Radiolarian distribution and the late pleistocene history of the Southeastern Indian Ocean

Abstract

A factor analysis, of radiolarian assemblages in 36 trigger-core tops from the Southeast Indian Ocean (between latitudes 40° to 65° S and longitudes 80° to 120° E) gives three temperature-related factors and one related primarily to near-bottom processes. A paleoecologic equation was written relating the surface factor values to the present-day observed sea-surface temperatures for summer and winter. By means of a regression technique, paleotemperatures were estimated at the level of the last glacial maximum (18, 000 years B.P.) in five Eltanin cores and for the last 600, 000 years in core E45-74. The average temperature difference along a longitudinal transect of cores crossing the Antarctic Convergence was 2.2° colder 18, 000 years ago than today. The estimated sea-surface paleotemperatures in E45-74 showed high correlations with radiolarian species diversity indices, the Subantarctic and Antarctic factor values, percent of CaCO 3, δ 13O, number of radiolarian fragments and percent Antarctissa strelkovi. Based on paleotemperatures and factor values down this core, it is estimated that the Antarctic Convergence was displaced northward to the position of E45-74 six times in the last 600, 000 years.