Fire dynamics potentially account for the asynchronous timing of the expansion of C₄ grasslands throughout the Mio‐Pliocene world. Yet how fire, climate, and ecosystems interacted in different settings remain poorly constrained because it is difficult to quantify fires and fuel source over these timescales. Here, we apply molecular proxies for fire occurrence alongside records of vegetation change and paleohydrology in Bengal Fan sediments (ODP Leg 116) to examine fire feedbacks on the south Asian continent. We employ abundances of polycyclic aromatic hydrocarbons (PAHs) to reconstruct fire occurrence and δ¹³C measurements of pyrogenic PAHs to constrain fuel source and grassland burning. This combination allowed us to test whether: (1) a fire‐seasonality forcing facilitated the expansion of grassland ecosystems and (2) a fire‐C₄ grass burning feedback maintained these systems. PAHs can be sourced from weathered fossil carbon (i.e., a petrogenic source) and from burned terrestrial biomass (i.e., a pyrogenic source). Alkylated and non‐alkylated structure abundance data distinguished pyrogenic from petrogenic sourced samples. A sharp increase in pyrogenic PAHs along with increases in δ²H and δ¹³C values of plant waxes at 7.4 Ma indicates increased fire coincided with the onset of C₄ expansion and hydrologic change in South Asia. The correlated ¹³C enrichment in PAHs, ¹³C enrichment in plant waxes, and increased abundances of PAHs suggest burning of C₄ grasslands likely maintained open ecosystems. Our results link fire to the initial opening of grassland ecosystems on a subcontinental‐scale and support disturbance as a critical mechanism of terrestrial biome transition.

中文翻译：

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印度次大陆上的中新世C4晚期草原火灾反馈

火灾动力学潜在地解释了整个上新世世界中C ₄草原扩张的异步时间。然而，火，气候和生态系统在不同环境中的相互作用仍然受到严格限制，因为在这些时间范围内难以量化火和燃料来源。在这里，我们将发生火灾的分子代理与孟加拉扇形沉积物中植被变化和古水文学的记录（ODP腿116）一起应用，以检查南亚大陆的火灾反馈。我们采用的多环芳香烃（PAHs），以重建火灾发生和Δ的丰度¹³热解PAHs的C测量，以限制燃料来源和草地燃烧。这种组合使我们能够测试：（1）火灾季节强迫是否促进了草地生态系统的扩张，以及（2）Fire-C ₄草燃烧反馈是否维持了这些系统。PAHs可以来自风化的化石碳（即成岩源）和燃烧的陆地生物质（即热源）。烷基化和非烷基化的结构丰度数据区分了热成因和岩石成因样品。急剧增加热解多环芳烃与δ增加沿² H和δ ^13个在7.4马植物蜡的C值表示增加火灾正值C的发病₄南亚的扩张和水文变化。在相关的¹³多环芳烃Ç富集，¹³植物蜡ç富集，并增加了多环芳烃的丰度建议燃烧的C _4和草原有可能保持开放的生态系统。我们的结果将火与次大陆规模的草地生态系统的初始开放联系起来，并支持扰动作为陆地生物群落过渡的关键机制。