Benthic foraminiferal response to Late Quaternary variations in surface water productivity and oxygenation in the northern Arabian Sea

This thesis discusses benthic foraminifera in Late Quaternary records from within and below the northern Arabian Sea OMZ and their interpretation in terms of past changes in surface water productivity and midwater oxygenation (Chapters 2-5). Because the present contention is that multiproxy studies lead to better assessment of the paleoenvironment, this research has been conducted in a multidisciplinary way. In particular, various geochemical tracers are employed (Chapters 2-4, 6), but a comparison is also made with a number of lithogenic proxies (Chapter 3). The overall picture shows that large variations occurred in the intensity of the OMZ during the last 225 kyr, and that the base of the OMZ occasionally extended well below its present-day position. Variability took place on orbital and sub-orbital time scales and is presumably controlled by 1) changes in summer monsoon wind strength, which controls summer surface water productivity via coastal and open ocean upwelling and thus subsurface oxygen consumption, and 2) deep convective mixing during periods of cold and intensified winter monsoons. The close correlation of sub-orbital monsoon-driven OMZ variability in the Arabian Sea with rapid climatic fluctuations at high northern latitudes suggests a close coupling between high and low latitude climates (Chapter 3)