Limited decrease of Southern Ocean sulfur productivity across the penultimate termination

Productivity in the Pleistocene glacial Southern Ocean was probably
enhanced owing to iron fertilization by aeolian dust. Marine sediments
indicate such an increase north of the modern Antarctic Polar Front but
reduced biogenic activity south of it. However, quantitative estimates for
the integrated net effect are difficult to obtain. Here we use the SO4
2− isotopic
composition and other geochemical ice core records from the Atlantic
sector of the Southern Ocean to reconstruct net changes in integrated
biogenic sulfur productivity in the surface ocean over the penultimate
glacial termination. We show that biogenic SO4
2− aerosol contributes
58% and 85% to the sulfate budget in Dronning Maud Land during glacial
and interglacial times, respectively, and that biogenic sulfate is derived
predominately from the seasonal sea ice zone. Using our quantitative
reconstruction of biogenic aerosol production in the Southern Ocean
source region, we show that the average biogenic sulfate production
integrated over the Atlantic sector was 16% higher in the penultimate
glacial 137,000–153,000 years ago compared with the later Last Interglacial
120,000–125,000 years ago. An intermittent decrease in productivity
observed during early peak interglacial warming suggests that a reduction
in the seasonal sea ice zone may disrupt Southern Ocean ecosystems.