ALBERT

Description: We will report on two drilling proposals within the International Ocean Discovery Program (IODP) to address open questions on Antarctic Ice-sheet (AIS) dynamics in a transect from the Weddell Sea to the Scotia Sea on the Atlantic side of the Southern Ocean. IODP proposal 848-pre (Ice-sheet and sea-level history of the Weddell Sea) shall drill three contourite drifts northeast of Riiser-Larson Ice Shelf on the slope of the southeastern Weddell Sea that contain high-resolution Mio-Pleistocene sections. As the southern extension of the Atlantic Ocean, the Weddell Sea is a key area to study Earth‘s past climate variability. It constitutes a major source of Antarctic Bottom Water formation, which influences the Atlantic Meridional Overturning Circulation. Moreover, the Weddell Gyre is an important cyclonic circulation system for water-mass communication between the Antarctic Ice Sheet and the Southern Ocean. One of the world's two largest ice shelves, the Filchner-Rønne Ice Shelf, drains into the Weddell Basin. Ice-sheet dynamics in the Weddell Sea sector of the East Antarctic Ice Sheet (EAIS) are highly susceptible to far-field changes in sea level. Practically all icebergs from the EAIS merge in the Weddell Sea before they exit Antarctica through the Scotia Sea, thereby providing a unique location to study AIS dynamics. Despite these paramount scientific issues that have, over the last two decades, identified the Weddell Sea as a key area to study past and present climate change, there has been no deep scientific drilling for high-resolution reconstruction of the Plio-Pleistocene. Our scientific objectives aim at achieving the first complete Late Neogene reconstruction for the Weddell Sea. We will address the overarching questions on changing ice-sheet dynamics, interhemispheric phasing of ice-sheet and climate events, ocean circulation, and bottom-water production. Specifically, we wish to unravel whether the formation of the contourite ridges north of Crary Fan were associated with a sea-level drop initiated through intensification of Northern Hemisphere glaciation during the Pliocene. Also, did the drainage pattern change during the Mid-Pleistocene Transition? Can we decipher ice-sheet dynamics on glacial-to-interglacial time scales and during the Last Glacial Maximum? Can we detect farfield sea-level effects and rates of sea-level rise from Iceberg Alley? Can we relate varve thickness variations obtained from counting and dating varved sediment on the contourite ridges to external (solar) or internal (ocean-atmosphere) variability on decadal-to-centennial time scales? IODP proposal 847-full revised (Plio-Pleistocene reconstruction of ice-sheet, atmosphere, and ocean dynamics in Iceberg Alley) shall drill two deep-ocean sites in the Scotia Sea farther north. We aim at delivering the first well-dated, high-resolution and spatially integrated record of variability in icebergs flux from Iceberg Alley, where a substantial number of Antarctic icebergs exit from the Weddell Sea into the warmer Antarctic Circumpolar Current (ACC). In particular, we will characterize the iceberg flux during the mid-Pliocene warm interval, the mid-Pleistocene transition, the warm interglacials of the last 800 kyr, and during glacial terminations. We will use the geochemical provenance of detrital material to determine regional sources of AIS mass loss; address inter-hemispheric phasing of ice-sheet and climate events, and the relation of AIS variability to sea level. We will also deliver critical information on changes in Drake Passage throughflow, meridional overturning in the Southern Ocean, CO2 transfer via wind-induced upwelling, sea-ice variability, bottom water outflow from the Weddell Sea, Antarctic weathering inputs, and changes in oceanic and atmospheric fronts in the vicinity of the ACC by comparing north-south variations across the Scotia Sea. Comparing changes in dust proxy records between the Scotia Sea and Antarctic ice cores will provide a detailed reconstruction of changes in the Southern Hemisphere westerlies on millennial and orbital time scales for the last 800 kyr. Extending this comparison beyond 800 kyr will help evaluating climate-dust couplings since the Pliocene, its potential role in iron fertilization and atmospheric CO2 drawdown during glacials, and whether dust and changes in Antarctic ice volume played a role in the mid-Pleistocene transition.

Description: The timing of the last maximum extent of the Antarctic ice sheets relative to those in the Northern Hemisphere remains poorly understood. We develop a chronology for the Weddell Sea sector of the East Antarctic Ice Sheet that, combined with ages from other Antarctic ice-sheet sectors, indicates that the advance to and retreat from their maximum extent was within dating uncertainties synchronous with most sectors of Northern Hemisphere ice sheets. Surface climate forcing of Antarctic mass balance would probably cause an opposite response, whereby a warming climate would increase accumulation but not surface melting. Our new data support teleconnections involving sea-level forcing from Northern Hemisphere ice sheets and changes in North Atlantic deep-water formation and attendant heat flux to Antarctic grounding lines to synchronize the hemispheric ice sheets.