Geochemical characteristics of deep-sea sediments from the Arabian Sea: a high-resolution study

Five deep-sea cores from the Arabian Sea, covering a lime interval of 170 k y, were sampled at high resolution and analysed for major and trace element s. The stratigraphy of the cores was obtained by comparing the Ba/Al ratio with the SPECMAP data. This method is based on the close correlation betwee n Ba concentrations (or Ba/Al ratios) and oxygen isotope ratios (delta(18)O ) of Foraminifera in Arabian Sea sediments. Ba/Al ratios, used as a product ivity proxy, are variable but high in all deep-sea cores of the Arabian Sea , indicating a basin-wide influence of nutrient-rich water masses. Compared to glacial intervals the warmer periods are characterised by higher elemen t/Al ratios of proxies, which are directly (Ba, Ca, Sr, P, i.e. hard parts of organisms) or indirectly (U, Th-230(ex)) related to biological productiv ity. Th-230(ex) provides evidence for intense boundary scavenging caused by high productivity due to enhanced upwelling and terrigenous input from the Indus fan. The Mn distribution in a core from the western Arabian Sea show s enrichments during interglacial periods and may indicate Mn export owing to the presence of a stronger oxygen-minimum zone. Several processes limit the applicability of proxies. Intercalated turbidites in the Jeep-sea cores can be identified by means of Si:AI, Ti/Al and Zr/Al ratios versus depth d ue to the enrichment of quartz, Ti-minerals and zircon in the basal layer. These elements are also important for the reconstruction of the history and extent of the the colian dust input. Diagenetic redistribution of redox se nsitive elements occurs at the boundaries between turbidites and "normal" p elagic sedimentation and may mask or destroy primary signals. (C) 2000 Else vier Science Ltd. All rights reserved.