The influence of the NE winter monsoon on productivity changes in the Gulfof Aden, NW Arabian Sea, during the last 530 ka as recorded by foraminifera

Benthic and selected planktic foraminifera and stable isotope records were determined in a piston core from the Gulf of Aden, NW Arabian Sea that span s the last 530 ka. The benthic foraminifera were grouped into four principa l assemblages using Q-mode Principal Component Analyses. Comparison of each of these assemblages with the fauna of the nearby regions enabled us to id entify their specific environmental requirements as a function of variabili ty in food supply and strength of the oxygen minimum zone and by that to us e them as indicators of surface water productivity. The benthic foraminifer al productivity indicators coupled with the record of Globigerina bulloides , a planktic foraminifer known to be sensitive to productivity changes in t he region, all indicate higher productivity during glacial intervals and pr oductivity similar to present or even reduced during interglacial stages. T his trend is opposite to the productivity pattern related to the SW summer monsoon of the Arabian Sea and indicates the role of the NE winter monsoon on the productivity of the Gulf of Aden. A period of exceptionally enhanced productivity is recognized in the Gulf of Aden region between similar to 6 0 and 13 kyr indicating the intensification of the NE winter monsoon to its maximal activity. Contemporaneous indication of increased productivity in other parts of the Arabian Sea, unexplained so far by the SW summer monsoon variability, might be related to the intensification of the NE winter mons oon. Another prominent event of high productivity, second in its extent to the last glacial productivity event is recognized between 430 and 460 kyr. These two events seem to correspond to periods of similar orbital positioni ng of rather low precession land eccentricity) amplitude for a relatively l ong period. Glacial boundary conditions seem to control to a large extent t he NE winter monsoon variability as also indicated by the dominance of the 100 ka cycle in the investigated time series. Secondary in their importance are the 23 and 41 ka cycles which seem also to contribute to the NE monsoo nal variability. Following the identification of productivity events relate d to the NE winter monsoon in the Gulf of Aden, it is possible now to exten d this observation to other parts of the Arabian Sea and consider the contr ibution of this monsoonal system to the productivity fluctuations preserved in the sedimentary records. (C) 2000 Elsevier Science B.V. All rights rese rved.