Reconstruction of upwelling intensity and paleo-nutrient gradients in the northwest Arabian Sea derived from stable carbon and oxygen isotopes of planktic foraminifera.

The Asian Monsoon system dominates the climate over large areas of the Asian and Indian continents and the rainfall prevailing during SW-monsoon is decisive for the agriculture of the entire region. The atmospheric monsoon system dominates the oceanographic surface circulation of the northern Indian Ocean and causes strong upwelling off Somalia and Arabia during SW-monsoon and makes the northwestern Arabian Sea to one of the most productive areas in the world oceans. Thus, productivity and nutrient gradients in the northwestern Arabian Sea are important parameters for an understanding of the oceanic response to monsoonal forcing.Stable oxygen and carbon isotopes (q I8 O, q l3 C) of seawater and planktic foraminifera reveal modern and past nutrient gradients in the monsoonal upwelling area of the northwestern Arabian Sea. The modern conditions were analyzed by hydrographic observations and seawater isotope measurements during the NE- and SW-monsoon season.