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  • Other Sources  (62)
  • ddc:551.46  (33)
  • ddc:549  (28)
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  • 2020-2024  (62)
  • 1
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    The Deep‐Water Plume in the Northwestern Weddell Sea, Antarctica: Mean State, Seasonal Cycle and Interannual Variability Influenced by Climate Modes (2023)
    Details
    Publication Date: 2023-06-21
    Description: We provide an updated estimate of the annual‐mean, seasonal cycle and interannual variability of the transports and properties of the Weddell Sea Bottom Water (WSBW) plume in the northwestern Weddell Sea. For this we used a densely instrumented mooring array deployed across the continental slope between January 2017 and January 2019. We found that the annual‐mean WSBW transport is 3.4 ± 1.5 Sv, corresponding to a cross‐section area of 35 km2 and a maximum thickness of 203 m. The annual mean transport‐weighted properties of WSBW are −0.99°C (Θ), 34.803 g/kg (SA) and 28.44 kg/m3 (γn). The WSBW is characterized by 3 bottom‐intensified velocity cores, which display seasonal variations in flow speed and transport different varieties of WSBW. The seasonal peak of WSBW transport and density is reached in May (4.7 Sv, 28.443 kg m−3) while the minimum values are observed in February (2.8 Sv, 28.435 kg m−3). The coldest WSBW is found between March and May, and the warmest between August and October. The density decrease of WSBW observed in the austral autumn of 2018 can be explained by warmer ambient waters being entrained during the formation of WSBW. This was enabled by the weakening of the along‐shore winds associated with a positive Southern Annular Mode index, reinforced by a La Niña event in early 2018. The synchronous decrease of total WSBW transport and volume between September 2018 and February 2019 indicates a reduction in the export of the dense precursors of WSBW from the Weddell Sea continental shelf.
    Description: Plain Language Summary: The Meridional Overturning Circulation (MOC) redistributes heat and carbon dioxide in the world ocean. Thus, it plays an important role in the regulation of our planet's climate. The Weddell Sea is the main contributor to the deep branch of the MOC in the Southern Hemisphere. Despite the importance of this contribution, uncertainties still remain associated to the plume of dense waters transported along the continental slope of the Weddell Sea. To reduce these uncertainties, we analyzed the most densely instrumented mooring array deployed across the continental slope in the northwestern Weddell Sea. We found that this plume flows faster close to the seafloor and that it presents important seasonal and interannual variability. The Weddell Sea Bottom Water interannual variability is influenced by changes in the along‐shore winds driven by the phase of two important climate modes, the Southern Annular Mode and the El Niño‐Southern Oscillation, but also by changes in the export of the dense precursors of WSBW in its formation areas. Increasing our knowledge on the along‐slope plume variability and properties is important to better understand the causes behind the variability of the MOC observed further downstream.
    Description: Key Points: The Weddell Sea Bottom Water (WSBW) plume presents 3 velocity cores and a clear seasonal cycle, with maximum transports and densities in May and minimum in February. A +SAM, reinforced by a ‐ENSO, favors the warming of WSBW via a wind‐driven warming of the ambient waters entrained during its formation. We observed a marked decrease in WSBW density and transports between September 2018 and February 2019 compared to the previous year.
    Description: EU Horizon 2020 Research and Innovation Program
    Description: German Research Foundation
    Description: Alfred Wegener Institute Helmholtz‐Center
    Description: https://doi.org/10.5281/zenodo.7500163
    Keywords: ddc:551.46 ; Weddell Sea ; WSBW ; Meridional Overturning Circulation ; SAM ; ENSO ; deep‐water plume
    Language: English
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  • 2
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    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
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  • 3
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    Winter Vertical Diffusion Rates in the Arctic Ocean, Estimated From 7Be Measurements and Dissipation Rate Profiles (2023)
    Details
    Publication Date: 2023-10-26
    Description: Ocean turbulent mixing is a key process affecting the uptake and redistribution of heat, carbon, nutrients, oxygen and other dissolved gasses. Vertical turbulent diffusivity sets the rates of water mass transformations and ocean mixing, and is intrinsically an average quantity over process time scales. Estimates based on microstructure profiling, however, are typically obtained as averages over individual profiles. How representative such averaged diffusivities are, remains unexplored in the quiescent Arctic Ocean. Here, we compare upper ocean vertical diffusivities in winter, derived from the 7Be tracer‐based approach to those estimated from direct turbulence measurements during the year‐long Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, 2019–2020. We found that diffusivity estimates from both methods agree within their respective measurement uncertainties. Diffusivity estimates obtained from dissipation rate profiles are sensitive to the averaging method applied, and the processing and analysis of similar data sets must take this sensitivity into account. Our findings indicate low characteristic diffusivities around 10〈sup〉−6〈/sup〉 m〈sup〉2〈/sup〉 s〈sup〉−1〈/sup〉 and correspondingly low vertical heat fluxes.
    Description: Plain Language Summary: Ocean turbulent mixing plays an important role in the uptake and redistribution of heat, carbon, nutrients, oxygen and other properties. For example, this process delivers nutrients to the sunlit surface ocean where they are utilized to produce plants (phytoplankton) for the ecosystem food web. However, strong changes in density within the upper Arctic Ocean hinder vertical transport of nutrients, such that nutrient fluxes are generally smaller than those observed elsewhere in the world ocean. Furthermore, low vertical transport rates isolate the surface ocean from heat input from below which helps protect the ice from melting. Here, we compare the strength of upper ocean mixing, an important parameter for the calculation of vertical transport, derived from two independent methods during the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) ice drift experiment, 2019–2020. This comparison allows us to better quantify the vertical diffusivity, and in turn also the vertical transport of for example, heat and nutrients in the ocean.
    Description: Key Points: Arctic Ocean vertical diffusivity (K〈sub〉z〈/sub〉) in the upper halocline in winter is O(10〈sup〉−6〈/sup〉) m〈sup〉2〈/sup〉 s〈sup〉−1〈/sup〉. Diffusivity estimates from 〈sup〉7〈/sup〉Be measurements and ocean microstructure profiling agree within a factor of 2. K〈sub〉z〈/sub〉 estimates from turbulent dissipation rate profiles are sensitive to the averaging method.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Research Council of Norway
    Description: National Science Foundation http://dx.doi.org/10.13039/100000001
    Description: https://doi.org/10.1594/PANGAEA.939816
    Description: https://doi.org/10.26008/1912/bco-dmo.861596.1
    Keywords: ddc:551.46 ; Arctic Ocean ; vertical mixing ; halocline ; winter ; turbulent diffusivity ; microstructure profiling
    Language: English
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  • 4
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    Upper limits of water contents in olivine and orthopyroxene of equilibrated chondrites and several achondrites (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"〉Hydroxyl defects in nominally anhydrous minerals (NAMs) were potential carriers of water in the early Solar System and might have contributed to the accretion of terrestrial water. To better understand this, we have conducted a nanoscale secondary ion mass spectrometry survey of water contents in olivine and orthopyroxene from a set of equilibrated ordinary chondrites of the L and LL groups (Baszkówka, Bensour, Kheneg Ljouâd, and Tuxtuac) and several ultramafic achondrites (Zakłodzie, Dhofar 125, Northwest Africa [NWA] 4969, NWA 6693, and NWA 7317). For calibration, we used terrestrial olivine and orthopyroxene with H〈sub〉2〈/sub〉O contents determined by Fourier transform infrared. Our 99.7% (~3SD) detection limits are 3.6–5.4 ppmw H〈sub〉2〈/sub〉O for olivine and 7.7–10.9 ppmw H〈sub〉2〈/sub〉O for orthopyroxene. None of the meteoritic samples studied consistently shows water contents above the detection limits. A few exceptions slightly above the detection limits are suspected of terrestrial contamination by ferric oxyhydroxides. If the meteorite samples investigated accreted in the presence of small amounts of water ice, the upper limits of water contents provided by our survey suggest that the retention of hydrogen during thermal metamorphism and differentiation was ineffective. We suggest that loss occurred through combinations of low internal pressures, high permeability along grain boundaries, and speciation of hydrogen into reduced compounds such as H〈sub〉2〈/sub〉 and methane, which are less soluble in NAMs than in water.〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Europlanet 2020 RI
    Keywords: ddc:549 ; chondrites ; achondrites ; olivine ; orthopyroxene ; water contents
    Language: English
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  • 5
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    Temperature and Salinity Anomalies in the Sea Surface Microlayer of the South Pacific During Precipitation Events (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"〉We present the results of salinity (ΔS) and temperature (ΔT) anomalies in the sea surface microlayer (SML) in relation to the underlying mixed bulk water (bulk). Several light to moderate rain events were recorded in the southern Pacific near Fiji using our remotely operated catamaran. Precipitation and evaporation drive freshwater fluxes across the sea surface (i.e., the SML) and are the most essential processes of the hydrologic cycle. However, measurements of the SML during precipitation are rare, but necessary to fully understand freshwater exchange at the air‐sea interface. Here we show that freshwater can mix rapidly with the bulk water through wind‐induced mixing, as ΔS and ΔT show a clear dependence on wind speed. At high wind speeds (5.1–11.6 m s〈sup〉−1〈/sup〉), anomalies approach zero (ΔS = −0.02 ± 0.49 g kg〈sup〉−1〈/sup〉, ΔT = −0.09 ± 0.46°C) but can reach ΔS = 1.00 ± 0.20 g kg〈sup〉−1〈/sup〉 and ΔT = −0.37 ± 0.09°C at lower wind speeds (0–2 m s〈sup〉−1〈/sup〉). We find shallow freshwater lenses and fronts, likely caused by past rainfall, with ΔS and ΔT of up to −1.11 g kg〈sup〉−1〈/sup〉 and 1.77°C, respectively. Our observations suggest that freshwater lenses can be very shallow (〈1 m depth) and missed by conventional measurements. In addition, the temperature and salinity in the SML respond to freshwater fluxes instantaneously. It highlights the role of the SML in a mechanistic understanding of the fate of freshwater over the ocean and, therefore, the global hydrologic cycle.〈/p〉
    Description: Plain Language Summary: Rain and evaporation are the most important processes in the global water cycle, causing either the supply to or the removal of freshwater from the upper ocean, thereby changing the salinity of the sea surface. Evaporation also removes heat and lowers the temperature on the ocean surface. We used the measurements of sea surface microlayer (SML) salinity and temperature as key indicators to study hydrologic cycle processes during our cruise with the RV Falkor in the South Pacific and found that freshwater mixes rapidly with the underlying bulk water during strong winds (5.1–11.6 m s〈sup〉−1〈/sup〉). We also detected shallow freshwater lenses and fronts, most likely caused by past rainfall, with ΔS and ΔT of up to −1.11 g kg〈sup〉−1〈/sup〉 and 1.77°C, respectively. Our observations suggest that freshwater lenses can occur at the sea surface and that the SML respond to freshwater fluxes instantaneously. It highlights the role of the SML for future studies of the global hydrologic cycle.〈/p〉
    Description: Key Points: Small scale air‐sea interactions (freshwater fluxes) during precipitation were investigated in the southern Pacific. Temperature and salinity anomalies occur with a high spatial variability.Measurements with remote controlled catamaran revealed shallow freshwater lenses, which were not detectable with ship based measurements.
    Description: German Research Foundation
    Description: https://doi.org/10.7284/908805
    Description: https://www.rvdata.us/search/cruise/FK191120
    Description: https://bec.icm.csic.es/
    Description: https://smos-diss.eo.esa.int/
    Description: https://doi.org/10.48670/moi-00165
    Description: https://disc.gsfc.nasa.gov/datasets/GPM_3IMERGHH_06/summary
    Keywords: ddc:551.46 ; salinity and temperature anomalies ; sea surface microlayer ; freshwater fluxes ; global hydrologic cycle ; research catamaran
    Language: English
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  • 6
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    Rhine flood stories: Spatio‐temporal analysis of historic and projected flood genesis in the Rhine River basin (2023)
    John Wiley & Sons, Inc. | Hoboken, USA
    Details
    Publication Date: 2023-07-19
    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 genesis of floods in large river basins often is complex. Streamflow originating from precipitation and snowmelt and different tributaries can superimpose and cause high water levels, threatening cities and communities along the riverbanks. For better understanding the mechanisms (origin and composition) of flood events in large and complex basins, we capture and share the story behind major historic and projected streamflow peaks in the Rhine River basin. Our analysis is based on hydrological simulations with the mesoscale Hydrological Model forced with both meteorological observations and an ensemble of climate projections. The spatio‐temporal analysis of the flood events includes the assessment and mapping of antecedent liquid precipitation, snow cover changes, generated and routed runoff, areal extents of events, and the above‐average runoff from major sub‐basins up to 10 days before a streamflow peak. We introduce and assess the analytical setup by presenting the flood genesis of the two well‐known Rhine floods that occurred in January 1995 and May 1999. We share our extensive collection of event‐based Rhine River flood genesis, which can be used in‐ and outside the scientific community to explore the complexity and diversity of historic and projected flood genesis in the Rhine basin. An interactive web‐based viewer provides easy access to all major historic and projected streamflow peaks at four locations along the Rhine. The comparison of peak flow genesis depending on different warming levels elucidates the role of changes in snow cover and precipitation characteristics in the (pre‐)Alps for flood hazards along the entire channel of the Rhine. Furthermore, our results suggest a positive correlation between flood magnitudes and areal extents of an event. Further hydro‐climatological research is required to improve the understanding of the climatic impact on the Rhine and beyond.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The genesis of riverine floods in large river basins often is complex. Streamflow originating from precipitation and snowmelt and different tributaries can superimpose and cause high water levels threatening cities and communities along the riverbanks. In this study, we capture and share the story behind major historic and projected streamflow peaks in the large and complex basin of the Rhine River.〈boxed-text position="anchor" content-type="graphic" id="hyp14918-blkfxd-0001" xml:lang="en"〉 〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:08856087:media:hyp14918:hyp14918-toc-0001"〉
    Description: https://doi.org/10.5281/zenodo.3239055
    Description: https://github.com/ERottler/rhine-flood-genesis
    Description: http://natriskchange.ad.umwelt.uni-potsdam.de:3838/rhine-flood-genesis
    Description: https://b2share.eudat.eu/records/72d7a4f5d38043d1a137228b39c7ecc3
    Keywords: ddc:551.46 ; climate change ; flood composition ; flood genesis ; mHM ; model simulations ; quantile extent ; Rhine River ; spatio‐temporal analysis ; web‐based dashboard
    Language: English
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  • 7
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    Changes in Seasonality of Saltwater Inflows Caused Exceptional Warming Trends in the Western Baltic Sea (2023)
    Details
    Publication Date: 2023-07-19
    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"〉During the last decades, the Baltic Sea has been among the fastest warming seas in the world. The warming is mainly driven by increasing air temperatures but deeper water layers can also be warmed by lateral advection of heat. By analyzing a 159 years long (1850–2008) hindcast simulation of the Baltic Sea, we link the exceptionally strong bottom water warming in the western Baltic Sea to a shift in the seasonality of saltwater inflows from the North Sea to the Baltic Sea. Over the model period, warm summer and early autumn inflows have increased while cold winter inflows have decreased. Sensitivity experiments reveal that these changes were partly driven by a shift in river runoff seasonality. The strong warming could lead to faster oxygen depletion in the affected layers and thus have ecological consequences.〈/p〉
    Description: Plain Language Summary: The Baltic Sea is home to various marine and freshwater species and an important economic factor for the surrounding countries. Like other seas, the Baltic Sea is getting warmer due to climate change. The water at the surface warms especially fast because it takes up heat from the warming atmosphere. After some time, temperatures also increase in deeper layers. However, some deep parts in the western Baltic Sea are warming even faster than the sea surface. In our study, we investigate if the exceptional warming can be explained by an increase in warm saltwater inflows from the North Sea. Hence, we use a model simulation of the Baltic Sea for over 150 years to compare long time series of warm inflows and the temperatures in the deep layers of the western Baltic Sea. We find a strong correlation. Thus, we can link the exceptional warming in the deep layers of the western Baltic Sea during the last decades to an increase in warm inflows. The warming has ecological consequences since in warmer water, the oxygen is consumed faster and the deep water layers of the Baltic Sea are suffering from low oxygen concentrations.〈/p〉
    Description: Key Points: Summer and early autumn salt import into the Baltic Sea increased significantly since 1851 compared to the annual salt import.〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Salt import between June and October is highly correlated with the annual sub‐thermocline temperature maximum in the western Baltic Sea.〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The shift in inflow seasonality was partly caused by seasonal changes in river runoff.〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: https://doi.io-warnemuende.de/10.12754/data-2023-0006
    Description: https://doi.io-warnemuende.de/10.12754/data-2018-0004
    Keywords: ddc:551.46 ; Baltic Sea ; saltwater inflows ; salinity dynamics ; global warming ; water temperature ; regional climate variability
    Language: English
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  • 8
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    Evolution of Global Ocean Tide Levels Since the Last Glacial Maximum (2023)
    Details
    Publication Date: 2023-07-19
    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 study addresses the evolution of global tidal dynamics since the Last Glacial Maximum focusing on the extraction of tidal levels that are vital for the interpretation of geologic sea‐level markers. For this purpose, we employ a truly‐global barotropic ocean tide model which considers the non‐local effect of Self‐Attraction and Loading. A comparison to a global tide gauge data set for modern conditions yields agreement levels of 65%–70%. As the chosen model is data‐unconstrained, and the considered dissipation mechanisms are well understood, it does not have to be re‐tuned for altered paleoceanographic conditions. In agreement with prior studies, we find that changes in bathymetry during glaciation and deglaciation do exert critical control over the modeling results with minor impact by ocean stratification and sea ice friction. Simulations of 4 major partial tides are repeated in time steps of 0.5–1 ka and augmented by 4 additional partial tides estimated via linear admittance. These are then used to derive time series from which the tidal levels are determined and provided as a global data set conforming to the HOLSEA format. The modeling results indicate a strengthened tidal resonance by M〈sub〉2〈/sub〉, but also by O〈sub〉1〈/sub〉, under glacial conditions, in accordance with prior studies. Especially, a number of prominent changes in local resonance conditions are identified, that impact the tidal levels up to several meters difference. Among other regions, resonant features are predicted for the North Atlantic, the South China Sea, and the Arctic Ocean.〈/p〉
    Description: Plain Language Summary: We discuss changes in ocean tides during the last 21,000 years. This time marks the Last Glacial Maximum when large parts of the Earth's surface were covered by ice and the sea level was more than 100 m lower than today. Such a low sea level means that many regions of the Earth became land and the ocean's depth changed markedly. The distribution of land and water dominates changes in the tidal levels like the spring or neap tide. With a tidal computer model recently developed by our group, we determine these tidal levels for different times steps from 21,000 years to today. Tidal levels are important for geologists who want to understand former sea level changes with samples found at ancient shorelines. As many of such samples were deposited at a specific tidal level, our modeled information will help them to relate their height to the mean sea‐level. Of course, our model is not the only one that can estimate such changes, but we discuss the advantages of our recent development over previous tools available.〈/p〉
    Description: Key Points: Evolution of four major partial tides from Last Glacial Maximum until present times.〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Validation of the employed ocean tide model with present‐day tide gauge data and dissipation rates.〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Diligent derivation of global tidal levels for the interpretation of sea level indexpoints.〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551.46 ; ocean tide modeling ; tidal dissipation ; tidal levels ; indicative range ; sea level index points ; numerical modeling
    Language: English
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  • 9
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    Silicon and iron isotopes in components of enstatite chondrites: Implications for metal–silicate–sulfide fractionation in the solar nebula (2023)
    Details
    Publication Date: 2023-07-19
    Description: Silicon and iron isotope compositions of different physically separated components of enstatite chondrites (EC) were determined in this study to understand the role of nebular and planetary scale events in fractionating Si and Fe isotopes of the terrestrial planet‐forming region. We found that the metal–sulfide nodules of EC are strongly enriched in light Si isotopes (δ〈sup〉30〈/sup〉Si ≥ −5.61 ± 0.12‰, 2SD), whereas the δ〈sup〉30〈/sup〉Si values of angular metal grains, magnetic, slightly magnetic, and non‐magnetic fractions become progressively heavier, correlating with their Mg# (Mg/(Mg+Fe)). White mineral phases, composed primarily of SiO〈sub〉2〈/sub〉 polymorphs, display the heaviest δ〈sup〉30〈/sup〉Si of up to +0.23 ± 0.10‰. The data indicate a key role of metal–silicate partitioning on the Si isotope composition of EC. The overall lighter δ〈sup〉30〈/sup〉Si of bulk EC compared to other planetary materials can be explained by the enrichment of light Si isotopes in EC metals along with the loss of isotopically heavier forsterite‐rich silicates from the EC‐forming region. In contrast to the large Si isotope heterogeneity, the average Fe isotope composition (δ〈sup〉56〈/sup〉Fe) of EC components was found to vary from −0.30 ± 0.08‰ to +0.20 ± 0.04‰. A positive correlation between δ〈sup〉56〈/sup〉Fe and Ni/S in the components suggests that the metals are enriched in heavy Fe isotopes whereas sulfides are the principal hosts of light Fe isotopes in the non‐magnetic fractions of EC. Our combined Si and Fe isotope data in different EC components reflect an inverse correlation between δ〈sup〉30〈/sup〉Si and δ〈sup〉56〈/sup〉Fe, which illustrates that partitioning of Si and Fe among metal, silicate, and sulfidic phases has significantly fractionated Si and Fe isotopes under reduced conditions. Such isotope partitioning must have occurred before the diverse components were mixed to form the EC parent body. Evaluation of diffusion coefficients of Si and Fe in the metal and non‐metallic phases suggests that the Si isotope compositions of the silicate fractions of EC largely preserve information of their nebular processing. On the other hand, the Fe isotopes might have undergone partial or complete re‐equilibration during parent body metamorphism. The relatively uniform δ〈sup〉56〈/sup〉Fe among different types of bulk chondrites and the Earth, despite Fe isotope differences among their components, demonstrates that the chondrite parent bodies were not formed by random mixing of chondritic components from different locations in the disk. Instead, the chondrite components mostly originated in the same nebular reservoir and Si and Fe isotopes were fractionated either due to gas–solid interactions and associated changes in physicochemical environment of the nebular reservoir and/or during parent body processing. The heavier Si isotope composition of the bulk silicate Earth may require accretion of chondritic and/or isotopically heavier EC silicates along with cumulation of refractory forsterite‐rich heavier silicates lost from the EC‐forming region to form the silicate reservoir of the Earth.〈/p〉
    Description: DFG, German Research Foundation
    Keywords: ddc:549 ; enstatite chondrites ; silicon istotopes ; iron isotopes ; isotopic evolution
    Language: English
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  • 10
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    Bottom‐Current Variability and the Relationship With Topography and Sedimentary Processes in the Drake Passage (2023)
    Details
    Publication Date: 2024-02-21
    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"〉Bottom‐current related sediments have been commonly used for paleoceanographic reconstructions. However, the strength and variability of bottom currents are poorly understood and thus the processes that control sedimentation in deep environments are not clear. In this study, we focus on the Drake Passage, which is connected to the Antarctic Circumpolar Current, that has a major impact on the global climate. We studied the intensity and variability of bottom currents and how they are related to sedimentary processes. For this purpose, we used 27‐years from GLORYS12 Mercator Ocean reanalysis at high resolution to evaluate the bottom current dynamics. Geophysical data and surface grain size measurements were used to identify the type of sediment deposits. Our results show that the dynamics of bottom currents is disconnected from the sea surface dynamics, and bottom circulation is strongly controlled by the rough topography of the Drake Passage. The patterns for the first modes of bottom‐current variability are related to the local topography and seem to generally control the distribution of contourites. The second and third EOF modes show patterns in the bottom currents that differ from the mean field, and they may affect the rate of erosion and deposition differently. Time series of bottom currents reveals multiple high‐speed current events, but contourite drifts seem to accumulate preferentially in zones of slow and stable bottom currents. Our study highlights the potential of using ocean reanalysis to better constrain bottom currents in zones of scarce data and to plan future campaigns of direct measurements.〈/p〉
    Description: Plain Language Summary: As a result of its unique geography, the Southern Ocean contains the largest ocean current in the world ocean, the Antarctic Circumpolar Current (ACC). The Drake Passage (DP) is the major geographic constriction for the ACC and exerts a strong control on the exchange of physical, chemical, and biological properties between the ocean basins. Yet, the bottom dynamics and the relation with sedimentary processes remain to be studied. We analyzed the currents flowing near the seafloor using a high resolution (1°/12°) reanalysis and compared the bottom dynamics with the characteristics of the seafloor sediments obtained using geophysical data sets and sediment cores. We found that the complex topography of the DP plays an essential role in bottom‐current dynamics and that the circulation pattern near the seabed is often different from the sea surface circulation. The largest sediment deposits are located in the zones with weakest bottom current activity.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉The variability of bottom currents in the Drake Passage is described using the ocean reanalysis GLORYS12〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Bottom currents are strongly controlled by the topography and are often disconnected from the surface circulation〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Sedimentary processes are dominated by the influence of local topography and bottom currents〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Deutscher Akademischer Austauschdienst http://dx.doi.org/10.13039/501100001655
    Description: https://doi.org/10.48670/moi-00021
    Description: https://doi.org/10.17882/59800
    Description: https://doi.org/10.1594/PANGAEA.864950
    Description: https://doi.org/10.1594/PANGAEA.864807
    Description: https://doi.org/10.1594/PANGAEA.862944
    Description: https://doi.pangaea.de/10.1594/PANGAEA.907140
    Description: https://doi.org/10.1038/s41597-022-01366-7
    Description: http://www.eoas.ubc.ca/7Erich/map.html
    Description: https://odv.awi.de/
    Keywords: ddc:551.46 ; Drake Passage ; bottom currents ; sedimentary features ; Southern Ocean ; bathymetry
    Language: English
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  • 11
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    High‐Resolution Simulations of the Plume Dynamics in an Idealized 79°N Glacier Cavity Using Adaptive Vertical Coordinates (2023)
    Details
    Publication Date: 2024-02-21
    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"〉For better projections of sea level rise, two things are needed: an improved understanding of the contributing processes and their accurate representation in climate models. A major process is basal melting of ice shelves and glacier tongues by the ocean, which reduces ice sheet stability and increases ice discharge into the ocean. We study marine melting of Greenland's largest floating ice tongue, the 79° North Glacier, using a high‐resolution, 2D‐vertical ocean model. While our fjord model is idealized, the results agree with observations of melt rate and overturning strength. Our setup is the first application of adaptive vertical coordinates to an ice cavity. Their stratification‐zooming allows a vertical resolution finer than 1 m in the entrainment layer of the meltwater plume, which is important for the plume development. We find that the plume development is dominated by entrainment only initially. In the stratified upper part of the cavity, the subglacial plume shows continuous detrainment. It reaches neutral buoyancy near 100 m depth, detaches from the ice, and transports meltwater out of the fjord. Melting almost stops there. In a sensitivity study, we show that the detachment depth depends primarily on stratification. Our results contribute to the understanding of ice–ocean interactions in glacier cavities. Furthermore, we suggest that our modeling approach with stratification‐zooming coordinates will improve the representation of these interactions in global ocean models. Finally, our idealized model topography and forcing are close to a real fjord and completely defined analytically, making the setup an interesting reference case for future model developments.〈/p〉
    Description: Plain Language Summary: The global increase of sea levels is a consequence of human‐induced climate change. It presents a threat to coastal regions and demands action to protect human life and infrastructure near the coast. Planning protective measures requires projections of sea level rise, computed with climate models. We present an approach to improve the simulation of an important contributor to sea level rise: melting of floating ice shelves by ocean circulation. Our modeling approach uses a vertical model grid that evolves over time. The temporal evolution depends on the density structure of the ocean. Large density differences appear just below an ice shelf, where fresh meltwater mixes with salty seawater. The adaptive grid of our model resolves this mixing process in great detail. This is important for an accurate computation of the melt rate and enables us to study in depth the ice shelf–ocean interactions. We study them at the glacier tongue of the 79° North Glacier, which is Greenland's largest ice shelf. The physical understanding gained from our simulations is also applicable to other floating glacier tongues and ice shelves. We suggest that using the presented model technique in global ocean models can improve projections of melting and sea level rise.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Melting of the 79° North Glacier ice tongue by turbulent ocean currents is studied with an idealized 2D‐vertical fjord model〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The subglacial plume behaves like an entraining plume close to the grounding line and like a detraining gravity current further downstream〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉A vertical resolution finer than 1 m is achieved in the subglacial plume by using adaptive vertical coordinates that zoom to stratification〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: German Academic Exchange Service
    Description: https://doi.org/10.5281/zenodo.7755753
    Description: https://doi.org/10.5281/zenodo.7755908
    Description: https://doi.org/10.5281/zenodo.7741925
    Description: https://doi.org/10.1594/PANGAEA.885358
    Keywords: ddc:551.46 ; numerical model ; glacier fjord ; Greenland ; physical oceanography ; ice melting ; high‐resolution
    Language: English
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  • 12
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    High‐Resolution, Basin‐Scale Simulations Reveal the Impact of Intermediate Zonal Jets on the Atlantic Oxygen Minimum Zones (2023)
    Details
    Publication Date: 2024-02-05
    Description: Eastward zonal jets at intermediate depths of 300–800 m connect the oxygen‐rich western boundary of the Atlantic basin with the oxygen minimum zones (OMZs) on the eastern boundary. They are not well represented in climate models because the low horizontal resolution of these models yields excessive viscosity. We use two physical‐biogeochemical model configurations of the Tropical Atlantic to show that the increase in resolution results in more robust intermediate zonal jets and a better representation of the OMZs. The OMZ structure is distorted at low‐resolution as surface, westward jets advect low‐oxygen waters from the eastern boundary much further west than in the climatology. The emergence of robust eastward jets in the high‐resolution run alleviate this problem and reproduce the Atlantic OMZs more accurately. The asymmetry between westward and eastward jets occurs because the former are associated with homogenous potential vorticity regions originating in the eastern boundary while the latter are associated with potential vorticity gradients. Intermediate, eastward jets constrain the westward expansion of the OMZs by supplying oxygen to their western edge. Within the OMZs, higher resolution allows a better representation of the boundary current system and eddying processes at depth which redistribute of low oxygen values from the productive eastern boundary. Basin‐scale, high‐resolution simulations reproduce more accurately the transfer of energy across scales that results in robust zonal jets as well as their impact on the ocean biogeochemistry. Accurate model predictions provide a pathway to disentangle natural and anthropogenic causes of ocean deoxygenation.
    Description: Plain Language Summary: Long‐term averages of ocean velocities reveal the existence of east‐west, alternating currents along multiple latitudes. These currents are difficult to observe and model because of their small speeds at great depths. Despite their low intensity, in the long‐term they can transport tracers across the ocean basins with oxygen being a very important one as it provides conditions for aerobic respiration in so‐called oxygen minimum zones (OMZs) on the eastern side of the basin. Long‐term measurements show that oxygen concentrations are decreasing in various regions of the ocean and that OMZs are expanding, which can be a problem as these regions may become inhospitable for aerobic life. That is why we need to understand the processes that supply oxygen to OMZs and are important for their evolution with time. Models can be used as tools for testing hypotheses regarding the expansion or contraction of OMZs in the future. However, models must be shown to correctly simulate the dynamics and biogeochemistry of the region as a whole. Our results show that these intermediate east‐west current systems are important in structuring the OMZs and that higher‐resolution, basin‐scale simulations are necessary to correctly simulate their impact on oxygen concentrations in the ocean.
    Description: Key Points: Intermediate, eastward zonal jets are an important oxygen supply route to the oxygen minimum zones and modulate their westward extent. Robust, intermediate zonal jets emerge in a high‐resolution (3 km), basin‐scale simulation with robust eddying motions at depth. A correct representation of the zonal jets in climate models is key for reliable, long‐term forecasts of ocean deoxygenation.
    Description: Changing Earth ‐ Helmholtz Association
    Description: https://doi.org/10.5281/zenodo.7229219
    Description: https://doi.org/10.5281/zenodo.7081664
    Description: https://doi.org/10.5281/zenodo.7234366
    Keywords: ddc:551.46 ; zonal jets ; oxygen minimum zones ; biogeochemical modeling ; Tropical Atlantic
    Language: English
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  • 13
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    Aluminum Components in Bridgmanite Coexisting With Corundum and the CF‐Phase With Temperature (2023)
    Details
    Publication Date: 2023-11-02
    Description: Abstract Phase relations in the MgSiO〈sub〉3〈/sub〉–MgAl〈sub〉2〈/sub〉O〈sub〉4〈/sub〉–Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 system are investigated at 27 GPa and 2000–2600 K using a multi‐anvil apparatus. The AlAlO〈sub〉3〈/sub〉 content in the bridgmanite increases from 8.6 to 20.0 mol% with increasing temperature from 2000 to 2600 K, while the MgAlO〈sub〉2.5〈/sub〉 content remains nearly constant, that is, 3–4 mol% at these temperatures. Therefore, the presence of an additional Al‐bearing phase suppresses the oxygen vacancy substitution for Al〈sup〉3+〈/sup〉 in bridgmanite. Conversely, significant amounts of the Al〈sub〉8/3〈/sub〉O〈sub〉4〈/sub〉 component can be dissolved into the calcium‐ferrite type MgAl〈sub〉2〈/sub〉O〈sub〉4〈/sub〉–Mg〈sub〉2〈/sub〉SiO〈sub〉4〈/sub〉–Al〈sub〉8/3〈/sub〉O〈sub〉4〈/sub〉 phase (CF‐phase), implying that the CF‐phase likely contains some amount of vacancies. Therefore, the CF‐phase could also be a candidate mineral for transporting volatiles into the lower mantle. Our results, combined with previous studies on Al‐bearing bridgmanite, indicate that, once the Al per formula unit exceeds 0.12 in bridgmanite, the MgAlO〈sub〉2.5〈/sub〉 content remains nearly constant and the AlAlO〈sub〉3〈/sub〉 component becomes dominant.
    Description: Plain Language Summary: Bridgmanite, the most abundant mineral in the Earth's mantle, can contain Al〈sup〉3+〈/sup〉 in the forms of MgAlO〈sub〉2.5〈/sub〉 and AlAlO〈sub〉3〈/sub〉. To constrain the substitution mechanism of Al〈sup〉3+〈/sup〉 in bridgmanite, we investigate the MgAlO〈sub〉2.5〈/sub〉 and AlAlO〈sub〉3〈/sub〉 contents in bridgmanite coexisting with a calcium‐ferrite type phase and corundum at different temperatures. Our results demonstrate that the MgAlO〈sub〉2.5〈/sub〉 content reaches saturation (3–4 mol%) when an additional Al‐bearing phase exists in the system.
    Description: Key Points: The MgAlO〈sub〉2.5〈/sub〉 content in bridgmanite remains constant with temperature when bridgmanite coexists with corundum and the CF‐phase. The MgAlO〈sub〉2.5〈/sub〉 content in bridgmanite reaches a solubility of 3–4 mol% when bridgmanite coexists with an additional Al‐bearing phase. A significant amount of the Al〈sub〉8/3〈/sub〉O〈sub〉4〈/sub〉 component can be dissolved into the CF‐phase.
    Description: HORIZON EUROPE European Research Council http://dx.doi.org/10.13039/100019180
    Description: Japan Society for the Promotion of Science London http://dx.doi.org/10.13039/501100000646
    Description: cooperative research program of the Earthquake Research Institute
    Description: https://doi.org/10.5281/zenodo.7512647
    Keywords: ddc:549 ; Al‐bearing bridgmanite ; Al substitute mechanism ; phase relation ; volatile
    Language: English
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  • 14
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    Twinned calcite as an indicator of high differential stresses and low shock pressure conditions during impact cratering (2023)
    Details
    Publication Date: 2023-11-02
    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"〉Shock‐related calcite twins are characterized in calcite‐bearing metagranite cataclasites within crystalline megablocks of the Ries impact structure, Germany, as well as in cores from the FBN1973 research drilling. The calcite likely originates from pre‐impact veins within the Variscan metagranites and gneisses, while the cataclasis is due to the Miocene impact. Quartz in the metagranite components does not contain planar deformation features, indicating low shock pressures (〈7 GPa). Calcite, however, shows a high density (>1/μm) of twins with widths 〈100 nm. Different types of twins (〈italic toggle="no"〉e〈/italic〉‐, 〈italic toggle="no"〉f‐〈/italic〉, and 〈italic toggle="no"〉r〈/italic〉‐twins) crosscutting each other can occur in one grain. Interaction of 〈italic toggle="no"〉r〈/italic〉‐ and 〈italic toggle="no"〉f〈/italic〉‐twins results in 〈italic toggle="no"〉a〈/italic〉‐type domains characterized by a misorientation relative to the host with a misorientation angle of 35°–40° and a misorientation axis parallel to an 〈italic toggle="no"〉a〈/italic〉‐axis. Such 〈italic toggle="no"〉a〈/italic〉‐type domains have not been recorded from deformed rocks in nature before. The high twin density and activation of different twin systems in one grain require high differential stresses (on the order of 1 GPa). Twinning of calcite at high differential stresses is consistent with deformation during impact cratering at relatively low shock pressure conditions. The twinned calcite microstructure can serve as a valuable low shock barometer.〈/p〉
    Description: Bavarian Natural History Collections
    Keywords: ddc:549 ; Ries impact structure ; twinned calcites ; cataclasis
    Language: English
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  • 15
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    A zircon classification scheme for sedimentary provenance analysis using radiation damage (2023)
    John Wiley & Sons, Inc. | Hoboken, USA
    Details
    Publication Date: 2023-11-17
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Detrital single‐grain zircon U–Pb geochronology is a powerful tool for provenance studies if information on the source rocks is available. This paper proposes a new source‐rock classification tool that uses the degree of annealing of radiation damage in detrital zircon; the annealing is expressed by the relationship between the width (full‐width at half‐maximum; FWHM) of the 〈italic toggle="no"〉v〈/italic〉〈sub〉3〈/sub〉[SiO〈sub〉4〈/sub〉] Raman band at ~1008 cm〈sup〉−1〈/sup〉 and the calculated α‐dose. The host rocks of the zircons are classified into three types according to their emplacement process and/or thermal history: volcanic and rapidly cooled plutonic and high‐grade metamorphic rocks (type 1); rocks with hydrothermal zircons (type 2); slowly cooled igneous and metamorphic rocks (type 3). We construct a naive Bayes prediction model by training it with a collection of zircons of known types. The unknown zircons are assigned a probability of derivation from a specific host‐rock type. This classification scheme is best used as an accessory tool in provenance studies that apply detrital zircon U–Pb geochronology.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Zircons are classified into three types based on annealing state revealed by Raman analysis and calculated α‐dose. This classification can be used to distinguish zircon in provenance study.〈boxed-text position="anchor" content-type="graphic" id="gj4751-blkfxd-0001" xml:lang="en"〉 〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:00721050:media:gj4751:gj4751-toc-0001"〉 〈/graphic〉 〈/boxed-text〉〈/p〉
    Description: Natural Science Foundation of Hubei Province http://dx.doi.org/10.13039/501100003819
    Description: National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809
    Keywords: ddc:549 ; annealing ; Bayesian probability ; provenance analysis ; radiation damage ; zircon classification
    Language: English
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  • 16
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    Mid‐Infrared Spectroscopy of Feldspars From the Bühl Basalt (Northern Hesse, Germany) Formed Under Reducing Conditions as Terrestrial Analogue of Mercury for MERTIS (2023)
    Details
    Publication Date: 2023-12-19
    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 MErcury Radiometer and Thermal Infrared Spectrometer instrument onboard the BepiColombo spacecraft is designed to investigate Mercury’s surface in the mid‐infrared (mid‐IR). Based on MESSENGER data and modeling, Mercury is thought to be evolved under highly reducing conditions (e.g., McCubbin et al., 2017, 〈ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1002/2017JE005367"〉https://doi.org/10.1002/2017JE005367〈/ext-link〉; Namur & Charlier, 2017, 〈ext-link ext-link-type="uri" xlink:href="https://doi.org/10.1038/ngeo2860"〉https://doi.org/10.1038/ngeo2860〈/ext-link〉). The modeling also indicates that Mercury's surface is rich in feldspar. However, it is unknown if reducing conditions during the emplacement of volcanic melts have an influence on the IR properties of feldspars. Therefore, we investigated basaltic samples from the Bühl quarry in northern Hesse, Germany, that evolved under reducing conditions in the mid‐IR and compared the spectra with samples that experienced more oxidizing conditions during their formation. The Bühl samples are feldspar‐rich and contain metallic iron in some areas. Our investigations show that there are no differences between feldspars that formed under different oxidizing conditions. All spectral properties could be explained by well‐known factors that affect mid‐IR spectra of silicates.〈/p〉
    Description: Plain Language Summary: ESA's and Japan Aerospace Exploration Agency’s spacecraft BepiColombo is equipped, beside other instruments, with a thermal infrared (IR) radiometer and spectrometer called MErcury Radiometer and Thermal Infrared Spectrometer (MERTIS). For the accurate interpretation of the data from the MERTIS instrument, laboratory analog material is necessary. This analog material must fulfill different characteristics, such as different chemical and mineralogical compositions. Another not yet studied property is the availability of oxygen during the formation of the minerals. Depending on how much oxygen is available, different minerals form. However, this is an important feature, because Mercury is thought to have evolved under highly reducing conditions, as opposed to Earth where nearly all material formed significant more oxidizing conditions. One phase that is strongly associated with reducing magma formation conditions is metallic iron. There are only few natural outcrops on Earth, were stronger reducing conditions were present so that metallic iron could be formed. One of these outcrops is the Bühl quarry in northern Hesse, Germany. From there we used different samples to analyze the effect of oxygen availability on mid‐IR spectra of plagioclase feldspars.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉We present infrared spectra of basaltic samples from the Bühl, Hesse, Germany in preparation of the MERTIS experiment〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Comparison of feldspars formed at different oxygen fugacities showed no spectral differences〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉This is an important result for MERTIS, which will investigate Mercury that formed under reducing conditions〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: DLR
    Description: http://bc-mertis-pi.uni-muenster.de/
    Keywords: ddc:549 ; infrared reflectance spectroscopy ; feldspars ; Bühl basalt ; reducing conditions ; Mercury ; MERTIS
    Language: English
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  • 17
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    Growth of kyanite and Fe‐Mg chloritoid in Fe2O3‐rich high‐pressure–low‐temperature metapelites and metapsammites: A case study from the Massa Unit (Alpi Apuane, Italy) (2023)
    Details
    Publication Date: 2024-01-26
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Chloritoid and kyanite coexist in metapelites from the high‐pressure/low‐temperature Massa Unit in the Alpi Apuane metamorphic complex (Northern Apennines, Italy). The composition of chloritoid is extremely variable throughout the Massa Unit. Fe‐chloritoid occurs in association with hematite‐free, graphite‐bearing schists, whereas strongly zoned Fe‐Mg chloritoid is found with hematite and kyanite. We investigated the effect of different bulk Fe〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 contents in controlling chloritoid composition through phase equilibria modelling of four selected samples, representative of the different chloritoid‐bearing parageneses found in the Massa Unit. The ferric iron content, measured through wet chemical titration, ranges from 0 (graphite‐chloritoid schist) to 73% of the total iron (hematite‐chloritoid schist). We show that Mg‐rich chloritoid compositions and stability of kyanite at greenschist to blueschist facies conditions can be reproduced in the MnO–Na〈sub〉2〈/sub〉O–K〈sub〉2〈/sub〉O–FeO–MgO–Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉–SiO〈sub〉2〈/sub〉–H〈sub〉2〈/sub〉O–TiO〈sub〉2〈/sub〉–O (MnNKFMASHTO) chemical system only considering the presence of significant amounts of ferric iron as part of the bulk composition. The stabilization of kyanite at lower grade is directly linked to the presence of Fe〈sub〉2〈/sub〉O〈sub〉3〈/sub〉, which renders the reactive bulk rock composition effectively enriched in Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 with respect to Fe and Mg. We also document that high Fe〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 contents exacerbate the effect of chloritoid fractionation, producing strongly zoned Fe‐Mg‐chloritoid grains. Finally, the P–T modelling of the Massa Units performed in this study allows, for the first time, the recognition of a two‐stage evolution at peak conditions, with an earlier pressure peak (1.2–1.3 GPa at 350–400°C), and a later thermal peak (0.7–1.1 GPa at 440–480°C), compatible with subduction, underthrusting and exhumation of the Adria continental margin during growth of the Northern Apennine orogenic wedge.〈/p〉
    Description: https://data.mendeley.com/datasets/wm3nwkrd4m/1
    Keywords: ddc:549 ; chloritoid ; ferric iron ; kyanite ; Northern Apennines ; phase equilibria modelling
    Language: English
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  • 18
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    Seasonal Prediction of Arabian Sea Marine Heatwaves (2023)
    Details
    Publication Date: 2024-01-30
    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"〉Marine heatwaves are known to have a detrimental impact on marine ecosystems, yet predicting when and where they will occur remains a challenge. Here, using a large ensemble of initialized predictions from an Earth System Model, we demonstrate skill in predictions of summer marine heatwaves over large marine ecosystems in the Arabian Sea seven months ahead. Retrospective forecasts of summer (June to August) marine heatwaves initialized in the preceding winter (November) outperform predictions based on observed frequencies. These predictions benefit from initialization during winters of medium to strong El Niño conditions, which have an impact on marine heatwave characteristics in the Arabian Sea. Our probabilistic predictions target spatial characteristics of marine heatwaves that are specifically useful for fisheries management, as we demonstrate using an example of Indian oil sardine (〈italic〉Sardinella longiceps〈/italic〉).〈/p〉
    Description: Plain Language Summary: Marine heatwaves (MHWs) are prolonged extreme events associated with exceptionally high ocean water temperatures. Such events impose heat stress on marine life, and thus predicting such events is beneficial for management applications. In this work we show that the occurrence of MHWs in summer in the Arabian Sea can be skilfully predicted seven month in advance. Our prediction system benefits from the information of sea surface temperature anomalies in the eastern Pacific Ocean in the preceding winter, among other aspects. Our predictions suggest potential for using climate information in fisheries management in this region.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Summer marine heatwaves in the Arabian Sea are predictable seven months in advance〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉The prediction skill in summer is mainly associated with a preceding El Niño event in winter〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Probabilistic predictions of Arabian Sea area under heatwave can be tailored to benefit fisheries〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: DFG
    Description: Universität Hamburg http://dx.doi.org/10.13039/501100005711
    Description: Cedars‐Sinai Medical Center http://dx.doi.org/10.13039/100013015
    Description: Marine Institute http://dx.doi.org/10.13039/501100001627
    Description: Copernicus Climate Change Service
    Description: Aigéin, Aeráid, agus athrú Atlantaigh
    Description: EU
    Description: http://dx.doi.org/10.7289/V5SQ8XB5
    Description: http://hdl.handle.net/hdl:21.14106/f2fdc61b13828ed5284f4e4ab41e63f8a84c6e52
    Description: http://hdl.handle.net/hdl:21.14106/27e73ed39cd59d2033e018a494e342383db53a0b
    Keywords: ddc:551.46 ; Arabian Sea ; marine heatwaves
    Language: English
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  • 19
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    Relative contributions of local heat storage and ocean heat transport to cold‐season Arctic Ocean surface energy fluxes in CMIP6 models (2023)
    John Wiley & Sons, Ltd | Chichester, UK
    Details
    Publication Date: 2024-03-25
    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 Arctic near‐surface air temperature increases most strongly during the cold season, and ocean heat storage has often been cited as a crucial component in linking the ice‐albedo radiative feedback, which is active in summer, and near‐surface air temperature increase in winter, when the lapse rate feedback contributes to Arctic warming. Here, we first estimate how much local heat storage and ocean heat transport contribute to net surface energy fluxes on a seasonal scale in CMIP6 models. We then compare contributions in a base state under weak anthropogenic forcing to a near‐present‐day state in which significant Arctic amplification is simulated. Our analysis indicates that, in a few regions, ocean heat transport plays a larger role for cold‐season net surface energy fluxes compared with local heat storage. Analyzing differences between past and near‐present‐day conditions suggests that the lapse rate feedback, which mainly acts during the cold season in warm water inflow regions, may be more strongly influenced than previously thought by increased ocean heat transport from lower latitudes.〈/p〉
    Description: 〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Arctic Ocean net upward surface energy fluxes in the cold season were decomposed into contributions from local heat storage (yellow, see schematic) and ocean heat transport (red). Our analysis of CMIP6 model output suggests that, in a few inflow regions, ocean heat transport contributes more to cold‐season net surface energy fluxes compared with local heat storage. In parts of these inflow regions, the relative contribution of ocean heat transport increased with time. 〈boxed-text position="anchor" id="qj4496-blkfxd-0001" content-type="graphic" xml:lang="en"〉〈graphic position="anchor" id="jats-graphic-1" xlink:href="urn:x-wiley:00359009:media:qj4496:qj4496-toc-0001"〉 〈/graphic〉 〈/boxed-text〉〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://esgf-node.llnl.gov/projects/cmip6/
    Description: https://nsidc.org/data/g10010
    Keywords: ddc:551.46 ; Arctic amplification ; CMIP6 ; heat storage and transport
    Language: English
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  • 20
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    Phase Stability of Al‐Bearing Dense Hydrous Magnesium Silicates at Topmost Lower Mantle Conditions: Implication for Water Transport in the Mantle (2022)
    Details
    Publication Date: 2023-01-17
    Description: In this study, we investigated the phase stability of Al‐free and Al‐bearing superhydrous phase B (shy‐B) up to 55 GPa and 2500 K. In comparison with Al‐free shy‐B, the incorporation of 11.7 wt.% Al2O3 in shy‐B expands the stability by ∼400–800 K at 20–30 GPa. The determined dehydration boundary for Al‐bearing phase D indicates that it could be present even at normal mantle geotherm conditions at 30–40 GPa. Up to 23.8 mol.% Al2O3 can be dissolved into the structures of akimotoite and bridgmanite as a result of the decomposition reactions of Al‐bearing shy‐B and phase D between 20 and 40 GPa. Results of further experiments indicate that δ‐AlOOH is the stable hydrous phase coexisting with Al‐depleted bridgmanite at pressures above 52 GPa. This study shows that the incorporation of Al in dense hydrous magnesium silicates can have a profound impact on our picture of the water cycle in the deep Earth.
    Description: Plain Language Summary: Constraining the deep cycle of water has a tremendous impact on our picture of the current state of the Earth and the evolution of the Earth's interior. Dense hydrous magnesium silicates (DHMSs) are considered potential H2O carriers in the Earth's mantle. However, the DHMSs can only be present at the relatively cold conditions of subduction slabs due their limited thermal stability. We determined the phase stability of Al‐bearing DHMSs at high pressure and temperature (P‐T) conditions. Our results show that the thermal stability of Al‐bearing shy‐B extends by 400–800 K with respect to its Al‐free counterpart at 600–800 km depth. The incorporation of Al also expands the phase stability of phase D and enhances the likelihood of its occurrence at normal mantle conditions at 800–1100 km. In addition, we observe that 23.8 mol.% Al2O3 can be dissolved into the structures of akimotoite and bridgmanite as a result of the decomposition reactions of Al‐bearing shy‐B and phase D between 600 and 100 km depth. Furthermore, δ‐AlOOH is the stable hydrous phase coexisting with Al‐depleted bridgmanite in the MgO‐SiO2‐Al2O3‐H2O system at pressures above 52 GPa and 1500 K.
    Description: Key Points: In comparison with Al‐free shy‐B, the incorporation of 11.7 wt.% Al2O3 in superhydrous phase B (shy‐B) expands the stability by ∼400–800 K at 20–30 GPa. Al‐bearing phase D could be present even at normal mantle geotherm conditions at 30–40 GPa. δ‐AlOOH is the stable hydrous phase coexisting with Al‐depleted bridgmanite at pressures above 52 GPa.
    Description: Center for Molecular Water Science, CMWS
    Description: https://doi.org/10.5281/zenodo.6320835
    Keywords: ddc:549 ; Al‐bearing superhydrous phase B ; phase D ; phase stability ; high pressure and temperature ; deep Earth water cycle
    Language: English
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  • 21
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    Multi‐episodic formation of baddeleyite and zircon in polymetamorphic anorthosite and rutile‐bearing ilmenitite from the Chiapas Massif Complex, Mexico (2022)
    Details
    Publication Date: 2023-01-13
    Description: Massif‐type anorthosite and comagmatic associations of rutile‐bearing ilmenitite (RBI) and oxide‐apatite‐rich amphibolite (OARA) from the Chiapas Massif Complex (CMC) in southeastern Mexico display a protracted billion‐year accessory mineral record encompassing magmatic crystallization at c. 1.0 Ga to recent ductile shear deformation at c. 3.0 Ma. Multiple discrete zircon populations between these age end‐members resulted from neoformation/recrystallization during local to regional metamorphism that affected the southeastern portion of the CMC. The ubiquitous presence of relict baddeleyite (ZrO2), along with various zircon generations spatially associated with pristine to partly retrogressed Zr‐bearing igneous and metamorphic minerals (e.g., ilmenite, rutile, högbomite and garnet), suggests significant Zr diffusive re‐equilibration (exsolution) during slow cooling and mineral breakdown followed by crystallization of baddeleyite. The subsequent transformation of baddeleyite into zircon was likely driven by reaction with Si‐bearing fluids in several geochronologically identified metamorphic stages. Strikingly contrasting compositional signatures in coeval zircon from anorthosite (silicate‐dominated) and comagmatic RBI (Ti‐Fe‐oxide‐dominated) indicate a major role of fluids locally equilibrating with the rock matrix, as indicated by distinct zircon trace element and oxygen isotopic compositions. A high‐grade metamorphic event at c. 950 Ma is likely responsible for the formation of coarse‐grained rutile (~0.1–10 mm in diameter), srilankite, zircon and garnet with rutile inclusions as well as metamorphic högbomite surrounding Fe‐Mg spinel. Zr‐in‐rutile minimum temperatures suggest 〉730°C for this event, which may correlate to rutile‐forming granulite facies metamorphism in other Grenvillian‐aged basement rocks in Mexico and northern South America. A younger generation of baddeleyite exsolution occurred during post‐peak cooling of coarse‐grained rutile, reflected in rimward Zr depletion and formation of discontinuous baddeleyite coronas. Baddeleyite around rutile was then transformed into zircon possibly during subsequent metamorphism at c. 920 or 620 Ma, resulting from syn‐kinematic and contact metamorphism, respectively. Regional metamorphism at c. 450 and 250 Ma extensively overprinted the existing zircon population, especially during the Triassic event, as suggested by a significant presence of zircon with this age. Nearly pristine baddeleyite occurring interstitial to ilmenite yielded an isochron age of c. 232 Ma according to in situ U–Pb secondary ion mass spectrometry (SIMS), suggesting either formation during metamorphic peak conditions or post‐peak cooling. Zircon with ages of c. 80–100 Ma in anorthosite is identified for the first time within the CMC and coincides with cooling ages of c. 100 Ma for coarse‐grained rutile. This age is similar to those of rocks occurring ~200 km further to the east in Guatemala, which are also bounded to the Polochic fault system but overprinted by eclogite facies metamorphism. A high‐pressure event in the southern CMC after 200 Ma, however, is presently unsupported. Although the abundance of rutile and ilmenite is unusually high in the CMC anorthosite assemblage compared with common igneous rocks, the reactions documented here nonetheless stress the importance of these phases for generating Zr‐bearing accessory minerals over a wide range of metamorphic conditions.
    Description: Consejo Nacional de Ciencia y Tecnología (CONACYT) http://dx.doi.org/10.13039/501100003141
    Description: Deutsche Forschungsgemeinschaft (DFG)
    Keywords: ddc:549 ; Diffusion ; SIMS ; Srilankite ; Ti‐Fe deposits ; Ti‐in‐zircon ; Zr‐in‐rutile
    Language: English
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  • 22
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    Surface Wave and Roller Dissipation Observed With Shore‐Based Doppler Marine Radar (2022)
    Details
    Publication Date: 2023-01-19
    Description: Surface wave energy and dissipation are observed across the surf zone. Utilizing the concept of surface rollers, a new scaling is introduced to obtain the energy flux and dissipation related to rollers from Doppler velocities measured by a shore‐based X‐band marine radar. The dissipation of wave energy and hence the transformation of the incoming wave height (or energy) is derived using the coupled wave and roller energy balance equations. Results are compared to in‐situ wave measurements obtained from a wave rider buoy and two bottom mounted pressure wave gauges. A good performance in reproducing the significant wave height is found yielding an overall root‐mean‐square error of 0.22 m and a bias of −0.12 m. This is comparable to the skill of numerical wave models. In contrast to wave models, however, the radar observations of the wave and roller energy flux and dissipation neither require knowledge of the bathymetry nor the incident wave height. Along a 1.5 km long cross‐shore transect on a double‐barred, sandy beach in the southern North Sea, the highest dissipation rates are observed at the inner bar over a relatively short distance of less than 100 m. During the peak of a medium‐severe storm event with significant wave heights over 3 m, about 50% of the incident wave energy flux is dissipated at the outer bar.
    Description: Plain Language Summary: Ocean waves are carrying a large amount of mechanical energy which they have gained from the wind blowing over the ocean surface. At the coast this energy supply generates strong water motions, creates forces on coastal structures, moves sand, and can cause coastal erosion. It is therefore important to know when, where, and to what extent wave energy is reduced under different environmental conditions. The majority of the energy is removed by wave breaking. However, this process is still not completely understood which is partly due to fact that it is difficult to observe. This is particularly the case during storm conditions when it is very complicated to install and recover measurement equipment in the ocean. The present work describes a methodology to obtain such measurements using a special radar device which is installed at the beach; hence, it is not being impacted by harsh wave conditions. This approach will enable scientists to perform long‐term monitoring of wave breaking thus opening new opportunities to study beach processes and coastal changes.
    Description: Key Points: high‐resolution observations of surface wave and roller dissipation as well as the transformation of wave height across the surf zone. the concept of surface rollers is applied to shore‐based X‐band Doppler radar data. in storm conditions, 50% of the wave energy is dissipated at a submerged outer sandbar, but strongest dissipation occurs further inshore.
    Description: Helmholtz Association http://dx.doi.org/10.13039/501100009318
    Description: http://codm.hzg.de/codm
    Description: https://doi.org/10.1594/683PANGAEA.898407
    Description: https://doi.org/10.1594/PANGAEA.942014
    Description: https://doi.org/10.5281/zenodo.5787131
    Keywords: ddc:551.46 ; wave breaking ; X‐band radar ; roller concept ; close‐range remote sensing ; energy dissipation ; wave transformation
    Language: English
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  • 23
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    Non‐exchangeable stable hydrogen isotope ratios in clay minerals and soil clay fractions: A method test (2022)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2023-01-20
    Description: Stable hydrogen isotope ratios (δ2H values) in structural hydroxyl groups of pedogenic clay minerals are inherited from the surrounding water at the time of their formation. Only non‐exchangeable H preserves the environmental forensic and paleoclimate information (δ2Hn value). To measure δ2Hn values in structural H of clay minerals and soil clay fractions, we adapted a steam equilibration method by accounting for high hygroscopicity. Our δ2Hn values for USGS57 biotite (−95.3 ± SD 0.9‰) and USGS58 muscovite (30.7 ± 1.4‰) differed slightly but significantly from the reported δ2H values (−91.5 ± 2.4‰ and −28.4 ± 1.6‰), because the minerals contained 1.1%–4.4% of exchangeable H. The low SD of replicate measurements (n = 3) confirmed a high precision. The clay separation method including destruction of Fe oxides, carbonates and soil organic matter, and dispersion did not significantly change the δ2Hn values of five different clay minerals. However, we were unable to remove all organic matter from the soil clay fractions resulting in an estimated bias of 1‰ in two samples and 15‰ in the carbon‐richest sample. Our results demonstrate that δ2Hn values of structural H of clay minerals and soil clay fractions can be reliably measured without interference from atmospheric water and the method used to separate the soil clay fraction. Highlights We tested steam equilibration to determine stable isotope ratios of structural H in clay. Gas‐tight capsule sealing in Ar atmosphere was necessary to avoid remoistening. Our steam equilibration method showed a high accuracy and precision. The clay separation method did not change stable isotope ratios of structural H in clay.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:549 ; controlled isotope exchange technique ; deuterium ; montmorillonite ; soil clay separation ; soil organic matter removal ; steam equilibration ; structural H ; USGS57 biotite ; vermiculite ; δ2H
    Language: English
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  • 24
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    Decadal Prediction of Marine Heatwaves in MPI‐ESM (2022)
    Details
    Publication Date: 2023-01-20
    Description: Marine Heatwaves (MHW) are SST extremes that can have devastating impacts on marine ecosystems and can influence circulation patterns in the ocean and the atmosphere. Here, we present a first attempt to study the decadal predictability of MHW in an ensemble of decadal hindcasts based on the Max Planck Institute Earth System Model. For the global mean we find significant skill for the multiyear MHW trends but we cannot predict the interannual to decadal variability of MHW. In the Subpolar North Atlantic, we can predict the interannual to decadal variability of MHW days and frequency up to lead year 8. We demonstrate that in the Subpolar North Atlantic, any increase in SST is accompanied by more MHW and vice versa. Thereby we gain additional information about the decadal evolution of SST that go beyond predicting the yearly mean SST.
    Description: Plain Language Summary: Marine Heatwaves (MHW) are periods with extremely warm ocean temperatures that can be disruptive for many marine ecosystems. Here, we provide an attempt to predict the evolution of MHW in the global ocean for the following two to ten years. With this analysis we improve our understanding of the predictability of surface temperatures in the global ocean. We find that there are strong regional differences in the predictability of MHW. One region where MHW can be predicted successfully is the Subpolar North Atlantic. We show that an increase in mean ocean temperature also results in an increase in MHW.
    Description: Key Points: Global mean multiyear trends for Marine Heatwaves (MHW) days and frequency can be skillfully predicted for the following two to eight years. In the Subpolar North Atlantic, yearly characteristics MHW days and frequency are predictable up to leadyear eight. Any increase in SST in the Subpolar North Atlantic is accompanied by an increase in MHW and vice versa.
    Description: Copernicus Climate Change Service
    Description: Deutsche Forschungsgemeinschaft
    Description: http://hdl.handle.net/hdl:21.14106/f2fdc61b13828ed5284f4e4ab41e63f8a84c6e52
    Keywords: ddc:551.46 ; Marine Heatwaves ; decadal predictions ; North Atlantic ; extreme events
    Language: English
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  • 25
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    Partial melting and reaction along deformation features in plagioclase (2022)
    Details
    Publication Date: 2023-10-26
    Description: Geological processes involving deformation and/or reactions are highly influenced by the rock grain size, especially if diffusion‐controlled processes take place such as metamorphic reactions and diffusion creep. Although many processes, inducing grain‐size reduction, are documented and understood at relatively high stresses and low temperatures (e.g., cataclasis) as well as at lower stress and higher temperature conditions (e.g., bulging and subgrain rotation), deformation twinning, a plastic deformation mechanism active in various minerals at lower temperatures, has been neglected as nucleation site for melting and reaction and thus as a cause for grain‐size reduction so far. We conducted experiments on natural plagioclase‐bearing aggregates at 2.5 to 3 GPa confining pressure and temperatures of 700°C to 950°C using two different deformation apparatus, a deformation multianvil apparatus (DDIA) and a Griggs press, as well as a piston‐cylinder apparatus. Regardless of the apparatus type, we observe the breakdown of plagioclase into an eclogite‐facies paragenesis, which is associated with partial melting in the high temperature domain of the eclogite facies. Partial melting mostly takes place along the grain and interphase boundaries. However, several melt patches or plagioclase decomposition products coincide with the occurrence of deformation twins and grain‐scale microcracking in plagioclase indicating intracrystalline melting and reaction in addition to melting and reaction along grain and interphase boundaries. In the present study, we demonstrate how the interplay between brittle microcracking and plastic deformation twinning can cause intracrystalline melting and/or reaction, which has the potential to lower the effective grain size of plagioclase‐rich rocks and thus impacts their reactivity and deformation behaviour.
    Description: European Research Council http://dx.doi.org/10.13039/501100000781
    Description: Alexander von Humboldt‐foundation http://dx.doi.org/10.13039/100005156
    Keywords: ddc:549 ; ddc:552.4 ; continental crust ; deformation twinning ; partial melting ; plagioclase deformation ; semibrittle regime
    Language: English
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  • 26
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    Wind Effects on Small‐Scale River and Creek Plumes (2022)
    Details
    Publication Date: 2023-11-24
    Description: In contrast to large river plumes, Coriolis effects are weak, and inertia is quickly depleted so that the fate and structure of small‐scale plumes are more sensitive to tide and wind. Advected alongshore by reversing tidal currents in absence of wind forcing, small buoyant plumes are persistently deflected downwind in presence of alongshore winds and exhibit little tidal variability. The effect of different upwelling/downwelling winds on buoyant outflows ∼10 m3 s−1 is explored. With increasing wind, tidal variability decreases, as does asymmetry in plume characteristics—for strong winds upwelling/downwelling plume structure is similar as the plume is retained closer to the shore. Wind forcing is exerted directly by wind stress on the surface of the plume and indirectly by wind‐driven currents that deflect the upwind boundary of the plume. While inertia and buoyancy dominate the inner plume, and wind dominates the outer plume, the mid‐plume responds to an interaction of wind and buoyancy forcing that can be indexed by a Plume Wedderburn Number Wpl (wind stress vs. density gradients): for weaker winds (Wpl 〈 1) surface stress enhances stratification through straining, lengthening the reach of low‐salinity waters, whereas for stronger winds (Wpl 〉 1) surface stress mixes the plume vertically, shortening the reach of low‐salinity waters. However, dilute plume waters extend furthest in strong winds, passively advected several kilometers downwind. Shoreline exposure to outflow transitions from a quasi‐symmetrical tide‐averaged zone of impact under zero‐wind to a heavily skewed zone with persistent weak wind and a one‐sided zone for strong wind.
    Description: Plain Language Summary: Compared to large river plumes, outflow from small rivers and mountainous streams is more sensitive to tides and winds because of the weak Coriolis effect and quickly reduced inertia. Alongshore (upwelling/downwelling) winds carry these small plumes in their direction. We use a numerical model to study the effect of these upwelling/downwelling winds on plumes spreading from small rivers with discharge rates of 10 m3 s−1 or less. Increasing wind reduces tidal fluctuations in plume patterns such that with strong winds the plume spreads similarly for upwelling and downwelling winds as it remains close to the shore. Wind affects the plume surface directly and the upwind‐plume boundary indirectly via wind‐driven currents. Inertia and buoyancy control the inner plume while wind and buoyancy control the mid‐plume and wind controls the outer plume. Weaker winds increase the plume length and layering by horizontally tilting the density gradients. Stronger winds shorten the plume by vertically mixing it. However, dilute plume waters extend furthest in strong winds, passively advected several kilometers downwind.
    Description: Key Points: Plume bends downwind, with upstream boundary deflected by ambient current and downstream boundary deflected by surface wind stress. Asymmetry in plume shape between weak upwelling versus downwelling winds vanishes with strong winds that retain the plume nearshore where Ekman transport negligible. Inertia & buoyancy control the near‐field; wind forcing & buoyancy control the mid‐field; wind mixing & passive advection control the far‐field.
    Description: National Science Foundation http://dx.doi.org/10.13039/100000001
    Description: Leibniz Institute für Ostseeforschung Warnemünde
    Description: http://doi.io-warnemuende.de/10.12754/data-2022-0009
    Keywords: ddc:551.46 ; small‐scale river plumes ; creek plumes ; upwelling downwelling winds ; high resolution river plume dynamics ; idealized numerical model
    Language: English
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  • 27
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    Interannual Changes in Tidal Conversion Modulate M2 Amplitudes in the Gulf of Maine (2022)
    Details
    Publication Date: 2023-07-27
    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 Gulf of Maine's lunar semidiurnal (M〈sub〉2〈/sub〉) ocean tide exhibits spatially coherent amplitude changes of ∼1–3 cm on interannual time scales, though no causative mechanism has been identified. Here we show, using a specially designed numerical modeling framework, that stratification changes account for 32%–48% (Pearson coefficient 0.58–0.69) of the observed M〈sub〉2〈/sub〉 variability at tide gauges from 1994 to 2019. Masking experiments and energy diagnoses reveal that the modeled variability is primarily driven by fluctuations in barotropic‐to‐baroclinic energy conversion on the continental slope south of the gulf's mouth, with a 1‐cm amplitude increase at Boston corresponding to a ∼7% (0.30 GW) drop in the area‐integrated conversion rate. Evidence is given for the same process to have caused the decade‐long M〈sub〉2〈/sub〉 amplitude decrease in the Gulf of Maine beginning in 1980/81. The study has implications for nuisance flooding predictions and space geodetic analyses seeking highest accuracies.〈/p〉
    Description: Plain Language Summary: The height of the twice‐daily tide at Boston is about 135 cm, but researchers have long noted that this value fluctuates by about 1–3 cm from year to year. Here we show that the annual tidal height changes—seen in fact throughout the Gulf of Maine—are closely linked to how seawater density is distributed three‐dimensionally in the region. In particular, as tidal currents enter the gulf over steep underwater topography, the vertical distribution of density determines how much of the incoming wave energy is scattered back as internal tides into the deeper Northwest Atlantic. In years where this conversion of wave energy drops by 7% from its nominal value of 4 Gigawatt, the surface tide at Boston typically increases by 1 cm. Climate‐induced changes in ocean temperature and density may strengthen or weaken the conversion effect and thus slightly alter the role of tides in coastal flood events.〈/p〉
    Description: Key Points〈: We propagate the M〈sub〉2〈/sub〉 tide through realistic, annually varying density structures (1993–2019) in a regional Gulf of Maine model. Stratification changes explain 32%–48% of the observed, cm‐level M〈sub〉2〈/sub〉 amplitude variability at coastal tide gauges from 1994 to 2019. Modeled M〈sub〉2〈/sub〉 changes mainly reflect fluctuations in the barotropic‐baroclinic energy conversion rate on the New England continental slope.
    Description: Austrian Science Fund http://dx.doi.org/10.13039/501100002428
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://www.gesla.org/
    Description: https://www.tpxo.net/global/tpxo9-atlas
    Description: https://doi.pangaea.de/10.1594/PANGAEA.856844
    Description: https://marine.copernicus.eu/access-data
    Description: https://www.ncei.noaa.gov/products/northwest-atlantic-regional-climatology
    Keywords: ddc:551.46 ; ocean tides ; tidal conversion ; Gulf of Maine ; nuisance flooding
    Language: English
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  • 28
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    Authigenic Formation of Clay Minerals in the Abyssal North Pacific (2022)
    Details
    Publication Date: 2023-07-19
    Description: Present estimates of the biogeochemical cycles of calcium, strontium, and potassium in the ocean reveal large imbalances between known input and output fluxes. Using pore fluid, incubation, and solid sediment data from North Pacific multi‐corer cores we show that, contrary to the common paradigm, the top centimeters of abyssal sediments can be an active site of authigenic precipitation of clay minerals. In this region, clay authigenesis is the dominant sink for potassium and strontium and consumes nearly all calcium released from benthic dissolution of calcium carbonates. These observations support the idea that clay authigenesis occurring over broad regions of the world ocean may be a major buffer for ocean chemistry on the time scale of the ocean overturning circulation, and key to the long‐term stability of Earth's climate.
    Description: Key Points: North Pacific red clay sediments are a sink for marine calcium, strontium, and potassium. Authigenic formation of clay minerals is prevalent in pelagic sediments throughout the North Pacific. The main mechanism for clay formation is recrystallization of aluminosilicates, neoformation can occur in biogenic silica rich sediments.
    Description: EC H2020 PRIORITY “Excellent science” H2020 European Research Council http://dx.doi.org/10.13039/100010663
    Description: Blavatnik Family Foundation http://dx.doi.org/10.13039/100011643
    Description: Isaac Newton Trust http://dx.doi.org/10.13039/501100004815
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: National Science Foundation http://dx.doi.org/10.13039/100000001
    Description: https://doi.pangaea.de/10.1594/PANGAEA.946881
    Keywords: ddc:549 ; reverse weathering ; clay authigenesis ; calcium ; potassium ; porewater ; strontium
    Language: English
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    Incomplete Crack Sealing Causes Localization of Fracturing in Hydrothermal Quartz Veins (2022)
    Details
    Publication Date: 2023-01-26
    Description: Cyclic microfracturing and epitaxial crystal growth have long been recognized in crack‐seal veins, but an understanding of a single crack‐seal cycle is still missing. Here we present a phase‐field model that includes both fracture mechanics of crack propagation, and epitaxial crystal growth on the fracture walls, repeating this cycle multiple times in a polycrystalline, microporous quartz rock. Our simulations have two end members: If a vein completely seals, it is stronger than the host rock, cracking is delocalized, forming many single‐seal microveins. Incomplete sealing makes the vein weaker than the host rock and localizes the new fracture inside the vein, leading to multi‐crack‐seal. We suggest that the sealing degree is a key parameter in hydrothermal systems and multi‐crack‐seal veins are long‐lived, microporous sites of mechanical weakness. We generalize the phase‐field approach to conduct probabilistic simulations in between these two types, and show how systems of microveins and multi‐crack‐seal veins emerge.
    Description: Plain Language Summary: Fluids in the Earth's crust can alter permeability and porosity, precipitate and dissolve minerals, transport material and interact with deformation. This affects the transport and mechanical properties of the rock system and in turn has consequences for example, in subsurface engineering applications. In this work we simulate the processes of fracturing and crystal growth on grain scale in a microporous rock structure and show how different crystal structures form. The basic steps of a crack‐seal process and how fracturing and sealing interact are explored. Our results show that if a fracture completely seals a new crack will form in the host rock and many thin microveins form. In contrast, an incomplete sealing makes the vein weaker than the host rock and leads to a new cracking inside the vein, which enlarges the existing structure with each cycle. This implies that the degree of sealing is the cause of this division, where crack‐seal veins are microporous sites of mechanical weakness. Additionally, we perform probabilistic simulations which show how many single‐seal microveins form side‐by‐side with a few multi‐crack‐seal veins. Our studies provide valuable insight in structure‐property linkages and enable a better prediction of fracture‐sealing.
    Description: Key Points: Systematic phase‐field study captures elementary steps of the crack‐seal process at grain scale. Incomplete sealing makes a vein weaker than the host rock and localizes a new fracture inside the vein which leads to multi‐crack‐seal. Probabilistic simulations show how systems of many microveins and a few thick crack‐seal veins form side by side.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.5281/zenodo.6337652
    Keywords: ddc:549 ; hydrothermal quartz veins ; fluids ; fracturing ; crystal growth ; simulations
    Language: English
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    The Role of Turbulence in Fueling the Subsurface Chlorophyll Maximum in Tidally Dominated Shelf Seas (2022)
    Details
    Publication Date: 2023-01-26
    Description: Glider observations show a subsurface chlorophyll maximum (SCM) at the base of the seasonal pycnocline in the North Sea during stable summer conditions. A colocated peak in the dissipation rate of turbulent kinetic energy suggests the presence of active turbulence that potentially generates a nutrient flux to fuel the SCM. A one‐dimensional turbulence closure model is used to investigate the dynamics behind this local maximum in turbulent dissipation at the base of the pycnocline (PCB) as well as its associated nutrient fluxes. Based on a number of increasingly idealized forcing setups of the model, we are able to draw the following conclusions: (a) only turbulence generated inside the stratified PCB is able to entrain a tracer (e.g., nutrients) from the bottom mixed layer into the SCM region; (b) surface wind forcing only plays a secondary role during stable summer conditions; (c) interfacial shear from the tide accounts for the majority of turbulence production at the PCB; (d) in stable summer conditions, the strength of the turbulent diapycnal fluxes at the PCB is set by the strength of the anticyclonic component of the tidal currents.
    Description: Plain Language Summary: Many midlatitude shelf seas are vertically stratified in summer, where a warm surface layer sits on top of a cold, dense bottom layer. Both of these layers are unproductive environments for phytoplankton—the bottom layer is light limited, and the surface layer is nutrient‐limited. However, abundant phytoplankton is observed directly at the interface between surface and bottom layers. In order to sustain this phytoplankton, nutrient‐rich bottom water needs to be mixed with interface water. While both wind and tides are major causes for mixing in the coastal ocean, we find that the tides alone provide sufficient stirring at the right place to potentially act as an effective fuel pump for the phytoplankton. Interestingly, it is not the strength of the tides alone that counts, rather the sense of rotation of the tidal currents; rotation opposite to the Earth's spin causes more stirring than rotation along with it.
    Description: Key Points: Turbulence and chlorophyll both peak at the base of the pycnocline on a mid‐latitude shelf. Locally generated turbulence at the pycnocline base is a fuel pump for the subsurface chlorophyll maximum. Amplitude and polarity of the M2 tide govern the local generation of turbulence at the pycnocline base.
    Description: Helmholtz Association
    Description: https://doi.org/10.5281/zenodo.3525787
    Description: https://oceancolor.gsfc.nasa.gov/l3/
    Description: https://www.cen.uni-hamburg.de/icdc/data/ocean/nsbc.html
    Keywords: ddc:551.46 ; shelf seas ; storms ; North Sea ; turbulence ; straification ; marginal stability ; subsurface chlorophyll maximum ; fuel pump ; modeling
    Language: English
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    ICON‐O: The Ocean Component of the ICON Earth System Model—Global Simulation Characteristics and Local Telescoping Capability (2022)
    Details
    Publication Date: 2023-01-25
    Description: We describe the ocean general circulation model Icosahedral Nonhydrostatic Weather and Climate Model (ICON‐O) of the Max Planck Institute for Meteorology, which forms the ocean‐sea ice component of the Earth system model ICON‐ESM. ICON‐O relies on innovative structure‐preserving finite volume numerics. We demonstrate the fundamental ability of ICON‐O to simulate key features of global ocean dynamics at both uniform and non‐uniform resolution. Two experiments are analyzed and compared with observations, one with a nearly uniform and eddy‐rich resolution of ∼10 km and another with a telescoping configuration whose resolution varies smoothly from globally ∼80 to ∼10 km in a focal region in the North Atlantic. Our results show first, that ICON‐O on the nearly uniform grid simulates an ocean circulation that compares well with observations and second, that ICON‐O in its telescope configuration is capable of reproducing the dynamics in the focal region over decadal time scales at a fraction of the computational cost of the uniform‐grid simulation. The telescopic technique offers an alternative to the established regionalization approaches. It can be used either to resolve local circulation more accurately or to represent local scales that cannot be simulated globally while remaining within a global modeling framework.
    Description: Plain Language Summary: Icosahedral Nonhydrostatic Weather and Climate Model (ICON‐O) is a global ocean general circulation model that works on unstructured grids. It rests on novel numerical techniques that belong to the class of structure‐preserving finite Volume methods. Unstructured grids allow on the one hand a uniform coverage of the sphere without resolution clustering, and on the other hand they provide the freedom to intentionally cluster grid points in some region of interest. In this work we run ICON‐O on an uniform grid of approximately 10 km resolution and on a grid with four times less degrees of freedom that is stretched such that in the resulting telescoping grid within the North Atlantic the two resolutions are similar, while outside the focal area the grid approaches smoothly ∼80 km resolution. By comparison with observations and reanalysis data we show first, that the simulation on the uniform 10 km grid provides a decent mesoscale eddy rich simulation and second, that the telescoping grid is able to reproduce the mesoscale rich circulation locally in the North Atlantic and on decadal time scales. This telescoping technique of unstructured grids opens new research directions.
    Description: Key Points: We describe Icosahedral Nonhydrostatic Weather and Climate Model (ICON‐O) the ocean component of ICON‐ESM 1.0, based on the ICON modeling framework. ICON‐O is analyzed in a globally mesoscale‐rich simulation and in a telescoping configuration. In telescoping configuration ICON‐O reproduces locally the eddy dynamics with less computational costs than the uniform configuration.
    Description: https://swiftbrowser.dkrz.de/public/dkrz_07387162e5cd4c81b1376bd7c648bb60/kornetal2021
    Description: https://mpimet.mpg.de/en/science/modeling-with-icon/code-availability
    Keywords: ddc:551.46 ; ocean modeling ; ocean dynamics ; unstructured grid modeling ; local refinement ; structure preservation numerics
    Language: English
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    Simulated Signatures of Greenland Melting in the North Atlantic: A Model Comparison With Argo Floats, Satellite Observations, and Ocean Reanalysis (2022)
    Details
    Publication Date: 2024-02-14
    Description: Increased Greenland ice sheet melting has an impact on global mean and regional sea level rise and the ocean circulation. In this study, we explore whether Greenland melting signatures found in ocean model simulations are visible in observations from radar altimetry, satellite gravimetry and Argo floats. We have included Greenland freshwater flux (GF) in the global Finite‐Element‐Sea ice‐Ocean Model (FESOM) for the years 1993–2016. The reference run is computed by excluding Greenland freshwater input. These experiments are performed on a low resolution (ca. 24 km) and a high resolution (ca. 6 km) eddy‐permitting mesh. For comparison with the model experiments, we use different observational data, such as Argo floats, satellite observations, and reanalyses. We find that surface GF maps into signatures in temperature and salinity down to about 100 m in the surroundings of Greenland. The simulated melting signatures are particularly visible in steric heights in Baffin Bay and Davis Strait. Here, we find an improvement of the mean square error of up to 30% when including GF. For the Nordic part of the Nordic Seas, however, we find no improvement when including GF. We compare steric heights with reanalysis data and a new setup of the inversion method from gravimetric and altimetric satellite data. We cannot confirm that the GF signatures on variables such as temperature and salinity are visible in the observations on the time scales considered. However, we find that increased model resolution often causes larger improvements than occur due to including the simulated melting effect.
    Description: Plain Language Summary: In recent years, Greenland's freshwater contribution to the ocean has increased due to the accelerated melting of its ice sheet and glaciers. In this study, we investigate the importance of this melting in reproducing the observed characteristics of the northern part of the North Atlantic Ocean in a numerical ocean model. To do that, we compare the results of two model simulations, one with and one without Greenland melt, with in situ observations or data from satellites. The inclusion of Greenland melt results in a better model representation of the ocean in terms of salinity, temperature, and sea level anomalies, especially in Baffin Bay on the west side of Greenland. We also discuss the role of a higher model resolution on the simulations in reproducing observations. Our study shows that progress in modeling how Greenland melt affects the nearby ocean is best achieved by improving model resolution so that small‐scale processes can be well represented.
    Description: Key Points: Greenland freshwater flow yields distinct signatures in temperature and salinity within the upper 100 m. Steric heights and sea level anomalies are sensitive to the Greenland freshwater intrusion especially in Baffin Bay. Increasing the spatial model resolution improves the agreement with observations more than if only Greenland meltwater is included.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: https://doi.org/10.5281/zenodo.6243822
    Keywords: ddc:551.46 ; ocean modeling ; FESOM ; Greenland freshwater discharge ; ocean reanalysis ; altimetry
    Language: English
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    The chondrite breccia of Antonin (L4‐5)—A new meteorite fall from Poland with a heterogeneous distribution of metal (2022)
    Bischoff, Addi ; Patzek, Markus ; Peters, Stefan T. M. ; [et al.]
    Details
    Publication Date: 2024-02-21
    Description: On July 15, 2021, a huge fireball was visible over Poland. After the possible strewn field was calculated, the first and so far only sample, with a mass of 350 g, was discovered 18 days after the fireball event. The Antonin meteorite was found August 3, 2021, on the edge of a forest close to a dirt road near Helenow, a small suburb of the city of Mikstat. The rock is an ordinary chondrite breccia and consists of equilibrated and recrystallized lithologies. The boundaries between different fragments are difficult to detect, and the lithologies are of petrologic type 5 and type 4. The rock is moderately shocked (S4) and contains local impact melt areas and thin shock veins. The low‐Ca pyroxene and olivine are equilibrated (Fs20.6 and Fa24.0, respectively), typical of L chondrites. The L chondrite classification is also supported by O isotope data and the results of bulk chemical analysis. The Ti isotope characteristics confirm that Antonin is related to the noncarbonaceous (NC) meteorites. One of the studied thin sections shows an unusual metal–chondrule assemblage, perhaps indicating that the metal in the chondrite is heterogeneously distributed, which is, however, not clearly visible in the element abundances.
    Description: Alexander von Humboldt‐Stiftung http://dx.doi.org/10.13039/100005156
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:549 ; Poland ; Antonin meteorite ; chondrite breccia ; metal distribution
    Language: English
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    Hydrogen Diffusion in Clinopyroxene at Low Temperatures (195°C–400°C) and Consequences for Subsurface Processes (2022)
    Details
    Publication Date: 2023-09-14
    Description: Studying diffusion of hydrogen in nominally anhydrous minerals, like clinopyroxene, at low temperatures is a challenging task due to experimental and analytical difficulties. In this study, to overcome these problems we have produced H concentration gradients in single crystals of natural diopsidic clinopyroxene by ion implantation and measured the nanoscale profiles before and after diffusion anneals using Nuclear Resonance Reaction Analysis. These steps allowed us to conduct experiments at temperatures between 195°C and 400°C. Obtained diffusion rates show a consistent Arrhenius relation D〈sub〉H〈/sub〉= 5.47(±13.98) · 10−8 · exp (−115.64(±11.5) kJ mol〈sup〉−1〈/sup〉/RT) m〈sup〉2〈/sup〉s〈sup〉−1〈/sup〉. Notably, our results lie well within the range of extrapolations from high temperature experiments (≥600°C) of previous studies. This implies that fast diffusion of hydrogen (compared to other elements) extends to low temperatures. We used these results in a non‐isothermal diffusion model that simulates the ascent of crystals (0.5, 1.0, and 2.0 mm) along two representative P‐T‐paths from 600°C to 100°C, to assess potential re‐equilibration of H contents in clinopyroxene at low temperatures. Our model highlights the need to carefully consider boundary conditions, which are a function of P‐T‐f O〈sub〉2〈/sub〉, that control the concentration gradient at the crystal's rim. The results from this model help to assess, as a function of crystal size and cooling rate, when re‐equilibration must be considered.
    Description: Key Points: Diffusion rates of hydrogen in clinopyroxene in the low temperature range (195°C–400°C) were quantified for the first time. Diffusion coefficients at low temperatures lie within the range of extrapolations from high temperature experiments. Non‐isothermal modeling was applied to evaluate potential re‐equilibration of clinopyroxene crystals at low temperatures.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://doi.org/10.5281/zenodo.7290350
    Keywords: ddc:549 ; diffusion ; hydrogen ; clinopyroxene ; equilibration ; low‐temperature
    Language: English
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    Causes for Atlantic Freshwater Content Variability in the GECCO3 Ocean Synthesis (2022)
    Details
    Publication Date: 2024-01-26
    Description: Regional freshwater content (FWC) changes are studied over the period 1961–2018 using the GECCO3 ocean synthesis. In four dynamically distinct regions of the Atlantic, the study identifies causes for FWC variability with a focus on interannual and decadal time‐scale changes. Results show that in each region, it is a combination of the surface freshwater flux and the net freshwater transport across the region's boundaries that act jointly in changing the respective FWC. Surface flux mainly contributes to the FWC variability on multi‐decadal time scales. The impact of surface flux also increases toward the tropics. On shorter time scales, it is especially horizontal transport fluctuations, leading to FWC changes in mid and high latitudes. Going from north to the south, the transport across a single meridional boundary becomes less correlated with the FWC changes but the net transport across both boundaries plays an increasingly important role. Moreover, the subpolar box is mainly gyre driven, which differs from the other two, essentially overturning driven, North Atlantic boxes. In the tropical Atlantic, the shallow overturning cell and the deep overturning contribute about equal amounts to the freshwater variations.
    Description: Plain Language Summary: Causes for freshwater content (FWC) variability in the Atlantic Ocean are analyzed for four study areas over the period 1961–2018 based on a model simulation (GECCO3 ocean synthesis). Targeting relatively long time scales, interannual, decadal to multi‐decadal FWC changes are separated into the contributions from variations of the freshwater input/output through the ocean surface and from freshwater transport (FWT) variations related to the ocean circulation changes. Surface freshwater flux is more influential on multi‐decadal time scales, and its impact increases toward the tropics. On shorter time scales, the oceanic FWT across the boundaries of the region dominates the FWC changes in mid and high latitudes. The transport variability in the subpolar region is mainly driven by the horizontal circulation, while transports resulting from vertical salinity differences are more important at lower latitudes. Moreover, in the tropics transports related to shallow salinity differences are not negligible on interannual time scales.
    Description: Key Points: The net freshwater transport across the meridional boundaries dominates the freshwater content variations in mid and high latitudes. The importance of surface freshwater flux variations increases toward the tropics and on multi‐decadal time scales. Subpolar changes are mainly gyre driven, while overturning and especially the shallow overturning cells contribute more at lower latitudes.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://icdc.cen.uni-hamburg.de/en/gecco3.html
    Description: http://www.metoffice.gov.uk/hadobs/en4/download-en4-2-2.html
    Description: https://www.cen.uni-hamburg.de/en/icdc/data/atmosphere/hoaps.html
    Keywords: ddc:551.46 ; Atlantic Ocean ; freshwater content (FWC) ; regional changes ; GECCO3
    Language: English
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    Thermocline Salinity Minima Due To Wind‐Driven Differential Advection (2022)
    Details
    Publication Date: 2024-01-30
    Description: Observations from the global ocean have long confirmed the ubiquity of thermohaline inversions in the upper ocean, often accompanied by a clear signal in biogeochemical properties. Their emergence has been linked to different processes such as double diffusion, mesoscale stirring, frontal subduction, and the recently discussed submesoscale features. This study uses the central Baltic Sea as a natural laboratory to explore the formation of salinity inversions in the thermocline region during summer. We use realistic high‐resolution simulations complemented by field observations to identify the dominant generation mechanism and potential hotspots of their emergence. We propose that the strongly stratified thermocline can host distinct salinity minima during summer conditions resulting primarily from the interaction between lateral surface salinity gradients and wind‐induced differential advection. Since this is a generic mechanism, such salinity inversions can likely constitute a typical feature of the upper ocean in regions with distinct thermoclines and shallow mixed layers.
    Description: Plain Language Summary: The upper ocean is characterized by a well‐mixed surface layer, below which temperature decreases rapidly with depth, forming the so‐called thermocline region. A corresponding salinity increase with depth is typically anticipated for stable density stratification to occur. Temperature and salinity inversions can, however, emerge in the upper ocean. Such thermohaline inversions have been observed in different regions of the world's oceans, and various mechanisms have been proposed to explain their generation. Here, the central basin of the Baltic Sea is used as a natural laboratory to explore the formation of distinct salinity minima in the thermocline region during summer conditions. Using high‐resolution numerical simulations and measurements from a field campaign, we show that inversions are abundant and can emerge throughout the entire basin. They increase with increasing wind speeds and concentrate mainly in regions with strong lateral salinity differences. We propose that thermocline salinity minima can occur during summer when the wind transports saltier water over less saline surface waters. This is a generic mechanism that can therefore be responsible for the formation of the salinity inversions observed worldwide in areas with distinct thermoclines and shallow mixed layers.
    Description: Key Points: Observations collected in the central Baltic Sea during summer indicate patches of distinct salinity minima in the thermocline region. Realistic high‐resolution simulations are used to explore the origin of the salinity minima and to identify the hotspots of their genesis. Lateral surface salinity gradients interacting with wind‐induced differential advection are shown to generate most of the inversions.
    Description: German Research Foundation
    Description: http://doi.io-warnemuende.de/10.12754/data-2022-0001
    Keywords: ddc:551.46 ; salinity inversions ; thermohaline intrusions ; subduction ; submesoscales ; differential advection ; Baltic Sea
    Language: English
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    Determination of phase relations of the olivine–ahrensite transition in the Mg2SiO4–Fe2SiO4 system at 1740 K using modern multi-anvil techniques (2021)
    Chanyshev, Artem ; Bondar, Dmitry ; Fei, Hongzhan ; [et al.]
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-07-04
    Description: The phase relations of iron-rich olivine and its high-pressure polymorphs are important for planetary science and meteoritics because these minerals are the main constituents of terrestrial mantles and meteorites. The olivine–ahrensite binary loop was previously determined by thermochemical calculations in combination with high-pressure experiments; however, the transition pressures contained significant uncertainties. Here we determined the binary loop of the olivine–ahrensite transition in the (Mg,Fe)2SiO4 system at 1740 K in the pressure range of 7.5–11.2 GPa using a multi-anvil apparatus with the pressure determined using in situ X-ray diffraction, compositional analysis of quenched run products, and thermochemical calculation. Based on the determined binary loop, a user-friendly software was developed to calculate pressure from the coexisting olivine and ahrensite compositions. The software is used to estimate the shock conditions of several L6-type chondrites. The obtained olivine–ahrensite phase relations can also be applied for precise in-house multi-anvil pressure calibration at high temperatures.
    Description: BMBF
    Description: H2020 European Research Council http://dx.doi.org/10.13039/100010663
    Description: Deutsches Elektronen-Synchrotron (DESY) (4201)
    Keywords: ddc:549 ; Experimental ; Olivine ; Ahrensite ; Phase transition ; Thermobarometry ; Meteorites
    Language: English
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    Water contents of nominally anhydrous orthopyroxenes from oceanic peridotites determined by SIMS and FTIR (2021)
    Springer Vienna
    Details
    Publication Date: 2023-07-04
    Description: This study presents new secondary ion mass spectrometry (SIMS) reference materials (RMs) for measuring water contents in nominally anhydrous orthopyroxenes from upper mantle peridotites. The enstatitic reference orthopyroxenes from spinel peridotite xenoliths have Mg#s between 0.83 and 0.86, Al2O3 ranges between 4.02 and 5.56 wt%, and Cr2O3 ranges between 0.21 and 0.69 wt%. Based on Fourier-transform infrared spectroscopy (FTIR) characterizations, the water contents of the eleven reference orthopyroxenes vary from dry to 249 ± 6 µg/g H2O. Using these reference grains, a set of orthopyroxene samples obtained from variably altered abyssal spinel peridotites from the Atlantic and Arctic Ridges as well as from the Izu-Bonin-Mariana forearc region was analyzed by SIMS and FTIR regarding their incorporation of water. The major element composition of the sample orthopyroxenes is typical of spinel peridotites from the upper mantle, characterized by Mg#s between 0.90 and 0.92, Al2O3 between 1.66 and 5.34 wt%, and Cr2O3 between 0.62 and 0.96 wt%. Water contents as measured by SIMS range from 68 ± 7 to 261 ± 11 µg/g H2O and correlate well with Al2O3 contents (r = 0.80) and Cr#s (r. = -0.89). We also describe in detail an optimized strategy, employing both SIMS and FTIR, for quantifying structural water in highly altered samples such as abyssal peridotite. This approach first analyzes individual oriented grains by polarized FTIR, which provides an overview of alteration. Subsequently, the same grain along with others of the same sample is measured using SIMS, thereby gaining information about homogeneity at the hand sample scale, which is key for understanding the geological history of these rocks.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Bavarian Equal Opportunities Sponsorship - Realization Equal Opportunities for Women in Research and Teaching
    Description: Friedrich-Alexander-Universität Erlangen-Nürnberg (1041)
    Keywords: ddc:549 ; FTIR ; Hydrogen ; Nominally anhydrous minerals ; Orthopyroxene ; SIMS ; Spinel peridotite
    Language: English
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    Mineralogical and geochemical investigation of megaspherulites from Argentina, Germany, and the USA (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-14
    Description: Textures and whole-rock chemistry, as well as mineral composition, were analyzed in megaspherulites (high-temperature crystallization domains [HTCDs]) that formed in different geographical and geotectonic contexts and during different geological periods (Silver Cliff, CO, USA—Paleogene; El Quevar, Argentina—Miocene; Meissen Volcanic Complex, Germany—Late Carboniferous). All of these megaspherulites have formed exclusively in rhyolitic lava, and their mineral composition is dominated by K-feldspar (sanidine) and SiO2 phases (quartz, cristobalite, tridymite). All megaspherulites represent composite HTCDs, comprising three zones: inner domain (ID), outer domain (OD), and a marginal domain (MD). Early evolution of megaspherulites is characterized by either central cavities and sector- to full-sphere spherulites or dendritic quartz-sanidine domains. The latter consist of bundles of fibrils each radiating from a single point reflecting relatively high growth rates. A common feature of OD and MD of all three megaspherulite occurrences is autocyclic banding. It mainly comprises fibrous (≤ 100 μm length), radially oriented sanidine and quartz, which formed at a temperature close to glass transition temperature (Tg). The termination of megaspherulite growth is marked by centimeter-sized sector-sphere spherulites on the surface. Megaspherulite formation requires limited nucleation, which is probably related to the low phenocryst content of the hosting lava. Latent heat from overlying crystallizing lithoidal rhyolite maintained low undercooling conditions keeping nucleation density low and facilitating high diffusion and growth rates. Late megaspherulite growth and its termination under low diffusion conditions is controlled by cooling close to Tg. Calculations based on literature data suggest that the megaspherulite growth presumably lasted less than 60 years, perhaps 30 to 40 years.
    Keywords: ddc:549 ; Rhyolitic lava ; SEM ; CL ; XRD ; EPMA ; Cristobalite ; Tridymite
    Language: English
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    The provenance signal of climate–tectonic interactions in the evolving St. Elias orogen: framework component analysis and pyroxene and epidote single grain geochemistry of sediments from IODP 341 sites U1417 and U1418 (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-08-17
    Description: The St. Elias orogen and the Surveyor Fan in the adjacent Gulf of Alaska are a coupled source to sink system recording the interplay of tectonics and variable degrees of glaciation during the collision of the Yakutat terrane with the southern Alaska margin since the Miocene. The Miocene to Holocene sediments of the Surveyor Fan were drilled during IODP expedition 341. The recovered material is used to constrain information on changes in erosion centers during the last 10 Ma to study the impact of climatic and tectonic processes on orogen evolution. Point counting of sand- and silt-sized light framework components and geochemical single grain analysis of heavy mineral groups epidote and pyroxene is applied to analyze patterns of sedimentary provenance of two sites on the distal and proximal Surveyor Fan (Site U1417 and U1418, respectively). The studied sands and silts of Miocene to Pleistocene age are slightly enriched in feldspar (plag 〉〉 kf) at the proximal site, compositions at both sites do not show systematical changes with time of deposition. Framework component spectra uniformly reflect the expected active margin provenance. Epidote and pyroxene compositions are very consistent and show no change with time of deposition. Associations of epidote and pyroxene with albite, titanite and pumpellyite are in line with near-shore sources in the Chugach Metamorphic Complex and the metabasite belt at its southern border, and in units of recycled detritus exposed in the fold and thrust belt on the western Yakutat Terrane, respectively. Rock fragments indicate input from mainly metamorphic sources during the Miocene and Pliocene and an increase of input from low-grade metamorphic and sedimentary rocks in the Pleistocene, a finding also indicated by the abundance of epidote and pyroxene. This implies increasing erosion of the near-shore areas of the fold and thrust belt with advance of glaciers to the shore since the Miocene, being enhanced by the onset of the Northern Hemisphere glaciation at the beginning of the Pleistocene. Climate changes connected to the mid-Pleistocene transition did not result in appreciable changes in the petrographic compositions. Glaciers seem to have remained nested in their topographically predefined positions, continuously feeding material with uniform characteristics into the fan.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Westfälische Wilhelms-Universität Münster (1056)
    Keywords: ddc:549 ; Alaska ; Provenance ; Framework components ; Pyroxene ; Epidote ; Climate–tectonic interactions
    Language: English
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    Impact of climate variability of the Western Tropical Pacific on maximum salinity water in the South China Sea (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-08-18
    Description: Salinity observations in the Vietnamese upwelling area in June 2016 indicated a significant increase in the salinity of the maximum salinity water (MSW). The source of MSW inflow into the South China Sea (SCS) is a mixture of the Western North Pacific Central Water and the North Pacific Equatorial Water. Although the East Asian winter monsoon is correlated with both the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO), the mean salinity of MSW is only spuriously lag correlated to the PDO, but highly correlated to all tropical climate modes (except El Niño Modoki) with a time lag up to 7 months. Composite analyses indicate that the modulation of ENSO by a PDO in a positive phase results in optimal inflow conditions. A comparison of two post-El Niño years with different PDO polarity (negative in 2003 and positive in 2016) shows that the dominant driver is the variability in outgoing long-wave radiation (OLR) and in zonal wind in the tropics. In 2003, enhanced convective activity over the West Pacific warm pool resulted in a cyclonic circulation. In 2016, convective activity was weak and an anticyclonic circulation was intensified, which transported the saltier North Pacific Equatorial Water into the SCS. This observed increase in the salinity of MSW requires a modification of the previous definitions of characteristic water masses, which is presented here. The question of whether or not the increase in MSW salinity is a transient phenomenon cannot be answered. It might be possible that the increase in salinity is related to global warming.
    Description: Deutsche Forschungsgemeinschaft DFG
    Description: Leibniz-Institut für Ostseeforschung Warnemünde (IOW) (3484)
    Keywords: ddc:551.46 ; ENSO ; PDO ; East Asian monsoon ; Water mass analysis ; South China Sea ; Western Tropical Pacific
    Language: English
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  • 42
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    Garnet major-element composition as an indicator of host-rock type: a machine learning approach using the random forest classifier (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-07-20
    Description: The major-element chemical composition of garnet provides valuable petrogenetic information, particularly in metamorphic rocks. When facing detrital garnet, information about the bulk-rock composition and mineral paragenesis of the initial garnet-bearing host-rock is absent. This prevents the application of chemical thermo-barometric techniques and calls for quantitative empirical approaches. Here we present a garnet host-rock discrimination scheme that is based on a random forest machine-learning algorithm trained on a large dataset of 13,615 chemical analyses of garnet that covers a wide variety of garnet-bearing lithologies. Considering the out-of-bag error, the scheme correctly predicts the original garnet host-rock in (i) 〉 95% concerning the setting, that is either mantle, metamorphic, igneous, or metasomatic; (ii) 〉 84% concerning the metamorphic facies, that is either blueschist/greenschist, amphibolite, granulite, or eclogite/ultrahigh-pressure; and (iii) 〉 93% concerning the host-rock bulk composition, that is either intermediate–felsic/metasedimentary, mafic, ultramafic, alkaline, or calc–silicate. The wide coverage of potential host rocks, the detailed prediction classes, the high discrimination rates, and the successfully tested real-case applications demonstrate that the introduced scheme overcomes many issues related to previous schemes. This highlights the potential of transferring the applied discrimination strategy to the broad range of detrital minerals beyond garnet. For easy and quick usage, a freely accessible web app is provided that guides the user in five steps from garnet composition to prediction results including data visualization.
    Description: deutsche forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Georg-August-Universität Göttingen (1018)
    Description: http://134.76.17.86:443/garnetRF/
    Keywords: ddc:549 ; Garnet major-element composition ; Database ; Host-rock discrimination ; Machine-learning ; Provenance ; Web app
    Language: English
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  • 43
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    Sedimentological evidence for seiching in a swell-dominated headland-bay system: Table Bay, Western Cape, South Africa (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-07-27
    Description: Table Bay, South Africa, is a typical headland-bay system with a shoreline that can be described by a logarithmic spiral. A peculiarity and unique feature of Table Bay is the juxtaposition of Robben Island opposite its headland. As a consequence, the bathymetry defines an ellipsoidal basin which was postulated to potentially resonate in the form of long-period standing waves (seiches). One aim of this study, therefore, was to investigate whether any evidence for such resonant oscillations could be detected in the geomorphology and sediment distribution patterns. Indeed, the ellipsoidal shape of the basin can be framed by two converging log-spirals with their centres located opposite each other, one off Robben Island and the other on the Cape Town side of the bay. The so-called apex line, which divides the two spirals into equal parts is aligned SW–NE, i.e. more or less parallel to the direction of ocean wave propagation. The distribution patterns of all sedimentary parameters were found to be characterised by a strikingly similar trend to either side of the apex line. This supports the hypothesis that the basin of Table Bay appears to resonate in the form of a mode 1 standing wave, with the node positioned above the apex line in the centre of the bay. The maximum period of such a standing wave was calculated to be around 37 min. The study demonstrates that large-scale sediment distribution patterns can reveal the existence of specific hydrodynamic processes in coastal embayments. It is recommended that this phenomenon be investigated in greater detail aimed at verifying the existence of resonant oscillations in Table Bay and, in the event, at establishing its precise nature and trigger mechanism.
    Description: Council for Geoscience and CSIR South Africa
    Description: Senckenberg Gesellschaft für Naturforschung (SGN) (3507)
    Keywords: ddc:551.46 ; Oceanography ; South Africa ; Table Bay ; ellipsoidal shape ; sediment distribution ; seiches
    Language: English
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  • 44
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    Hurricane Matthew in 2100: effects of extreme sea level rise scenarios on a highly valued coastal area (Palm Beach, FL, USA) (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-07-27
    Description: Sea-level rise represents a severe hazard for populations living within low-elevation coastal zones and is already largely affecting coastal communities worldwide. As sea level continues to rise following unabated greenhouse gas emissions, the exposure of coastal communities to inundation and erosion will increase exponentially. These impacts will be further magnified under extreme storm conditions. In this paper, we focus on one of the most valuable coastal real estate markets globally (Palm Beach, FL). We use XBeach, an open-source hydro and morphodynamic model, to assess the impact of a major tropical cyclone (Hurricane Matthew, 2016) under three different sea-level scenarios. The first scenario (modern sea level) serves as a baseline against which other model runs are evaluated. The other two runs use different 2100 sea-level projections, localized to the study site: (i) IPCC RCP 8.5 (0.83 m by 2100) and (ii) same as (i), but including enhanced Antarctic ice loss (1.62 m by 2100). Our results show that the effective doubling of future sea level under heightened Antarctic ice loss amplifies flow velocity and wave height, leading to a 46% increase in eroded beach volume and the overtopping of coastal protection structures. This further exacerbates the vulnerability of coastal properties on the island, leading to significant increases in parcel inundation.
    Description: Universität Bremen (1013)
    Description: https://github.com/pboyden/Palm_Beach_XBeach
    Keywords: ddc:551.46 ; Oceanography ; tropical cyclones ; coastal areas ; sea level scenarios ; hydrodynamic modeling ; morphodynamic modeling
    Language: English
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  • 45
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    Clay mineral formation in Permian rocks of a geothermal borehole at Northern Upper Rhine Graben, Germany (2021)
    Nguyen-Thanh, Lan ; Mählmann, Rafael Ferreiro ; Hoang-Minh, Thao ; [et al.]
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-07-19
    Description: Hydrothermally altered rhyolite rocks in the Permian Donnersberg Formation of a geothermal borehole in the Northern Upper Rhine Graben (Germany) were investigated to find out answers for the low hydraulic conductivity of the rocks. The composition of clay minerals and the temperature of smectite–illite transformation were carried out using X-ray diffraction, X-ray fluorescence, transmission electron microscopy, Fourier transform infrared spectroscopy, and polarized-light microscopy analyses. Clay mineral (CM) composition includes illite/muscovite (1M and 2M1 polytypes), illite–smectite interstratifications (IS-ml), smectite, and chlorite; and non-clay minerals such as quartz, feldspars, epidote, calcite, dolomite, and hematite were detected. The 2M1-polytype mica might be the only primary sheet silicates from the parent rocks, while the others occur as authigenic neo-formed CMs under heat flow and geothermal gradient. The development of CMs indicates different mechanisms of illitization and smectitization. Based on the texture, morphology, structure/polytype, and chemistry of rocks and minerals, in particular CMs, the study grouped the CM formation into three transformation processes: smectitization during magma cooling and possible contact metamorphisms with decreasing and low temperature, smectite illitization controlled by burial diagenesis and hydrothermal alteration, and illite smectitization followed exhumation and Cenozoic subsidence with decreasing temperature. The rhyolites were altered to all of the orders IS-R0, IS-R1, and IS-R3 by the dissolution-precipitation and layer-to-layer mechanisms. The first one supported small xenomorphic plates and flakes of 1Md, elongated particles of 1M, and pseudo-hexagonal forms of 2M1. The second one could lead to the platy particles of 1Md and 2M1 polytypes. The dominant temperature range for the transformation in the area has been 140–170 °C– ~ 230 °C.
    Description: Technische Universität Darmstadt (3139)
    Keywords: ddc:549 ; Geothermal borehole ; Clay mineral ; Smectite illitization ; Thermal gradient ; Upper Rhine Graben ; Donnersberg Formation
    Language: English
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  • 46
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    An extremeness threshold determines the regional response of floods to changes in rainfall extremes (2021)
    Nature Publishing Group UK
    Details
    Publication Date: 2023-07-19
    Description: Precipitation extremes will increase in a warming climate, but the response of flood magnitudes to heavier precipitation events is less clear. Historically, there is little evidence for systematic increases in flood magnitude despite observed increases in precipitation extremes. Here we investigate how flood magnitudes change in response to warming, using a large initial-condition ensemble of simulations with a single climate model, coupled to a hydrological model. The model chain was applied to historical (1961–2000) and warmer future (2060–2099) climate conditions for 78 watersheds in hydrological Bavaria, a region comprising the headwater catchments of the Inn, Danube and Main River, thus representing an area of expressed hydrological heterogeneity. For the majority of the catchments, we identify a ‘return interval threshold’ in the relationship between precipitation and flood increases: at return intervals above this threshold, further increases in extreme precipitation frequency and magnitude clearly yield increased flood magnitudes; below the threshold, flood magnitude is modulated by land surface processes. We suggest that this threshold behaviour can reconcile climatological and hydrological perspectives on changing flood risk in a warming climate.
    Description: The response of flood risk in Bavaria, Germany to increases in rainfall extremes in a warming climate is modulated by land surface processes below a precipitation threshold, but not above, suggest ensemble simulations with a hydrological model.
    Description: Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (Swiss National Science Foundation) https://doi.org/10.13039/501100001711
    Description: National Science Foundation (NSF) https://doi.org/10.13039/100000001
    Description: Funder: Bavarian State Ministry for the Environment and Consumer Protection Reference Number: 81-0270-024570/2015
    Description: http://www.hydroshare.org/resource/945d7b4f61d145d789eb090f0bf51cb5
    Keywords: ddc:551.46 ; Atmospheric science ; Climate-change impacts ; Hydrology ; Natural hazards
    Language: English
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  • 47
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    Strong glacial-interglacial variability in upper ocean hydrodynamics, biogeochemistry, and productivity in the southern Indian Ocean (2021)
    Nature Publishing Group UK
    Details
    Publication Date: 2024-02-28
    Description: In the southern Indian Ocean, the position of the subtropical front – the boundary between colder, fresher waters to the south and warmer, saltier waters to the north – has a strong influence on the upper ocean hydrodynamics and biogeochemistry. Here we analyse a sedimentary record from the Agulhas Plateau, located close to the modern position of the subtropical front and use alkenones and coccolith assemblages to reconstruct oceanographic conditions over the past 300,000 years. We identify a strong glacial-interglacial variability in sea surface temperature and productivity associated with subtropical front migration over the Agulhas Plateau, as well as shorter-term high frequency variability aligned with variations in high latitude insolation. Alkenone and coccolith abundances, in combination with diatom and organic carbon records indicate high glacial export productivity. We conclude that the biological pump was more efficient and strengthened during glacial periods, which could partly account for the reported reduction in atmospheric carbon dioxide concentrations.
    Description: Migration of the Subtropical Front during glacial and interglacial periods resulted in variability in the strength of the biological pump in the Southern Ocean sector of the Indian Ocean, according to sedimentary records from the Agulhas Plateau.
    Description: https://doi.pangaea.de/10.1594/PANGAEA.912467
    Keywords: ddc:551.46 ; palaeoceanography ; southern Indian Ocean ; Agulhas Plateau ; upper ocean hydrodynamics ; biogeochemistry
    Language: English
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    Submesoscale flows impact Agulhas leakage in ocean simulations (2021)
    Nature Publishing Group UK
    Details
    Publication Date: 2023-11-14
    Description: Agulhas leakage, the warm and salty inflow of Indian Ocean water into the Atlantic Ocean, is of importance for the climate-relevant Atlantic Meridional Overturning Circulation. South of Africa, the eastward turning Agulhas Current sheds Agulhas rings, cyclones and filaments of order 100 km that carry the Indian Ocean water into the Cape Basin and further into the Atlantic. Here, we show that the resolution of submesoscale flows of order 10 km in an ocean model leads to 40 % more Agulhas leakage and more realistic Cape Basin water-masses compared to a parallel non-submesoscale resolving simulation. Moreover, we show that submesoscale flows strengthen shear-edge eddies and in consequence lee cyclones at the northern edge of the Agulhas Current, as well as the leakage pathway in the region of the filaments that takes place outside of mesoscale eddies. This indicates that the increase in leakage can be attributed to stronger Agulhas filaments, when submesoscale flows are resolved.
    Description: Leakage of warm, salty waters from the Indian Ocean into the Atlantic increases by up to 40 % in high-resolution numerical ocean model simulations, suggesting that low-resolution models underestimate this key part of the global meridional overturning circulation.
    Description: Agence Nationale de la Recherche (French National Research Agency) https://doi.org/10.13039/501100001665
    Description: https://hdl.handle.net/20.500.12085/c572cde8-a82c-4c2d-9bd7-288dfc8f1939
    Description: https://www.aoml.noaa.gov/phod/gdp/data.php
    Description: https://resources.marine.copernicus.eu/?option=com_csw&view=details&product_id=GLOBAL_REANALYSIS_PHY_001_030
    Description: https://resources.marine.copernicus.eu/?option=com_csw&view=details&product_id=SEALEVEL_GLO_PHY_L4_REP_OBSERVATIONS_008_047
    Keywords: ddc:551.46 ; Climate and Earth system modelling ; Physical oceanography
    Language: English
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    The role of clay content and mineral surface area for soil organic carbon storage in an arable toposequence (2021)
    Springer International Publishing
    Details
    Publication Date: 2023-09-13
    Description: Correlations between organic carbon (OC) and fine mineral particles corroborate the important role of the abundance of soil minerals with reactive surfaces to bind and increase the persistence of organic matter (OM). The storage of OM broadly consists of particulate and mineral-associated forms. Correlative studies on the impact of fine mineral soil particles on OM storage mostly combined data from differing sites potentially confounded by other environmental factors. Here, we analyzed OM storage in a soil clay content gradient of 5–37% with similar farm management and mineral composition. Throughout the clay gradient, soils contained 14 mg OC g−1 on average in the bulk soil without showing any systematic increase. Density fractionation revealed that a greater proportion of OC was stored as occluded particulate OM in the high clay soils (18–37% clay). In low clay soils (5–18% clay), the fine mineral-associated fractions had up to two times higher OC contents than high clay soils. Specific surface area measurements revealed that more mineral-associated OM was related to higher OC loading. This suggests that there is a potentially thicker accrual of more OM at the same mineral surface area within fine fractions of the low clay soils. With increasing clay content, OM storage forms contained more particulate OC and mineral-associated OC with a lower surface loading. This implies that fine mineral-associated OC storage in the studied agricultural soils was driven by thicker accrual of OM and decoupled from clay content limitations.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Technische Universität München (1025)
    Description: https://doi.org/10.14459/2018mp1462414
    Keywords: ddc:549 ; Soil organic matter ; Fine mineral particles ; Organic carbon storage ; Clay content ; Organic carbon loading ; Nanoscale secondary ion mass spectrometry
    Language: English
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  • 50
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    Vorkommen von Vanadium im Grundwasser der Vulkaneifel (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-21
    Description: In Quellwasserproben rund um den Ringseitert-Vulkankomplex südöstlich der Gemeinde Kirchweiler (Westeifel) wurden weit über dem Geringfügigkeitsschwellenwert erhöhte Vanadiumkonzentrationen mit einem Maximalwert von 28 μg/l nachgewiesen. Generell zeigten die im Bereich der Känozoischen Vulkanite entnommenen Wasserproben erheblich höhere Konzentrationen als die im umliegenden Paläozoikum. Lokale Vulkanitproben weisen bis zu vierfach über dem Krustenmittel erhöhte Gesamtgehalte an Vanadium auf. Elutionsuntersuchungen ergaben eine erhöhte Vanadiumfreisetzung. Zur weiteren mikroanalytischen Suche nach der geogenen Quelle für diese Anomalie wurden Dünnschliffe der Gesteinsproben hergestellt und mittels Elektronenmikrosonde analysiert. Die Elementverteilungsbilder zeigten nicht die erwartete Korrelation zwischen den Elementen Fe und V, wohl jedoch eine Korrelation zwischen P und V. Hotspot-Analysen von V‑reichen Mineralkörnern weisen auf das Mineral Fluorapatit mit bis zu 5 Gew.-% Vanadat als Substitution für das Phosphat als geogene Vanadiumquelle in den Vulkaniten hin. Eine hydrogeochemische Modellierung mit PhreePlot zeigt übereinstimmend, dass die Wasserproben mit erhöhten Vanadiumkonzentrationen alle im pe/pH-Prädominanzfeld der Vanadat(V)-Komplexe liegen.
    Description: Johannes Gutenberg-Universität Mainz (1030)
    Keywords: ddc:551.46 ; Volcanic aquifer ; Vanadium mobility ; Vanadate ; V‑bearing Fluorapatite
    Language: German
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  • 51
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    Global tide simulations with ICON-O: testing the model performance on highly irregular meshes (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-21
    Description: The global tide is simulated with the global ocean general circulation model ICON-O using a newly developed tidal module, which computes the full tidal potential. The simulated coastal M2 amplitudes, derived by a discrete Fourier transformation of the output sea level time series, are compared with the according values derived from satellite altimetry (TPXO-8 atlas). The experiments are repeated with four uniform and sixteen irregular triangular grids. The results show that the quality of the coastal tide simulation depends primarily on the coastal resolution and that the ocean interior can be resolved up to twenty times lower without causing considerable reductions in quality. The mesh transition zones between areas of different resolutions are formed by cell bisection and subsequent local spring optimisation tolerating a triangular cell’s maximum angle up to 84°. Numerical problems with these high-grade non-equiangular cells were not encountered. The results emphasise the numerical feasibility and potential efficiency of highly irregular computational meshes used by ICON-O.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551.46 ; Ocean modelling ; Tides ; Unstructured grids ; Mesh refinement ; ICON-O
    Language: English
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    Tidal response to sea level rise and bathymetric changes in the German Wadden Sea (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-21
    Description: Tidally dominated coasts are directly affected not only by projected rise in mean sea level, but also by changes in tidal dynamics due to sea level rise and bathymetric changes. By use of a hydrodynamic model, which covers the entire German Bight (South-Eastern North Sea), we analyse the effects of sea level rise and potential bathymetric changes in the Wadden Sea on tidal current velocities. The model results indicate that tidal current velocities in the tidal inlets and channels of the Wadden Sea are increased in response to sea level rise. This is explained by the increased ratio of tidal prism to tidal inlet cross-sectional area, which is due to the characteristic hypsometry of tidal basins in the Wadden Sea including wide and shallow tidal flats and relatively narrow tidal channels. The results further indicate that sea level rise decreases ebb dominance and increases flood dominance in tidal channels. This is, amongst others, related to a decreased intertidal area again demonstrating the strong interaction between tidal wave and tidal basin hypsometry in the Wadden Sea. The bathymetry scenario defined in this study includes elevated tidal flats and deepened tidal channels, which is considered a potential future situation under accelerated sea level rise. Application of these bathymetric changes to the model mostly compensates the effects of sea level rise. Furthermore, changes in current velocity due to the altered bathymetry are in the same order of magnitude as changes due to mean sea level rise. This highlights the significance of considering potential bathymetric changes in the Wadden Sea for regional projections of the tidal response to sea level rise.
    Description: Bundesanstalt für Wasserbau (4234)
    Keywords: ddc:551.46 ; Sea level rise ; Tidal basin ; Tidal asymmetry ; Hypsometric control ; Hydrodynamic model ; Wadden Sea
    Language: English
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  • 53
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    Improvements in turbulence model realizability for enhanced stability of ocean forecast and its importance for downstream components (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-21
    Description: The numerical stability of ocean circulation models is of high significance in operational forecasting. A substantial improvement in numerical stability of the 3D-ocean model HBM could be achieved by the implementation of new realizability criteria in the turbulence closure scheme. Realizability criteria which were already well documented for closure functions without double diffusion were therefore extended to those using double diffusion. A purely technical validation method called ε-test which is suitable for the detection of numerical stability problems is presented, and the effect of the development in turbulence model is demonstrated under severe weather conditions during extreme storm events. Evaluation of statistics of longer simulations indicate that instabilities appeared only locally and temporary; nevertheless, a significant impact on drift products relying on the current forecasts could be demonstrated, which underlines the importance of realizability in turbulence closure schemes in comprehensive operational model systems including ocean circulation and downstream drift components.
    Description: Bundesamt für Seeschifffahrt und Hydrographie (BSH) (4225)
    Keywords: ddc:551.46 ; turbulence closure ; numerical stability / realizability ; operational forecasting systems
    Language: English
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  • 54
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    Estimates of wind power and radiative near-inertial internal wave flux (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-21
    Description: Energy transfer mechanisms between the atmosphere and the deep ocean have been studied for many years. Their importance to the ocean’s energy balance and possible implications on mixing are widely accepted. The slab model by Pollard (Deep-Sea Res Oceanogr Abstr 17(4):795–812, 1970) is a well-established simulation of near-inertial motion and energy inferred through wind-ocean interaction. Such a model is set up with hourly wind forcing from the NCEP-CFSR reanalysis that allows computations up to high latitudes without loss of resonance. Augmenting the one-dimensional model with the horizontal divergence of the near-inertial current field leads to direct estimates of energy transfer spectra of internal wave radiation from the mixed layer base into the ocean interior. Calculations using this hybrid model are carried out for the North Atlantic during the years 1989 and 1996, which are associated with positive and negative North Atlantic Oscillation index, respectively. Results indicate a range of meridional regimes with distinct energy transfer ratios. These are interpreted in terms of the mixed layer depth, the buoyancy frequency at the mixed layer base, and the wind field structure. The average ratio of radiated energy fluxes from the mixed layer to near-inertial wind power for both years is approximately 12%. The dependence on the wind structure is supported by simulations of idealized wind stress fronts with variable width and translation speeds.
    Description: Deutsche Forschungsgemeinschaft https://doi.org/10.13039/501100001659
    Description: Canadian Network for Research and Innovation in Machining Technology, Natural Sciences and Engineering Research Council of Canada https://doi.org/10.13039/501100002790
    Keywords: ddc:551.46 ; Near inertial waves ; Wind ocean coupling ; Internal gravity waves
    Language: English
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    Interactions between barotropic tides and mesoscale processes in deep ocean and shelf regions (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-21
    Description: The interactions between barotropic tides and mesoscale processes were studied using the results of a numerical model in which tidal forcing was turned on and off. The research area covered part of the East Atlantic Ocean, a steep continental slope, and the European Northwest Shelf. Tides affected the baroclinic fields at much smaller spatial scales than the barotropic tidal scales. Changes in the horizontal patterns of the M2 and M4 tidal constituents provided information about the two-way interactions between barotropic tides and mesoscale processes. The interaction between the atmosphere and ocean measured by the work done by wind was also affected by the barotropic tidal forcing. Tidal forcing intensified the transient processes and resulted in a substantial transformation of the wave number spectra in the transition areas from the deep ocean to the shelf. Tides flattened the sea-surface height spectra down to ~ k−2.5 power law, thus reflecting the large contribution of the processes in the high-frequency range compared to quasi-geostrophic motion. The spectra along sections parallel or normal to the continental slope differ from each other, which indicates that mesoscale turbulence was not isotropic. An analysis of the vorticity spectra showed that the flattening was mostly due to internal tides. Compared with the deep ocean, no substantial scale selectivity was observed on the shelf area. Particle tracking showed that the lengths of the Lagrangian trajectories increased by approximately 40% if the barotropic tidal forcing was activated, which contributed to changed mixing properties. The ratio between the horizontal and vertical scales of motion varied regionally depending on whether barotropic tidal forcing was included. The overall conclusion is that the barotropic tides affect substantially the diapycnal mixing.
    Description: Ministry of Science and Culture of Lower Saxony
    Description: BMBF
    Keywords: ddc:551.46 ; Tides ; Mesoscale processes ; Nonlinear interactions ; Diapycnal mixing ; Spectral energy ; European Northwest Shelf
    Language: English
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    Sea-state contributions to sea-level variability in the European Seas (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-19
    Description: The contribution of sea-state-induced processes to sea-level variability is investigated through ocean-wave coupled simulations. These experiments are performed with a high-resolution configuration of the Geestacht COAstal model SysTem (GCOAST), implemented in the Northeast Atlantic, the North Sea and the Baltic Sea which are considered as connected basins. The GCOAST system accounts for wave-ocean interactions and the ocean circulation relies on the NEMO (Nucleus for European Modelling of the Ocean) ocean model, while ocean-wave simulations are performed using the spectral wave model WAM. The objective is to demonstrate the contribution of wave-induced processes to sea level at different temporal and spatial scales of variability. When comparing the ocean-wave coupled experiment with in situ data, a significant reduction of the errors (up to 40% in the North Sea) is observed, compared with the reference. Spectral analysis shows that the reduction of the errors is mainly due to an improved representation of sea-level variability at temporal scales up to 12 h. Investigating the representation of sea-level extremes in the experiments, significant contributions (〉 20%) due to wave-induced processes are observed both over continental shelf areas and in the Atlantic, associated with different patterns of variability. Sensitivity experiments to the impact of the different wave-induced processes show a major impact of wave-modified surface stress over the shelf areas in the North Sea and in the Baltic Sea. In the Atlantic, the signature of wave-induced processes is driven by the interaction of wave-modified momentum flux and turbulent mixing, and it shows its impact to the occurrence of mesoscale features of the ocean circulation. Wave-induced energy fluxes also have a role (10%) in the modulation of surge at the shelf break.
    Keywords: ddc:551.46 ; Sea state ; Ocean-wave interactions ; Sea level ; Surge
    Language: English
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    Numerische Simulationen des Ausbreitungsverhaltens von Wärmeträgerfluid-Inhaltsstoffen aus Erdwärmesonden in Trinkwassereinzugsgebieten (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-20
    Description: Aufgrund deutlich erhöhter Wärmebedarfsdichten urbaner Räume besteht in besonderem Maße hier die Möglichkeit und Erfordernis, durch eine nachhaltige Wärmeversorgung und saisonale Wärmespeicherung im geologischen Untergrund einen wesentlichen Beitrag zu den national und international gesetzten Klimaschutzzielen zu liefern. Eine effiziente Möglichkeit zur Wärmegewinnung und -speicherung bieten hierfür Erdwärmesonden, die jedoch aus Gründen des vorbeugenden Grundwasserschutzes in Bereichen der Trinkwassernutzung heutzutage meist nicht oder nur beschränkt genehmigt werden. Numerische Simulationen einer Erdwärmesondenleckage für Randbedingungen eines zur Trinkwassergewinnung genutzten norddeutschen Aquifers auf Grundlage von aufgearbeiteten stoffspezifischen Abbauratenkonstanten zeigen, dass Grenzwerte für die meisten handelsüblichen Wärmeträgerfluid-Inhaltsstoffe bereits bei einem Abstand von nur 100 m zwischen Erdwärmesonde und Trinkwasserentnahme aufgrund starker Verdünnung und mikrobiellen Abbaus mit einem Faktor 〉 10 unterschritten werden. Vor dem Hintergrund dieser Ergebnisse und angesichts der Zielsetzung einer Reduktion fossiler Primärenergiequellen um 80–95 % bis 2050, erscheinen pauschale Abstandsvorgaben (von zurzeit 〉 1000 m) daher zumindest hinsichtlich der Trinkwassergefährdung durch Erdwärmesondenleckagen diskussionswürdig.
    Description: Christian-Albrechts-Universität zu Kiel (3094)
    Keywords: ddc:549 ; Borehole heat exchanger ; Heat transfer fluids ; Additives ; Groundwater ; Risk assessment
    Language: German
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    Lateral variations in the Unit 7–8 boundary zone of the Rum Eastern Layered Intrusion, NW Scotland: implications for the origin and timing of Cr-spinel seam formation (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-23
    Description: The Rum Layered Suite, NW Scotland, hosts Cr-spinel seams at the bases of peridotite–troctolite macro-rhythmic units in the eastern portion of the intrusion. Here, we present detailed field observations together with microstructural and mineral chemical analyses for the Unit 7–8 Cr-spinel seam and associated cumulates in the Eastern Layered Intrusion. Detailed mapping and sampling reveal significant lateral variations in the structural characteristics and mineral compositions of the Unit 7–8 boundary zone rocks. Although the Cr-spinel seam is laterally continuous over ~ 3 km, it is absent towards the centre and the margins of the intrusion. The compositional characteristics of Cr-spinel and plagioclase vary systematically along strike, exhibiting a chemical evolution towards more differentiated compositions with increasing distance from the main feeder conduit of the Rum intrusion; the Long Loch Fault. On the basis of our combined datasets, we propose that the upper part of the troctolite, the anorthosite layer underlying the Cr-spinel seam and the seam itself formed during a multi-stage magma replenishment event. The stages can be summarised as follows: (1) peridotite schlieren and anorthosite autoliths formed following melt infiltration and cumulate assimilation in the crystal mush of the Unit 7 troctolite. (2) The anorthosite layer then formed from the Unit 7 troctolite crystal mush by thermal erosion and dissolution due to infiltrating magma. (3) Subsequent dissolution of the anorthosite layer by new replenishing magma led to peritectic in situ crystallisation of the Unit 7–8 Cr-spinel seam, with (4) continued magma input eventually producing the overlying Unit 8 peridotite. In the central part of the Rum Layered Suite, the aforementioned assimilation of the troctolitic footwall formed the anorthosite layer. However, the absence of anorthosite in close proximity to the Long Loch Fault can be explained by enhanced thermochemical erosion close to the feeder zone, and its absence close to the margins of the intrusion, at maximum distance from the Long Loch Fault, may be due to cooling of the magma and loss of erosion potential. In line with other recent studies on PGE-bearing chromitites in layered intrusions, we highlight the importance of multi-stage intrusive magma replenishment to the formation of spatially coupled anorthosite and Cr-spinel seams, as well as the lateral mineral chemical variations observed in the Unit 7–8 boundary zone cumulates.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Keywords: ddc:549 ; Mineralogy ; Cr-spinel seam
    Language: English
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    Natural blue zircon from Vesuvius (2020)
    Springer Vienna
    Details
    Publication Date: 2023-06-23
    Description: Zircon from syenitic ejecta of Vesuvius (Campania, Italy) is unusually blue, a property shared with gem zircon from Ratanakiri province (Cambodia), which turns from natural reddish-brown to blue when heated under reducing conditions. Here, the origins of these unusual crystals were traced through geochronology, trace elements, and O-Hf isotopic compositions. The causes of its colour were investigated through optical and electron microscopy, optical absorption spectroscopy, and Raman microspectroscopy. Colour stability upon heating and ultraviolet light (UV) exposure was tested using Ratanakiri zircon as a control. Vesuvius zircon contains vesiculated zones with abundant inclusions ~2.5 μm to 〈100 nm in diameter (mostly U-rich thorianite and pyrochlore-group minerals), while homogeneous zircon domains are high in Th and U (up to 5.9 and 1.8 wt%, respectively). Its blue colouration is stable under UV radiation, as well as heat-treatment under reducing conditions (1000 °C; 〉15 h). Turbid domains rich in large inclusions change to yellow-brown after heating under oxidizing conditions, while transparent domains remain pale blue or colourless. Optical absorption spectra display sharp absorption lines attributed to U4+, and slightly elevated absorption towards shorter wavelengths. The ~1007 cm−1 ν3(SiO4) Raman band is broadened due to lattice distortion by non-stoichiometric elements in high-Th/-U zircon, whereas narrow bands in inclusion-rich domains indicate a decrease in lattice strain due to inclusion precipitation. Blue colouration in Vesuvius zircon is explained by the effect of light scattering (Rayleigh and/or Mie scattering) on highly refractive actinide-rich inclusions ranging in size from 〈1/10 to few multiples of the wavelengths of visible light. Inclusions likely formed during fluid-mediated coupled dissolution-reprecipitation that locally transformed lattice-strained actinide-rich zircon within several hundreds of years prior to eruption.
    Description: Ruprecht-Karls-Universität Heidelberg (1026)
    Keywords: ddc:549 ; Blue zircon ; Vesuvius ; Rayleigh/Mie scattering ; Optical absorption ; Raman microspectroscopy ; Mineral inclusions ; Syenite
    Language: English
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    Mid-infrared spectroscopy of alkali feldspar samples for space application (2020)
    Springer Vienna
    Details
    Publication Date: 2023-06-23
    Description: Feldspars are major components of terrestrial planetary surfaces. For future space application and the setup of a comprehensive reference database, Na- and K-rich alkali feldspars, NaAlSi3O8 – KAlSi3O8, have been investigated by infrared reflectance spectroscopy. We related the feldspar spectra to the chemical composition and state of Al,Si order/disorder. The infrared measurements were analyzed with respect to band shifts and peak shapes using the autocorrelation function. Natural samples served as starting materials. Some samples were treated by the alkali exchange method to produce pure end-members, which were then heated to generate various states of Al,Si disorder. X-ray diffraction (XRD) methods served to determine the Al,Si distribution. Our autocorrelation allowed to differentiate between the compositional and the order/disorder influences seen in the spectra in the wavelength range between 7 μm up to 14 μm (1429 cm− 1 to 714 cm− 1). Space missions often analyze the surfaces of planetary bodies using remote sensing. Therefore, our results are essential to characterize and distinguish alkali feldspars on the surfaces of terrestrial planetary bodies like Mercury.
    Description: Deutsches Zentrum für Luft- und Raumfahrt https://doi.org/10.13039/501100002946
    Keywords: ddc:549 ; Alkali feldspars ; Infrared spectroscopy ; X-ray diffraction ; Al,Si distribution
    Language: English
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    Reassessing zircon-monazite thermometry with thermodynamic modelling: insights from the Georgetown igneous complex, NE Australia (2020)
    Volante, S. ; Collins, W. J. ; Blereau, E. ; [et al.]
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-06-23
    Description: Accessory mineral thermometry and thermodynamic modelling are fundamental tools for constraining petrogenetic models of granite magmatism. U–Pb geochronology on zircon and monazite from S-type granites emplaced within a semi-continuous, whole-crust section in the Georgetown Inlier (GTI), NE Australia, indicates synchronous crystallisation at 1550 Ma. Zircon saturation temperature (Tzr) and titanium-in-zircon thermometry (T(Ti–zr)) estimate magma temperatures of ~ 795 ± 41 °C (Tzr) and ~ 845 ± 46 °C (T(Ti-zr)) in the deep crust, ~ 735 ± 30 °C (Tzr) and ~ 785 ± 30 °C (T(Ti-zr)) in the middle crust, and ~ 796 ± 45 °C (Tzr) and ~ 850 ± 40 °C (T(Ti-zr)) in the upper crust. The differing averages reflect ambient temperature conditions (Tzr) within the magma chamber, whereas the higher T(Ti-zr) values represent peak conditions of hotter melt injections. Assuming thermal equilibrium through the crust and adiabatic ascent, shallower magmas contained 4 wt% H2O, whereas deeper melts contained 7 wt% H2O. Using these H2O contents, monazite saturation temperature (Tmz) estimates agree with Tzr values. Thermodynamic modelling indicates that plagioclase, garnet and biotite were restitic phases, and that compositional variation in the GTI suites resulted from entrainment of these minerals in silicic (74–76 wt% SiO2) melts. At inferred emplacement P–T conditions of 5 kbar and 730 °C, additional H2O is required to produce sufficient melt with compositions similar to the GTI granites. Drier and hotter magmas required additional heat to raise adiabatically to upper-crustal levels. S-type granites are low-T mushes of melt and residual phases that stall and equilibrate in the middle crust, suggesting that discussions on the unreliability of zircon-based thermometers should be modulated.
    Description: Centre of Excellence for Core to Crust Fluid Systems, Australian Research Council http://dx.doi.org/10.13039/100012537
    Description: Ruhr-Universität Bochum (1007)
    Keywords: ddc:549 ; Zircon and monazite thermometry ; Water content ; Granitic melts ; Complete crustal section ; Phase equilibria diagrams
    Language: English
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    Interspinifex Ni sulfide ore from Victor South-McLeay, Kambalda, Western Australia (2020)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2024-02-12
    Description: Spinifex-textured olivine plates hosted in sulfides are usually named “interspinifex ore” in komatiite-hosted sulfide deposits. This ore type is rare but provides important genetic information on sulfide deposits, komatiite volcanology and thermomechanical erosion processes. Occurrences in Victor South-McLeay and Moran South (Kambalda, Western Australia) differ significantly from previously reported occurrences in their stratigraphic location, position within the ore profile and textural appearance. Thus, their formation process has to be reconsidered. Interspinifex ore reported here is situated in the lower portion of the basal lava flow between massive and net-textured sulfides in the centre of the embayment and between massive sulfides and older basalt in a “pinchout” where the sulfides melted sideways into older basalt on the embayment edge. Interspinifex ore is composed of up to 10-cm-long aggregates of parallel plates in the upper portion of massive sulfides and is overlain by barren komatiite. The texture does not allow for a classic single explanation. Thus, two possible formation mechanisms are envisaged: (1) A younger komatiite melt intrudes into its own olivine and sulfide liquid cumulate pile, while the sulfides are still liquid. The injection on top of the sulfides causes the formation of an emulsion, from which the spinifex forms due to the temperature gradient between the melts. (2) Interspinifex ore is a relic of an early komatiite flow formed in a series of successive pulses of komatiite and sulfide liquid. The spinifex of the komatiite is invaded by a younger batch of sulfide liquid replacing interstitial silicate melt.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:549 ; Interspinifex ore ; Kambalda ; Komatiite-hosted Ni sulfide deposit ; Emulsion ; Sulfide infiltration
    Language: English
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