LARGE REGIONAL GLACIAL-INTERGLACIAL CHANGES IN HYDROGEN ISOTOPIC COMPOSITION OF ALKENONES NEAR THE CHILEAN MARGIN

Abstract

Summary Paleosalinity is an important oceanographic parameter which cannot be reconstructed with reasonable accuracy based on sedimentary records yet. Sea water isotopes correlate with salinity and are incorporated by organisms e.g. in a calcitic shell or organic material. Published down-core reconstructions of salinity from hydrogen isotope ratios of alkenones are promising but show different sensitivities regionally. Here we present a new hydrogen isotope ratio record of long-chain alkenones (δ2HC37 ratio) in combination with oxygen isotopes of foraminifera (δ18OForaminifera) from the same samples, from the Chilean margin (ODP site 1235). We observed a decrease in both δ2HC37 and δ18OForaminifera during the last deglaciation (from 20–0 ka) and detected hydrogen isotope enrichment before the last glaciation (∼100–30 ka). Weiss et al. (2019) observed similar shifts in δ2HC37 of >20‰ and in the δ18OForaminifera in the same time frame, suggesting a consistent regional pattern. The δ2HC37 ratios suggest salinity changes of >2 psu between now and the Last Glacial Maximum, larger than assumed ( Adkins 2002 ; Broecker, 2002 ). Further analysis of both hydrogen and oxygen isotopes of both cores combined with paleo seasurfacetemperature will help to determine why the salinity shift reconstructed based on hydrogen isotopes does not match with other proxies or models.