Aerosol deposited in East Antarctica over the last glacial cycle:: Detailed apportionment of continental and sea-salt contributions

The major ions, sodium (Na+), calcium (Ca2+), and chloride (Cl-), deposited in central Antarctica and preserved in ice cores originate from both marine and continental sources. They provide important proxy records, helping to reconstruct past climatic processes. However, it is difficult to clearly separate the individual contributions from the two sources, particularly the continental one during glacial periods. On the basis of Na+ and Ca2+ records at an unprecedented resolution from the European Project for Ice Coring in Antarctica (EPICA) Dome C ice core back to the penultimate glacial period, mean ion mass ratios were deduced for the continental and the sea-salt aerosol body over East Antarctica. The sea-salt ion mass ratios are in the range predicted for both wind-induced bubble bursting of breaking waves on the open ocean and sea ice brine-derived aerosols, respectively, thus allowing no clear decision on the contribution of sea ice to the central Antarctic sea-salt aerosol. The continental ion mass ratios point to a substantial contribution by halide aerosols, which is in agreement with the source properties in southern South America, although these ratios do not rule out the continental shelf exposed during glacial stages as an additional source. While during cold glacial periods continental sources accounted for more than 90% of the total Ca2+ input, this contribution was highly variable during the remaining glacial periods covarying with the Antarctic warm events. During the Holocene it was less than 50%, but it was significantly higher during the last interglacial period. The sea-salt aerosol contribution to the total Na+ input, which was mostly dominant and higher than 90%, was reduced to only two thirds during the last two glacial maxima and the period around 60 ka. Thus the glacial continental Na+ contribution appears to be more important than previously assumed, implying that Na+ records not corrected for continental Na+ do not represent a pure marine signal at the East Antarctic plateau during glacial times.