Ranges of moisture-source temperature estimated from Antarctic ice cores stable isotope records over glacial–interglacial cycles

摘要

A single isotope ratio (δD or δ18O) of water is widely used as an air-temperature proxy in Antarctic ice core records. These isotope ratios, however, do not solely depend on air-temperature but also on the extent of distillation of heavy isotopes out of atmospheric water vapor from an oceanic moisture source to a precipitation site. The temperature changes at the oceanic moisture source (Δ T_source) and at the precipitation site (Δ T_site) can be retrieved by using deuterium-excess (d) data. A new d record from Dome Fuji, Antarctica spanning the past 360 000 yr is presented and compared with records from Vostok and EPICA Dome C ice cores. In previous studies, to retrieve Δ T_source and Δ T_site information, different linear regression equations were proposed using theoretical isotope distillation models. A major source of uncertainty lies in the coefficient of regression, β_site which is related to the sensitivity of d to Δ T_site. We show that different ranges of temperature and selections of isotopic model outputs may increase the value of β_site by more than a factor of two. To explore the impacts of this coefficient on reconstructed temperatures, we apply for the first time the exact same methodology to the isotope records from the three Antarctica ice cores. We show that uncertainties in the β_site coefficient strongly affect (i) the glacial–interglacial magnitude of Δ T_source; (ii) the imprint of obliquity in Δ T_source and in the site-source temperature gradient. By contrast, we highlight the robustness of Δ T_site reconstruction using water isotopes records.