High concentrations of biogenic barium in Pacific sediments after Termination I—a signal of changes in productivity and deep water chemistry

Abstract

Abstract High concentrations of barium have been found in sediments deposited on the Chilean continental slope after glacial Termination I. When compared to independent proxies of paleoproductivity, the pattern of biogenic barium accumulation does not match the changes in paleoproductivity in this region and cannot be explained by changes in the terrigenous supply of barium alone. This leaves an increased concentration of dissolved barium in sea water as the most likely cause of the observed barium anomalies. Based upon the accumulation rate of biogenic barium and the paleoproductivity index, which was calculated from the accumulation rates of organic carbon, biogenic opal and carbonate, the changes in the concentration of dissolved barium in the Pacific Ocean in the course of the last glacial and through the Holocene could be modelled. This model shows that barium concentrations in the Pacific during the last glacial were comparable to today (150 nmol kg1). The highest dissolved barium concentrations were calculated for the Early and Middle Holocene (190 nmol kg1). The resulting pattern of variations in the barium concentration in the seawater agrees well with Ba/Ca ratios in benthic foraminifera published in the literature. The observed changes are probably driven by the Holocene shoaling of the Pacific carbonate compensation depth, which is assumed to have caused an increased flux of previously carbonate-bound barium from the sediment to the deep ocean waters, leading to the observed longstanding maximum of dissolved barium in the Pacific during the Holocene.