Iceberg Alley and Subantarctic Ice and Ocean Dynamics

Thomas.Ronge [ at ]


International Ocean Discovery Program Expedition 382, Ice-berg Alley and Subantarctic Ice and Ocean Dynamics, investigatedthe long-term climate history of Antarctica, seeking to understandhow polar ice sheets responded to changes in insolation and atmo-spheric CO2 in the past and how ice sheet evolution influencedglobal sea level and vice versa. Five sites (U1534–U1538) weredrilled east of the Drake Passage: two sites at 53.2°S at the northernedge of the Scotia Sea and three sites at 57.4°–59.4°S in the southernScotia Sea. We recovered continuously deposited late Neogene sed-iments to reconstruct the past history and variability in AntarcticIce Sheet (AIS) mass loss and associated changes in oceanic and at-mospheric circulation.The sites from the southern Scotia Sea (Sites U1536–U1538)will be used to study the Neogene flux of icebergs through “IcebergAlley,” the main pathway along which icebergs calved from the mar-gin of the AIS travel as they move equatorward into the warmer wa-ters of the Antarctic Circumpolar Current (ACC). In particular,sediments from this area will allow us to assess the magnitude oficeberg flux during key times of AIS evolution, including the follow-ing: •The middle Miocene glacial intensification of the East Antarctic Ice Sheet, •The mid-Pliocene warm period, •The late Pliocene glacial expansion of the West Antarctic Ice Sheet, •The mid-Pleistocene transition (MPT), and •The “warm interglacials” and glacial terminations of the last 800 ky. We will use the geochemical provenance of iceberg-rafted detri-tus and other glacially eroded material to determine regionalsources of AIS mass loss. We will also address interhemisphericphasing of ice sheet growth and decay, study the distribution andhistory of land-based versus marine-based ice sheets around thecontinent over time, and explore the links between AIS variabilityand global sea level.By comparing north–south variations across the Scotia Sea be-tween the Pirie Basin (Site U1538) and the Dove Basin (Sites U1536and U1537), Expedition 382 will also deliver critical information onhow climate changes in the Southern Ocean affect ocean circulationthrough the Drake Passage, meridional overturning in the region,water mass production, ocean–atmosphere CO2 transfer by wind-induced upwelling, sea ice variability, bottom water outflow fromthe Weddell Sea, Antarctic weathering inputs, and changes in oce-anic and atmospheric fronts in the vicinity of the ACC.Comparing changes in dust proxy records between the ScotiaSea and Antarctic ice cores will also provide a detailed reconstruc-tion of changes in the Southern Hemisphere westerlies on millen-nial and orbital timescales for the last 800 ky. Extending the oceandust record beyond the last 800 ky will help to evaluate dust-climatecouplings since the Pliocene, the potential role of dust in iron fertil-ization and atmospheric CO2 drawdown during glacials, andwhether dust input to Antarctica played a role in the MPT. The principal scientific objective of Subantarctic Front SitesU1534 and U1535 at the northern limit of the Scotia Sea is to recon-struct and understand how intermediate water formation in thesouthwest Atlantic responds to changes in connectivity between theAtlantic and Pacific basins, the “cold water route.” The SubantarcticFront contourite drift, deposited between 400 and 2000 m waterdepth on the northern flank of an east–west trending trough off theChilean continental shelf, is ideally situated to monitor millennial-to orbital-scale variability in the export of Antarctic IntermediateWater beneath the Subantarctic Front. During Expedition 382, werecovered continuously deposited sediments from this drift span-ning the late Pleistocene (from ~0.78 Ma to recent) and from thelate Pliocene (~3.1–2.6 Ma). These sites are expected to yield a widearray of paleoceanographic records that can be used to interpretpast changes in the density structure of the Atlantic sector of theSouthern Ocean, track migrations of the Subantarctic Front, andgive insights into the role and evolution of the cold water route oversignificant climate episodes, including the following: •The most recent warm interglacials of the late Pleistocene and •The intensification of Northern Hemisphere glaciation.

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Weber, M. , Raymo, M. , Peck, V. , Williams, T. , Ronge, T. and Expedition 382, S. (2021): Iceberg Alley and Subantarctic Ice and Ocean Dynamics , [Other]

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