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  • 1. Arneborg, L.
    et al.
    Wåhlin, A. K.
    Björk, G.
    Liljebladh, B.
    Orsi, A. H.
    Persistent inflow of warm water onto the central Amundsen shelf2012In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 5, no 12, p. 876-880Article in journal (Refereed)
    Abstract [en]

    The West Antarctic Ice Sheet contains enough ice to raise global sea level by several metres and, because it is grounded mainly below sea level, it is sensitive to ocean warming 1 . Accelerated thinning of glaciers that discharge into the Amundsen Sea over the past decades 2–4 has been proposed to be related to the presence of warmer waters beneath the ice shelves 4–6 . Three deep troughs crosscut the continental shelf of the Amundsen Sea, forming passages through which warm ocean waters can access the ice shelves, but oceanographic data has been limited. Here we present direct measurements from an ocean mooring and ship transect of the temperatures, salinities and velocities from one of these troughs in the central Amundsen Sea during the year 2010. The data show persistent inflow towards the ice shelf of relatively warm and salty water at the bottom of the trough throughout the year, and outflow of colder water above. Superposed on this background flow are barotropic current fluctuations that do not contribute significantly to the overall transport. In contrast to numerical models 7,8 , which show seasonal inflow changes in response to regional winds, we find that warm water is supplied to the Central Amundsen Shelf without strong seasonal variability.

  • 2. Cronin, T. M.
    et al.
    Dwyer, G. S.
    Farmer, J.
    Bauch, H. A.
    Spielhagen, R. F.
    Jakobsson, M.
    Nilsson, J.
    Briggs, Jr., W. M.
    Stepanova, A.
    Deep Arctic Ocean warming during the last glacial cycle2012In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 5, no 9, p. 631-634Article in journal (Refereed)
    Abstract [en]

    In the Arctic Ocean, the cold and relatively fresh water beneath the sea ice is separated from the underlying warmer and saltier Atlantic Layer by a halocline. Ongoing sea ice loss and warming in the Arctic Ocean(1-7) have demonstrated the instability of the halocline, with implications for further sea ice loss. The stability of the halocline through past climate variations(8-10) is unclear. Here we estimate intermediate water temperatures over the past 50,000 years from the Mg/Ca and Sr/Ca values of ostracods from 31 Arctic sediment cores. From about 50 to 11 kyr ago, the central Arctic Basin from 1,000 to 2,500 m was occupied by a water mass we call Glacial Arctic Intermediate Water. This water mass was 1-2 degrees C warmer than modern Arctic Intermediate Water, with temperatures peaking during or just before millennial-scale Heinrich cold events and the Younger Dryas cold interval. We use numerical modelling to show that the intermediate depth warming could result from the expected decrease in the flux of fresh water to the Arctic Ocean during glacial conditions, which would cause the halocline to deepen and push the warm Atlantic Layer into intermediate depths. Although not modelled, the reduced formation of cold, deep waters due to the exposure of the Arctic continental shelf could also contribute to the intermediate depth warming.

  • 3. Darby, Dennis A.
    Ephemeral formation of perennial sea ice in the Arctic Ocean during the middle Eocene2014In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 7, no 3, p. 210-213Article in journal (Refereed)
    Abstract [en]

    Sea ice in the Arctic Ocean is a key component of the modern climate system(1), but less is known about the evolution of Arctic sea ice throughout Earth’s history(2-5), particularly in warmer climate states. Following early Palaeogene greenhouse conditions, seasonal sea ice in the Arctic developed during a period of relative cooling in the middle Eocene(6), some 47.5 million years ago. However, perennial sea ice has only been documented as recently as 18 million years ago(2,3). Here I document the provenance of iron grains in marine sediments from the central Arctic Ocean, and show that during several intervals, beginning about 44 million years ago, they were carried from distal Arctic shelf sources. The grains are too coarse to have been delivered by ocean currents or aeolian transport, and therefore must have been rafted by sea ice. Because grains entrained from the shelf sources would need to drift for more than one year to reach the depositional site, I conclude that sea ice must have persisted throughout the year. However, the presence of grains from these distal sources only occur in intervals of less than 100,000 years in the oldest part of the records, suggesting that perennial sea ice existed only ephemerally until 36.7 million years ago.

  • 4. Lomax, Barry H.
    et al.
    Fraser, Wesley T.
    Sephton, Mark A.
    Callaghan, Terry V.
    Self, Stephen
    Harfoot, Michael
    Pyle, John A.
    Wellman, Charles H.
    Beerling, David J.
    Plant spore walls as a record of long-term changes in ultraviolet-B radiation2008In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 1, p. 592-596Article in journal (Refereed)
    Abstract [en]

    Stratospheric ozone screens the Earth’s surface from harmful ultraviolet-B radiation. Concentrations of stratospheric ozone are governed by a variety of natural and anthropogenic factors, including solar cycles1, volcanic aerosols2, ozone-depleting substances3 and climate change4. However, assessing this variability before instrumental records has proved difficult owing to the lack of a well-constrained proxy5. Here, we use microspectroscopy to analyse the chemical composition of herbarium samples of clubmoss (Lycophyta) spores originating from high- and low-latitude localities, where they were exposed to different ultraviolet-B histories. We show that the concentration of two ultraviolet-B-absorbing compounds in the walls of high-northern- and southern-latitude spores is strongly regulated by historical variations in ultraviolet-B radiation. Conversely, we find little change in the concentration of these compounds in spores originating from tropical Ecuador, where ultraviolet levels have remained relatively stable. Using spores from Greenland, we reconstruct past (1907–1993) changes in ozone concentration and ultraviolet-B flux; we reveal strong similarities between spore-wall reconstructions, and independent instrumental records6 and model results7. Our findings suggest that ultraviolet-B-absorbing compounds in plant spore walls have the potential to act as a proxy for past changes in terrestrial ultraviolet-B radiation and stratospheric ozone. The chemical signature of plant spore walls in herbaria, and possibly also in sedimentary and ice-core archives, may therefore prove valuable for reconstructing past variations in stratospheric ozone and their connections with changes in solar radiation and climate.

  • 5. Semiletov, Igor
    et al.
    Pipko, Irina
    Gustafsson, Orjan
    Anderson, Leif G.
    Sergienko, Valentin
    Pugach, Svetlana
    Dudarev, Oleg
    Charkin, Alexander
    Gukov, Alexander
    Broder, Lisa
    Andersson, August
    Spivak, Eduard
    Shakhova, Natalia
    Acidification of East Siberian Arctic Shelf waters through addition of freshwater and terrestrial carbon2016In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 9, no 5Article in journal (Refereed)
    Abstract [en]

    Ocean acidification affects marine ecosystems and carbon cycling, and is considered a direct effect of anthropogenic carbon dioxide uptake from the atmosphere(1-3). Accumulation of atmospheric CO2 in ocean surface waters is predicted to make the ocean twice as acidic by the end of this century(4). The Arctic Ocean is particularly sensitive to ocean acidification because more CO2 can dissolve in cold water(5,6). Here we present observations of the chemical and physical characteristics of East Siberian Arctic Shelf waters from 1999,2000-2005,2008 and 2011, and find extreme aragonite undersaturation that reflects acidity levels in excess of those projected in this region for 2100. Dissolved inorganic carbon isotopic data and Markov chain Monte Carlo simulations of water sources using salinity and delta O-18 data suggest that the persistent acidification is driven by the degradation of terrestrial organic matter and discharge of Arctic river water with elevated CO2 concentrations, rather than by uptake of atmospheric CO2. We suggest that East Siberian Arctic Shelf waters may become more acidic if thawing permafrost leads to enhanced terrestrial organic carbon inputs and if freshwater additions continue to increase, which may affect their effciency as a source of CO2.

  • 6. Semiletov, Igor
    et al.
    Pipko, Irina
    Gustafsson, Orjan
    Anderson, Leif G.
    Sergienko, Valentin
    Pugach, Svetlana
    Dudarev, Oleg
    Charkin, Alexander
    Gukov, Alexander
    Broder, Lisa
    Andersson, August
    Spivak, Eduard
    Shakhova, Natalia
    Addendum: Acidification of East Siberian Arctic Shelf waters through addition of freshwater and terrestrial carbon (vol 9, pg 361, 2016)2016In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 9, no 9Article in journal (Refereed)
  • 7. Serikova, S.
    et al.
    Pokrovsky, O. S.
    Ala-Aho, P.
    Kazantsev, V.
    Kirpotin, S. N.
    Kopysov, S. G.
    Krickov, I. V.
    Laudon, H.
    Manasypov, R. M.
    Shirokova, L. S.
    Soulsby, C.
    Tetzlaff, D.
    Karlsson, J.
    High riverine CO2 emissions at the permafrost boundary of Western Siberia2018In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 11, p. 825-829Article in journal (Refereed)
    Abstract [en]

    The fate of the vast stocks of organic carbon stored in permafrost of the Western Siberian Lowland, the world’s largest peatland, is uncertain. Specifically, the amount of greenhouse gas emissions from rivers in the region is unknown. Here we present estimates of annual CO2 emissions from 58 rivers across all permafrost zones of the Western Siberian Lowland, between 56 and 67° N. We find that emissions peak at the permafrost boundary, and decrease where permafrost is more prevalent and in colder climatic conditions. River CO2 emissions were high, and on average two times greater than downstream carbon export. We suggest that high emissions and emission/export ratios are a result of warm temperatures and the long transit times of river water. We show that rivers in the Western Siberian Lowland play an important role in the carbon cycle by degassing terrestrial carbon before its transport to the Arctic Ocean, and suggest that changes in both temperature and precipitation are important for understanding and predicting high-latitude river CO2 emissions in a changing climate.

  • 8. Shakhova, Natalia
    et al.
    Semiletov, Igor
    Leifer, Ira
    Sergienko, Valentin
    Salyuk, Anatoly
    Kosmach, Denis
    Chernykh, Denis
    Stubbs, Chris
    Nicolsky, Dmitry
    Tumskoy, Vladimir
    Gustafsson, Orjan
    Ebullition and storm-induced methane release from the East Siberian Arctic Shelf2014In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 7, no 1, p. 64-70Article in journal (Refereed)
    Abstract [en]

    Vast quantities of carbon are stored in shallow Arctic reservoirs, such as submarine and terrestrial permafrost. Submarine permafrost on the East Siberian Arctic Shelf started warming in the early Holocene, several thousand years ago. However, the present state of the permafrost in this region is uncertain. Here, we present data on the temperature of submarine permafrost on the East Siberian Arctic Shelf using measurements collected from a sediment core, together with sonar-derived observations of bubble flux and measurements of seawater methane levels taken from the same region. The temperature of the sediment core ranged from -1.8 to 0 degrees C. Although the surface layer exhibited the lowest temperatures, it was entirely unfrozen, owing to significant concentrations of salt. On the basis of the sonar data, we estimate that bubbles escaping the partially thawed permafrost inject 100-630 mg methane m(-2) d(-1) into the overlying water column. We further show that water-column methane levels had dropped significantly following the passage of two storms. We suggest that significant quantities of methane are escaping the East Siberian Shelf as a result of the degradation of submarine permafrost over thousands of years. We suggest that bubbles and storms facilitate the flux of this methane to the overlying ocean and atmosphere, respectively.

  • 9. Vonk, Jorien E.
    et al.
    Gustafsson, Orjan
    Permafrost-carbon complexities2013In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 6, no 9, p. 675-676Article in journal (Refereed)
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