Sulfate isotopes over termination II - Source decomposition and Southern Ocean productivity changes
Journal Article
Overview
abstract
An important ingredient in the glacial reduction of atmospheric CO2 is the increase of marine biological productivity in the Southern Ocean region due to an alleviation of Fe limitation in glacial times. This is indeed documented in marine sediments north of the modern Antarctic Polar Front (APF). In contrast, productivity south of it appears to be reduced, however the marine information is incomplete due to the prevalence of winter and summer sea ice in major parts of this region during glacial times. The high-resolution Antarctic ice core sulfate aerosol record, which, among other sources, is influenced by the marine biogenic emission of dimethylsulfide, was so far unable to provide unambiguous estimates of such productivity changes. In particular, sulfate deposition fluxes in the EPICA Dome C ice core (EDC) showed no glacial/interglacial changes whatsoever, while the same data in the EPICA Dronning Maud Land core (EDML) suggested a slight increase in the glacial, despite the fact that these records should be dominated by biogenic sources south of the APF.; New high-precision stable sulfur isotope measurements on ice core sulfate over termination II on the EDML core together with high-resolution sulfate, sea-salt and mineral dust aerosol concentration records allow us for the first time to perform a quantitative decomposition of the sea salt, terrestrial, volcanic and biogenic sulfate contributions. This shows that despite a significant increase in terrestrial sulfate in the glacial, marine biogenic emissions are still by far the dominating source of sulfate during that time at least for the Atlantic sector of Antarctica but likely for the entire Antarctic plateau.; Using a simple atmospheric aerosol transport model to correct for the loss of sulfate aerosol en route by wet and dry deposition, we are able to reconstruct the atmospheric sulfate aerosol concentrations changes over the Atlantic sector of the Southern Ocean source region mainly south of the APF. This shows that despite lower sulfate ice concentrations at EDML during interglacials, atmospheric aerosol concentration at the ocean source south of the APF - hence marine biogenic sulfur emissions - were up to a factor of 2 higher during the last interglacial and the late termination II than during the penultimate glacial maximum.
