| Summary: | Two sediment cores from the western Arabian Sea, NIOP905 and 74KL, were analyzed to determine sea surface temperature (SST) variations over the last 23 kyr. Two organic molecular SST proxies were used, the well-established U37K' based on long-chain unsaturated ketones synthesized by haptophyte algae and the newly proposed TEX86 derived from the membrane lipids of Crenarchaeota. Comparison of NIOP905 and 74KL core top data with present-day SST (0-10 m) values indicates that both proxies yield temperatures similar to local annual mean SSTs. However, TEX86 and U37K' SST down-core records derived from the same cores differ in magnitude and phasing. The alkenone SST record of NIOP905 shows small changes in SST (∼0.5°C) over the last 23 kyr, while that of core 74KL shows a ∼2°C increase from the Last Glacial Maximum (LGM) (23-19 calendar (cal) kyr B.P.) through the Holocene (the last 11.5 cal kyr B.P.) synchronous with changes in the Northern Hemisphere. In contrast, the TEX86 records of both cores show a large increase in SST from 22°-23°C in the LGM to 28°-30°C during Termination I (19-11.5 cal kyr B.P.), decreasing to present-day annual means of ∼26°C. A cold phase between 14.5 and 12 cal kyr B.P. that may correspond to the Antarctic cold reversal is also observed. This implies a Southern Hemisphere control on tropical SST reconstructed by the TEX86, possibly related to SW monsoon. Our results suggest that the application of both TEX86 and U37K' give different but complementary information on SST developments in past marine environments.
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