Sea salt as an ice core proxy for past sea ice extent: a process-based model study

Sea ice is a reflection of, and a feedback on the Earth's climate. We explore here, using a global atmospheric chemistry-transport model, the use of sea salt in Antarctic ice cores to obtain continuous long-term, regionally-integrated records of past sea ice extent, synchronous with ice core records of climate. The model includes the production, transport and deposition of sea salt aerosol from the open ocean and ‘blowing snow’ on sea ice. Under current climate conditions, we find that meteorology, not sea ice extent, is the dominant control on the atmospheric concentration of sea salt reaching coastal- and continental Antarctic sites on inter-annual timescales. However, through a series of idealised sensitivity experiments, we demonstrate that sea salt has potential as a proxy for larger changes in sea ice extent (e.g. glacial-interglacial). Treating much of the sea ice under glacial conditions as a source of salty blowing snow, we demonstrate that the increase in sea ice extent alone (without changing the meteorology) could drive, for instance, a 68% increase in atmospheric sea salt concentration at the site of the Dome C ice core, which exhibits an approximate two-fold glacial increase in sea salt flux. We also show how the sensitivity of this potential proxy decreases towards glacial sea ice extent—the basis of an explanation previously proposed for the lag observed between changes in sea salt flux and δD (an ice core proxy for air temperature) at glacial terminations. The data thereby permit simultaneous changes in sea ice extent and climate.