A multi-proxy approach to investigating orbital and millennial paleoclimate variability in the Arabian Sea basin
Description
Organic and inorganic geochemical proxies from two cores in the northeastern (NE) and western Arabian Sea were employed to study orbital and suborbital climate variability of the Indian Ocean monsoons. In the NE Arabian Sea 230Th-nonnalized 232Th fluxes and authigenic uranium concentrations were interpreted as indicators for eolian input and paleo-productivity, respectively. The highest eolian fluxes occur at times consistent with the North Atlantic (NA) millennial-scale cold intervals recorded in the GISP2 ice core. Paleoproductivity was highest during warn interstadials when the SW monsoon was intensified. Maximum average eolian fluxes coincide with the timing of marine isotopic stage 2 and 4, while minimum fluxes occur during MIS 1, 3 and 5 231Pa/230Th activity ratios and diatom biomarker fluxes were measured in sediments from NE Arabian Sea to examine the influence global thermohaline circulation (THC) over the last 50 ka. 231Pa/230Th were significantly higher than the production ratio of 0.093, which indicates exceptionally high rates of particle scavenging. Lower average 231Pa/230Th ratios occurred during the last glacial with lowest 231Pa/230Th ratios coinciding with the timing of Heinrich Events 1 - 5. In the Holocene, high 231pa/230Th ratios may indicate enhanced 231 Pa export from the southern to the northern Indian Ocean via intensified THC Organic biomarker fluxes and alkenone-derived sea surface temperatures (SST) were measured in sediments from the western Arabian Sea. The average glacial-Holocene temperature difference was ∼3°C with an interval of exceptionally low SSTs between 19 to 18.1 ka BP (15.3°C at 18.5 ka). The lowest SSTs coincided with highest cumulative biomarker fluxes. We propose that intensification of the winter NE monsoon winds during the glacial period resulted in cold SSTs, deep convective mixing, and enhanced primary productivity. Following the last termination, and within the Holocene, SSTs vary by ∼2°C with high CBFs occurring at times of relatively warmer SSTs. Transitioning from the glacial to the Holocene, diatom fluxes relative to the total flux of organisms increased, while those of coccolithophorids decreased. A shift in the planktonic ecosystem structure in the Arabian Sea may have important implications for the global biogeochemical cycle of carbon