Climate controls on deuterium excess in Antarctic precipitation - insights from an isotope-enabled atmospheric GCM ECHAM

Abstract

We present new work that improves our understanding of the controls on Antarctic precipitation and ice cores. This is critical for gaining insights into polar changes. The work relies on our implementation of innovative water tracing diagnostics in an atmospheric general circulation model. These tracers provide new precise information on moisture source locations and properties of Antarctic precipitation - and allow us to evaluate how one should interpret water isotopic profiles of Antarctic ice cores. Heavy precipitation in Antarctica is sourced by longer-range moisture transport: it comes from 2.9° (300 km, averaged over Antarctica) more equatorward (distant) sources compared to the rest of precipitation. Precipitation during negative phases of the Southern Annular Mode (SAM) also comes from more equatorward moisture sources (by 2.4°, averaged over Antarctica) than precipitation during positive SAM phases, likely due to amplified planetary waves during negative SAM phases. Our new, more precise information on moisture source properties also shows that the logarithmic definition of deuterium excess exhibits a stronger correlation with moisture source properties than the classical linear definition of deuterium excess. Results support the conventional practice of interpreting deuterium excess in terms of source sea surface temperature, without concerning source 2 m relative humidity and source 10 m wind speed. We find there is no added value to include δD for the reconstruction of source temperature in addition to deuterium excess, but including deuterium excess does bring some (small) added benefit in reconstructing site temperature in addition to δD. Nevertheless, it is arguable whether one should incorporate deuterium excess considering uncertainties in the transfer function and post-depositional effects on deuterium excess. Our results demonstrate that improving our understanding of the physics underlying supersaturation function could also help constrain the key uncertainties associated with these model results. Overall, our novel water tracing diagnostics enhance our understanding of the controlling factors of Antarctic precipitation and ice cores.