NOAA/WDS Paleoclimatology - Oppo and Sun 2005 South China Sea d18O and Mg/Ca Data and SST Reconstruction

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 d18O 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 d18O 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.

取自西热带太平洋半封闭盆地——南海北部某沉积岩芯（sediment core）的有孔虫壳体（foraminiferal shells）镁钙比（Magnesium/calcium, Mg/Ca），记录了过去14.5万年以来的海面温度（sea-surface temperature, SST）变化。冰期海面温度较间冰期偏低4℃。在末次冰消期（last deglaciation）阶段，多数升温过程发生在大陆冰盖（continental ice-sheet）衰退已经启动之后的一次单一突变升温事件中，但倒数第二次冰消期（penultimate deglaciation）的升温与冰盖消亡几乎同步。过去1.5万年间的突发海面温度变化，显然与东亚季风降水（East Asian monsoon rainfall）事件同步，这表明季风环流及其对西太平洋表层环流的影响，对南海北部海面温度具有极强的调控作用。我们认为这一关联在此前的13万年中持续存在，在此期间南海北部发生了轨道尺度（orbital-scale）的2~3℃海面温度波动，以及数次幅度为2℃的小型突发海面温度事件。以底栖氧同位素（benthic δ¹⁸O）时间标尺衡量，南海北部海面温度与中国东部一则定年精确的石笋记录（speleothem record）在时间上高度吻合，这表明与倒数第二次冰消期相关的冰盖消亡并未早于北半球夏季日照量的增加。我们的研究结果显示，夏季风强盛时期的表层水体氧同位素18值高于季风衰弱时期，这大概率反映了夏季风强盛时陆地留存的贫18O降水，在季风衰弱时被重新分配至西太平洋区域。