New insights into Southern Hemisphere temperature changes from Vostok ice cores using deuterium excess correction

Abstract

The combination of both Vostok ice core deuterium and deuterium excess histories over the last four climate cycles back to 420 ka BP offers a unique opportunity for reconstructions of vapor source region and local temperature variations (ΔTsource and ΔTsite respectively) relative to their modern values. Our study is based on an inversion of ice isotopic composition using a Rayleigh-based isotopic model which estimates the dependence of Vostok precipitation isotopic composition on different climate controls (moisture source temperature, local deposition temperature and ocean isotopic composition). Both reconstructed local and source temperatures show no substantial effects from this correction, in the sense that none of the rapid or large variations in raw deuterium and deuterium excess profiles can be entirely attributed to a second order climate control. Our discussion is focused on moisture source temperature and meridional temperature gradient history (ΔTsource−ΔTsite). First, using sea surface temperature time series, we confirm that moisture source temperature signal recorded in Vostok deuterium excess over the last 150 ka fully reflects the obliquity time-varying relative contribution of low and high ocean latitudes to Vostok precipitation. Second, comparisons of source-to-site meridional temperature gradient with the Vostok sodium record over 420 ka suggest that moisture transport and sea salt transport to the ice sheet are controlled by processes in different latitudes (the sea salt being more of a high-latitude signal).