New Insights Into Southern Hemisphere Temperature Changes From Vostok ice Cores Using Deuterium Excess Correction Over the Last 420,000 Years

Isotopic composition of the ice, deuterium (delta D) and deuterium excess (d), are currently used to infer both ice sheet and vapor source region temperature changes respectively. However, modeling studies (from simple to comprehensive models) show that to improve interpretation of isotopic profiles from ice cores we need to consider other controls on both deuterium and deuterium excess. Actually, both local and source temperatures affect delta D and d. In addition, ocean isotopic composition is also of primary importance. Thus, using Rayleigh model based estimates, we propose to combine both Vostok deuterium and deuterium excess histories to reconstruct, on a common time scale, temperature variations at both location of deposition and oceanic moisture source over the last 420,000 years. We examine each of these temperature histories regarding raw isotopic profiles. We show that source temperature recorded by deuterium excess is a source temperature gradient signal between low and mid latitudes rather than a low latitude signal of temperature. We also discuss the so-deduced Southern Hemisphere meridional temperature gradient, strongly modulated by the obliquity period. We show that this temperature gradient is well correlated with logarithm of sodium and dust recorded in Vostok cores, suggesting a strong link with atmospheric meridional transport. Finally, the combination of these results with new modeling studies using both a coupled ocean-atmosphere GCM (IPSL model) and an intermediate complexity climate model (CLIMBER model) provides interesting inputs to discuss climate mechanisms involved over glacial inceptions, between southern low and high latitudes.