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

24份Porite样本来自日本的Kikaijima和菲律宾的吕宋岛西北部。从4960yrBP珊瑚重建的平均海温、夏季海温和冬季海温显示出比Kikaijima现代海温更高的海温。5712年和3235年BP比今天相对凉爽。由吕宋岛西北部4200年BP珊瑚重建的平均SST与现在相当，但较暖月份的持续时间较短。在全新世中晚期，菲律宾热带海区比日本南部副热带海区温暖，这是由地球化学和珊瑚生长证据支持的。西北太平洋的海洋状况受到季风环流季节变化的调制，季风环流在东亚夏季风期间具有暖(冷)海表面温度、高(低)降雨量、低(高)盐度和负(正)δ180度海水。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口中有所不同。结合日本南部以往研究的δ180珊瑚记录，我们证实了东亚夏季风降水在全新世中晚期的减弱。负δ18O海水和δ13C珊瑚定义了菲律宾北部东亚夏季风的持续时间为6-11月，这一持续时间比现在相对较长。与现代持续温暖(28-30℃)的SST相比，我们的4200BP珊瑚表明，8月份热带SST的突然下降降低了经向(15-30°N)SST梯度和东亚温带外的水汽供应。

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.