A key aspect of East Asian climate is its summer monsoonal system which influences nearly one-third of the world's population. Recent results indicate that the primary response of the East Asian summer monsoon (EASM) to anthropogenic forced climate warming may be a shift in geographical range instead of an intensity change, which would lead to spatial coexistence of floods and droughts over southeastern Asia. The predicted EASM variability in the future has made it paramount to study its past changes and the associated tempo-spatial pattern of aridity and humidity in its purview. In order to decipher past changes in EASM, we applied a multi-proxy geochemical approach to the sediment core ORI-891-16-P1 located in the northern South China Sea. The position of this sediment core on top of a seamount makes it uniquely sensitive to changes in the terrigenous input into northern South China Sea unbiased by sea level-induced downslope transport processes. Utilizing the ln(Ti/Ca) ratio throughout the sediment sequence we trace terrigenous influx changes reflecting EASM prevalence during the last ~40 kyrs. Based on the comparison of our results to previous studies we infer that the Last Glacial Maximum (LGM; ~ 20 ka BP) was characterized by a steep N-S humidity gradient. This spatial pattern was in line with a southward shift or contraction of the summer monsoonal trough of 10–15° from its current position toward the centre of the South China Sea. Superimposed on orbital time scale fluctuations we also find strong indication of millennial-scale variability related to Heinrich Stadials. The impact of Heinrich Stadials on the EASM seems amplified during insolation minima, while high summer insolation seems to buffer the monsoonal system to such perturbations. We infer that (i) the humidity-aridity distribution during the LGM mimics predictions of the proposed future EASM configuration, and (ii) that the sensitivity of the EASM to weakening in the Atlantic Meridional Overturning Circulation is the strongest since the last glacial.

东亚气候的一个关键方面是夏季季风系统，它影响着世界近三分之一的人口。最近的研究结果表明，东亚夏季风（EASM）对人为强迫气候变暖的主要响应可能是地理范围的变化，而不是强度变化，这将导致东南亚地区洪水和干旱的空间共存。预测的未来 EASM 变化使得研究其过去的变化以及相关的干旱和湿度时空模式变得至关重要。为了破译 EASM 过去的变化，我们对位于南海北部的沉积岩芯 ORI-891-16-P1 应用了多代理地球化学方法。该沉积物核心位于海山顶部，使其对南海北部陆源输入的变化特别敏感，不受海平面引起的下坡输送过程的影响。利用整个沉积物序列中的 ln(Ti/Ca) 比率，我们追踪反映了过去 40 kyrs 期间 EASM 流行的陆源流入变化。根据我们的结果与先前研究的比较，我们推断末次冰期最大值 (LGM; ~ 20 ka BP) 的特征是陡峭的 NS 湿度梯度。这种空间格局与夏季季风槽从当前位置向南海中心的南移或收缩10-15°相一致。叠加在轨道时间尺度波动上，我们还发现与 Heinrich Stadials 相关的千禧年尺度变化的强烈迹象。Heinrich Stadials 对 EASM 的影响在日照最小值期间似乎被放大，而夏季高日照似乎缓冲了季风系统对这种扰动的影响。我们推断 (i) LGM 期间的湿度 - 干旱分布模拟了对拟议的未来 EASM 配置的预测，以及 (ii) EASM 对大西洋经向翻转环流减弱的敏感性是自上次冰川以来最强的。