Modern tropical and subtropical C₄ grasslands and savannas were established during the late‐Miocene and Pliocene, over 20 Myr after evolutionary originations of the C₄ photosynthetic pathway. This lag suggests environmental factors first limited and then favored C₄ plants. Here, we examine the timing and drivers for the establishment of C₄ grasslands on the Indian Subcontinent using carbon and hydrogen isotope signatures of plant‐wax n‐alkanes recovered from turbidites in the Bengal Fan. Like prior studies, we find C₄ ecosystems in the Ganges‐Brahmaputra catchment first emerged at 7.4 Ma and subsequently expanded between 6.9 to ∼6.0 Ma. Hydrogen isotope values varied from 10.2 to 7.4 Ma and then increased after 7.4, which suggests intermittent drying began before the establishment of C₄ grasslands with further drying at the onset of C₄ expansion. Synthesis of published plant fossil data from the Siwalik Group of the Himalayan foreland basin documents an ecosystem trajectory from evergreen tropical forests to seasonally deciduous forests, and then expansive C₄ grasslands. This trajectory coincided with a seasonally uneven drying trend due to both increased evaporation of plant leaf and soil waters and reduced rainfall, as identified in soil carbonate and tooth enamel data sets. Collectively the fossil, biomarker, and isotopic evidence reveal the development of modern C₄ ecosystems on the Indian Subcontinent followed a series of ecosystem transformations driven by drying and fire feedbacks, and possibly declining atmospheric pCO₂, beginning at 10.2 Ma and strengthening through the late Miocene.

中文翻译：

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水文变化推动了印度北部次大陆C4草原的中新世晚期扩张

在中新世和上新世晚期，在C ₄光合途径的进化起源之后，超过20 Myr，建立了现代热带和亚热带C ₄草原和热带稀树草原。这种滞后表明环境因素首先受到限制，然后有利于C ₄植物。在这里，我们使用从孟加拉扇混浊物中回收的植物蜡正烷烃的碳和氢同位素特征，研究了在印度次大陆上建立C ₄草原的时机和动因。像以前的研究一样，我们发现C ₄恒河-布拉马普特拉河流域的生态系统首先出现在7.4 Ma处，然后在6.9Ma〜〜6.0 Ma之间扩展。氢同位素值从10.2到7.4 Ma，然后在7.4 Ma之后增加，这表明间歇干燥开始于建立C ₄草原之前，并在C ₄膨胀开始时进一步干燥。喜马拉雅前陆盆地西瓦利克群已发表植物化石数据的综合记录了从常绿热带森林到季节性落叶森林再到膨胀C ₄的生态系统轨迹草原。如土壤碳酸盐和牙釉质数据集所示，由于植物叶片和土壤水分的蒸发增加以及降雨减少，该轨迹与季节性不均匀的干燥趋势相吻合。化石，生物标志物和同位素证据共同揭示了印度次大陆上现代C ₄生态系统的发展，此过程是由干旱和火灾反馈驱动的一系列生态系统转变所致，大气pCO ₂可能下降，始于10.2 Ma，并一直持续到后期。中新世。