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

Five deep-sea cores from the Arabian Sea, covering a time interval of 170 ky, were sampled at high resolution and analysed for major and trace elements. 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 between Ba concentrations (or Ba/Al ratios) and oxygen isotope ratios (δ18O) of foraminifera in Arabian Sea sediments. Ba/Al ratios, used as a productivity 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 element/Al ratios of proxies, which are directly (Ba, Ca, Sr, P, i.e. hard parts of organisms) or indirectly (U, 230Thex) related to biological productivity. 230Thex 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 shows 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 deep-sea cores can be identified by means of Si/Al, Ti/Al and Zr/Al ratios versus depth due 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 eolian dust input. Diagenetic redistribution of redox sensitive elements occurs at the boundaries between turbidites and “normal” pelagic sedimentation and may mask or destroy primary signals.