Influence of East Asian Monsoon and ENSO to the Holocene Hydroclimate deduced from Northwestern Pacific corals

在日本菊海岛和菲律宾吕宋岛西北部采集了24份孔隙岩样品。4960 yrBP重建的平均海温、夏季海温和冬季海温均高于现代海温，5712和3235 yrBP的海温相对较低。吕宋岛西北部4200年BP珊瑚的重建平均海温与现在相当，但温暖月份的持续时间较短。地球化学和珊瑚生长证据支持了全新世中晚期热带菲律宾比亚热带日本南部更温暖。西北太平洋的海洋状况受季风环流的季节变化所调节，在东亚季风（EAWM）期间，海表温度（SST）变暖（冷）、降水高（低）、盐度低（高）和δ 18o为负（正）。然而，这些季节性信号的时间在热带和亚热带地区的不同时间窗中有所不同。结合以往日本南部地区的δ18Ocoral记录，我们发现全新世中后期东亚季风降水减弱。负的δ 18o海水和δ13Ccoral决定了6 - 11月菲律宾北部的东亚季风持续时间，比现在的时间要长。与持续温暖（28-30°C）的现代海温相比，4200 BP的珊瑚表明，8月份热带海温的突然下降减少了东亚热带外经（15-30°N）海温梯度和水分供应。

Twenty-four Porites samples were collected from Kikaijima, Japan and Northwest Luzon, Philippines. Sr/Ca-based reconstructed mean, summer, and winter SSTs from 4960 yrBP coral show higher values relative to the modern SST in Kikaijima. 5712 and 3235 yr BP were relatively cooler than the present-day. Reconstructed mean SST from 4200 yr BP coral from Northwest Luzon was comparable to the present-day but the duration of warmer months was shorter. The tropical Philippines was warmer than subtropical Southern Japan during mid- to late Holocene transition as supported by geochemical and coral growth evidence.The ocean condition in Northwestern Pacific is modulated by the seasonal shift of monsoon circulation with warm (cool) sea surface temperature (SST), high (low) rainfall, low (high) salinity and negative (positive) δ18Oseawater during EASM (EAWM). However, the timing of these seasonal signals varies in different time-windows across the tropical and subtropical region. Together with δ18Ocoral records of previous studies from Southern Japan, we demonstrate the weakening of EASM rainfall from mid- to late Holocene. Negative δ18Oseawater and δ13Ccoral define the duration of the EASM in Northern Philippines from June to November, which was relatively longer than the present-day. In contrast to the sustained warm (28-30°C) modern-day SST, our 4200 BP coral suggests that sudden drop of tropical SST in August has reduced the meridional (15-30°N) SST gradient and moisture supply in extratropical East Asia.