IODP EXP. 374 PROVIDES CLUES INTO PAST GLACIAL PROCESSES OF THE ANTARCTIC ICE SHEET

The IODP (International Ocean Discovery Program) 2018 Expedition 374 recovered new geological data from a latitudinal and depth transect across the continental shelf, slope and rise of the Ross Sea, Antarctica. This transect is located along one of the largest glacial valleys cut into the continental shelf by Antarctic Ice Streams and along the oceanward flow pathway of dense and cold water, forming in the Ross Sea polynya and mixing with Circumpolar Deep Water at the continental shelf edge.

The IODP Exp. 374 sites U1521 and U1522 recovered a Miocene to Plio-Pleistocene geological record of past expansion and retreat of ice streams emanating from the East and West Antarctic Ice Sheets across the Ross Sea continental shelf. Geochemical and petrographic signature in the glacimarine sediments of site U1521 in particular provides the earliest geological evidence proving large WAIS expansions occurred during the Early Miocene (~17.72–17.40 Ma).

Site U1523 targeted a Miocene to Pleistocene current-controlled sediment drift on the outermost continental shelf and informs about the changing vigor of the eastward flowing Antarctic Slope Current (ASC) through time, a key control on regulating heat flux onto the continental shelf.

Sites U1524 and U1525 cored a continental rise levee system near the flank of the Hillary Canyon, with a near-continuous record of the downslope flow of Ross Sea Bottom Water and turbidity currents, but also of ASC vigor and iceberg discharge. The integration of the seismic and stratigraphic data document a bottom current activity since the Early Miocene, with a reduction in intensity during the mid-Pliocene Warm Period.

Exp. 374 sediments are providing key chronological constraints on the major Ross Sea seismic unconformities, enabling reconstruction of paleo-bathymetry and assessment of the geomorphological changes associated with Neogene ice sheet and ocean circulation changes.