Paleosensitivity of Hydrogen Isotope Ratios of Long-Chain Alkenones to Salinity Changes at the Chile Margin

Hydrogen isotope ratios of long-chain alkenones (δ²H_C37 ratios) have been shown to correlate with salinity in several culture studies. However, it is uncertain how applicable the δ²H_C37-salinity relationship is to reconstruct past salinity. The δ²H_C37 ratios were measured on sediments from a drill core (ODP site 1234) at the Chilean Margin covering the last ~150 kyr. High δ²H_C37 values corresponded to glacial time periods and interglacial periods are characterized by lower δ²H_C37 values, aligning with δ¹⁸O ratios measured on planktonic foraminifera from the same core. Effects of parameters such as species composition, the δ²H-δ¹⁸O relationship used for ice volume corrections, and nutrient- or light-controlled growth rate, did not appear to significantly alter δ²H_C37 ratios at ODP 1234. We used linear regression equations from batch culture experiments, marine surface sediments, and suspended particulate organic matter to quantitatively characterize salinity changes over the last ~150 kyr at ODP 1234. However, most of these equations yielded larger salinity shifts than previously suggested, a phenomenon also observed for other δ²H_C37 records. This suggests that the paleosensitivity of δ²H_C37 ratios to salinity was larger in the geologic record than has been observed in any modern environment or laboratory settings, or that glacial to interglacial salinity shifts might have been larger than currently believed.