Glacial-interglacial seawater isotope change near the Chilean Margin as reflected by δ²H values of C₃₇ alkenones

Stable hydrogen isotopic compositions of long-chain alkenones with 37 carbon atoms (δ²HC₃₇) have been shown to reflect seawater salinity in culture and environmental studies, and this potential sea surface salinity proxy has been applied to several downcore records from different regions. However, previous studies were based solely on a single sediment core and often suggested unlikely large changes in salinity based on existing proxy calibrations. Here we present a new δ²HC₃₇ record, in combination with oxygen isotopes of benthic foraminifera from the same samples, from a sediment core from the Chilean Margin (ODP Site 1235). The observed negative shift in δ²HC₃₇ of 20 ‰ during the last deglaciation was identical to that of a previously published δ²HC₃₇ record from the nearby, but deeper, ODP Site 1234, suggesting a regionally consistent shift in δ²HC₃₇. This change translates into a negative hydrogen isotope shift in the surface seawater of ca. 14 ‰, similar to glacial-interglacial reconstructions based on other δ²HC₃₇ records. The reconstructed bottom seawater oxygen isotope change based on benthic foraminifera during the last deglaciation is approximately -0.8 ‰, in line with previous studies. When translated into hydrogen isotopes of bottom seawater using the modern open-ocean water line, this would suggest a negative change of ca. 5 ‰, smaller than the reconstructed surface seawater shift based on alkenones. The larger change in surface water isotopes suggests that it experienced more freshening during the Holocene than bottom waters, either due to increased freshwater input, reduced evaporation, or a combination of the two.