During glacial periods, the productivity in the Southern Ocean rises. This increase has been attributed to the greater availability of iron, which serves to fertilize the Southern Ocean. By drawing carbon dioxide from the atmosphere, the increased productivity feeds back positively, leading to an even cooler climate. According to the "iron hypothesis," the iron is delivered via dust blown into the ocean from arid regions, and Antarctic ice cores do indeed show more dust during glacial periods.
Latimer and Filippelli now offer evidence for a different source of the all-important iron. They have analyzed sediment cores from the South Atlantic and southern Indian Oceans to determine changes in sediment fluxes and productivity. During glacial times, productivity and iron fluxes are indeed higher, but most of the iron does not originate from eolian (wind-borne) dust. Rather, it is attributed to substantially increased weathering and delivery of material from continental shelves, indicating that increases in productivity may have been fueled by upwelling. Therefore, eolian iron might have constituted a much smaller contribution than previously proposed. -- JU
Paleoceanography,10.1029/2000PA000586.
