Pelagic productivity changes in the equatorial area of the northwest Indian Ocean during the last 400,000 years

摘要: Abstract Major and selected trace element (Al, Fe, Mg, K, Ba, P, Mn, V, Cu, Ni, Ti) records were analyzed in two cores recovered from the northwestern Indian Ocean (core MD 90940 on Madingley Rise core 85668 Somali Basin) order to monitor sedimentary response pelagic productivity this area during last 400,000 years. Geochemical proxies such as bulk mass accumulation rate (MAR), Al-normalized major contents, MARs compared biologic markers of palaeoproductivity: a new radiolarian index (rad ratio), variations foraminiferal assemblages. Special attention being paid barium record, sequential leaching procedure determined main Ba-carrier fraction sediment, and, thus, amount biogenic barium. The `blue ocean' sedimentation 90940) is characterized by low MAR an insignificant terrigenous input. are directly related rad ratio, reflecting direct link between surface at site. In mainly found barite can be considered palaeoproductivity proxy. Basin 85668), inputs relatively higher, but still productivity. No was linked A comparison sites points out differences both sites. Despite location domain, geochemical especially one, different one other. MAR, which reflects productivity, presents significant discrepancies 90940), peak values recorded glacial intervals, their maximum observed interglacial isotope Stage 9. high periods occurred stages. episode Rise, absence 8/7 transition basin, well time lag indicate that is, area, controlled more local palaeoceanographic patterns than global climatic changes, e.g. glacial/interglacial alternations.