晚第四纪热带表层海水氧同位素演化与水循环

Tropical hydrological cycle is a crucial aspect for a full understanding of past global change. We propose to study the hydrological cycle through checking changes in the tropical sea surface oxygen isotope. Accordingly to current dataset we notice some distinct characteristics in the late Quaternary tropical sea surface oxygen isotope records, including anomalous positive excursions at glacial terminations and secular trends across glacial cycles. These distinct signals are also observed in oxygen isotope records of atmospheric oxygen and stalagmites. We further propose a scientific hypothesis that past changes in the moisture flux between the sea and the land (monsoon rainfall) rather than the ice volume drive these special changes in sea surface oxygen isotope records. In order to verify this hypothesis, a research plan is suggested: (1) A re-compilation of global sea surface oxygen isotope reconstructions is necessary. (2) A high-resolution of the late Quaternary sea surface oxygen isotope record from the western Pacific will be produced. These together will lead to a generation of a new integrated tropical sea surface oxygen isotope record, which can be employed to test the existence of the aforementioned distinct isotopic signals. (3) Existing data suggest that the evolution of the African monsoon possibly shows secular trends across glacial cycles. A marine sedimentary sequence from the eastern Mediterranean is therefore used to reconstruct the North African monsoon history during the Quaternary, which is further used to test the possible linkage between monsoon and sea surface oxygen isotopic evolution.

热带水循环是全球古环境研究的重要课题。本项目以表层海水氧同位素记录为切入点来研究水循环变化。在前期研究中我们发现晚第四纪全球热带表层海水氧同位素记录呈现出一些独特的演化特征，包括冰期终止期时的异常重值信号和跨越冰期旋回尺度的长期趋势。这些特殊演化信号也同样出现在大气氧气和石笋氧同位素记录中。本项目提出一个假说，认为这些特殊信号很可能指示了海洋向陆地输送水汽量的变化(即季风降雨变化)。为了验证该假说，提出如下计划：(1)重新收集和处理全球热带大洋相关数据。(2)为了弥补现有数据不足，在西太平洋选取一个钻孔进行高分辨率的表层海水氧同位素记录重建。最终将得到一个新的热带表层海水氧同位素合成记录并且验证上述独特的演化信号是否真实存在。(3)已有数据表明非洲季风变化最有可能展示出跨越冰期旋回的长趋势变化。因此计划利用东地中海沉积记录重建晚第四纪北非季风历史，并且验证季风系统与海水同位素演化的关联性。

热带表层海水氧同位素是理解低纬水循环的重要切入点。本项目通过收集已有数据和重建新的海水同位素记录，并结合同位素数值模拟结果，探索第四纪表层海水氧同位素演化特征及其对陆地降水同位素记录的影响。项目取得三个主要认识：首先，发现第四纪热带表层海水同位素与陆地降水同位素的演化存在相似特征，说明海-陆之间的水汽输送可以传递独特的同位素信号。其次，以表层海水氧同位素作为校正基准，提出80万年以来“道尔效应”波动可以指示低纬陆地降水量变化。道尔效应明确展示了2万年岁差周期对低纬水循环强度的主控作用。 第三，利用表层海水氧同位素校正陆地石笋和陆源烷烃氢同位素记录，发现晚第四纪东亚低纬降水同位素变化在岁差周期上存在空间差异性。这种差异性揭示岁差会改变进入东亚大陆的太平洋/印度洋水汽配比。..在项目支持下，已经发表3篇SCI一区论文，其中一篇论文发表在高影响力期刊Science Advances上。项目成果以大会邀请报告形式在全国学术会议上展示。项目负责人在2021年获得国家自然科学基金“优秀青年基金”项目的资助，将“低纬水循环地质演变”研究从第四纪扩展到温暖的中新世，探索不同气候边界条件下低纬水循环的演化特征和机理。