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Volume 14, issue 7 | Copyright
Clim. Past, 14, 991-1014, 2018
https://doi.org/10.5194/cp-14-991-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 10 Jul 2018

Research article | 10 Jul 2018

Paleoceanography and ice sheet variability offshore Wilkes Land, Antarctica – Part 1: Insights from late Oligocene astronomically paced contourite sedimentation

Ariadna Salabarnada1,*, Carlota Escutia1, Ursula Röhl2, C. Hans Nelson1, Robert McKay3, Francisco J. Jiménez-Espejo4, Peter K. Bijl5, Julian D. Hartman5, Stephanie L. Strother6, Ulrich Salzmann6, Dimitris Evangelinos1, Adrián López-Quirós1, José Abel Flores7, Francesca Sangiorgi5, Minoru Ikehara8, and Henk Brinkhuis5,9 Ariadna Salabarnada et al.
  • 1Instituto Andaluz de Ciencias de la Tierra, CSIC-Univ. de Granada, Armilla, 18100, Spain
  • 2MARUM – Center for Marine Environmental Sciences, University of Bremen, Leobener Strasse 8, 28359 Bremen, Germany
  • 3Antarctic Research Centre, Victoria University of Wellington, Wellington, 6140, New Zealand
  • 4Department of Biogeochemistry, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Kanagawa, 237-0061, Japan
  • 5Department of Earth Sciences, Marine Palynology and Palaeoceanography, Faculty of Geosciences, Laboratory of Palaeobotany and Palynology, Utrecht University, Princetonlaan 8a, 3584 CB Utrecht, the Netherlands
  • 6Department of Geography and Environmental Sciences, Faculty of Engineering and Environment, Northumbria University, Newcastle upon Tyne, NE1 8ST, UK
  • 7Department of Geology, University of Salamanca, Salamanca, 37008, Spain
  • 8Center for Advanced Marine Core research, Kochi University, Nankoku, Kochi, 783-8502, Japan
  • 9NIOZ, Royal Netherlands Institute for Sea Research, and Utrecht University, Landsdiep 4, 1797SZ 't Horntje, Texel, the Netherlands
  • *Invited contribution by Ariadna Salabarnada, recipient of the EGU Climate: Past, Present & Future Outstanding Student Poster and PICO Award 2016.

Abstract. Antarctic ice sheet and Southern Ocean paleoceanographic configurations during the late Oligocene are not well resolved. They are however important to understand the influence of high-latitude Southern Hemisphere feedbacks on global climate under CO2 scenarios (between 400 and 750ppm) projected by the IPCC for this century, assuming unabated CO2 emissions. Sediments recovered by the Integrated Ocean Drilling Program (IODP) at Site U1356, offshore of the Wilkes Land margin in East Antarctica, provide an opportunity to study ice sheet and paleoceanographic configurations during the late Oligocene (26–25Ma). Our study, based on a combination of sediment facies analysis, magnetic susceptibility, density, and X-ray fluorescence geochemical data, shows that glacial and interglacial sediments are continuously reworked by bottom currents, with maximum velocities occurring during the interglacial periods. Glacial sediments record poorly ventilated, low-oxygenation bottom water conditions, interpreted as resulting from a northward shift of westerly winds and surface oceanic fronts. Interglacial sediments record more oxygenated and ventilated bottom water conditions and strong current velocities, which suggests enhanced mixing of the water masses as a result of a southward shift of the polar front. Intervals with preserved carbonated nannofossils within some of the interglacial facies are interpreted as forming under warmer paleoclimatic conditions when less corrosive warmer northern component water (e.g., North Atlantic sourced deep water) had a greater influence on the site. Spectral analysis on the late Oligocene sediment interval shows that the glacial–interglacial cyclicity and related displacements of the Southern Ocean frontal systems between 26 and 25Ma were forced mainly by obliquity. The paucity of iceberg-rafted debris (IRD) throughout the studied interval contrasts with earlier Oligocene and post-Miocene Climate Optimum sections from Site U1356 and with late Oligocene strata from the Ross Sea, which contain IRD and evidence for coastal glaciers and sea ice. These observations, supported by elevated sea surface paleotemperatures, the absence of sea ice, and reconstructions of fossil pollen between 26 and 25Ma at Site U1356, suggest that open-ocean water conditions prevailed. Combined, this evidence suggests that glaciers or ice caps likely occupied the topographic highs and lowlands of the now marine Wilkes Subglacial Basin (WSB). Unlike today, the continental shelf was not overdeepened and thus ice sheets in the WSB were likely land-based, and marine-based ice sheet expansion was likely limited to coastal regions.

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Here we reconstruct ice sheet and paleoceanographic configurations in the East Antarctic Wilkes Land margin based on a multi-proxy study conducted in late Oligocene (26–25 Ma) sediments from IODP Site U1356. The new obliquity-forced glacial–interglacial sedimentary model shows that, under the high CO2 values of the late Oligocene, ice sheets had mostly retreated to their terrestrial margins and the ocean was very dynamic with shifting positions of the polar fronts and associated water masses.
Here we reconstruct ice sheet and paleoceanographic configurations in the East Antarctic Wilkes...
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