Glacial-Interglacial Circulation and Climatic Changes in the South Indian Ocean (Kerguelen Plateau Region) Recorded by Detrital and Biogenic Magnetic Minerals

The Southern Ocean (SO) plays a fundamental role in global climate due to the presence of the intense eastward-flowing Antarctic Circumpolar Current (ACC), one of the most important ocean current systems. The configuration of the frontal systems of the ACC is controlled by the orbital- and millennial-scale variations of the Southern Hemisphere westerly winds (SHWW) and the SO upwelling. However, the reconstruction of paleoclimate and paleocurrent in the SO remains controversial possibly because of the complex interpretation of paleo-proxies and the regional variations. Here, we present results from rock magnetic measurements and electron microscopic analyses on marine core MD11-3353 over the past 150 Kyr, which is located in the Polar Front Zone, west of the Kerguelen Plateau. Our data sets indicate that magnetic mineral assemblages in the core are dominated by detrital magnetic minerals mixed with biogenic magnetic minerals (i.e., magnetofossils formed by magnetotactic bacteria) during the interglacial periods. Changes in the detrital magnetic mineral content indicate a strong modulation of the ACC intensity and the SHWW stress at the orbital scale over the last climatic cycle with an enhanced activity during the glacial periods. The increase in magnetofossils content during the interglacial periods indicates an enhanced nutrient supply from the SO upwelling resulting from the southward migration of the Antarctic Polar Front. Our results suggest that the variations of concentration and assemblage of magnetic minerals can be used as faithful proxies for reconstructing ocean circulation and upwelling changes in the South Indian Ocean over the past 150 Kyr.