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Amplitude and timing of sea-surface temperature change in the northern South China Sea: Dynamic link to the East Asian monsoon

¹ Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
² Department of Earth and Planetary Science, University of Tokyo, Tokyo 113-0033, Japan

Magnesium/calcium (Mg/Ca) ratios of foraminiferal shells from a sediment core from the northern South China Sea, a semi-enclosed basin in the western tropical Pacific, document variations in sea-surface temperature (SST) during the past 145 k.y. Glacial SSTs were 4 °C colder than interglacial SSTs. During the last deglaciation, most of the warming was accomplished in a single abrupt step after continental ice-sheet decay had already begun, but warming and ice-sheet demise were nearly synchronous during the penultimate deglaciation. Abrupt SST changes of the past 15 k.y. were apparently synchronous with events in East Asian monsoon rainfall, suggesting that variations in monsoon winds and their influence on surface circulation of the western Pacific exerted a strong control on northern South China Sea SSTs. We suggest that this link persisted for the previous 130 k.y., during which time orbital-scale 2–3 °C SST changes and several small (2 °C) abrupt SST events occurred in the northern South China Sea. The similar timing of northern South China Sea SST, on a benthic ¹⁸O time scale, to a well-dated speleothem record from eastern China suggests that the demise of ice sheets associated with the penultimate deglaciation did not precede Northern Hemisphere summer insolation increase. Our results suggest that surface waters had higher ¹⁸O values during times of strong summer monsoon than during times of weak monsoon, likely reflecting a redistribution of ¹⁸O-depleted rainfall from land during times of strong summer monsoons, to the western Pacific during times of weaker summer monsoons.

Key Words: Ocean Drilling Program Leg 184 • South China Sea • Mg/Ca • sea-surface temperature • East Asian summer monsoon • sea level.