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  • American Association for the Advancement of Science  (280,579)
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  • 1
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    American Association for the Advancement of Science
    Online: 2019 –
    Publisher: American Association for the Advancement of Science
    Electronic ISSN: 2643-6515
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 2
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    American Association for the Advancement of Science
    Publication Date: 2016-01-07
    Repository Name: EPIC Alfred Wegener Institut
    Type: PANGAEA Documentation , NonPeerReviewed
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  • 3
    Publication Date: 2019-01-15
    Description: Grounding zones, where ice sheets transition between resting on bedrock to full floatation, help regulate ice flow. Exposure of the sea floor by the 2002 Larsen-B Ice Shelf collapse allowed detailed morphologic mapping and sampling of the embayment sea floor. Marine geophysical data collected in 2006 reveal a large, arcuate, complex grounding zone sediment system at the front of Crane Fjord. Radiocarbon-constrained chronologies from marine sediment cores indicate loss of ice contact with the bed at this site about 12,000 years ago. Previous studies and morphologic mapping of the fjord suggest that the Crane Glacier grounding zone was well within the fjord before 2002 and did not retreat further until after the ice shelf collapse. This implies that the 2002 Larsen-B Ice Shelf collapse likely was a response to surface warming rather than to grounding zone instability, strengthening the idea that surface processes controlled the disintegration of the Larsen Ice Shelf .
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 4
    Publication Date: 2017-08-03
    Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Science Advances 2 (2016): e1600883, doi:10.1126/sciadv.1600883.
    Description: The formation of the Isthmus of Panama stands as one of the greatest natural events of the Cenozoic, driving profound biotic transformations on land and in the oceans. Some recent studies suggest that the Isthmus formed many millions of years earlier than the widely recognized age of approximately 3 million years ago (Ma), a result that if true would revolutionize our understanding of environmental, ecological, and evolutionary change across the Americas. To bring clarity to the question of when the Isthmus of Panama formed, we provide an exhaustive review and reanalysis of geological, paleontological, and molecular records. These independent lines of evidence converge upon a cohesive narrative of gradually emerging land and constricting seaways, with formation of the Isthmus of Panama sensu stricto around 2.8 Ma. The evidence used to support an older isthmus is inconclusive, and we caution against the uncritical acceptance of an isthmus before the Pliocene.
    Description: This study was supported by the Smithsonian Tropical Research Institute to A.O., J.B.C.J., N.K., and H.A.L.; the NSF (EAR 1325683) to A.O., P.G.R.-D., and E.L.G.; the National System of Investigators to A.O.; the Secretaría Nacional de Ciencia, Tecnología e Innovación (Panamá) to A.O., H.A.L., and S.E.C.; the U.S. Geological Survey to R.F.S.; and the Consejo Nacional de Investigaciones Científicas y Técnicas (Argentina) to A.L.C., G.M.G., E.S., and L.S.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
    Publication Date: 2018-02-05
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Science Advances 4 (2018): eaao4842, doi:10.1126/sciadv.aao4842.
    Description: In response to warming climate, methane can be released to Arctic Ocean sediment and waters from thawing subsea permafrost and decomposing methane hydrates. However, it is unknown whether methane derived from this sediment storehouse of frozen ancient carbon reaches the atmosphere. We quantified the fraction of methane derived from ancient sources in shelf waters of the U.S. Beaufort Sea, a region that has both permafrost and methane hydrates and is experiencing significant warming. Although the radiocarbon-methane analyses indicate that ancient carbon is being mobilized and emitted as methane into shelf bottom waters, surprisingly, we find that methane in surface waters is principally derived from modern-aged carbon. We report that at and beyond approximately the 30-m isobath, ancient sources that dominate in deep waters contribute, at most, 10 ± 3% of the surface water methane. These results suggest that even if there is a heightened liberation of ancient carbon–sourced methane as climate change proceeds, oceanic oxidation and dispersion processes can strongly limit its emission to the atmosphere.
    Description: The National Science Foundation (PLR-1417149; awarded to J.D.K.) primarily supported this work with additional support provided by the U.S. Department of Energy (DE-FE0028980; awarded to J.D.K.). Atmospheric 14C-CH4 measurements were funded by NASA via the Jet Propulsion Laboratory (Earth Ventures project “Carbon in Arctic Reservoirs Vulnerability Experiment”) to the University of Colorado under contract 1424124. K.M.S. acknowledges support from the University of Minnesota Grant-in-Aid program.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 6
    Publication Date: 2017-02-15
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Science Advances 3 (2017): e1601426, doi:10.1126/sciadv.1601426.
    Description: Southern Ocean abyssal waters, in contact with the atmosphere at their formation sites around Antarctica, not only bring signals of a changing climate with them as they move around the globe but also contribute to that change through heat uptake and sea level rise. A repeat hydrographic line in the Indian sector of the Southern Ocean, occupied three times in the last two decades (1994, 2007, and, most recently, 2016), reveals that Antarctic Bottom Water (AABW) continues to become fresher (0.004 ± 0.001 kg/g decade−1), warmer (0.06° ± 0.01°C decade−1), and less dense (0.011 ± 0.002 kg/m3 decade−1). The most recent observations in the Australian-Antarctic Basin show a particularly striking acceleration in AABW freshening between 2007 and 2016 (0.008 ± 0.001 kg/g decade−1) compared to the 0.002 ± 0.001 kg/g decade−1 seen between 1994 and 2007. Freshening is, in part, responsible for an overall shift of the mean temperature-salinity curve toward lower densities. The marked freshening may be linked to an abrupt iceberg-glacier collision and calving event that occurred in 2010 on the George V/Adélie Land Coast, the main source region of bottom waters for the Australian-Antarctic Basin. Because AABW is a key component of the global overturning circulation, the persistent decrease in bottom water density and the associated increase in steric height that result from continued warming and freshening have important consequences beyond the Southern Indian Ocean.
    Description: The 2016 I08S cruise and the analysis and science performed at sea, as well as the individual principal investigators were funded through multiple National Oceanic and Atmospheric Administration (NOAA) and NSF grants including NSF grant OCE-1437015. The research for this article was mainly completed at sea. For land-based work, V.V.M. relied on her postdoctoral funding through NSF grant OCE-1435665, and A.M.M. was supported in part by NSF grant OCE-1356630 and NOAA grant NA11OAR4310063.
    Keywords: Salinity ; AABW ; Changes ; Water masses ; T-S properties ; Iceberg ; Calving ; Antartica ; Abyss ; Climate change
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 7
    Publication Date: 2017-08-23
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Science Advances 3 (2017): e1701020, doi:10.1126/sciadv.1701020.
    Description: The rates of marine deoxygenation leading to Cretaceous Oceanic Anoxic Events are poorly recognized and constrained. If increases in primary productivity are the primary driver of these episodes, progressive oxygen loss from global waters should predate enhanced carbon burial in underlying sediments—the diagnostic Oceanic Anoxic Event relic. Thallium isotope analysis of organic-rich black shales from Demerara Rise across Oceanic Anoxic Event 2 reveals evidence of expanded sediment-water interface deoxygenation ~43 ± 11 thousand years before the globally recognized carbon cycle perturbation. This evidence for rapid oxygen loss leading to an extreme ancient climatic event has timely implications for the modern ocean, which is already experiencing large-scale deoxygenation.
    Description: We would like to acknowledge support from the NSF grant OCE 1434785 (to J.D.O. and S.G.N.), the NASA Exobiology grant NNX16AJ60G (to J.D.O. and S.G.N.), a WHOI Summer Student Fellowship (to C.M.O.), and an Agouron Postdoctoral Fellowship (to J.D.O.). This material is based on work supported by the NSF Graduate Research Fellowship Program under grant no. 026257-001.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 8
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    American Association for the Advancement of Science
    Publication Date: 2018-03-09
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Science Advances 4 (2018): e1701504, doi:10.1126/sciadv.1701504.
    Description: Salinity, rather than temperature, is the leading influence on density in some regions of the world’s upper oceans. In the Bay of Bengal, heavy monsoonal rains and runoff generate strong salinity gradients that define density fronts and stratification in the upper ~50 m. Ship-based observations made in winter reveal that fronts exist over a wide range of length scales, but at O(1)-km scales, horizontal salinity gradients are compensated by temperature to alleviate about half the cross-front density gradient. Using a process study ocean model, we show that scale-selective compensation occurs because of surface cooling. Submesoscale instabilities cause density fronts to slump, enhancing stratification along-front. Specifically for salinity fronts, the surface mixed layer (SML) shoals on the less saline side, correlating sea surface salinity (SSS) with SML depth at O(1)-km scales. When losing heat to the atmosphere, the shallower and less saline SML experiences a larger drop in temperature compared to the adjacent deeper SML on the salty side of the front, thus correlating sea surface temperature (SST) with SSS at the submesoscale. This compensation of submesoscale fronts can diminish their strength and thwart the forward cascade of energy to smaller scales. During winter, salinity fronts that are dynamically submesoscale experience larger temperature drops, appearing in satellite-derived SST as cold filaments. In freshwater-influenced regions, cold filaments can mark surface-trapped layers insulated from deeper nutrient-rich waters, unlike in other regions, where they indicate upwelling of nutrient-rich water and enhanced surface biological productivity.
    Description: This work was carried out under the Office of Naval Research’s ASIRI (grants N000141612470 and N000141310451) in collaboration with the Indian Ministry of Earth Science’s OMM initiative supported by the Monsoon Mission
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 9
    Publication Date: 2018-11-26
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Science Advances 4 (2018): eaap7567, doi:10.1126/sciadv.aap7567.
    Description: Very large eruptions (〉50 km3) and supereruptions (〉450 km3) reveal Earth’s capacity to produce and store enormous quantities (〉1000 km3) of crystal-poor, eruptible magma in the shallow crust. We explore the interplay between crustal evolution and volcanism during a volcanic flare-up in the Taupo Volcanic Zone (TVZ, New Zealand) using a combination of quartz-feldspar-melt equilibration pressures and time scales of quartz crystallization. Over the course of the flare-up, crystallization depths became progressively shallower, showing the gradual conditioning of the crust. Yet, quartz crystallization times were invariably very short (〈100 years), demonstrating that very large reservoirs of eruptible magma were transient crustal features. We conclude that the dynamic nature of the TVZ crust favored magma eruption over storage. Episodic tapping of eruptible magmas likely prevented a supereruption. Instead, multiple very large bodies of eruptible magma were assembled and erupted in decadal time scales.
    Description: This work was supported by the NSF (EAR-1151337) and by two Vanderbilt University Discovery Grants.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 10
    Publication Date: 2017-02-15
    Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Science Advances 2 (2016): e1600445, doi:10.1126/sciadv.1600445.
    Description: Saharan mineral dust exported over the tropical North Atlantic is thought to have significant impacts on regional climate and ecosystems, but limited data exist documenting past changes in long-range dust transport. This data gap limits investigations of the role of Saharan dust in past climate change, in particular during the mid-Holocene, when climate models consistently underestimate the intensification of the West African monsoon documented by paleorecords. We present reconstructions of African dust deposition in sediments from the Bahamas and the tropical North Atlantic spanning the last 23,000 years. Both sites show early and mid-Holocene dust fluxes 40 to 50% lower than recent values and maximum dust fluxes during the deglaciation, demonstrating agreement with records from the northwest African margin. These quantitative estimates of trans-Atlantic dust transport offer important constraints on past changes in dust-related radiative and biogeochemical impacts. Using idealized climate model experiments to investigate the response to reductions in Saharan dust’s radiative forcing over the tropical North Atlantic, we find that small (0.15°C) dust-related increases in regional sea surface temperatures are sufficient to cause significant northward shifts in the Atlantic Intertropical Convergence Zone, increased precipitation in the western Sahel and Sahara, and reductions in easterly and northeasterly winds over dust source regions. Our results suggest that the amplifying feedback of dust on sea surface temperatures and regional climate may be significant and that accurate simulation of dust’s radiative effects is likely essential to improving model representations of past and future precipitation variations in North Africa.
    Description: This study was supported, in part, by NSF awards OCE-1030784 (to D.M. and P.B.d.) and OCE-09277247 (to P.B.d.); NASA grant NN14AP38G (to C. Heald, Massachusetts Institute of Technology), which supports D.A.R.; and the Columbia University Center for Climate and Life. A.F. is supported by the NSF grant AGS-1116885 and the National Oceanic and Atmospheric Administration (NOAA) grant NA14OAR4310277. S.H. is supported by the NASA Earth and Space Sciences Fellowship. We also acknowledge computational support from the NSF/NCAR Yellowstone Supercomputing Center and the Yale University High Performance Computing Center.
    Keywords: Mineral dust ; North Africa ; Paleoclimate ; African Humid Period
    Repository Name: Woods Hole Open Access Server
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