, that can be detected by those seismic stations being part of the International Monitoring System network. The method is based on measurements of ambient seismic noise levels at the individual seismic stations along with global distance corrections terms for the body wave magnitude. The results suggest that an average global detection capability of approximately body wave magnitude 4.0 can be achieved using only stations from the primary seismic network of the International Monitoring System. The incorporation of seismic stations from the auxiliary seismic network leads to a slight improvement of the detection capability, while the use and analysis of wave arrivals from distances greater than 120∘ results in a significant improvement of the detection capability. Temporal variations in terms of hourly and monthly changes of the global detection capability can not be observed. Overall, comparisons between detection capability and manually retrieved body wave magnitudes from the Reviewed Event Bulletin suggest, that our method yields a more conservative estimation of the detection capability and that in reality detection thresholds might be even lower than estimated.
    Description: Bundesanstalt für Geowissenschaften und Rohstoffe (BGR) (4230)
    Keywords: ddc:551.22 ; International monitoring system ; seismology ; detection capability ; ambient seismic noise ; body wave magnitude correction curves
    Language: English
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    Long- and Short-Term Monitoring of a Dam in Response to Seasonal Changes and Ground Motion Loading: The Test Case of the Kurpsai Dam, Western Kyrgyz Republic (2021)
    Springer International Publishing
    Details
    Publication Date: 2023-06-20
    Description: An experimental multi-parameter structural monitoring system has been installed on the Kurpsai dam, western Kyrgyz Republic. This system consists of equipment for seismic and strain measurements for making longer- (days, weeks, months) and shorter- (minutes, hours) term observations, dealing with, for example seasonal (longer) effects or the response of the dam to ground motion from noise or seismic events. Fibre-optic strain sensors allow the seasonal and daily opening and closing of the spaces between the dam’s segments to be tracked. For the seismic data, both amplitude (in terms of using differences in amplitudes in the Fourier spectra for mapping the modes of vibration of the dam) and their time–frequency distribution for a set of small to moderate seismic events are investigated and the corresponding phase variabilities (in terms of lagged coherency) are evaluated. Even for moderate levels of seismic-induced ground motion, some influence on the structural response can be detected, which then sees the dam quickly return to its original state. A seasonal component was identified in the strain measurements, while levels of noise arising from the operation of the dam's generators and associated water flow have been provisionally identified.
    Description: Bundesministerium für Forschung und Technologie http://dx.doi.org/10.13039/501100004937
    Description: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Keywords: ddc:551.22 ; Structural health monitoring ; Dam engineering ; Operational and environmental effects ; Strong-motion ; Strain ; Elastic response ; Kurpsai dam
    Language: English
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    A regionally-adaptable “scaled backbone” ground motion logic tree for shallow seismicity in Europe: application to the 2020 European seismic hazard model (2020)
    Springer Netherlands
    Details
    Publication Date: 2023-06-20
    Description: The selection of ground motion models, and the representation of their epistemic uncertainty in the form of a logic tree, is one of the fundamental components of probabilistic seismic hazard and risk analysis. A new ground motion model (GMM) logic tree has been developed for the 2020 European seismic hazard model, which develops upon recently compiled ground motion data sets in Europe. In contrast to previous European seismic hazard models, the new ground model logic tree is built around the scaled backbone concept. Epistemic uncertainties are represented as calibrations to a reference model and aim to characterise the potential distributions of median ground motions resulting from variability in source scaling and attenuation. These scaled backbone logic trees are developed and presented for shallow crustal seismic sources in Europe. Using the new European strong motion flatfile, and capitalising on recent perspectives in ground motion modelling in the scientific literature, a general and transferable procedure is presented for the construction of a backbone model and the regionalisation of epistemic uncertainty. This innovative approach forms a general framework for revising and updating the GMM logic tree at national and European scale as new strong motion data emerge in the future.
    Description: Horizon 2020 http://dx.doi.org/10.13039/501100007601
    Keywords: ddc:551.22 ; Probabilistic seismic hazard assessment ; Ground motion models ; Epistemic uncertainty ; Regionalisation
    Language: English
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    Regional broad-band ground-shaking modelling over extended and thick sedimentary basins: an example from the Lower Rhine Embayment (Germany) (2020)
    Springer Netherlands
    Details
    Publication Date: 2023-06-20
    Description: The simulation of broad-band (0.1 to 10 + Hz) ground-shaking over deep and spatially extended sedimentary basins at regional scales is challenging. We evaluate the ground-shaking of a potential M 6.5 earthquake in the southern Lower Rhine Embayment, one of the most important areas of earthquake recurrence north of the Alps, close to the city of Cologne in Germany. In a first step, information from geological investigations, seismic experiments and boreholes is combined for deriving a harmonized 3D velocity and attenuation model of the sedimentary layers. Three alternative approaches are then applied and compared to evaluate the impact of the sedimentary cover on ground-motion amplification. The first approach builds on existing response spectra ground-motion models whose amplification factors empirically take into account the influence of the sedimentary layers through a standard parameterization. In the second approach, site-specific 1D amplification functions are computed from the 3D basin model. Using a random vibration theory approach, we adjust the empirical response spectra predicted for soft rock conditions by local site amplification factors: amplifications and associated ground-motions are predicted both in the Fourier and in the response spectra domain. In the third approach, hybrid physics-based ground-motion simulations are used to predict time histories for soft rock conditions which are subsequently modified using the 1D site-specific amplification functions computed in method 2. For large distances and at short periods, the differences between the three approaches become less notable due to the significant attenuation of the sedimentary layers. At intermediate and long periods, generic empirical ground-motion models provide lower levels of amplification from sedimentary soils compared to methods taking into account site-specific 1D amplification functions. In the near-source region, hybrid physics-based ground-motions models illustrate the potentially large variability of ground-motion due to finite source effects.
    Description: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Keywords: ddc:551.22 ; Ground-motion modelling ; Site effects ; Scenario ; Random vibration theory ; Hybrid modelling
    Language: English
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    A ground motion logic tree for seismic hazard analysis in the stable cratonic region of Europe: regionalisation, model selection and development of a scaled backbone approach (2020)
    Springer Netherlands
    Details
    Publication Date: 2023-06-20
    Description: Regions of low seismicity present a particular challenge for probabilistic seismic hazard analysis when identifying suitable ground motion models (GMMs) and quantifying their epistemic uncertainty. The 2020 European Seismic Hazard Model adopts a scaled backbone approach to characterise this uncertainty for shallow seismicity in Europe, incorporating region-to-region source and attenuation variability based on European strong motion data. This approach, however, may not be suited to stable cratonic region of northeastern Europe (encompassing Finland, Sweden and the Baltic countries), where exploration of various global geophysical datasets reveals that its crustal properties are distinctly different from the rest of Europe, and are instead more closely represented by those of the Central and Eastern United States. Building upon the suite of models developed by the recent NGA East project, we construct a new scaled backbone ground motion model and calibrate its corresponding epistemic uncertainties. The resulting logic tree is shown to provide comparable hazard outcomes to the epistemic uncertainty modelling strategy adopted for the Eastern United States, despite the different approaches taken. Comparison with previous GMM selections for northeastern Europe, however, highlights key differences in short period accelerations resulting from new assumptions regarding the characteristics of the reference rock and its influence on site amplification.
    Description: Horizon 2020 Framework Programme http://dx.doi.org/10.13039/100010661
    Description: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Keywords: ddc:551.22 ; Ground motion models ; Stable craton ; Regionalisation ; Epistemic uncertainty ; Europe
    Language: English
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    Incorporation of Rare Earths and Yttrium in Calcite: A Critical Re-evaluation (2020)
    Springer Netherlands
    Details
    Publication Date: 2023-06-20
    Description: The reported partition coefficients of REE with calcite are reviewed and critically discussed. In some of the reported experimental sets, REE concentrations are found to be supersaturated with respect to individual REE2(CO3)3 but never to REE(OH)3. Although the solutions are unsaturated with respect to individual REY carbonates, REY including Y are incorporated in calcite surfaces, where they are overgrown by calcite. Charge balances may be obtained by building {REY–Na-(CO3)2}n or by exchange of 2Ca2+ against REY3+ + blank space calcite lattice. These surface compounds may either be homogeneously distributed or clustered. Both the size and frequency of clusters increase with [REY]/[Ca] or [ΣREY3+]/[Ca2+] in solution. If these surface precipitates are removed into solutions saturated with respect to ΣREE2(CO3)3, they start growing in the aqueous phase. In this case, the apparent DREY and kREY values decrease with increasing REY concentrations in solution. In previous studies, only the individual distribution coefficients are reported not considering that the entirety of REY determines their behavior in partitioning. Given enough time, these surface clusters equilibrate with the aqueous phase before being overgrown by calcite. In the double logarithmic plots of {REY}/{Ca} versus [REY]/[Ca] or [REY3+]/[Ca2+], two relationships evolve characterizing the REY distribution in marine calcite and experimental calcites grown in Mg2+-free solutions. The double logarithmic plots of partition coefficients of REYi3+ in calcite grown from seawater show a slope exceeding unity, whereas those from fluids without Mg2+ depict slopes less than unity being both in contrast to the Henderson–Kracek rule.
    Keywords: ddc:551.9 ; Partitioning of rare earths with calcite ; Formation of REY–Na carbonate compounds ; Homogeneous partitioning ; Individual versus entirety of rare earths’ partitioning between calcite and ambient solution
    Language: English
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    A regionally-adaptable ground-motion model for shallow crustal earthquakes in Europe (2020)
    Springer Netherlands
    Details
    Publication Date: 2023-06-20
    Description: To complement the new European Strong-Motion dataset and the ongoing efforts to update the seismic hazard and risk assessment of Europe and Mediterranean regions, we propose a new regionally adaptable ground-motion model (GMM). We present here the GMM capable of predicting the 5% damped RotD50 of PGA, PGV, and SA(T = 0.01 − 8 s) from shallow crustal earthquakes of 3 ≤ M W ≤ 7.4 occurring 0 〈 RJB ≤ 545 km away from sites with 90 ≤ Vs30 ≤ 3000 m s−1 or 0.001 ≤ slope ≤ 1 m m−1. The extended applicability derived from thousands of new recordings, however, comes with an apparent increase in the aleatory variability (σ). Firstly, anticipating contaminations and peculiarities in the dataset, we employed robust mixed-effect regressions to down weigh only, and not elimi nate entirely, the influence of outliers on the GMM median and σ. Secondly, we regionalised the attenuating path and localised the earthquake sources using the most recent models, to quantify region-specific anelastic attenuation and locality-specific earthquake characteristics as random-effects, respectively. Thirdly, using the mixed-effect variance–covariance structure, the GMM can be adapted to new regions, localities, and sites with specific datasets. Consequently, the σ is curtailed to a 7% increase at T 〈 0.3 s, and a sub stantial 15% decrease at T ≥ 0.3 s, compared to the RESORCE based partially non-ergodic GMM. We provide the 46 attenuating region-, 56 earthquake localities-, and 1829 site-spe cific adjustments, demonstrate their usage, and present their robustness through a 10-fold cross-validation exercise.
    Description: SIGMA2 consortium (EDF, CEA, PG&E, SwissNuclear,. Areva, CEZ, CRIEPI)
    Description: H2020 Research Infrastructures http://dx.doi.org/10.13039/100010666
    Keywords: ddc:551.22 ; Ground-motion model ; Response spectra ; Robust mixed-effects regression ; Regionally adaptable ; Seismic hazard and risk ; Europe
    Language: English
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    Spectral decomposition of the Engineering Strong Motion (ESM) flat file: regional attenuation, source scaling and Arias stress drop (2020)
    Springer Netherlands
    Details
    Publication Date: 2023-06-20
    Description: We perform a spectral decomposition of the Fourier amplitude spectra disseminated along with the Engineering Strong Motion (ESM) flat file for Europe and Middle East. We apply a non-parametric inversion schema to isolate source, propagation and site effects, introducing a regionalization for the attenuation model into three domains. The obtained propagation and source components of the model are parametrized in terms of geometrical spreading, quality factor, seismic moment, and corner frequency assuming a ω2 source model. The non-parametric spectral attenuation values show a faster decay for earthquakes in Italy than in the other regions. Once described in terms of geometrical spreading and frequency-dependent quality factor, slopes and breakpoint locations of the piece-wise linear model for the geometrical spreading show regional variations, confirming that the non-parametric models capture the effects of crustal heterogeneities and differences in the anelastic attenuation. Since they are derived in the framework of a single inversion, the source spectra of the largest events which have occurred in Europe in the last decades can be directly compared and the scaling of the extracted source parameters evaluated. The Brune stress drop varies over about 2 orders of magnitude (the 5th, 50th and 95th percentiles of the ∆σ distribution are 0.76, 2.94, and 13.07 MPa, respectively), with large events having larger stress drops. In particular, the 5th, 50th and 95th percentiles for M 〉 5.5 are 2.87, 6.02, and 23.5 MPa, respectively whereas, for M 〈 5.5, the same percentiles are 0.73, 2.84, and 12.43 MPa. If compared to the residual distributions associated to a ground motion prediction equation previously derived using the same Fourier amplitude spectra, the source parameter and the empirical site amplification effects correlate well with the inter-event and inter-station residuals, respectively. Finally, we calibrated both non-parametric and parametric attenuation models for estimating the stress drop from the ratio between Arias intensity and significant duration. The results confirm that computing the Arias stress drop is a suitable approach for complementing the seismic moment with information controlling the source radiation at high frequencies for rapid response applications.
    Description: https://esm.mi.ingv.it//flatfile-2018/
    Keywords: ddc:551.22 ; Ground motion models ; Spectral decomposition ; Arias intensity ; Source parameters
    Language: English
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    Origin and fate of dissolved organic matter in four shallow Baltic Sea estuaries (2020)
    Springer International Publishing
    Details
    Publication Date: 2023-06-20
    Description: Coastal waters have strong gradients in dissolved organic matter (DOM) quantity and characteristics, originating from terrestrial inputs and autochthonous production. Enclosed seas with high freshwater input therefore experience high DOM concentrations and gradients from freshwater sources to more saline waters. The brackish Baltic Sea experiences such salinity gradients from east to west and from river mouths to the open sea. Furthermore, the catchment areas of the Baltic Sea are very diverse and vary from sparsely populated northern areas to densely populated southern zones. Coastal systems vary from enclosed or open bays, estuaries, fjords, archipelagos and lagoons where the residence time of DOM at these sites varies and may control the extent to which organic matter is biologically, chemically or physically modified or simply diluted with transport off-shore. Data of DOM with simultaneous measurements of dissolved organic (DO) nitrogen (N), carbon (C) and phosphorus (P) across a range of contrasting coastal systems are scarce. Here we present data from the Roskilde Fjord, Vistula and Öre estuaries and Curonian Lagoon; four coastal systems with large differences in salinity, nutrient concentrations, freshwater inflow and catchment characteristics. The C:N:P ratios of DOM of our data, despite high variability, show site specific significant differences resulting largely from differences residence time. Microbial processes seemed to have minor effects, and only in spring did uptake of DON in the Vistula and Öre estuaries take place and not at the other sites or seasons. Resuspension from sediments impacts bottom waters and the entire shallow water column in the Curonian Lagoon. Finally, our data combined with published data show that land use in the catchments seems to impact the DOC:DON and DOC:DOP ratios of the tributaries most.
    Description: Academy of Sciences of Finland
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: BONUS COCOA and Bundesministerium für Bildung und Forschung
    Description: Academy of Finland
    Description: Danish Research Council for Independent Research
    Description: BONUS COCOA Project
    Description: Leibniz-Institut für Ostseeforschung Warnemünde (IOW) (3484)
    Keywords: ddc:551.9 ; Coastal systems ; Dissolved organic matter ; Riverine input ; Baltic Sea
    Language: English
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    Stress Drop, Seismogenic Index and Fault Cohesion of Fluid-Induced Earthquakes (2021)
    Springer Vienna
    Details
    Publication Date: 2023-06-22
    Description: Sometimes, a rather high stress drop characterizes earthquakes induced by underground fluid injections or productions. In addition, long-term fluid operations in the underground can influence a seismogenic reaction of the rock per unit volume of the fluid involved. The seismogenic index is a quantitative characteristic of such a reaction. We derive a relationship between the seismogenic index and stress drop. This relationship shows that the seismogenic index increases with the average stress drop of induced seismicity. Further, we formulate a simple and rather general phenomenological model of stress drop of induced earthquakes. This model shows that both a decrease of fault cohesion during the earthquake rupture process and an enhanced level of effective stresses could lead to high stress drop. Using these two formulations, we propose the following mechanism of increasing induced seismicity rates observed, e.g., by long-term gas production at Groningen. Pore pressure depletion can lead to a systematic increase of the average stress drop (and thus, of magnitudes) due to gradually destabilizing cohesive faults and due to a general increase of effective stresses. Consequently, elevated average stress drop increases seismogenic index. This can lead to seismic risk increasing with the operation time of an underground reservoir.
    Description: PHASE University consortium project of Freie Universität Berlin
    Description: Freie Universität Berlin (1008)
    Keywords: ddc:551.22 ; Induced seismicity ; Hydrocarbon production ; Fluid injection ; Geo-Energy ; Seismic hazard ; Reservoir Geomechancs
    Language: English
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    Understanding Micropolar Theory in the Earth Sciences I: The Eigenfrequency $\omega_r$ (2021)
    Springer International Publishing
    Details
    Publication Date: 2023-06-12
    Description: Even though micropolar theories are widely applied for engineering applications such as the design of metamaterials, applications in the study of the Earth’s interior still remain limited and in particular in seismology. This is due to the lack of understanding of the required elastic material parameters present in the theory as well as the eigenfrequency $\omega _r$ which is not observed in seismic data. By showing that the general dynamic equations of the Timoshenko’s beam is a particular case of the micropolar theory we are able to connect micropolar elastic parameters to physically measurable quantities. We then present an alternative micropolar model that, based on the same physical basis as the original model, circumvents the problem of the original eigenfrequency $\omega _r$ laking in seismological data. We finally validate our model with a seismic experiment and show it is relevant to explain observed seismic dispersion curves.
    Description: Westfälische Wilhelms-Universität Münster (1056)
    Keywords: ddc:551.22 ; Timoshenko beam theory ; plate theory ; Cosserat theory ; micropolar theory ; seismology
    Language: English
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    Understanding Micropolar Theory in the Earth Sciences II: The Seismic Moment Tensor (2021)
    Springer International Publishing
    Details
    Publication Date: 2023-06-12
    Description: Seismic events produced by block rotations about vertical axis occur in many geodynamic contexts. In this study, we show that these rotations can be accounted for using the proper theory, namely micropolar theory, and a new asymmetric moment tensor can be derived. We then apply this new theory to the Kaikōura earthquake (2016/11/14), Mw 7.8, one of the most complex earthquakes ever recorded with modern instrumental techniques. Using advanced numerical techniques, we compute synthetic seismograms including a full asymmetric moment tensor and we show that it induces measurable differences in the waveforms proving that seismic data can record the effects of the block rotations observed in the field. Therefore, the theory developed in this work provides a full framework for future dynamic source inversions of asymmetric moment tensors.
    Description: Westfälische Wilhelms-Universität Münster (1056)
    Keywords: ddc:551.22 ; Seismology ; asymmetric moment tensor ; micropolar theory ; Kaikōura earthquake
    Language: English
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    Multiphase-field modelling of crack propagation in geological materials and porous media with Drucker-Prager plasticity (2020)
    Späth, Michael ; Herrmann, Christoph ; Prajapati, Nishant ; [et al.]
    Springer International Publishing
    Details
    Publication Date: 2023-06-12
    Description: A multiphase-field approach for elasto-plastic and anisotropic brittle crack propagation in geological systems consisting of different regions of brittle and ductile materials is presented and employed to computationally study crack propagation. Plastic deformation in elasto-plastic materials such as frictional, granular or porous materials is modelled with the pressure-sensitive Drucker-Prager plasticity model. This plasticity model is combined with a multiphase-field model fulfilling the mechanical jump conditions in diffuse solid-solid interfaces. The validity of the plasticity model with phase-inherent stress and strain fields is shown, in comparison with sharp interface finite element solutions. The proposed model is capable of simulating crack formation in heterogeneous multiphase systems comprising both purely elastic and inelastic phases. We investigate the influence of different material parameters on the crack propagation with tensile tests in single- and two-phase materials. To show the applicability of the model, crack propagation in a multiphase domain with brittle and elasto-plastic components is performed.
    Keywords: ddc:550.78 ; Multiphase-field ; Drucker-Prager plasticity ; Brittle fracture ; Elasto-plastic fracture
    Language: English
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    Release characteristics of overpressurised gas from complex vents: implications for volcanic hazards (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-23
    Description: Many explosive volcanic eruptions produce underexpanded starting gas-particle jets. The dynamics of the accompanying pyroclast ejection can be affected by several parameters, including magma texture, gas overpressure, erupted volume and geometry. With respect to the latter, volcanic craters and vents are often highly asymmetrical. Here, we experimentally evaluate the effect of vent asymmetry on gas expansion behaviour and gas jet dynamics directly above the vent. The vent geometries chosen for this study are based on field observations. The novel element of the vent geometry investigated herein is an inclined exit plane (5, 15, 30° slant angle) in combination with cylindrical and diverging inner geometries. In a vertical setup, these modifications yield both laterally variable spreading angles as well as a diversion of the jets, where inner geometry (cylindrical/diverging) controls the direction of the inclination. Both the spreading angle and the inclination of the jet are highly sensitive to reservoir (conduit) pressure and slant angle. Increasing starting reservoir pressure and slant angle yield (1) a maximum spreading angle (up to 62°) and (2) a maximum jet inclination for cylindrical vents (up to 13°). Our experiments thus constrain geometric contributions to the mechanisms controlling eruption jet dynamics with implications for the generation of asymmetrical distributions of proximal hazards around volcanic vents.
    Description: European Research Council http://dx.doi.org/10.13039/501100000781
    Keywords: ddc:550.78 ; Explosive eruptions ; Crater asymmetry ; Vent asymmetry ; Gas jets ; Inclined jets ; Tilted eruptions
    Language: English
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    Vesicle shrinkage in hydrous phonolitic melt during cooling (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-23
    Description: The ascent of hydrous magma prior to volcanic eruptions is largely driven by the formation of H2O vesicles and their subsequent growth upon further decompression. Porosity controls buoyancy as well as vesicle coalescence and percolation, and is important when identifying the differences between equilibrium or disequilibrium degassing from textural analysis of eruptive products. Decompression experiments are routinely used to simulate magma ascent. Samples exposed to high temperature (T) and pressure (P) are decompressed and rapidly cooled to ambient T for analysis. During cooling, fluid vesicles may shrink due to decrease of the molar volume of H2O and by resorption of H2O back into the melt driven by solubility increase with decreasing T at P 〈 300 MPa. Here, we quantify the extent to which vesicles shrink during cooling, using a series of decompression experiments with hydrous phonolitic melt (5.3–3.3 wt% H2O, T between 1323 and 1373 K, decompressed from 200 to 110–20 MPa). Most samples degassed at near-equilibrium conditions during decompression. However, the porosities of quenched samples are significantly lower than expected equilibrium porosities prior to cooling. At a cooling rate of 44 K·s−1, the fictive temperature Tf, where vesicle shrinkage stops, is up to 200 K above the glass transition temperature (Tg), Furthermore, decreasing cooling rate enhances vesicles shrinkage. We assess the implications of these findings on previous experimental degassing studies using phonolitic melt, and highlight the importance of correctly interpreting experimental porosity data, before any comparison to natural volcanic ejecta can be attempted.
    Description: German Science Foundation
    Keywords: ddc:550.78 ; Decompression experiments ; Vesiculation ; Vesicle shrinkage ; Quench effect ; H2O resorption ; Fictive temperature
    Language: English
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    The effect of initial H2O concentration on decompression-induced phase separation and degassing of hydrous phonolitic melt (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-23
    Description: Supersaturation of H2O during magma ascent leads to degassing of melt by formation and growth of vesicles that may power explosive volcanic eruptions. Here, we present experiments to study the effect of initially dissolved H2O concentration (cH2Oini) on vesicle formation, growth, and coalescence in phonolitic melt. Vesuvius phonolitic melts with cH2Oini ranging between 3.3 and 6.3 wt% were decompressed at rates of 1.7 and 0.17 MPa·s−1 and at temperatures ≥ 1323 K. Decompression started from 270 and 200 MPa to final pressures of 150–20 MPa, where samples were quenched isobarically. Optical microscopy and Raman spectroscopic measurements confirm that the glasses obtained were free of microcrystals and Fe-oxide nanolites, implying that the experiments were superliquidus and phase separation of the hydrous melt was homogeneous. A minimum number of the initially formed vesicles, defined by the number density normalized to vesicle-free glass volume (VND), is observed at ~ 5 wt% cH2Oini with a logVND of ~ 5 (in mm−3). The logVND increases strongly towards lower and higher cH2Oini by one order of magnitude. Furthermore, an important transition in evolution of vesiculation occurs at ~ 5.6 wt% cH2Oini. At lower cH2Oini, the initial VND is preserved during further decompression up to melt porosities of 30–50%. At higher cH2Oini, the initial vesicle population is erased at low melt porosities of 15–21% during further decompression. This observation is attributed to vesicle coalescence favored by low melt viscosity. In conclusion, cH2Oini determines the VND of initial phase separation and the evolution of vesiculation during decompression that controls the style of volcanic eruptions.
    Description: German Science Foundation
    Keywords: ddc:550.78 ; Vesicle number density ; Phonolitic melt ; Spinodal decomposition ; Melt degassing ; H2O concentration ; Fe-oxide nanolites
    Language: English
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    Geochemical focusing and sequestration of manganese during eutrophication of Lake Stechlin (NE Germany) (2020)
    Scholtysik, Grzegorz ; Dellwig, Olaf ; Roeser, Patricia ; [et al.]
    Springer International Publishing
    Details
    Publication Date: 2023-06-17
    Description: Significant sedimentation of manganese (Mn) in form of manganese oxides (MnOx) and the subsequent formation of authigenic calcium-rich rhodochrosite (Mn(Ca)CO3) were observed in the seasonally stratified hard water Lake Stechlin in north-eastern Germany. This manganese enrichment was assumed to be associated with recent eutrophication of the formerly oligotrophic lake. The mechanisms and processes involved were examined by analysing: (i) short sediment cores obtained from seven locations along a depth transect ranging from 69.5 m (the deepest point) to 38 m; (ii) sediment traps located at 20 m and 60 m water depths; (iii) water column profiles; and (iv) porewater profiles at 69.5 m and 58 m depths. Sedimentary Mn enrichment was observed at water depths below 56 m and increased to more than 25 wt% at the deepest site. Between 2010 and 2017, Mn accumulation at the deepest site was 815 g Mn m−2. Transfer of Mn from the shallower towards the deepest parts of the lake was initiated by reductive dissolution of MnOx and diffusion of dissolved Mn from the sediment to the overlying water column. Manganese was then dissipated via turbulent mixing and subsequently oxidised to MnOx before being transported towards the deepest zone. Transformation of the redeposited MnOx to Mn(Ca)CO3 favoured the final burial of Mn. We show that eutrophication and the areal spreading of anoxic conditions may intensify diagenetic processes and cause the spatial redistribution of Mn as well as its effective burial. Contrary to many previous findings, we show that increases of Mn and Mn/Fe can also be used as indicators for increasing anoxic conditions in previously oligotrophic lakes.
    Description: Leibniz-Gemeinschaft http://dx.doi.org/10.13039/501100001664
    Description: Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB) im Forschungsverbund Berlin e.V. (3473)
    Keywords: ddc:551.9 ; Lacustrine sediments ; Geochemical focusing ; Eutrophication ; Diagenesis ; Rhodochrosite ; Varves
    Language: English
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    Experimental Investigation on Static and Dynamic Bulk Moduli of Dry and Fluid-Saturated Porous Sandstones (2020)
    Springer Vienna
    Details
    Publication Date: 2023-06-17
    Description: Knowledge of pressure-dependent static and dynamic moduli of porous reservoir rocks is of key importance for evaluating geological setting of a reservoir in geo-energy applications. We examined experimentally the evolution of static and dynamic bulk moduli for porous Bentheim sandstone with increasing confining pressure up to about 190 MPa under dry and water-saturated conditions. The static bulk moduli (Ks) were estimated from stress–volumetric strain curves while dynamic bulk moduli (Kd) were derived from the changes in ultrasonic P- and S- wave velocities (~ 1 MHz) along different traces, which were monitored simultaneously during the entire deformation. In conjunction with published data of other porous sandstones (Berea, Navajo and Weber sandstones), our results reveal that the ratio between dynamic and static bulk moduli (Kd/Ks) reduces rapidly from about 1.5 − 2.0 at ambient pressure to about 1.1 at high pressure under dry conditions and from about 2.0 − 4.0 to about 1.5 under water-saturated conditions, respectively. We interpret such a pressure-dependent reduction by closure of narrow (compliant) cracks, highlighting that Kd/Ks is positively correlated with the amount of narrow cracks. Above the crack closure pressure, where equant (stiff) pores dominate the void space, Kd/Ks is almost constant. The enhanced difference between dynamic and static bulk moduli under water saturation compared to dry conditions is possibly caused by high pore pressure that is locally maintained if measured using high-frequency ultrasonic wave velocities. In our experiments, the pressure dependence of dynamic bulk modulus of water-saturated Bentheim sandstone at effective pressures above 5 MPa can be roughly predicted by both the effective medium theory (Mori–Tanaka scheme) and the squirt-flow model. Static bulk moduli are found to be more sensitive to narrow cracks than dynamic bulk moduli for porous sandstones under dry and water-saturated conditions.
    Description: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Keywords: ddc:550.78 ; Porous sandstone ; Static bulk modulus ; Dynamic bulk modulus ; Narrow (compliant) cracks ; Equant (stiff) pores
    Language: English
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    Sea Level Changes Affect Seismicity Rates in a Hydrothermal System Near Istanbul (2023)
    Details
    Publication Date: 2023-10-24
    Description: Small stress changes such as those from sea level fluctuations can be large enough to trigger earthquakes. If small and large earthquakes initiate similarly, high‐resolution catalogs with low detection thresholds are best suited to illuminate such processes. Below the Sea of Marmara section of the North Anatolian Fault, a segment of ≈ $\approx $150 km is late in its seismic cycle. We generated high‐resolution seismicity catalogs for a hydrothermal region in the eastern Sea of Marmara employing AI‐based and template matching techniques to investigate the link between sea level fluctuations and seismicity over 6 months. All high resolution catalogs show that local seismicity rates are larger during time periods shortly after local minima of sea level, when it is already rising. Local strainmeters indicate that seismicity is promoted when the ratio of differential to areal strain is the largest. The strain changes from sea level variations, on the order of 30–300 nstrain, are sufficient to promote seismicity.
    Description: Plain Language Summary: Quasi‐periodic phenomena are a natural probe to test how the Earth's responses to a certain stress perturbation. High‐resolution catalogs with low detection thresholds may provide a new opportunity to look for this type of earthquake triggering. A segment of 150 km below the Sea of Marmara section of the North Anatolian Fault is late in its seismic cycle. Here, we generated high‐resolution seismicity catalogs for 6 months covering a hydrothermal region south of Istanbul in the eastern Sea of Marmara including seismicity up to MW 4.5. For first time in this region, we document a strong effect of the Sea of Marmara water level changes on the local seismicity. Both high‐resolution catalogs show that local seismicity rates are significantly larger during time periods shortly after local minima on sea level, when the sea level is rising. The available local instrumentation provided an estimate of the strain changes that were sufficient to promote seismicity. If such small stress perturbations from sea level changes are enough to trigger seismicity, it may suggest that the region is very close to failure.
    Description: Key Points: We generated enhanced seismicity catalogs to investigate the potential link between sea level change and seismicity in a hydrothermal region. Higher seismicity rates from the entire and declustered catalogs are observed during time periods when sea level is rising. Strain estimates from local strainmeters show that seismicity was promoted during reduced normal and enhanced shear strain conditions.
    Description: Helmholtz Association http://dx.doi.org/10.13039/501100009318
    Description: Alexander von Humboldt‐Stiftung http://dx.doi.org/10.13039/100005156
    Description: National Science Foundation http://dx.doi.org/10.13039/100000001
    Description: National Aeronautics and Space Administration http://dx.doi.org/10.13039/100000104
    Description: VW momentum
    Description: https://tdvms.afad.gov.tr/
    Description: http://www.koeri.boun.edu.tr/sismo/2/earthquake-catalog/
    Description: https://www.unavco.org/data/strain-seismic/bsm-data/bsm-data.html
    Keywords: ddc:551.22 ; seismicity catalog ; sea level change ; hydrothermal region ; strain ; strainmeter ; solid Earth tides
    Language: English
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    Understanding Micropolar Theory in the Earth Sciences I: The Eigenfrequency ωr (2021)
    Springer International Publishing
    Details
    Publication Date: 2023-12-05
    Description: Even though micropolar theories are widely applied for engineering applications such as the design of metamaterials, applications in the study of the Earth’s interior still remain limited and in particular in seismology. This is due to the lack of understanding of the required elastic material parameters present in the theory as well as the eigenfrequency ωr which is not observed in seismic data. By showing that the general dynamic equations of the Timoshenko’s beam is a particular case of the micropolar theory we are able to connect micropolar elastic parameters to physically measurable quantities. We then present an alternative micropolar model that, based on the same physical basis as the original model, circumvents the problem of the original eigenfrequency ωr laking in seismological data. We finally validate our model with a seismic experiment and show it is relevant to explain observed seismic dispersion curves.
    Description: Westfälische Wilhelms-Universität Münster (1056)
    Keywords: ddc:551.22 ; Timoshenko beam theory ; plate theory ; Cosserat theory ; micropolar theory ; seismology
    Language: English
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    Accessories in Kaiserstuhl carbonatites and related rocks as accurate and faithful recorders of whole rock age and isotopic composition (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-07-06
    Description: The accessories perovskite, pyrochlore, zirconolite, calzirtite and melanite from carbonatites and carbonate-rich foidites from the Kaiserstuhl are variously suited for the in situ determination of their U–Pb ages and Sr, Nd- and Hf-isotope ratios by LA-ICP-MS. The 143Nd/144Nd ratios may be determined precisely in all five phases, the 176Hf/177Hf ratios only in calzirtite and the 87Sr/86Sr ratios in perovskites and pyrochlores. The carbonatites and carbonate-rich foidites belong to one of the three magmatic groups that Schleicher et al. (1990) distinguished in the Kaiserstuhl on the basis of their Sr, Nd and Pb isotope ratios. Tephrites, phonolites and essexites (nepheline monzogabbros) form the second and limburgites (nepheline basanites) and olivine nephelinites the third. Our 87Sr/86Sr isotope data from the accessories overlap with the carbonatite and olivine nephelinite fields defined by Schleicher et al. (1990) but exhibit a much narrower range. These and the εNd and εHf values plot along the mantle array in the field of oceanic island basalts relatively close to mid-ocean ridge basalts. Previously reported K–Ar, Ar–Ar and fission track ages for the Kaiserstuhl lie between 16.2 and 17.8 Ma. They stem entirely from the geologically older tephrites, phonolites and essexites. No ages existed so far for the geologically younger carbonatites and carbonate-rich foidites except for one apatite fission track age (15.8 Ma). We obtained precise U–Pb ages for zirconolites and calzirtites of 15.66, respectively 15.5 Ma (± 0.1 2σ) and for pyrochlores of 15.35 ± 0.24 Ma. Only the perovskites from the Badberg soevite yielded a U–P concordia age of 14.56 ± 0.86 Ma while the perovskites from bergalites (haüyne melilitites) only gave 206Pb/238U and 208Pb/232Th ages of 15.26 ± 0.21, respectively, 15.28 ± 0.48 Ma. The main Kaiserstuhl rock types were emplaced over a time span of 1.6 Ma almost 1 million years before the carbonatites and carbonate-rich foidites. These were emplaced within only 0.32 Ma.
    Description: Frankfurt Institute for Advanced Studies (FIAS) (4401)
    Keywords: ddc:551.9 ; In situ determination of Sr, Nd and Hf isotope ratios ; In situ determination of U–Pb ages ; Accessories in carbonatites ; Kaiserstuhl
    Language: English
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    Oxygen Consumption of Resuspended Sediments of the Upper Elbe Estuary: Process Identification and Prognosis (2021)
    Springer Netherlands
    Details
    Publication Date: 2023-08-25
    Description: The resuspension of sediment leads to an increased release of nutrients and organic substances into the overlying water column, which can have a negative effect on the oxygen budget. Especially in the warmer months with a lower oxygen saturation and higher biological activity, the oxygen content can reach critical thresholds in estuaries like the upper Elbe estuary. Many studies have dealt with the nutrient fluxes that occur during a resuspension event. However, the sediment properties that influence the oxygen consumption potential (OCP) and the different biochemical processes have not been examined in detail. To fill this gap, we investigated the biogeochemical composition, texture, and OCP of sediments at 21 locations as well as the temporal variability within one location for a period of 2 years (monthly sampling) in the upper Elbe estuary. The OCP of sediments during a seven-day resuspension event can be described by the processes of sulphate formation, nitrification, and mineralisation. Chlorophyll, total nitrogen (Ntotal), and total organic carbon showed the highest correlations with the OCP. Based on these correlations, we developed a prognosis model to calculate the OCP for the upper Elbe estuary with a single sediment parameter (Ntotal). The model is well suited to calculate the oxygen consumption of resuspended sediments in the Hamburg port area during the relevant warmer months and shows a normalised root mean squared error of 〈 0.11 ± 0.13. Thus, the effect of maintenance measures such as water injection dredging and ship-induced wave on the oxygen budget of the water can be calculated.
    Description: Hamburg Port Authority
    Description: Universität Hamburg (1037)
    Keywords: ddc:551.9 ; Sediment ; Resuspension ; Oxygen consumption ; Nutrients ; Elbe estuary ; Modelling
    Language: English
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    Triple‐Element Stable Isotope Analysis of Chloromethane Emitted by Royal Fern and Degraded by Club Moss (2023)
    Details
    Publication Date: 2023-09-12
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Chloromethane (CH〈sub〉3〈/sub〉Cl) is the most abundant natural chlorinated organic compound in the atmosphere playing an important role in catalyzing stratospheric ozone loss. Vegetation emits the largest amounts of CH〈sub〉3〈/sub〉Cl to the atmosphere but its source strength is highly uncertain leading also to large uncertainties in the global budget of CH〈sub〉3〈/sub〉Cl. Triple‐element stable isotope analysis may help to reduce uncertainties because it provides additional process‐level information compared to conventional quantification methods. In this study we performed experiments to obtain a first triple‐elemental isotopic fingerprint (〈sup〉2〈/sup〉H, 〈sup〉13〈/sup〉C, 〈sup〉37〈/sup〉Cl) of CH〈sub〉3〈/sub〉Cl emitted by a relevant plant species (royal fern, 〈italic〉Osmunda regalis〈/italic〉). Isotopic values of all three elements showed considerable differences compared to isotopic values of industrially manufactured CH〈sub〉3〈/sub〉Cl which bodes well for future applications to distinguish individual sources. Isotopic analysis of potential precursors (rain, methoxy groups) of CH〈sub〉3〈/sub〉Cl in plants revealed no measurable change of hydrogen and chlorine isotopic ratios during formation which may provide a simpler route to estimate the isotopic composition of CH〈sub〉3〈/sub〉Cl emissions. Plant degradation experiments of CH〈sub〉3〈/sub〉Cl were carried out with club moss (〈italic〉Selaginella kraussiana〈/italic〉) revealing significant isotopic fractionation for all three elements. The fractionation pattern characterized by epsilon and lambda is inconsistent with known biotic dechlorination reactions indicating a yet unreported biotic degradation mechanism for CH〈sub〉3〈/sub〉Cl. Overall, this study provides first insights into the triple‐elemental isotopic fingerprint of plant emissions and degradation. The results may represent important input data for future isotope‐based models to improve global budget estimates of CH〈sub〉3〈/sub〉Cl and to explore the yet unknown degradation pathways.〈/p〉
    Description: Plain Language Summary: Chloromethane is the most abundant chlorinated organic compound in the atmosphere. It contributes to the destruction of the ozone layer that protects us from skin cancer and genetic damage. Currently, we do not have a good understanding of the sources and removal processes of chloromethane in the atmosphere. In this paper, we use a technique that takes advantage of the different varieties of a chemical element. These so‐called isotopes behave differently during chemical reactions that lead to individual isotopic fingerprints depending on the source or removal process. We used isotopic fingerprints of all three chemical elements in chloromethane and showed that chloromethane produced by a plant (royal fern) differs substantially from chloromethane manufactured by industry. Other plant species such as club moss are able to remove chloromethane from the atmosphere but it is often not clear how this occurs. Isotopic analysis revealed that the studied club moss uses a unique, thus far unknown, way to break down chloromethane. This study demonstrates how information extracted from isotopic fingerprints will help to improve our understanding of sources and removal processes of chloromethane in the atmosphere. It can help to better predict how ozone destruction in the stratosphere affects us in the future.〈/p〉
    Description: Key Points: First triple‐element isotopic characterization of plant CH〈sub〉3〈/sub〉Cl emission and degradation. Plant degradation experiments suggest another yet unknown transformation pathway. Important input data for future isotope based models to improve understanding of global CH〈sub〉3〈/sub〉Cl budget.
    Description: Helmholtz Association http://dx.doi.org/10.13039/501100009318
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.48758/ufz.13388
    Keywords: ddc:551.9 ; CH3Cl ; ozone depletion ; isotopes ; plant emissions ; halogens
    Language: English
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    Induced seismicity due to hydraulic fracturing near Blackpool, UK: source modeling and event detection (2021)
    Springer Netherlands
    Details
    Publication Date: 2023-07-20
    Description: Monitoring small magnitude induced seismicity requires a dense network of seismic stations and high-quality recordings in order to precisely determine events’ hypocentral parameters and mechanisms. However, microseismicity (e.g. swarm activity) can also occur in an area where a dense network is unavailable and recordings are limited to a few seismic stations at the surface. In this case, using advanced event detection techniques such as template matching can help to detect small magnitude shallow seismic events and give insights about the ongoing process at the subsurface giving rise to microseismicity. In this paper, we study shallow microseismic events caused by hydrofracking of the PNR-2 well near Blackpool, UK, in 2019 using recordings of a seismic network which was not designed to detect and locate such small events. By utilizing a sparse network of surface stations, small seismic events are detected using template matching technique. In addition, we apply a full-waveform moment tensor inversion to study the focal mechanisms of larger events (ML 〉 1) and used the double-difference location technique for events with high-quality and similar waveforms to obtain accurate relative locations. During the stimulation period, temporal changes in event detection rate were in agreement with injection times. Focal mechanisms of the events with high-quality recordings at multiple stations indicate a strike-slip mechanism, while a cross-section of 34 relocated events matches the dip angle of the active fault.
    Description: Karlsruher Institut für Technologie (KIT) (4220)
    Description: https://earthquakes.bgs.ac.uk/data/broadband_stationbook.html
    Keywords: ddc:551.22 ; Event detection ; Microseismicity ; Source modeling ; Template matching
    Language: English
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    The Interface Between Magma and Earth's Atmosphere (2022)
    Details
    Publication Date: 2023-07-20
    Description: Volatiles released from magma can form bubbles and leave the magma body to eventually mix with atmospheric air. The composition of those volatiles, as derived from measurements made after their emission, is used to draw conclusions on processes in the Earth's interior or their influences on Earth's atmosphere. So far, the discussion of the influence of high‐temperature mixing with atmospheric air (in particular oxygen) on the measured volcanic gas composition is almost exclusively based on thermodynamic equilibrium (TE) considerations. By modeling the combined effects of C‐H‐O‐S reaction kinetics, turbulent mixing, and associated cooling during the first seconds after magmatic gas release into the atmosphere we show that the resulting gas compositions generally do not represent TE states, with individual species (e.g., CO, H2, H2S, OCS, SO3, HO2, H2O2) deviating by orders of magnitude from equilibrium levels. Besides revealing the chemical details of high‐temperature emission processes, our results question common interpretations of volcanic gas studies, particularly affecting the present understanding of auto‐catalytic conversion of volcanic halogen species in the atmosphere and redox state determination from volcanic plume gas measurements.
    Description: Plain Language Summary: A major fraction of magmatic gas emissions are released into the atmosphere from open vents. The emission processes are characterized by fast turbulent mixing with atmospheric air (within seconds) and associated rapid cooling. Hardly anything is known about the chemical kinetics within this brief mixing and cooling period. We simulate the chemical kinetics during the first seconds of hot magmatic gases in the atmosphere and find severe deviation to common interpretations and central thermodynamic equilibrium assumptions prevailing in volcanic gas geochemistry.
    Description: Key Points: We model the chemical kinetics of high‐temperature volcanic gas emissions within the first seconds of mixing with atmospheric air. We identify key chemical processes within the magma‐atmosphere interface and quantify influences on the volcanic plume composition. Our results question common assumptions prevailing in volcanic gas geochemistry and refine interpretations of gas emissions from open vents.
    Description: German Research Foundation
    Keywords: ddc:551.9 ; volcanic gas emissions ; kinetic chemistry modeling ; atmospheric chemistry ; magmatic redox states ; reactive halogen chemistry
    Language: English
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    Seismic and Aseismic Preparatory Processes Before Large Stick–Slip Failure (2020)
    Springer International Publishing
    Details
    Publication Date: 2023-07-20
    Description: Natural earthquakes often have very few observable foreshocks which significantly complicates tracking potential preparatory processes. To better characterize expected preparatory processes before failures, we study stick-slip events in a series of triaxial compression tests on faulted Westerly granite samples. We focus on the influence of fault roughness on the duration and magnitude of recordable precursors before large stick–slip failure. Rupture preparation in the experiments is detectable over long time scales and involves acoustic emission (AE) and aseismic deformation events. Preparatory fault slip is found to be accelerating during the entire pre-failure loading period, and is accompanied by increasing AE rates punctuated by distinct activity spikes associated with large slip events. Damage evolution across the fault zones and surrounding wall rocks is manifested by precursory decrease of seismic b-values and spatial correlation dimensions. Peaks in spatial event correlation suggest that large slip initiation occurs by failure of multiple asperities. Shear strain estimated from AE data represents only a small fraction (〈 1%) of total shear strain accumulated during the preparation phase, implying that most precursory deformation is aseismic. The relative contribution of aseismic deformation is amplified by larger fault roughness. Similarly, seismic coupling is larger for smooth saw-cut faults compared to rough faults. The laboratory observations point towards a long-lasting and continuous preparation process leading to failure and large seismic events. The strain partitioning between aseismic and observable seismic signatures depends on fault structure and instrument resolution.
    Description: Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ http://dx.doi.org/10.13039/501100010956
    Description: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Keywords: ddc:551.22 ; Earthquakes ; rupture ; stick–slip tests ; seismic ; aseismic
    Language: English
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    Thermal stress, cooling-rate and fictive temperature of silicate melts (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-08-08
    Description: The unknown cooling-rate history of natural silicate melts can be investigated using differential scanning heat capacity measurements together with the limiting fictive temperature analysis calculation. There are a range of processes occurring during cooling and re-heating of natural samples which influence the calculation of the limiting fictive temperature and, therefore, the calculated cooling-rate of the sample. These processes occur at the extremes of slow cooling and fast quenching. The annealing of a sample at a temperature below the glass transition temperature upon cooling results in the subsequent determination of cooling-rates which are up to orders of magnitude too low. In contrast, the internal stresses associated with the faster cooling of obsidian in air result in an added exothermic signal in the heat capacity trace which results in an overestimation of cooling-rate. To calculate cooling-rate of glass using the fictive temperature method, it is necessary to create a calibration curve determined using known cooling- and heating-rates. The calculated unknown cooling-rate of the sample is affected by the magnitude of mismatch between the original cooling-rate and the laboratory heating-rate when using the matched cooling-/heating-rate method to derive a fictive temperature/cooling-rate calibration curve. Cooling-rates slower than the laboratory heating-rate will be overestimated, while cooling-rates faster than the laboratory heating-rate are underestimated. Each of these sources of error in the calculation of cooling-rate of glass materials—annealing, stress release and matched cooling/heating-rate calibration—can affect the calculated cooling-rate by factor of 10 or more.
    Description: Georg-August-Universität Göttingen (1018)
    Keywords: ddc:550.78 ; Fictive temperature ; Annealing ; Thermal stress ; Cooling-rate ; Calorimetry
    Language: English
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    Influence of CO2 on the rheology of melts from the Colli Albani Volcanic District (Italy): foidite to phonolite (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-08-08
    Description: In this study, the influence of CO〈sub〉2〈/sub〉 on the rheology of silica poor and K-rich melts from highly explosive eruptions from the Colli Albani Volcanic District (Italy) (CAVD) is measured for the first time. The investigated melts range from foidite to tephri-phonolite to tephrite from the CAVD to a phonolite from the Vesuvius (Italy) with CO〈sub〉2〈/sub〉 concentrations up to 0.50 wt%. Viscosity and calorimetric measurements are performed in the glass transition range Tg between 600 and 780 °C. Although nominally anhydrous, the investigated melts contain H〈sub〉2〈/sub〉O concentrations up to 0.23 wt%. The data exhibit a decrease in viscosity of approx. 100.40 Pa s for the phonolitic composition with ~ 0.07 wt% CO〈sub〉2〈/sub〉 and a Tg reduced by approx. 14 °C. For the tephritic composition, Tg is approx. 5 °C lower and has a viscosity reduced by 100.25 Pa s for the sample containing ~ 0.5 wt% CO〈sub〉2〈/sub〉. Calorimetric measurements of the tephri-phonolite show lowered onset of Tg by approx. 6 °C for the melt with ~ 0.11 wt% CO2 and Tg of the foidite appears not to be influenced by a CO〈sub〉2〈/sub〉 concentration of ~ 0.37 wt% CO〈sub〉2〈/sub〉. However, these tephri-phonolitic and foiditic melts foamed during calorimetric measurements preventing a reliable measurement. It would appear that most of this overall drop in viscosity is caused by the small amounts of H〈sub〉2〈/sub〉O in the melts with CO〈sub〉2〈/sub〉 slightly reducing the viscosity or having no effect on viscosity. Additionally, it is shown that the reduction in viscosity decreases with an increasing degree of the depolymerisation for the investigated melts. Consequently, the explosive style of the CAVD eruptions is mainly caused by crystals and bubbles which form and rise during magma storage and ascent which increases the magma viscosity whereas the CO〈sub〉2〈/sub〉 in the melt slightly reduces the viscosity.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Georg-August-Universität Göttingen (1018)
    Keywords: ddc:550.78 ; Viscosity ; Calorimetry ; Colli Albani ; Carbon dioxide ; Glass transition ; Foidite
    Language: English
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    The redox dependence of titanium isotope fractionation in synthetic Ti-rich lunar melts (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-08-08
    Description: Equilibria between Ti oxides and silicate melt lead to Ti isotope fractionation in terrestrial samples, with isotopically light Ti oxides and isotopically heavy coexisting melt. However, while Ti is mostly tetravalent in terrestrial samples, around 10% of the overall Ti is trivalent at f〈sub〉O2〈/sub〉 relevant to lunar magmatism (~ IW-1). The different valences of Ti in lunar samples, could additionally influence Ti stable isotope fractionation during petrogenesis of lunar basalts to an unknown extent. We performed an experimental approach using gas mixing furnaces to investigate the effect of Ti oxide formation at different f〈sub〉O2〈/sub〉 on Ti stable isotope fractionation during mare basalt petrogenesis. Two identical bulk compositions were equilibrated simultaneously during each experiment to guarantee comparability. One experiment was investigated with the EPMA to characterize the petrology of experimental run products, whereas the second experiment was crushed, and fabricated phases (i.e., oxides, silicates and glass) were handpicked, separated and digested. An aliquot of each sample was mixed with a Ti double-spike, before Ti was separated from matrix and interfering elements using a modified HFSE chemistry. Our study shows f〈sub〉O2〈/sub〉-dependent fractionation within seven samples from air to IW-1, especially ∆49Ti〈subs〈armalcolite〈/sub〉-melt and ∆49Ti〈sub〉armalcolite-orthopyroxene〈/sub〉 become more fractionated from oxidized to reduced conditions (− 0.092 ± 0.028-  − 0.200 ± 0.033 ‰ and  − 0.089 ± 0.027- − 0.250 ± 0.049 ‰, respectively), whereas ∆49Ti〈sub〉orthopyroxene〈/sub〉-melt shows only a minor fractionation (− 0.002 ± 0.017-0.050 ± 0.025 ‰). The results of this study show that Ti isotope fractionation during mare basalt petrogenesis is expected to be redox dependent and mineral-melt fractionation as commonly determined for terrestrial fO2 may not be directly applied to a lunar setting. This is important for the evaluation of Ti isotope fractionation resulting from lunar magmatism, which takes place under more reducing conditions compared to the more oxidized terrestrial magmatism.
    Description: Deutsche Forschungsgemeinschaft
    Description: Projekt DEAL
    Keywords: ddc:550.78 ; Titanium isotopes ; Lunar magma ocean ; Fractionation ; Experiments ; Ti oxides ; Armalcolite
    Language: English
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    Experimental observations of aquifer storage and recovery in brackish aquifers using multiple partially penetrating wells (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-08-08
    Description: Aquifer storage and recovery systems using multiple partially penetrating wells (MPPW-ASR) can form a viable solution to the problem of freshwater buoyancy when using brackish aquifers for freshwater storage. This study presents the result of a series of laboratory experiments that aimed at visualizing the shape of freshwater bodies injected into a brackish aquifer and determining the effect on the recovery efficiency (RE) of several MPPW-ASR operational variables. A model aquifer was built in a Plexiglas tank using glass beads and water was injected and abstracted through point and vertical wells, which were operated in various combinations. Numerical models were used to support the interpretation of the time-lapse photographs, and showed that three-dimensional flow effects had to be considered for a correct interpretation of the visible dye patterns. Upward migration of both fresh (during injection) and brackish water (during recovery) along the vertical wells was observed, indicating that the role of well infrastructure as conduits is a critical design criterion for real-world systems. Gravitational instabilities formed when freshwater did not extend all the way to the top of the aquifer, and this negatively impacted the RE by causing greater mixing. The positive freshwater buoyancy led to freshwater bodies that became narrower with depth, and the formation of thin, elongated buffer zones along the aquifer top in multicycle experiments. Up-coning below abstraction wells resulted in lower RE values, reinforcing the potential of scavenger wells to enhance MPPW-ASR system performance.
    Description: Bundesanstalt für Geowissenschaften und Rohstoffe (BGR) (4230)
    Keywords: ddc:550.78 ; Artificial recharge ; Laboratory experiments/measurements ; Numerical modelling ; Multiple partially penetrating wells ; Salt-water/fresh-water relations
    Language: English
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    Trace element fractionation between biotite, allanite, and granitic melt (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-08-08
    Description: The partitioning of a large suite of trace elements between biotite and water-saturated granitic melt was measured at 2 kbar and 700—800 ˚C. To reach equilibrium and to grow biotite crystals large enough for analysis, runs usually lasted from 30 to 45 days. In every charge, a few trace elements were initially doped at the 0.1—0.5 wt. % level and analyzed by electron microprobe after the run. First-row transition metal ions are highly compatible in biotite with D〈sup〉biotite/melt〈/sup〉 of 17 for Ti, 35 for V, 47 for Co, 174 for Ni, and 5.8 for Zn. A very notable exception is Cu with D〈sup〉biotite/melt〈/sup〉 〈 0.9. This is likely one of the reasons why Cu is enriched together with Mo (D〈sup〉biotite/melt〈/sup〉 = 0.29) in porphyry deposits associated with intermediate to felsic plutons, while the other transition metals are not. Both Nb and Ta are mildly compatible in biotite with D〈sup〉biotite/melt〈/sup〉 being larger for Nb (3.69) than for Ta (1.89). Moderate (15—30%) biotite fractionation would be sufficient to reduce the Nb/Ta ratio from the chondritic value to the range observed in the continental crust. Moreover, the strong partitioning of Ti into biotite implies that already modest biotite fractionation suppresses the saturation of Ti-oxide phases and thereby indirectly facilitates the enrichment of Ta over Nb in the residual melt. The heavy alkalis, alkaline earths, and Pb are only mildly fractionated between biotite and melt (D〈sup〉biotite/melt〈/sup〉 = 3.8 for Rb, 0.6 for Cs, 0.6 for Sr, 1.8 for Ba, 0.7 for Pb). The rare earth elements are generally incompatible in biotite, with a minimum for Dbiotite/melt of 0.03–0.06 at Gd, Tb, and Dy, while both the light and heavy rare earths are less incompatible (e.g. D〈sup〉biotite/melt〈/sup〉 = 0.6 for La and 0.3 for Yb). This behavior probably reflects a partitioning into two sites, the K site for the light rare earths and the octahedral Mg site for the heavy rare earths. There is no obvious dependence of the rare earth partition coefficients on tetrahedral Al in the biotite, presumably because charge balancing by cation vacancies is possible. Allanite was found as run product in some experiments. For the light rare earths, D〈sup〉allanite/melt〈/sup〉 is very high (e.g. 385 to 963 for Ce and Nd) and appears to increase with decreasing temperatures. However, the rather high solubility of allanite in the melts implies that it likely only crystallizes during the last stages of cooling of most magmas, except if the source magma is unusually enriched in rare earths.
    Description: Deutsche Forschungsgemeinschaft
    Description: Universität Bayreuth (3145)
    Keywords: ddc:550.78 ; Biotite ; Allanite ; Granite ; Partitioning ; Solubility ; Rare earths ; Niobium ; Tantalum ; Nb/Ta ratio ; Porphyry copper deposits
    Language: English
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    Sub-arc mantle enrichment in the Sunda rear-arc inferred from HFSE systematics in high-K lavas from Java (2021)
    Kirchenbaur, M. ; Schuth, S. ; Barth, A. R. ; [et al.]
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-08-08
    Description: Many terrestrial silicate reservoirs display a characteristic depletion in Nb, which has been explained in some studies by the presence of reservoirs on Earth with superchondritic Nb/Ta. As one classical example, K-rich lavas from the Sunda rear-arc, Indonesia, have been invoked to tap such a high-Nb/Ta reservoir. To elucidate the petrogenetic processes active beneath the Java rear-arc and the causes for the superchondritic Nb/Ta in some of these lavas, we studied samples from the somewhat enigmatic Javanese rear-arc volcano Muria, which allow conclusions regarding the across-arc variations in volcanic output, source mineralogy and subduction components. We additionally report some data for an along-arc sequence of lavas from the Indonesian part of the Sunda arc, extending from Krakatoa in the west to the islands of Bali and Lombok in the east. We present major and trace element concentrations, Sr–Nd–Hf–Pb isotope compositions, and high-field-strength element (HFSE: Nb, Ta, Zr, Hf, W) concentrations obtained via isotope dilution and MC-ICP-MS analyses. The geochemical data are complemented by melting models covering different source compositions with slab melts formed at variable P–T conditions. The radiogenic isotope compositions of the frontal arc lavas in combination with their trace element systematics confirm previously established regional variations of subduction components along the arc. Melting models show a clear contribution of a sediment-derived component to the HFSE budget of the frontal arc lavas, particularly affecting Zr–Hf and W. In contrast, the K-rich rear-arc lavas tap more hybrid and enriched mantle sources. The HFSE budget of the rear-arc lavas is in particular characterized by superchondritic Nb/Ta (up to 25) that are attributed to deep melting involving overprint by slab melts formed from an enriched garnet–rutile-bearing eclogitic residue. Sub-arc slab melting was potentially triggered along a slab tear beneath the Sunda arc, which is the result of the forced subduction of an oceanic basement relief ~ 8 Myr ago as confirmed by geophysical studies. The purported age of the slab tear coincides with a paucity in arc volcanism, widespread thrusting of the Javanese basement crust as well as the short-lived nature of the K-rich rear-arc volcanism at that time.
    Description: Deutscher Akademischer Austauschdienst http://dx.doi.org/10.13039/501100001655
    Description: Gottfried Wilhelm Leibniz Universität Hannover (1038)
    Keywords: ddc:551.9 ; Rear-arc volcanism ; Superchondritic Nb/Ta ; Muria ; Sunda arc
    Language: English
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    Determination of Fracture Toughness of Mode I Fractures from Three-Point Bending Tests at Elevated Confining Pressures (2021)
    Springer Vienna
    Details
    Publication Date: 2023-07-27
    Description: Fracture toughness is one of the key parameters for the characterization of brittle rock fracturing. Yet, constraints on it mainly rest on measurements performed at ambient pressure, although rock fracturing frequently occurs at elevated pressures even in geotechnical applications. To address the lack of a generally accepted evaluation procedure for tests at elevated pressure we explored the conditions for initiation and propagation of mode I fractures in samples subjected to bending at elevated pressure by numerical modeling and analytical considerations of the involved angular moments. We derived an evaluation procedure and applied it to experimental observations for specimens with either a chevron or a single-edge notch of four different rocks (a granite, a limestone, a marble and a sandstone) subjected to three-point bending at confining pressures up to 30 MPa. Two sealing methods were considered. Specimens were either varnished or jacketed by a rubber tube, differing in whether pressure is allowed to build up inside the pre-fabricated notch or not, respectively. Irrespective of notch geometry and sealing method, the determined toughness values increase significantly with confining pressure. The apparent toughness determined for jacketed specimens is, however, larger than that for varnished specimens, for which toughness seems to reach a plateau with increasing pressure. The similarity of the pressure dependence of the toughness determined for varnished, i.e., uniformly pressurized, samples with that of other physical properties suggests that it is controlled by the closure of pre-existing micro-cracks; the absence of pressure dependence beyond some tens of MPa suggests that non-linearity effects may not be as severe at depths beyond a few kilometers as previously discussed. Our study points to the necessity of resolving numerical issues associated with compressed fractures and of further improving experimental facilities for the determination of fracture toughness at elevated pressure.
    Description: German Federal Ministry of Economy
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Ruhr-Universität Bochum (1007)
    Keywords: ddc:550.78 ; Toughness ; Confining pressure ; Three-point bending tests ; Chevron-edge notch
    Language: English
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    Damage Evolution of Coal with Inclusions Under Triaxial Compression (2021)
    Springer Vienna
    Details
    Publication Date: 2023-07-27
    Description: Along with the advance of the working face, coal experiences different loading stages. Laboratory tests and numerical simulations of fracture and damage evolution aim to better understand the structural stability of coal layers. Three-dimensional lab tests are performed and coal samples are reconstructed using X-ray computer tomography (CT) technique to get detailed information about damage and deformation state. Three-dimensional discrete element method (DEM)-based numerical models are generated. All models are calibrated against the results obtained from uniaxial compressive strength (UCS) tests and triaxial compression (TRX) tests performed in the laboratory. A new approach to simulate triaxial compression tests is established in this work with significant improved handling of the confinement to get realistic simulation results. Triaxial tests are simulated in 3D with the particle-based code PFC3D using a newly developed flexible wall (FW) approach. This new numerical simulation approach is validated by comparison with laboratory tests on coal samples. This approach involves an updating of the applied force on each wall element based on the flexible nature of a rubber sleeve. With the new FW approach, the influence of the composition (matrix and inclusions) of the samples on the peak strength is verified. Force chain development and crack distributions are also affected by the spatial distribution of inclusions inside the sample. Fractures propagate through the samples easily at low confining pressures. On the contrary, at high confining pressure, only a few main fractures are generated with orientation towards the side surfaces. The evolution of the internal fracture network is investigated. The development of microcracks is quantified by considering loading, confinement, and structural character of the rock samples. The majority of fractures are initiated at the boundary between matrix and inclusions, and propagate along their boundaries. The internal structure, especially the distribution of inclusions has significant influence on strength, deformation, and damage pattern.
    Description: Technische Universität Bergakademie Freiberg (3135)
    Keywords: ddc:550.78 ; Coal sample ; X-ray CT ; Sample reconstruction ; Triaxial compression test ; Discrete element modeling ; Flexible wall approach
    Language: English
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  • 88
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    Archaeoseismological study of the Cherichira aqueduct bridge, Kairouan, Tunisia (2021)
    Springer International Publishing
    Details
    Publication Date: 2023-07-21
    Description: In the past, several destructive earthquakes have occurred in the North African Atlas Mountain ranges located along the Africa–Eurasia plate boundary. Although the region is rich with impressive archaeological sites, including those in modern Tunisia, few comprehensive archaeoseismological studies have been conducted. Historic sources account at least three damaging earthquakes in the Kairouan area in central Tunisia between AD 859 and 1041. Little is known about which faults triggered these earthquakes or the size of these events. The water supply of the city of Kairouan depended on a 32-km-long aqueduct with a large bridge (now partially collapsed) at the confluence of the de Mouta and Cherichira rivers. The original bridge of Roman construction was retrofitted twice during the Aghlabid period (AD 800–903) and probably in AD 995 during the Fatimid period. The ruined section of the bridge shows damage which might be related to the AD 859 earthquake shaking. Here, we present a detailed study of the history, the status and the damage of the Cherichira aqueduct bridge using previous historic accounts and written works, a 3D laser scan model, local geological and seismological characteristics, and include results of radiocarbon dating and a timeline of events. In addition to earthquake ground motions, we consider severe flash floods on the bridge as a potential cause of the damage. We estimate the severity of such flash floods and develop a model with 18 earthquake scenarios on local reverse and strike-slip faults with magnitudes between MW 6.1 and 7.2. While a few damage patterns might be indicative of flooding, most damage can be attributed to earthquakes. It is highly probable that the earthquake in AD 859 caused enough damage to the Aghlabid bridge to render it dysfunctional; however, to resolve the question of whether another earthquake in AD 911 or 1041 caused the complete destruction of the previously retrofitted aqueduct by the Fatimids requires dating of additional sections of the bridge.
    Description: Universität zu Köln (1017)
    Keywords: ddc:551.22 ; Archaeoseismology ; Cherichira aqueduct ; Kairouan ; Historic earthquake ; Flash flood ; Laser scan ; Dating ; Synthetic seismogram
    Language: English
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  • 89
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    The composition of subduction zone fluids and the origin of the trace element enrichment in arc magmas (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-07-21
    Description: The partitioning of major and trace elements between eclogite and aqueous fluids with variable salinity was studied at 700–800 °C and 4–6 GPa in piston cylinder and multi anvil experiments. Fluid compositions were determined using the diamond trap technique combined with laser ablation ICP-MS measurements in the frozen state. In addition to NaCl, SiO2 is the main solute in the fluids. The fluid/eclogite partition coefficients of the large ion lithophile elements (LILE), such as Rb, Cs, Sr, and Ba as well as those of the light rare earths (LREE), of Pb, and of U increase by up to three orders of magnitude with salinity. These elements will therefore be efficiently transported by saline fluids. On the other hand, typical high field strength elements, such as Ti, Nb, and Ta, are not mobilized even at high salinities. Increasing temperature and pressure gradually increases the partitioning into the fluid. In particular, Th is mobilized by silica-rich fluids at 6 GPa already at low salinities. We show that we can fully reproduce the trace element enrichment pattern of primitive arc basalts by adding a few percent of saline fluid (with 5–10 wt% Cl) released from the basaltic slab to the zone of melting in the mantle wedge. Assuming 2 wt% of rutile in the eclogite equilibrated with the saline fluid produces a negative Nb Ta anomaly that is larger than in most primitive arc basalts. Therefore, we conclude that the rutile fraction in the subducted eclogite below most arcs is likely 〈 1 wt%. In fact, saline fluids would even produce a noticeable negative Nb Ta anomaly without any rutile in the eclogite residue. Metasomatism by sediment melts alone, on the other hand, is unable to produce the enrichment pattern seen in arc basalts. We, therefore, conclude that at least for primitive arc basalts, the release of hydrous fluids from the basaltic part of the subducted slab is the trigger for melting and the main agent of trace element enrichment. The contribution of sediment melts to the petrogenesis of these magmas is likely negligible. In the supplementary material, we provide a “Subduction Calculator” in Excel format, which allows the calculation of the trace element abundance pattern in primitive arc basalts as function of fluid salinity, the amount of fluid released from the basaltic part of the subducted slab, the fluid fraction added to the source, and the degree of melting.
    Description: DFG
    Description: Universität Bayreuth (3145)
    Keywords: ddc:551.9 ; Subduction zone fluids ; Fluid/eclogite partitioning ; Arc magmas ; Salinity ; Trace elements ; Nb Ta anomaly ; Primitive arc basalts
    Language: English
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    The Energetic 2022 Seismic Unrest Related to Magma Intrusion at the North Mid‐Atlantic Ridge (2023)
    Details
    Publication Date: 2023-07-21
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉A seismic swarm affected the 53.3°–54.3° Latitude North section of the Mid‐Atlantic Ridge from 26 September to 10 December 2022. We rely on regional, teleseismic and array data to relocate 61 hypocenters and derive 77 moment tensors. The 2022 swarm released a cumulative moment equivalent to Mw 6.3. Seismicity was shallow (7 ± 3 km depth). Most earthquakes are located along the ridge axis with typical, NS oriented normal faulting mechanisms, but a few among the largest and latest earthquakes have unusual thrust mechanisms and locations as far as ∼25 km from the ridge. We attribute the swarm to a shallow magmatic intrusion, with a vertical dike first propagating ∼60 km along axis, accompanied by shallow normal faulting, and then thickening and triggering thrust earthquakes off the ridge, in response to compressive stress buildup. The unrest provides a rare example of an energetic, magmatic driven swarm episode at the mid‐ocean ridge.〈/p〉
    Description: Plain Language Summary: The largest plate boundary systems on Earth are Mid‐ocean ridges (MOR), where the plates continuously drift apart and new lithosphere is constantly being formed. Although the process is well understood, we rarely detect spreading events at MOR, mainly because these regions are remote and local monitoring is rarely possible. In September–November 2022 a large, unusual seismic swarm occurred along a spreading center ridge segment of the North Mid‐Atlantic Ridge. Despite the remoteness of the region, we managed to model regional and teleseismic data to perform earthquake relocation, depth estimation and moment tensor inversion. In this way, we could reconstruct the geometry and the evolution of the seismicity. We found that in the early days of the swarm, seismicity migrated unilaterally over ∼60 km along the ridge axis, from North to South, triggering normal faulting earthquakes, which are typical at MOR. Later, large thrust mechanisms, anomalous in an extensional environment, appeared and quickly became predominant. We explain seismological observations by a magmatic intrusion, which first propagated southward, producing shallow normal faulting earthquakes above the vertical magma dike, and later thickened, increasing compressional stresses on its sides, and triggering large thrust earthquakes.〈/p〉
    Description: Key Points: Analysis of a short, intense seismic swarm at the Mid‐Atlantic Ridge. Identification of unusual, thrust focal mechanisms in an extensional environment. Swarm triggered by dike intrusion at the mid‐ocean ridge.
    Description: German BMBF project EWRICA
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.5281/zenodo.8089070
    Keywords: ddc:551.22 ; seismic swarm ; Mid‐Atlantic Ridge ; seismicity ; magma dyke
    Language: English
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    Cone penetration tests in dry and saturated Ticino sand (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-07-29
    Description: It is commonly assumed that dry and saturated sands exhibit similar cone resistance–relative density relationships. Some studies pointed out that partial saturation and calcareous sands with considerable fines content are potential factors affecting these relationships. However, there is experimental evidence in Shaqour Bull Eng Geol Environ 66:59-70, (2006) that clean uncemented quartz sand may exhibit lower cone resistance in saturated conditions. The present study aims on contributing towards better understanding the effect of water saturation on cone resistance in sand. For this purpose, Ticino sand samples were prepared dry and saturated in a calibration chamber and cone penetration tests were performed over a wide range of relative densities and at two consolidation stresses. Overall, it was observed that dry and saturated samples exhibited similar cone resistances. Only slightly higher cone resistances were observed for dry samples at the lower consolidation stress. Two anomalous samples, which were tested dry at medium relative density, were found to exhibit way higher cone resistances than expected from published cone resistance–relative density relationships. The Young's modulus was observed to be proportional to cone resistance and independent of whether a sample was tested dry or saturated, being therefore considered as more robust soil property for cone resistance relationships.
    Description: Bundesministerium für Wirtschaft und Energie http://dx.doi.org/10.13039/501100006360
    Keywords: ddc:550.78 ; Cone penetration test ; Water saturation ; Dry sand ; Calibration chamber ; Relative density ; Young’s modulus
    Language: English
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  • 92
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    Linking gas and particle ejection dynamics to boundary conditions in scaled shock-tube experiments (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-08-02
    Description: Predicting the onset, style and duration of explosive volcanic eruptions remains a great challenge. While the fundamental underlying processes are thought to be known, a clear correlation between eruptive features observable above Earth’s surface and conditions and properties in the immediate subsurface is far from complete. Furthermore, the highly dynamic nature and inaccessibility of explosive events means that progress in the field investigation of such events remains slow. Scaled experimental investigations represent an opportunity to study individual volcanic processes separately and, despite their highly dynamic nature, to quantify them systematically. Here, impulsively generated vertical gas-particle jets were generated using rapid decompression shock-tube experiments. The angular deviation from the vertical, defined as the “spreading angle”, has been quantified for gas and particles on both sides of the jets at different time steps using high-speed video analysis. The experimental variables investigated are 1) vent geometry, 2) tube length, 3) particle load, 4) particle size, and 5) temperature. Immediately prior to the first above-vent observations, gas expansion accommodates the initial gas overpressure. All experimental jets inevitably start with a particle-free gas phase (gas-only), which is typically clearly visible due to expansion-induced cooling and condensation. We record that the gas spreading angle is directly influenced by 1) vent geometry and 2) the duration of the initial gas-only phase. After some delay, whose length depends on the experimental conditions, the jet incorporates particles becoming a gas-particle jet. Below we quantify how our experimental conditions affect the temporal evolution of these two phases (gas-only and gas-particle) of each jet. As expected, the gas spreading angle is always at least as large as the particle spreading angle. The latter is positively correlated with particle load and negatively correlated with particle size. Such empirical experimentally derived relationships between the observable features of the gas-particle jets and known initial conditions can serve as input for the parameterisation of equivalent observations at active volcanoes, alleviating the circumstances where an a priori knowledge of magma textures and ascent rate, temperature and gas overpressure and/or the geometry of the shallow plumbing system is typically chronically lacking. The generation of experimental parameterisations raises the possibility that detailed field investigations on gas-particle jets at frequently erupting volcanoes might be used for elucidating subsurface parameters and their temporal variability, with all the implications that may have for better defining hazard assessment.
    Description: Seventh Framework Programme http://dx.doi.org/10.13039/501100004963
    Description: Deutsche Forschungsgemeinschaft
    Description: European Research Council http://dx.doi.org/10.13039/501100000781
    Description: https://doi.org/10.5880/fidgeo.2020.030
    Keywords: ddc:550.78 ; Explosive volcanism, ; Experimental volcanology, ; Spreading angle, ; Shock-tube
    Language: English
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    Systematic and Temporal Geochemical Changes in the Upper Deccan Lavas: Implications for the Magma Plumbing System of Flood Basalt Provinces (2023)
    Details
    Publication Date: 2023-07-19
    Description: Large Igneous Provinces (LIPs) are unusual volcanic events in which massive amounts of melt (∼106 km3) erupt in relatively short time periods (〈106 years). Most LIP magmas have undergone extensive fractional crystallization and crustal contamination, but the crustal magmatic plumbing systems and the processes triggering eruptions are poorly understood. We present new major and trace element and radiogenic isotope data for 43 individual lava flows from a continuous 1,200 m thick stratigraphic profile through the upper, most voluminous part of the Deccan LIP (Bushe to Mahabaleshwar Formations). Eruption rates for this section are constrained by published paleomagnetic directions and absolute U‐Pb ages for zircons from weathered flow tops exposed in the profile. We find four magmatic sequences each lasting ∼104–∼105 years during which major and trace element compositions change systematically, followed by an abrupt change in geochemistry at the start of a new sequence. Within each sequence, the MgO content and proportion of crustal contamination decrease progressively, indicating a continuous replenishment of the associated magma reservoirs with less contaminated but more evolved melts. These geochemical signatures are best explained by repeated episodes of melt recharge, mixing, and eruption of variably evolved magmas originating from relatively small magma reservoir located in different crustal levels.
    Description: Plain Language Summary: Volcanism occurs predominantly at plate boundaries, either at mid‐ocean ridges or subduction zones, where most mantle melts are produced. However, the Earth's history is punctuated by volcanic events which are not related to plate boundary processes and during which large amounts of melt erupt (∼106 km3) in relatively short periods of time (〈106 years). These Large Igneous Provinces (LIPs) are associated with the activity of mantle plumes and eruption rates during their main stages are significantly higher than those of today's largest magmatic systems. However, since no LIP is currently active, the architecture of the associated plumbing systems is relatively unknown. In order to understand the magmatic processes during the emplacement of a LIP, we generated geochemical data from a continuous stratigraphic profile covering the most voluminous stage of the ∼66 Ma Deccan LIP. By combining these new data with published paleomagnetic directions and absolute U‐Pb ages for zircons, we found four eruption sequences each lasting ∼104–∼105 years. During these sequences, geochemical compositions change systematically, which is best explained by repeated episodes of melt recharge, mixing, and eruption of variably evolved magmas originating from relatively small magma reservoirs located at different crustal levels.
    Description: Key Points: Four recharge‐crystallization‐eruption sequences fed the most voluminous Deccan lava. Magmatic plumbing system with interconnected small‐ to medium‐sized magma reservoirs. Complex emplacement history including multiple stages of ascent, mixing, and storage.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.26022/IEDA/112672
    Keywords: ddc:551.9 ; intraplate processes ; magma chamber processes ; magma genesis and partial melting ; major and trace element geochemistry ; radiogenic isotope geochemistry
    Language: English
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  • 94
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    Authigenic and Detrital Carbonate Nd Isotope Records Reflect Pulses of Detrital Material Input to the Labrador Sea During the Heinrich Stadials (2023)
    Details
    Publication Date: 2023-07-19
    Description: Limited constraints on the variability of the deep‐water production in the Labrador Sea complicate reconstructions of the strength of the Atlantic Meridional Overturning Circulation (AMOC) during the Late Quaternary. Large volumes of detrital carbonates were repeatedly deposited in the Labrador Sea during the last 32 kyr, potentially affecting radiogenic Nd isotope signatures. To investigate this the Nd isotope compositions of deep and intermediate waters were extracted from the authigenic Fe‐Mn oxyhydroxide fraction, foraminiferal coatings, the residual silicates and leachates of dolostone grains. We provide a first order estimation of Nd release via dissolution of detrital carbonates and its contribution to the authigenic ԑNd signatures in the Labrador Sea. During the Last Glacial Maximum the Nd isotope signatures in the Labrador Sea would allow active water mass mixing with more radiogenic ɛNd values (−12.6 and −14) prevailing in its eastern part whereas less radiogenic values (ɛNd ∼ −18.4) were found on the western Labrador slope. The deposition of detrital carbonates during Heinrich stadials (2,1) was accompanied by negative detrital and authigenic Nd isotope excursions (ɛNd ∼ −31) that were likely controlled by dissolution of dolostone or dolostone associated mineral inclusions. This highly unradiogenic signal dominated the authigenic phases and individual water masses in the Labrador Sea, serving as potential source of highly unradiogenic Nd to the North Atlantic region, while exported southward. The Holocene authigenic ɛNd signatures of the coatings and leachates significantly differed from those of the detrital silicates, approaching modern bottom water mass signatures during the Late Holocene.
    Description: Plain Language Summary: The Labrador Sea is an important region for deep water formation and for the ocean circulation in the Atlantic region. Over the last 32 thousand years, numerous discharges from melting glaciers added freshwater to the Labrador Sea which could help understand the future effects of current melting glaciers. This information is necessary to better constrain climate predictions in order to gauge the effects on the Global Ocean Water Circulation. However, past deep water production in the Labrador is still poorly constrained, complicating reconstruction of the Atlantic Meridional Overturning Circulation on different timescales. In this study we investigated changes in deep and intermediate water mass circulation patterns over the last 32 kyr based on the radiogenic Nd isotope compositions that serve as a water mass circulation proxy. Analysis of four marine sediment cores show that the deposition of large volumes of detrital carbonates during studied period had a large effect on the recorded in the sediment column signals. New data suggest active water mass circulation during the maximum extent of glacial ice sheets. The modern day ocean circulation patterns have emerged during the Late Holocene (6 ka).
    Description: Key Points: Estimation of Nd release via dissolution of detrital carbonates and its contribution to the authigenic ԑNd signatures in the Labrador Sea. Dissolution of detrital dolostones in the water column during Heinrich stadials at least partially controlled ɛNd signatures. During the LGM generally more radiogenic signatures possibly indicate active water mass advection and mixing in the Labrador Sea.
    Description: GEOMAR Helmholtz‐Zentrum für Ozeanforschung Kiel http://dx.doi.org/10.13039/501100003153
    Description: Kiel University
    Description: https://doi.org/10.1594/PANGAEA.952659
    Keywords: ddc:551.9 ; Labrador Sea ; Late Quaternary ; Paleoceanography ; neodymium isotopes ; dolostone ; AMOC ; carbonate dissolution ; Heinrich stadials
    Language: English
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    Stable Carbon Isotope Signature of Methane Released From Phytoplankton (2023)
    Details
    Publication Date: 2023-07-26
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Aquatic ecosystems play an important role in global methane cycling and many field studies have reported methane supersaturation in the oxic surface mixed layer (SML) of the ocean and in the epilimnion of lakes. The origin of methane formed under oxic condition is hotly debated and several pathways have recently been offered to explain the “methane paradox.” In this context, stable isotope measurements have been applied to constrain methane sources in supersaturated oxygenated waters. Here we present stable carbon isotope signatures for six widespread marine phytoplankton species, three haptophyte algae and three cyanobacteria, incubated under laboratory conditions. The observed isotopic patterns implicate that methane formed by phytoplankton might be clearly distinguished from methane produced by methanogenic archaea. Comparing results from phytoplankton experiments with isotopic data from field measurements, suggests that algal and cyanobacterial populations may contribute substantially to methane formation observed in the SML of oceans and lakes.〈/p〉
    Description: Plain Language Summary: Methane plays an important role in atmospheric chemistry and physics as it contributes to global warming and to the destruction of ozone in the stratosphere. Knowing the sources and sinks of methane in the environment is a prerequisite for understanding the global atmospheric methane cycle but also to better predict future climate change. Measurements of the stable carbon isotope composition of carbon—the ratio between the heavy and light stable isotope of carbon—help to identify methane sources in the environment and to distinguish them from other formation processes. We identified the carbon isotope fingerprint of methane released from phytoplankton including algal and cyanobacterial species. The observed isotope signature improves our understanding of methane cycling in the surface layers of aquatic environments helping us to better estimate methane emissions to the atmosphere.〈/p〉
    Description: Key Points: Stable carbon isotope values of methane emitted from six phytoplankton cultures incubated in the laboratory. Isotope fractionation between methane source signature and biomass of widespread algal and cyanobacterial species. Isotopic patterns of methane released by phytoplankton may be clearly distinguished from methane formed by methanogenic archaea.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Spanish Ministry of Universities
    Description: https://doi.org/10.11588/data/YYLEKU
    Keywords: ddc:551.9 ; methane ; stable isotopes ; phytoplankton ; algae ; cyanobacteria ; methane paradox
    Language: English
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    Pseudo-total antimony content in topsoils of the Berlin Metropolitan Area (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-08
    Description: Purpose: Sb is a metalloid that naturally occurs in traces in the Northern German Lowland Area, only. Its frequent and still growing demand for industrial purposes and its release during coal combustion and by vehicular emissions lead to an enrichment of Sb in topsoils. Numerous analyses on heavy metals have been conducted in the urban environment so far, but although Sb can be ecologically harmful and potentially carcinogenic, only few studies on Sb in soils were carried out.
    Description: Materials and methods: Due to the formation of anthropogenic soils by men, especially in the course of industrialization and after World War II, more than 50% of the Berlin soils consist of anthropogenic material like redeposited natural material, debris, waste, or ashes. This composition of soils of the Berlin Metropolitan Area can function as a model for other metropolitan regions of Central Europe. In the urban and peri-urban area of Berlin, analysis of more than 900 topsoil samples has been performed measuring the content of 12 heavy metals and metalloids (Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sb, and Zn). As a reference for the natural environment, soil profiles of typical parent rock material have been investigated taking also the regional (0.3 mg/kg), the local background value (0.61 mg/kg), and the baseline value (0.07 mg/kg) for Sb into account.
    Description: Results: By doing so, we could show the spatial distributional pattern of Sb in the Berlin Metropolitan Area and statistically evaluate our results in dependency of land-use, parent material, and soil parameters such as organic carbon content and pH. Thereby, we could prove an average enrichment two to six times over the regional background value. Median Sb content is very low in forest topsoils (0.54 mg/kg) and reaches its maximum in roadside soils (1.75 mg/kg). Technogenic materials, vehicular emissions, industrial processes, and (former) land-use are the predominant factors for Sb enrichment and distribution in the study area. Some single samples show an enrichment of up to 600% of the regional background value for topsoils.
    Description: Conclusion: Our study revealed that the Sb content in the Berlin Metropolitan Area is elevated compared to natural environments. Furthermore, we could demonstrate that Sb is a previously neglected key pollutant, specific to metropolitan areas. Due to the high environmental relevance, further Sb data from selected investigated spaces in other metropolises and specific land-use types are needed to assess the potential environmental risk of Sb in metropolitan areas.
    Description: Humboldt-Universität zu Berlin (1034)
    Keywords: ddc:551.9 ; Trace metals ; Urban geochemistry ; Pollution index ; Technogenic soils ; Antimony (Sb) ; Urban structure type
    Language: English
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    Impact of sedimentation history for As distribution in Late Pleistocene-Holocene sediments in the Hetao Basin, China (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-08
    Description: Purpose: To understand the impact of geochemical sedimentation history for arsenic (As) distribution in the sediment profiles of the Hetao Basin, we (1) evaluated sediments provenance and variations of weathering intensities, (2) attempted to reconstruct the depositional environments, and (3) explored the As and Fe speciation in the sediments. Combining the information above, different sedimentation facies were distinguished in the vertical profiles.
    Description: Methods: Two sediments cores were drilled up to 80 m depth. Major and trace element compositions, including rare earth elements (REE), were analyzed. Carbon isotope ratios (δ13Corg) of embedded organic matter in the sediments were analyzed by isotope ratio mass spectrometry (IR-MS). Arsenic and Fe speciation of the sediments were determined by sequential extractions.
    Description: Results and discussion: The similar REE geochemistry of rocks from the Lang Mountains and sediments in the Hetao Basin indicated that the sediments originated from the Lang Mountains. The C/N ratio (~ 4 to ~ 10) in combination with δ13Corg (− 27‰ to −2 4‰) suggested that sediments were mainly deposited in aquatic environments. The unconfined aquifer equaled the lacustrine deposit with less intensive weathering during last glacial maximum (LGM). Here, the As content (average, 5.4 mg kg−1) was higher than in the aquifer sediments below (average, 3.6 mg kg−1).
    Description: Conclusion: Higher content of releasable As in combination with paleolake-derived organic matter aquifer sediments probably contributes to higher groundwater As concentration in the unconfined aquifer. This study provides the first insight into the impact of sedimentation history on As distributions in sediment profiles in the Hetao Basin.
    Description: China Scholarship Council http://dx.doi.org/10.13039/501100004543
    Keywords: ddc:551.9 ; Sediment basin ; Sedimentation history ; Arsenic provenance ; Weathering intensities ; Organic carbon isotopic signature ; Arsenic speciation
    Language: English
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    Stress-based, statistical modeling of the induced seismicity at the Groningen gas field, The Netherlands (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-08
    Description: Groningen is the largest onshore gas field under production in Europe. The pressure depletion of the gas field started in 1963. In 1991, the first induced micro-earthquakes have been located at reservoir level with increasing rates in the following decades. Most of these events are of magnitude less than 2.0 and cannot be felt. However, maximum observed magnitudes continuously increased over the years until the largest, significant event with ML=3.6 was recorded in 2014, which finally led to the decision to reduce the production. This causal sequence displays the crucial role of understanding and modeling the relation between production and induced seismicity for economic planing and hazard assessment. Here we test whether the induced seismicity related to gas exploration can be modeled by the statistical response of fault networks with rate-and-state-dependent frictional behavior. We use the long and complete local seismic catalog and additionally detailed information on production-induced changes at the reservoir level to test different seismicity models. Both the changes of the fluid pressure and of the reservoir compaction are tested as input to approximate the Coulomb stress changes. We find that the rate-and-state model with a constant tectonic background seismicity rate can reproduce the observed long delay of the seismicity onset. In contrast, so-called Coulomb failure models with instantaneous earthquake nucleation need to assume that all faults are initially far from a critical state of stress to explain the delay. Our rate-and-state model based on the fluid pore pressure fits the spatiotemporal pattern of the seismicity best, where the fit further improves by taking the fault density and orientation into account. Despite its simplicity with only three free parameters, the rate-and-state model can reproduce the main statistical features of the observed activity.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551.22 ; Induced seismicity ; Modeling ; Statistical seismology ; Forecast
    Language: English
    Type: doc-type:article
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    Single-station seismic microzonation using 6C measurements (2020)
    Springer Netherlands
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    Publication Date: 2023-06-09
    Description: Microzonation is one of the essential tools in seismology to mitigate earthquake damage by estimating the near-surface velocity structure and developing land usage plans and intelligent building design. The number of microzonation studies increased in the last few years as induced seismicity becomes more relevant, even in low-risk areas. While of vital importance, especially in densely populated cities, most of the traditional techniques suffer from different shortcomings. The microzonation technique presented here tries to reduce the existing ambiguity of the inversion results by the combination of single-station six-component (6C) measurements, including three translational and three rotational motions, and more traditional H/V techniques. By applying this new technique to a microzonation study in the downtown area of Munich (Germany) using an iXblue blueSeis-3A rotational motion sensor together with a Nanometrics Trillium Compact seismometer, we were able to estimate Love and Rayleigh wave dispersion curves. These curves together with H/V spectral ratios are then inverted to obtain P- and S-wave velocity profiles of the upper 100 m. In addition, there is a good correlation between the estimated velocity models and borehole-derived lithology, indicating the potential of this single-station microzonation approach.
    Description: European Research Council https://doi.org/10.13039/501100000781
    Description: Bundesministerium für Wirtschaft und Energie https://doi.org/10.13039/501100006360
    Keywords: ddc:551.22 ; Microzonation ; Rotational seismology ; Ambient noise
    Language: English
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    Seiscloud, a tool for density-based seismicity clustering and visualization (2020)
    Springer Netherlands
    Details
    Publication Date: 2023-06-09
    Description: Clustering algorithms can be applied to seismic catalogs to automatically classify earthquakes upon the similarity of their attributes, in order to extract information on seismicity processes and faulting patterns out of large seismic datasets. We describe here a Python open-source software for density-based clustering of seismicity named seiscloud, based on the pyrocko library for seismology. Seiscloud is a tool to dig data out of large local, regional, or global seismic catalogs and to automatically recognize seismicity clusters, characterized by similar features, such as epicentral or hypocentral locations, origin times, focal mechanisms, or moment tensors. Alternatively, the code can rely on user-provided distance matrices to identify clusters of events sharing indirect features, such as similar waveforms. The code can either process local seismic catalogs or download selected subsets of seismic catalogs, accessing different global seismicity catalog providers, perform the seismic clustering over different steps in a flexible, easily adaptable approach, and provide results in form of declustered seismic catalogs and a number of illustrative figures. Here, the algorithm usage is explained and discussed through an application to Northern Chile seismicity.
    Description: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Keywords: ddc:551.22 ; Seismicity ; Clustering ; Location ; Moment tensor
    Language: English
    Type: doc-type:article
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