ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Other Sources  (90)
  • ddc:551  (57)
  • ddc:550.78  (32)
  • Deutschland
  • 2020-2024  (90)
  • 1
    facet.materialart.
    Unknown
    Atmospheric CO2 Concentration Based on Boron Isotopes Versus Simulations of the Global Carbon Cycle During the Plio‐Pleistocene (2023)
    Details
    Publication Date: 2023-09-13
    Description: Atmospheric carbon dioxide concentrations (pCO〈sub〉2〈/sub〉) beyond ice core records have been reconstructed from δ〈sup〉11〈/sup〉B derived from planktic foraminifera found in equatorial sediment cores. Here, I applied a carbon cycle model over the Plio‐Pleistocene to evaluate the assumptions leading to these numbers. During glacials times, simulated atmospheric pCO〈sub〉2〈/sub〉 was unequilibrated with pCO〈sub〉2〈/sub〉 in the equatorial surface ocean by up to 35 ppm while the δ〈sup〉11〈/sup〉B‐based approaches assume unchanged (quasi)equilibrium between both. In the Pliocene, δ〈sup〉11〈/sup〉B‐based estimates of surface ocean pH are lower in the Pacific than in the Atlantic resulting in higher calculated pCO〈sub〉2〈/sub〉. This offset in pH between ocean basins is not supported by models. To calculate pCO〈sub〉2〈/sub〉 in surface waters out of the δ〈sup〉11〈/sup〉B‐based pH some assumptions on either total alkalinity or dissolved inorganic carbon are necessary. However, the assumed values of these under‐constrained variables were according to my results partly inconsistent with chemically possible combinations within the marine carbonate system. The model results show glacial/interglacial variability in total alkalinity of the order of 100 μmol/kg, which is rarely applied to proxy reconstructions. Simulated atmospheric pCO〈sub〉2〈/sub〉 is tightly (r〈sup〉2〈/sup〉 〉 0.9) related to equatorial surface‐ocean pH, which can be used for consistency checks. Long‐term trends in volcanic CO〈sub〉2〈/sub〉 outgassing and the strength of the continental weathering fluxes are still unconstrained, allowing for a wide range of possible atmospheric pCO〈sub〉2〈/sub〉 across the Plio‐Pleistocene. Nevertheless, this carbon cycle analysis suggests that reported atmospheric pCO〈sub〉2〈/sub〉 above 500 ppm in the Pliocene might, for various reasons, need to be revised to smaller numbers.
    Description: Key Points: Simulated equatorial surface ocean 𝑝CO〈sub〉2〈/sub〉 is near‐equilibrium with atmosphere during interglacials but enriched (≤35 ppm) during glacials. Models suggest similar equatorial surface 𝑝H in Pacific and in Atlantic in high CO〈sub〉2〈/sub〉 worlds while Pliocene reconstructions show offsets. Carbon cycle model analysis suggests that reported CO〈sub〉2〈/sub〉 values above 500 ppm in the Pliocene might need revisions to smaller numbers.
    Keywords: ddc:551 ; carbon cycle ; modeling ; CO2 ; boron isotopes ; pH ; Plio‐Pleistocene
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 2
    facet.materialart.
    Unknown
    Impact of Diurnal Warm Layers on Atmospheric Convection (2023)
    Details
    Publication Date: 2023-12-05
    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"〉This manuscript presents a study of oceanic diurnal warm layers (DWLs) in kilometer‐scale global coupled simulations and their impact on atmospheric convection in the tropics. With the implementation of thin vertical levels in the ocean, DWLs are directly resolved, and sea surface temperature (SST) fluctuations of up to several Kelvin appear in regions with low wind and high solar radiation. The increase of SST during the day causes an abrupt afternoon increase of atmospheric moisture due to enhanced latent heat flux (LHF), followed by an increase in cloud cover (CC) and cloud liquid water (CLW). However, although the diurnal SST amplitude is even exaggerated in comparison to reanalysis, this effect only lasts for 5–6 hr and leads to an absolute difference of 1% for CC and 0.01 kg m〈sup〉−2〈/sup〉 for CLW. This can be explained by the fact that the low wind over the SST anomalies dampens their potential effect on the LHF and hence clouds. All in all, the impact of DWLs on convective CC is found to be negligible in the tropical mean.〈/p〉
    Description: Plain Language Summary: The diurnal fluctuations of sea surface temperature (SST) have been extensively studied for the last decades, but the assessment of the importance of this phenomenon for atmospheric convection on the global scale has come within reach only very recently, thanks to the development of simulations with a horizontal resolution of O(1 km). In this manuscript we show that we can indeed observe an impact of SST fluctuations on moisture in the atmosphere. However, the impact on the amount of clouds in the tropics is found to be short‐lived and its magnitude negligible on average.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉diurnal warm layers (DWLs) increase atmospheric moisture〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The increase of cloud cover (CC) following the formation of a DWL is immediate and only lasts for several hours〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The magnitude of the CC increase is small and has no discernible influence on the global mean〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://gotm.net/
    Description: https://hdl.handle.net/21.11116/0000-000C-1447-E
    Keywords: ddc:551 ; diurnal warm layers (DWLs) ; atmospheric moisture ; cloud cover ; convection
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 3
    facet.materialart.
    Unknown
    Impact of Cyclonic Wind Anomalies Caused by Massive Winter Sea Ice Retreat in the Barents Sea on Atlantic Water Transport Toward the Arctic: A Model Study (2023)
    Details
    Publication Date: 2023-12-05
    Description: The Arctic is warming much faster than the global average. This is known as Arctic Amplification and is caused by feedbacks in the local climate system. In this study, we explore a previously proposed hypothesis that an associated wind feedback in the Barents Sea could play an important role by increasing the warm water inflow into the Barents Sea. We find that the strong recent decrease in Barents Sea winter sea ice cover causes enhanced ocean‐atmosphere heat flux and a local air temperature increase, thus a reduction in sea level pressure and a local cyclonic wind anomaly with eastward winds in the Barents Sea Opening. By investigating various reanalysis products and performing high‐resolution perturbation experiments with the ocean and sea ice model FESOM2.1, we studied the impact of cyclonic atmospheric circulation changes on the warm Atlantic Water import into the Arctic via the Barents Sea and Fram Strait. We found that the observed wind changes do not significantly affect the warm water transport into the Barents Sea, which rejects the wind‐feedback hypothesis. At the same time, the cyclonic wind anomalies in the Barents Sea increase the amount of Atlantic Water recirculating westwards in Fram Strait by a downslope shift of the West Spitsbergen Current, and thus reduce Atlantic Water reaching the Arctic basin via Fram Strait. The resulting warm‐water anomaly in the Greenland Sea Gyre drives a local anticyclonic circulation anomaly.
    Description: Plain Language Summary: The Barents Sea has been experiencing a rapid decrease in its winter sea ice extent during the last 30 years. The loss of sea ice creates new areas where, in winter, the relatively warm ocean loses heat to the cold atmosphere. As warm air rises, the warming reduces the sea level air pressure, changing the atmospheric circulation to develop a local anticlockwise wind system centered over the northern Barents Sea. The associated eastward winds in the Barents Sea Opening and southeastward winds in Fram Strait affect how warm water from the North Atlantic moves toward the Arctic. There has been a long debate on whether this wind anomaly can increase the warm Atlantic Water transport into the Barents Sea and thus cause a positive feedback mechanism for further reducing the sea ice through melting. We find that the observed atmospheric circulation changes have no significant impact on the Barents Sea warm water inflow and thus reject the wind feedback as a strong player in contributing to Arctic Amplification. However, strong anomalous southeastward winds in Fram Strait and the northern Nordic Seas cause a southward shift of the warm Atlantic Water recirculation and reduce its flow toward the Arctic.
    Description: Key Points: A hypothesis that a wind feedback contributes to Arctic Amplification is rejected by performing dedicated wind perturbation simulations. Winter sea ice retreat in the northern Barents Sea causes anomalous cyclonic winds by locally enhancing ocean heat loss. Anomalous cyclonic winds result in less Atlantic Water transport through Fram Strait.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: North‐German Supercomputing Alliance
    Description: https://github.com/FESOM/fesom2
    Description: https://doi.org/10.7265/N5K072F8
    Description: https://doi.org/10.5065/D6HH6H41
    Description: https://doi.org/10.5065/D6WH2N0S
    Description: https://github.com/FESOM/pyfesom2
    Description: https://doi.org/10.5281/zenodo.7458143
    Keywords: ddc:551 ; Barents Sea ; Arctic Amplification ; feedback ; Atlantic water ; modeling ; Fram Strait
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 4
    facet.materialart.
    Unknown
    Insights Into NOx and HONO Chemistry in the Tropical Marine Boundary Layer at Cape Verde During the MarParCloud Campaign (2023)
    Details
    Publication Date: 2023-11-15
    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"〉Chemical processing of reactive nitrogen species, especially of NO〈sub〉〈italic〉x〈/italic〉〈/sub〉 (= NO + NO〈sub〉2〈/sub〉) and nitrous acid (HONO), determines the photochemical ozone production and oxidation capacity in the troposphere. However, sources of HONO and NO〈sub〉〈italic〉x〈/italic〉〈/sub〉 in the remote marine atmosphere are still poorly understood. In this work, the multiphase chemistry mechanism CAPRAM in the model framework SPACCIM was used to study HONO formation at Cape Verde (CVAO) in October 2017, adopted with the input of current parameterizations for various HONO sources. Three simulations were performed that adequately reproduced ambient HONO levels and its diurnal pattern. The model performance for NO〈sub〉〈italic〉x〈/italic〉〈/sub〉 and O〈sub〉3〈/sub〉 improves significantly when considering dust‐surface‐photocatalytic conversions of reactive nitrogen compounds with high correlation coefficients up to 0.93, 0.56, and 0.89 for NO, NO〈sub〉2〈/sub〉, and O〈sub〉3〈/sub〉, respectively. Photocatalytic conversion of the adsorbed HNO〈sub〉3〈/sub〉 on dust is modeled to be the predominant contributor for daytime HONO at CVAO, that is, accounting for about 62% of the chemical formation rate at noontime. In contrast, the ocean‐surface‐mediated conversion of NO〈sub〉2〈/sub〉 to HONO and other discussed pathways are less important. The average OH levels at midday (9:00–16:00) modeled for cluster trajectory 1, 2, and 3 are 5.2, 5.1, and 5.2 × 10〈sup〉6〈/sup〉 molecules cm〈sup〉−3〈/sup〉, respectively. Main OH formation is driven by O〈sub〉3〈/sub〉 photolysis with a contribution of 74.6% to the total source rate, while HONO photolysis is negligible (∼1.8%). In summary, this study highlights the key role of dust aerosols for HONO formation and NO〈sub〉〈italic〉x〈/italic〉〈/sub〉 cycling at CVAO and possibly in other dust‐affected regions, urgently calling for further investigations using field and model studies.〈/p〉
    Description: Plain Language Summary: Chemical processing of NO〈sub〉〈italic〉x〈/italic〉〈/sub〉 (= NO + NO〈sub〉2〈/sub〉) and nitrous acid (HONO) is important for the tropospheric O〈sub〉3〈/sub〉 budget and oxidation capacity. However, the sources of HONO and cycling of NO〈sub〉〈italic〉x〈/italic〉〈/sub〉 in the remote marine atmosphere are still poorly explored. A detailed multiphase chemistry model simulation showed a better performance of HONO, NO〈sub〉〈italic〉x〈/italic〉〈/sub〉 and O〈sub〉3〈/sub〉 when considering dust‐surface‐photocatalytic conversions of reactive nitrogen compounds, especially the photocatalytic conversion of the adsorbed HNO〈sub〉3〈/sub〉 on dust. The simulations demonstrated that OH formation is mainly driven by the O〈sub〉3〈/sub〉 photolysis, while HONO photolysis is a negligible OH radical source due to its low concentration levels at Cape Verde. The study highlights the key role of dust aerosols for HONO and NO〈sub〉〈italic〉x〈/italic〉〈/sub〉 chemistry in the remote marine boundary layer.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉The sources of HONO and NO〈sub〉〈italic〉x〈/italic〉〈/sub〉 at Cape Verde are well modeled with CAPRAM〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Photocatalytic conversion of adsorbed HNO〈sub〉3〈/sub〉 on dust is the predominant contributor for daytime HONO〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Photolysis of O〈sub〉3〈/sub〉 is the prevailing source of OH radical at Cape Verde, while HONO photolysis is a negligible OH radical source〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Leibniz Association SAW
    Description: Horizon 2020 Framework Programme http://dx.doi.org/10.13039/100010661
    Description: National Key Research and Development Program of China http://dx.doi.org/10.13039/501100012166
    Description: National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809
    Description: https://doi.org/10.5281/zenodo.8070265
    Description: http://mcm.york.ac.uk/
    Description: https://capram.tropos.de/
    Description: https://ebas.nilu.no/
    Description: https://www.ready.noaa.gov/HYSPLIT_traj.php
    Keywords: ddc:551 ; HONO ; NOx ; CAPRAM ; heterogenous chemistry ; mineral dust ; OH radical ; marine boundary layer
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 5
    facet.materialart.
    Unknown
    Revealing the Extent of Submarine Permafrost and Gas Hydrates in the Canadian Arctic Beaufort Sea Using Seismic Reflection Indicators (2023)
    Details
    Publication Date: 2023-12-12
    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"〉The Canadian Arctic Southern Beaufort Sea is characterized by prominent relict submarine permafrost and gas hydrate occurrences formed by subaerial exposure during extensive glaciations in Pliocene and Pleistocene. Submarine permafrost is still responding to the thermal change as a consequence of the marine transgression that followed the last glaciation. Submarine permafrost is still underexplored and is currently the focus of several research projects as its degradation releases greenhouse gases that contribute to climate change. In this study, seismic reflection indicators are used to investigate the presence of submarine permafrost and gas hydrates on the outer continental shelf where the base of permafrost is expected to cross‐cut geological layers. To address the challenges of marine seismic data collected in shallow water environments, we utilize a representative synthetic model to assess the data processing and the detection of submarine permafrost and gas hydrate by seismic data. The synthetic model allows us to minimize the misinterpretation of acquisition and processing artifacts. In the field data, we identify features along with characteristics arising from the top and base of submarine permafrost and the base of the gas hydrate stability zone. This work shows the distribution of the present submarine permafrost along the southern Canadian Beaufort Sea region and confirms its extension to the outer continental shelf. It supports the general shape suggested by previous works and previously published numerical models.〈/p〉
    Description: Plain Language Summary: Submarine permafrost, ground beneath the seafloor that perennially remains below 0°C, is present on the continental shelf of the Canadian Beaufort Sea. During the Late Pleistocene (∼1 Million years ago), the continental shelf was subaerially exposed to the cold Arctic air causing the formation of ice in the ground. This period was followed by a sea level rise that flooded the continental shelf with warmer waters, resulting in an intensive change of the thermal regime. The relict permafrost still reacts to this thermal change and is continuously thawing. Associated with the presence of relict permafrost, extensive gas hydrates exist to >1,000 m below the seafloor. Climate warming threatens both the stability of permafrost and associated gas hydrates. Their thawing and decomposition can cause a release of greenhouse gases which in turn amplifies climate warming. This study uses marine seismic reflection data to identify permafrost and gas hydrate in the southern Canadian Beaufort Sea. We find indicators of the top and base of permafrost and the base of the gas hydrate stability zone in the outer continental shelf area. Our work shows that the permafrost and gas hydrates still extend to the outer continental shelf and thereby supports previously published numerical models.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Seismic reflection data reveal occurrences and extent of submarine permafrost and associated gas hydrates at the Canadian Beaufort Shelf〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Synthetic modeling of permafrost and gas hydrate is required to assess seismic processing minimizing the potential for misinterpretation〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Indicators of top and base of permafrost and the base of gas hydrate stability support previously published numerical models〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Korean Ministry of Oceans and Fisheries
    Description: Environmental Geoscience Program of the Geological Survey of Canada
    Description: https://dx.doi.org/doi:10.22663/KOPRI-KPDC-00001958.3
    Keywords: ddc:551 ; submarine permafrost ; gas hydrate ; marine seismic ; Canadian Beaufort Sea ; seismic reflection
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 6
    facet.materialart.
    Unknown
    Oxygen Dependent Temperature Regulation of Benthic Fluxes in Reservoirs (2023)
    Details
    Publication Date: 2023-12-16
    Description: Temperature and dissolved oxygen concentration are critical factors affecting the exchange of solutes between sediment and water; both factors will be affected by warming of lakes and thereby influence water quality. Temperature and oxygen responses of single solute fluxes are well known; however, not much is known about the interaction of temperature and oxygen in regulating the balance of different fluxes in the benthic environment. We analyzed benthic flux (mobilization and immobilization) data of various solutes (dissolved organic carbon (DOC), CH〈sub〉4〈/sub〉, NO〈sub〉3〈/sub〉〈sup〉−〈/sup〉‐N, NH〈sub〉4〈/sub〉+〈/sup〉‐N, SRP, SO〈sub〉4〈/sub〉〈sup〉−〈/sup〉, Fe, Mn, and O〈sub〉2〈/sub〉) collected from laboratory incubations of 142 sediment cores from 5 different reservoirs incubated under varying in situ temperature and oxygen conditions. Oxygen was the primary driver of benthic fluxes, while temperature and total organic content were secondary. Temperature effects on benthic fluxes were stronger under anoxic conditions which imply that warming will substantially increase the benthic fluxes if the sediment surface becomes anoxic. The varying temperature response of processes underlying the studied fluxes will result in a shift of their relative importance in the benthic environment, especially in shallow lakes that are more vulnerable to warming. For example, more anoxic conditions will shift the equilibrium between net sulfate reduction and methane release toward the latter. We also predict that physical effects of warming leading to hypolimnetic oxygen depletion, that is, stronger stratification and longer hypolimnetic confinement will increase the benthic mobilization of phosphorus, DOC, and methane into water and immobilization of sulfate by the sediments even in deep lakes.
    Description: Plain Language Summary: Temperature and dissolved oxygen concentration control the release of undesirable components buried in lake or reservoir sediments, that is, nutrients, metals, and organic matter, which can cause water quality problems. We investigated the effects of rising temperature and levels of oxygen on the release of undesirable components by performing experiments using sediments and water from five different reservoirs. The sediments with a layer of water on top were incubated under different in situ temperature (low and high) and oxygen conditions (with and without). Our results show that the absence of oxygen was the main cause of the release of nutrients and metals. When there was no oxygen in the sediment and water, nutrients and metals were released from the sediment into the water and this effect increased when temperature was high. There is higher possibility that phosphorus, dissolved organic carbon, and methane will be released from sediments in some reservoirs as a result of global warming.
    Description: Key Points: Solute fluxes from benthic lake sediments varied in response to temperature, with oxygen fluxes responding most strongly. Temperature effects on the magnitude of benthic fluxes were stronger under anoxic than oxic conditions. Direct temperature effects on reservoir water quality will be small compared to indirect effects through anoxia facilitation.
    Description: German Federal Ministry of Education and Research
    Description: MINECO
    Description: https://doi.pangaea.de/10.1594/PANGAEA.928570
    Keywords: ddc:551 ; temperature dependency ; oxygen ; benthic fluxes ; reservoirs ; anoxia ; activation energy
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 7
    facet.materialart.
    Unknown
    Advances in New Zealand's Tephrochronostratigraphy Using Marine Drill Sites: The Neogene (2023)
    Details
    Publication Date: 2023-12-16
    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"〉Three volcanic arcs have been the source of New Zealand's volcanic activity since the Neogene: Northland arc, Coromandel Volcanic Zone (CVZ) and Taupō Volcanic Zone (TVZ). The eruption chronology for the Quaternary, sourced by the TVZ, is well studied and established, whereas the volcanic evolution of the precursor arc systems, like the CVZ (central activity c. 18 to 2 Ma), is poorly known due to limited accessibility to, or identification of, onshore volcanic deposits and their sources. Here, we investigate the marine tephra record of the Neogene, mostly sourced by the CVZ, of cores from IODP Exp. 375 (Sites U1520 and U1526), ODP Leg 181 (Sites 1123, 1124 and 1125), IODP Leg 329 (Site U1371) and DSDP Leg 90 (Site 594) offshore of New Zealand. In total, we identify 306 primary tephra layers in the marine sediments. Multi‐approach age models (e.g. biostratigraphy, zircon ages) are used in combination with geochemical fingerprinting (major and trace element compositions) and the stratigraphic context of each marine tephra layer to establish 168 tie‐lines between marine tephra layers from different holes and sites. Following this approach, we identify 208 explosive volcanic events in the Neogene between c. 17.5 and 2.6 Ma. This is the first comprehensive study of New Zealand's Neogene explosive volcanism established from tephrochronostratigraphic studies, which reveals continuous volcanic activity between c. 12 and 2.6 Ma with an abrupt compositional change at c. 4.5 Ma, potentially associated with the transition from CVZ to TVZ.〈/p〉
    Description: Plain Language Summary: Since 18 Ma, volcanic activity in New Zealand is dominantly sourced by the Coromandel Volcanic Zone (CVZ). Most caldera systems of the CVZ identified so far are located on Coromandel Peninsula in the NW of North Island, New Zealand, but studies of the CVZ are rare mainly due to the limited accessibility of its volcanic deposits, as well as missing stratigraphic continuity between different outcrops and the volcanic source. Here, our ocean drilling tephra record—mainly volcanic ash from explosive eruptions, distributed and falling out over the ocean—has a great potential to reveal the eruption history of the CVZ because it is preserved in marine sediments in a nearly undisturbed stratigraphic context. We analyzed ∼400 marine tephra layers from multiple ocean sediment cores off the coast of New Zealand for their geochemical glass compositions and identified 306 as largely undisturbed ash deposits. These primary ash deposits correspond to a total number of 208 Neogene volcanic events. Different dating methods result in a continuous marine tephra record for the last 12 Ma, equivalent to a unique and most complete eruptive history for the CVZ. This enables us to further unravel changes in the composition of the associated magmas with time.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉New Zealand's Neogene explosive volcanism based on the marine tephra record〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Geochemical fingerprinting of marine tephra layers across the study area to establish volcanic events〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Insights into geochemical variations with time, repose times and spatiotemporal distribution〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: DFG
    Description: Marsden project
    Description: https://doi.org/10.14379/iodp.proc.372B375.210.2023
    Keywords: ddc:551 ; marine tephrochronostratigraphy ; geochemical fingerprinting ; correlations of marine tephras between individual drill sites ; IODP ; ODP and DSDP drill sites ; neogene eruption record of New Zealand
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 8
    facet.materialart.
    Unknown
    A Comparison Study of Mg/Ca‐, Alkenone‐, and TEX86‐Derived Temperatures for the Brazilian Margin (2023)
    Details
    Publication Date: 2023-12-14
    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"〉The reconstruction of accurate sea‐surface temperatures (SST) is of utmost importance due to the ocean's central role in the global climate system. Yet, a number of environmental processes might bias reliable SST estimations. Here, we investigate the fidelity of SST reconstructions for the western tropical South Atlantic (WTSA) for the interval covered by Marine Isotope Stages (MIS) 6–5, utilizing a core collected off eastern Brazil at ∼20°S. This interval was selected as previous SST estimates based on Mg/Ca ratios of planktic foraminifera suggested a peculiar pooling of warm surface waters in the WTSA during MIS 6 despite glacial boundary conditions. To ground‐truth the Mg/Ca‐based SST data we generated SST reconstructions on the same core material using the alkenone and TEX〈sub〉86〈/sub〉 paleothermometers. Comparison with alkenone‐based temperature estimates corroborate the previous Mg/Ca‐based SST reconstructions, supporting the suggestion of a warm‐water anomaly during MIS 6. In contrast, TEX〈sub〉86〈/sub〉‐derived temperatures, albeit representing annual mean SST in recent core top samples, are up to 6°C colder than Mg/Ca‐ and alkenone‐based SST reconstructions. We interpret the periods of anomalously cold TEX〈sub〉86〈/sub〉‐temperatures as a result of a vertical migration of the TEX〈sub〉86〈/sub〉 producers (heterotrophic marine Thaumarchaeota) toward greater water depths, following food availability during phases of enhanced fluvial suspension input. Likewise, the data suggest that alkenone‐based SST are, albeit to a minor degree when compared to TEX〈sub〉86〈/sub〉, affected by river run‐off and/or a seasonal bias in the growth season of haptophyte algae.〈/p〉
    Description: Plain Language Summary: In this study, we investigate the accuracy of sea‐surface temperature (SST) reconstructions for the western tropical South Atlantic (WTSA) for the interval covered by Marine Isotope Stages (MIS) 6–5—the penultimate glacial‐interglacial cycle (ca. 190,000 to 70,00 years before present). This time interval was selected because previous SST estimates based on Mg/Ca ratios of planktic foraminifera suggested a pooling of warm surface waters in the WTSA during late MIS 6 despite the cold glacial conditions. To verify the Mg/Ca‐based SST data, we generated temperature reconstructions from a core located off Eastern Brazil using two common paleothermometers that based on lipid biomarkers: alkenone and TEX〈sub〉86〈/sub〉. The alkenone‐based temperature estimates agree with previous Mg/Ca‐based SST reconstructions, supporting the existence of a warm‐water anomaly in the WTSA during MIS 6. On the other hand, TEX〈sub〉86〈/sub〉‐derived temperatures were up to 6°C colder than Mg/Ca‐ and alkenone‐based SST reconstructions. This discrepancy might be a result of a vertical migration of the TEX86 producers toward greater water depths where they feed on particles of organic matter. These migrations into deeper waters occurred during phases of increased river run‐off fluvial suspension input which enhanced surface primary productivity and facilitated vertical particle flux through the water column.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Parallel Mg/Ca (〈italic〉Globigerinoides ruber〈/italic〉), alkenone and TEX〈sub〉86〈/sub〉‐based temperature estimates in the western tropical South Atlantic (WTSA) across Marine Isotope Stages (MIS) 6–5〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Mg/Ca and alkenones represent annual mean sea surface temperatures, but most TEX〈sub〉86〈/sub〉‐based temperatures deviate to colder values〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Anomalous sea surface warming in the WTSA during late MIS 6 appears as a robust signal〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: R/V METEOR
    Description: DFG
    Description: CNPq
    Description: FAPESP
    Description: Alexander von Humboldt‐Stiftung http://dx.doi.org/10.13039/100005156
    Description: https://doi.org/10.1594/PANGAEA.956207
    Keywords: ddc:551 ; Mg/Ca ; alkenones ; TEX86 ; MIS 6 ; Brazilian Margin ; MIS 5
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 9
    facet.materialart.
    Unknown
    Dissolved gases in the deep North Atlantic track ocean ventilation processes (2023)
    Details
    Publication Date: 2023-03-21
    Description: Gas exchange between the atmosphere and ocean interior profoundly impacts global climate and biogeochemistry. However, our understanding of the relevant physical processes remains limited by a scarcity of direct observations. Dissolved noble gases in the deep ocean are powerful tracers of physical air-sea interaction due to their chemical and biological inertness, yet their isotope ratios have remained underexplored. Here, we present high-precision noble gas isotope and elemental ratios from the deep North Atlantic (~32°N, 64°W) to evaluate gas exchange parameterizations using an ocean circulation model. The unprecedented precision of these data reveal deep-ocean undersaturation of heavy noble gases and isotopes resulting from cooling-driven air-to-sea gas transport associated with deep convection in the northern high lati-tudes. Our data also imply an underappreciated and large role for bubble-mediated gas exchange in the global air-sea transfer of sparingly soluble gases, including O2, N2, and SF6. Using noble gases to validate the physical representation of air-sea gas exchange in a model also provides a unique opportunity to distinguish physical from biogeochemical signals. As a case study, we compare dissolved N2/Ar measurements in the deep North Atlantic to physics-only model predictions, revealing excess N2 from benthic denitrification in older deep waters (below 2.9 km). These data indicate that the rate of fixed N removal in the deep Northeastern Atlantic is at least three times higher than the global deep-ocean mean, suggesting tight coupling with organic carbon export and raising potential future implications for the marine N cycle.
    Description: NSF, UK NERC, University of Oxford Advanced Research Computing facility
    Description: https://www.bco-dmo.org/project/887496
    Description: research
    Keywords: ddc:551 ; gas exchange ; nitrogen cycle ; overturning circulation ; air-sea interaction ; noble gases
    Language: English
    Type: doc-type:article , publishedVersion
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 10
    facet.materialart.
    Unknown
    Deciphering the Whisper of Volcanoes: Monitoring Velocity Changes at Kamchatka's Klyuchevskoy Group With Fluctuating Noise Fields (2023)
    Details
    Publication Date: 2023-06-21
    Description: Volcanic inflation and deflation often precede eruptions and can lead to seismic velocity changes (dv/v $dv/v$) in the subsurface. Recently, interferometry on the coda of ambient noise‐cross‐correlation functions yielded encouraging results in detecting these changes at active volcanoes. Here, we analyze seismic data recorded at the Klyuchevskoy Volcanic Group in Kamchatka, Russia, between summer of 2015 and summer of 2016 to study signals related to volcanic activity. However, ubiquitous volcanic tremors introduce distortions in the noise wavefield that cause artifacts in the dv/v $dv/v$ estimates masking the impact of physical mechanisms. To avoid such instabilities, we propose a new technique called time‐segmented passive image interferometry. In this technique, we employ a hierarchical clustering algorithm to find periods in which the wavefield can be considered stationary. For these periods, we perform separate noise interferometry studies. To further increase the temporal resolution of our results, we use an AI‐driven approach to find stations with similar dv/v $dv/v$ responses and apply a spatial stack. The impacts of snow load and precipitation dominate the resulting dv/v $dv/v$ time series, as we demonstrate with the help of a simple model. In February 2016, we observe an abrupt velocity drop due to the M7.2 Zhupanov earthquake. Shortly after, we register a gradual velocity increase of about 0.3% at Bezymianny Volcano coinciding with surface deformation observed using remote sensing techniques. We suggest that the inflation of a shallow reservoir related to the beginning of Bezymianny's 2016/2017 eruptive cycle could have caused this local velocity increase and a decorrelation of the correlation function coda.
    Description: Plain Language Summary: Before eruptions, volcanoes inflate due to the rising magma from below. Previous studies have found that these deformations can lead to small changes in the properties of the surrounding rock. We use passive image interferometry, a method that relies on the omnipresent background vibration of the Earth—mostly induced by the oceans, to measure these changes at the Klyuchevskoy Volcanic Group in Kamchatka, Russia. However, in Kamchatka, this background noise is masked and distorted by small earthquakes and tremors originating from the volcanoes themselves. We combine machine learning techniques with established monitoring methods to find times when these tremors remain similar. Afterward, we use data from these time periods in the conventional way to observe changes in the soil and the rock. Our results show that rain‐ and snowfall and the thickness of the snow cover exert the strongest influence on the properties of the rocks. Additionally, we found that a large magnitude 7.2 earthquake, which struck Kamchatka during our study, caused a slight weakening of the rocks due to microstructural damage. We register changes shortly before an eruption and suggest a connection to the beginning of an eruptive cycle in 2016.
    Description: Key Points: Fluctuating noise conditions lead to distortions in noise interferometry studies, which we avoid with the help of machine learning. The seismic velocity on Kamchatka is affected by numerous mechanisms, amongst them environmental, tectonic, and volcanic events. We observe a velocity increase at Bezymianny during February 2016 and link it to the beginning of the eruptive cycle.
    Description: German Research Foundation
    Description: https://doi.org/10.14470/K47560642124
    Description: https://doi.org/10.24381/cds.e2161bac
    Description: https://doi.org/10.5880/GFZ.2.4.2022.002
    Description: https://doi.org/10.5281/zenodo.7481934
    Keywords: ddc:551 ; seismology ; volcano monitoring ; machine learning ; ambient noise ; seismic velocity change ; time varying earth structure
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 11
    facet.materialart.
    Unknown
    High Heat Flow Anomaly Within the St Paul Fracture Zone: Heat Advection and/or Inherent Thermal Structure? (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"〉Heat flow across oceanic transform faults (TFs) and fracture zones (FZs) has rarely been studied in detail, despite these features representing distinct thermal boundaries within the oceanic lithosphere. Here, we present heat flow measurements across the St Paul fracture zone (SPFZ) in the equatorial Atlantic Ocean, from 48 Ma crust in the south to 71 Ma in the north. To the north of the FZ we find a basal heat flow of 63 mWm〈sup〉−2〈/sup〉, and to the south a basal heat flow of 79 mWm〈sup〉−2〈/sup〉, both in agreement with plate cooling models. However, within the SPFZ we find a heat flow of 83 mWm〈sup〉−2〈/sup〉, greater than the values of the adjacent crust and 10–15 mWm〈sup〉−2〈/sup〉 higher than predicted from conductive cooling models, suggesting that the thermal structure of the FZ has been modified. Evidence from seismic and sub‐bottom profiler data indicate recent active deformation within the SPFZ, potentially driven by lithospheric flexure across the FZ or temporal changes in TF configuration. We propose that this deformation may enable fluid circulation and heat advection within the basement, creating the seafloor heat flow anomaly within the FZ. These findings suggest that FZs may remain important zones predisposed to host deformation and fluid flow in the oceanic lithosphere, despite not being active plate boundaries.〈/p〉
    Description: Key Points: A high heat flow anomaly of 10–15 mWm〈sup〉−2〈/sup〉 is observed in the St Paul fracture zone compared to the adjacent oceanic crust. The heat flow anomaly is likely due to tectonically driven fluid flow but thermal rejuvenation at the transform fault could also contribute. Fracture zones may act as high permeability pathways for fluid flow, and form and evolve differently to standard oceanic lithosphere.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: FP7 Ideas: European Research Council http://dx.doi.org/10.13039/100011199
    Description: https://doi.pangaea.de/10.1594/PANGAEA.950419
    Description: https://doi.pangaea.de/10.1594/PANGAEA.950420
    Keywords: ddc:551 ; fracture zone ; heat flow ; oceanic crust ; St Paul ; fluid flow ; lithosphere
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 12
    facet.materialart.
    Unknown
    Zur Land- und Bodendegradation – ein Rück- und Ausblick deutschland- und weltweit (2023)
    Details
    Publication Date: 2023-06-12
    Description: Soils and landscapes are bridges of space and time, as they simultaneously and authentically show essential aspects that were previously separated by time and space (such as cultural and activity-related aspects from past and present) to the trained observer - albeit only in excerpts. Therefore, this article presents a series of impact indicators for soil changes, starting with extreme (anthropogenic) interventions and ending with equally extreme ("natural") events. An essential difference to specifically planning-relevant or human ecological concepts, which, for example, specify land use/load categories, is that the following impact indicators perceive soils as a phenomenon in themselves and do not define them through attributed functions. Particular attention is focused on their changeability and vital development potential, as well as on their property as a sphere of penetration of living and material things, with emphasis on the noetic effect. The intervention or event spaces on the earth's surface can be differentiated quantitatively through the type, strength, and duration of the phenomena. The intensity of all processes can be described by amplitude (the strength of the interventions/events) and frequency (the repetition rate of the interventions/events) and can be specifically identified and quantified by, for example, material inputs or outputs per unit of time. For the first time, there would be a system for measuring the ecological quality of anthropogenic land use, which could serve as an "alert system for the external technological culture," and could help us become aware of our "inner" culture.
    Description: research
    Keywords: ddc:550 ; Boden ; Landschaft ; Bodendegeneration ; Deutschland ; Anthropogene Bodenveränderung
    Language: German
    Type: doc-type:article
    Format: 9
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 13
    facet.materialart.
    Unknown
    North Atlantic Drift Sediments Constrain Eocene Tidal Dissipation and the Evolution of the Earth‐Moon System (2023)
    Details
    Publication Date: 2023-11-18
    Description: Cyclostratigraphy and astrochronology are now at the forefront of geologic timekeeping. While this technique heavily relies on the accuracy of astronomical calculations, solar system chaos limits how far back astronomical calculations can be performed with confidence. High‐resolution paleoclimate records with Milankovitch imprints now allow reversing the traditional cyclostratigraphic approach: Middle Eocene drift sediments from Newfoundland Ridge are well‐suited for this purpose, due to high sedimentation rates and distinct lithological cycles. Per contra, the stratigraphies of Integrated Ocean Drilling Program Sites U1408–U1410 are highly complex with several hiatuses. Here, we built a two‐site composite and constructed a conservative age‐depth model to provide a reliable chronology for this rhythmic, highly resolved (〈1 kyr) sedimentary archive. Astronomical components (g‐terms and precession constant) are extracted from proxy time‐series using two different techniques, producing consistent results. We find astronomical frequencies up to 4% lower than reported in astronomical solution La04. This solution, however, was smoothed over 20‐Myr intervals, and our results therefore provide constraints on g‐term variability on shorter, million‐year timescales. We also report first evidence that the g〈sub〉4〈/sub〉–g〈sub〉3〈/sub〉 “grand eccentricity cycle” may have had a 1.2‐Myr period around 41 Ma, contrary to its 2.4‐Myr periodicity today. Our median precession constant estimate (51.28 ± 0.56″/year) confirms earlier indicators of a relatively low rate of tidal dissipation in the Paleogene. Newfoundland Ridge drift sediments thus enable a reliable reconstruction of astronomical components at the limit of validity of current astronomical calculations, extracted from geologic data, providing a new target for the next generation of astronomical calculations.
    Description: Plain Language Summary: The traditional cyclostratigraphic approach is to align and correlate a geologic depth‐series with an astronomical solution. However, the chaotic nature of the Solar System prevents astronomers from precisely calculating planetary motions beyond 40–50 million years ago. This in turn limits the options for geologists to use the resulting oscillations in Earth's climate system as a metronome for determining geologic time. In this study, we reversed the cyclostratigraphic approach and used the highly rhythmical sedimentary deposits from Newfoundland Ridge (North Atlantic) to back‐calculate planetary motions at ∼41 million years ago. The superior quality of the Newfoundland Ridge geoarchive originates from the combination of relatively high sedimentation rates (∼4 cm/kyr) and the time‐continuous character of our two‐site composite record between 39.5 and 42.8 million years ago. In this work, we had to first overcome considerable challenges in reconstructing the timing of sediment deposition, which we did with highly resolved geochemical measurements from two sites. We then were able to extract information on the Earth's planetary motion and on the Earth‐Moon interactions. These astronomical reconstructions based on geological data can now be used by astronomers to describe the evolution of the solar system further back in time than was previously possible.
    Description: Key Points: A new precession‐based cyclostratigraphy for the middle Eocene intervals of IODP Sites U1408 and U1410. Variability in astronomical fundamental frequencies (g‐terms) on million‐year timescales is larger than previously assumed. Our precession constant estimate for 41 Ma (51.28 ± 0.56″/year) confirms earlier indicators of slower tidal dissipation in the Paleogene.
    Description: National Science Foundation http://dx.doi.org/10.13039/100000001
    Description: University of California http://dx.doi.org/10.13039/100005595
    Description: Belgian American Educational Foundation http://dx.doi.org/10.13039/100001491
    Description: https://paloz.marum.de/AstroComputation/index.html
    Description: https://paloz.marum.de/confluence/display/ESPUBLIC/NAFF
    Keywords: ddc:551 ; North Atlantic ; Eocene ; cyclostratigraphy ; astrochronology
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 14
    facet.materialart.
    Unknown
    Sources of Inaccuracy in Boron Isotope Measurement Using LA‐MC‐ICP‐MS (2023)
    Details
    Publication Date: 2023-11-17
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Laser ablation multi‐collector‐inductively coupled plasma‐mass spectrometry (LA‐MC‐ICP‐MS) has become a valuable tool for the 〈italic toggle="no"〉in situ〈/italic〉 measurement of the boron isotope composition of geological samples at high (tens to hundreds of μm) spatial resolution. That said, this application suffers from significant analytical challenges. We focus in this study on the underlying processes of two of the main causes for inaccuracies using this technique. We provide empirical evidence that not only Ca ions (Sadekov 〈italic〉et al〈/italic〉. 2019, Standish 〈italic〉et al〈/italic〉. 2019, Evans 〈italic〉et al〈/italic〉. 2021) but also Ar ions, that are reflected within the flight tube of the mass spectrometer, are the source for previously reported issues with spectral baselines. We also address the impact of plasma conditions on the instrumental mass fractionation as a source for matrix‐ and mass‐load‐related analytical biases. Comparing experimental data with the results of a dedicated release and diffusion model (RDM) we estimate that a close to complete (~ 97%) release of boron from the sample aerosol is needed to allow for consistently accurate LA boron isotope measurement results without the need for corrections.〈/p〉
    Description: Key Points: 〈list list-type="bullet" id="ggr12500-list-0101"〉 〈list-item〉〈p〉Two separate main sources for inaccuracy of boron isotope measurements by laser ablation: B isotope fractionation in the ICP and the known scattered ion baseline problem.〈/p〉〈/list-item〉 〈list-item〉〈p〉Boron isotope fractionation in the ICP varies systematically with plasma condition (NAI).〈/p〉〈/list-item〉 〈list-item〉〈p〉Behaviour of B isotopes within the ICP simulated by a release and diffusion model (RDM).〈/p〉〈/list-item〉 〈/list〉 〈boxed-text position="anchor" content-type="graphic" id="ggr12511-blkfxd-0001" xml:lang="en"〉 〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:16394488:media:ggr12511:ggr12511-toc-0001"〉 〈/graphic〉 〈/boxed-text〉 〈/p〉
    Keywords: ddc:550.78 ; boron isotopes ; laser ablation ; scattered ions ; mass fractionation ; plasma conditions
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 15
    facet.materialart.
    Unknown
    Analog Models of Lithospheric‐Scale Rifting Monitored in an X‐Ray CT Scanner (2023)
    Details
    Publication Date: 2023-11-13
    Description: Rifting and continental break‐up are fundamental tectonic processes, the understanding of which is of prime importance. However, the vast temporal and spatial scales involved pose major limitations to researchers. Analog tectonic modeling represents a great means to mitigate these limitations, but studying the complex internal deformation of lithospheric‐scale models remains a challenge. We therefore present a novel method for lithospheric‐scale rifting models that are uniquely monitored in an X‐ray CT scanner, which combined with digital image correlation (DIC) techniques, provides unparalleled insights into model deformation. Our first models illustrate how the degree of coupling between competent lithospheric layers, which are separated by a weak lower crustal layer, strongly impacts rift system development. Low coupling isolates the upper crust from the upper lithospheric mantle layer below, preventing an efficient transfer of deformation between both layers. By contrast, fast rifting increases coupling, so that deformation in the mantle is efficiently transferred to the upper crust, inducing either a symmetric or asymmetric (double) rift system. Furthermore, oblique divergence may lead to en echelon graben arrangements and delayed exhumation of the lower crustal layer. The successful application of our novel modeling approach, yielding these first‐order insights, provides a clear incentive to continue running lithospheric‐scale rifting models, and to apply advanced monitoring techniques to extract as much information from models as possible. There is indeed a broad range of opportunities for follow‐up studies within (and beyond) the field of rift tectonics.
    Description: Plain Language Summary: The Earth's surface consists of tectonic plates that are in constant motion, driven by titanic forces deep within the planet. One of the key plate tectonic processes is the stretching (rifting) and eventual break‐up of continents, leading to the opening of oceanic basins. Understanding the mechanisms involved is of great importance. However, studying continental break‐up is challenging due to the vast size of plate tectonic systems, and the extensive timescales over which they evolve: plate tectonic processes can rarely be directly observed. A practical solution to this issue is the use of analog experiments, which reproduce these processes in a matter of hours or days in a modestly sized laboratory. However, a major obstacle that remains is the opacity of these models: similar to tectonic plates, these models are opaque, so that their internal evolution remains hidden. X‐ray CT‐scanning provides an unrivaled means to reveal a model's internal structures during a model run. Here we present the first‐ever application of CT‐scanning to monitor relatively complex lithospheric‐scale models of continental rifting. The CT scans provide unique insights into the internal evolution of such models, and we point out various possibilities for interesting follow‐up studies.
    Description: Key Points: We present the first‐ever lithospheric‐scale analog models of rifting monitored in a CT scanner, revealing their complex internal deformation. We quantify this deformation via Digital Image Correlation analysis, and show the impact of coupling and oblique rifting on rift evolution. The successful application of our novel modeling approach provides a strong incentive for follow‐up tectonic modeling studies.
    Description: Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung http://dx.doi.org/10.13039/501100001711
    Description: Helmholtz‐Zentrum Potsdam ‐ Deutsches GeoForschungsZentrum GFZ http://dx.doi.org/10.13039/501100010956
    Description: https://doi.org/10.5880/fidgeo.2022.030
    Description: https://doi.org/10.5880/fidgeo.2022.008
    Description: https://doi.org/10.5880/fidgeo.2023.006
    Description: https://doi.org/10.5880/fidgeo.2023.005
    Keywords: ddc:550.78 ; rifting ; analog modeling ; continental break‐up ; X‐ray CT‐scanning ; visualization ; monitoring
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 16
    facet.materialart.
    Unknown
    Neogene aridification and lake development in the Issyk‐Kul basin, Kyrgyzstan (2023)
    Details
    Publication Date: 2023-11-24
    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"〉Uplift of the Tian Shan range modified regional climate during Cenozoic aridification in Central Asia. This study presents facies analyses and Neogene oxygen and carbon isotopic records from magnetostratigraphically dated terrestrial sedimentary sections on the southern side of the intermontane Issyk‐Kul basin in the Kyrgyz Tian Shan and 〈sup〉26〈/sup〉Al/〈sup〉10〈/sup〉Be isochron burial ages from the southern and eastern sides of the basin. The δ〈sup〉18〈/sup〉O and δ〈sup〉13〈/sup〉C data show a positive ca. 2‰ shift in values between ca. 8 and 7 Ma and a change from a negative to a positive trend. This change is attributed to the upwind growth of the Kyrgyz, Kungey and Trans Ili (Zaili) ranges, which diverted the westerlies, thereby changing the Issyk‐Kul basin from a windward to a leeward position, enhancing aridification and establishing the modern‐day spring and summer precipitation regime within the basin. Two 4 to 5 Ma 〈sup〉26〈/sup〉Al/〈sup〉10〈/sup〉Be isochron burial ages constrain the onset of Sharpyl Dak deposition on the eastern side of the basin; southward paleocurrent directions there suggest the eastward growth of the Kungey range in the Pliocene. Increased subsidence on the southern side of the basin and local tectonically induced river system reorganization led to the commencement of lake formation at ca. 5 Ma, followed by a ca. 2 Ma local depositional hiatus. The transition from sandstones of the Chu sedimentary group to conglomerates of the Sharpyl Dak group, marking a change from fluvial‐alluvial deposits to a proximal alluvial fan, is dated at 2.6–2.8 Ma by 〈sup〉26〈/sup〉Al/〈sup〉10〈/sup〉Be isochron burial dating on the southern side of the basin, driven either by tectonics or Northern Hemisphere glaciation. This study concludes that the late Miocene–Pliocene northward growth of Tian Shan significantly altered environmental conditions within the range, preventing the moisture‐bearing westerlies from reaching the intermontane Issyk‐Kul basin and promoting lake formation and expansion.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The late Miocene–Pliocene northward growth of Tian Shan created an orographic barrier that diverted the moisture‐bearing westerlies and enhanced aridification in the Issyk‐Kul basin. Reorganization of the river systems and enhanced subsidence led to the formation of an internally drained lake in Pliocene. The transition from sandstone to conglomerate (Sharpyl Dak group) deposition, linked to a change in climate and/or tectonic activity, occurred diachronously within the basin.〈boxed-text position="anchor" content-type="graphic" id="bre12751-blkfxd-0001" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:0950091X:bre12751:bre12751-toc-0001"〉 〈/graphic〉〈/boxed-text〉〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: University of Wollongong http://dx.doi.org/10.13039/501100001777
    Keywords: ddc:551 ; Cenozoic aridification ; Central Asia ; cosmogenic 26Al/10Be ; tectonic uplift ; westerlies ; δ18O and δ13C stable isotopes
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 17
    facet.materialart.
    Unknown
    A Snapshot on the Buildup of the Stable Water Isotopic Signal in the Upper Snowpack at EastGRIP on the Greenland Ice Sheet (2023)
    Zuhr, Alexandra M. ; Wahl, Sonja ; Steen‐Larsen, Hans Christian ; [et al.]
    Details
    Publication Date: 2024-04-19
    Description: The stable water isotopic composition in firn and ice cores provides valuable information on past climatic conditions. Because of uneven accumulation and post‐depositional modifications on local spatial scales up to hundreds of meters, time series derived from adjacent cores differ significantly and do not directly reflect the temporal evolution of the precipitated snow isotopic signal. Hence, a characterization of how the isotopic profile in the snow develops is needed to reliably interpret the isotopic variability in firn and ice cores. By combining digital elevation models of the snow surface and repeated high‐resolution snow sampling for stable water isotope measurements of a transect at the East Greenland Ice‐core Project campsite on the Greenland Ice Sheet, we are able to visualize the buildup and post‐depositional changes of the upper snowpack across one summer season. To this end, 30 cm deep snow profiles were sampled on six dates at 20 adjacent locations along a 40 m transect. Near‐daily photogrammetry provided snow height information for the same transect. Our data shows that erosion and redeposition of the original snowfall lead to a complex stratification in the δ〈sup〉18〈/sup〉O signature. Post‐depositional processes through vapor‐snow exchange affect the near surface snow with d‐excess showing a decrease in surface and near‐surface layers. Our data suggests that the interplay of stratigraphic noise, accumulation intermittency, and local post‐depositional processes form the proxy signal in the upper snowpack.
    Description: Plain Language Summary: We study the process of the formation of the stable water isotope signal in surface snow on the Greenland Ice Sheet to better understand temperature information which is stored as a climate proxy in snow and ice. Our data consist of high‐resolution surface topography information illustrating the timing and location of snowfall, erosion, and redeposition along a transect of 40 m, as well as stable water isotope records of the upper 30 cm of the snowpack sampled biweekly on 20 positions at the same 40 m long transect. The data cover a 2‐month period during the summer of 2019. We find that the isotopic composition shows spatial variability of layers with low and high values, presumably winter and summer layers. We further observe that prevailing surface structures, such as dunes, influence the snow deposition and contribute to the found variable structure of the climatic information. Eventually, snow accumulation alone cannot explain all of the observed patterns in the isotopic data which is likely related to exchange processes between the snow and the atmosphere which modify the signal in the snow column after deposition.
    Description: Key Points: Combining digital elevation models and repeated snow sampling reveals the heterogeneous buildup of δ〈sup〉18〈/sup〉O signal in the snow column. Surface structures (stratigraphic noise) substantially contribute to internal heterogeneity in δ〈sup〉18〈/sup〉O signature in the upper snowpack. Proxy signals are formed in the surface layer by local processes, advected downwards with limited post‐depositional influences below 10 cm.
    Description: Horizon 2020 Framework Programme http://dx.doi.org/10.13039/100010661
    Description: A. P. Møller Foundation, University of Copenhagen
    Description: US National Science Foundation, Office of Polar Programs
    Description: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research
    Description: National Institute of Polar Research and Arctic Challenge for Sustainability
    Description: University of Bergen
    Description: Trond Mohn Foundation
    Description: Swiss National Science Foundation
    Description: French Polar Institute Paul‐Emile Victor, Institute for Geosciences and Environmental Research
    Description: University of Manitoba
    Description: Chinese Academy of Sciences
    Description: Beijing Normal University
    Description: https://doi.org/10.1594/PANGAEA.954944
    Description: https://doi.org/10.1594/PANGAEA.954945
    Description: https://doi.org/10.1594/PANGAEA.951583
    Description: https://doi.org/10.1594/PANGAEA.925618
    Description: https://doi.org/10.1594/PANGAEA.928827
    Description: https://www.agisoft.com/downloads/installer/
    Keywords: ddc:551 ; proxy ; Greenland ; isotopes ; structure‐from‐motion ; snow accumulation ; ice core
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 18
    facet.materialart.
    Unknown
    Preparatory Slip in Laboratory Faults: Effects of Roughness and Load Point Velocity (2023)
    Details
    Publication Date: 2024-02-14
    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"〉Aseismic slip may occur during a long preparatory phase preceding earthquakes, and what controls it remains poorly understood. In this study, we explored the role of load point velocity and surface roughness on slow slip during the preparatory stage prior to stick‐slip events. To that end, we conducted displacement‐rate controlled friction experiments by imposing varying load point velocities on sawcut granite samples with different surface roughness at a confining pressure of 35 MPa. We measured the average slip along the fault with the recorded far‐field displacements and strain changes, while acoustic emission sensors and local strain gages were used to capture local slip variations. We found that the average amount of aseismic slip during the preparatory stage increases with roughness, whereas precursory slip duration decreases with increased load point velocity. These results reveal a complex slip pattern on rough faults which leads to dynamic ruptures at high load point velocities.〈/p〉
    Description: Plain Language Summary: Earthquakes occur mostly along preexisting faults in the earth crust. These faults exhibit various geometrical complexities and are subjected to different strain rates. In the laboratory, we produce earthquake analogs by sliding sawcut granite blocks. We vary the geometrical complexity of the faults by roughening their surfaces and modify the strain rate by displacing the blocks at varying velocities. Under these different conditions, we measure how the forces accumulated by friction are released, by measuring stresses and displacements applied on the block's edges, using local strain deformation sensors, and by recording very small earthquakes occurring during sliding along the sawcut faults. We find that smooth sawcut faults tend to release all the energy accumulated very abruptly, after a very small amount of slip, regardless of the load point velocity applied. The processes leading to failure in the case of a rough fault are much more complex, involving a large amount of slip, and numerous small earthquakes which are distributed heterogeneously in space and time.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Acoustic emissions highlight the complex preparatory phase prior stick‐slips on rough faults〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Preparatory slip increases with roughness and the duration of the preparatory phase decreases with increasing load point velocity〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Rough and heterogeneous faults are more stable than smooth faults, but can become unstable with a small increase of load point velocity〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: SAIDAN
    Description: https://doi.org/10.5281/zenodo.6411819
    Keywords: ddc:550.78 ; rock friction ; roughness ; dynamic rupture ; acoustic emissions
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 19
    facet.materialart.
    Unknown
    Northern Hemisphere Summer Insolation and Ice Volume Driven Variations in Hydrological Environment in Southwest China (2023)
    Details
    Publication Date: 2024-05-30
    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"〉The interpretation of stalagmite δ〈sup〉18〈/sup〉O in terms of reflecting Asian summer monsoon (ASM) precipitation is still elusive. Here, we present high‐resolution stalagmite trace element ratios (X/Ca, X = Mg, Sr, Ba) records from southwest China covering 116.09 to 4.07 ka BP. δ〈sup〉18〈/sup〉O, δ〈sup〉13〈/sup〉C, and X/Ca values exhibit clear precessional cycles, with δ〈sup〉18〈/sup〉O values reflecting ASM circulation/intensity, while X/Ca ratios capture local precipitation or evapotranspiration variations. Our results show that Northern Hemisphere summer insolation (NHSI) is the main driver of ASM intensity and precipitation phase variation, but global ice volume modulates the response magnitude of summer precipitation to insolation. During the Last Glacial Maximum, high ice volumes caused significant monsoon precipitation to decrease. In contrast to modern observations of the tripolar distribution of precipitation in China, our record is consistent with paleo‐precipitation records in southern and northern China.〈/p〉
    Description: Plain Language Summary: While it is well known that global changes have led to variations in the intensity and spatial distribution of Asian monsoon precipitation, the mechanisms behind this are not well understood. Paleoclimate records are essential for revealing the drivers behind monsoon variation. However, speleothem records from the Asian monsoon region rarely provide direct information on the amount of rainfall. Here we report on multiple indicator data sets from a stalagmite in southwestern China. It could help explore the variation of monsoon precipitation over the last ∼100,000 years. We find that the increase/decrease of Northern Hemisphere summer insolation controls the increase/decrease of Asian summer monsoon rainfall. In addition, global ice volume moderates the magnitude of rainfall response to insolation, and precipitation decreases significantly during high ice volume periods. Based on the present paleo‐precipitation records evidence, the existence of the spatial pattern of increasing/decreasing rainfall in central China corresponding to decreasing/increasing rainfall in northern and southern China remains ambiguous on the orbital scales, although the feature has been captured by some of the model simulations.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Stalagmite trace elements are indicators of regional hydrological environmental variations in Southwestern China〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Northern Hemisphere summer insolation and global ice volume modulate the phase and amplitude variations of regional hydrological environment〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The meridional tripolar spatial pattern of precipitation in monsoon region in China on the orbital scale remains ambiguous〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: German Science Grant
    Description: Structure and Innovation Fund of the Region of Baden Württemberg
    Description: China Scholarship Council http://dx.doi.org/10.13039/501100004543
    Description: National Nature Science Foundation of China
    Description: Yunnan Fundamental Research Projects
    Description: Young and Middle‐age Academic and Technical Leader in Yunnan Province
    Description: https://doi.org/10.5281/zenodo.10072475
    Keywords: ddc:551 ; stalagmite ; trace elements ; Asian summer monsoon ; Northern Hemisphere summer insolation ; global ice volume ; regional hydrological environment
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 20
    facet.materialart.
    Unknown
    The geodynamic and limnological evolution of Balkan Lake Ohrid, possibly the oldest extant lake in Europe (2022)
    Details
    Publication Date: 2023-12-04
    Description: Studies of the upper 447 m of the DEEP site sediment succession from central Lake Ohrid, Balkan Peninsula, North Macedonia and Albania provided important insights into the regional climate history and evolutionary dynamics since permanent lacustrine conditions established at 1.36 million years ago (Ma). This paper focuses on the entire 584‐m‐long DEEP sediment succession and a comparison to a 197‐m‐long sediment succession from the Pestani site ~5 km to the east in the lake, where drilling ended close to the bedrock, to unravel the earliest history of Lake Ohrid and its basin development. 26Al/10Be dating of clasts from the base of the DEEP sediment succession implies that the sedimentation in the modern basin started at c. 2 Ma. Geophysical, sedimentological and micropalaeontological data allow for chronological information to be transposed from the DEEP to the Pestani succession. Fluvial conditions, slack water conditions, peat formation and/or complete desiccation prevailed at the DEEP and Pestani sites until 1.36 and 1.21 Ma, respectively, before a larger lake extended over both sites. Activation of karst aquifers to the east probably by tectonic activity and a potential existence of neighbouring Lake Prespa supported filling of Lake Ohrid. The lake deepened gradually, with a relatively constant vertical displacement rate of ~0.2 mm a−1 between the central and the eastern lateral basin and with greater water depth presumably during interglacial periods. Although the dynamic environment characterized by local processes and the fragmentary chronology of the basal sediment successions from both sites hamper palaeoclimatic significance prior to the existence of a larger lake, the new data provide an unprecedented and detailed picture of the geodynamic evolution of the basin and lake that is Europe’s presumed oldest extant freshwater lake.
    Keywords: ddc:551 ; Balkan Peninsula ; Lake Ohrid ; DEEP sediment succession ; Pestani succession ; evolutionary dynamics ; regional climate history
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 21
    facet.materialart.
    Unknown
    Identifying Dominant Processes in Time and Space: Time‐Varying Spatial Sensitivity Analysis for a Grid‐Based Nitrate Model (2022)
    Details
    Publication Date: 2023-01-14
    Description: Distributed models have been increasingly applied at finer spatiotemporal resolution. However, most diagnostic analyses aggregate performance measures in space or time, which might bias subsequent inferences. Accordingly, this study explores an approach for quantifying the parameter sensitivity in a spatiotemporally explicit way. We applied the Morris method to screen key parameters within four different sampling spaces in a grid‐based model (mHM‐Nitrate) for NO3‐N simulation in a mixed landuse catchment using a 1‐year moving window for each grid. The results showed that an overly wide range of aquatic denitrification rates could mask the sensitivity of the other parameters, leading to their spatial patterns only related to the proximity to outlet. With adjusted parameter space, spatial sensitivity patterns were determined by NO3‐N inputs and hydrological transport capacity, while temporal dynamics were regulated by annual wetness conditions. The relative proportion of parameter sensitivity further indicated the shifts in dominant hydrological/NO3‐N processes between wet and dry years. By identifying not only which parameter(s) is(are) influential, but where and when such influences occur, spatial sensitivity analysis can help evaluate current model parameterization. Given the marked sensitivity in agricultural areas, we suggest that the current NO3‐N parameterization scheme (land use‐dependent) could be further disentangled in these regions (e.g., into croplands with different rotation strategies) but aggregated in non‐agricultural areas; while hydrological parameterization could be resolved into a finer level (from spatially constant to land use‐dependent especially in nutrient‐rich regions). The spatiotemporal sensitivity pattern also highlights NO3‐N transport within soil layers as a focus for future model development.
    Description: Key Points: A diagnostic analysis was conducted to disentangle the parameter sensitivity for NO3‐N simulations in catchment modeling in space and time. Sensitivity differed within sampling spaces, but was controlled spatially by NO3‐N supply/water fluxes while temporally by wetness condition. Analysis suggests finer‐level parameterization needs in arable land, and prioritizes NO3‐N transport in soils for improved conceptualization.
    Description: Chinese Scholarship Council
    Description: Leverhulme Trust http://dx.doi.org/10.13039/501100000275
    Description: Einstein Stiftung Berlin http://dx.doi.org/10.13039/501100006188
    Description: Berlin University Alliance http://dx.doi.org/10.13039/501100021727
    Description: https://doi.org/10.5281/zenodo.6497225
    Description: https://fred.igb-berlin.de/data/package/629
    Keywords: ddc:551 ; spatial time‐varying sensitivity analysis ; distributed nitrate modeling
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 22
    facet.materialart.
    Unknown
    Sediment Release in the Benguela Upwelling System Dominates Trace Metal Input to the Shelf and Eastern South Atlantic Ocean (2022)
    Details
    Publication Date: 2023-01-21
    Description: Upwelling of subsurface waters injects macronutrients (fixed N, P, and Si) and micronutrient trace metals (TMs) into surface waters supporting elevated primary production in Eastern Boundary Upwelling Regions. The eastern South Atlantic features a highly productive shelf sea transitioning to a low productivity N‐Fe (co)limited open ocean. Whilst a gradient in most TM concentrations is expected in any off‐shelf transect, the factors controlling the magnitude of cross‐shelf TM fluxes are poorly constrained. Here, we present dissolved TM concentrations of Fe, Co, Mn, Cd, Ni, and Cu within the Benguela Upwelling System from the coastal section of the GEOTRACES GA08 cruise. Elevated dissolved Fe, Co, Mn, Cd, Ni, Cu and macronutrient concentrations were observed near shelf sediments. Benthic sources supplied 2.22 ± 0.99 μmol Fe m−2 day−1, 0.05 ± 0.03 μmol Co m−2 day−1, 0.28 ± 0.11 μmol Mn m−2 day−1 and were found to be the dominant source to shallow shelf waters compared to atmospheric depositions. Similarly, off‐shelf transfer was a more important source of TMs to the eastern South Atlantic Ocean compared to atmospheric deposition. Assessment of surface (shelf, upper 200 m) and subsurface (shelf edge, 200–500 m) fluxes of Fe and Co indicated TM fluxes from subsurface were 2–5 times larger than those from surface into the eastern South Atlantic Ocean. Under future conditions of increasing ocean deoxygenation, these fluxes may increase further, potentially contributing to a shift toward more extensive regional limitation of primary production by fixed N availability.
    Description: Key Points: Shelf sediments release redox‐sensitive trace metals (TMs) to overlying oxygen‐depleted waters in the Benguela Upwelling System. Sediment‐derived TMs are upwelled and laterally transported constituting a major source to shelf waters and to the eastern South Atlantic. Subsurface fluxes of dissolved Fe and Co from the shelf edge play an important role in supplying Fe and Co to the eastern South Atlantic.
    Description: China Scholarship Council, CSC http://dx.doi.org/10.13039/501100004543
    Description: GEOMAR and German Research Foundation
    Description: German DFG
    Description: German Research Foundation
    Description: https://doi.pangaea.de/10.1594/PANGAEA.947275
    Keywords: ddc:551 ; dissolved trace metals ; Benguela Upwelling Systems ; fluxes ; Eastern Boundary Upwelling Systems Regions
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 23
    facet.materialart.
    Unknown
    Dynamics of Greenhouse Gases (CH4 and CO2) in Meromictic Lake Burgsee, Germany (2022)
    Details
    Publication Date: 2023-01-21
    Description: Extraordinary amounts of greenhouse gases can be stored within the monimolimnion of meromictic lakes, that is, in the water body which is excluded from mixing events. Lake Burgsee (Thuringia, Germany) is a shallow (depth 〈5 m) lake with a approximately 24 m deep sinkhole, which is fed by underground brine sources and has formed such a monimolimnion. We investigated the carbon dioxide and methane dynamics in this meromictic lake, from production potentials in the sediment via concentrations in the monimolimnion and mixolimnion to emissions to the atmosphere. In the monimolimnion, we found one of the highest methane concentrations (up to 〉5 mmol L−1) ever reported for a natural freshwater lake, while carbon dioxide concentrations in the water and methane production rates in the sediments were rather ordinary and within the range of holomictic eutrophic lakes. At the thermocline, gas concentrations accumulated to approximately 100 μmol L−1 CH4 and 80–230 μmol L−1 CO2. Estimated fluxes to the atmosphere reached considerable 3.5 mmol CH4 m−2 d−1 and 1.5 mmol CO2 m−2 d−1 above the sinkhole and 0.8 mmol CH4 m−2 d−1 and 0.4 mmol CO2 m−2 d−1 above the near‐by shallow lake center in 2018. Our results demonstrate that lakes in natural brine areas may provide significant storages and releases of greenhouse gases and require further investigation.
    Description: Plain Language Summary: In meromictic lakes, the deepest water layer, the monimolimnion, is stagnant and not included in seasonal water circulation. Organic matter continuously sinks down into the oxygen‐free monimolimnion, where it is decomposed into the final gaseous products carbon dioxide (CO2) and methane (CH4). Lake Burgsee is a meromictic shallow (depth 〈5 m), brine‐fed lake with a approximately 24 m deep sinkhole. At the bottom of the narrow sinkhole, salinities are as high as in brackish water and cause a chemical stratification of the water body—a monimolimnion—in approximately 18 m depth. CH4 concentrations above the sediment reach 〉5 mmol L−1, which is more than one order of magnitude higher than at the water surface and among the highest CH4 concentrations found in freshwater lakes worldwide. Further, emissions of CH4 and CO2 from the water to the atmosphere were considerable in 2018, and about four times higher above the sinkhole than above the shallow lake center. These results demonstrate, that lakes in natural brine areas may store and release significant amounts of greenhouse gases and require further investigation.
    Description: Key Points: In the urban meromictic Lake Burgsee, methane production potentials in the sediment are similar to eutrophic holomictic lakes. At its deepest site, it contains one of the highest methane concentrations (〉5 mmol L−1 CH4) ever reported for a natural freshwater lake. Lake Burgsee emits up to 〉3 mmol m−2 d−1 CH4 to the atmosphere above the sinkhole and 〈1 mmol m−2 d−1 CH4 at a near‐by shallow site.
    Keywords: ddc:551 ; meromictic lake ; sinkhole ; salinity ; greenhouse gases ; methane flux ; carbon dioxide
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 24
    facet.materialart.
    Unknown
    Evidence for Secondary Ice Production in Southern Ocean Maritime Boundary Layer Clouds (2022)
    Details
    Publication Date: 2023-01-25
    Description: Maritime boundary‐layer clouds over the Southern Ocean (SO) have a large shortwave radiative effect. Yet, climate models have difficulties in representing these clouds and, especially, their phase in this observationally sparse region. This study aims to increase the knowledge of SO cloud phase by presenting in‐situ cloud microphysical observations from the Southern Ocean Clouds, Radiation, Aerosol, Transport Experimental Study (SOCRATES). We investigate the occurrence of ice in summertime marine stratocumulus and cumulus clouds in the temperature range between 6 and −25°C. Our observations show that in ice‐containing clouds, maximum ice number concentrations of up to several hundreds per liter were found. The observed ice crystal concentrations were on average one to two orders of magnitude higher than the simultaneously measured ice nucleating particle (INP) concentrations in the temperature range below −10°C and up to five orders of magnitude higher than estimated INP concentrations in the temperature range above −10°C. These results highlight the importance of secondary ice production (SIP) in SO summertime marine boundary‐layer clouds. Evidence for rime splintering was found in the Hallett‐Mossop (HM) temperature range but the exact SIP mechanism active at lower temperatures remains unclear. Finally, instrument simulators were used to assess simulated co‐located cloud ice concentrations and the role of modeled HM rime‐splintering. We found that CAM6 is deficient in simulating number concentrations across the HM temperature range with little sensitivity to the model HM process, which is inconsistent with the aforementioned observational evidence of highly active SIP processes in SO low‐level clouds.
    Description: Plain Language Summary: Clouds in the Southern Ocean are important for climate but not well represented in climate models. Observations in this remote region have been rare. This study presents results from a recent airborne campaign that took place in the Southern Ocean where low‐ and mid‐level clouds were investigated by detecting individual cloud particles within the clouds. Although large fraction of the observed clouds did not contain ice crystals, occasionally high amounts of ice crystals were observed that cannot be explained by ice formation on aerosol particles but were result of multiplication of existing ice crystals. We tested the capability of a commonly used climate model to represent the observed ice concentrations and their sensitivity to one ice multiplication process parameterized in the model. These investigations revealed that the in the model the ice multiplication process was not responsible for generation of ice, which is in contradiction with the observations.
    Description: Key Points: Ice concentrations several orders of magnitude higher than ice nucleating particle concentrations were observed. Secondary ice production was believed to be responsible for the observed high ice number concentrations. Comparison with climate model indicated that secondary ice processes are still inadequately represented in the model.
    Description: National Science Foundation http://dx.doi.org/10.13039/100000001
    Description: U.S. Department of Energy http://dx.doi.org/10.13039/100000015
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: NSF Polar Programs
    Keywords: ddc:551 ; southern ocean ; mixed‐phase clouds ; in‐situ observations ; ice crystals ; secondary ice ; ice nucleating particles
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 25
    facet.materialart.
    Unknown
    Groundwater Responses to Earth Tides: Evaluation of Analytical Solutions Using Numerical Simulation (2022)
    Details
    Publication Date: 2023-01-12
    Description: Harmonic Earth tide components in well water levels have been used to estimate hydraulic and geomechanical subsurface properties. However, the robustness of various methods based on analytical solutions has not been established. First, we review the theory and examine the latest analytical solution used to relate well water levels to Earth tides. Second, we develop and verify a novel numerical model coupling hydraulics and geomechanics to Earth tide strains. Third, we assess subsurface conditions over depth for a range of realistic properties. Fourth, we simulate the well water level response to Earth tide strains within a 2D poroelastic layered aquifer system confined by a 100 m thick aquitard. We find that the non‐linear inversion of analytical solutions to match two observations (amplitudes and phases) to multiple unknown parameters is sensible to the initial guess. We reveal that undrained, confined conditions are necessary for the analytical solution to be valid. This occurs for the dominant M2 frequency at depths 〉50 m and requires specific storage at constant strain of Sϵ ≥ 10−6 m−1, hydraulic conductivity of the aquitard of kl ≤ 5 ⋅ 10−5 ms−1 and aquifer of ka ≥ 10−4 ms−1. We further illustrate that the analytical solution is valid in unconsolidated systems, whereas consolidated systems require additional consideration of the Biot modulus. Overall, a priori knowledge of the subsurface system supports interpretation of the groundwater response. Our results improve understanding of the effect of Earth tides on groundwater systems and its interpretation for subsurface properties.
    Description: Plain Language Summary: Earth tide induced strains in the subsurface lead to well water level fluctuations in groundwater monitoring wells. This groundwater response has been interpreted with analytical solutions to estimate aquifer properties. However, analytical solutions are based on simplified assumptions whose accuracy have not yet been tested. We develop a new approach to simulate the influence of Earth tides on groundwater based on fundamental physical principles. We simulate realistic conditions and compare our results to those from analytical solution to determine the hydraulic and subsurface conditions under which simplified interpretations are valid. Our results improve understanding of the effects of Earth tides on groundwater systems and interpretation of subsurface properties from well water levels.
    Description: Key Points: We develop and verify a numerical model for the well water level response to Earth tides. Subsurface property estimation requires undrained and confined conditions occurring at depths 〉50 m. Amplitudes and phases from numerical and analytical solutions systematically diverge reflecting theory simplifications.
    Description: German Research Council
    Description: https://doi.org/10.5281/zenodo.6950492
    Keywords: ddc:551 ; tidal subsurface analysis ; numerical modeling ; Earth tides
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 26
    facet.materialart.
    Unknown
    Drought Conditions Enhance Groundwater Table Fluctuations Caused by Hydropower Plant Management (2022)
    Details
    Publication Date: 2023-01-13
    Description: Management of hydropower plants strongly influences streamflow dynamics and hence the interaction between surface water and groundwater. As dam operations cause variations in river stages, these can result in changes in the groundwater level at multiple temporal scales. In this work, we study the case of an Alpine aquifer, where weekly fluctuations are particularly pronounced. We consider an area with four river reaches differently impacted by reservoir operations and investigate the influence of these rivers on the common aquifer. Using continuous wavelet transform and wavelet coherence analysis, we show that weekly fluctuations in the groundwater table are particularly pronounced in dry years, in particular in the winter season, although the area of the aquifer impacted by dam operations remains almost unchanged. We thus observe that in Alpine catchments, surface water‐groundwater interaction is sensitive to the conditions determined by a specific hydrological year. We also investigate the influences of the river‐aquifer water fluxes and show that under dry conditions hydropeaking mainly affects their temporal dynamics. Our observations have significant consequences for predicting nutrient and temperature dynamics/regimes in river‐aquifer systems impacted by hydropower plant management.
    Description: Plain Language Summary: The operation of hydropower plants affects the water level in the downstream part of the river, which in turn can alter the groundwater level. In this work, we study an Alpine aquifer crossed by rivers differently impacted by hydropower production. We use statistical tools to analyze the interaction between the rivers and the groundwater, and observe that this interaction is sensitive to the conditions of the hydrological year, such as dry periods.
    Description: Key Points: Wavelet power spectrum and coherence analysis is used to study river‐aquifer interactions under dam operations in an Alpine catchment. The impact of reservoir operations on the aquifer is strongest under low flow conditions but the area impacted shows little variation. Under low flow conditions, dam operations considerably influence the frequency of the water exchange between rivers and aquifer.
    Description: Consejo Nacional de Ciencia y Tecnología http://dx.doi.org/10.13039/501100003141
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Consejo Veracruzano de Investigación Científica y Desarrollo Tecnológico
    Description: https://doi.org/10.17632/97jchhz4s8.2
    Keywords: ddc:551 ; surface water‐groundwater interaction ; hydropower ; managed rivers ; groundwater modeling
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 27
    facet.materialart.
    Unknown
    Earthquake Rupture on Multiple Splay Faults and Its Effect on Tsunamis (2022)
    Details
    Publication Date: 2023-01-19
    Description: Detailed imaging of accretionary wedges reveals splay fault networks that could pose a significant tsunami hazard. However, the dynamics of multiple splay fault activation during megathrust earthquakes and the consequent effects on tsunami generation are not well understood. We use a 2‐D dynamic rupture model with complex topo‐bathymetry and six curved splay fault geometries constrained from realistic tectonic loading modeled by a geodynamic seismic cycle model with consistent initial stress and strength conditions. We find that all splay faults rupture coseismically. While the largest splay fault slips due to a complex rupture branching process from the megathrust, all other splay faults are activated either top down or bottom up by dynamic stress transfer induced by trapped seismic waves. We ascribe these differences to local non‐optimal fault orientations and variable along‐dip strength excess. Generally, rupture on splay faults is facilitated by their favorable stress orientations and low strength excess as a result of high pore‐fluid pressures. The ensuing tsunami modeled with non‐linear 1‐D shallow water equations consists of one high‐amplitude crest related to rupture on the longest splay fault and a second broader wave packet resulting from slip on the other faults. This results in two episodes of flooding and a larger run‐up distance than the single long‐wavelength (300 km) tsunami sourced by the megathrust‐only rupture. Since splay fault activation is determined by both variable stress and strength conditions and dynamic activation, considering both tectonic and earthquake processes is relevant for understanding tsunamigenesis.
    Description: Plain Language Summary: In subduction zones, where one tectonic plate moves beneath another, earthquakes can occur on many different faults. Splay faults are relatively steep faults that branch off the largest fault (the megathrust) in a subduction zone. As they are steeper than the megathrust, the same amount of movement on them could result in more vertical displacement of the seafloor. Therefore, splay faults are thought to play an important role in the generation of tsunamis. Here, we use computer simulations to study if an earthquake can break multiple splay faults at once and how this affects the resulting tsunami. We find that multiple splay faults can indeed fail during a single earthquake due to the stress changes from trapped seismic waves, which promote rupture on splay faults. Rupture on splay faults results in larger seafloor displacements with smaller wavelengths, so the ensuing tsunami is bigger and results in two main flooding episodes at the coast. Our results show that it is important to consider rupture on splay faults when assessing tsunami hazard.
    Description: Key Points: Multiple splay faults can be activated during a single earthquake by megathrust slip and dynamic stress transfer due to trapped waves. Splay fault activation is facilitated by their favorable orientation with respect to the local stress field and their closeness to failure. Long‐term geodynamic stresses and fault geometries affect dynamic splay fault rupture and the subsequent tsunami.
    Description: Volkswagen Foundation (VolkswagenStiftung) http://dx.doi.org/10.13039/501100001663
    Description: Royal Society (The Royal Society) http://dx.doi.org/10.13039/501100000288
    Description: EC | H2020 | H2020 Priority Excellent Science | H2020 European Research Council (ERC) http://dx.doi.org/10.13039/100010663
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Description: National Science Foundation (NSF) http://dx.doi.org/10.13039/100000001
    Description: https://github.com/TUM-I5/SWE
    Description: https://doi.org/10.5281/zenodo.6969455
    Keywords: ddc:551 ; earthquake ; tsunami ; subduction zone ; dynamic rupture ; splay fault ; numerical modeling
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 28
    facet.materialart.
    Unknown
    The Interconnected Magmatic Plumbing System of the Natron Rift (2022)
    Details
    Publication Date: 2023-01-20
    Description: Understanding the magmatic plumbing system of rift volcanoes is essential when examining the interplay between magmatic and tectonic forces. Recent seismicity, volcanic activity, magma emplacement, and volatile release make the Natron basin the ideal location to study these processes in the East African Rift System. Here, we present the first high‐resolution tomographic imaging of Oldoinyo Lengai volcano and surrounding volcanic systems using attenuation mapping. High scattering and absorption features reveal fluid‐filled fracture networks below regions of magmatic volatile release at the surface and a close spatial association between carbonatite volcanism and deeply penetrating, fluid‐filled faults. High‐absorption features appear sensitive to fluids and thermal gradients, revealing a central sill complex and connected plumbing system down to the mid‐crust, which links volcanoes and rift segments across the developing magmatic rift.
    Description: Plain Language Summary: The interplay between magmatic and tectonic forces during rifting is still debated. While they are a key component of rift development, the complex structures of rifts and melt storage systems scatter and absorb seismic waves passing through them: in turn, this deteriorates the quality of the subsurface images we obtain from them. In this study, we use the loss of energy suffered by seismic waves to image the Natron basin, which hosts extinct volcanoes and the only active natrocarbonatite volcano on Earth, Oldoinyo Lengai. The results identify areas of melt storage and fracture networks that feed volatiles and melt to this volcano. Results suggest that carbonatite melts may ascend through the crust efficiently along deep‐seated faults systems, while silicate melts in the region may be primarily sourced from a separate melt reservoir. This reservoir, which is elongate and oriented oblique to the general trend of the rift, may act as a magmatic transfer zone between two rift segments.
    Description: Key Points: First fine‐scale 3D images reveal an interconnected rift plumbing system using scattering and absorption mapping. High scattering and absorption mark fluid‐filled faults that degas magmatic fluids and act as potential conduits for carbonatite melts. A high absorption melt reservoir feeds eruptions at Oldoinyo Lengai and dike intrusions and acts as a transfer zone between rift segments.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: National Science Foundation http://dx.doi.org/10.13039/100000001
    Description: Terrestrial Magmatic Systems
    Description: https://github.com/LucaDeSiena/MuRAT
    Description: https://doi.org/10.14470/4W7564850022
    Description: http://doi.org/10.6084/m9.figshare.20101232
    Keywords: ddc:551 ; rift plumbing system ; attenuation imaging ; magma‐fault interactions ; Oldoinyo Lengai ; Natron Basin
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 29
    facet.materialart.
    Unknown
    Seamless Integration of the Coastal Ocean in Global Marine Carbon Cycle Modeling (2022)
    Details
    Publication Date: 2023-01-20
    Description: We present the first global ocean‐biogeochemistry model that uses a telescoping high resolution for an improved representation of coastal carbon dynamics: ICON‐Coast. Based on the unstructured triangular grid topology of the model, we globally apply a grid refinement in the land‐ocean transition zone to better resolve the complex circulation of shallow shelves and marginal seas as well as ocean‐shelf exchange. Moreover, we incorporate tidal currents including bottom drag effects, and extend the parameterizations of the model's biogeochemistry component to account explicitly for key shelf‐specific carbon transformation processes. These comprise sediment resuspension, temperature‐dependent remineralization in the water column and sediment, riverine matter fluxes from land including terrestrial organic carbon, and variable sinking speed of aggregated particulate matter. The combination of regional grid refinement and enhanced process representation enables for the first time a seamless incorporation of the global coastal ocean in model‐based Earth system research. In particular, ICON‐Coast encompasses all coastal areas around the globe within a single, consistent ocean‐biogeochemistry model, thus naturally accounting for two‐way coupling of ocean‐shelf feedback mechanisms at the global scale. The high quality of the model results as well as the efficiency in computational cost and storage requirements proves this strategy a pioneering approach for global high‐resolution modeling. We conclude that ICON‐Coast represents a new tool to deepen our mechanistic understanding of the role of the land‐ocean transition zone in the global carbon cycle, and to narrow related uncertainties in global future projections.
    Description: Plain Language Summary: The coastal ocean is an area hardly taken into account by current climate change assessment activities. Yet, its capacity in carbon dioxide (CO2) uptake and storage is crucial to be included in a science‐based development of sustainable climate change mitigation and adaptation strategies. Earth system models are powerful tools to investigate the marine carbon cycle of the open ocean. The coastal ocean, however, is poorly represented in global models to date, because of missing key processes controlling coastal carbon dynamics and too coarse spatial resolutions to adequately simulate coastal circulation features. Here, we introduce the first global ocean‐biogeochemistry model with a dedicated representation of the coastal ocean and associated marine carbon dynamics: ICON‐Coast. In this model, we globally apply a higher resolution in the coastal ocean and extend the accounted physical and biogeochemical processes. This approach enables for the first time a consistent, seamless incorporation of the global coastal ocean in model‐based Earth system research. In particular, ICON‐Coast represents a new tool to deepen our understanding about the role of the land‐ocean transition zone in the global climate system, and to narrow related uncertainties in possible and plausible climate futures.
    Description: Key Points: We introduce the first global ocean‐biogeochemistry model with a dedicated representation of coastal carbon dynamics. We globally apply a grid refinement in the coastal ocean to better resolve regional circulation features, including ocean‐shelf exchange. We explicitly incorporate key physical and biogeochemical processes controlling coastal carbon dynamics.
    Description: German Research Foundation, Excellence Strategy EXC 2037 (CLICCS)
    Description: European Union, Horizon2020 Research and Innovation Program (ESM2025)
    Description: German Federal Ministry of Education
    Description: https://doi.org/10.5281/zenodo.6630352
    Keywords: ddc:551 ; coastal ocean ; global modeling ; marine carbon cycle ; variable‐resolution grid ; ocean‐biogiochemistry ; high‐resolution modeling
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 30
    facet.materialart.
    Unknown
    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
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 31
    facet.materialart.
    Unknown
    Spatial and temporal dynamics of water isotopes in the riverine‐marine mixing zone along the German Baltic Sea coast (2022)
    John Wiley & Sons, Inc. | Hoboken, USA
    Details
    Publication Date: 2023-01-27
    Description: River estuaries are characterized by mixing processes between freshwater discharge and marine water masses. Since the first are depleted in heavier stable isotopes compared with the marine realm, estuaries often show a linear correlation between salinity and water stable isotopes (δ18O and δ2H values). In this study, we evaluated spatial and seasonal isotope dynamics along three estuarine lagoon transects, located at the northern German Baltic Sea coast. The data show strong seasonality of isotope values, even at locations located furthest from the river mouths. They further reveal a positive and linear salinity‐isotope correlation in spring, but ‐in two of the three studied transects‐ hyperbolic and partially reverse correlations in summers. We conclude that additional hydrological processes partially overprint the two‐phase mixing correlation during summers: aside from the isotope seasonality of the riverine inflows, the shallow inner lagoons in the studied estuaries are influenced by evaporation processes. In contrast the estuarine outflow regions are under impact of significant salinity and isotope fluctuations of the Baltic Sea. Deciphering those processes is crucial for the understanding of water isotope and salinity dynamics. This is also of relevance in context of ecological studies, for example, when interpreting oxygen and hydrogen isotope data in aquatic organisms that depend on ambient estuarine waters.
    Description: Spatial and seasonal water isotope dynamics were evaluated along three estuarine lagoon transects at the German Baltic Sea coast. Data reveal a positive and linear salinity‐isotope correlation in spring, but partially reverse correlations in summers. The results show that evaporation processes in the shallow inner lagoons and varying Baltic Sea influence in the outer estuary regions are able to overprint the two‐phase mixing correlation between riverine and marine water masses.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.1594/PANGAEA.937990
    Keywords: ddc:551 ; δ2H ; δ18O ; Baltic Sea ; bodden ; Rügen ; salinity ; Schlei ; Zingst
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 32
    facet.materialart.
    Unknown
    Early Eocene magnetostratigraphy and tectonic evolution of the Xining Basin, NE Tibet (2022)
    Meijer, Niels ; Dupont‐Nivet, Guillaume ; Licht, Alexis ; [et al.]
    Details
    Publication Date: 2023-06-14
    Description: The Cenozoic strata of the Xining Basin, NE Tibet, have provided crucial records for understanding the tectonic and palaeo‐environmental evolution of the region. Yet, the age of the lower part of the sedimentary stratigraphy and, consequently, the early tectonic evolution of the basin remain debated. Here, we present the litho‐ and magnetostratigraphy of various early Eocene sections throughout the Xining Basin independently constrained by the U–Pb radiometric age of a carbonate bed. Our study extends the dated stratigraphy down to 53.0 Ma (C24n.1r) and reveals highly variable accumulation rates during the early Eocene ranging from 0.5 to 8 cm/ka. This is in stark contrast to the low but stable accumulation rates (2–3 cm/ka) observed throughout the overlying Palaeogene and Neogene strata. Such a pattern of basin infill is not characteristic of flexural subsidence as previously proposed, but rather supports an extensional origin of the Xining Basin with multiple depocentres, which subsequently coalesced into a more stable and slowly subsiding basin. Whether this extension was related to the far‐field effects of the subducting Pacific Plate or the India–Asia collision remains to be confirmed by future studies.
    Description: European Research Council http://dx.doi.org/10.13039/501100000781
    Description: Hessisches Ministerium für Wissenschaft und Kunst http://dx.doi.org/10.13039/501100003495
    Keywords: ddc:551 ; Eocene ; geochronology ; northeast Tibet ; palaeomagnetism ; stratigraphy ; Xining Basin
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 33
    facet.materialart.
    Unknown
    Particle‐Phase Uptake and Chemistry of Highly Oxygenated Organic Molecules (HOMs) From α‐Pinene OH Oxidation (2022)
    Poulain, L. ; Tilgner, A. ; Brüggemann, M. ; [et al.]
    Details
    Publication Date: 2023-06-16
    Description: Secondary organic aerosol (SOA) forms a major part of the tropospheric submicron particle mass. Still, the exact formation mechanisms of SOA have remained elusive. It is now admitted that highly oxygenated organic molecules (HOMs) can contribute to a large fraction of SOA formation. In this study, we performed a set of chamber experiments to investigate the SOA formation, and the HOMs uptake and processing directly formed by OH‐radical initiated oxidation of α‐pinene under two different aerosol seed conditions. Numerous HOM compounds were identified using advanced online and offline analytical techniques, and grouped into four classes according to their different uptake behaviors. For the first time, individual HOMs uptake coefficients ranging from 1.1 × 10−2 to 1.5 × 10−1 were experimentally determined and analyzed using a resistance model which considers uptake limitations by individual gas‐ and/or particle‐phase processes. This study demonstrates that the uptake coefficients of HOMs strongly depend on their molar mass and their respective O/C ratio. Results show that aerosol seed composition and phase state affect the initial uptake of HOMs. Furthermore, the study demonstrates that the acidity and/or different seed phase‐state can significantly enhance the subsequent uptake through occurring acidity‐driven reactions reflected in a reactive behavior, particularly under (NH4)HSO4 seed conditions, promoting up to 3 times a higher SOA mass formation including the formation of highly oxidized organosulfates (HOOS). Overall, the present study implies that HOMs and their subsequent chemical processing can play an important role in both the early growth of newly formed particles and SOA formation when particle acidity is high.
    Description: Plain Language Summary: Tropospheric organic aerosol (OA) compounds represent a large part of submicron particulate matter. A big fraction of OA is formed from oxidation of emitted gaseous volatile organic compounds such as α‐pinene. Oxidation products are less‐volatile compounds that tend to condense on aerosol particles. Recently identified “highly oxygenated organic molecules” (HOMs) are formed by gas‐phase autoxidation processes and exhibit very low vapor pressures. Therefore, HOMs are expected to efficiently contribute to secondary organic aerosol (SOA). However, up to now, SOA formation potential of HOMs is still not well described because of lacking experimental investigations and analysis. Consequently, this study aims to investigate the mentioned HOMs partitioning and subsequent SOA formation from the OH‐radical initiated oxidation of α‐pinene under both Na2SO4 and (NH4)HSO4 aerosol seed conditions through complex chamber experiments. For the first time, individual HOMs uptake coefficients were determined experimentally. Further investigations demonstrated that the uptake coefficients of HOMs strongly depend on their molar mass, as well as on their respective O/C ratio. Finally, the results show that aerosol acidity and/or phase state significantly enhances the HOMs uptake and promotes up to three times higher SOA mass formation under (NH4)HSO4 seed conditions compared to that under neutral seed conditions.
    Description: Key Points: Uptake coefficients of numerous highly oxygenated organic molecules (HOMs) were experimentally determined for the first time. HOMs uptake and secondary organic aerosol formation were significantly enhanced by acidic (NH4)HSO4 seed. Highly oxidized organosulfates formation were observed under acidic (NH4)HSO4 seed conditions.
    Description: European Commission http://dx.doi.org/10.13039/501100000780
    Description: National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809
    Description: https://doi.org/10.25326/FJNF-7224
    Description: https://doi.org/10.25326/KC8N-DY53
    Keywords: ddc:551 ; aerosol study ; highly oxygenated organic molecules
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 34
    facet.materialart.
    Unknown
    Rinikerfeld Palaeolake (Northern Switzerland) – a sedimentary archive of landscape and climate change during the penultimate glacial cycle (2022)
    Gegg, Lukas ; Anselmetti, Flavio S. ; Deplazes, Gaudenz ; [et al.]
    Details
    Publication Date: 2024-01-19
    Description: While timing and ice extent of the last glacial maximum are generally well known, the courses of earlier glaciations have remained poorly constrained, with one of the main reasons being the scarcity of sedimentary archives. This study introduces a new palaeolake record from a Mid‐Pleistocene glaciofluvial channel system in the Lower Aare Valley (Northern Switzerland). The record of Rinikerfeld comprises a 〉40 m long succession of Quaternary deposits that are targeted by multi‐method sedimentological analysis. Sedimentary facies together with geochemical and geotechnical parameters, pollen content, as well as luminescence ages allow the reconstruction of the establishment, evolution and infilling of the early Marine Isotope Stage 6‐aged Rinikerfeld Palaeolake. A drastic change in lake sediment composition and structure indicates cessation of the initial glacially derived input, which is explained by landscape modification and drainage rerouting during the Penultimate (Beringen) Glaciation. Geochemical and palynological data further reveal cold, initially periglacial but slightly ameliorating, climate conditions, while the lake was progressively filled up by local runoff, before being buried by periglacial colluvial diamicts, and potentially overridden by ice. It is therefore concluded that the onset of the Beringen Glaciation was an environmentally as well as geomorphically dynamic time period in the Northern Alpine Foreland.
    Description: NATIONALE GENOSSENSCHAFT FÜR DIE LAGERUNG RADIOAKTIVER ABFÄLLE
    Keywords: ddc:551 ; Northern Alpine foreland ; palaeolake ; penultimate glaciation ; periglacial lake ; sedimentary archive
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 35
    facet.materialart.
    Unknown
    Riparian Microtopography Affects Event‐Driven Stream DOC Concentrations and DOM Quality in a Forested Headwater Catchment (2022)
    Blaurock, Katharina ; Garthen, Phil ; da Silva, Maria P. ; [et al.]
    Details
    Publication Date: 2024-01-19
    Description: The transport of dissolved organic carbon (DOC) from the soils to inland waters plays an important role in the global carbon cycle. Widespread increases in DOC concentrations have been observed in surface waters over the last few decades, affecting carbon balances, ecosystem functioning and drinking water treatment. However, the primary hydrological controls on DOC mobilization are still uncertain. The aim of this study was to investigate the role of microtopography in the riparian zone for DOC export and DOM quality. DOC concentration and DOM quality in the shallow groundwater of a riparian zone and in streamflow in a forested headwater catchment was investigated using fluorescence and absorbance characteristics. We found higher DOC concentrations with a higher aromaticity in the microtopographical depressions, which were influenced by highly dynamic shallow groundwater levels, than in the flat forest soil. As a result of the frequent wet‐dry cycles in the upper soil layers, aromatic DOC accumulated in the shallow groundwater within and below the microtopographical depressions. Rising groundwater levels during precipitation events led to the connection of the microtopographical depressions to the stream, resulting in a change toward more aromatic DOC in the stream. Increasing stream DOC concentrations were accompanied by increasing concentrations of iron and aluminum, suggesting the coupled release of these metals with DOC from the riparian zone. Our results highlight the importance of the interplay between microtopography and groundwater level dynamics in the riparian zone for DOC export from headwater catchments.
    Description: Plain Language Summary: Dissolved organic carbon (DOC) is the result of the continuous breakdown of organic material, such as leaves. It accumulates in the soil and is transported to streams mainly during precipitation events. In this study, we analyzed the shallow groundwater of two differing sites in the Bavarian Forest National Park. Both sites were located close to the stream, but one was characterized by typical forest soil and one by small ponds, which were occasionally filled with water. The site with ponds showed much higher DOC concentrations and the DOC was chemically different from the other site. During a precipitation event, we observed a shift in chemical composition of stream water parameters toward the chemical characteristics found at the site with ponds. Therefore, we conclude that the ponds contribute substantially to DOC mobilization, once they fill with water and get connected to the stream.
    Description: Key Points: This study found small‐scale differences in dissolved organic carbon (DOC) concentrations and dissolved organic matter (DOM) quality in the riparian zone. Microtopographical depressions were characterized by high DOC concentrations and aromatic DOC. In‐stream DOC concentrations and DOM quality during a precipitation event resembled shallow groundwater below microtopographical depressions.
    Description: Stifterverband http://dx.doi.org/10.13039/501100008384
    Description: Helmholtz Association http://dx.doi.org/10.13039/501100009318
    Description: Rudolf and Helene Glaser Foundation
    Description: European Regional Development Funds
    Description: https://doi.org/10.6084/m9.figshare.19086455
    Description: https://doi.org/10.48758/ufz.12908
    Keywords: ddc:551 ; dissolved organic carbon ; hydrology ; microtopography ; DOM quality
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 36
    facet.materialart.
    Unknown
    Fluvial and permafrost history of the lower Lena River, north‐eastern Siberia, over late Quaternary time (2022)
    Schwamborn, Georg ; Schirrmeister, Lutz ; Mohammadi, Ali ; [et al.]
    Details
    Publication Date: 2023-11-18
    Description: Arctic warming and permafrost thaw visibly expose changes in the landscape of the Lena River delta, the largest Arctic delta. Determining the past and modern river regime of thick deltaic deposits shaping the Lena River mouth in north‐eastern Siberia is critical for understanding the history of delta formation and carbon sequestration. Using a 65 m long sediment core from the delta apex a set of sedimentological techniques is applied to aid in reconstructing the Lena River history. The analysis includes: (i) grain‐size measurements and the determination of the bedload composition; (ii) X‐ray fluorescence, X‐ray diffractometry, and magnetic susceptibility measurements and heavy mineral analysis for tracking mineral change; (iii) pH, electrical conductivity, ionic concentrations, and the δ〈sub〉18〈/sub〉O and δD stable isotope composition from ground ice for reconstructing permafrost formation. In addition; (iv) total and dissolved organic carbon is assessed. Chronology is based on; (vi) radiocarbon dating of organic material (accelerator mass spectrometry and conventional) and is complemented by two infrared – optically stimulated luminescence dates. The record stretches back approximately to Marine Isotope Stage 7. It holds periods from traction, over saltation, to suspension load sedimentation. Minerogenic signals do not indicate provenance change over time. They rather reflect the change from high energy to a lower energy regime after Last Glacial Maximum time parallel to the fining‐up grain‐size trend. A prominent minimum in the ground ice stable isotope record at early Holocene highlights that a river arm migration and an associated refreeze of the underlying river talik has altered the isotopic composition at that time. Fluvial re‐routing might be explained by internal dynamics in the Lena River lowland or due to a tectonic movement, since the study area is placed in a zone of seismic activity. At the southern Laptev Sea margin, onshore continental compressional patterns are bordering offshore extensional normal faults.
    Description: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research
    Description: https://doi.org/10.1594/PANGAEA.945355
    Keywords: ddc:551 ; Lena River ; north‐eastern Siberia ; palaeoenvironment ; permafrost ; Quaternary
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 37
    facet.materialart.
    Unknown
    Quantifying Ice‐Sheet Derived Lead (Pb) Fluxes to the Ocean; A Case Study at Nioghalvfjerdsbræ (2022)
    Details
    Publication Date: 2023-11-17
    Description: Concentrations of the toxic element lead (Pb) are elevated in seawater due to historical emissions. While anthropogenic atmospheric emissions are the dominant source of dissolved Pb (dPb) to the Atlantic Ocean, evidence is emerging of a natural source associated with subglacial discharge into the ocean but this has yet to be constrained around Greenland. Here, we show subglacial discharge from the cavity underneath Nioghalvfjerdsbræ floating ice tongue, is a previously unrecognized source of dPb to the NE Greenland Shelf. Contrasting cavity‐inflowing and cavity‐outflowing waters, we constrain the associated net‐dPb flux as 2.2 ± 1.4 Mg·yr−1, of which ∼90% originates from dissolution of glacial bedrock and cavity sediments. We propose that the retreat of the floating ice tongue, the ongoing retreat of many glaciers on Greenland, associated shifts in sediment dynamics, and enhanced meltwater discharges into shelf waters may result in pronounced changes, possibly increases, in net‐dPb fluxes to coastal waters.
    Description: Plain Language Summary: Lead (Pb) is a toxic element. Hundreds of thousands of tons have historically been emitted into the atmosphere through use of leaded gasoline, ore‐smelting and coal‐combustion which led to large‐scale deposition of Pb into the ocean and onto the Greenland Ice Sheet. Since the phase‐out of leaded gasoline, concentrations of dissolved Pb in the surface ocean have declined, increasing the relative importance of other, natural sources of Pb to the marine environment. In 2016, we conducted a survey near Nioghalvfjerdsbræ, one of Greenland’s largest marine‐terminating glaciers, to investigate if Greenland Ice Sheet discharge is a source of Pb to the Northeast Greenland Shelf. We observed elevated dissolved Pb concentrations at intermediate depths within a ⁓60 km radius downstream of the Nioghalvfjerdsbræ terminus. The Pb enrichment originates from underneath the glacier’s floating ice tongue. Lead sources underneath Nioghalvfjerdsbræ likely include Pb from eroded bedrock and exchange with fjord sediments. Our calculations suggest that Nioghalvfjerdsbræ dissolved Pb discharge is comparable to that from small Arctic rivers. Given the widespread occurance of Pb‐rich minerals across Greenland, observed increases in meltwater discharge and the retreat of marine‐terminating glaciers could increase dPb supply to Greenlandic shelf regions.
    Description: Key Points: Helium and neon show strong evidence for a subglacial source of Pb discharging onto the NE Greenland Shelf. Contrasting inflowing and outflowing waters beneath the floating ice tongue of Nioghalvfjerdsbræ shows a 2‐3‐fold dPb enrichment. The dissolved Pb flux from Nioghalvfjerdsbræ (2.2 ± 1.4 Mg·yr−1) is comparable to small Arctic rivers, with ∼90% of a sedimentary origin.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Kuwait Institute for Scientific Research http://dx.doi.org/10.13039/501100005074
    Description: Swiss Polar Foundation
    Description: https://doi.pangaea.de/10.1594/PANGAEA.871028
    Description: https://doi.pangaea.de/10.1594/PANGAEA.871030
    Description: https://doi.pangaea.de/10.1594/PANGAEA.879197
    Description: https://doi.pangaea.de/10.1594/PANGAEA.905347
    Description: https://doi.pangaea.de/10.1594/PANGAEA.933431
    Description: https://doi.pangaea.de/10.1594/PANGAEA.931336
    Description: https://doi.org/10.5194/essd-8-543-2016
    Keywords: ddc:551 ; Greenland ice sheet ; Arctic ; marine‐terminating glacier ; Nioghalvfjerdsbrae ; lead fluxes ; GEOTRACES
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 38
    facet.materialart.
    Unknown
    Experimental Evaluation of Fluid Connectivity in Two‐Phase Flow in Porous Media During Drainage (2022)
    Details
    Publication Date: 2024-03-25
    Description: This study aims to experimentally investigate the possibility of combining two extended continuum theories for two‐phase flow. One of these theories considers interfacial area as a separate state variable, and the other explicitly discriminates between connected and disconnected phases. This combination enhances our potential to effectively model the apparent hysteresis, which generally dominates two‐phase flow. Using optical microscopy, we perform microfluidic experiments in quasi‐2D artificial porous media for various cyclic displacement processes and boundary conditions. Specifically for a number of sequential drainage processes, with detailed image (post‐)processing, pore‐scale parameters such as the interfacial area between the phases (wetting, non‐wetting, and solid), and local capillary pressure, as well as macroscopic parameters like saturation, are estimated. We show that discriminating between connected and disconnected clusters and the concept of the interfacial area as a separate state variable can be an appropriate way of modeling hysteresis in a two‐phase flow scheme. The drainage datasets of capillary pressure, saturation, and specific interfacial area, are plotted as a surface, given by f (P〈sup〉c〈/sup〉, s〈sup〉w〈/sup〉, a〈sup〉wn〈/sup〉) = 0. These surfaces accommodate all data points within a reasonable experimental error, irrespective of the boundary conditions, as long as the corresponding liquid is connected to its inlet. However, this concept also shows signs of reduced efficiency as a modeling approach in datasets gathered through combining experiments with higher volumetric fluxes. We attribute this observation to the effect of the porous medium geometry on the phase distribution. This yields further elaboration, in which this speculation is thoroughly studied and analyzed.
    Description: Key Points: A large number of two‐phase displacement microfluidic experiments under different boundary conditions are performed. A code has been developed in order to spatially and temporally resolve the experiments with high accuracy. Including both connectivity and interfacial area as state variables in two‐phase flow continuum theories improves modeling hysteresis.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Stuttgart Center for Simulation Science, Universität Stuttgart http://dx.doi.org/10.13039/501100022175
    Description: https://doi.org/10.18419/darus-2250
    Keywords: ddc:550.78 ; microfluidic experiments ; optical microscopy ; two‐phase flow in porous medium ; image processing ; extended theory of porous medium ; phase connectivity
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 39
    facet.materialart.
    Unknown
    Imaging of Small‐Scale Heterogeneity and Absorption Using Adjoint Envelope Tomography: Results From Laboratory Experiments (2022)
    Details
    Publication Date: 2024-04-03
    Description: To complement the information provided by deterministic seismic imaging at length scales above a certain resolution limit we present the first application of adjoint envelope tomography (AET) to experimental data. AET uses the full envelopes of seismic records including scattered coda waves to obtain information about the distribution of absorption and small‐scale heterogeneity which provide complementary information about the investigated medium. Being below the resolution limit this small‐scale structure cannot be resolved by conventional tomography but still affects wave propagation by attenuating ballistic waves and generating scattered waves. Using ultrasound data from embedded sensors in a meter‐sized concrete specimen we image the distribution of absorption and heterogeneity expressed by the intrinsic quality factor Q〈sup〉−1〈/sup〉 and the fluctuation strength ɛ that characterizes the strength of the heterogeneity. The forward problem is solved by modeling the 2‐D multiple nonisotropic scattering in an acoustic medium with spatially variable heterogeneity and attenuation using the Monte‐Carlo method. Gradients for the model updates are obtained by convolution with the back‐propagated envelope misfit using the adjoint formalism in analogy to full waveform inversion. We use a late coda time window to invert for absorption and an earlier time window to infer the distribution of heterogeneity. The results successfully locate an area of salt concrete with increased scattering and concentric anomalies of intrinsic attenuation. The resolution test shows that the recovered anomalies constitute reasonable representations of internal structure of the specimen.
    Description: Plain Language Summary; No matter how small the structures are that a seismic imaging method is able to resolve, there is structure with smaller length scale. On the one hand this small‐scale structure causes unwanted signals for conventional imaging approaches. But on the other hand it provides complementary information about the investigated medium. To turn this to our advantage we, for the first time, apply a new imaging method that uses the waves which are caused by the small‐scale structure. Using data of an experiment in a concrete block we demonstrate that we can identify areas of anomalous small‐scale structure. The results may help in the future to locate minute perturbations in the medium as they occur in the advent of volcanic eruptions or after earthquakes and to obtain new information about the geologic history of subsurface materials. The approach can be transferred to investigate man‐made materials and structures, such as deteriorating concrete constructions.
    Description: Key Points: Adjoint envelope tomography is for the first time applied to image the scattering and absorption structure with the real data. The iterative inversion uses envelopes of ultrasound signals from embedded transducers in a meter‐sized reinforced concrete specimen. We successfully image the distribution of statistical parameters characterizing the small‐scale heterogeneity and attenuation.
    Description: China Scholarship Council http://dx.doi.org/10.13039/501100004543
    Description: https://doi.org/10.5281/zenodo.7152278
    Keywords: ddc:550.78 ; seismic tomography ; adjoint method ; small‐scale heterogeneity ; attenuation ; ultrasonic experiment ; reinforced concrete
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 40
    facet.materialart.
    Unknown
    Do Emergent Constraints on Carbon Cycle Feedbacks Hold in CMIP6? (2022)
    Details
    Publication Date: 2024-02-21
    Description: Emergent constraints on carbon cycle feedbacks in response to warming and increasing atmospheric CO〈sub〉2 〈/sub〉 concentration have previously been identified in Earth system models participating in the Coupled Model Intercomparison Project (CMIP) Phase 5. Here, we examine whether two of these emergent constraints also hold for CMIP6. The spread of the sensitivity of tropical land carbon uptake to tropical warming in an idealized simulation with a 1% per year increase of atmospheric CO〈sub〉2 〈/sub〉 shows only a slight decrease in CMIP6 (−52 ± 35 GtC/K) compared to CMIP5 (−49 ± 40 GtC/K). For both model generations, the observed interannual variability in the growth rate of atmospheric CO〈sub〉2 〈/sub〉 yields a consistent emergent constraint on the sensitivity of tropical land carbon uptake with a constrained range of −37 ± 14 GtC/K for the combined ensemble (i.e., a reduction of ∼30% in the best estimate and 60% in the uncertainty range relative to the multimodel mean of the combined ensemble). A further emergent constraint is based on a relationship between CO〈sub〉2 〈/sub〉 fertilization and the historical increase in the CO〈sub〉2 〈/sub〉 seasonal cycle amplitude in high latitudes. However, this emergent constraint is not evident in CMIP6. This is in part because the historical increase in the amplitude of the CO〈sub〉2 〈/sub〉 seasonal cycle is more accurately simulated in CMIP6, such that the models are all now close to the observational constraint.
    Description: Plain Language Summary: The statistical model of so‐called emergent constraints help to better understand the sensitivity of Earth system processes in a changing climate. Here, we analyze the robustness of two previously found emergent constraints on carbon cycle feedbacks, using models from the Coupled Model Intercomparison Project (CMIP) of Phases 5 and 6. First the decrease of carbon storage in the tropics due to increasing near‐surface air temperatures, which is found to be robust on the choise of model ensemble. Giving a constraint estimate of −52 ± 35 GtC/K for CMIP6 models, being within the range of uncertainty for the previously estimated result for CMIP5. Second, the increase of carbon storage in high latitudes due to CO〈sub〉2 〈/sub〉 fertilization effect, which is found to be not evident among CMIP6 models. This is in part because the historical increase in the amplitude of the CO〈sub〉2 〈/sub〉 seasonal cycle is more accurately simulated in CMIP6, such that the models are all now close to the observational constraint.
    Description: Key Points: An emergent constraint on the sensitivity of tropical land carbon to global warming, originally derived from Coupled Model Intercomparison Project Phase 5 (CMIP5), also holds for CMIP6. The combined CMIP5 + CMIP6 ensemble gives an emergent constraint on the sensitivity of tropical land carbon to global warming of −37 ± 14 GtC/K. An emergent constraint on the fertilization feedback due to rising CO〈sub〉2 〈/sub〉 levels, previously derived, is not evident in CMIP6.
    Description: Horizon 2020 Framework Programme http://dx.doi.org/10.13039/100010661
    Description: ERC
    Description: https://doi.org/10.5281/zenodo.6900341
    Description: https://doi.org/10.5281/zenodo.3387139
    Description: https://github.com/ESMValGroup
    Description: https://docs.esmvaltool.org/
    Keywords: ddc:551 ; carbon cycle ; emergent constraint ; CMIP5 ; CMIP6 ; fertilization effect ; temperature warming
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 41
    facet.materialart.
    Unknown
    Particulate Organic Matter Mobilization and Transformation Along a Himalayan River Revealed by ESI‐FT‐ICR‐MS (2022)
    Details
    Publication Date: 2024-02-09
    Description: Tracing pathways and transformations of particulate organic carbon from landscape sources to oceanic sinks is commonly done using the isotopic composition or biomarker content of particulate organic matter (POM). However, similarity of source characteristics and complex mixing in rivers often preclude a robust deconvolution of individual contributions. Moreover, these approaches are limited in detecting organic matter transformations. This impedes understanding of carbon cycling. Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT‐ICR‐MS) can simultaneously identify many molecular formulas from mixtures of organic matter, and provide direct information on its compositional variability. Here, we investigate how FT‐ICR‐MS can give insight into POM dynamics on a landscape scale, focusing on the trans‐Himalayan Kali Gandaki River, Nepal. Using molecular information, we identify source tracers in the solvent extractable lipid fraction of riverine POM, finding up to 102 indicative molecular formulas for individual sources. Further, we assess molecular transformations of the lipid fraction of POM during its transfer from litter into topsoil, and onwards into the river. A large number of shared mass formulas and a well‐preserved isoprenoidal patterns suggest efficient incorporation of litter into topsoil. In contrast, we observe a selective loss of mass formulas and a preferential export of formulas with low double bond equivalents and a low nominal oxidation state of carbon after organic matter entrainment in the river. Our results demonstrate the potential of FT‐ICR‐MS for source‐to‐sink studies, allowing detailed organic matter source characterization and discrimination, and tracking of molecular transformations along organic matter pathways spanning different spatial and temporal scales.
    Description: Plain Language Summary: The transfer of organic matter (OM) by rivers from landscape sources into the ocean followed by its burial in marine sediments is an important carbon sink. Therefore, OM is often traced along this journey using its isotopic or biomarker composition. But contributions of OM sources to river sediments can be difficult to estimate because of similar source characteristics, mixing of many sources and changes of the molecular composition along the way. Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT‐ICR‐MS) is a novel method able to identify many molecular formulas from OM mixtures at once providing direct information about their molecular composition. Here, we investigate how FT‐ICR‐MS contributes to understanding the transport and transformation of particulate OM focusing on a Himalayan river in Nepal. We use the molecular information to identify tracers for individual OM sources in the landscape. We then assess molecular transformations during the transfer of litter into topsoil, and onwards into the river. Our data suggest efficient incorporation of litter into topsoil, but we observe a selective loss of molecular formulas upon entrainment of sources into the river. Our results reveal that FT‐ICR‐MS is useful for detailed source characterization and tracking of molecular transformations along OM pathways.
    Description: Key Points: Organic matter sourcing and transformations in a Himalayan river studied by FT‐ICR‐MS measurements of solvent extractable lipids. Identification of up to 102 indicator mass formulas for different organic matter sources in the landscape using indicator species analysis. Mass formulas preserved during incorporation of litter into topsoil but selectively lost during entrainment of sources into the river.
    Description: Helmholtz Impuls und Vernetzungsfond
    Description: GFZ expedition funding
    Description: http://doi.org/10.5880/GFZ.4.6.2022.002
    Keywords: ddc:551 ; particulate organic carbon ; solvent extractable lipids ; FT‐ICR‐MS ; Himalaya ; carbon cycling ; indicator species analysis
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 42
    facet.materialart.
    Unknown
    The Toba supervolcano eruption caused severe tropical stratospheric ozone depletion (2021)
    Nature Publishing Group UK
    Details
    Publication Date: 2023-09-12
    Description: Supervolcano eruptions have occurred throughout Earth’s history and have major environmental impacts. These impacts are mostly associated with the attenuation of visible sunlight by stratospheric sulfate aerosols, which causes cooling and deceleration of the water cycle. Supereruptions have been assumed to cause so-called volcanic winters that act as primary evolutionary factors through ecosystem disruption and famine, however, winter conditions alone may not be sufficient to cause such disruption. Here we use Earth system model simulations to show that stratospheric sulfur emissions from the Toba supereruption 74,000 years ago caused severe stratospheric ozone loss through a radiation attenuation mechanism that only moderately depends on the emission magnitude. The Toba plume strongly inhibited oxygen photolysis, suppressing ozone formation in the tropics, where exceptionally depleted ozone conditions persisted for over a year. This effect, when combined with volcanic winter in the extra-tropics, can account for the impacts of supereruptions on ecosystems and humanity.
    Description: Stratospheric sulfur emissions from the Toba supereruption about 74,000 years ago suppressed ozone formation which caused severe tropical ozone layer depletion and enhanced solar ultraviolet radiation stress, according to Earth system model simulations.
    Description: King Abdullah University of Science and Technology (KAUST) https://doi.org/10.13039/501100004052
    Description: http://hdl.handle.net/10754/667404
    Description: https://github.com/SeregaOsipov/NASA-GISS-ModelE/releases/tag/toba_o3
    Description: https://simplex.giss.nasa.gov/snapshots/
    Keywords: ddc:551 ; Atmospheric chemistry ; Natural hazards ; Palaeoclimate ; Volcanology
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 43
    facet.materialart.
    Unknown
    Plane strain shear strength of unsaturated fiber-reinforced fine-grained soils (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-09-14
    Description: Discrete randomly distributed fibers are commonly used to improve the engineering characteristics of the soil and thus soil properties such as shear strength, compressibility, density, and hydraulic conductivity. Most studies have so far focused on describing the behavior of soils containing randomly distributed fibers under dried or saturated conditions. However, the water table may seasonally fluctuate, thus generating unsaturated soil conditions. Therefore, a better understanding of the hydro-mechanical properties of unsaturated improved soils is of high necessity. In this research, the shear strength parameters of fine-grained soils were evaluated using the biaxial device available at Ruhr Universität Bochum. The applied device was modified to test unsaturated fine-grained soils with various degrees of saturation using axis translation and vapor equilibrium techniques. The experiments were conducted on fine soils containing 0, 0.5, and 1% fiber contents under a wide range of matric suctions. The ductile behavior was more noticeable in samples with lower suctions and higher straw contents. Furthermore, the shear strength of both unreinforced and reinforced fine-grained soils considerably increased by an increase in the suction. Finally, shear band inclination increased by the suction while decreasing by straw content.
    Description: Ruhr-Universität Bochum (1007)
    Keywords: ddc:550.78 ; Plane strain condition ; Shear strength ; Soil reinforcement ; Suction ; SWCC
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 44
    facet.materialart.
    Unknown
    Black Sea hydroclimate and coupled hydrology was strongly controlled by high-latitude glacial climate dynamics (2021)
    Nature Publishing Group UK
    Details
    Publication Date: 2023-09-14
    Description: Abstract The Black Sea experienced pronounced millennial-scale changes in temperature and rainfall during the last glacial coinciding with Dansgaard-Oeschger cycles. However, little is known regarding the amount and sources of freshwater reaching this inland basin. Here, we present detailed ostracod δ〈sup〉18〈/sup〉O data from the glacial Black Sea showing subdued Dansgaard-Oeschger cyclicity and four prominent longer-term saw-tooth shaped Bond-like cycles. We propose that the δ〈sup〉18〈/sup〉Oostracods signature primarily reflects changes in the atmospheric circulation in response to the waxing and waning Eurasian Ice Sheet. The millennial-scale ice sheet variations likely resulted not only in latitudinal migrations of atmospheric frontal systems but also in shifts of dominant moisture sources for the Black Sea. Heavier isotopic precipitation arrived from the North Atlantic-Mediterranean realm during the warmer interstadials and lighter isotopic precipitation from the Eurasian continental interior during the colder stadials. The subdued Dansgaard-Oeschger variability likely reflects an integrated precipitation signal additionally affected by the long mixing times of the large Black Sea volume up to 1,500 years as suggested from hydrologic-isotope-balance modelling.
    Description: Moisture sources to the Black Sea changed in response to atmospheric frontal displacements driven by Eurasian Ice Sheet dynamics during the last glacial period, according to analyses of ostracod oxygen and strontium isotope data from Black Sea sediments.
    Description: Deutsche Forschungsgemeinschaft (German Research Foundation) https://doi.org/10.13039/501100001659
    Description: https://doi.org/10.5281/zenodo.4545579
    Keywords: ddc:551 ; paleohydrology ; palaeoclimate ; Black Sea ; Archangelsky Ridge ; isotope geochemistry ; Dansgaard-Oeschger cycles
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 45
    facet.materialart.
    Unknown
    Hydromechanical Investigations on the Self-propping Potential of Fractures in Tight Sandstones (2021)
    Springer Vienna
    Details
    Publication Date: 2023-11-15
    Description: The hydromechanical properties of single self-propping fractures under stress are of fundamental interest for fractured-rock hydrology and a large number of geotechnical applications. This experimental study investigates fracture closure and hydraulic aperture changes of displaced tensile fractures, aligned tensile fractures, and saw-cut fractures for two types of sandstone (i.e., Flechtinger and Fontainebleau) with contrasting mechanical properties, cycling confining pressure between 5 and 30 MPa. Emphasis is placed on how surface roughness, fracture wall offset, and the mechanical properties of the contact asperities affect the self-propping potential of these fractures under normal stress. A relative fracture wall displacement can significantly increase fracture aperture and hydraulic conductivity, but the degree of increase strongly depends on the fracture surface roughness. For smooth fractures, surface roughness remains scale-independent as long as the fracture area is larger than a roll-off wavelength and thus any further displacement does not affect fracture aperture. For rough tensile fractures, these are self-affine over a larger scale so that an incremental fracture wall offset likely leads to an increase in fracture aperture. X-ray microtomography of the fractures indicates that the contact area ratio of the tensile fractures after the confining pressure cycle inversely correlates with the fracture wall offset yielding values in the range of about 3–25%, depending, first, on the respective surface roughness and, second, on the strength of the asperities in contact. Moreover, the contact asperities mainly occur isolated and tend to be preferentially oriented in the direction perpendicular to the fracture wall displacement which, in turn, may induce flow anisotropy. This, overall, implies that relatively harder sedimentary rocks have a higher self-propping potential for sustainable fluid flow through fractures in comparison to relatively soft rocks when specific conditions regarding surface roughness and fracture wall offset are met.
    Description: Bundesministerium für Wirtschaft und Energie (DE)
    Description: China Scholarship Council http://dx.doi.org/10.13039/501100004543
    Description: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Keywords: ddc:550.78 ; Self-propping fracture ; Mechanical aperture ; Hydraulic aperture ; Normal stress ; Fracture wall offset ; Surface roughness
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 46
    facet.materialart.
    Unknown
    Permeability Evolution During Shear Zone Initiation in Low-Porosity Rocks (2021)
    Springer Vienna
    Details
    Publication Date: 2023-11-15
    Description: Using an innovative experimental set-up (Punch-Through Shear test), we initiated a shear zone (microfault) in Flechtingen sandstone and Odenwald granite under in situ reservoir conditions while monitoring permeability and fracture dilation evolution. The shear zone, which has a cylindrical geometry, is produced by a self-designed piston assembly that punches down the inner part of the sample. Permeability and fracture dilation were measured for the entire duration of the experiment. After the shear zone generation, the imposed shear displacement was increased to 1.2 mm and pore pressure changes of ±5 or ±10 MPa were applied cyclically to simulate injection and production scenarios. Thin sections and image analysis tools were used to identify microstructural features of the shear zone. The geometry of the shear zone is shown to follow a self-affine scaling invariance, similar to the fracture surface roughness. The permeability evolution related to the onset of the fracture zone is different for both rocks: almost no enhancement for the Flechtingen sandstone and an increase of more than 2 orders of magnitude for the Odenwald granite. Further shear displacement resulted in a slight increase in permeability. A fault compaction is observed after shear relaxation which is associated to a permeability decrease by a factor more than 3. Permeability changes during pressure cycling are reversible when varying the effective pressure. The difference in permeability enhancement between the sandstone and the granite is related to the larger width of the shear zones.
    Description: ReSalt Project
    Description: H2020 European Research Council http://dx.doi.org/10.13039/100010663
    Description: Projekt DEAL
    Keywords: ddc:550.78 ; Microfault ; Fracture permeability ; Microstructure ; Fault architecture ; Roughness ; Sandstone ; Granite
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 47
    facet.materialart.
    Unknown
    Verification of Coupled Hydraulic Fracturing Simulators Using Laboratory-Scale Experiments (2021)
    Springer Vienna
    Details
    Publication Date: 2023-11-15
    Description: In this work, we aim to verify the predictions of the numerical simulators, which are used for designing field-scale hydraulic stimulation experiments. Although a strong theoretical understanding of this process has been gained over the past few decades, numerical predictions of fracture propagation in low-permeability rocks still remains a challenge. Against this background, we performed controlled laboratory-scale hydraulic fracturing experiments in granite samples, which not only provides high-quality experimental data but also a well-characterized experimental set-up. Using the experimental pressure responses and the final fracture sizes as benchmark, we compared the numerical predictions of two coupled hydraulic fracturing simulators—CSMP and GEOS. Both the simulators reproduced the experimental pressure behavior by implementing the physics of Linear Elastic Fracture Mechanics (LEFM) and lubrication theory within a reasonable degree of accuracy. The simulation results indicate that even in the very low-porosity (1–2 %) and low-permeability (10〈sup〉−18〈/sup〉 m〈sup〉2〈/sup〉 − 10〈sup〉−19〈/sup〉 m〈sup〉2〈/sup〉) crystalline rocks, which are usually the target of EGS, fluid-loss into the matrix and unsaturated flow impacts the formation breakdown pressure and the post-breakdown pressure trends. Therefore, underestimation of such parameters in numerical modeling can lead to significant underestimation of breakdown pressure. The simulation results also indicate the importance of implementing wellbore solvers for considering the effect of system compressibility and pressure drop due to friction in the injection line. The varying injection rate as a result of decompression at the instant of fracture initiation affects the fracture size, while the entry friction at the connection between the well and the initial notch may cause an increase in the measured breakdown pressure.
    Description: European Union's Horizon 2020 Research and Innovation programme
    Description: Commonwealth Scientific and Industrial Research Organisation http://dx.doi.org/10.13039/501100000943
    Description: RWTH Aachen (3131)
    Description: http://doi.org/10.5281/zenodo.3710746
    Keywords: ddc:550.78 ; Laboratory-experiments ; Hydraulic fracturing ; Simulation ; Leak-off ; Fracture toughness ; System compressibility ; Fracture radius ; Acoustic emission
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 48
    facet.materialart.
    Unknown
    Authors’ Reply to the Discussion by Crisci et al. (2021) on “Experimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions Mechanical Properties and the Influence of Rock Fabric” (2021)
    Springer Vienna
    Details
    Publication Date: 2023-11-15
    Description: This is a repond to the comments raised in Crisci´s et al. paper “Discussion on “Experimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions ¬ Mechanical Properties and the Influence of Rock Fabric” (2021). We are pleased to use the opportunity to clarify issues related to testing procedures and interpretation in more detail.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Helmholtz-Gemeinschaft http://dx.doi.org/10.13039/501100001656
    Description: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Keywords: ddc:550.78 ; Opalinus Clay ; Testing procedure ; Pore pressure generation ; Strain rate ; Drying-induced micro cracks
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 49
    facet.materialart.
    Unknown
    Immiscible silicate liquids: K and Fe distribution as a test for chemical equilibrium and insight into the kinetics of magma unmixing (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-11-15
    Description: Silicate liquid immiscibility leading to formation of mixtures of distinct iron-rich and silica-rich liquids is common in basaltic and andesitic magmas at advanced stages of magma evolution. Experimental modeling of the immiscibility has been hampered by kinetic problems and attainment of chemical equilibrium between immiscible liquids in some experimental studies has been questioned. On the basis of symmetric regular solutions model and regression analysis of experimental data on compositions of immiscible liquid pairs, we show that liquid–liquid distribution of network-modifying elements K and Fe is linked to the distribution of network-forming oxides SiO2, Al2O3 and P2O5. We use the responding equation for testing chemical equilibrium in experiments not included in the regression analysis and compositions of natural immiscible melts found as glasses in volcanic rocks. Departures from equilibrium that the test revealed in crystal-rich multiphase experimental products and in natural volcanic rocks imply kinetic competition between liquid–liquid and crystal–liquid element partitioning. Immiscible liquid droplets in volcanic rocks appear to evolve along a metastable trend due to rapid crystallization. Immiscible liquids may be closer to chemical equilibrium in large intrusions where cooling rates are lower and crystals may be spatially separated from liquids.
    Description: DeutscheForschungsGemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Russian Science Foundation http://dx.doi.org/10.13039/501100006769
    Description: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Keywords: ddc:550.78 ; Experimental petrology ; Igneous rocks ; Silicate melts ; Liquid–liquid element distribution ; Symmetric regular solutions
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 50
    facet.materialart.
    Unknown
    Experimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions: Mechanical Properties and the Influence of Rock Fabric (2021)
    Springer Vienna
    Details
    Publication Date: 2023-11-15
    Description: The mechanical behavior of the sandy facies of Opalinus Clay (OPA) was investigated in 42 triaxial tests performed on dry samples at unconsolidated, undrained conditions at confining pressures (pc) of 50–100 MPa, temperatures (T) between 25 and 200 °C and strain rates (ε˙) of 1 × 10〈sup〉–3〈/sup〉–5 × 10〈sup〉–6〈/sup〉 s〈sup〉−1〈/sup〉. Using a Paterson-type deformation apparatus, samples oriented at 0°, 45° and 90° to bedding were deformed up to about 15% axial strain. Additionally, the influence of water content, drainage condition and pre-consolidation was investigated at fixed p〈sub〉c〈/sub〉–T conditions, using dry and re-saturated samples. Deformed samples display brittle to semi-brittle deformation behavior, characterized by cataclastic flow in quartz-rich sandy layers and granular flow in phyllosilicate-rich layers. Samples loaded parallel to bedding are less compliant compared to the other loading directions. With the exception of samples deformed 45° and 90° to bedding at p〈sub〉c〈/sub〉 = 100 MPa, strain is localized in discrete shear zones. Compressive strength (σ〈sub〉max〈/sub〉) increases with increasing p〈sub〉c〈/sub〉, resulting in an internal friction coefficient of ≈ 0.31 for samples deformed at 45° and 90° to bedding, and ≈ 0.44 for samples deformed parallel to bedding. In contrast, pre-consolidation, drainage condition, T and ε˙ do not significantly affect deformation behavior of dried samples. However, σ〈sub〉max〈/sub〉 and Young’s modulus (E) decrease substantially with increasing water saturation. Compared to the clay-rich shaly facies of OPA, sandy facies specimens display higher strength σmax and Young’s modulus E at similar deformation conditions. Strength and Young’s modulus of samples deformed 90° and 45° to bedding are close to the iso-stress Reuss bound, suggesting a strong influence of weak clay-rich layers on the deformation behavior.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Helmholtz-Gemeinschaft http://dx.doi.org/10.13039/501100001656
    Description: Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
    Keywords: ddc:550.78 ; Clay rock ; Sandy facies of Opalinus Clay ; Triaxial deformation experiments ; Microstructural deformation mechanisms ; Pressure-, temperature- and strain rate-dependent mechanical behaviour ; Anisotropy
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 51
    facet.materialart.
    Unknown
    Experimental study and numerical modeling of the thermo-hydro-mechanical processes in soil freezing with different frost penetration directions (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-11-16
    Description: This research work presents an experimental and numerical study of the coupled thermo-hydro-mechanical (THM) processes that occur during soil freezing. With focusing on the artificial ground freezing (AGF) technology, a new testing device is built, which considers a variety of AGF-related boundary conditions and different freezing directions. In the conducted experiments, a distinction is made between two thermal states: (1) The thermal transient state, which is associated with ice penetration, small deformations, and insignificant water suction. (2) The thermal (quasi-) steady state, which has a much longer duration and is associated with significant ice lens formation due to water suction. In the numerical modeling, a special focus is laid on the processes that occur during the thermal transient state. Besides, a demonstration of the micro-cryo-suction mechanism and its realization in the continuum model through a phenomenological retention-curve-like formulation is presented. This allows modeling the ice lens formation and the stiffness degradation observed in the experiments. Assuming a fully saturated soil as a biphasic porous material, a phase-change THM approach is applied in the numerical modeling. The governing equations are based on the continuum mechanical theory of porous media (TPM) extended by the phase-field modeling (PFM) approach. The model proceeds from a small-strain assumption, whereas the pore fluid can be found in liquid water or solid ice state with a unified kinematics treatment of both states. Comparisons with the experimental data demonstrate the ability and usefulness of the considered model in describing the freezing of saturated soils.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: RWTH Aachen (3131)
    Keywords: ddc:550.78 ; Experimental study ; Frost heave ; Ice lens formation ; Phase-field modeling ; Soil freezing ; Thermo-hydro-mechanical coupling
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 52
    facet.materialart.
    Unknown
    Influence of plastic fines content on the liquefaction susceptibility of sands: monotonic loading (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-12-19
    Description: The paper presents an experimental study on the effect of plastic fines content on the undrained behavior and liquefaction susceptibility of sand–fines mixtures under monotonic loading. The results of undrained monotonic triaxial compression tests conducted on mixtures of Hostun sand with varying amount (0–20%) and type (kaolin and calcigel bentonite) of plastic fines are presented. The specimens were prepared with different initial densities using the moist tamping method and consolidated at two different isotropic effective stresses. The results demonstrate that for both types of plastic fines, an increase in the fines content leads to a more contractive response and lower values of mobilized deviatoric stress. Despite similar relative density and fines content, the sand–kaolin mixtures showed a more contractive behavior than the sand–calcigel specimens. The steady-state lines (SSLs) in e–p´ space generally move downwards with increasing clay content. While the slopes of the SSLs for the clean Hostun sand and the mixtures with 10 and 20% kaolin are quite similar, the SSL lines for the specimens containing 10% or 20% calcigel run steeper or flatter, respectively. The inclination of the SSL in the q–p′ plane was found independent of clay type and content. The sand–kaolin mixtures were observed to be more susceptible to instability and flow liquefaction than the sand–calcigel mixtures.
    Keywords: ddc:550.78 ; Instability line ; Plastic fines content ; Sand–fines mixtures ; Steady-state line ; Undrained monotonic triaxial tests
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 53
    facet.materialart.
    Unknown
    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
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 54
    facet.materialart.
    Unknown
    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
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 55
    facet.materialart.
    Unknown
    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
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 56
    facet.materialart.
    Unknown
    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
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 57
    facet.materialart.
    Unknown
    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
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 58
    facet.materialart.
    Unknown
    Age and origin of groundwater resources in the Ararat Valley, Armenia: a baseline study applying hydrogeochemistry and environmental tracers (2021)
    Schubert, Michael ; Michelsen, Nils ; Schmidt, Axel ; [et al.]
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-08-08
    Description: Within the Ararat Valley (Armenia), a continuously growing water demand (for irrigation and fish farming) and a simultaneous decline in groundwater recharge (due to climate change) result in increasing stress on the local groundwater resources. This detrimental development is reflected by groundwater-level drops and an associated reduction of the area with artesian conditions in the valley centre. This situation calls for increasing efforts aimed at more sustainable water resources management. The aim of this baseline study was the collection of data that allows for study on the origin and age distribution of the Ararat Valley groundwater based on environmental tracers, namely stable (δ〈sup〉2〈/sup〉H, δ〈sup〉18〈/sup〉O) and radioactive (〈sup〉35〈/sup〉S, 〈sup〉3〈/sup〉H) isotopes, as well as physical-chemical indicators. The results show that the Ararat Valley receives modern recharge, despite its (semi-)arid climate. While subannual groundwater residence times could be disproved (〈sup〉35〈/sup〉S), the detected 〈sup〉3〈/sup〉H pattern suggests groundwater ages of several decades, with the oldest waters being recharged around 60 years ago. The differing groundwater ages are reflected by varying scatter of stable isotope and hydrochemical signatures. The presence of young groundwater (i.e., younger that the 1970s), some containing nitrate, indicates groundwater vulnerability and underscores the importance of increased efforts to achieve sustainable management of this natural resource. Since stable isotope signatures indicate the recharge areas to be located in the mountains surrounding the valley, these efforts must not be limited to the central part of the valley where most of the abstraction wells are located.
    Description: Technische Universität Darmstadt (3139)
    Keywords: ddc:551 ; Groundwater residence time ; Tritium ; Radiosulphur ; Stable isotopes ; Armenia
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 59
    facet.materialart.
    Unknown
    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
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 60
    facet.materialart.
    Unknown
    Late Oligocene—Early Miocene shortening in the Thrace Basin, northern Aegean (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-07-20
    Description: Late Cenozoic was a period of large-scale extension in the Aegean. The extension is mainly recorded in the metamorphic core complexes with little data from the sedimentary sequences. The exception is the Thrace Basin in the northern Aegean, which has a continuous record of Middle Eocene to Oligocene marine sedimentation. In the Thrace Basin, the Late Oligocene–Early Miocene was characterized by north-northwest (N25°W) shortening leading to the termination of sedimentation and formation of large-scale folds. We studied the stratigraphy and structure of one of these folds, the Korudağ anticline. The Korudağ anticline has formed in the uppermost Eocene–Lower Oligocene siliciclastic turbidites with Early Oligocene (31.6 Ma zircon U–Pb age) acidic tuff beds. The turbidites are underlain by a thin sequence of Upper Eocene pelagic limestone. The Korudağ anticline is an east-northeast (N65°E) trending fault-propagation fold, 9 km wide and 22 km long and with a subhorizontal fold axis. It is asymmetric with shallowly-dipping northern and steeply-dipping southern limbs. Its geometry indicates about 1 km of shortening in a N25°W direction. The folded strata are unconformably overlain by Middle Miocene continental sandstones, which constrain the age of folding. The Korudağ anticline and other large folds in the Thrace Basin predate the inception of the North Anatolian Fault (NAF) by at least 12 myr. The Late Oligocene–Early Miocene (28–17 Ma) shortening in the Thrace Basin and elsewhere in the Balkans forms an interlude between two extensional periods, and is probably linked to changes in the subduction dynamics along the Hellenic trench.
    Description: TÜBİTAK
    Description: İTÜ-BAP
    Description: TÜBA
    Description: Freie Universität Berlin (1008)
    Keywords: ddc:551 ; Thrace Basin ; Shortening ; Oligocene ; Miocene ; Aegean
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 61
    facet.materialart.
    Unknown
    The birth of the Alps: Ediacaran to Paleozoic accretionary processes and crustal growth along the northern Gondwana margin (2021)
    Siegesmund, S. ; Oriolo, S. ; Schulz, B. ; [et al.]
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-07-20
    Description: New whole-rock geochemical and coupled U–Pb and Lu–Hf LA-ICP-MS zircon data of metasedimentary rocks of the Austroalpine, South Alpine and Penninic basement domains are presented, to disentangle the pre-Variscan tectonic evolution of the proto-Alps. The studied units seem to record distinct stages of protracted Late Ediacaran to Carboniferous tectonosedimentary processes prior to the Variscan collision. In the case of Austroalpine and South Alpine units, nevertheless, no major differences in terms of provenance are observed, since most detrital zircon samples are characterized by a major Pan-African peak. Their detrital zircon spectra record a provenance from the northeastern Saharan Metacraton and the Sinai basement at the northern Arabian-Nubian Shield, being thus located along the eastern Early Paleozoic northern Gondwana margin, whereas sources located further west are inferred for the Penninic Unit, which might have been placed close to the Moldanubian Unit of the Bohemian Massif. In any case, it is thus clear that the Alpine basement remained in a close position to the Gondwana mainland at least during the Early Paleozoic. The Late Ediacaran to Silurian tectonic evolution, which includes Cadomian and Cenerian tectonometamorphic and magmatic processes, seem thus to record a continuum related to a retreating-mode accretionary orogen, with diachronous back-arc basin opening and possibly discrete compressional/transpressional pulses linked to changes in subduction zone dynamics. On the other hand, it is inferred that the Alpine basement essentially comprises Pan-African metasedimentary and subordinate metaigneous rocks, possibly with very few Early Neoproterozoic relics. This basement was significantly reworked during the protracted Paleozoic orogenic evolution, due to anatexis and/or assimilation by mantle-derived juvenile magmatism.
    Description: Georg-August-Universität Göttingen (1018)
    Keywords: ddc:551 ; Alpine basement ; Cadomian orogeny ; Cenerian orogeny ; Retreating-mode accretionary orogen ; Sedimentary provenance ; Detrital zircons
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 62
    facet.materialart.
    Unknown
    Implications for sedimentary transport processes in southwestern Africa: a combined zircon morphology and age study including extensive geochronology databases (2021)
    Gärtner, Andreas ; Hofmann, Mandy ; Zieger, Johannes ; [et al.]
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-07-27
    Description: Extensive morphological and age studies on more than 4600 detrital zircon grains recovered from modern sands of Namibia reveal complex mechanisms of sediment transport. These data are further supplemented by a zircon age database containing more than 100,000 single grain analyses from the entire southern Africa and allow for hypothesising of a large Southern Namibian Sediment Vortex located between the Damara Orogen and the Orange River in southern Namibia. The results of this study also allow assuming a modified model of the Orange River sand highway, whose origin is likely located further south than previously expected. Moreover, studied samples from other parts of Namibia give first insights into sediment movements towards the interior of the continent and highlight the potential impact of very little spatial variations of erosion rates. Finally, this study points out the huge potential of detrital zircon morphology and large geo-databases as an easy-to-use additional tool for provenance analysis.
    Description: deutsche forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Senckenberg Naturhistorische Sammlungen Dresden (3507)
    Keywords: ddc:551 ; Namibia ; Zircon ; Mineral morphology ; Sediment transport ; Geochronology ; Database
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 63
    facet.materialart.
    Unknown
    New constraints on the exhumation history of the western Tauern Window (European Alps) from thermochronology, thermokinematic modeling, and topographic analysis (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-07-27
    Description: The Brenner normal fault bounds the Tauern Window to the west and accommodated a significant portion of the orogen-parallel extension in the Eastern Alps. Here, we use zircon (U–Th)/He, apatite fission track, and apatite (U–Th)/He dating, thermokinematic modeling, and a topographic analysis to constrain the exhumation history of the western Tauern Window in the footwall of the Brenner fault. ZHe ages from an E–W profile (parallel to the slip direction of the fault) decrease westwards from ~ 11 to ~ 8 Ma and suggest a fault-slip rate of 3.9 ± 0.9 km/Myr, whereas AFT and AHe ages show no spatial trends. ZHe and AFT ages from an elevation profile indicate apparent exhumation rates of 1.1 ± 0.7 and 1.0 ± 1.3 km/Myr, respectively, whereas the AHe ages are again spatially invariant. Most of the thermochronological ages are well predicted by a thermokinematic model with a normal fault that slips at a rate of 4.2 km/Myr between ~ 19 and ~ 9 Ma and produces 35 ± 10 km of extension. The modeling reveals that the spatially invariant AHe ages are caused by heat advection due to faulting and posttectonic thermal relaxation. The enigmatic increase of K–Ar phengite and biotite ages towards the Brenner fault is caused by heat conduction from the hot footwall to the cooler hanging wall. Topographic profiles across an N–S valley in the fault footwall indicate 1000 ± 300 m of erosion after faulting ceased, which agrees with the results of our thermokinematic model. Valley incision explains why the Brenner fault is located on the western valley shoulder and not at the valley bottom. We conclude that the ability of thermokinematic models to quantify heat transfer by rock advection and conduction is crucial for interpreting cooling ages from extensional fault systems.
    Description: Westfälische Wilhelms-Universität Münster (1056)
    Description: https://github.com/jeanbraun
    Keywords: ddc:551 ; European Alps ; Tauern Window ; Thermochronology ; Thermokinematic modeling
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 64
    facet.materialart.
    Unknown
    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
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 65
    facet.materialart.
    Unknown
    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
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 66
    facet.materialart.
    Unknown
    Two-phase late Paleozoic magmatism (~ 313–312 and ~ 299–298 Ma) in the Lusatian Block and its relation to large scale NW striking fault zones: evidence from zircon U–Pb CA–ID–TIMS geochronology, bulk rock- and zircon chemistry (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-07-21
    Description: Late Paleozoic (Variscan) magmatism is widespread in Central Europe. The Lusatian Block is located in the NE Bohemian Massif and it is part of the Saxothuringian Zone of the Variscan orogen. It is bordered by two major NW-trending shear zones, the Intra-Sudetic Fault Zone towards NE and the Elbe Fault Zone towards SW. The scarce Variscan igneous rocks of the Lusatian Block are situated close to these faults. We investigated 19 samples from Variscan plutonic and volcanic rocks of the Lusatian Block, considering all petrological varieties (biotite-bearing granites from the Koenigshain and Stolpen plutons, amphibole-bearing granites from three boreholes, several volcanic dykes, and two volcanites from the intramontane Weissig basin). We applied whole-rock geochemistry (18 samples) and zircon evaporation dating (19 samples). From the evaporation data, we selected six representative samples for additional zircon SHRIMP and CA–ID–TIMS dating. For the Koenigshain pluton, possible protoliths were identified using whole-rock Nd-isotopes, and zircon Hf- and O-isotopes. The new age data allow a subdivision of Variscan igneous rocks in the Lusatian Block into two distinct magmatic episodes. The spatial relation of the two age groups to either the Elbe Fault Zone (298–299 Ma) or the Intra-Sudetic Fault Zone (312–313 Ma) together with reports on the fault-bound character of the dated intrusions suggests an interpretation as two major post-collisional faulting episodes. This assumption of two distinct magmatic periods is confirmed by a compilation of recently published zircon U–Pb CA–ID–TIMS data on further Variscan igneous rocks from the Saxothuringian Zone. New geochemical data allow us to exclude a dominant sedimentary protolith for the Koenigshain pluton as supposed by previous investigations. This conclusion is mainly based on new O- and Hf-isotope data on zircon and the scarcity of inherited zircons. Instead, acid or intermediate igneous rocks are supposed as the main source for these I-type granitoids from the Koenigshain pluton.
    Description: Technische Universität Bergakademie Freiberg (3135)
    Keywords: ddc:551 ; Geochronology ; Zircon ; Variscan granites ; Lusatian block
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 67
    facet.materialart.
    Unknown
    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
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 68
    facet.materialart.
    Unknown
    Cyclostratigraphy and paleoenvironmental inference from downhole logging of sediments in tropical Lake Towuti, Indonesia (2021)
    Springer Netherlands
    Details
    Publication Date: 2023-06-14
    Description: Lake Towuti is located on central Sulawesi/Indonesia, within the Indo Pacific Warm Pool, a globally important region for atmospheric heat and moisture budgets. In 2015 the Towuti Drilling Project recovered more than 1000 m of drill core from the lake, along with downhole geophysical logging data from two drilling sites. The cores constitute the longest continuous lacustrine sediment succession from the Indo Pacific Warm Pool. We combined lithological descriptions with borehole logging data and used multivariate statistics to better understand the cyclic sequence, paleoenvironments, and geochronology of these sediments. Accurate chronologies are crucial to analyze and interpret paleoclimate records. Astronomical tuning can help build age-depth models and fill gaps between age control points. Cyclostratigraphic investigations were conducted on a downhole magnetic susceptibility log from the lacustrine facies (10–98 m below lake floor) from a continuous record of sediments in Lake Towuti. This study provides insights into the sedimentary history of the basin between radiometric ages derived from dating a tephra layer (~ 797 ka) and C14-ages (~ 45 ka) in the cores. We derived an age model that spans from late marine isotope stage (MIS) 23 to late MIS 6 (903 ± 11 to 131 ± 67 ka). Although uncertainties caused by the relatively short record and the small differences in the physical properties of sediments limited the efficacy of our approach, we suggest that eccentricity cycles and/or global glacial-interglacial climate variability were the main drivers of local variations in hydroclimate in central Indonesia. We generated the first nearly complete age-depth model for the lacustrine facies of Lake Towuti and examined the potential of geophysical downhole logging for time estimation and lithological description. Future lake drilling projects will benefit from this approach, since logging data are available just after the drilling campaign, whereas core descriptions, though more resolved, only become available months to years later.
    Description: Deutsche Forschungsgemeinschaft (DE)
    Description: Projekt DEAL
    Keywords: ddc:551 ; Paleoclimate ; Geophysical downhole logging ; Cyclostratigraphy ; Lake Towuti ; Indo Pacific Warm Pool
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 69
    facet.materialart.
    Unknown
    Holocene paleoenvironmental change inferred from two sediment cores collected in the Tibetan lake Taro Co (2021)
    Springer Netherlands
    Details
    Publication Date: 2023-07-06
    Description: The Tibetan Plateau, also known as the “Water Tower of Asia” because of its function as a water storage and supply region, responds dramatically to modern climate changes. Paleoecological shifts inferred from lake sediment archives provide essential insights into past climate changes, and the processes that drove those shifts. This is especially true for studies of lakes in endorheic basins on the Tibetan Plateau, where lake level is regulated predominantly by Monsoon intensity. Such water bodies provide excellent opportunities to reconstruct past changes in humidity. Most paleolimnological investigations of lakes on the Tibetan Plateau, however, have involved the study of a single sediment core, making it difficult to discern between changes caused by local events and those caused by lake-wide or regional processes. Here we present results from a paleolimnological study of Lake Taro Co, a currently closed-basin lake in Central Tibet. We compared a sediment record from the central part of the lake to a record from the near-shore area, and present results of sedimentological and bioindicator (chironomid, diatom, pollen) analyses from both records. Results show three periods of lake-wide ecosystem change (〉 ca. 5250, 5250–2250 and 〈 since about 2250 cal year BP), which reflect a continuous drying trend throughout the Middle and Late Holocene. In addition to this lake-wide trend, we identified two local events in the sediment core from the southeastern, nearshore site. These include (1) a hiatus between 12,400 and 5400 cal year BP and (2) an 1800-year period of distinct paleoenvironmental conditions (5400–3600 cal year BP). We hypothesize that both events were caused by relocation of a river in the southeast sector of the lake’s catchment. We propose that the first relocation caused an erosion event that removed sediment, thereby producing the hiatus. During the following 1800 years, the core site may have been located on the river delta, before another river relocation at 3600 cal year BP established the modern prodelta situation. Our study demonstrates the value of using multiple sediment cores from a lake, to better identify processes that control widespread versus local events.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Fellowships for Young International Scientists http://dx.doi.org/10.13039/501100010895
    Description: NSFC Research Fund for International Young Scientists (CN)
    Description: Deutsche Forschungsgemeinschaft (DFG) (DE)
    Description: National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809
    Description: Technische Universität Braunschweig (1042)
    Keywords: ddc:551 ; Monsoon ; Chironomidae ; Diatoms ; Geochemistry ; XRF ; Paleolimnology
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 70
    facet.materialart.
    Unknown
    The Late Carboniferous deeply eroded Tharandt Forest caldera–Niederbobritzsch granite complex: a post-Variscan long-lived magmatic system in central Europe (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-08-17
    Description: Samples and documentation of outcrops and drillings, facies analysis, whole rock geochemistry and radiometric ages have been employed to re-evaluate the Late Carboniferous Tharandt Forest caldera (TFC) and the co-genetic Niederbobritzsch granite (NBG) in the eastern Erzgebirge near Dresden, Germany. The c. 52 km2 TFC harbours strongly welded ignimbrites with a preserved minimum thickness of 550 m. Composition of initial fallout tephra at the base of the TFC fill, comprising lithics of rhyolitic and basic lava, and of silica-rich pyroclastic rocks, suggests a bimodal volcanic activity in the area prior to the climactic TFC eruption. The lower part of the TFC fill comprises quartz-poor ignimbrites, overlain by quartz-rich ignimbrites, apparently without a depositional break. Landslides originating from the collapse collar of the caldera plunged into the still hot TFC fill producing monolithic gneiss mesobreccia with clasts ≤ 1 m in a pyroclastic matrix. Aphanitic and porphyritic rhyolitic magma formed ring- and radial dykes, and subvolcanic bodies in the centre of TFC. Whole rock geochemical data indicate a high silica (most samples have 〉 73 wt% SiO2) rhyolitic composition of the TFC magma, and a similar granodiorite–granitic composition for the NBG. Based on drillings and caldera extent, a minimum volume of 22 km3 of TFC fill is preserved, the original fill is assumed at about 33 km3. This estimate translates into a denudation of at least c. 210 m during Late Paleozoic to pre-Cenomanian. Telescopic subsidence of the TFC took place in two, perhaps three stages. A possible TFC outflow facies has been completely eroded and distal TFC tuff has not been recognized in neighboring basins. New CA-ID-TIMS measurements on two TFC samples gave mean zircon ages of 313.4 ± 0.4 Ma and 311.9 ± 0.4 Ma; two samples from NBG resulted in 318.2 ± 0.5 Ma and 319.5 ± 0.4 Ma. In addition, for one sample of the ring dyke an age of ca. 314.5 ± 0.5 Ma has been obtained. These ages, together with field relations, allow for a model of a long-standing evolution of an upper crustal magmatic system (~ 5 Ma?), where pulses of magmatic injection and crustal doming alternate with magmatic quietness and erosion. Together with the Altenberg–Teplice Volcanic Complex, located some 10 km to the southeast, the TFC–NBG Complex represents an early post-Variscan magmatic activity in central Europe.
    Description: Technische Universität Bergakademie Freiberg (3135)
    Keywords: ddc:551 ; Single phase caldera evolution ; Caldera wall landslides ; Freiberg gneiss dome ; CA-ID-TIMS zircon dating
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 71
    facet.materialart.
    Unknown
    Local radon flux maxima in the quaternary sediments of Schleswig–Holstein (Germany) (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-08-17
    Description: This paper presents radon flux profiles from four regions in Schleswig–Holstein (Northern Germany). Three of these regions are located over deep-rooted tectonic faults or salt diapirs and one is in an area without any tectonic or halokinetic activity, but with steep topography. Contrary to recently published studies on spatial patterns of soil radon gas concentration we measured flux of radon from soil into the atmosphere. All radon devices of each profile were deployed simultaneously to avoid inconsistencies due to strong diurnal variations of radon exhalation. To compare data from different seasons, values had to be normalized. Observed radon flux patterns are apparently related to the mineralogical composition of the Quaternary strata (particularly to the abundance of reddish granite and porphyry), and its grain size (with a flux maximum in well-sorted sand/silt). Minimum radon flux occurs above non-permeable, clay-rich soil layers. Small amounts of water content in the pore space increase radon flux, whereas excessive water content lessens it. Peak flux values, however, are observed over a deep-rooted fault system on the eastern side of Lake Plön, i.e., at the boundary of the Eastholstein Platform and the Eastholstein Trough. Furthermore, high radon flux values are observed in two regions associated with salt diapirism and near-surface halokinetic faults. These regions show frequent local radon flux maxima, which indicate that the uppermost strata above salt diapirs are very inhomogeneous. Deep-rooted increased permeability (effective radon flux depth) or just the boundaries between permeable and impermeable strata appear to concentrate radon flux. In summary, our radon flux profiles are in accordance with the published evidence of low radon concentrations in the “normal” soils of Schleswig–Holstein. However, very high values of radon flux are likely to occur at distinct locations near salt diapirism at depth, boundaries between permeable and impermeable strata, and finally at the tectonically active flanks of the North German Basin.
    Description: Bundesministerium für Wirtschaft und Energie http://dx.doi.org/10.13039/501100006360
    Description: Johannes Gutenberg-Universität Mainz (1030)
    Keywords: ddc:551 ; Radon flux ; Local radon flux maxima ; Permeability ; Quaternary sediments ; Salt tectonics ; Schleswig–Holstein
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 72
    facet.materialart.
    Unknown
    Simulation of direct shear tests using a forces on fracture surfaces (FFS) approach (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-11-13
    Description: The aim of this work is to provide a complete data set of direct shear tests and to propose a corresponding simulation approach. Tests have been conducted on crystalline rock samples applying constant normal load (CNL) and constant normal stiffness (CNS) boundary conditions. A physical consistent algorithm which explicitly calculates the forces acting on the fracture surface (FFS) has been developed. This FFS approach can explain the occurrence of surface degradation and shows the main shear characteristics. After all, shearing of rough rock joints remains a complex process and the differences between laboratory and simulation results are still significant in some cases. All data and input files are provided free for download and testing.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Technische Universität Bergakademie Freiberg (3135)
    Description: http://www.ufz.de/record/dmp/archive/7925
    Description: http://www.ufz.de/record/dmp/archive/7924
    Description: https://github.com/Poetschke/Ecodist
    Keywords: ddc:550.78 ; GeomInt project ; Direct shear test ; Rock surface scanning ; Rock joint ; Joint constitutive model
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 73
    facet.materialart.
    Unknown
    Soil erosion and sediment transport modelling using hydrological models and remote sensing techniques in Wadi Billi, Egypt (2021)
    Springer International Publishing
    Details
    Publication Date: 2024-02-14
    Description: Modelling soil erosion and sediment transport are vital to assess the impact of the flash floods. However, limited research works have studied sediment transport, especially in Egypt. This paper employs the HEC-HMS lumped hydrological model to predict the sediment load due to the flood event of 9th March 2014 in Wadi Billi, Egypt. The Modified USLE model has been used to calculate the total upland erosion, while Laursen-Copeland has been used to simulate load streams’ sediment transport potential. The Normalized Difference Vegetation Index (NDVI) has been applied over Landsat 8 image captured on 20th February 2014 using ArcMap 10.5 to determine the vegetation cover based on its spectral footprint. The resulted sedigraph showed accumulation of more than five thousand tons of sediments at the Wadi’s outlet. The results are crucial to design a suitable stormwater management system to protect the downstream urban area and to use flood water for groundwater recharge.
    Description: Technische Universität Berlin (3136)
    Description: https://www.hec.usace.army.mil/software/hec-hms/
    Keywords: ddc:551 ; MUSLE model ; HEC-HMS ; Wadi system ; Remote sensing ; Sedigraph ; Egypt
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 74
    facet.materialart.
    Unknown
    The 12 December 2017 Baumgarten Gas Hub Explosion: A Case Study on Understanding the Occurrence of a Large Infrasound Azimuth Residual and a Lack of Seismic Observations (2020)
    Springer International Publishing
    Details
    Publication Date: 2023-11-27
    Description: The Baumgarten explosion occurred on 12 December 2017 at a gas storage site about 30 km east of Vienna, Austria. Acoustic arrivals from this accidental surface explosion were detected at dozens of stations of the AlpArray seismic network to distances up to 150 km, mainly in easterly directions. Thus it was expected that the Hungarian infrasound array PSZI located about 230 km to the east-southeast of Baumgarten would detect this acoustic wave as well. Standard progressive multichannel correlation processing and frequency-wavenumber analysis identified a signal emerging at 7:57:55 UTC from an azimuth of 296°–300° and with trace-velocity 〉 400 m/s. The extraordinarily high trace-velocity and excessive backazimuth residual, relative to the explosion site direction of 282°, however cast strong doubts on the arrival’s connection to the Baumgarten event. Accounting for the effect of non-planar geometry of the infrasound array results in a reduction of the azimuth residual by half. Additionally, 2D and 3D raytracing methods are used including the European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric model to further explain the remaining azimuth residual as well as to elucidate the large trace velocity estimates. The prevailing stratospheric winds in excess of 150 m/s are identified as the underlying cause. Including both factors the initial azimuth residual of up to 18° decreases to ~ 4°, allowing to associate the infrasound signal at PSZI with the Baumgarten event. Finally, the data from a seismic station at 30 km range is re-investigated for magnitude estimation. The local magnitude of ML 〈 1.0 explains well the scarcity of seismic observations within 50 km range, where three or four stations show signals, mainly consisting of Rg-type surface waves, but no body waves.
    Description: https://www.geofon.gfz-potsdam.de/doi/network/HN
    Description: https://doi.org/10.14470/UA114590
    Description: https://www.geofon.gfz-potsdam.de/doi/network/SK
    Description: https://www.ecmwf.int/
    Description: https://www.github.com/LANL-Seismoacoustics/GeoAc
    Keywords: ddc:551 ; Infrasound ; Baumgarten explosion ; array data processing ; backazimuth residual ; atmospheric sound propagation ; detection threshold
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 75
    facet.materialart.
    Unknown
    Return to rapid ice loss in Greenland and record loss in 2019 detected by the GRACE-FO satellites (2020)
    Sasgen, Ingo ; Wouters, Bert ; Gardner, Alex S. ; [et al.]
    Nature Publishing Group UK
    Details
    Publication Date: 2023-11-16
    Description: Between 2003-2016, the Greenland ice sheet (GrIS) was one of the largest contributors to sea level rise, as it lost about 255 Gt of ice per year. This mass loss slowed in 2017 and 2018 to about 100 Gt yr〈sup〉−1〈/sup〉. Here we examine further changes in rate of GrIS mass loss, by analyzing data from the GRACE-FO (Gravity Recovery and Climate Experiment – Follow On) satellite mission, launched in May 2018. Using simulations with regional climate models we show that the mass losses observed in 2017 and 2018 by the GRACE and GRACE-FO missions are lower than in any other two year period between 2003 and 2019, the combined period of the two missions. We find that this reduced ice loss results from two anomalous cold summers in western Greenland, compounded by snow-rich autumn and winter conditions in the east. For 2019, GRACE-FO reveals a return to high melt rates leading to a mass loss of 223 ± 12 Gt month〈sup〉−1〈/sup〉 during the month of July alone, and a record annual mass loss of 532 ± 58 Gt yr〈sup〉−1〈/sup〉.
    Description: Mass loss from the Greenland ice sheet returned to record levels in 2019, following unusually small loss in 2017-18, according to an analysis of satellite data from GRACE and its follow-on mission GRACE-FO.
    Description: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (Alfred-Wegener- Institute, Helmholtz Centre for Polar and Marine Research) https://doi.org/10.13039/501100003207
    Description: Helmholtz Association https://doi.org/10.13039/501100009318
    Description: http://geoweb.princeton.edu/people/simons/software.html
    Keywords: ddc:551 ; Climate change ; Cryospheric science ; Greenland ; ice loss
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 76
    facet.materialart.
    Unknown
    Deglacial to Holocene variability in surface water characteristics and major floods in the Beaufort Sea (2020)
    Wu, Junjie ; Stein, Ruediger ; Fahl, Kirsten ; [et al.]
    Nature Publishing Group UK
    Details
    Publication Date: 2023-06-05
    Description: Surface water characteristics of the Beaufort Sea have global climate implications during the last deglaciation and the Holocene, as (1) sea ice is a critical component of the climate system and (2) Laurentide Ice Sheet meltwater discharges via the Mackenzie River to the Arctic Ocean and further, to its outflow near the deep-water source area of the Atlantic Meridional Overturning Circulation. Here we present high-resolution biomarker records from the southern Beaufort Sea. Multi-proxy biomarker reconstruction suggests that the southern Beaufort Sea was nearly ice-free during the deglacial to Holocene transition, and a seasonal sea-ice cover developed during the mid-late Holocene. Superimposed on the long-term change, two events of high sediment flux were documented at ca. 13 and 11 kyr BP, respectively. The first event can be attributed to the Younger Dryas flood and the second event is likely related to a second flood and/or coastal erosion.
    Description: The Beaufort Sea was nearly ice-free during the transition from the last deglacial to the Holocene, a period in which two episodes of high sediment flux suggest major glacial flood events, according to high-resolution multi-proxy biomarker records.
    Description: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (Alfred-Wegener- Institute, Helmholtz Centre for Polar and Marine Research) https://doi.org/10.13039/501100003207
    Description: China Scholarship Council (CSC) https://doi.org/10.13039/501100004543
    Description: National Research Foundation of Korea (NRF) https://doi.org/10.13039/501100003725
    Keywords: ddc:551 ; Biogeochemistry ; Cryospheric science ; Palaeoceanography
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 77
    facet.materialart.
    Unknown
    Higher than present global mean sea level recorded by an Early Pliocene intertidal unit in Patagonia (Argentina) (2020)
    Rovere, Alessio ; Pappalardo, Marta ; Richiano, Sebastian ; [et al.]
    Nature Publishing Group UK
    Details
    Publication Date: 2023-06-05
    Description: Reconstructions of global mean sea level from earlier warm periods in Earth’s history can help constrain future projections of sea level rise. Here we report on the sedimentology and age of a geological unit in central Patagonia, Argentina, that we dated to the Early Pliocene (4.69–5.23 Ma, 2σ) with strontium isotope stratigraphy. The unit was interpreted as representative of an intertidal environment, and its elevation was measured with differential GPS at ca. 36 m above present-day sea level. Considering modern tidal ranges, it was possible to constrain paleo relative sea level within  ±2.7 m (1σ). We use glacial isostatic adjustment models and estimates of vertical land movement to calculate that, when the Camarones intertidal sequence was deposited, global mean sea level was 28.4 ± 11.7 m (1σ) above present. This estimate matches those derived from analogous Early Pliocene sea level proxies in the Mediterranean Sea and South Africa. Evidence from these three locations indicates that Early Pliocene sea level may have exceeded 20m above its present level. Such high global mean sea level values imply an ice-free Greenland, a significant melting of West Antarctica, and a contribution of marine-based sectors of East Antarctica to global mean sea level.
    Description: Global mean sea level was 28.4 ± 11.7 m higher than at present during the Early Pliocene, at atmospheric CO2 levels of no more than 450 ppm and temperatures of 2–3 ∘C above preindustrial levels, suggests a reconstruction from Patagonia.
    Description: National Science Foundation (NSF) https://doi.org/10.13039/100000001
    Keywords: ddc:551 ; Geomorphology ; Palaeoclimate
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 78
    facet.materialart.
    Unknown
    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
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 79
    facet.materialart.
    Unknown
    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
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 80
    facet.materialart.
    Unknown
    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
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 81
    facet.materialart.
    Unknown
    Revisiting afro-alpine Lake Garba Guracha in the Bale Mountains of Ethiopia: rationale, chronology, geochemistry, and paleoenvironmental implications (2020)
    Springer Netherlands
    Details
    Publication Date: 2023-06-08
    Description: Previous paleolimnological studies demonstrated that the sediments of Garba Guracha, situated at 3950 m asl in the afro-alpine zone of the Bale Mountains of Ethiopia, provide a complete Late Glacial and Holocene paleoclimate and environmental archive. We revisited Garba Guracha in order to retrieve new sediment cores and to apply new environmental proxies, e.g. charcoal, diatoms, biomarkers, and stable isotopes. Our chronology is established using 210Pb dating and radiocarbon dating of bulk sedimentary organic matter, bulk n-alkanes, and charcoal. Although bedrock was not reached during coring, basal ages confirm that sedimentation started at the earliest ~ 16 cal kyr BP. The absence of a systematic age offset for the n-alkanes suggests that “pre-aging” is not a prominent issue in this lake, which is characterised by a very small afro-alpine catchment. X-ray fluorescence scans and total organic carbon contents show a prominent transition from minerogenic to organic-rich sediments around 11 cal kyr BP coinciding with the Holocene onset. While an unambiguous terrestrial versus aquatic source identification seems challenging, the n-alkane-based Paq proxy, TOC/N ratios, δ13C values, and the sugar biomarker patterns suggest a predominantly autochthonous organic matter source. Supraregional climate events, such as the African Humid Period, the Younger Dryas (YD), a 6.5 cal kyr BP short drying event, and the 4.2 cal kyr BP transition to overall drier climate are recorded in our archive. The Garba Guracha record suggests that northern hemisphere forcings played a role in the Eastern African highland paleoclimate.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551 ; Paleolimnology ; Afro-alpine ; Radiocarbon dating ; XRF scanning ; Sedimentation rate ; Biomarkers
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 82
    facet.materialart.
    Unknown
    The 1994 Piedmont flood: an archetype of extreme precipitation events in Northern Italy (2020)
    Springer International Publishing
    Details
    Publication Date: 2023-06-08
    Description: Extreme precipitation events (EPEs) are meteorological phenomena of major concern for the densely populated regions of northern and central Italy. Although statistically rare, they tend to be recurrent in autumn and share common characteristics in the large-scale dynamical evolution responsible for their generation. Past studies on EPEs have reported, as the main triggering factor, a meridionally elongated upper-level trough embedded in an incoming Rossby wave packet. In this respect, we show how the meteorological conditions leading to the devastating 1994 Piedmont flood represent a typical flow evolution for this type of extreme events. Exploiting the systematic classification of EPEs recently published by the authors and taking advantage of a new observational dataset, this article revisits the role of the large-scale flow on this and similar cases of past EPEs.
    Description: Ludwig-Maximilians-Universität, Meteorologisches Institut, München, Germany
    Keywords: ddc:551 ; Extreme precipitation ; Floods ; Po river ; Atmospheric rivers ; Rossby wave packets ; Downstream development
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 83
    facet.materialart.
    Unknown
    Geological development of the Limpopo Shelf (southern Mozambique) during the last sealevel cycle (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-17
    Description: Paleo-shorelines on continental shelves give insights into the complex development of coastlines during sealevel cycles. This study investigates the geologic development of the Limpopo Shelf during the last sealevel cycle using multichannel seismic and acoustic datasets acquired on the shelf in front of the Limpopo River mouth. A detailed investigation of seismic facies, shelf bathymetry, and a correlation to sea level revealed the presence of numerous submerged shorelines on the shelf. These shorelines are characterized by distinct topographic ridges and are interpreted as coastal dune ridges that formed in periods of intermittent sealevel still-/slowstand during transgression. The shorelines are preserved due to periods of rapid sealevel rise (melt water pulses) that led to the overstepping of the dune ridges as well as due to early cementation of accumulated sediments that increased the erosive resistance of the ridges. The high along-shelf variability of the submerged dune ridges is interpreted as a result of pre-existing topography affecting shoreline positions during transgression. The pre-existing topography is controlled by the underlying sedimentary deposits that are linked to varying fluvial sediment input at different points on the shelf. The numerous prominent submerged dune ridges form barriers for the modern fluvial sediment from the Limpopo River and dam sediment on the inner shelf. They may also facilitate along-shelf current-induced sediment transport.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551 ; Limpopo Shelf ; Geology
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 84
    facet.materialart.
    Unknown
    Slab break-offs in the Alpine subduction zone (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-17
    Description: After the onset of plate collision in the Alps, at 32–34 Ma, the deep structure of the orogen is inferred to have changed dramatically: European plate break-offs in various places of the Alpine arc, as well as a possible reversal of subduction polarity in the eastern Alps have been proposed. We review different high-resolution tomographic studies of the upper mantle and combine shear- and body-wave models to assess the most reliable geometries of the slabs. Several hypotheses for the tectonic evolution are presented and tested against the tomographic model interpretations and constraints from geologic and geodetic observations. We favor the interpretation of a recent European slab break-off under the western Alps. In the eastern Alps, we review three published scenarios for the subduction structure and propose a fourth one to reconcile the results from tomography and geology. We suggest that the fast slab anomalies are mainly due to European subduction; Adriatic subduction plays no or only a minor role along the Tauern window sections, possibly increasing towards the Dinarides. The apparent northward dip of the slab under the eastern Alps may be caused by imaging a combination of Adriatic slab, from the Dinaric subduction system, and a deeper lying European one, as well as by an overturned, retreating European slab.
    Description: GRNE graduate school
    Description: Deutsche Forschungsgemeinschaft (DE)
    Description: H2020 Marie Skłodowska-Curie Actions ()
    Description: http://www.orfeus-eu.org/eida
    Keywords: ddc:551 ; Seismic tomography ; Subduction slabs ; Alpine subduction system ; Slab break-off ; Slab polarity reversal
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 85
    facet.materialart.
    Unknown
    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
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 86
    facet.materialart.
    Unknown
    Mesozoic deposits of SW Gondwana (Namibia): unravelling Gondwanan sedimentary dispersion drivers by detrital zircon (2020)
    Zieger, J. ; Harazim, S. ; Hofmann, M. ; [et al.]
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-17
    Description: The Namibian Mesozoic successions may be remnant of a high dynamic sedimentary system that is characterized by multiple stages of sediment accumulation and erosion with contemporaneous homogenization starting with the deposition of the Permo-Carboniferous Dwyka Group strata and continues at least until the Lower Cretaceous. The Lower Cretaceous sedimentary system is interpreted to have involved at least an area covering the whole SW Gondwana, documenting the sedimentary history during the evolution from an ice house environment to an arid desert. To test the sediment homogenization hypothesis, we applied a combination of isotopic and morphometric data on detrital zircon grains, as well as whole-rock geochemical data of selected Mesozoic sandstones from Namibia. As a base for the interpretation of the detrital zircon age data we compiled a zircon age dataset with c. 44,000 analyses for the southern African region. All samples reveal a major detrital pan-African zircon age peak of c. 0.5–0.7 Ga sourced from the pan-African magmatic events occurring around the Kalahari Craton margin. The lowermost Triassic is characterized by the occurrence of additional Mesoproterozoic and Paleoproterozoic age peaks of c. 1.0–1.2 Ga and 1.8–2.0 Ga with a majority of zircon grains showing angular shapes. The protosource of these grains is interpreted to possibly be the Namaqua Metamorphic Complex and other Paleoproterozoic structural units deformed in course of the Namaqua orogeny. In contrast, other samples show a prominent Permo-Triassic age peak and completely rounded zircon grains, putatively derived from within the Gondwanides volcanic arc. The disparity in the zircon age pattern may point towards a change in provenance and also a change in the whole system of zircon recycling during the Mesozoic southern Gondwana. The Lower Triassic Neu Loore fm. are constrained to more local bedrock sources and short zircon transport distance. In contrast, zircon grains of the Middle Triassic Omingonde, the Jurassic Etjo und the Cretaceous Twyfelfontein formations are an expression for a major recycling and sediment homogenization system. The system was facilitated by an interplay between fluvial and eolian sedimentary transport systems.
    Keywords: ddc:551 ; Zircon U–pb ; Mesozoic ; Gondwana ; Karoo ; Namibia
    Language: English
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 87
    facet.materialart.
    Unknown
    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
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 88
    facet.materialart.
    Unknown
    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
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 89
    facet.materialart.
    Unknown
    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
    Type: doc-type:article
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
  • 90
    facet.materialart.
    Unknown
    Die Neuinterpretation von Claudius Ptolemäus’ Germania Magna (2020)
    Sven Mildner
    Details
    Publication Date: 2024-03-06
    Description: Diese Preprint Veröffentlichung mit dem Namen "Die Neuinterpretation von Claudius Ptolemäus’ Germania Magna - mit Hilfe computergestützter Bildverzerrung einer mittelalterlichen Kartendarstellung des Donnus Nicolaus Germanus - und Betrachtungen zur postglazialen Geodynamik Europas" ist ein interdisziplinärer Beitrag, der voraussichtlich zu neuen Erkenntnissen auf den Gebieten der Geologie (postglaziale Geodynamik), der historischen Geographie, der Sozialgeographie und insbesondere auch auf den unterschiedlichen Gebieten der Geschichtswissenschaften führen wird (Ur- und Frühgeschichte, römische Kaiserzeit, Völkerwanderung, frühes Mittelalter). Außerdem wird die vorliegende Interpretation der Germania Magna die archäologische Arbeit dahingehend beeinflussen, dass künftig eine bessere räumliche Verortung von aufgefundenen Siedlungen und Fundstätten zueinander vorgenommen werden kann. Zuletzt erfolgte ein entsprechender Versuch zur Verortung durch Kleineberg, Andreas & Nüsse, Hans-Jörg & Marx, Christian & Lelgemann, Dieter in "Germania magna - A new look at an old map: Rectifying Ptolemy's geographical data for ancient places between the Rhine and the Vistula. Germania. 89. 115-155." im Jahre 2010 am Institut für Geodäsie und Geoinformationstechnik der Technischen Universität Berlin, mittels geodätischer Entzerrung, in Kombination mit der Kenntnis über früh-zeitliche Handelsrouten, allerdings ohne Berücksichtigung einer umfassenderen Lanschaftstransformation durch geologische Prozesse. Die Kenntnis über das Landschaftsbild, das die Menschen noch vor etwa 2000 Jahren vorgefunden haben und über die geologisch-bedingten Veränderungen seit dieser Zeit, ermöglichen jedoch eine bessere geschichtliche und geographische Einordnung von Aufzeichnungen aus der Antike, aus der römischen Kaiserzeit, sowie von frühen kirchlichen Aufzeichnungen, die Christianisierung Europas betreffend. Ebenfalls führen weitergehende Betrachtungen zu einem besseren Verständnis über die postglaziale Geodynamik in Europa und über die Auswirkungen dieser Prozesse auf die weitere Kulturgeschichte früher Völker in Europa. Das Siedlungsgebiet frühzeitlicher Kulturen entlang der Küste, wie auch das der Wikinger, die auf zahlreichen Inseln nördlich der Germania Magna lebten, kann infolge dieser Interpretation möglicherweise neu betrachtet werden, da mit der Neuinterpretation der Karte auch eine präzisere Verortung archäologisch-bedeutender Siedlungen und Fundstätten aus germanischer Zeit ermöglicht wird. Es handelt sich bei dieser Arbeit aber auch um ein philosophisches Dokument des modernen Zeitgeschehens, das exemplarisch die Folgen aktueller politischer Entwicklungen für die moderne Forschungslandschaft aufzeigt und somit ein besseres Verständnis - auch für die Politik des römischen Reiches - ermöglicht, mit welchem sich der Leser bei einer weitergehenden Interpretation der Karte womöglich beschäftigen wird. So hatten schon vor über 2000 Jahren politische Intrigen und die Bestrebungen zum Machterhalt, aber auch die Expansionsbestrebungen des Reiches, nicht selten einen erheblichen Einfluss auf die wissenschaftlichen Arbeiten dieser Zeit und somit auch auf die Glaubwürdigkeit vieler Autoren, wenn sie heute rückblickend und mit entsprechendem Abstand betrachtet werden - also ohne, dass dabei tatsächlich alle Umstände ihrer Arbeit heute noch bekannt wären. Insbesondere in Phasen von politischer oder gesellschaftlicher Instabilität sind Regime für den eigenen Machterhalt stets darum bemüht, die Freiheitsrechte von Bürgern allgemein, aber auch die freie Ausübung der wissenschaftlichen Tätigkeit zu beschränken, die dann sehr leicht der jeweiligen Propaganda und einem gezieltem Framing zum Opfer fallen. Kritische Wissenschaftler, die wenigstens um ihre Reputation besorgt sein müssen, wenn sie sich nicht konform mit der gerade noch zulässigen politischen Meinung zeigen, verschieben ihre Veröffentlichungen teilweise oder passen sie den besonderen Gegebenheiten entsprechend an. Gelegentlich bleibt die Arbeit unvollendet oder geht sogar ganz verloren. Auch die multiple Krise unserer Zeit hat aufgrund der massiven Transformationsprozesse, die im täglichen Leben aller Bürger stattfinden, wohl einen anzunehmenden, aber bislang nur wenig beachteten Einfluss auf die Arbeit vieler Forscher und Autoren, die aus ganz ähnlichen Gründen wie schon in Jahrtausenden zuvor, zunächst nur selten Kritik an einer solchen Entwicklung äußern, so dass diese auch öffentlich vernommen werden könnte und welche auch nur dann zu einer ehrlichen Debatte beiträgt - als eine wesentliche Grundlage für den demokratischen Prozess. Und erst nach und nach erfahren die mutigen "Aufständler" ihrer jeweiligen Zeit vielleicht eine Rehabilitation für sich und ihre Arbeit - zumindest dann, wenn es ihnen zuvor gelungen ist, sich nicht in Gänze einem bestimmten Diktat zu unterwerfen und wenn sie mit ihrer Arbeit entsprechende Spuren hinterlassen haben, die eine spätere Interpretation des Entstehungsprozesses erleichtert, weil dieser unter gewöhnlichen Umständen vielleicht zu einem anderen Ergebnis geführt hätte. Das Dokument wurde daher bewusst im Entwurfsstadium veröffentlicht, an der Stelle der Ausarbeitung, an der es unter Umständen vielleicht niemals weitergeführt worden und stattdessen der Cancel Culture zum Opfer gefallen wäre. Vergleiche hierzu auch die "Behördenbriefe" des Autors, welcher darin bezüglich der politischen Entwicklungen, seine seit März 2020 zunächst bei Facebook veröffentlichten Argumente und Ausarbeitungen zusammenfassend dargelegt hat. Dieser Text bezieht sich auf die Preprint Veröffentlichung zu Mildner, Sven. (2020). Die Neuinterpretation von Claudius Ptolemäus’ Germania Magna - mit Hilfe computergestützter Bildverzerrung einer mittelalterlichen Kartendarstellung des Donnus Nicolaus Germanus - und Betrachtungen zur postglazialen Geodynamik Europas. 10.13140/RG.2.2.32850.73927.
    Description: ISBN 979-8573568980
    Description: Die Neuinterpretation von Claudius Ptolemäus’ Germania Magna - mit Hilfe computergestützter Bildverzerrung einer mittelalterlichen Kartendarstellung des Donnus Nicolaus Germanus - und Betrachtungen zur postglazialen Geodynamik Europas: Die geografische Beschreibung der ihm bekannten Welt durch den griechischen Universalgelehrten Claudius Ptolemäus, etwa 150 Jahre nach Christi Geburt, faszinierte zahlreiche Wissenschaftler nach seiner Zeit - und auch heute noch ist das Interesse an seinem Werk nicht verloren gegangen - im Gegensatz zur sagenumwobenen Insel „Thule“, die dank mystischer Erzählungen immer wieder das Interesse vieler Menschen geweckt hat. Auf der Suche nach geheimem Wissen, dem Atlantis des Nordens oder, um die Vergangenheit besser zu verstehen, versuchte man die von Ptolemäus angegebenen Koordinaten der jeweils bekannten Welt zuzuordnen und die eingezeichneten Orte, Flüsse und Gebirge zu identifizieren... Bei dieser Ausgabe handelt es sich um eine unvollständige Vorab-Erscheinung aus dem Jahr 2020, da die Zusammenarbeit mit der universitären Forschung im Zuge der Corona-Krise aus politischen Gründen leider nicht mehr möglich war. Eine Fertigstellung des Manuskripts, die fachliche Überprüfung der Inhalte und die Ausarbeitung zu einem umfangreicheren Werk konnte deshalb bis heute nicht erfolgen. Der Autor musste das Projekt aufgrund seines bürgerlich-gesellschaftlichen Engagements leider zurückstellen, veröffentlicht diese Vorab-Version aber dennoch, damit die Inhalte Teil einer wissenschaftlichen Überlegung werden können. Die Veröffentlichungs-Qualität der digitalen Ausgabe ist leider etwas eingeschränkt, da die Buch-Seiten aus einer bereits erstellten Datei-Kopie zurückgewonnen werden mussten. Im Zuge seines bürgerschaftlichen Engagements zur Bewahrung unserer Demokratie, gegen Faschismus und die Einschränkung unserer Grundrechte, wurde der Arbeitscomputer des Autors mit den Original-Dateien illegal von den Behörden beschlagnahmt und bis zum Tag der Veröffentlichung dieser Ausgabe widerrechtlich einbehalten.
    Description: abstract
    Keywords: ddc:551 ; ddc:554 ; Germania Magna ; postglaziale Landhebung ; Ostsee ; Nordsee ; Mitteleuropäische Senke ; Mecklenburg-Vorpommern ; Schleswig-Holstein ; Niedersachsen ; Brandenburg ; Fläming ; Vistula Fluvius ; Schwarze Elster ; Kleine Elster ; Holozän ; römische Kaiserzeit ; Völkerwanderung
    Language: German
    Type: doc-type:book , draft
    Format: 38
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    CITATION GEO-LEO
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...