AN ICE CORE INDEX OF ANTARCTIC SEA ICE PRODUCTION

Sea salt aerosol is one of the most common impurity components of polar ice cores. Until recently, it was assumed that the source of this sea salt was bubble bursting over open water. With this assumption, greater sea ice extent would lead to lower sea salt flux to Antarctica, and so it has been difficult to explain why (even with enhanced storminess) concentrations in both aerosol and snow, and in both Greenland and Antarctica, tend to peak in the winter half-year, and to increase in the last glacial maximum. For coastal Antarctica, it has been shown that the main source of sea salt is not open water, but rather the brine layer and frost flowers on the sea ice surface. We now suggest that the sea ice surface is also the source of sea salt to inland sites, and that sea salt in ice cores is closely related to the amount of annual sea ice production. With this re-interpretation, the profile of sea salt from the LGM to the present is consistent with our expectations based on marine evidence. The Antarctic sea salt record should no longer be considered as indicating past meridional circulation. We can also use the sea salt index to investigate the relationship between sea ice production, Antarctic bottom water production, and carbon dioxide uptake in the Southern Ocean. Finally we briefly consider how this interpretation affects what we see in Greenland ice cores.