Annual to Millennial Monsoonal Cyclicity Recorded in Holocene Varved Sediments from the NE Arabian Sea

Tbe Arabian Sea is a key area for addressing questions about the annual to millennial vmability of the Indian monsoon Dunng the Late Holocene, laminated (varved) sediments were deposlted 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 hthofacies analysis, X-ray fluorescence scanning, flux data 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 suggest that short-term heavy rainfall leads to flood events, causing the deposition of light-colored layers on the continental slope.

We used a high-resolution laminated sediment record from the OMZ off Pakistan to investigate the Late Holocene climatic change In great detail Three independent proxies - varve thickness, stable oxygen isotope ratios and inorganic geochemival composition- reflect the monsoon-driven "moisture history" in the northeastern Arabian Sea dunng the past 5000 years Maximum precipitation during the enhanced NE monsoon around 3 100-3200 yr B P was followed by the onset of a gradual andification around 3000 yr B P whrch continued until about 2000 to 2200 yr B P Alkenone derived Sea Surface Temperature (SST) and oxygen isotopes of planktonic forarminifera helped to reconstruct the monsoon variability dunng the Late Holocene.

We also searched for cyclicity in the series of varve thickness The sequence of cycles detected by autocorrelation and standard Founer analysis indicates that a large proportion of the cyclicity detected can be ascribed to lunar tidal action Similar cycles were detected In the Santa Barbara Basln, suggesting that these cycles are extraterrestrially forced and of global importance Our record also contains evidence for the presence of the 1470-year cycle that is well known from the Greenland ice record.