West Antarctic Ice Sheet and Ocean Dynamics in the Outer Amundsen Sea: Initial Results from IODP Expedition 379


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Karsten.Gohl [ at ] awi.de

Abstract

The Amundsen Sea sector of Antarctica has long been considered the most vulnerable part of the West Antarctic Ice Sheet because of the great water depth and retrograde slope at the grounding line, the observed incursion of warm Circumpolar Deep Water onto the shelf, and the lack of substantial buttressing ice shelves. Notably, ice flowing into the Amundsen Sea embayment has been undergoing rapid changes over recent decades. International Ocean Discovery Program (IODP) Expedition 379 accomplished two successful drill sites on the continental rise of the Amundsen Sea in January-March 2019, the first from this sector, despite significant logistical limitations, including persistent sea ice that prevented access to all proposed continental shelf sites and abundant mobile icebergs that forced loss of ~50% of drilling time. Site U1532 is located on a large sediment drift and penetrated to a depth of 794 m below seafloor with 90% recovery. Nearly continuous cores were collected from the Pleistocene into the upper Miocene. Site U1533 reached 383 m below seafloor (70% core recovery) in a more condensed sequence down to the upper Miocene at the lowermost flank of the same sediment drift. The cores from both sites contain unique records to study the cyclicity of ice sheet advance and retreat processes as well as ocean-bottom circulation and water mass changes. In particular, Site U1532 revealed a sequence of Pliocene lithofacies, with an excellent paleomagnetic record for very high-resolution, sub-orbital scale climate change studies of the previously sparsely sampled region. Coarse-grained sediments, interpreted as ice-rafted debris, were identified throughout all time periods recovered. Proximal sources in West Antarctica are confirmed for crystalline rock detritus in some intervals. Cyclicity interpreted to represent relatively warmer periods, variably characterized by higher microfossil abundance and higher counts of ice-rafted debris, alternating with transitional and colder periods, characterized by dominantly gray laminated terrigenous muds, is a dominant feature of the cores. Despite the lack of sites on the shelf, the records from the continental rise reveal the timing of glacial advances onto the shelf and, thus, the expansion of a continent-wide ice sheet in West Antarctica at least back to the Late Miocene.



Item Type
Conference (Talk)
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Primary Division
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Not peer-reviewed
Publication Status
Published
Event Details
AGU Fall Meeting, 09 Dec 2019 - 13 Dec 2019, San Francisco.
Eprint ID
50904
Cite as
Wellner, J. S. , Gohl, K. and Klaus, A. , Expedition 379 Scientific Party (2019): West Antarctic Ice Sheet and Ocean Dynamics in the Outer Amundsen Sea: Initial Results from IODP Expedition 379 , AGU Fall Meeting, San Francisco, 9 December 2019 - 13 December 2019 .


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