Preliminary results of geochemical proxies (biogenic opal, TOC, and CaCO3) at IODP Site U1523 on the Ross Sea Continental Shelf

Abstract

It is important to understand past ice sheet dynamics. Because the West and East Antarctic Ice Sheets merged on the Ross Sea, understanding the ice sheet variation particularly in the Ross Sea is crutial. Geochemical proxies respond to surface environmental changes on the shelf in association with ice sheet advance/retreat. Site U1523 was collected from the Ross Sea continental shelf during International Ocean Discovery Program (IODP) Expedition 374. We measured biogenic opal, total organic carbon (TOC), and CaCO3 concentrations from the top 16 m of Site U1523 to reconstruct the late Pleistocene surface water productivity changes in response to ice sheet advance/retreat and to reconstruct bottom water corrosivity changes. Since our preliminary results of biogenic opal and TOC concentrations show cyclical variations, the variation may be related to degree of duration of sea ice associated with ice sheet advance and retreat on the Ross Sea. Because CaCO3 preservation is related to bottom water mass property and surface carbonate production, changes in CaCO3 concentration would provide information on past changes in bottom water corrosivity or surface carbonate production on the Ross Sea. Generally, increased CaCO3 concentrations occurred togherther with increases in C/N ratio, indicating that CaCO3 preservation on the Ross Sea continental shelf is related to ice sheet advance. Because this is preliminary results, more detailed study will be done in the future.