Asian winter monsoon imprint on Holocene SST changes at the northern coast of the South China Sea

Independent inference of the Asian winter monsoon (AWM), albeit achieved at several sparse sites, has reached no consensus for its variability through the Holocene. A sediment core from the northern coast of the South China Sea (SCS) was utilized to analyze organic biomarkers at (bi-)decadal resolution, unveiling how SCS oceanic conditions fingerprint the AWM signal. Generally, alkenone sea surface temperature (SST) record, resembling the temporal structures of integrated tropical SST over the past 7,500 years, shows abnormal cool temperatures (up to similar to 4 degrees C) during the Little Ice Age and between similar to 1,200 and 2,500 years BP, when windborne terrigenous hopane compounds experienced considerable increases superimposed on a general increasing trend. Our results, together with augmented SST gradient between the SCS coast and open ocean, consistently suggest AWM strengthening toward the late Holocene. An intensified AWM during cold intervals like the Little Ice Age would have provided strong positive feedback to enhance coastal cooling. Plain Language Summary Reconstructions of the Holocene Asian winter monsoon (AWM) history from terrestrial proxies are not only limited but also opposite, with both strengthening and weakening trends as reported. This study sheds additional insight into this controversy by analyzing the organic geochemistry of a sediment core at the northern coast of the South China Sea, where oceanic conditions such as sea surface temperature intensively interact with the AWM. We observed substantial surface cooling and a remarkable increase in terrestrial-sourced hopane content concurrently toward the late Holocene, with the maximum taking place during the Little Ice Age and between 1,200 and 2,500 years ago. Together with enhanced temperature contrast between the coast and open ocean, our results clearly demonstrate an overall intensification of the Holocene AWM toward the present, antiphased with Asian summer monsoon changes.