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  • American Association for the Advancement of Science  (369,592)
  • American Geophysical Union (AGU)
  • Institute of Physics (IOP)
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  • 101
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    Offshore pelagic subsidies dominate carbon inputs to coral reef predators (2021)
    American Association for the Advancement of Science
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Skinner, C., Mill, A. C., Fox, M. D., Newman, S. P., Zhu, Y., Kuhl, A., & Polunin, N. V. C. Offshore pelagic subsidies dominate carbon inputs to coral reef predators. Science Advances, 7(8), (2021): eabf3792, https://doi.org/10.1126/sciadv.abf3792.
    Description: Coral reefs were traditionally perceived as productive hot spots in oligotrophic waters. While modern evidence indicates that many coral reef food webs are heavily subsidized by planktonic production, the pathways through which this occurs remain unresolved. We used the analytical power of carbon isotope analysis of essential amino acids to distinguish between alternative carbon pathways supporting four key reef predators across an oceanic atoll. This technique separates benthic versus planktonic inputs, further identifying two distinct planktonic pathways (nearshore reef-associated plankton and offshore pelagic plankton), and revealing that these reef predators are overwhelmingly sustained by offshore pelagic sources rather than by reef sources (including reef-associated plankton). Notably, pelagic reliance did not vary between species or reef habitats, emphasizing that allochthonous energetic subsidies may have system-wide importance. These results help explain how coral reefs maintain exceptional productivity in apparently nutrient-poor tropical settings, but also emphasize their susceptibility to future ocean productivity fluctuations.
    Description: Sample analysis funding was provided by NERC LSMSF grant BRIS/102/0717 and BRIS/125/1418. C.S. was supported by a Newcastle University SAgE DTA studentship and a cooperative agreement with Banyan Tree.
    Repository Name: Woods Hole Open Access Server
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  • 102
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    An early cretaceous subduction-modified mantle underneath the ultraslow spreading Gakkel Ridge, Arctic Ocean (2020)
    American Association for the Advancement of Science
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Richter, M., Nebel, O., Maas, R., Mather, B., Nebel-Jacobsen, Y., Capitanio, F. A., Dick, H. J. B., & Cawood, P. A. An early cretaceous subduction-modified mantle underneath the ultraslow spreading Gakkel Ridge, Arctic Ocean. Science Advances, 6(44), (2020): eabb4340, doi:10.1126/sciadv.abb4340.
    Description: Earth’s upper mantle, as sampled by mid-ocean ridge basalts (MORBs) at oceanic spreading centers, has developed chemical and isotopic heterogeneity over billions of years through focused melt extraction and re-enrichment by recycled crustal components. Chemical and isotopic heterogeneity of MORB is dwarfed by the large compositional spectrum of lavas at convergent margins, identifying subduction zones as the major site for crustal recycling into and modification of the mantle. The fate of subduction-modified mantle and if this heterogeneity transmits into MORB chemistry remains elusive. Here, we investigate the origin of upper mantle chemical heterogeneity underneath the Western Gakkel Ridge region in the Arctic Ocean through MORB geochemistry and tectonic plate reconstruction. We find that seafloor lavas from the Western Gakkel Ridge region mirror geochemical signatures of an Early Cretaceous, paleo-subduction zone, and conclude that the upper mantle can preserve a long-lived, stationary geochemical memory of past geodynamic processes.
    Description: O.N. was supported by the Australian Research Council (grant FT140101062). P.A.C. was supported by the Australian Research Council (grant FL160100168). H.J.B.D. was supported by the NSF (grants PLR 9912162, PLR 0327591, OCE 0930487, and OCE 1434452). M.R. was supported by a graduate scholarship of Monash University and the SEAE.
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  • 103
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    Archaea dominate oxic subseafloor communities over multimillion-year time scales (2019)
    American Association for the Advancement of Science
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).. The definitive version was published in Vuillemin, A., Wankel, S. D., Coskun, Ö. K., Magritsch, T., Vargas, S., Estes, E. R., Spivack, A. J., Smith, D. C., Pockalny, R., Murray, R. W., D'Hondt, S., & Orsi, W. D. Archaea dominate oxic subseafloor communities over multimillion-year time scales. Science Advances, 5(6), (2019): eaaw4108, doi: 10.1126/sciadv.aaw4108.
    Description: Ammonia-oxidizing archaea (AOA) dominate microbial communities throughout oxic subseafloor sediment deposited over millions of years in the North Atlantic Ocean. Rates of nitrification correlated with the abundance of these dominant AOA populations, whose metabolism is characterized by ammonia oxidation, mixotrophic utilization of organic nitrogen, deamination, and the energetically efficient chemolithoautotrophic hydroxypropionate/hydroxybutyrate carbon fixation cycle. These AOA thus have the potential to couple mixotrophic and chemolithoautotrophic metabolism via mixotrophic deamination of organic nitrogen, followed by oxidation of the regenerated ammonia for additional energy to fuel carbon fixation. This metabolic feature likely reduces energy loss and improves AOA fitness under energy-starved, oxic conditions, thereby allowing them to outcompete other taxa for millions of years.
    Description: This work was supported primarily by the Deutsche Forschungsgemeinschaft (DFG) project OR 417/1-1 granted to W.D.O. Preliminary work was supported by the Center for Dark Energy Biosphere Investigations project OCE-0939564 also granted to W.D.O. Publication of the manuscript was supported by the LMU Mentoring Program. The expedition was funded by the US National Science Foundation through grant NSF-OCE-1433150 to A.J.S, S.D., and R.P. R.W.M. led the expedition. This is a contribution of the Deep Carbon Observatory (DCO). S.D.W. acknowledges partial support from NASA Exobiology (NNX15AM04G). This is Center for Dark Energy Biosphere Investigations (C-DEBI) publication number 463. Portions of this material are based on work supported while R.W.M. was serving at the National Science Foundation. A portion of this work was performed as part of the LMU Masters Program “Geobiology and Paleobiology” (MGAP).
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  • 104
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    On the Damping Time Scale of EVP Sea Ice Dynamics (2021)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Advances in Modeling Earth Systems, American Geophysical Union (AGU), 13(10), ISSN: 1942-2466
    Details
    Publication Date: 2023-06-21
    Description: We propose to make the damping time scale, which governs the decay of pseudo-elastic waves in the Elastic Viscous Plastic (EVP) sea-ice solvers, independent of the external time step and large enough to warrant numerical stability for a moderate number of internal time steps. A necessary condition is that the forcing on sea ice varies slowly on the damping time scale, in which case an EVP solution may still approach a Viscous Plastic one, but on a time scale longer than a single external time step. In this case, the EVP method becomes very close to the recently proposed modified EVP (mEVP) method in terms of stability and simulated behavior. In a simple test case dealing with sea ice breaking under the forcing of a moving cyclone, the EVP method with an enlarged damping time scale can simulate linear kinematic features which are very similar to those from the traditional EVP implementation, although a much smaller number of internal time steps is used. There is more difference in sea-ice thickness and linear kinematic features simulated in a realistic Arctic configuration between using the traditional and our suggested choices of EVP damping time scales, but it is minor considering model uncertainties associated with choices of many other parameters in sea-ice models.
    Repository Name: EPIC Alfred Wegener Institut
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  • 105
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    The Role of Zooplankton Grazing and Nutrient Recycling for Global Ocean Biogeochemistry and Phytoplankton Phenology (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research Biogeosciences, American Geophysical Union (AGU), 127(10), ISSN: 2169-8953
    Details
    Publication Date: 2023-06-21
    Description: Zooplankton plays a notable role in ocean biogeochemical cycles. However, it is often simulated as one generic group and top closure term in ocean biogeochemical models. This study presents the description of three zooplankton functional types (zPFTs, micro-, meso- and macrozooplankton) in the ocean biogeochemical model FESOM-REcoM. In the presented model, microzooplankton is a fast-growing herbivore group, mesozooplankton is another major consumer of phytoplankton, and macrozooplankton is a slow-growing group with a low temperature optimum. Meso- and macrozooplankton produce fast-sinking fecal pellets. With three zPFTs, the annual mean zooplankton biomass increases threefold to 210 Tg C. The new food web structure leads to a 25% increase in net primary production and a 10% decrease in export production globally. Consequently, the export ratio decreases from 17% to 12% in the model. The description of three zPFTs reduces model mismatches with observed dissolved inorganic nitrogen and chlorophyll concentrations in the South Pacific and the Arctic Ocean, respectively. Representation of three zPFTs also strongly affects phytoplankton phenology: Fast nutrient recycling by zooplankton sustains higher chlorophyll concentrations in summer and autumn. Additional zooplankton grazing delays the start of the phytoplankton bloom by 3 weeks and controls the magnitude of the bloom peak in the Southern Ocean. As a result, the system switches from a light-controlled Sverdrup system to a dilution-controlled Behrenfeld system. Overall, the results suggest that representation of multiple zPFTs is important to capture underlying processes that may shape the response of ecosystems and ecosystem services to on-going and future environmental change in model projections.
    Repository Name: EPIC Alfred Wegener Institut
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  • 106
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    A Kinematic Kinetic Energy Backscatter Parametrization: From Implementation to Global Ocean Simulations (2020)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Advances in Modeling Earth Systems, American Geophysical Union (AGU), 12(12), ISSN: 1942-2466
    Details
    Publication Date: 2023-06-21
    Description: Ocean models at eddy-permitting resolution are generally overdissipative, damping the intensity of the mesoscale eddy field. To reduce overdissipation, we propose a simplified, kinematic energy backscatter parametrization built into the viscosity operator in conjunction with a new flow-dependent coefficient of viscosity based on nearest neighbor velocity differences. The new scheme mitigates excessive dissipation of energy and improves global ocean simulations at eddy-permitting resolution. We find that kinematic backscatter substantially raises simulated eddy kinetic energy, similar to an alternative, previously proposed dynamic backscatter parametrization. While dynamic backscatter is scale aware and energetically more consistent, its implementation is more complex. Furthermore, it turns out to be computationally more expensive, as it applies, among other things, an additional prognostic subgrid energy equation. The kinematic backscatter proposed here, by contrast, comes at no additional computational cost, following the principle of simplicity. Our primary focus is the discretization on triangular unstructured meshes with cell placement of velocities (an analog of B-grids), as employed by the Finite-volumE Sea ice-Ocean Model (FESOM2). The kinematic backscatter scheme with the new viscosity coefficient is implemented in FESOM2 and tested in the simplified geometry of a zonally reentrant channel as well as in a global ocean simulation on a 1/4° mesh. This first version of the new kinematic backscatter needs to be tuned to the specific resolution regime of the simulation. However, the tuning relies on a single parameter, emphasizing the overall practicality of the approach.
    Repository Name: EPIC Alfred Wegener Institut
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  • 107
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    Future Arctic Climate Change in CMIP6 Strikingly Intensified by NEMO‐Family Climate Models (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 50(4), ISSN: 0094-8276
    Details
    Publication Date: 2023-06-23
    Description: Climate change in the Arctic has substantial impacts on human life and ecosystems both within and beyond the Arctic. Our analysis of CMIP6 simulations shows that some climate models project much larger Arctic climate change than other models, including changes in sea ice, ocean mixed layer, air-sea heat flux, and surface air temperature in wintertime. In particular, dramatic enhancement of Arctic Ocean convection down to a few hundred meters is projected in these models but not in others. Interestingly, these models employ the same ocean model family (NEMO) while the choice of models for the atmosphere and sea ice varies. The magnitude of Arctic climate change is proportional to the strength of the increase in poleward ocean heat transport, which is considerably higher in this group of models. Establishing the plausibility of this group of models with high Arctic climate sensitivity to anthropogenic forcing is imperative given the implied ramifications.
    Repository Name: EPIC Alfred Wegener Institut
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  • 108
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    Sea‐Ice Forecasts With an Upgraded AWI Coupled Prediction System (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Advances in Modeling Earth Systems, American Geophysical Union (AGU), 14(12), ISSN: 1942-2466
    Details
    Publication Date: 2023-06-23
    Description: A new version of the AWI Coupled Prediction System is developed based on the Alfred Wegener Institute Climate Model v3.0. Both the ocean and the atmosphere models are upgraded or replaced, reducing the computation time by a factor of 5 at a given resolution. This allowed us to increase the ensemble size from 12 to 30, maintaining a similar resolution in both model components. The online coupled data assimilation scheme now additionally utilizes sea-surface salinity and sea-level anomaly as well as temperature and salinity profile observations. Results from the data assimilation demonstrate that the sea-ice and ocean states are reasonably constrained. In particular, the temperature and salinity profile assimilation has mitigated systematic errors in the deeper ocean, although issues remain over polar regions where strong atmosphere-ocean-ice interaction occurs. One-year-long sea-ice forecasts initialized on 1 January, 1 April, 1 July and 1 October from 2003 to 2019 are described. To correct systematic forecast errors, sea-ice concentration from 2011 to 2019 is calibrated by trend-adjusted quantile mapping using the preceding forecasts from 2003 to 2010. The sea-ice edge raw forecast skill is within the range of operational global subseasonal-to-seasonal forecast systems, outperforming a climatological benchmark for about 2 weeks in the Arctic and about 3 weeks in the Antarctic. The calibration is much more effective in the Arctic: Calibrated sea-ice edge forecasts outperform climatology for about 45 days in the Arctic but only 27 days in the Antarctic. Both the raw and the calibrated forecast skill exhibit strong seasonal variations.
    Repository Name: EPIC Alfred Wegener Institut
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  • 109
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    Turbulent heat exchange over polar leads revisited: A large eddy simulation study (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), ISSN: 2169-897X
    Details
    Publication Date: 2023-06-23
    Description: Sea ice leads play an important role in energy exchange between the ocean and atmosphere in polar regions, and therefore must be considered in weather and climate models. As sea ice leads are not explicitly resolved in such models, lead-averaged surface heat flux is of considerable interest for the parameterization of energy exchange. Measurements and numerical studies have established that the lead-averaged surface heat flux depends not only on meteorological parameters, but also on lead width. Nonetheless, few studies to date have investigated the dependency of surface heat flux on lead width. Most findings on that dependency are based on observations with lead widths smaller than a few hundred meters, but leads can have widths from a few meters to several kilometers. In this parameter study, we present the results of three series of large-eddy simulations of turbulent exchange processes above leads. We varied the lead width and air temperature, as well as the roughness length. As this study focused on conditions without background wind, ice-breeze circulation occurred, and was the main driver of the adjustment of surface heat flux. A previous large-eddy simulation study with uncommonly large roughness length found that lead-averaged surface heat flux exhibited a distinct maximum at lead widths of about 3 km, while our results show the largest heat fluxes for the smallest leads simulated (lead width of 50 m). At more realistic roughness lengths, we observed monotonously increasing heat fluxes with increasing lead width. Further, new scaling laws for the ice-breeze circulation are proposed.
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  • 110
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    Impact of Cyclonic Wind Anomalies Caused by Massive Winter Sea Ice Retreat in the Barents Sea on Atlantic Water Transport Toward the Arctic: A Model Study (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research - Oceans, American Geophysical Union (AGU), 128(3), ISSN: 2169-9275
    Details
    Publication Date: 2023-06-23
    Description: The Arctic is warming much faster than the global average. This is known as Arctic Amplification and is caused by feedbacks in the local climate system. In this study, we explore a previously proposed hypothesis that an associated wind feedback in the Barents Sea could play an important role by increasing the warm water inflow into the Barents Sea. We find that the strong recent decrease in Barents Sea winter sea ice cover causes enhanced ocean-atmosphere heat flux and a local air temperature increase, thus a reduction in sea level pressure and a local cyclonic wind anomaly with eastward winds in the Barents Sea Opening. By investigating various reanalysis products and performing high-resolution perturbation experiments with the ocean and sea ice model FESOM2.1, we studied the impact of cyclonic atmospheric circulation changes on the warm Atlantic Water import into the Arctic via the Barents Sea and Fram Strait. We found that the observed wind changes do not significantly affect the warm water transport into the Barents Sea, which rejects the wind-feedback hypothesis. At the same time, the cyclonic wind anomalies in the Barents Sea increase the amount of Atlantic Water recirculating westwards in Fram Strait by a downslope shift of the West Spitsbergen Current, and thus reduce Atlantic Water reaching the Arctic basin via Fram Strait. The resulting warm-water anomaly in the Greenland Sea Gyre drives a local anticyclonic circulation anomaly.
    Repository Name: EPIC Alfred Wegener Institut
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  • 111
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    The Impacts of Optimizing Model‐Dependent Parameters on the Antarctic Sea Ice Data Assimilation (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 50(22), ISSN: 0094-8276
    Details
    Publication Date: 2023-11-25
    Description: Given the role played by the historical and extensive coverage of sea ice concentration (SIC) observations in reconstructing the long‐term variability of Antarctic sea ice, and the limited attention given to model‐dependent parameters in current sea ice data assimilation studies, this study focuses on enhancing the performance of the Data Assimilation System for the Southern Ocean in assimilating SIC through optimizing the localization and observation error estimate, and two assimilation experiments were conducted from 1979 to 2018. By comparing the results with the sea ice extent of the Southern Ocean and the sea ice thickness in the Weddell Sea, it becomes evident that the experiment with optimizations outperforms that without optimizations due to achieving more reasonable error estimates. Investigating uncertainties of the sea ice volume anomaly modeling reveals the importance of the sea ice‐ocean interaction in the SIC assimilation, implying the necessity of assimilating more oceanic and sea‐ice observations.
    Repository Name: EPIC Alfred Wegener Institut
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  • 112
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    Snow‐Atmosphere Humidity Exchange at the Ice Sheet Surface Alters Annual Mean Climate Signals in Ice Core Records (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 50(20), ISSN: 0094-8276
    Details
    Publication Date: 2023-11-20
    Description: Surface processes alter the water stable isotope signal of the surface snow after deposition. However, it remains an open question to which extent surface post-depositional processes should be considered when inferring past climate information from ice core records. Here, we present simulations for the Greenland Ice Sheet, combining outputs from two climate models with an isotope-enabled snowpack model. We show that surface vapor exchange and associated fractionation imprint a climate signal into the firn, resulting in an increase in the annual mean value of δ18O by +2.3‰ and a reduction in d-excess by −6.3‰. Further, implementing isotopic fractionation during surface vapor exchange improves the representation of the observed seasonal amplitude in δ18O from 65.0% to 100.2%. Our results stress that surface vapor exchange is important in the climate proxy signal formation and needs consideration when interpreting ice core climate records.
    Repository Name: EPIC Alfred Wegener Institut
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  • 113
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    Preconditioning of Summer Melt Ponds From Winter Sea Ice Surface Temperature (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 50(4), ISSN: 0094-8276
    Details
    Publication Date: 2023-02-23
    Description: Comparing helicopter-borne surface temperature maps in winter and optical orthomosaics in summer from the year-long Multidisciplinary drifting Observatory for the Study of Arctic Climate expedition, we find a strong geometric correlation between warm anomalies in winter and melt pond location the following summer. Warm anomalies are associated with thinner snow and ice, that is, surface depression and refrozen leads, that allow for water accumulation during melt. Warm surface temperature anomalies in January were 0.3–2.5 K warmer on sea ice that later formed melt ponds. A one-dimensional steady-state thermodynamic model shows that the observed surface temperature differences are in line with the observed ice thickness and snow depth. We demonstrate the potential of seasonal prediction of summer melt pond location and coverage from winter surface temperature observations. A threshold-based classification achieves a correct classification for 41% of the melt ponds.
    Repository Name: EPIC Alfred Wegener Institut
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  • 114
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    Ventilation of the Deep Ocean Carbon Reservoir During the Last Deglaciation: Results From the Southeast Pacific (2019)
    American Geophysical Union (AGU)
    In:  EPIC3Paleoceanography and Paleoclimatology, American Geophysical Union (AGU), 34(12), pp. 2080-2097, ISSN: 2572-4517
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    Publication Date: 2023-03-31
    Description: Coeval changes in atmospheric CO2 and 14C contents during the last deglaciation are often attributed to ocean circulation changes that released carbon stored in the deep ocean during the Last Glacial Maximum (LGM). Work is being done to generate records that allow for the identification of the exact mechanisms leading to the accumulation and release of carbon from the oceanic reservoir, but these mechanisms are still the subject of debate. Here we present foraminifera 14C data from five cores in a transect across the Chilean continental margin between ~540 and ~3,100 m depth spanning the last 20,000 years. Our data reveal that during the LGM, waters at ~2,000 m were 50% to 80% more depleted in Δ14C than waters at ~1,500 m when compared to modern values, consistent with the hypothesis of a glacial deep ocean carbon reservoir that was isolated from the atmosphere. During the deglaciation, our intermediate water records reveal homogenization in the Δ14C values between ~800 and ~1,500 m from ~16.5–14.5 ka cal BP to ~14–12 ka cal BP, which we interpret as deeper penetration of Antarctic Intermediate Water. While many questions still remain, this process could aid the ventilation of the deep ocean at the beginning of the deglaciation, contributing to the observed ~40 ppm rise in atmospheric pCO2.
    Repository Name: EPIC Alfred Wegener Institut
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  • 115
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    Atmospheric CO2 concentration based on boron isotopes versus simulations of the global carbon cycle during the Plio‐Pleistocene (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Paleoceanography and Paleoclimatology, American Geophysical Union (AGU), 38, 22 p., pp. e2022PA004439-e2022PA004439, ISSN: 2572-4517
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    Publication Date: 2023-08-30
    Description: Atmospheric carbon dioxide concentrations (pCO2) beyond ice core records have been reconstructed from δ11B derived from planktic foraminifera found in equatorial sediment cores. Here, I applied a carbon cycle model over the Plio-Pleistocene to evaluate the assumptions leading to these numbers. During glacials times, simulated atmospheric pCO2 was unequilibrated with pCO2 in the equatorial surface ocean by up to 35 ppm while the δ11B-based approaches assume unchanged (quasi)equilibrium between both. In the Pliocene, δ11B-based estimates of surface ocean pH are lower in the Pacific than in the Atlantic resulting in higher calculated pCO2. This offset in pH between ocean basins is not supported by models. To calculate pCO2 in surface waters out of the δ11B-based pH some assumptions on either total alkalinity or dissolved inorganic carbon are necessary. However, the assumed values of these under-constrained variables were according to my results partly inconsistent with chemically possible combinations within the marine carbonate system. The model results show glacial/interglacial variability in total alkalinity of the order of 100 μmol/kg, which is rarely applied to proxy reconstructions. Simulated atmospheric pCO2 is tightly (r2 〉 0.9) related to equatorial surface-ocean pH, which can be used for consistency checks. Long-term trends in volcanic CO2 outgassing and the strength of the continental weathering fluxes are still unconstrained, allowing for a wide range of possible atmospheric pCO2 across the Plio-Pleistocene. Nevertheless, this carbon cycle analysis suggests that reported atmospheric pCO2 above 500 ppm in the Pliocene might, for various reasons, need to be revised to smaller numbers.
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  • 116
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    Stable Carbon Isotope Signature of Methane Released From Phytoplankton (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 50(12), ISSN: 0094-8276
    Details
    Publication Date: 2023-09-01
    Description: Aquatic ecosystems play an important role in global methane cycling and many field studies have reported methane supersaturation in the oxic surface mixed layer (SML) of the ocean and in the epilimnion of lakes. The origin of methane formed under oxic condition is hotly debated and several pathways have recently been offered to explain the “methane paradox.” In this context, stable isotope measurements have been applied to constrain methane sources in supersaturated oxygenated waters. Here we present stable carbon isotope signatures for six widespread marine phytoplankton species, three haptophyte algae and three cyanobacteria, incubated under laboratory conditions. The observed isotopic patterns implicate that methane formed by phytoplankton might be clearly distinguished from methane produced by methanogenic archaea. Comparing results from phytoplankton experiments with isotopic data from field measurements, suggests that algal and cyanobacterial populations may contribute substantially to methane formation observed in the SML of oceans and lakes.
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  • 117
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    Teardrop and Parabolic Lens Yield Curves for Viscous‐Plastic Sea Ice Models: New Constitutive Equations and Failure Angles (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Advances in Modeling Earth Systems, American Geophysical Union (AGU), 15(9), ISSN: 1942-2466
    Details
    Publication Date: 2023-09-04
    Description: 〈jats:title〉Abstract〈/jats:title〉〈jats:p〉Most viscous‐plastic sea ice models use the elliptical yield curve. This yield curve has a fundamental flaw: it excludes acute angles between deformation features at high resolution. Conceptually, the teardrop (TD) and parabolic lens (PL) yield curves offer an attractive alternative. These yield curves feature a non‐symmetrical shape, a Coulombic behavior for the low‐medium compressive stress, and a continuous transition to the ridging‐dominant mode, but their published formulation leads to negative or zero bulk and shear viscosities and, consequently, poor numerical convergence with stress states at times outside the yield curve. These issues are a consequence of the original assumption that the constitutive equations of the commonly used elliptical yield curve are also applicable to non‐symmetrical yield curves and yield curves with tensile strength. We derive a corrected formulation for the constitutive relations of the TD and PL yield curves. Results from simple uni‐axial loading experiments show that with the new formulation the numerical convergence of the solver improves and much smaller nonlinear residuals after a smaller number of total solver iterations can be reached, resulting in significant improvements in numerical efficiency and representation of the stress and deformation fields. The TD and PL yield curves lead to smaller angles of failure that better agree with observations. They are promising candidates to replace the elliptical yield curve in high‐resolution pan‐Arctic sea ice simulations.〈/jats:p〉
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    Antarctic Sedimentary Basins and Their Influence on Ice‐Sheet Dynamics (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Reviews of Geophysics, American Geophysical Union (AGU), 61(3), ISSN: 8755-1209
    Details
    Publication Date: 2023-10-09
    Description: Knowledge of Antarctica's sedimentary basins builds our understanding of the coupled evolution of tectonics, ice, ocean, and climate. Sedimentary basins have properties distinct from basement-dominated regions that impact ice-sheet dynamics, potentially influencing future ice-sheet change. Despite their importance, our knowledge of Antarctic sedimentary basins is restricted. Remoteness, the harsh environment, the overlying ice sheet, ice shelves, and sea ice all make fieldwork challenging. Nonetheless, in the past decade the geophysics community has made great progress in internationally coordinated data collection and compilation with parallel advances in data processing and analysis supporting a new insight into Antarctica's subglacial environment. Here, we summarize recent progress in understanding Antarctica's sedimentary basins. We review advances in the technical capability of radar, potential fields, seismic, and electromagnetic techniques to detect and characterize basins beneath ice and advances in integrated multi-data interpretation including machine-learning approaches. These new capabilities permit a continent-wide mapping of Antarctica's sedimentary basins and their characteristics, aiding definition of the tectonic development of the continent. Crucially, Antarctica's sedimentary basins interact with the overlying ice sheet through dynamic feedbacks that have the potential to contribute to rapid ice-sheet change. Looking ahead, future research directions include techniques to increase data coverage within logistical constraints, and resolving major knowledge gaps, including insufficient sampling of the ice-sheet bed and poor definition of subglacial basin structure and stratigraphy. Translating the knowledge of sedimentary basin processes into ice-sheet modeling studies is critical to underpin better capacity to predict future change.
    Repository Name: EPIC Alfred Wegener Institut
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    Retrieval of Wintertime Sea Ice Production in Arctic Polynyas Using Thermal Infrared and Passive Microwave Remote Sensing Data (2019)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), 124(8), pp. 5503-5528, ISSN: 2169-9275
    Details
    Publication Date: 2022-11-02
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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    Stable Barium Isotope Fractionation in Pore Waters of Estuarine Sediments (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geochemistry, Geophysics, Geosystems, American Geophysical Union (AGU), 24(6), ISSN: 1525-2027
    Details
    Publication Date: 2023-06-01
    Repository Name: EPIC Alfred Wegener Institut
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  • 121
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    Concentrations and Water Mass Transport of Legacy POPs in the Arctic Ocean (2018)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 45(23), pp. 12972-12981, ISSN: 0094-8276
    Details
    Publication Date: 2023-01-30
    Description: The Arctic Ocean is known to be contaminated by various persistent organic pollutants (POPs). The Fram Strait, the only deepwater passage to the Arctic Ocean (from the Atlantic Ocean), represents an unquantified gateway for POPs fluxes into and out of the Arctic. Polyethylene passive samplers were deployed in vertical profiles in the Fram Strait and in air and surface water in the Canadian Archipelago to determine the concentrations, profiles, and mass fluxes of dissolved polychlorinated biphenyls (PCBs) and organochlorine pesticides. In the Fram Strait, higher concentrations of ΣPCBs (1.3–3.6 pg/L) and dichlorodiphenyltrichloroethanes (ΣDDTs, 5.2–9.1 pg/L) were observed in the deepwater masses (below 1,000 m), similar to nutrient-like vertical profiles. There was net southward transport of hexachlorobenzene and hexachlorocyclohexanes (ΣHCHs) of 0.70 and 14 Mg/year but a net northward transport of ΣPCBs at 0.16 Mg/year through the Fram Strait.
    Repository Name: EPIC Alfred Wegener Institut
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    New Insights Into Cyclone Impacts on Sea Ice in the Atlantic Sector of the Arctic Ocean in Winter (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 49(22), ISSN: 0094-8276
    Details
    Publication Date: 2023-06-21
    Description: Based on the ERA5 reanalysis, we report on statistically significant impacts of transient cyclones on sea ice concentration (SIC) in the Atlantic sector of the Arctic Ocean in winter under “New Arctic” conditions (2000–2020). This includes a pattern of reduced SIC prior to and during cyclones for the whole study domain, while a regional difference between increased SIC in the Barents Sea and reduced SIC in the Greenland Sea is found as the net effect from 3 days prior to 5 days after the cyclone passage. Generally, locally low to medium SIC conditions combined with intense cyclones drive highest SIC changes. There are indications that both thermodynamic and dynamic effects contribute to the SIC changes, but a detailed quantification is required in future research. We provide evidence that cyclone impacts on SIC have amplified compared to the “Old Arctic” (1979–1999), particularly in the Barents Sea.
    Repository Name: EPIC Alfred Wegener Institut
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    The Impact of Different Atmospheric CO2 Concentrations on Large Scale Miocene Temperature Signatures (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Paleoceanography and Paleoclimatology, American Geophysical Union (AGU), ISSN: 2572-4517
    Details
    Publication Date: 2023-02-03
    Repository Name: EPIC Alfred Wegener Institut
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  • 124
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    Permafrost Carbon: Progress on Understanding Stocks and Fluxes Across Northern Terrestrial Ecosystems (2024)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research: Biogeosciences, American Geophysical Union (AGU), 129(3), ISSN: 2169-8953
    Details
    Publication Date: 2024-02-27
    Description: Significant progress in permafrost carbon science made over the past decades include the identification of vast permafrost carbon stocks, the development of new pan‐Arctic permafrost maps, an increase in terrestrial measurement sites for CO〈jats:sub〉2〈/jats:sub〉 and methane fluxes, and important factors affecting carbon cycling, including vegetation changes, periods of soil freezing and thawing, wildfire, and other disturbance events. Process‐based modeling studies now include key elements of permafrost carbon cycling and advances in statistical modeling and inverse modeling enhance understanding of permafrost region C budgets. By combining existing data syntheses and model outputs, the permafrost region is likely a wetland methane source and small terrestrial ecosystem CO〈jats:sub〉2〈/jats:sub〉 sink with lower net CO〈jats:sub〉2〈/jats:sub〉 uptake toward higher latitudes, excluding wildfire emissions. For 2002–2014, the strongest CO〈jats:sub〉2〈/jats:sub〉 sink was located in western Canada (median: −52 g C m〈jats:sup〉−2〈/jats:sup〉 y〈jats:sup〉−1〈/jats:sup〉) and smallest sinks in Alaska, Canadian tundra, and Siberian tundra (medians: −5 to −9 g C m〈jats:sup〉−2〈/jats:sup〉 y〈jats:sup〉−1〈/jats:sup〉). Eurasian regions had the largest median wetland methane fluxes (16–18 g CH〈jats:sub〉4〈/jats:sub〉 m〈jats:sup〉−2〈/jats:sup〉 y〈jats:sup〉−1〈/jats:sup〉). Quantifying the regional scale carbon balance remains challenging because of high spatial and temporal variability and relatively low density of observations. More accurate permafrost region carbon fluxes require: (a) the development of better maps characterizing wetlands and dynamics of vegetation and disturbances, including abrupt permafrost thaw; (b) the establishment of new year‐round CO〈jats:sub〉2〈/jats:sub〉 and methane flux sites in underrepresented areas; and (c) improved models that better represent important permafrost carbon cycle dynamics, including non‐growing season emissions and disturbance effects.〈/jats:p〉
    Repository Name: EPIC Alfred Wegener Institut
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    Late Holocene Dust Deposition Fluxes Over the Entire South Atlantic Ocean (2024)
    American Geophysical Union (AGU)
    In:  EPIC3Geochemistry Geophysics Geosystems, American Geophysical Union (AGU), 25(1), ISSN: 1525-2027
    Details
    Publication Date: 2024-03-04
    Description: Mineral dust accumulated on the ocean floor is an important archive for reconstructing past atmospheric circulation changes and climatological conditions in the source areas. Dust emitted from Southern Hemisphere dust sources is widely deposited over the oceans. However, there are few records of dust deposition over the open ocean, and a large need for extended geographical coverage exists. We present a large data set (134 surface sediment samples) of Late Holocene dust deposition from seafloor surface sediments covering the entire South Atlantic Ocean. Polymodal grain-size distributions of the lithogenic fraction indicate that the sediments are composed of multiple sediment components. By using end-member modeling, we attempt to disentangle the dust signal from non-aeolian sediments. Combined with 230Th-normalized lithogenic fluxes, we quantified the specific deposition fluxes for mineral dust, crrent-sorted sediments and ice-rafted debris (IRD). Although the method could not completely separate the different components in every region, it shows that dust deposition off the most prominent dust source for the South Atlantic Ocean—southern South America—amounts up to approximately 0.7 g cm−2 Kyr−1 and decreases downwind. Bottom-current-sorted sediments and IRD are mostly concentrated around the continental margins. The ratio of the coarse to fine dust end members reveals input from north African dust sources to the South Atlantic. The majority of the observations are in good agreement with new model simulations. This extensive and relevant data set of dust grain size and deposition fluxes to the South Atlantic could be used to calibrate and validate further model simulations.
    Repository Name: EPIC Alfred Wegener Institut
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    The Role of Coastal Yedoma Deposits and Continental Shelf Sediments in the Arctic Ocean Silicon Cycle (2024)
    American Geophysical Union (AGU)
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union (AGU), 38(1), ISSN: 0886-6236
    Details
    Publication Date: 2024-02-13
    Description: The availability of silicon (Si) in the ocean plays an important role in regulating biogeochemical and ecological processes. The Si budget of the Arctic Ocean appears balanced, with inputs equivalent to outputs, though it is unclear how a changing climate might aggravate this balance. In this study, we focus on Si cycling in Arctic coastal areas and continental shelf sediments to better constrain the Arctic Ocean Si budget. We provide the first estimate of amorphous Si (ASi) loading from erosion of coastal Yedoma deposits (30–90 Gmol yr−1), demonstrating comparable rates to particulate Si loading from rivers (10–90 Gmol yr−1). We found a positive relationship between surface sediment ASi and organic matter content on continental shelves. Combining these values with published Arctic shelf sediment properties and burial rates we estimate 70 Gmol Si yr−1 is buried on Arctic continental shelves, equivalent to 4.5% of all Si inputs to the Arctic Ocean. Sediment dissolved Si fluxes increased with distance from river mouths along cruise transects of shelf regions influenced by major rivers in the Laptev and East Siberian seas. On an annual basis, we estimate that Arctic shelf sediments recycle approximately up to twice as much DSi (680 Gmol Si) as is loaded from rivers (340–500 Gmol Si).
    Repository Name: EPIC Alfred Wegener Institut
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    A Synthesis of Global Coastal Ocean Greenhouse Gas Fluxes (2024)
    American Geophysical Union (AGU)
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union (AGU), 38(1), ISSN: 0886-6236
    Details
    Publication Date: 2024-02-13
    Description: The coastal ocean contributes to regulating atmospheric greenhouse gas concentrations by taking up carbon dioxide (CO2) and releasing nitrous oxide (N2O) and methane (CH4). In this second phase of the Regional Carbon Cycle Assessment and Processes (RECCAP2), we quantify global coastal ocean fluxes of CO2, N2O and CH4 using an ensemble of global gap-filled observation-based products and ocean biogeochemical models. The global coastal ocean is a net sink of CO2 in both observational products and models, but the magnitude of the median net global coastal uptake is ∼60% larger in models (−0.72 vs. −0.44 PgC year−1, 1998–2018, coastal ocean extending to 300 km offshore or 1,000 m isobath with area of 77 million km2). We attribute most of this model-product difference to the seasonality in sea surface CO2 partial pressure at mid- and high-latitudes, where models simulate stronger winter CO2 uptake. The coastal ocean CO2 sink has increased in the past decades but the available time-resolving observation-based products and models show large discrepancies in the magnitude of this increase. The global coastal ocean is a major source of N2O (+0.70 PgCO2-e year−1 in observational product and +0.54 PgCO2-e year−1 in model median) and CH4 (+0.21 PgCO2-e year−1 in observational product), which offsets a substantial proportion of the coastal CO2 uptake in the net radiative balance (30%–60% in CO2-equivalents), highlighting the importance of considering the three greenhouse gases when examining the influence of the coastal ocean on climate.
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    Quantifying Sub\xe2\x80\x90Seasonal Growth Rate Changes in Fossil Giant Clams Using Wavelet Transformation of Daily Mg/Ca Cycles (2023)
    American Geophysical Union (AGU)
    In:  Geochemistry, Geophysics, Geosystems vol. 24 no. 10
    Details
    Publication Date: 2024-02-08
    Description: Shells of the giant clam Tridacna can provide decade-long records of past environmental conditions via their geochemical composition and structurally through growth banding. Counting the daily bands can give an accurate internal age model with high temporal resolution, but daily banding is not always visually retrievable, especially in fossil specimens. We show that daily geochemical cycles (e.g., Mg/Ca) are resolvable via highly spatially resolved laser-ablation inductively coupled plasma mass spectrometry (LA-ICPMS; 3 \xc3\x97 33 \xce\xbcm laser slit) in our Miocene (\xe2\x88\xbc10 Ma) specimen, even in areas where daily banding is not visually discernible. By applying wavelet transformation on the measured daily geochemical cycles, we quantify varying daily growth rates throughout the shell. These growth rates are thus used to build an internal age model independent of optical daily band countability. Such an age model can be used to convert the measured elemental ratios from a function of distance to a function of time, which helps evaluate paleoenvironmental proxy data, for example, regarding the timing of sub-seasonal events. Furthermore, the quantification of daily growth rates across the shell facilitates the evaluation of (co)dependencies between growth rates and corresponding elemental compositions.
    Keywords: Tridacna
    Repository Name: National Museum of Natural History, Netherlands
    Type: info:eu-repo/semantics/article
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    Selective Sorting and Degradation of Permafrost Organic Matter in the Nearshore Zone of Herschel Island (Yukon, Canada) (2024)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research Biogeosciences, American Geophysical Union (AGU), 129(1), ISSN: 2169-8953
    Details
    Publication Date: 2024-01-26
    Description: 〈jats:title〉Abstract〈/jats:title〉〈jats:p〉Erosion of permafrost coasts due to climate warming releases large quantities of organic carbon (OC) into the Arctic Ocean. While burial of permafrost OC in marine sediments potentially limits degradation, resuspension of sediments in the nearshore zone potentially enhances degradation and greenhouse gas production, adding to the “permafrost carbon feedback.” Recent studies, focusing on bulk sediments, suggest that permafrost OC derived from coastal erosion is predominantly deposited close to shore. However, bulk approaches disregard sorting processes in the coastal zone, which strongly influence the OC distribution and fate. We studied soils and sediments along a transect from the fast‐eroding shoreline of Herschel Island—〈jats:italic〉Qikiqtaruk〈/jats:italic〉 (Yukon, Canada) to a depositional basin offshore. Sample material was fractionated by density (1.8 g cm〈jats:sup〉−3〈/jats:sup〉) and size (63 μm), separating loose OC from mineral‐associated OC. Each fraction was analyzed for element content (TOC, TN), carbon isotopes (δ〈jats:sup〉13〈/jats:sup〉C, Δ〈jats:sup〉14〈/jats:sup〉C), molecular biomarkers (〈jats:italic〉n〈/jats:italic〉‐alkanes, 〈jats:italic〉n〈/jats:italic〉‐alkanoic acids, lignin phenols, cutin acids), and mineral surface area. The OC partitioning between fractions changes considerably along the transect, highlighting the importance of hydrodynamic sorting in the nearshore zone. Additionally, OC and biomarker loadings decrease along the land‐ocean transect, indicating significant loss of OC during transport. However, molecular proxies for degradation show contrasting trends, suggesting that OC losses are not always well reflected in its degradation state. This study, using fraction partitioning that crosses land‐ocean boundaries in a way not done before, aids to disentangle sorting processes from degradation patterns, and provides quantitative insight into losses of thawed and eroded permafrost OC.〈/jats:p〉
    Repository Name: EPIC Alfred Wegener Institut
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    Postdepositional Behavior of Molybdenum in Deep Sediments and Implications for Paleoredox Reconstruction (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 50(21), ISSN: 0094-8276
    Details
    Publication Date: 2023-11-01
    Description: Molybdenum (Mo) is a trace element sensitive to oceanic redox conditions. The fidelity of sedimentary Mo as a paleoredox proxy of coeval seawater depends on the extent of Mo remobilization during postdepositional processes. Here we present the Mo content and isotope profiles for deep sediments from the Nankai Trough, Japan. The Mo signature suggests that these sediments have experienced extensive early diagenesis and hydrothermal alteration at depth. Iron (Fe)‐manganese (Mn) (oxyhydr)oxide alteration combined with Mo thiolation leads to a more than twenty‐fold enrichment of Mo within the sulfate reduction zone. Hydrothermal fluids and Mo adsorption onto Fe‐Mn (oxyhydr)oxides cause extremely negative Mo‐isotope values at the underthrust zone. These postdepositional Mo signals might be misinterpreted as expanded anoxia in the water column. Our findings highlight the importance of constraining postdepositional effects on Mo‐based proxies during paleoredox reconstruction.
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    A Modeling Perspective on the Lingering Glacial Sea Surface Temperature Conundrum (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 49(23), ISSN: 0094-8276
    Details
    Publication Date: 2023-09-19
    Description: The strong cooling during the Last Glacial Maximum (LGM, 21 ka BP) provides a rigorous test of climate models' ability to simulate past and future climate changes. We force an atmospheric general circulation model with two recent global LGM sea surface temperature (SST) reconstructions, one suggesting a weak and the other a more pronounced cooling, and compare the simulated land surface temperatures (LSTs) to reconstructed data. Our results do not confirm either SST reconstruction. The cold SST data set leads to good agreement between simulated and observed LSTs at low latitudes, but is systematically too cold at mid-latitudes. The opposite is true for the warm SST data set. Differences between the simulated LSTs are caused by varying land surface albedos, which is lower for the warmer SST reconstruction. The inconsistency between reconstructed and simulated climate points to a potentially significant bias in the proxy reconstructions and/or the climate sensitivity of current climate models.
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    Cyclone Impacts on Sea Ice Concentration in the Atlantic Arctic Ocean: Annual Cycle and Recent Changes (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 50(17), ISSN: 0094-8276
    Details
    Publication Date: 2023-09-08
    Description: We quantify sea ice concentration (SIC) changes related to synoptic cyclones separately for each month of the year in the Greenland, Barents and Kara Seas for 1979–2018. We find that these SIC changes can be statistically significant throughout the year. However, their strength varies from region to region and month to month, and their sign strongly depends on the considered time scale (before/during vs. after cyclone passages). Our results show that the annual cycle of cyclone impacts on SIC is related to varying cyclone intensity and traversed sea ice conditions. We further show that significant changes in these cyclone impacts have manifested in the last 40 years, with the strongest changes occurring in October and November. For these months, SIC decreases before/during cyclones have more than doubled in magnitude in the Barents and Kara Seas, while SIC increases following cyclones have weakened (intensified) in the Barents Sea (Kara Sea).
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    An Assessment of CO2 Uptake in the Arctic Ocean From 1985 to 2018 (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union (AGU), 37(11), ISSN: 0886-6236
    Details
    Publication Date: 2023-12-19
    Description: As a contribution to the Regional Carbon Cycle Assessment and Processes phase 2 (RECCAP2) project, we present synthesized estimates of Arctic Ocean sea-air CO2 fluxes and their uncertainties from surface ocean pCO2-observation products, ocean biogeochemical hindcast and data assimilation models, and atmospheric inversions. For the period of 1985–2018, the Arctic Ocean was a net sink of CO2 of 116 ± 4 TgC yr−1 in the pCO2 products, 92 ± 30 TgC yr−1 in the models, and 91 ± 21 TgC yr−1 in the atmospheric inversions. The CO2 uptake peaks in late summer and early autumn, and is low in winter when sea ice inhibits sea-air fluxes. The long-term mean CO2 uptake in the Arctic Ocean is primarily caused by steady-state fluxes of natural carbon (70% ± 15%), and enhanced by the atmospheric CO2 increase (19% ± 5%) and climate change (11% ± 18%). The annual mean CO2 uptake increased from 1985 to 2018 at a rate of 31 ± 13 TgC yr−1 dec−1 in the pCO2 products, 10 ± 4 TgC yr−1 dec−1 in the models, and 32 ± 16 TgC yr−1 dec−1 in the atmospheric inversions. Moreover, 77% ± 38% of the trend in the net CO2 uptake over time is caused by climate change, primarily due to rapid sea ice loss in recent years. Furthermore, true uncertainties may be larger than the given ensemble standard deviations due to common structural biases across all individual estimates.
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    Seasonal Variability of the Surface Ocean Carbon Cycle: A Synthesis (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union (AGU), 37(9), ISSN: 0886-6236
    Details
    Publication Date: 2024-01-06
    Description: The seasonal cycle is the dominant mode of variability in the air-sea CO2 flux in most regions of the global ocean, yet discrepancies between different seasonality estimates are rather large. As part of the Regional Carbon Cycle Assessment and Processes Phase 2 project (RECCAP2), we synthesize surface ocean pCO2 and air-sea CO2 flux seasonality from models and observation-based estimates, focusing on both a present-day climatology and decadal changes between the 1980s and 2010s. Four main findings emerge: First, global ocean biogeochemistry models (GOBMs) and observation-based estimates (pCO2 products) of surface pCO2 seasonality disagree in amplitude and phase, primarily due to discrepancies in the seasonal variability in surface DIC. Second, the seasonal cycle in pCO2 has increased in amplitude over the last three decades in both pCO2 products and GOBMs. Third, decadal increases in pCO2 seasonal cycle amplitudes in subtropical biomes for both pCO2 products and GOBMs are driven by increasing DIC concentrations stemming from the uptake of anthropogenic CO2 (Cant). In subpolar and Southern Ocean biomes, however, the seasonality change for GOBMs is dominated by Cant invasion, whereas for pCO2 products an indeterminate combination of Cant invasion and climate change modulates the changes. Fourth, biome-aggregated decadal changes in the amplitude of pCO2 seasonal variability are largely detectable against both mapping uncertainty (reducible) and natural variability uncertainty (irreducible), but not at the gridpoint scale over much of the northern subpolar oceans and over the Southern Ocean, underscoring the importance of sustained high-quality seasonally resolved measurements over these regions.
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    Magnitude, Trends, and Variability of the Global Ocean Carbon Sink From 1985 to 2018 (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union (AGU), 37(10), ISSN: 0886-6236
    Details
    Publication Date: 2024-01-06
    Description: This contribution to the RECCAP2 (REgional Carbon Cycle Assessment and Processes) assessment analyzes the processes that determine the global ocean carbon sink, and its trends and variability over the period 1985–2018, using a combination of models and observation-based products. The mean sea-air CO2 flux from 1985 to 2018 is −1.6 ± 0.2 PgC yr−1 based on an ensemble of reconstructions of the history of sea surface pCO2 (pCO2 products). Models indicate that the dominant component of this flux is the net oceanic uptake of anthropogenic CO2, which is estimated at −2.1 ± 0.3 PgC yr−1 by an ensemble of ocean biogeochemical models, and −2.4 ± 0.1 PgC yr−1 by two ocean circulation inverse models. The ocean also degasses about 0.65 ± 0.3 PgC yr−1 of terrestrially derived CO2, but this process is not fully resolved by any of the models used here. From 2001 to 2018, the pCO2 products reconstruct a trend in the ocean carbon sink of −0.61 ± 0.12 PgC yr−1 decade−1, while biogeochemical models and inverse models diagnose an anthropogenic CO2-driven trend of −0.34 ± 0.06 and −0.41 ± 0.03 PgC yr−1 decade−1, respectively. This implies a climate-forced acceleration of the ocean carbon sink in recent decades, but there are still large uncertainties on the magnitude and cause of this trend. The interannual to decadal variability of the global carbon sink is mainly driven by climate variability, with the climate-driven variability exceeding the CO2-forced variability by 2–3 times. These results suggest that anthropogenic CO2 dominates the ocean CO2 sink, while climate-driven variability is potentially large but highly uncertain and not consistently captured across different methods.
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    The Southern Ocean Carbon Cycle 1985–2018: Mean, Seasonal Cycle, Trends, and Storage (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union (AGU), 37(11), ISSN: 0886-6236
    Details
    Publication Date: 2023-12-20
    Description: We assess the Southern Ocean CO2 uptake (1985–2018) using data sets gathered in the REgional Carbon Cycle Assessment and Processes Project Phase 2. The Southern Ocean acted as a sink for CO2 with close agreement between simulation results from global ocean biogeochemistry models (GOBMs, 0.75 ± 0.28 PgC yr−1) and pCO2-observation-based products (0.73 ± 0.07 PgC yr−1). This sink is only half that reported by RECCAP1 for the same region and timeframe. The present-day net uptake is to first order a response to rising atmospheric CO2, driving large amounts of anthropogenic CO2 (Cant) into the ocean, thereby overcompensating the loss of natural CO2 to the atmosphere. An apparent knowledge gap is the increase of the sink since 2000, with pCO2-products suggesting a growth that is more than twice as strong and uncertain as that of GOBMs (0.26 ± 0.06 and 0.11 ± 0.03 Pg C yr−1 decade−1, respectively). This is despite nearly identical pCO2 trends in GOBMs and pCO2-products when both products are compared only at the locations where pCO2 was measured. Seasonal analyses revealed agreement in driving processes in winter with uncertainty in the magnitude of outgassing, whereas discrepancies are more fundamental in summer, when GOBMs exhibit difficulties in simulating the effects of the non-thermal processes of biology and mixing/circulation. Ocean interior accumulation of Cant points to an underestimate of Cant uptake and storage in GOBMs. Future work needs to link surface fluxes and interior ocean transport, build long overdue systematic observation networks and push toward better process understanding of drivers of the carbon cycle.
    Repository Name: EPIC Alfred Wegener Institut
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  • 137
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    Spatial Variability of Dissolved Organic Carbon, Solutes, and Suspended Sediment in Disturbed Low Arctic Coastal Watersheds (2020)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research Biogeosciences, American Geophysical Union (AGU), 125(2), ISSN: 2169-8953
    Details
    Publication Date: 2024-01-30
    Description: Climate change in the Arctic leads to permafrost degradation and to associated changes infreshwater geochemistry. There is a limited understanding of how disturbances such as active layerdetachments or retrogressive thaw slumps impact water quality on a catchment scale. This study investigateshow permafrost degradation affects concentrations of dissolved organic carbon (DOC), total dissolvedsolids (TDS), suspended sediment, and stable water isotopes in adjacent Low Arctic watersheds. Weincorporated data on disturbance between 1952 and 2015, as well as sporadic runoff and geochemistry dataof streams nearby. Our results show that the total disturbed area decreased by 41% between 1952 and 2015,whereas the total number of disturbances increased by 66% in all six catchments. The spatial variabilityof hydrochemical parameters is linked to catchment properties and not necessarily reflected at the outflow.Degrading ice‐wedge polygons were found to increase DOC concentrations upstream in Ice Creek West,whereas hydrologically connected disturbances were linked to increases in TDS and suspended sediment.Although we found a great spatial variability of hydrochemical concentrations along the paired watershed,there was a linear relationship between catchment size and daily DOC, total dissolved nitrogen, and TDSfluxes for all six streams. Suspended sedimentflux on the contrary did not show a clear relationship as onehydrologically connected retrogressive thaw slump impacted the overallflux in one of the streams.Understanding the spatial variability of water quality will help to model the lateral geochemicalfluxes fromArctic catchments
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  • 138
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    Isotopic Characterization of Water Masses in the Southeast Pacific Region: Paleoceanographic Implications (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research - Oceans, American Geophysical Union (AGU), 127(1), ISSN: 2169-9275
    Details
    Publication Date: 2024-01-31
    Description: In this study, we used stable isotopes of oxygen (δ18O), deuterium (δD), and dissolved inorganic carbon (δ13CDIC) in combination with temperature, salinity, oxygen, and nutrient concentrations to characterize the coastal (71°–78°W) and an oceanic (82°–98°W) water masses (SAAW—Subantarctic Surface Water; STW—Subtropical Water; ESSW—Equatorial Subsurface water; AAIW—Antarctic Intermediate Water; PDW—Pacific Deep Water) of the Southeast Pacific (SEP). The results show that δ18O and δD can be used to differentiate between SAAW-STW, SAAW-ESSW, and ESSW-AAIW. δ13CDIC signatures can be used to differentiate between STW-ESSW (oceanic section), SAAW-ESSW, ESSW-AAIW, and AAIW-PDW. Compared with the oceanic section, our new coastal section highlights differences in both the chemistry and geometry of water masses above 1,000 m. Previous paleoceanographic studies using marine sediments from the SEP continental margin used the present-day hydrological oceanic transect to compare against, as the coastal section was not sufficiently characterized. We suggest that our new results of the coastal section should be used for past characterizations of the SEP water masses that are usually based on continental margin sediment samples.
    Repository Name: EPIC Alfred Wegener Institut
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  • 139
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    Ultrahigh-precision noble gas isotope analyses reveal pervasive subsurface fractionation in hydrothermal systems (2024)
    American Association for the Advancement of Science
    Details
    Publication Date: 2024-01-12
    Description: Mantle-derived noble gases in volcanic gases are powerful tracers of terrestrial volatile evolution, as they contain mixtures of both primordial (from Earth's accretion) and secondary (e.g., radiogenic) isotope signals that characterize the composition of deep Earth. However, volcanic gases emitted through subaerial hydrothermal systems also contain contributions from shallow reservoirs (groundwater, crust, atmosphere). Deconvolving deep and shallow source signals is critical for robust interpretations of mantle-derived signals. Here, we use a novel dynamic mass spectrometry technique to measure argon, krypton, and xenon isotopes in volcanic gas with ultrahigh precision. Data from Iceland, Germany, United States (Yellowstone, Salton Sea), Costa Rica, and Chile show that subsurface isotope fractionation within hydrothermal systems is a globally pervasive and previously unrecognized process causing substantial nonradiogenic Ar-Kr-Xe isotope variations. Quantitatively accounting for this process is vital for accurately interpreting mantle-derived volatile (e.g., noble gas and nitrogen) signals, with profound implications for our understanding of terrestrial volatile evolution.
    Description: Published
    Description: eadg2566
    Description: OSV2: Complessità dei processi vulcanici: approcci multidisciplinari e multiparametrici
    Description: JCR Journal
    Keywords: noble gases ; earth degassing
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 140
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    Counteracting Contributions of the Upper and Lower Meridional Overturning Limbs to the North Atlantic Nutrient Budgets: Enhanced Imbalance in 2010 (2021)
    American Geophysical Union (AGU)
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union (AGU), 35(6), ISSN: 0886-6236
    Details
    Publication Date: 2024-01-18
    Description: The North Atlantic Basin is a major sink for atmospheric carbon dioxide (CO2) due in part to the extensive plankton blooms which form there supported by nutrients supplied by the three-dimensional ocean circulation. Hence, changes in ocean circulation and/or stratification may influence primary production and biological carbon export. In this study, we assess this possibility by evaluating inorganic nutrient budgets for 2004 and 2010 in the North Atlantic based on observations from the transatlantic A05-24.5°N and the Greenland-Portugal OVIDE hydrographic sections, to which we applied a box inverse model to solve the circulation and estimate the across-section nutrient transports. Full water column nutrient budgets were split into upper and lower meridional overturning circulation (MOC) limbs. According to our results, anomalous circulation in early 2010, linked to extreme negative NAO conditions, led to an enhanced northward advection of more nutrient-rich waters by the upper overturning limb, which resulted in a significant nitrate and phosphate convergence north of 24.5°N. Combined with heaving of the isopycnals, this anomalous circulation event in 2010 favored an enhancement of the nutrient consumption (5.7 ± 4.1 kmol-P s−1) and associated biological CO2 uptake (0.25 ± 0.18 Pg-C yr−1, upper-bound estimate), which represents a 50% of the mean annual sea–air CO2 flux in the region. Our results also suggest a transient state of deep silicate divergence in both years. Both results are indicative of a MOC-driven modulation of the biological carbon uptake (by the upper MOC limb) and nutrient inventories (by the lower MOC limb) in the North Atlantic.
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  • 141
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    On the polar bias in ice core 10Be data (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), ISSN: 2169-897X
    Details
    Publication Date: 2024-01-22
    Repository Name: EPIC Alfred Wegener Institut
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  • 142
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    Local Seismicity and Sediment Deformation in the West Svalbard Margin: Implications of Neotectonics for Seafloor Seepage (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geochemistry Geophysics Geosystems, American Geophysical Union (AGU), 24(12), ISSN: 1525-2027
    Details
    Publication Date: 2024-01-22
    Description: In the Fram Strait, mid-ocean ridge spreading is represented by the ultra-slow system of the Molloy Ridge, the Molloy Transform Fault and the Knipovich Ridge. Sediments on oceanic and continental crust are gas charged and there are several locations with documented seafloor seepage. Sedimentary faulting shows recent stress release in the sub-surface, but the drivers of stress change and its influence on fluid flow are not entirely understood. We present here the results of an 11-month-long ocean bottom seismometer survey conducted over the highly faulted sediment drift northwards from the Knipovich Ridge to monitor seismicity and infer the regional state of stress. We obtain a detailed earthquake catalog that improves the spatial resolution of mid-ocean ridge seismicity compared with published data. Seismicity at the Molloy Transform Fault is occurring southwards from the bathymetric imprint of the fault, as supported by a seismic profile. Earthquakes in the northern termination of the Knipovich Ridge extend eastwards from the ridge valley, which together with syn-rift faulting identified in seismic reflection data, suggests that a portion of the currently active spreading center is buried under sediments away from the bathymetric expression of the rift valley. This hints at the direct link between crustal rifting processes and faulting in shallow sediments. Two earthquakes occur close to the seepage system of the Vestnesa Ridge further north from the network. We suggest that deeper rift structures, reactivated by gravity and/or post-glacial subsidence, may lead to accommodation of stress through shallow extensional faults, therefore impacting seepage dynamics.
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  • 143
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    Assessing Seasonal and Inter‐Annual Marine Sediment Climate Proxy Data (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Paleoceanography and Paleoclimatology, American Geophysical Union (AGU), 38(10), ISSN: 2572-4517
    Details
    Publication Date: 2024-03-13
    Description: Three recently published papers including Napier et al. (2022, https://doi.org/10.1029/2021PA004355) utilize novel microanalytical approaches with varved marine sediments to demonstrate the potential to reconstruct seasonal and inter-annual climate variability. Obtaining paleoclimate data at a resolution akin to the observational record is vitally important for improving our understanding of climate phenomena such as monsoons and modes of variability such as the El Niño Southern Oscillation, for which appraisals of past inter-annual variability is critical. The ability to generate seasonal and inter annual resolution sea surface temperature proxy time series spanning a thousand years or more is revolutionary and has the potential to fill gaps in our knowledge of climate variability. Although generally limited to sediments from regions with oxygen depleted bottom waters, there is great potential to integrate shorter seasonal resolution climate “snap shots” from other archives such as annually banded corals into composite time series. But as paleoceanographic data are used more by the observational and modeling fields, we make the case for conducting a thorough case-by-case assessment of the processes that influence the climate signal recovered from proxies, using careful replication to validate new approaches. Understanding or exploring the potential influence of processes which effectively filter the climate signal will lead to more quantitative paleoceanographic data that will better serve the broader climate science community.
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  • 144
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    Intensification of the East Australian Current After ∼1400 CE (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 49(24), ISSN: 0094-8276
    Details
    Publication Date: 2024-03-13
    Description: The East Australian Current (EAC) is the western boundary current of the South Pacific Subtropical Gyre that transports warm tropical waters to higher southern latitudes and significantly impacts the climate of Australia and New Zealand. Modern observations show that the EAC has strengthened with rising global temperatures. However, little is known about the pre-industrial variability of the EAC and the forcing mechanisms. Planktic foraminifera Globigerinoides ruber (white) Mg/Ca-based sea surface temperature reconstructions offshore northeastern Australia between 15° and 26°S reveal an increase by ∼1.2°C after ∼1400 CE. We infer that the increase in temperature is related to a stronger EAC heat transport that is likely driven by a strengthening of the Southern Hemisphere subtropical gyre circulation due to a progressive shift of the Southern annular mode toward its positive phase and of El Niño-Southern Oscillation toward more El Niño-like conditions.
    Repository Name: EPIC Alfred Wegener Institut
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  • 145
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    Seismic Risk Communication in Europe: Lessons Learned and Future Perspectives (2024)
    American Geophysical Union (AGU)
    Details
    Publication Date: 2024-03-13
    Description: Since the 1980s various international directives and frameworks have acknowledged the potential of risk communication to foster community empowerment. However, to achieve empowerment, communication has to be effective. When it comes to natural disasters, such as earthquakes, science communication requires the involvement of communities as a whole, promoting bottom-up strategies and proactive engagement. In this light, we conducted a scoping review of scientific publications on seismic risk communication in Europe published between 2000 and 2022. We focused on how seismic risk communication has changed in that time span, looking for targeted approaches, tools, recipients and channels. Here we provide an overview of the results obtained from the analysis of 109 selected publications, also highlighting the importance of scientific communication as a transnational problem, due to the mobility of modern society. Our study reveals that seismic risk communication in Europe is becoming increasingly proactive, focusing on a bottom-up strategy that relies on youth to build the resilience of future generations. The potential for the community empowerment has been primarily addressed with seismic risk communication during the pre-crisis phase of the disaster, when risk awareness can be effectively raised. Social media are increasingly used to provide timely and actionable information in times of crisis, to engage citizens within a two-way risk communication model, in the pre-crisis time, and to provide scientific data for post-disaster processing. The future agenda of seismic risk communication in Europe should focus on building trust with the public, moving towards a three-way model of seismic risk communication and, even more importantly, taking action to curb the spread of fake news and their negative impact on disaster management. Last but not least, more efforts should be made to link practice and theory and explicitly build seismic risk communication on theoretical models.
    Description: Published
    Description: San Francisco, California, USA
    Description: OS: Terza missione
    Keywords: Seismic risk ; communication ; Europe ; scoping review ; 04.06. Seismology ; 05.08. Risk ; 05.09
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 146
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    Volcano-Tectonic seismicity during the unrest phase on the island of Vulcano (Italy) from mid-September 2021 to December 2022 (2024)
    American Geophysical Union (AGU)
    Details
    Publication Date: 2024-03-13
    Description: In mid-September 2021 there was a rapid increase in geophysical and geochemical parameters on the island of Vulcano, Italy, reaching alarming values. This phase of unrest aroused serious concern among Civil Protection, local authorities and the scientific community due to the risk of phreatomagmatic activity, with potentially serious repercussions on the inhabitants of the island and on visiting tourists. The beginning of the unrest was marked by a high occurrence rate of local micro-seismicity related to fluid dynamics within the shallower hydrothermal system (mainly Long Period and Very Long Period events); Volcano-Tectonic (VT) earthquakes increased in late October after most of the monitored parameters reached their climax. Afterwards, major episodes of VT activity were also recorded from March to April and at the end of the year 2022, when an earthquake of ML 4.6 occurred on December 4, SW of the island of Vulcano. Here, we analyze the VT earthquakes from January 2020 to December 2022, in terms of space-time distribution, energy release and focal mechanisms in the framework of the regional geodynamic context and in the light of the main characteristics of the seismic activity recorded in the Vulcano area over the past 36 years.
    Description: Published
    Description: San Francisco, California, USA
    Description: OST3 Vicino alla faglia
    Keywords: earthquakes ; monitoring ; volcano unrest ; Vulcano ; 04.06. Seismology ; 04.07. Tectonophysics ; 04.08. Volcanology
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  • 147
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    Sediment Freeze‐On and Transport Near the Onset of a Fast‐Flowing Glacier in East Antarctica (2024)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 51(6), ISSN: 0094-8276
    Details
    Publication Date: 2024-03-18
    Description: Understanding the material properties and physical conditions of basal ice is crucial for a comprehensive understanding of Antarctic ice‐sheet dynamics. Yet, direct data are sparse and difficult to acquire. Here, we employ ultra‐wideband radar to map high‐backscatter zones near the glacier bed within East Antarctica's Jutulstraumen drainage basin. Our backscatter analysis reveals that the basal ice in an area of ∼10,000 km² is composed of along‐flow oriented sediment‐laden basal ice units connected to the basal substrate, extending up to several hundred meters thick. Three‐dimensional thermomechanical modeling supports that these units form via basal freeze‐on of subglacial water that originated from further upstream. Our findings suggest that basal freeze‐on, and the entrainment and transport of subglacial material play a significant role in an accurate representation of material, physical, and rheological properties of the Antarctic ice sheet's basal ice, ultimately enhancing the accuracy and reliability of ice‐sheet modeling.
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  • 148
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    Anthropogenic Influence on Tropospheric Reactive Bromine Since the Pre‐industrial: Implications for Arctic Ice‐Core Bromine Trends (2024)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 51(5), ISSN: 0094-8276
    Details
    Publication Date: 2024-03-21
    Description: Tropospheric reactive bromine (Bry) influences the oxidation capacity of the atmosphere by acting as a sink for ozone and nitrogen oxides. Aerosol acidity plays a crucial role in Bry abundances through acid-catalyzed debromination from sea-salt-aerosol, the largest global source. Bromine concentrations in a Russian Arctic ice-core, Akademii Nauk, show a 3.5-fold increase from pre-industrial (PI) to the 1970s (peak acidity, PA), and decreased by half to 1999 (present day, PD). Ice-core acidity mirrors this trend, showing robust correlation with bromine, especially after 1940 (r = 0.9). Model simulations considering anthropogenic emission changes alone show that atmospheric acidity is the main driver of Bry changes, consistent with the observed relationship between acidity and bromine. The influence of atmospheric acidity on Bry should be considered in interpretation of ice-core bromine trends.
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  • 149
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    Implications of Snowpack Reactive Bromine Production for Arctic Ice Core Bromine Preservation (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), 128(20), ISSN: 2169-897X
    Details
    Publication Date: 2024-03-21
    Description: Snowpack emissions are recognized as an important source of gas-phase reactive bromine in the Arctic and are necessary to explain ozone depletion events in spring caused by the catalytic destruction of ozone by halogen radicals. Quantifying bromine emissions from snowpack is essential for interpretation of ice-core bromine. We present ice-core bromine records since the pre-industrial (1750 CE) from six Arctic locations and examine potential post-depositional loss of snowpack bromine using a global chemical transport model. Trend analysis of the ice-core records shows that only the high-latitude coastal Akademii Nauk (AN) ice core from the Russian Arctic preserves significant trends since pre-industrial times that are consistent with trends in sea ice extent and anthropogenic emissions from source regions. Model simulations suggest that recycling of reactive bromine on the snow skin layer (top 1 mm) results in 9–17% loss of deposited bromine across all six ice-core locations. Reactive bromine production from below the snow skin layer and within the snow photic zone is potentially more important, but the magnitude of this source is uncertain. Model simulations suggest that the AN core is most likely to preserve an atmospheric signal compared to five Greenland ice cores due to its high latitude location combined with a relatively high snow accumulation rate. Understanding the sources and amount of photochemically reactive snow bromide in the snow photic zone throughout the sunlit period in the high Arctic is essential for interpreting ice-core bromine, and warrants further lab studies and field observations at inland locations.
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  • 150
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    Presence, Sources and Transport of Polycyclic Aromatic Hydrocarbons in the Arctic Ocean (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 50(1), ISSN: 0094-8276
    Details
    Publication Date: 2024-03-28
    Repository Name: EPIC Alfred Wegener Institut
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  • 151
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    The Chemical Effect of Increased Water Vapor From the Hunga Tonga‐Hunga Ha'apai Eruption on the Antarctic Ozone Hole (2024)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 51(4), ISSN: 0094-8276
    Details
    Publication Date: 2024-03-27
    Description: The eruption of the Hunga Tonga‐Hunga Ha'apai volcano on 15 January 2022 was one of the most explosive eruptions of the last decades. The amount of water vapor injected into the stratosphere was unprecedented in the observational record, increasing the stratospheric water vapor burden by about 10%. Using model runs from the ATLAS chemistry and transport model and Microwave Limb Sounder (MLS) satellite observations, we show that while 20%–40% more water vapor than usual was entrained into the Antarctic polar vortex in 2023 as it formed, the direct chemical effect of the increased water vapor on Antarctic ozone depletion in June through October was minor (less than 4 DU). This is because low temperatures in the vortex, as occur every year in the Antarctic, limit water vapor to the saturation pressure and thus reset any anomalies through the process of dehydration before they can affect ozone loss.
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  • 152
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    The Subglacial Lake That Wasn't There: Improved Interpretation From Seismic Data Reveals a Sediment Bedform at Isunnguata Sermia (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research Earth Surface, American Geophysical Union (AGU), 128(10), ISSN: 2169-9003
    Details
    Publication Date: 2024-03-14
    Description: Radio Echo Sounding (RES) surveys conducted in May 2010 and April 2011 revealed a 2 km2 flat area with increased bed reflectivity at the base of Isunnguata Sermia at the western margin of the Greenland Ice Sheet. This flat reflector was located within a localized subglacial hydraulic potential (hydropotential) minimum, as part of a complex and elongated trough system. By analogy with comparable features in Antarctica, the initial interpretation of such a feature was a potential subglacial lake. In September 2013 a co-located seismic survey revealed a 1,750 m by 540 and 37 m thick stratified lens-shaped bedform at the base of a subglacial trough system. Amplitude Versus Angle (AVA) analysis yields a derived reflection coefficient R = 0.09 ± 0.14 indicative of consolidated sediments possibly overlain by dilatant till. The bed and flank on the northern side of the trough consist of unconsolidated, possibly water-bearing sediments with R = −0.10 ± 0.08, whereas on the southern side it consists of more consolidated material. We interpret the trough as a key component of the wider subglacial drainage network, for which the sediments on its northern side act as a localized water-storage reservoir. Given the observation of seasonally forming and rapidly draining supraglacial meltwater lakes in this area, we interpret the lens-shaped bedform as deposited by episodically ponding meltwater within the subglacial trough system. Our results highlight the importance of transient subglacial hydrological and sedimentological processes such as drainage events for the interaction of ice sheets and their substrates, to understand ice dynamics in a warming climate.
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  • 153
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    Clouds and Radiation Processes in Regional Climate Models Evaluated Using Observations Over the Ice‐free Arctic Ocean (2021)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), 126(1), ISSN: 2169-897X
    Details
    Publication Date: 2024-03-14
    Description: The presence of clouds in the Arctic regulates the surface energy budget (SEB) over the sea-ice surface and the ice-free ocean. Following several previous field campaigns, the cloud-radiation relationship, including cloud vertical structure and phase, has been elucidated; however, modeling of this relationship has matured slowly. In recognition of the recent decline in the Arctic sea-ice extent, representation of the cloud system in numerical models should consider the effects of areas covered by sea ice and ice-free areas. Using an in situ stationary meteorological observation data set obtained over the ice-free Arctic Ocean by the Japanese Research Vessel Mirai (September 2014), coordinated evaluation of six regional climate models (RCMs) with nine model runs was performed by focusing on clouds and the SEB. The most remarkable findings were as follows: (1) reduced occurrence of unstable stratification with low-level cloud water in all models in comparison to the observations, (2) significant differences in cloud water representations between single- and double-moment cloud schemes, (3) extensive differences in partitioning of hydrometeors including solid/liquid precipitation, and (4) pronounced lower-tropospheric air temperature biases. These issues are considered as the main sources of SEB uncertainty over ice-free areas of the Arctic Ocean. The results from a coupled RCM imply that the SEB is constrained by both the atmosphere and the ocean (and sea ice) with considerable feedback. Coordinated improvement of both stand-alone atmospheric and coupled RCMs would promote a more comprehensive and improved understanding of the Arctic air-ice-sea coupled system.
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  • 154
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    Bedforms of Thwaites Glacier, West Antarctica: Character and Origin (2021)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research Earth Surface, American Geophysical Union (AGU), 126(12), ISSN: 2169-9003
    Details
    Publication Date: 2024-03-14
    Description: Bedforms of Thwaites Glacier, West Antarctica both record and affect ice flow, as shown by geophysical data and simple models. Thwaites Glacier flows across the tectonic fabric of the West Antarctic rift system with its bedrock highs and sedimentary basins. Swath radar and seismic surveys of the glacier bed have revealed soft-sediment flutes 100 m or more high extending 15 km or more across basins downglacier from bedrock highs. Flutes end at prominent hard-bedded moats on stoss sides of the next topographic highs. We use simple models to show that ice flow against topography increases pressure between ice and till upglacier along the bed over a distance that scales with the topography. In this basal zone of high pressure, ice-contact water would be excluded, thus increasing basal drag by increasing ice-till coupling and till flux, removing till to allow bedrock erosion that creates moats. Till carried across highlands would then be deposited in lee-side positions forming bedforms that prograde downglacier over time, and that remain soft on top through feedbacks that match till-deformational fluxes from well upglacier of the topography. The bedforms of the part of Thwaites surveyed here are prominent because ice flow has persisted over a long time on this geological setting, not because ice flow is anomalous. Bedform development likely has caused evolution of ice flow over time as till and lubricating water were redistributed, moats were eroded and bedforms grew.
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  • 155
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    Atmosphere‐Snow Exchange Explains Surface Snow Isotope Variability (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 49(20), pp. e2022gl099529-e2022gl099529, ISSN: 0094-8276
    Details
    Publication Date: 2024-03-14
    Description: The climate signal imprinted in the snow isotopic composition allows to infer past climate variability from ice core stable water isotope records. The concurrent evolution of vapor and surface snow isotopic composition between precipitation events indicates that post-depositional atmosphere-snow humidity exchange influences the snow and hence the ice core isotope signal. To date, however, this is not accounted for in paeleoclimate reconstructions from isotope records. Here we show that vapor-snow exchange explains 36% of the summertime day-to-day δ18O variability of the surface snow between precipitation events, and 53% of the δD variability. Through observations from the Greenland Ice Sheet and accompanying modeling we demonstrate that vapor-snow exchange introduces a warm bias on the summertime snow isotope value relevant for ice core records. In case of long-term variability in atmosphere-snow exchange the relevance for the ice core signal is also variable and thus paleoclimate reconstructions from isotope records should be revisited.
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  • 156
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    Nitrous Oxide Fluxes in Permafrost Peatlands Remain Negligible After Wildfire and Thermokarst Disturbance (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research Biogeosciences, American Geophysical Union (AGU), 128(4), ISSN: 2169-8953
    Details
    Publication Date: 2024-04-19
    Description: The greenhouse gas (GHG) balance of boreal peatlands in permafrost regions will be affected by climate change through disturbances such as permafrost thaw and wildfire. Although the future GHG balance of boreal peatlands including ponds is dominated by the exchange of both carbon dioxide (CO2) and methane (CH4), disturbance impacts on fluxes of the potent GHG nitrous oxide (N2O) could contribute to shifts in the net radiative balance. Here, we measured monthly (April to October) fluxes of N2O, CH4, and CO2 from three sites located across the sporadic and discontinuous permafrost zones of western Canada. Undisturbed permafrost peat plateaus acted as N2O sinks (−0.025 mg N2O m−2 d−1), but N2O uptake was lower from burned plateaus (−0.003 mg N2O m−2 d−1) and higher following permafrost thaw in the thermokarst bogs (−0.054 mg N2O m−2 d−1). The thermokarst bogs had below-ambient N2O soil gas concentrations, suggesting that denitrification consumed atmospheric N2O during reduction to dinitrogen. Atmospheric uptake of N2O in peat plateaus and thermokarst bogs increased with soil temperature and soil moisture, suggesting sensitivity of N2O consumption to further climate change. Four of five peatland ponds acted as N2O sinks (−0.018 mg N2O m−2 d−1), with no influence of thermokarst expansion. One pond with high nitrate concentrations had high N2O emissions (0.30 mg N2O m−2 d−1). Overall, our study suggests that the future net radiative balance of boreal peatlands will be dominated by impacts of wildfire and permafrost thaw on CH4 and CO2 fluxes, while the influence from N2O is minor.
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  • 157
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    Anthropogenic Perturbations Change the Quality and Quantity of Terrestrial Carbon Flux to the Coastal Ocean (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research Biogeosciences, American Geophysical Union (AGU), 128(10), ISSN: 2169-8953
    Details
    Publication Date: 2024-04-11
    Description: Human activities have increasingly changed terrestrial particulate organic carbon (POC) export to the coastal ocean since the Industrial Age (19th century). However, the influence of human perturbations on the composition and flux of terrestrial biospheric and petrogenic POC sub-pools remains poorly constrained. Here, we examined 13C and 14C compositions of bulk POC and source-specific biomarkers (fatty acids, FA) from two nearshore sediment cores collected in the Pearl River-derived mudbelt, to determine the impacts of human perturbations of the Pearl River watershed on the burial of terrestrial POC in the coastal ocean over the last century. Our results show that although agricultural practices and deforestation during the 1930s–1950s increased C4 plant coverage in the watershed, the export fluxes of terrestrial biospheric and petrogenic POC remained rather unchanged; however, added perturbations since 1974, including increasing coal consumption, embankment and dam constructions caused massive export of both petrogenic POC and relatively fresh terrestrial biospheric POC from the river delta. Our data reveal that human activities substantially enhance the transfer of petrogenic POC and fresh biospheric POC to the coastal ocean after ca. 1974, with the latter process acting as an important sink for anthropogenic CO2.
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  • 158
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    A Snapshot on the Buildup of the Stable Water Isotopic Signal in the Upper Snowpack at EastGRIP on the Greenland Ice Sheet (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research Earth Surface, American Geophysical Union (AGU), 128(2), ISSN: 2169-9003
    Details
    Publication Date: 2024-04-29
    Description: The stable water isotopic composition in firn and ice cores provides valuable information on past climatic conditions. Because of uneven accumulation and post-depositional modifications on local spatial scales up to hundreds of meters, time series derived from adjacent cores differ significantly and do not directly reflect the temporal evolution of the precipitated snow isotopic signal. Hence, a characterization of how the isotopic profile in the snow develops is needed to reliably interpret the isotopic variability in firn and ice cores. By combining digital elevation models of the snow surface and repeated high-resolution snow sampling for stable water isotope measurements of a transect at the East Greenland Ice-core Project campsite on the Greenland Ice Sheet, we are able to visualize the buildup and post-depositional changes of the upper snowpack across one summer season. To this end, 30 cm deep snow profiles were sampled on six dates at 20 adjacent locations along a 40 m transect. Near-daily photogrammetry provided snow height information for the same transect. Our data shows that erosion and redeposition of the original snowfall lead to a complex stratification in the δ18O signature. Post-depositional processes through vapor-snow exchange affect the near surface snow with d-excess showing a decrease in surface and near-surface layers. Our data suggests that the interplay of stratigraphic noise, accumulation intermittency, and local post-depositional processes form the proxy signal in the upper snowpack.
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  • 159
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    Fast Ice Thickness Distribution in the Western Ross Sea in Late Spring (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research - Oceans, American Geophysical Union (AGU), 128(2), ISSN: 2169-9275
    Details
    Publication Date: 2024-05-01
    Description: We present a 700 km airborne electromagnetic survey of late-spring fast ice and sub-ice platelet layer (SIPL) thickness distributions from McMurdo Sound to Cape Adare, providing a first-time inventory of fast ice thickness close to its annual maximum. The overall mode of the consolidated ice (including snow) thickness was 1.9 m, less than its mean of 2.6 ± 1.0 m. Our survey was partitioned into level and rough ice, and SIPL thickness was estimated under level ice. Although level ice, with a mode of 2.0 m and mean of 2.0 ± 0.6 m, was prevalent, rough ice occupied 41% of the transect by length, 50% by volume, and had a mode of 3.3 m and mean of 3.2 ± 1.2 m. The thickest 10% of rough ice was almost 6 m on average, inclusive of a 2 km segment thicker than 8 m in Moubray Bay. The thickest ice occurred predominantly along the northwestern Ross Sea, due to compaction against the coast. The adjacent pack ice was thinner (by ∼1 m) than the first-year fast ice. In Silverfish Bay, offshore Hells Gate Ice Shelf, New Harbor, and Granite Harbor, the SIPL transect volume was a significant fraction (0.30) of the consolidated ice volume. The thickest 10% of SIPLs averaged nearly 3 m thick, and near Hells Gate Ice Shelf the SIPL was almost 10 m thick, implying vigorous heat loss to the ocean (∼90 W m −2). We conclude that polynya-induced ice deformation and interaction with continental ice influence fast ice thickness in the western Ross Sea.
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  • 160
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    Reversals in Temperature‐Precipitation Correlations in the Northern Hemisphere Extratropics During the Holocene (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 49(22), ISSN: 0094-8276
    Details
    Publication Date: 2024-04-23
    Description: Future precipitation levels remain uncertain because climate models have struggled to reproduce observed variations in temperature-precipitation correlations. Our analyses of Holocene proxy-based temperature-precipitation correlations and hydrological sensitivities from 2,237 Northern Hemisphere extratropical pollen records reveal a significant latitudinal dependence and temporal variations among the early, middle, and late Holocene. These proxy-based variations are largely consistent with patterns obtained from transient climate simulations (TraCE21k). While high latitudes and subtropical monsoon areas show mainly stable positive correlations throughout the Holocene, the mid-latitude pattern is temporally and spatially more variable. In particular, we identified a reversal from positive to negative temperature-precipitation correlations in the eastern North American and European mid-latitudes from the early to mid-Holocene that mainly related to slowed down westerlies and a switch to moisture-limited convection under a warm climate. Our palaeoevidence of past temperature-precipitation correlation shifts identifies those regions where simulating past and future precipitation levels might be particularly challenging.
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  • 161
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    Interdecadal Pacific Oscillation in Northern Greenland Dust Concentration Variability During the Last 400 Years (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 49(24), ISSN: 0094-8276
    Details
    Publication Date: 2024-04-22
    Description: Statistical analysis of reanalysis and observed data reveals that high dust surface mass concentration in northern Greenland is associated with a Pacific Decadal Oscillation like pattern in its negative phase in the North Pacific as well as with La Niña conditions in the tropical Pacific region. The sea surface temperature anomalies in the Pacific realm resemble the Interdecadal Pacific Oscillation (IPO). The associated atmospheric circulation pattern, in the form of a wave-train from the North Pacific to the Eurasian continent, favors enhanced dust uptake and transport toward the northern Greenland. Similar patterns are associated with a low-resolution stacked record of five Ca2+ ice cores, that is, ngt03C93.2 (B16), ngt14C93.2 (B18), ngt27C94.2 (B21), GISP2−B, and NEEM-2011-S1, from northern Greenland, a proxy for regional dust concentration, during the last 400 years. We argue that northern Greenland ice core dust records could be used as proxies for the IPO and related teleconnections.
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  • 162
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    Tectono‐Stratigraphic Evolution of the Kerguelen Large Igneous Province: The Conjugate William’s Ridge‐Broken Ridge Rifted Margins (2024)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), 129(3), ISSN: 2169-9313
    Details
    Publication Date: 2024-04-24
    Description: 〈jats:title〉Abstract〈/jats:title〉〈jats:p〉Extensive investigation of continental rift systems has been fundamental for advancing the understanding of extensional tectonics and modes of formation of new ocean basins. However, current rift classification schemes do not account for conjugate end members formed by Large Igneous Province crust, referring to thick mafic crust, sometimes including continental fragments. Here, we investigate the rifting of William's Ridge (Kerguelen Plateau) and Broken Ridge, components of the Kerguelen Large Igneous Province now situated in the Southeast Indian Ocean, and incorporate these end members into the deformation migration concept for rifted margins. We use multichannel seismic reflection profiles and data from scientific drill cores acquired on both conjugate margins to propose, for the first time, a combined tectono‐stratigraphic framework. We interpret seismic patterns, tectonic features, and magnetic anomaly picks to determine an across‐strike structural domain classification. This interpretation considers the rift system overall to be “magma‐poor” despite being located proximal to the Kerguelen plume but suggests that syn‐rift interaction between the Kerguelen mantle plume and the lithospheric structure of William's Ridge and Broken Ridge has controlled the along‐strike segmentation of both conjugates. We integrate seismic reflection and bathymetric data to test the hypothesis of predominantly transform motion, between the Australian and Antarctic plates, in Late Cretaceous and Paleogene time.〈/jats:p〉
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  • 163
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    Structure and Seasonal Variability of the Arctic Boundary Current North of Severnaya Zemlya (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research - Oceans, American Geophysical Union (AGU), 128(1), ISSN: 2169-9275
    Details
    Publication Date: 2024-05-08
    Description: We assessed the spatial and temporal variability of the Arctic Boundary Current (ABC) using seven oceanographic moorings, deployed across the continental slope north of Severnaya Zemlya in 2015–2018. Transports and individual water masses were quantified based on temperature and salinity recorders and current profilers. Our results were compared with observations from the northeast Svalbard and the central Laptev Sea continental slopes to evaluate the hydrographic transformation along the ABC pathway. The highest velocities (〉0.30 m s−1) of the ABC occurred at the upper continental slope and decreased offshore to below 0.03 m s−1 in the deep basin. The ABC showed seasonal variability with velocities two times higher in winter than in summer. Compared to upstream conditions in Svalbard, water mass distribution changed significantly within 20 km of the shelf edge due to mixing with- and intrusion of shelf waters. The ABC transported 4.15 ± 0.3 Sv in the depth range 50–1,000 m, where 0.88 ± 0.1, 1.5 ± 0.2, 0.61 ± 0.1 and 1.0 ± 0.15 Sv corresponded to Atlantic Water (AW), Dense Atlantic Water (DAW), Barents Sea Branch Water (BSBW) and Transformed Atlantic Water (TAW). 62–70% of transport was constrained to within 30–40 km of the shelf edge, and beyond 84 km, transport increases were estimated to be 0.54 Sv. Seasonality of TAW derived from local shelf-processes and advection of seasonal-variable Fram Strait waters, while BSBW transport variability was dominated by temperature changes with maximum transport coinciding with minimum temperatures. Further Barents Sea warming will likely reduce TAW and BSBW transport leading to warmer conditions along the ABC pathway.
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  • 164
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    Sensitivity of Sea Ice Growth to Snow Properties in Opposing Regions of the Weddell Sea in Late Summer (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 49(19), ISSN: 0094-8276
    Details
    Publication Date: 2024-05-08
    Description: The sensitivity of sea ice to the contrasting seasonal and perennial snow properties in the southeastern and northwestern Weddell Sea is not yet considered in sea ice model and satellite remote sensing applications. However, the analysis of physical snowpack properties in late summer in recent years reveals a high fraction of melt-freeze forms resulting in significant higher snow densities in the northwestern than in the eastern Weddell Sea. The resulting lower thermal conductivity of the snowpack, which is only half of what has been previously assumed in models in the eastern Weddell Sea, reduces the sea ice bottom growth by 18 cm during winter. In the northwest, however, the potentially formed snow ice thickness of 22 cm at the snow/ice interface contributes to additional 7 cm of thermodynamic ice growth at the bottom. This sensitivity study emphasizes the enormous impact of unappreciated regional differences in snowpack properties on the thermodynamic ice growth.
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  • 165
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    The Performance of the ERA‐Interim and ERA5 Atmospheric Reanalyses Over Weddell Sea Pack Ice (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research - Oceans, American Geophysical Union (AGU), 127(9), ISSN: 2169-9275
    Details
    Publication Date: 2024-05-08
    Description: We use meteorological measurements from three drifting buoys to evaluate the performance of the ERA-Interim and ERA5 atmospheric reanalyses from the European Center for Medium-Range Weather Forecasts over the Weddell Sea ice zone. The temporal variability in surface pressure and near-surface air temperature is captured well by the two reanalyses but both reanalyses exhibit a warm bias relative to the buoy measurements. This bias is small at temperatures close to 0°C but reaches 5–10°C at −40°C. For two of the buoys the mean temperature bias in ERA5 is significantly smaller than that in ERA-Interim while for the third buoy the biases in the two products are comparable. 10 m wind speed biases in both reanalyses are small and may largely result from measurement errors associated with icing of the buoy anemometers. The biases in downwelling shortwave and longwave radiation are significant in both reanalyses but we caution that the pattern of bias is consistent with potential errors in the buoy measurements, caused by accumulation of snow and ice on the radiometers. Overall, our study suggests that, with the exception of near-surface temperature, both reanalyses reproduce the buoy measurements to within the limits of measurement uncertainty. We suggest that the significant biases in near-surface air temperature may result from the simplified representation of sea ice used in the reanalysis models, and we recommend the use of a more sophisticated representation of sea ice, including variable ice and snow thicknesses, in future reanalyses.
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  • 166
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    Moisture Sources and Pathways Determine Stable Isotope Signature of Himalayan Waters in Nepal (2023)
    American Geophysical Union (AGU)
    In:  EPIC3AGU Advances, American Geophysical Union (AGU), 4(1), ISSN: 2576-604X
    Details
    Publication Date: 2024-05-08
    Description: The Himalayan mountain range produces one of the steepest and largest rainfall gradients on Earth, with 〉3 m/yr rainfall difference over a ∼100 km distance. The Indian Summer Monsoon (ISM) contributes more than 80% to the annual precipitation budget of the central Himalayas. The remaining 20% falls mainly during pre-ISM season. Understanding the seasonal cycle and the transfer pathways of moisture from precipitation to the rivers is crucial for constraining water availability in a warming climate. However, the partitioning of moisture into the different storage systems such as snow, glacier, and groundwater and their relative contribution to river discharge throughout the year remains under-constrained. Here, we present novel field data from the Kali Gandaki, a trans-Himalayan river, and use 4-year time series of river and rain water stable isotope composition (δ18O and δ2H values) as well as river discharge, satellite Global Precipitation Measurement amounts, and moisture source trajectories to constrain hydrological variability. We find that rainfall before the onset of the ISM is isotopically distinct and that ISM rain and groundwater have similar isotopic values. Our study lays the groundwork for using isotopic measurements to track changes in precipitation sources during the pre-ISM to ISM transition in this key region of orographic precipitation. Specifically, we highlight the role of pre-ISM precipitation, derived from the Gangetic plain, to define the seasonal river isotopic variability across the central Himalayas. Lastly, isotopic values across the catchment document the importance of a large well-mixed groundwater reservoir supplying river discharge, especially during the non-ISM season.
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  • 167
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    Snow Loss Into Leads in Arctic Sea Ice: Minimal in Typical Wintertime Conditions, but High During a Warm and Windy Snowfall Event (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Geophysical Research Letters, American Geophysical Union (AGU), 50(12), ISSN: 0094-8276
    Details
    Publication Date: 2024-05-08
    Description: The amount of snow on Arctic sea ice impacts the ice mass budget. Wind redistribution of snow into open water in leads is hypothesized to cause significant wintertime snow loss. However, there are no direct measurements of snow loss into Arctic leads. We measured the snow lost in four leads in the Central Arctic in winter 2020. We find, contrary to expectations, that under typical winter conditions, minimal snow was lost into leads. However, during a cyclone that delivered warm air temperatures, high winds, and snowfall, 35.0 ± 1.1 cm snow water equivalent (SWE) was lost into a lead (per unit lead area). This corresponded to a removal of 0.7–1.1 cm SWE from the entire surface—∼6%–10% of this site's annual snow precipitation. Warm air temperatures, which increase the length of time that wintertime leads remain unfrozen, may be an underappreciated factor in snow loss into leads.
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  • 168
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    Turbulent Mixing During Late Summer in the Ice–Ocean Boundary Layer in the Central Arctic Ocean: Results From the MOSAiC Expedition (2022)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research - Oceans, American Geophysical Union (AGU), 127(8), ISSN: 2169-9275
    Details
    Publication Date: 2024-05-08
    Description: We examined mixing processes within the ice–ocean boundary layer (IOBL) close to the geographic North Pole, with an emphasis on wind-driven sea ice drift. Observations were conducted from late August to late September 2020, during the final leg of the international Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. Measurements of ice motion, and profiles of currents, hydrography, and microstructure turbulence were conducted. The multifarious direct observations of sea ice and the upper ocean were used to quantify the transport of momentum, heat, and salt in the IOBL. The ice drift was mostly characterized by the inertial oscillation at a semi-diurnal frequency, which forced an inertial current in the mixed layer. Observation-derived heat and salinity fluxes at the ice–ocean interface suggest early termination of basal melting and transitioning to refreezing, resulting from a rise in the freezing point temperature by the presence of freshened near-surface water. Based on the friction velocity, the measured dissipation rate (ε) of turbulent energy can be approximated as 1.4–1.7 times of the “Law of the Wall” criterion. We also observed a spiraling Ekman flow and find its vertical extent in line with the estimate from ε-based diffusivity. Following passage of a storm, the enhanced oscillatory motions of the ice drift caused trapping of the near-inertial waves (NIWs) that exclusively propagated through the base of the weakly stratified mixed layer. We accounted Holmboe instabilities and NIWs for the observed distinct peak of the dissipation rate near the bottom of the mixed layer.
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  • 169
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    Process‐Based Intercomparison of Water Isotope‐Enabled Models and Reanalysis Nudging Effects (2024)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), 129(1), ISSN: 2169-897X
    Details
    Publication Date: 2024-05-21
    Description: The products from the Stable Water Isotope Intercomparison Group, Phase 2, are currently used for numerous studies, allowing water isotope model-data comparisons with various isotope-enabled atmospheric general circulation model (AGCMs) outputs. However, the simulations under this framework were performed using different parameterizations and forcings. Therefore, a uniform experimental design with state-of-the-art AGCMs is required to interpret isotope observations rigorously. Here, we evaluate the outputs from three isotope-enabled numerical models nudged by three different reanalysis products and investigate the ability of the isotope-enabled AGCMs to reproduce the spatial and temporal patterns of water isotopic composition observed at the surface and in the atmospheric airborne water. Through correlation analyses at various spatial and temporal scales, we found that the model's performance depends on the model or reanalysis we use, the observations we compare, and the vertical levels we select. Moreover, we employed the stable isotope mass balance method to conduct decomposition analyses on the ratio of isotopic changes in the atmosphere. Our goal was to elucidate the spread in simulated atmospheric column δ18O, which is influenced by factors such as evaporation, precipitation, and horizontal moisture flux. Satisfying the law of conservation of water isotopes, this budget method is expected to explain various fractionation phenomena in atmospheric meteorological and climatic events. It also aims to highlight the spreads in modeled isotope results among different experiments using multiple models and reanalyses, which are primarily dominated by uncertainties in moisture flux and precipitation, respectively.
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  • 170
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    Is the Isotopic Composition of Precipitation a Robust Indicator for Reconstructions of Past Tropical Cyclones Frequency? A Case Study on Réunion Island From Rain and Water Vapor Isotopic Observations (2024)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), 129(3), ISSN: 2169-897X
    Details
    Publication Date: 2024-05-21
    Description: Based on a 6-year long record (2014–2020) of the isotopic composition of rain (δ18Op) at Réunion Island (55°E, 22°S), in the South-West Indian Ocean, this study shows that the annual isotopic composition of precipitation in this region is strongly controlled by the number of cyclones, the number of best-track days, and the proportion of cyclonic rain during the year. Our results support the use of δ18Op in annual-resolved tropical climate archives as a reliable proxy of past cyclone frequency. The influence of the proportion of cyclonic rain on the annual isotopic composition arises from the systematically more depleted precipitation and water vapor during cyclonic events than during less organized convective systems. The analysis of the daily to hourly isotopic composition of water vapor (δ18Ov) during low-pressure systems and the reproduction of daily δ18Ov observations by AGCMs with a global medium to coarse resolution (LMDZ-iso and ECHAM6-wiso) suggest that during cyclonic periods the stronger depletion mainly arises from both enhanced large-scale precipitation and water vapor-rain interactions under humid conditions.
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  • 171
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    Contrasting Seasonal Isotopic Signatures of Near‐Surface Atmospheric Water Vapor in the Central Arctic During the MOSAiC Campaign (2023)
    American Geophysical Union (AGU)
    In:  EPIC3Journal of Geophysical Research: Atmospheres, American Geophysical Union (AGU), 128(24), ISSN: 2169-897X
    Details
    Publication Date: 2024-05-21
    Description: The Arctic is experiencing unprecedented moistening which is expected to have far-reaching impact on global climate and weather patterns. However, it remains unclear whether this newly sourced moisture originates locally from ice-free ocean regions or is advected from lower latitudes. In this study, we use water vapor isotope measurements in combination with trajectory-based diagnostics and an isotope-enabled atmosphere general circulation model, to assess seasonal shifts in moisture sources and transport pathways in the Arctic. Continuous measurements of near-surface vapor, δ18O, and δD were performed onboard RV Polarstern during the Multidisciplinary drifting Observatory for the Study of Arctic Climate expedition from October 2019 to September 2020. Combining this isotope data set with meteorological observations reveals that the spatiotemporal evolution of δ18O mimics changes in local temperature and humidity at synoptic to seasonal time scales, while corresponding d-excess changes suggest a seasonal shift in the origin of moisture. Simulation results from the particle dispersion model FLEXPART support these findings, indicating that summer moisture originates from nearby open ocean, while winter moisture comes from more remote sources with longer residence time over sea-ice. Results from a nudged ECHAM6-wiso simulation also indicate that evaporative processes from the ocean surface reproduce summer isotope values, but are insufficient to explain measured winter isotope values. Our study provides the first isotopic characterization of Central Arctic moisture over the course of an entire year, helping to differentiate the influence of local processes versus large-scale vapor transport on Arctic moistening. Future process-based investigations should focus on assessing the non-equilibrium isotopic fractionation during airmass transformation over sea-ice.
    Repository Name: EPIC Alfred Wegener Institut
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    Growing underwater heat blob speeds demise of Arctic sea ice (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-25
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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    Do Republicans or Democrats benefit from mail-in voting? It turns out, neither (2020)
    American Association for the Advancement of Science
    Details
    Publication Date: 2020-08-26
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 174
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    How ‘elite controllers’ tame HIV without drugs (2020)
    American Association for the Advancement of Science
    Details
    Publication Date: 2020-08-26
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 175
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    Immunotherapy via PD-L1–presenting biomaterials leads to long-term islet graft survival (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-01
    Description: Antibody-mediated immune checkpoint blockade is a transformative immunotherapy for cancer. These same mechanisms can be repurposed for the control of destructive alloreactive immune responses in the transplantation setting. Here, we implement a synthetic biomaterial platform for the local delivery of a chimeric streptavidin/programmed cell death-1 (SA-PD-L1) protein to direct “reprogramming” of local immune responses to transplanted pancreatic islets. Controlled presentation of SA-PD-L1 on the surface of poly(ethylene glycol) microgels improves local retention of the immunomodulatory agent over 3 weeks in vivo. Furthermore, local induction of allograft acceptance is achieved in a murine model of diabetes only when receiving the SA-PD-L1–presenting biomaterial in combination with a brief rapamycin treatment. Immune characterization revealed an increase in T regulatory and anergic cells after SA-PD-L1-microgel delivery, which was distinct from naïve and biomaterial alone microenvironments. Engineering the local microenvironment via biomaterial delivery of checkpoint proteins has the potential to advance cell-based therapies, avoiding the need for systemic chronic immunosuppression.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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  • 176
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    The NEMP family supports metazoan fertility and nuclear envelope stiffness (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-01
    Description: Human genome-wide association studies have linked single-nucleotide polymorphisms (SNPs) in NEMP1 (nuclear envelope membrane protein 1) with early menopause; however, it is unclear whether NEMP1 has any role in fertility. We show that whole-animal loss of NEMP1 homologs in Drosophila, Caenorhabditis elegans, zebrafish, and mice leads to sterility or early loss of fertility. Loss of Nemp leads to nuclear shaping defects, most prominently in the germ line. Biochemical, biophysical, and genetic studies reveal that NEMP proteins support the mechanical stiffness of the germline nuclear envelope via formation of a NEMP-EMERIN complex. These data indicate that the germline nuclear envelope has specialized mechanical properties and that NEMP proteins play essential and conserved roles in fertility.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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  • 177
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    Accumulation of collagen molecular unfolding is the mechanism of cyclic fatigue damage and failure in collagenous tissues (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-01
    Description: Overuse injuries to dense collagenous tissues are common, but their etiology is poorly understood. The predominant hypothesis that micro-damage accumulation exceeds the rate of biological repair is missing a mechanistic explanation. Here, we used collagen hybridizing peptides to measure collagen molecular damage during tendon cyclic fatigue loading and computational simulations to identify potential explanations for our findings. Our results revealed that triple-helical collagen denaturation accumulates with increasing cycles of fatigue loading, and damage is correlated with creep strain independent of the cyclic strain rate. Finite-element simulations demonstrated that biphasic fluid flow is a possible fascicle-level mechanism to explain the rate dependence of the number of cycles and time to failure. Molecular dynamics simulations demonstrated that triple-helical unfolding is rate dependent, revealing rate-dependent mechanisms at multiple length scales in the tissue. The accumulation of collagen molecular denaturation during cyclic loading provides a long-sought “micro-damage” mechanism for the development of overuse injuries.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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  • 178
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    Nanoparticle-enhanced chemo-immunotherapy to trigger robust antitumor immunity (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-01
    Description: Mounting evidence suggests that immunotherapies are a promising new class of anticancer therapies. However, the immunosuppressive tumor microenvironment (TME), poor immunogenicity, and off-target toxicity hinder the broader implementation of immunotherapies. Here, we describe a novel strategy combining chemotherapy and immunotherapy to modulate the TME by systemically and concurrently delivering the chemotherapeutic agent SN38 (7-ethyl-10-hydroxycamptothecin) and the STING agonist DMXAA (5,6-dimethylxanthenone-4-acetic acid) into tumors using triblock copolymer nanoparticles, named PS3D1@DMXAA, which enhances antigen cross-presentation and induces the conversion of the immunosuppressive TME to immunogenic TME through the newly found synergistic function between SN38 and STING activation. PS3D1@DMXAA thus shows potent therapeutic efficacy in three mice tumor models and elicits remarkable therapeutic benefit when combined with anti–PD-1 therapy. Our engineered nanosystem offers a rational design of an effective immunotherapy combination regimen to convert uninflamed “cold” tumors into “hot” tumors, addressing the major challenges immunotherapies faced.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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    Primate-restricted KRAB zinc finger proteins and target retrotransposons control gene expression in human neurons (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-01
    Description: In the first days of embryogenesis, transposable element–embedded regulatory sequences (TEeRS) are silenced by Kruppel-associated box (KRAB) zinc finger proteins (KZFPs). Many TEeRS are subsequently co-opted in transcription networks, but how KZFPs influence this process is largely unknown. We identify ZNF417 and ZNF587 as primate-specific KZFPs repressing HERVK (human endogenous retrovirus K) and SVA (SINE-VNTR-Alu) integrants in human embryonic stem cells (ESCs). Expressed in specific regions of the human developing and adult brain, ZNF417/587 keep controlling TEeRS in ESC-derived neurons and brain organoids, secondarily influencing the differentiation and neurotransmission profile of neurons and preventing the induction of neurotoxic retroviral proteins and an interferon-like response. Thus, evolutionarily recent KZFPs and their TE targets partner up to influence human neuronal differentiation and physiology.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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    Disruption in ACTL7A causes acrosomal ultrastructural defects in human and mouse sperm as a novel male factor inducing early embryonic arrest (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-01
    Description: Early embryonic arrest is a challenge for in vitro fertilization (IVF). No genetic factors were previously revealed in the sperm-derived arrest of embryonic development. Here, we reported two infertile brothers presenting normal in conventional semen analysis, but both couples had no embryos for transfer after several IVF and intracytoplasmic sperm injection (ICSI). Whole-exome sequencing identified a homozygous missense mutation of ACTL7A in both brothers. This mutation is deleterious and causes sperm acrosomal ultrastructural defects. The Actl7a knock-in mouse model was generated, and male mutated mice showed sperm acrosomal defects, which were completely consistent with the observations in patients. Furthermore, the sperm from ACTL7A/Actl7a-mutated men and mice showed reduced expression and abnormal localization of PLCζ as a potential cause of embryonic arrest and failure of fertilization. Artificial oocyte activation could successfully overcome the Actl7a-mutated sperm-derived infertility, which is meaningful in the future practice of IVF/ICSI for the ACTL7A-associated male infertility.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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    Academia needs a reality check: Life is not back to normal (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-28
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 182
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    Microbiota-modulated CART+ enteric neurons autonomously regulate blood glucose (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-27
    Description: The gut microbiota affects tissue physiology, metabolism, and function of both the immune and nervous systems. We found that intrinsic enteric-associated neurons (iEAN) in mice are functionally adapted to the intestinal segment they occupy; ileal and colonic neurons are more responsive to microbial colonization than duodenal neurons. Specifically, a microbially-responsive subset of viscerofugal CART+ neurons, enriched in the ileum and colon, modulated feeding and glucose metabolism. These CART+ neurons send axons to the prevertebral ganglia and are poly-synaptically connected to the liver and pancreas. Microbiota depletion led to NLRP6– and Caspase 11-dependent loss of CART+ neurons, and impaired glucose regulation. Hence, iEAN subsets appear to be capable of regulating blood glucose levels independently from the central nervous system.
    Print ISSN: 0036-8075
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  • 183
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    In ‘milestone,’ FDA OKs simple, accurate coronavirus test that could cost just $5 (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-27
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 184
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    To save this palm-filled paradise, biologists must kill the trees (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-27
    Print ISSN: 0036-8075
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    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 185
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    Cannabis research database shows how U.S. funding focuses on harms of the drug (2020)
    American Association for the Advancement of Science
    Details
    Publication Date: 2020-08-27
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 186
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    Arctic sea ice under attack, and ancient records that can predict the future effects of climate change (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-27
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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    A tiny fish takes on its predators—and wins, transforming the Baltic coast (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-27
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 188
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    Kondo physics in antiferromagnetic Weyl semimetal Mn3+xSn1−x films (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-01
    Description: Topology and strong electron correlations are crucial ingredients in emerging quantum materials, yet their intersection in experimental systems has been relatively limited to date. Strongly correlated Weyl semimetals, particularly when magnetism is incorporated, offer a unique and fertile platform to explore emergent phenomena in novel topological matter and topological spintronics. The antiferromagnetic Weyl semimetal Mn3Sn exhibits many exotic physical properties such as a large spontaneous Hall effect and has recently attracted intense interest. In this work, we report synthesis of epitaxial Mn3+xSn1−x films with greatly extended compositional range in comparison with that of bulk samples. As Sn atoms are replaced by magnetic Mn atoms, the Kondo effect, which is a celebrated example of strong correlations, emerges, develops coherence, and induces a hybridization energy gap. The magnetic doping and gap opening lead to rich extraordinary properties, as exemplified by the prominent DC Hall effects and resonance-enhanced terahertz Faraday rotation.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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    Neogene precipitation, vegetation, and elevation history of the Central Andean Plateau (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-01
    Description: Andean uplift played a fundamental role in shaping South American climate and species distribution, but the relationship between the rise of the Andes, plant composition, and local climatic evolution is poorly known. We investigated the fossil record (pollen, leaves, and wood) from the Neogene of the Central Andean Plateau and documented the earliest evidence of a puna-like ecosystem in the Pliocene and a montane ecosystem without modern analogs in the Miocene. In contrast to regional climate model simulations, our climate inferences based on fossil data suggest wetter than modern precipitation conditions during the Pliocene, when the area was near modern elevations, and even wetter conditions during the Miocene, when the cordillera was around ~1700 meters above sea level. Our empirical data highlight the importance of the plant fossil record in studying past, present, and future climates and underscore the dynamic nature of high elevation ecosystems.
    Electronic ISSN: 2375-2548
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    Cardiolipin, conformation, and respiratory complex-dependent oligomerization of the major mitochondrial ADP/ATP carrier in yeast (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-01
    Description: The phospholipid cardiolipin has pleiotropic structural and functional roles that are collectively essential for mitochondrial biology. Yet, the molecular details of how this lipid supports the structure and function of proteins and protein complexes are poorly understood. To address this property of cardiolipin, we use the mitochondrial adenosine 5′-diphosphate/adenosine 5′-triphosphate carrier (Aac) as a model. Here, we have determined that cardiolipin is critical for both the tertiary and quaternary assembly of the major yeast Aac isoform Aac2 as well as its conformation. Notably, these cardiolipin-provided structural roles are separable. In addition, we show that multiple copies of Aac2 engage in shared complexes that are largely dependent on the presence of assembled respiratory complexes III and IV or respiratory supercomplexes. Intriguingly, the assembly state of Aac2 is sensitive to its transport-related conformation. Together, these results expand our understanding of the numerous structural roles provided by cardiolipin for mitochondrial membrane proteins.
    Electronic ISSN: 2375-2548
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    Cryo-EM structure of human Cx31.3/GJC3 connexin hemichannel (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-01
    Description: Connexin family proteins assemble into hexameric channels called hemichannels/connexons, which function as transmembrane channels or dock together to form gap junction intercellular channels (GJIChs). We determined the cryo–electron microscopy structures of human connexin 31.3 (Cx31.3)/GJC3 hemichannels in the presence and absence of calcium ions and with a hearing-loss mutation R15G at 2.3-, 2.5-, and 2.6-Å resolutions, respectively. Compared with available structures of GJICh in open conformation, Cx31.3 hemichannel shows substantial structural changes of highly conserved regions in the connexin family, including opening of calcium ion–binding tunnels, reorganization of salt-bridge networks, exposure of lipid-binding sites, and collocation of amino-terminal helices at the cytoplasmic entrance. We also found that the hemichannel has a pore with a diameter of ~8 Å and selectively transports chloride ions. Our study provides structural insights into the permeant selectivity of Cx31.3 hemichannel.
    Electronic ISSN: 2375-2548
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    Wirelessly controlled, bioresorbable drug delivery device with active valves that exploit electrochemically triggered crevice corrosion (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-01
    Description: Implantable drug release platforms that offer wirelessly programmable control over pharmacokinetics have potential in advanced treatment protocols for hormone imbalances, malignant cancers, diabetic conditions, and others. We present a system with this type of functionality in which the constituent materials undergo complete bioresorption to eliminate device load from the patient after completing the final stage of the release process. Here, bioresorbable polyanhydride reservoirs store drugs in defined reservoirs without leakage until wirelessly triggered valve structures open to allow release. These valves operate through an electrochemical mechanism of geometrically accelerated corrosion induced by passage of electrical current from a wireless, bioresorbable power-harvesting unit. Evaluations in cell cultures demonstrate the efficacy of this technology for the treatment of cancerous tissues by release of the drug doxorubicin. Complete in vivo studies of platforms with multiple, independently controlled release events in live-animal models illustrate capabilities for control of blood glucose levels by timed delivery of insulin.
    Electronic ISSN: 2375-2548
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    Glove-based sensors for multimodal monitoring of natural sweat (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-01
    Description: Sweat sensors targeting exercise or chemically induced sweat have shown promise for noninvasive health monitoring. Natural thermoregulatory sweat is an attractive alternative as it can be accessed during routine and sedentary activity without impeding user lifestyles and potentially preserves correlations between sweat and blood biomarkers. We present simple glove-based sensors to accumulate natural sweat with minimal evaporation, capitalizing on high sweat gland densities to collect hundreds of microliters in just 30 min without active sweat stimulation. Sensing electrodes are patterned on nitrile gloves and finger cots for in situ detection of diverse biomarkers, including electrolytes and xenobiotics, and multiple gloves or cots are worn in sequence to track overarching analyte dynamics. Direct integration of sensors into gloves represents a simple and low-overhead scheme for natural sweat analysis, enabling sweat-based physiological monitoring to become practical and routine without requiring highly complex or miniaturized components for analyte collection and signal transduction.
    Electronic ISSN: 2375-2548
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    Predicting short-range order and correlated phenomena in disordered crystalline materials (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-01
    Description: Disordered crystalline materials are used in a wide variety of energy-related technologies. Recent results from neutron total scattering experiments have shown that the atomic arrangements of many disordered crystalline materials are not random nor are they represented by the long-range structure observed from diffraction experiments. Despite the importance of disordered materials and the impact of disorder on the expression of physical properties, the underlying fundamental atomic-scale rules of disordering are not currently well understood. Here, we report that heterogeneous disordering (and associated structural distortions) can be understood by the straightforward application of Pauling’s rules (1929). This insight, corroborated by first principles calculations, can be used to predict the short-range, atomic-scale changes that result from structural disordering induced by extreme conditions associated with energy-related applications, such as high temperature, high pressure, and intense radiation fields.
    Electronic ISSN: 2375-2548
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    Neuronal metabolic rewiring promotes resilience to neurodegeneration caused by mitochondrial dysfunction (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-01
    Description: Neurodegeneration in mitochondrial disorders is considered irreversible because of limited metabolic plasticity in neurons, yet the cell-autonomous implications of mitochondrial dysfunction for neuronal metabolism in vivo are poorly understood. Here, we profiled the cell-specific proteome of Purkinje neurons undergoing progressive OXPHOS deficiency caused by disrupted mitochondrial fusion dynamics. We found that mitochondrial dysfunction triggers a profound rewiring of the proteomic landscape, culminating in the sequential activation of precise metabolic programs preceding cell death. Unexpectedly, we identified a marked induction of pyruvate carboxylase (PCx) and other anaplerotic enzymes involved in replenishing tricarboxylic acid cycle intermediates. Suppression of PCx aggravated oxidative stress and neurodegeneration, showing that anaplerosis is protective in OXPHOS-deficient neurons. Restoration of mitochondrial fusion in end-stage degenerating neurons fully reversed these metabolic hallmarks, thereby preventing cell death. Our findings identify a previously unappreciated pathway conferring resilience to mitochondrial dysfunction and show that neurodegeneration can be reversed even at advanced disease stages.
    Electronic ISSN: 2375-2548
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    Ingestible transiently anchoring electronics for microstimulation and conductive signaling (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-01
    Description: Ingestible electronic devices enable noninvasive evaluation and diagnosis of pathologies in the gastrointestinal (GI) tract but generally cannot therapeutically interact with the tissue wall. Here, we report the development of an orally administered electrical stimulation device characterized in ex vivo human tissue and in in vivo swine models, which transiently anchored itself to the stomach by autonomously inserting electrically conductive, hooked probes. The probes provided stimulation to the tissue via timed electrical pulses that could be used as a treatment for gastric motility disorders. To demonstrate interaction with stomach muscle tissue, we used the electrical stimulation to induce acute muscular contractions. Pulses conductively signaled the probes’ successful anchoring and detachment events to a parenterally placed device. The ability to anchor into and electrically interact with targeted GI tissues controlled by the enteric nervous system introduces opportunities to treat a multitude of associated pathologies.
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    Watch amoebas solve a microscopic version of London’s Hampton Court Maze (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-27
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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    Wnt signaling activates MFSD2A to suppress vascular endothelial transcytosis and maintain blood-retinal barrier (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-01
    Description: Breakdown of the blood-retinal barrier (BRB) causes retinal edema and vision loss. We investigated the role of Wnt signaling in maintaining the BRB by limiting transcytosis. Mice lacking either the Wnt co-receptor low-density lipoprotein receptor–related protein 5 (Lrp5−/−) or the Wnt ligand Norrin (Ndpy/−) exhibit increased retinal vascular leakage and enhanced endothelial transcytosis. Wnt signaling directly controls the transcription of an endothelium-specific transcytosis inhibitor, major facilitator superfamily domain–containing protein 2a (MFSD2A), in a β-catenin–dependent manner. MFSD2A overexpression reverses Wnt deficiency–induced transcytosis in endothelial cells and in retinas. Moreover, Wnt signaling mediates MFSD2A-dependent vascular endothelium transcytosis through a caveolin-1 (CAV-1)–positive caveolae pathway. In addition, levels of omega-3 fatty acids are also decreased in Wnt signaling–deficient retinas, reflecting the basic function of MFSD2A as a lipid transporter. Our findings uncovered the Wnt/β-catenin/MFSD2A/CAV-1 axis as a key pathway governing endothelium transcytosis and inner BRB integrity.
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    Unmasking selective path integration deficits in Alzheimer’s disease risk carriers (2020)
    American Association for the Advancement of Science
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    Publication Date: 2020-08-01
    Description: Alzheimer’s disease (AD) manifests with progressive memory loss and spatial disorientation. Neuropathological studies suggest early AD pathology in the entorhinal cortex (EC) of young adults at genetic risk for AD (APOE ε4-carriers). Because the EC harbors grid cells, a likely neural substrate of path integration (PI), we examined PI performance in APOE ε4-carriers during a virtual navigation task. We report a selective impairment in APOE ε4-carriers specifically when recruitment of compensatory navigational strategies via supportive spatial cues was disabled. A separate fMRI study revealed that PI performance was associated with the strength of entorhinal grid-like representations when no compensatory strategies were available, suggesting grid cell dysfunction as a mechanistic explanation for PI deficits in APOE ε4-carriers. Furthermore, posterior cingulate/retrosplenial cortex was involved in the recruitment of compensatory navigational strategies via supportive spatial cues. Our results provide evidence for selective PI deficits in AD risk carriers, decades before potential disease onset.
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    3D printed patient-specific aortic root models with internal sensors for minimally invasive applications (2020)
    American Association for the Advancement of Science
    Details
    Publication Date: 2020-08-01
    Description: Minimally invasive surgeries have numerous advantages, yet complications may arise from limited knowledge about the anatomical site targeted for the delivery of therapy. Transcatheter aortic valve replacement (TAVR) is a minimally invasive procedure for treating aortic stenosis. Here, we demonstrate multimaterial three-dimensional printing of patient-specific soft aortic root models with internally integrated electronic sensor arrays that can augment testing for TAVR preprocedural planning. We evaluated the efficacies of the models by comparing their geometric fidelities with postoperative data from patients, as well as their in vitro hemodynamic performances in cases with and without leaflet calcifications. Furthermore, we demonstrated that internal sensor arrays can facilitate the optimization of bioprosthetic valve selections and in vitro placements via mapping of the pressures applied on the critical regions of the aortic anatomies. These models may pave exciting avenues for mitigating the risks of postoperative complications and facilitating the development of next-generation medical devices.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science
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