Current climate change may induce positive carbon cycle feedbacks that amplify anthropogenic warming on time scales of centuries to millennia. Similar feedbacks might have been active during a phase of carbon cycle perturbation and global warming, termed the Paleocene‐Eocene Thermal Maximum (PETM, 56 million years ago). The PETM may help constrain these feedbacks and their sensitivity to warming. We present new high‐resolution carbon isotope and sea surface temperature data from Ocean Drilling Program Site 959 in the Equatorial Atlantic. With these and existing data from the New Jersey Shelf and Maud Rise, Southern Ocean, we quantify the lead‐lag relation between PETM warming and the carbon input that caused the carbon isotope excursion (CIE). We show ~2 °C of global warming preceded the CIE by millennia, strongly implicating CO₂‐driven warming triggered a positive carbon cycle feedback. We further compile new and published barium (Ba) records encompassing continental shelf, slope, and deep ocean settings. Based on this compilation, we calculate that average Ba burial rates approximately tripled during the PETM, which may require an additional source of Ba to the ocean. Although the precipitation pathway is not well constrained, dissolved Ba stored in sulfate‐depleted pore waters below methane hydrates could represent an additional source. We speculate the most complete explanation for early warming and rise in Ba supply is that hydrate dissociation acted as a positive feedback and caused the CIE. These results imply hydrates are more temperature sensitive than previously considered, and may warrant reconsideration of the political assignment of 2 °C warming as a safe future scenario.

中文翻译：

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古新世-始新世热最大值之前广泛的变暖和钡埋葬的升高：甲烷水合物释放的证据吗？

当前的气候变化可能会引发积极的碳循环反馈，从而在数百年至几千年的时间尺度上放大人为变暖。在碳循环扰动和全球变暖阶段，类似的反馈可能是活跃的，这被称为古新世-始新世最大热（PETM，5600万年前）。PETM可能有助于限制这些反馈及其对变暖的敏感性。我们提供了来自赤道大西洋海洋钻探计划959号站点的新高分辨率碳同位素和海面温度数据。利用来自新泽西大陆架和南大洋州莫德里斯的现有数据，我们可以量化PETM变暖与引起碳同位素偏移（CIE）的碳输入之间的超前滞后关系。我们显示，全球升温约2°C在CIE之前已有数千年，这强烈暗示了CO₂受驱动的变暖触发了积极的碳循环反馈。我们进一步编辑了新的和已发布的钡（Ba）记录，包括大陆架，斜坡和深海环境。根据此汇编，我们计算出在PETM期间平均Ba埋葬率大约增加了三倍，这可能需要向海洋中添加额外的Ba。尽管没有很好地限制降水途径，但溶解在甲烷水合物以下的硫酸盐枯竭的孔隙水中的溶解钡可能是另外的来源。我们推测，对于早期变暖和钡供应增加的最完整的解释是，水合物的离解充当了正反馈并导致了CIE。这些结果表明水合物比以前认为的对温度更敏感，