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      Lake sediments with Azorean tephra reveal ice-free conditions on coastal northwest Spitsbergen during the Last Glacial Maximum

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          Abstract

          Lake sediments reveal that parts of the High Arctic were ice free and vegetated during the culmination of the Last Ice Age.

          Abstract

          Lake sediments retrieved from the beds of former nonerosive ice sheets offer unique possibilities to constrain changes in the extent and style of past glaciation, and place them in an absolutely dated context. We present the first pre-Holocene lake sediments from Arctic Svalbard. Radiocarbon dating of terrestrial plant fossils reveals that the investigated catchment was unglaciated and vegetated between 30 and 20 ka B.P. during the global Last Glacial Maximum. The presence of volcanic ash from a contemporaneous Azorean eruption also provides evidence for ice-free conditions. Indicators of sediment compaction and a depositional hiatus suggest subsequent coverage by nonerosive ice until 11 ka B.P. Comparison with regional paleoclimate data indicates that sea ice variability controlled this pattern of ice sheet evolution by modulating moisture supply. Facing rapid regional sea ice losses, our findings have implications for the future response of the Arctic’s cryosphere, a major driver of global sea-level rise.

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          The central role of diminishing sea ice in recent Arctic temperature amplification.

          The rise in Arctic near-surface air temperatures has been almost twice as large as the global average in recent decades-a feature known as 'Arctic amplification'. Increased concentrations of atmospheric greenhouse gases have driven Arctic and global average warming; however, the underlying causes of Arctic amplification remain uncertain. The roles of reductions in snow and sea ice cover and changes in atmospheric and oceanic circulation, cloud cover and water vapour are still matters of debate. A better understanding of the processes responsible for the recent amplified warming is essential for assessing the likelihood, and impacts, of future rapid Arctic warming and sea ice loss. Here we show that the Arctic warming is strongest at the surface during most of the year and is primarily consistent with reductions in sea ice cover. Changes in cloud cover, in contrast, have not contributed strongly to recent warming. Increases in atmospheric water vapour content, partly in response to reduced sea ice cover, may have enhanced warming in the lower part of the atmosphere during summer and early autumn. We conclude that diminishing sea ice has had a leading role in recent Arctic temperature amplification. The findings reinforce suggestions that strong positive ice-temperature feedbacks have emerged in the Arctic, increasing the chances of further rapid warming and sea ice loss, and will probably affect polar ecosystems, ice-sheet mass balance and human activities in the Arctic.
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            Future increases in Arctic precipitation linked to local evaporation and sea-ice retreat.

            Precipitation changes projected for the end of the twenty-first century show an increase of more than 50 per cent in the Arctic regions. This marked increase, which is among the highest globally, has previously been attributed primarily to enhanced poleward moisture transport from lower latitudes. Here we use state-of-the-art global climate models to show that the projected increases in Arctic precipitation over the twenty-first century, which peak in late autumn and winter, are instead due mainly to strongly intensified local surface evaporation (maximum in winter), and only to a lesser degree due to enhanced moisture inflow from lower latitudes (maximum in late summer and autumn). Moreover, we show that the enhanced surface evaporation results mainly from retreating winter sea ice, signalling an amplified Arctic hydrological cycle. This demonstrates that increases in Arctic precipitation are firmly linked to Arctic warming and sea-ice decline. As a result, the Arctic mean precipitation sensitivity (4.5 per cent increase per degree of temperature warming) is much larger than the global value (1.6 to 1.9 per cent per kelvin). The associated seasonally varying increase in Arctic precipitation is likely to increase river discharge and snowfall over ice sheets (thereby affecting global sea level), and could even affect global climate through freshening of the Arctic Ocean and subsequent modulations of the Atlantic meridional overturning circulation.
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              Determination of Carbonate and Organic Matter in Calcareous Sediments and Sedimentary Rocks by Loss on Ignition: Comparison With Other Methods

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                Author and article information

                Journal
                Sci Adv
                Sci Adv
                SciAdv
                advances
                Science Advances
                American Association for the Advancement of Science
                2375-2548
                October 2019
                23 October 2019
                : 5
                : 10
                : eaaw5980
                Affiliations
                [1 ]Department of Earth Science, University of Bergen, Allégaten 41, 5007 Bergen, Norway.
                [2 ]Bjerknes Centre for Climate Research, Bergen, Norway.
                [3 ]Department of Geography, University of Cambridge, Downing Place, CB2 3EN Cambridge, UK.
                Author notes
                [* ]Corresponding author. Email: willemvanderbilt@ 123456uib.no
                Author information
                http://orcid.org/0000-0003-3157-451X
                http://orcid.org/0000-0001-9206-3903
                Article
                aaw5980
                10.1126/sciadv.aaw5980
                6810458
                d9c60a62-6cd7-45fc-b5b8-33c0e9c58f8c
                Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution License 4.0 (CC BY).

                This is an open-access article distributed under the terms of the Creative Commons Attribution license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 08 January 2019
                : 18 September 2019
                Funding
                Funded by: Norwegian Research Council;
                Award ID: SHIFTS (210004)
                Funded by: University of Bergen;
                Award ID: MOMENTUM
                Funded by: EU COST Action;
                Award ID: ES0907
                Categories
                Research Article
                Research Articles
                SciAdv r-articles
                Climatology
                Geology
                Geology
                Custom metadata
                Nielsen Marquez

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