THE PLIOCENE RECORD OF ANTARCTIC SEDIMENTATION IN THE JANE BASIN, NORTHWEST WEDDELL SEA, ODP SITE 697

The Antarctic plays a crucial role in climate regulation and the waxing and waning of its ice sheets contributes to changes in global changes sea level height. Today, this ice-covered continent is thermally isolated from the rest of the ocean by the Antarctic Circumpolar Current (ACC). This is the deepest and largest current in the ocean, transporting between 100-150 million cubic meters of water per second. In the Northwestern part of the Weddell Sea, the densest water in the ocean, Antarctic Bottom Water (AABW) forms and flows into the ACC. Our knowledge of history of this crucial arm of the ocean conveyor belt is poor. This hampers our ability to predict and model future bottom water formation and ice sheet dynamics in response to a warming planet. To contribute to the base of knowledge we examined Pliocene-age sediment from ODP Site 697. This lies in the Jane Basin, beyond the northern end of the Antarctic Peninsula, south of the South Orkney Islands. At 3480 meters water depth, it is a deepest of a three-site transect to examine the history of circum-Antarctic water masses. There 320 m of Pleistocene and Pliocene sediment was recovered, dominated by terrigeneous mud with 0-40% diatoms and isolated ash layers. Site 697 was cored in 1987 and only a single hole penetrated the sediment column. This means that even with good recovery, recovery is incomplete. This is because of disturbance while coring, such as difficult to core material (sand and dropstones), and because the drilling technique itself causes core disturbance.

We will present multiple data sets that show changes in iceberg melting and provenance (sand and gravel %, mineral age and composition), productivity (diatom species, % biosilica, and % organic carbon), and bottom current strength (sortable silt). For example, between about 3.8 and 3.3 Ma, IRD was abundant, with some ice bergs traveling over 2000 km to read the site. Biosilica abundance which ranged from about 20 to 100 g/cm²/kyr, does not track IRD wt.%, suggesting that we have a mechanism to identify intervals of open ocean with high productivity free from and infested by melting icebergs and times when ice cover prevents both productivity and ice berg discharge.