Millennial-Scale Variations in Alkenone-Based Sea-Surface Temperature and Productivity Reconstructions in the Arabian Sea

The Arabian Sea is strongly influenced by upwelling induced by the SW Indian Monsoon, particularly on the Oman Margin. Monsoon strength has been shown to vary over millennial timescales as a result of insolation changes and atmospheric teleconnections to the North Atlantic. These variations are recorded by alkenones preserved in the Oman Margin sediments. Deep-sea sediments from two sites in the NW Arabian Sea were analyzed for alkenones to determine the record of millennial scale variations in sea surface temperature and productivity between 0 and 15 mbsf (approximately 0-70ka from correlations to d18O of Greenland ice cores GRIP &. GISP2). Sites 723 (ODP) and RC27-14 are located on the Oman Margin at water depths of 808m and 590m, respectively. Both cores are located within the Oxygen Minimum Zone (OMZ), which is characterized by high sedimentation rates and well-preserved organic matter. SST estimates were established from measurements of the alkenone unsaturation index (Uk'37) while productivity variations were estimated by total alkenone concentrations. SST's appear to be positively related to total alkenone concentrations on millennial timescales and inversely correlated over longer periods of time. Additionally, alkenone-based SST values and total alkenone concentration both display covariance to proxy measurements of productivity and OMZ strength, including d15N, %N and chlorin abundance, all of which have been successfully correlated to Dansgaard-Oeschger cycles recorded in Greenland ice cores. More specifically, on the millennial timescale, periods of increased SST and high productivity in the Arabian Sea, presumably periods of a relatively strong SW Monsoon, correspond to milder periods within the Dansgaard-Oeschger oscillations. This work suggests that the strength of the SW Indian Monsoon, which affects SST and productivity in the region, responds to millennial-scale climate oscillations that are recorded in Arabian Sea sediments.