轨道-亚轨道尺度上西太平洋热带辐合带的演化及其驱动机制

The intensity and distribution of precipitation in the Western Pacific Warm Pool (WPWP), East Asia and Southeast Asia are mainly controlled by the Intertropical Convergence Zone (ITCZ) varies in the western Pacific. To date, the researches largely focus on its variations on decadal- and centennial-scale. However, little is known about its variabilities on long time scales such as multi-millennial scale and precession-scale. Moreover, there are also lots of contradictory views on the evolution and related driving mechanism of ITCZ on different time scales. For the purpose of better cognizing the precipitation in the past and simulating trend of precipitation in the future in the WPWP area, it’s critical to understand the evolution pattern and related major drivers in long scales and to qualify the boundary conditions of models and check the accuracy of the prediction results. In this program, we plan to reconstruct the variation of sea surface temperature, salinity and vertical structure in the core region of WPWP over the past 360, 000 years using the δ18O and Mg/Ca of multi-species planktonic foraminiferal calcite in the core KX97322-4, which is taken from the Ontong Java Plateau. Combined with other records in the western Pacific and multiple proxies of East Asia summer monsoon precipitation, we aim to reconstruct the distribution of precipitation in the western Pacific during the last four glacial-interglacial cycles and to reveal the evolutionary pattern of ITCZ on orbital- and sub-orbital-scales. Based on spectral analysis, wavelet analysis, cause-effect relationship analysis between time series and model simulation, we propose to discover the correlation between the evolution of ITCZ and changes of insolation, high and low latitude process (ice volume variation, paleo-ENSO and thermohaline circulation) and ultimately, to explore the main driving mechanism of the ITCZ evolution.

西太平洋地区热带辐合带（ITCZ）的演变对西太平洋暖池（WPWP）、东亚和东南亚的降雨强度和分布状况等具有重要影响。但目前对其演变的研究多集中于百年和年代际尺度，更长尺度的研究相对匮乏。另外，不同尺度上ITCZ的演化规律及驱动机制也存在很多争议。为了解过去和准确模拟未来西太平洋地区的降雨变化趋势，需要明确ITCZ在长尺度上的演化过程及驱动机制。本项目拟利用翁通-爪哇海台KX97322-4岩心生活在不同水深的多种浮游有孔虫壳体氧同位素和镁钙比指标，重建过去36万年来WPWP表层水体的垂直结构、温度、盐度等参数的变化；再结合西太平洋其他钻孔结果及多种与东亚夏季风降雨相关的指标记录，重建最近四个冰期旋回中西太平洋地区的降雨分布状况，反映ITCZ在轨道-亚轨道尺度上的演化过程；最后通过数据分析和模型模拟等多种手段发掘ITCZ演变与太阳辐射、高低纬度过程之间的关系，探讨ITCZ演化的主要驱动机制。

西太平洋地区水文变化主要受控于热带辐合带（ITCZ）经向变化及厄尔尼诺-南方涛动（ENSO）过程的纬向变化的调节。而对二者的研究多集中于近代及短尺度，在千年以上的时间尺度上的研究相对匮乏，且存在诸多争议。本项目利用西太平洋海区翁通-爪哇海台KX97322-4岩心多种浮游有孔虫壳体记录的过去海水温盐信息，结合整个西太平洋海区多个沉积记录及陆地记录，重构了过去36万年以来西太平洋暖池区（WPWP）上部水体的温盐结构变化，并反演过去ITCZ和古ENSO的演化情况，揭示了相应的驱动机制。研究结果表明，在岁差尺度上，WPWP的次表层温盐变化比表层更加剧烈，且与古ENSO过程密切相关，并受南太平洋亚热带海表温盐状况的影响。结合模型模拟和沉积记录，本研究认为南半球亚热带潜沉区记录的太阳辐射信息受经向温度梯度调节，通过海洋隧道传送到赤道太平洋海区并改变该海区纬向上部水体的温盐结构（包括海表温度及温跃层梯度）以调控岁差尺度上古ENSO的演化过程。岁差极大值期对应古拉尼娜态，而岁差极小值期对应古厄尔尼诺态。另外，通过对西太平洋海区多个站位的海水氧同位素记录、陆地石笋氧同位素记录及植被记录等对比、分析，结果显示冰期WPWP范围缩小且向东移动，赤道与亚热带间温度梯度加大并导致ITCZ向赤道收缩。本研究认为，在冰期间冰期的变化上，西太平洋海区可划分为五个区域（东中国海、南中国海、热带东印度洋、印尼海区及西太平洋东部的暖池核心区）。其中，东中国海在冰期间冰期上海水氧同位素较稳定，而由于ITCZ在冰期向赤道收缩，东亚地区降水减少，低纬海区整体降水增多，石笋氧同位素和海水氧同位素近乎反相关。而间冰期ITCZ向高纬度扩张，导致东亚地区降水增多而低纬海区降水减少。ITCZ的经向收缩扩张对应岁差极值的变化，且降雨分布随着升温有湿者更湿、干者更干的现象。另外，冰期西太平洋东部海区降水增多而东热带印度洋降水减少，对应WPWP的东移或东缩。