Calcium carbonate undersaturation of bottom waters in the South Australian basin during the last 3.2 million years

Abstract

We analyzed deep-sea benthic foraminifera from three Eltanin piston cores (E45-21, E49-53, E50-2) to infer deep-water circulation in the western South Australian Basin during the past 3.2 million years. During the Gauss and early to middle Matuyama chrons, Epistominella umbonifera was the dominant species; Uvigerina spp. and Epistominella exigua increased in abundance during the late Matuyama, and became dominant during the Brunhes chron. The E. umbonifera data suggest that these cores were overlain by a cold, more highly carbonate-undersaturated bottom water relative to present day conditions during three periods: 1) early to middle Gauss (3.2 to 2.6 Ma.), 2) early Matuyama (2.3 to 2.0 Ma.), and 3) middle Matuyama (1.9 to 1.1 Ma.). During the Brunhes chron, cold, carbonate-undersaturated bottom water was replaced by bottom water having properties intermediate betweem present-day Antarctic Bottom Water and Circumpolar Deep Water. Comparison of our faunal data with previously published grain-size data (used to infer bottom-water velocities) indicates no direct relationship between bottom-water velocities and variation in cold, carbonate-undersaturated bottom water in the South Australian Basin.