Contrast in surface water δ18O distributions between the Last Glacial Maximum and the Holocene in the Southern South China Sea

Published core data of planktonic foraminiferal δ18O and alkenone sea surface temperature (SST) are used to investigate seawater δ18O (δwδw) distributions in the South China Sea (SCS) during the Last Glacial Maximum (LGM) and the Holocene. The Holocene δw distributions show a pattern correlated to modern salinity distributions displaying an increasing trend from the south to the north. However, the LGM δwδw distributions show a different pattern displaying increasing values from the central to the southern SCS, and the LGM-Holocene differences in δwδw (ΔδwΔδw) corrected by ice-volume effect, though negative in values, display decreasing amplitude toward the south, both of which could suggest increasing salinity toward the south by conventional approach. This is somewhat counter-intuitive because enhanced freshening could be expected for the southern SCS due to extra discharge from the river systems on the emerged Sunda Land during the LGM. Here, we propose an alternative explanation to reconcile the LGM δwδw and ΔδwΔδw distributions with the above expectation. In the proposal, changes in δwδw–salinity relationship, i.e. lowering the δwδw–salinity slope due to significant runoff contributions to freshwater input and less 18O-depleted precipitation during the LGM, are deeply discussed to reasonably explain the abnormity in LGM δwδw distributions.