Sea ice control of water isotope transport to Antarctica and implications for ice core interpretation

Abstract

Sea ice in the Southern Ocean is important for Antarctic climate and hydrology. The dependence of water isotope abundance (δ18O and deuterium excess) on the winter sea ice state is examined with the isotopic version of the Melbourne University general circulation model. Reductions in the ice concentration provide warmer temperatures in winter and allow higher precipitation totals further south, while the reverse occurs with increased ice extent. The model shows clear demarcation between the changes in the isotopic conditions over the sea ice pack, where local changes in surface exchange dominate, and those of the continent interior, which depend on the long‐ranged transport aloft. While less sensitive to the forcing, the interior response is influenced by changes in turbulent mixing over the ice pack and modification of the vertical transport associated with diabatic heating. The interior deuterium excess response is more strongly affected by sea ice as it captures changes in temperature over the ice rather than just the final vapor mass. Traditional reconstruction of temperature from a single isotopic nuclide would give erroneous interpretation of change in the global mean temperature unless the sea ice changes in parallel; instead, the spatial structure of the sea ice response gives some hope for extracting past sea ice conditions from multicore analysis. This study begins to explore the role of entropy production during transport such that the isotopic interpretation is more closely tied to the dynamics of the atmosphere than is expressed by idealized parcel analysis.