4:15pm - 4:45pmSession Keynote
Reconstructing past ice sheets and paleotopography using observations of past sea level and glacial geology
1Kumamoto University, Kumamoto, Japan; 2Alfred Wegener Institute, Bremerhaven, Germany; 3MARUM, University of Bremen, Bremen, Germany
During the Quaternary, large ice sheets repeatedly formed and retreated over continental North America and northern Europe, which in turn caused fluctuations in global sea level by up to 120 m. This caused substantial changes to the Earth's surface, changing the distribution of land, continental ice sheets, and ocean. I demonstrate a technique we use to reconstruct ice sheets and paleotopography, and its application for the past 800000 years. I show that with the use of observations from glacial geology and ice extent chronology, it is possible to determine the history of the ice sheet configuration even prior to the Last Glacial Maximum (19000-26000 years ago). During Marine Isotope Stage 3 (57000-27000 years ago), when there are few constraints on sea level, we determined that sea level was between about 25-50 m lower than present, substantially higher than estimates based on marine benthic oxygen proxies. We also determined that global sea level during the Last Glacial Maximum was about -115 m, about 15 m higher than previous estimates. This shows that it is possible that, given the current constraints on sea level, that past ice sheet configuration may be an non-unique problem. The growing community efforts to standardize and compile datasets on past sea level bring an opportunity to reduce the uncertainty on ice sheet configuration, and extend our reconstructions further into the past (such as the last interglacial).
4:45pm - 5:00pm
Paleogene polar plankton and paleoproductivity: new proxy data from the Eocene - Oligocene transition
The Museum für Naturkunde – Leibniz Institute for Evolution and Biodiversity Science,Berlin, Germany
Polar plankton plays a large role in global carbon cycling. There is a significant lack of knowledge of these biotas, however. The main goal of our project is to understand how plankton and oceans interacted in the past during the Eocene/Oligocene (E/O) transition, when significant climate shifts happened. We use a multiproxy approach by combining microfossils and geochemical data. Our study includes the first-ever comprehensive surveys of both diatom and radiolarian plankton diversity (siliceous protists dominating the preserved microfossil record in polar regions). We analyze abundance, diversity, speciation, and extinction rates between 40 and 30 Ma. This plankton data, correlated togeochemical and sedimentological proxies of ocean conditions and carbon pump activity, geographic water masses, and nutrient export data will contribute to global syntheses to determine the global significance and role of plankton in climate change at the E/O transition.
Our data comes from several deep-sea drilling Sites from the Atlantic and the Indian Ocean sectors of the Southern Ocean: 689, Weddell Sea; 511 and 1090, near the Atlantic sector polar front; and Indian sector 748, Kerguelen Plateau.
Our results show a latitudinally differentiated pattern of paleoceanographic and productivity change. Episodes of increased Southern Ocean productivity occurred well prior to the E/O boundary within the late Eocene, beginning at ca 36-37 Ma. Diversity of siliceous plankton increased with productivity, and shows major episodes of evolutionary turnoverin the late Eocene and at the E/O boundary correlated to productivity and temperature change.
5:00pm - 5:15pm
Decoupled dust deposition and ocean productivity in the Antarctic Zone of the Southern Ocean over the past 1.5 million years
1University of Bonn, Institute for Geosciences, Germany; 2Camborne School of Mines and Environmental Sustainability Institute, University of Exeter, Penryn Campus, Treliever Road, Cornwall TR10 9FE, UK; 3Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA; 4NASA Goddard Space Flight Center, Planetary Magnetospheres Laboratory, Greenbelt, MD 20771, USA; 5University of Maryland, Department of Astronomy, College Park, MD 20742, College Park, USA; 6Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA; 7Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research, 27568 Bremerhaven, Germany; 8Earth and Environmental Studies, Montclair State University, Montclair, NJ 07043, USA; 9International Ocean Discovery Program, Texas AM University, College Station, TX 77845, USA; 10School of Geography, Earth and Environmental Sciences, University of Plymouth, Plymouth, PL4 8AA, UK; 11Oeschger Centre for Climate Change Research, University of Bern, Switzerland; 12British Antarctic Survey, Cambridge CB3 0ET, UK; 13Australian Centre for Ancient DNA, Department of Ecology & Evolutionary Biology, University of Adelaide, South Australia 5005, Australia; 14School of Geography, Geology and the Environment, University of Keele, Staffordshire, UK; 15Departmento Oceanografia, Servicio de Hidrografia Naval, Ministerio de Defensa, Argentina; 16State Key Laboratory of Cryospheric Science, Northwest Institute of Eco-Environment and Resources, Lanzhou 730000, China; 17Geology Program, University of Vale do Rio dos Sinos, San Leopoldo RS 93022-750, Brazil; 18School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia; 19Andalusian Institute of Earth Science (CSIC-UGR). Armilla (Granada) 18100 Spain; 20Spanish Institute of Oceanography, Cádiz 11006, Spain; 21Wordy Bird Studio, Wake Field, Rhode Island, USA; 22College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA; 23College of Marine Science, University of South Florida, St. Petersburg, FL 33701, USA; 24GEOMAR Helmholtz Centre for Ocean Research Kiel, 24148 Kiel, Germany; 25Department of Earth Sciences, ETH Zurich, Sonneggstrasse 5, 8092 Zurich, Switzerland; 26Department of Earth Science, MarineMarine Palynology and Paleoceanography, Utrecht University, 3584 CB Utrecht, Netherlands; 27Earth Environmental Sciences, Korea Basic Science Institute, Chungbuk Cheongju, Republic of Korea; 28Knowledge Engineering, Tokyo City University, Tokyo setagaya-ku 158-0087, Japan; 29Center for Advanced Marine Core Research, Kochi University, Nankoku, Kochi 783-8502, Japan; 30Department of Earth Sciences, University of California Riverside, Riverside, CA 92521, USA; 31Department of Earth and Environmental Sciences, Wesleyan University, Middletown, CT 06459, USA; 32Institute of Low Temperature Science, Hokkaido University, Sapporo Hokkaido 060-0819, Japan; 33American Museum of Natural History, 200 Central Park West, New York NY 10024, USA; 34Marine Stable Isotope Lab, National Centre for Polar and Ocean Research, Ministry of Earth Sciences, Vasco Da Gama 403804, India; 35Department of Geoscience, Indiana University of Pennsylvania, Indiana, PA 15705, USA; 36South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China
Southern Ocean paleoceanography provides key insights into how iron fertilization and oceanic productivity developed through Pleistocene ice-ages and their role in influencing the carbon cycle. We report the first high-resolution record of dust deposition and ocean productivity for the Antarctic Zone, close to the main dust source, Patagonia. Our deep-ocean records cover the last 1.5 Ma, thus doubling that from Antarctic ice-cores. We find a ≥10-fold increase in dust deposition during glacials and a ≤5-fold increase in ocean productivity during interglacials. This antiphasing persisted throughout the last 25 glacial cycles. Dust deposition became more widespread across the Mid-Pleistocene Transition (MPT) and, at ~0.9 Ma, dominant ice-age cycles changed from 40,000 to 100,000-years, suggesting more severe glaciations thereafter. Productivity was intermediate pre-MPT, lowest during the MPT and highest since 0.4 Ma. Glacials experienced extended sea-ice cover, reduced bottom-water export and Weddell Gyre dynamics, which helped lower atmospheric CO2 levels.
5:15pm - 5:30pm
Antarctic sea ice reconstructions: pros and cons of highly branched isoprenoids as sea ice proxies
1Alfred Wegener Institute, Germany; 2University of Bremen, Germany
The reconstruction of past Antarctic sea ice coverage through the application of diatom assemblages is often hampered in near coastal environments due to silica dissolution effects. The more recently established approach of using highly branched isoprenoid biomarkers to identify past sea ice conditions seems a valid method to overcome this limitation and that may also provide insight into ice-shelf dynamics. Here, we evaluate the so-called PIPSO25 index applied to modern surface sediments from the Amundsen Sea, the Drake Passage and Bransfield Strait, and the Weddell Sea. The comparison of biomarker-based sea ice estimates with satellite-derived sea ice concentrations supports the potential of the proxy approach. In a next step, we generated biomarker records using two sediment cores from the western and eastern Weddell Sea to track sea ice variability over late Pleistocene glacial-interglacial cycles. Consideration of additional data such as XRF and multi-sensor core logging records as well as micropaleontological investigations enables a comprehensive assessment of the environmental changes in the Weddell Sea in response to large-scale climate transitions. While magnetic susceptibility and density data obtained for both cores display similar patterns, we note distinct differences between the biomarker records highlighting local feedback mechanisms affecting sea ice cover.