Glacial ice-sheet dynamics and retreat deduced from southeastern Weddell Sea sediment (LAMINAE)
Zusammenfassung der Projektergebnisse
To understand past ice sheet dynamics in Antarctica is a key to understand current and future climate change. Project LAMINAE investigated sediment cores from the WSE to determine the nature and mechanisms of varve formation of contourite ridges located in front of the AIS, and the timing of glacial termination, i.e., ice-sheet retreat. We used software-based tools for laminae recognition and counting, spectral and cross-spectral analysis, and RADIUS particle analyses, as well as sediment core studies on thin sections and X-radiographs, and X-ray fluorescence scanning. As a result, we identified a very dynamic sedimentation on the contourite ridges, depositing 1 – 3m/ka of varved sediment during the LGM (~25.5 – 19 ka), reflecting seasonal changes of a thermohaline convection during the LGM, which we related to changes in katabatic wind intensity and coastal polynya activity. Glacial retreat occurred first at 19 ka and, after a short, consecutive AIS advance, finally at 16 ka, coincident with major phases of enhanced iceberg routing observed for the Scotia Sea. Retreat phases are characterized by bioturbuted sediment deposited at only a few cm/ka, indicative for at least partially open water conditions, retreated sea-ice, and less-intense katabatic winds. Spectral analysis detected decadal-to-centennial-scale oscillations in varve thicknesses, strongly correlate with periods of solar cycles, therefore suggesting that solar insolation modulated glacial sedimentation and ocean circulation. The most surprising observation, and thereby the most stunning and valuable result were that both Weddell Sea and Scotia Sea records document, at least for the lower two meltwater events at 19 ka and 14 16 ka, the same events, although the applied methods for dating ( C vs MS tuning) and paleoclimate reconstruction (facies change for the Weddell Sea vs IBRD transport intensity for the Scotia Sea) differ substantially. This is a major revision of existing models with respect to the dynamics and the magnitude and timing of AIS retreat, with distinct implications for projections of future sea-level rise. Alongside the publication of the Science (Weber et al., 2012) and the Nature papers (Weber et al. 2014), there were a number of press releases and public media appearances from participating authors, some of which are listed below. Also, the science report led to over 60, the Nature letter to over 80 reports and discussions in the media worldwide, which will not be reported here in detail. Eiszeit: "Tauwetter" in der Antarktis und Arktis begann zeitgleich: http://www.scinexx.de/wissen-aktuell-14179-2011-12-02.html http://www.geopark-bayern.de/Public/Nachrichten/2011/News01.htm http://www.springer.com/earth+sciences+and+geography?SGWID=1-10006-6-1316322-0 Epoch Times Deutschland: Das Große Tauen: Zeitgleiches Tauen der Arktis und Antarktis 112.2011: Simultaneous ice melt in Antarctic and Arctic http://www.awi.de/en/news/press_releases/detail/item/pm_science_uebersetzung_einsetzen/?cHash=757 d4c1ed5634edcfa2809235316818c http://www.sciencecodex.com/read/simultaneous_ice_melt_in_antarctic_and_arctic-82441 Global Adventures, LLC: Arctic and Antarctica: Ice melting started 19000 years ago Medical Daily: Decline in Antarctic Ice Sheets Sooner than Thought (2011) Asia Africa Intelligence Wire: Melting of Arctic and Antarctic ice sheets may date back 19000 years Environmental News Network: The Beginning of the Last Ice Melt (2011) Neue Studie belegt: Instabiler Antarktischer Eisschild hat in der Vergangenheit zum rasanten Meeresspiegelanstieg geführt http://www.awi.de/de/aktuelles_und_presse/pressemitteilungen/detail/item/new_study_instable_antarctic_i ceshelf_has_to_rapid_sea_level_rise_in_the_past/?cHash=6d219f39f11b2fdd62b24226e63d02db Die Welt (28.05.2014): Antarktis-Schmelze ließ Meeresspiegel steigen Informationsdienst Wissenschaft (28.05.2014): Instabiler Antarktischer Eisschild hat in der Vergangenheit zum Meeresspiegelanstieg geführt Spiegel Online: Anstieg des Meeresspiegels nach Eiszeit durch Gletscher in Antarktis (2014) Berliner Morgenpost Online: Antarktis-Schmelze ließ Meeresspiegel steigen (29.05.2014) Weser-Kurier (30.05.2014, S. 28): Rasanter Eisverlust
Projektbezogene Publikationen (Auswahl)
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(2011): Glacial and Deglacial Trends in the Atlantic Sector of Antarctica during the last 25 ka. – XXVIII INQUA Congress, Bern
Sprenk, D., Weber, M.E., Kuhn, G., Rosén P.
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(2011): Glacial bottom-water production and contourite ridges in the Weddell Sea – a review. – 11th International Symposium on Antarctic Earth Sciences, abstract volume, Edinburgh
Weber, M.E.
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(2011): Interhemispheric ice-sheet synchronicity during the Last Glacial Maximum. – AGU Fall Meeting, EOS, Transactions, AGU, San Francisco
Weber, M.E., Clark, P. U., Ricken, W., Mitrovica, J. X., Hostetler, S. W., and Kuhn, G.
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(2011): Interhemispheric ice-sheet synchronicity during the Last Glacial Maximum. – Science, 334, 1265-1269
Weber, M.E., Clark, P. U., Ricken, W., Mitrovica, J. X., Hostetler, S. W., and Kuhn, G.
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(2012): Conception of IODP Proposal Weddell Sea ice-sheet dynamics and sea-level history. – Past Antarctic Ice Sheet dynamics (PAIS) workshop, Portland
Weber, M.E., Kuhn, G., and Clark, P. U.
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(2012): Dynamic Antarctic ice-sheet disintegration during the last deglaciation – contribution to meltwater pulse 1a. – AGU Fall Meeting, EOS, Transactions, AGU, San Francisco
Weber, M.E., Clark, P.U., Gladstone, R., Timmermann, A., Lohmann, G, Kuhn, G., and Sprenk, D.
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(2012): Interhemispheric ice-sheet synchronicity during the Last Glacial Maximum. – European Geoscience Union, General Assembly, Vienna
Weber, M.E., Clark, P. U., Ricken, W., Mitrovica, J. X., Hostetler, S. W., and Kuhn, G.
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(2012): The paleoceanography of the Antarctic Circumpolar Current and the Weddell Gyre from sedimentary records, a patchy story. – The Third Symposium on Polar Sciences, NIPR, Tokyo
Kuhn, G.
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(2012): The Weddell Gyre history from marine sedimentary records. – International Weddell Gyre workshop report, Delmenhorst
Kuhn, G, Hillenbrand, C.-D.
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(2013): Antarctic Ice Sheet dynamics during the last deglaciation. 11th International Conference on Paleoceanography (ICP X), abstract volume, Barcelona
Weber, M. E., Sprenk, D., Kuhn, G., Clark, P. U., Timmermann, A., Gladstone, R., Zhang, X., Lohmann, G., Menviel, L., Chikamoto, M., Friedrich, T.
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(2013): Decadal- to millennial-scale ice-sheet oscillations in southeastern Weddell Sea during the Last Glacial Maximum. – 25th International Symposium on Polar Research, abstract volume, Hamburg
Sprenk, D., Weber, M.E., and Kuhn, G.
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(2013): Dynamic Antarctic ice-sheet behavior during the last deglaciation – implications to past and future sea-level rise – Davos Atmosphere and Cryosphere Assembly DACA-13, Davos
Weber, M.E., Clark, P.U., Gladstone, R., Timmermann, A., Lohmann, G., Kuhn, G., and Sprenk, D.
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(2013): New insights on last glacial Ice-sheet dynamics deduced from Weddell Sea sediment. – PAGES 2nd Young Science Meeting, abstract volume, Goa
Sprenk, D., Weber, M.E., and Kuhn, G.
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(2013): Southern Ocean bioproductivity during the last glacial cycle – new detection method and decadal-scale insight from the Scotia Sea. In: Hambrey, M. J. et al. (eds). Antarctic Palaeoenvironments and Earth-Surface Processes. Geological Society, London, Special Publications, 381
Sprenk, D., Weber, M.E., Kuhn, G.,Rosén, P., Frank, M.,Molina-Kescher, M., Liebetrau, V., Röhling, H.-G.
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(2014). Millennial-scale variability in Antarctic ice-sheet discharge during the last deglaciation. Nature 510, 134-138
Weber, M. E., Clark, P. U., Kuhn, G., Timmermann, A., Sprenk, D., Gladstone, R., Zhang, X., Lohmann, G., Menviel, L., Chikamoto, M., Friedrich, T., Ohlwein, C.
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(2014): Seasonal changes in glacial polynya activity inferred from Weddell Sea varves. – Climates of the Past 10, 1239- 1251
Sprenk, D., Weber, M. E., Kuhn, G., Wennrich, V., Hartmann, T., and Seelos, K.
