Origin of detrital fluxes in the southeast Indian Ocean during the last climatic cycles

Because of a close relationship between detrital flux variations and magnetic susceptibility (MS) flux (MS cm −3 of bulk sediment multiplied by the linear sedimentation rate) variations in the southeast Indian basin of the southern ocean, MS flux profiles have been used to examine the spatial and temporal detrital flux changes in this basin during the last climatic cycle. Results indicate a general increase in detrital material input during the coldest periods, suggesting a widespread phenomenon, at least on the basin scale. Mineralogical data, geochemical data, and 87 Sr/ 86 Sr isotopic ratios have been used to determine the origin and transport mechanisms responsible for increased detrital flux during glacial periods. Mineralogical and geochemical data show that these glacial “highs” are due to increases in both Kerguelen‐Crozet volcanic and Antarctic detrital inputs. The 87 Sr/ 86 Sr isotopic composition of the >45‐µm fraction indicates that the Kerguelen‐Crozet province contributes to at least 50% of the coarse particule input to the west. This contribution decreases eastward to reach less than 10%. These tracers clearly indicate that the Crozet‐Kerguelen province was a major source region of detrital in the western part of the basin during glacial times. In contrast, material of Antarctic origin is well represented in the whole basin (fine and coarse fractions). Because of the minor amount of coarse particles in the sediments, volcanic particles from Kerguelen and crustal particles from Antarctica have most probably been transported by the Antarctic bottom water current and/or the Circumpolar deepwater current during glacial periods as is the case today. Nevertheless, the presence of coarse particles even in low amount suggests also a transport by ice rafting (sea‐ice and icebergs), originated from both Kerguelen and Antarctic sources. However, the relative importance of both hydrographic and ice‐rafting modes of transport cannot be identified accurately with our data. During low sea level stands (glacial maximum periods), increasing instability and erosion of the continental platform and shallow plateaus could have resulted in a more efficient transfer of crustal and volcano‐detrital material to the Southeast Indian basin. At the same time, extension of the grounded ice shelves over the continental margins and increase in the erosion rate of the Antarctic ice sheet could have induced a greater input of ice rafted detritus (IRD) to southern ocean basins. Enhancement of the circumpolar deepwater current strength might have also carried a more important flux of detrital material from Kerguelen. However, an increase in the bottom water flow is not necessarily required.