During the middle Miocene, Earth's climate changed from a global warm period (Miocene Climatic Optimum) into a colder one with the expansion of the Antarctic ice sheet. This prominent climate transition was also a period of drastic changes in global atmospheric circulation. The development of the South Asian monsoon is not well understood and mainly derived from proxy records of wind strength. Data for middle Miocene changes in rainfall are virtually non‐existent for India and the Arabian Sea prior to 11 Ma. This study presents planktic foraminiferal trace element (Mg/Ca and Ba/Ca) and stable oxygen isotope records from NGHP‐01 Site 01A off the coast of West India in the Eastern Arabian Sea (EAS) to reconstruct the regional surface hydrography and hydroclimate in the South Asian monsoon (SAM) region during the middle Miocene. The Ba/Ca and local seawater δ¹⁸O (δ¹⁸Osw) changes reveal a notable gradual increase in SAM rainfall intensity during the middle Miocene. Additionally to this long‐term increase in precipitation, the seawater δ¹⁸O is punctuated by a prominent decrease, i.e. freshening, at ~14 Ma contemporary with Antarctic glaciation. This suggests that Southern Ocean Intermediate Waters (SOIW) transmitted Antarctic salinity changes into the Arabian Sea via an “oceanic tunnel” mechanism. The middle Miocene increase in SAM rainfall is consistent with climate model simulations of an overall strengthening Asian monsoon from the Eocene to the middle/late Miocene with a further acceleration after the middle Miocene climate transition.

中文翻译：

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南亚季风降水的中新世中期加剧

在中新世中期，随着南极冰盖的扩大，地球的气候从全球温暖期（中新世最佳气候）转变为较冷的气候。这一突出的气候过渡时期也是全球大气环流急剧变化的时期。对南亚季风的发展还没有很好的了解，主要来自风强度的代理记录。在11 Ma之前，印度和阿拉伯海几乎没有中新世中期降水变化的数据。这项研究显示了东印度洋东部阿拉伯海（EAS）NGHP-01站点01A上的板状有孔虫微量元素（Mg / Ca和Ba / Ca）和稳定的氧同位素记录，以重建东亚海域的区域地表水文学和水文气候中新世中期的南亚季风（SAM）地区。¹⁸ O（δ ¹⁸ OSW）的变化揭示SAM降雨强度中中新世期间的显着逐渐增加。另外在此沉淀长期增长，δ海水¹⁸ O由一个突出的下降，即清新打断，在14〜马当代与南极冰川。这表明南大洋中间水域（SOIW）通过“海洋隧道”机制将南极盐度变化传播到阿拉伯海。中新世中期中雨量增加与气候模式模拟结果一致，该模拟模拟了从始新世到中/中新世中期总体上亚洲增强的季风，并且在中新世中期气候转变之后进一步加速。