Modeling water isotopologues during the last glacial: Implications for quantitative paleosalinity reconstruction

Abstract

Quantitative paleosalinity reconstructions with reasonable uncertainties remain a challenge in paleoceanography. In this study, we focus on stable isotope-based methods (δ18O and δ2H) to derive paleosalinity. We use the water isotopes-enabled fully coupled atmosphere/ocean/vegetation/land surface three-dimensional model of intermediate complexity iLOVECLIM to simulate the climate and water isotopes during the Last Glacial Maximum (LGM) and Heinrich event 1. We investigate how the isotopes in water can be used as reliable proxies to quantitatively reconstruct past changes in seawater salinity. Our results demonstrate that a quantitative salinity reconstruction during glacial conditions based on present-day regional δ18O-salinity relationships can lead to considerable errors (up to 25 g/kg in certain regions). However, we show that these eventual uncertainties on paleosalinity reconstruction can be reduced by allowing for model-derived regional δ18O-salinity relationships to vary through time. Our results indicate a rather stable dependence between δ2H and δ18O in surface seawater during the LGM. This suggest that quantitative reconstruction of salinity based on the δ2H measurement of alkenones (δ2Ha) might be possible if the slope and the intercept of the regression between the fractionation factor δ2Ha-δ2Hsw and salinity can be sufficiently tightly constrained in open ocean conditions. We confirm that pairing water isotopologues has a strong potential to reduce uncertainties on quantitative paleosalinity reconstructions, also under glacial boundary conditions.