C₄ grasslands proliferated later in Australia than they did on other continents (∼3.5 Ma vs. 10–5 Ma). It remains unclear whether this delay reflects differences in climate conditions or ecological feedbacks, such as fire, that promote C₄ ecosystems. Here, we evaluated these factors using terrestrial biomarkers from marine sediments off western Australia. Fire‐derived polycyclic aromatic hydrocarbons (PAH) indicate fire ecology did not substantially change during or following C₄ expansion. The presence of fire‐adapted C₃ woody vegetation likely diminished the role of fire and delayed C₄ expansion until it was prompted by climate drying between 3.5 and 3.0 Ma. At the same time, mass accumulation rates of weathered PAHs increased 100‐fold, which indicates a significant loss of soil carbon accompanied this ecosystem shift. The tight couplings between hydroclimate and carbon storage altered boundary conditions for Australian ecosystems, and similar abrupt behavior may shape environmental responses to climate change.

中文翻译：

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澳大利亚上新世C4草地扩张期间的土壤碳损失和弱火反馈

与其他大洲相比，澳大利亚的C ₄草原增殖较晚（〜3.5 Ma对10-5 Ma）。目前尚不清楚这种延迟是否反映了促进C ₄生态系统的气候条件或生态反馈（例如火灾）的差异。在这里，我们使用来自澳大利亚西部海洋沉积物的陆地生物标记物评估了这些因素。源自火的多环芳烃（PAH）表明，在C ₄膨胀期间或之后，火生态基本没有变化。具有火适应性的C ₃木本植物的存在可能会减少火的作用并延迟C ₄直到3.5到3.0 Ma之间的气候干燥促使它膨胀。同时，风化的PAHs的质量累积速率增加了100倍，这表明随着生态系统的变化，土壤碳的大量损失。水文气候和碳储存之间的紧密联系改变了澳大利亚生态系统的边界条件，类似的突变行为可能会影响对气候变化的环境响应。