Planktonic foraminiferal faunas from surface-sediment samples from the South China Sea and the western Pacific

We present 30 new planktonic foraminiferal census data of surface sediment samples from the South China Sea, recovered between 630 and 2883 m water depth. These new data, together with the 131 earlier published data sets from the western Pacific, are used for calibrating the SIMMAX-28 transfer function to estimate past sea-surface temperatures. This regional SIMMAX method offers a slightly better understanding of the marginal sea conditions of the South China Sea than the linear transfer function FP-12E, which is based only on open-ocean data. However, both methods are biased toward the tropical temperature regime because of the very limited data from temperate to subpolar regions. The SIMMAX formula was applied to sediment core 17940 from the northeastern South China Sea, with sedimentation rates of 20-80 cm/ka. Results revealed nearly unchanged summer temperatures around 28°C for the last 30 ky, while winter temperatures varied between 19.5°C in the last glacial maximum and 26°C during the Holocene. During Termination 1A, the winter estimates show a Younger Dryas cooling by 3°C subsequent to a temperature optimum of 24°C during the Bölling=Alleröd. Estimates of winter temperature differences between 0 and 100 m water depth document the seasonal variations in the thickness of the mixed layer and provide a new proxy for estimating past changes in the strength of the winter monsoon.

本研究报道了30组新的南海表层沉积物样品浮游有孔虫（planktonic foraminiferal）群落普查计数数据，样品采集自水深630~2883 m的海域。将这批新数据与西太平洋地区已发表的131组既往数据集相结合，用于校准SIMMAX-28转移函数（transfer function），以重建古海表温度。相较于仅基于开阔大洋数据构建的线性转移函数FP-12E，该区域化SIMMAX方法对南海边缘海环境的解析精度略有提升。但由于温带至亚极区的观测数据极为有限，两种方法均对热带温度域存在系统性偏差。研究将SIMMAX公式应用于南海东北部的17940号沉积岩芯，该岩芯的沉积速率为20~80 cm/ka。结果显示，过去3万年以来夏季海表温度基本维持在28℃左右，冬季海表温度则在末次冰盛期的19.5℃与全新世的26℃之间波动。在冰消期1A（Termination 1A）阶段，冬季温度重建结果显示，在博林-阿勒罗德暖期（Bølling-Allerød）达到24℃的温度峰值后，新仙女木事件（Younger Dryas）导致温度下降了3℃。通过估算0~100 m水深范围内的冬季温度差，可揭示混合层（mixed layer）厚度的季节变化特征，并为重建冬季风强度的古演化过程提供全新的代用指标（proxy）。