ANNUAL TO MILLENNIAL MONSOONAL VARIABILITY DURING THE PAST 75,000 YEARS RECORDED IN ARABIAN SEA SEDIMENTS: A REVIEW

The Arabian Sea is a key area for addressing questions about the annual to millennial variability of the Indian monsoon. During the Late Holocene laminated (varved) sediments were deposited in the oxygen minimum zone (OMZ) off Pakistan which can be correlated in all our cores and allow ultra-high-resolution paleoclimate studies. Varve counting, checked by AMS-¹⁴C dating, detailed lithofacies analysis, X-ray fluorescence scanning, flux rates from sediment traps, and the lamina-by-lamina-analysis of a five-year record (1993-1998) support our interpretation of the annual character of the varves.

We used a high-resolution laminated sediment record from the OMZ off Pakistan to investigate the Late Holocene climatic change in great detail. Independant proxies ( varve thickness, inorganic geochemical composition, alkenone-derived sea surface temperatures and oxygen isotopes of planktic foraminifera) reflect the monsoon-driven ”moisture history“ in the northeastern Arabian Sea during the past 5000 years. Maximum precipitation during the enhanced NE monsoon around 3100-3200 y BP was followed by an onset of a gradual aridification around 3000 yrs BP which continued until about 2000 to 2200 y BP.

Millennial changes of monsoonal intensity are also recorded in the Late Pleistocene sediments: Short-term “warm” interstadials (“Dansgard-Oeschger events”) alternate with cool stadials (“Heinrich events”) that can be correlated (by the Toba ashfall) with the same events in the ice cores from Greenland, and with many high-resolution climate records from subtropical northern hemisphere areas. Apparently, these synchronous teleconnections between the subtropical Indian Ocean and the high-latitude North Atlantic Ocean. are forced by the high-frequency varability of the atmospheric monsoon circulation.