Sedimentary fluxes: paleo-productivity and paleo-hydrology of the southern ocean during the last 150000 years before present

The aim of this study was to establish whether an increase of the biological production in high latitudes could explain the reduced values of atmospheric CO₂ during glacial times. To approach this problem, we estimated the glacial/interglacial variations of paleo-productivity in the Southern Indian Ocean using the variations of biogenic silica accumulation rates. On the other hand, detrital accumulation rates were used to follow the paleo-circulation variations in the same area. In the Sub-Antarctic zone, biogenic silica accumulation rates accumulated during the last glacial period are higher than during the Holocene. This is probably the consequence of the northward Polar Front Zone shift. In the Antarctic zone, north of 55 deg. S, these biogenic silica accumulation rates were at least similar to Holocene rates except on the Kerguelen plateau. Thereby, it seems that paleo-productivity variations in the Indian sector of the Southern Ocean cannot explain the atmospheric CO₂ decrease during glacial times. In this sector, detrital accumulation rates show that cold periods are characterized by a great increase of volcano-detrital materials originating from the Kerguelen plateau. This might be the result of an increase in oceanic circulation in response to atmospheric circulation forcing. (author)