The record of global change in circum-Antarctic marine sediments

Sediment drilling, using rigs located on sea ice inshore, and Ocean Drilling Program facilities farther offshore, have described the stepwise cooling of Antarctica through the Cenozoic, setting the scene for more detailed studies of short-period, recent change. Such studies will not be easy. The virtual absence of carbonate sediments and the strength of bottom currents in some regions are fundamental limitations. Nevertheless, Antarctic ocean sediments contain a record of global change which complements the record of the ice sheet, and extends it back in time. Pelagic and hemipelagic sediments of the ocean basins record changes in primary productivity, dissolution, sea ice extent and the strength of deep ocean circulation, and in the volume of the main circum-Antarctic water masses. Prograded sediments of the Antarctic continental shelf and slope contain a record of glacial/interglacial changes in ice sheet volume. Modem piston-coring techniques are capable of revealing changes over the last glacial cycle in some detail, in suitably expanded sections. At lower sediment accumulation rates, a less detailed but longer record can be obtained. It can already be shown that, at and around glacial maximum, (a) grounded ice sheets extended to the Antarctic continental shelf edge, (b) the marginal sea ice zone lay up to 5 degree farther north, and (c) Weddell Sea Bottom Water flow was far slower than at present These have implications for the carbon cycle in the oceans, which is of considerable importance in global change