IODP Exp. 374 provides clues into the dynamics of the Antarctic Ice Sheet during Cenozoic climate transitions

Abstract

The Eurofleets ANTSSS (Antarctic ice Sheet Stability from continental Slope process investigation) 2017 cruise and the IODP (International Ocean Discovery Program) 2018 Expedition 374 recovered new geological, geophysical, and oceanographic 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 West Antarctic Ice Streams that feed into the Hillary Canyon, which debouches downslope onto the continental rise. It is also located 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 new morphobathymetric geological and oceanographic data highlight that processes acting here during glacial and interglacial cycles likely drove large-scale shifts in outer shelf and canyon head processes, and the build-up of channel-levees on the continental rise. 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. Site U1523 targeted a Miocene to Pleistocene 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. A 20 cm-thick tephra matches a c. 1.3 Ma deposit on the caldera rim of the Chang Peak volcano 1300 km from the U1524 coring site adds a new marker for dating, correlation, and synchronization of marine and continental early Pleistocene records of West Antarctica. 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. Exp. 374 results are fundamental for improving the boundary conditions of numerical ice sheet, ocean, and coupled climate models, which are critically required for understanding past ice sheet and global sea level response during warm climate intervals. Such data, and improved model skill, will enable more accurate predictions of ice sheet behavior and sea level rise anticipated with future warming.