美国加州大学Kirtland Turner, Sandra团队的一项最新研究揭示了早始新世温室期间海洋环流对变暖的敏感性。相关论文于2024年6月3日发表于国际顶尖学术期刊《美国科学院院刊》杂志上。

据悉，早始新世出现了多次突发性变暖事件(“超高温”)，与深海温度升高2-4°C、海底碳酸盐溶解和负碳同位素(δ¹³C)漂移有关。超高温现象是否与全球海洋翻转环流的变化有关，对于理解其驱动机制和反馈以及深入了解环流对气候变暖的敏感性非常重要。

研究团队提供了在赤道深海和北大西洋的早始新世气候最适期(约53.26-49.14 Ma)的，高分辨率底栖有孔虫的稳定同位素(δ¹³C和δ¹⁸O)记录。结合南大西洋和太平洋的现有记录，研究结果表明，赤道大西洋深海的超高温期间δ¹³C偏移量持续放大。研究人员将这些观测结果与中等复杂地球系统模型的结果进行比较，证明这种δ¹³C偏移大小的空间格局是全球变暖引起的，海洋翻转环流变化的可预测结果。

在该模型中，短暂变暖导致南大洋的翻转环流减弱，大西洋经向水团老化梯度增强，赤道到北大西洋负δ¹³C偏移幅度放大。基于模式数据的一致性，研究组人员得出结论，始新世超高温与全球翻转环流的反复减弱相吻合。不考虑海洋环流对δ¹³C漂移的影响，将引起对驱动超热现象的碳释放幅度估计错误。结果显示，由于过去短暂的气候变暖，大西洋的倾覆强度会减弱，这与研究人员对未来温暖气候的预测是一致的。

附：英文原文

Title: Sensitivity of ocean circulation to warming during the Early Eocene greenhouse

Author: Kirtland Turner, Sandra, Ridgwell, Andy, Keller, Allison L., Vahlenkamp, Maximilian, Aleksinski, Adam K., Sexton, Philip F., Penman, Donald E., Hull, Pincelli M., Norris, Richard D.

Issue&Volume: 2024-6-3

Abstract: Multiple abrupt warming events (“hyperthermals”) punctuated the Early Eocene and were associated with deep-sea temperature increases of 2 to 4 °C, seafloor carbonate dissolution, and negative carbon isotope (δ¹³C) excursions. Whether hyperthermals were associated with changes in the global ocean overturning circulation is important for understanding their driving mechanisms and feedbacks and for gaining insight into the circulation’s sensitivity to climatic warming. Here, we present high-resolution benthic foraminiferal stable isotope records (δ¹³C and δ¹⁸O) throughout the Early Eocene Climate Optimum (~53.26 to 49.14 Ma) from the deep equatorial and North Atlantic. Combined with existing records from the South Atlantic and Pacific, these indicate consistently amplified δ¹³C excursion sizes during hyperthermals in the deep equatorial Atlantic. We compare these observations with results from an intermediate complexity Earth system model to demonstrate that this spatial pattern of δ¹³C excursion size is a predictable consequence of global warming-induced changes in ocean overturning circulation. In our model, transient warming drives the weakening of Southern Ocean-sourced overturning circulation, strengthens Atlantic meridional water mass aging gradients, and amplifies the magnitude of negative δ¹³C excursions in the equatorial to North Atlantic. Based on model-data consistency, we conclude that Eocene hyperthermals coincided with repeated weakening of the global overturning circulation. Not accounting for ocean circulation impacts on δ¹³C excursions will lead to incorrect estimates of the magnitude of carbon release driving hyperthermals. Our finding of weakening overturning in response to past transient climatic warming is consistent with predictions of declining Atlantic Ocean overturning strength in our warm future.

DOI: 10.1073/pnas.2311980121

Source: https://www.pnas.org/doi/abs/10.1073/pnas.2311980121