We reconstructed the variability of the Earth's strongest hydrological system, the Indian monsoon, over the interval 6.24 to 4.91 Ma at International Ocean Discovery Program (IODP) Expedition 353 Site U1448 in the Andaman Sea. We integrated high‐resolution benthic and planktic foraminiferal carbon and oxygen isotopes with Mg/Ca measurements of the mixed layer foraminifer Trilobatus sacculifer to reconstruct the isotopic composition of seawater (δ¹⁸O_sw) and the gradient between planktic and benthic foraminiferal δ¹³C. A prominent increase in mixed layer temperatures of ~4°C occurred between 5.55 and 5.28 Ma, accompanied by a change from precession‐ to obliquity‐driven variability in planktic δ¹⁸O and δ¹⁸O_sw. We suggest that an intensified cross‐equatorial transport of heat and moisture, paced by obliquity, led to increased summer monsoon precipitation during warm stages after 5.55 Ma. Transient cold stages were characterized by reduced mixed layer temperatures and summer monsoon failure, thus resembling late Pleistocene stadials. In contrast, an overall cooler background climate state with a strengthened biological pump prevailed prior to 5.55 Ma. These findings highlight the importance of internal feedback processes for the long‐term evolution of the Indian monsoon.

中文翻译：

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中新世-上新世过渡期安达曼海印度季风的变化

我们在安达曼海的国际海洋发现计划（IODP）353号考察站点U1448上重建了地球上最强的水文系统印度季风在6.24至4.91 Ma范围内的变异性。我们集成有孔虫混合层的镁/钙测量高分辨率海底和浮游有孔虫碳，氧同位素Trilobatus sacculifer重建海水的同位素组成（δ ¹⁸ ö _SW）和浮游和底栖有孔虫δ之间的梯度¹³ C. 5.55和5.28之间马发生在〜4℃的混合层的温度的一个突出的增加，伴随着从precession-到倾角驱动变异浮游δ的变化¹⁸ O和δ¹⁸ O _sw。我们认为，随着倾斜的加剧，越过赤道的热量和水分跨界输送会导致5.55 Ma之后的暖季夏季季风降水增加。瞬态寒冷阶段的特征是混合层温度降低和夏季季风破坏，因此类似于更新世晚期。相反，在5.55 Ma之前，总体上较凉爽的背景气候状态盛行，而生物泵则得到加强。这些发现凸显了内部反馈过程对于印度季风长期演变的重要性。