Alfred Wegener Institute (AWI) Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany.
MARUM - Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany.
Nature. 2024 Mar;627(8005):789-796. doi: 10.1038/s41586-024-07143-3. Epub 2024 Mar 27.
The Antarctic Circumpolar Current (ACC) represents the world's largest ocean-current system and affects global ocean circulation, climate and Antarctic ice-sheet stability. Today, ACC dynamics are controlled by atmospheric forcing, oceanic density gradients and eddy activity. Whereas palaeoceanographic reconstructions exhibit regional heterogeneity in ACC position and strength over Pleistocene glacial-interglacial cycles, the long-term evolution of the ACC is poorly known. Here we document changes in ACC strength from sediment cores in the Pacific Southern Ocean. We find no linear long-term trend in ACC flow since 5.3 million years ago (Ma), in contrast to global cooling and increasing global ice volume. Instead, we observe a reversal on a million-year timescale, from increasing ACC strength during Pliocene global cooling to a subsequent decrease with further Early Pleistocene cooling. This shift in the ACC regime coincided with a Southern Ocean reconfiguration that altered the sensitivity of the ACC to atmospheric and oceanic forcings. We find ACC strength changes to be closely linked to 400,000-year eccentricity cycles, probably originating from modulation of precessional changes in the South Pacific jet stream linked to tropical Pacific temperature variability. A persistent link between weaker ACC flow, equatorward-shifted opal deposition and reduced atmospheric CO during glacial periods first emerged during the Mid-Pleistocene Transition (MPT). The strongest ACC flow occurred during warmer-than-present intervals of the Plio-Pleistocene, providing evidence of potentially increasing ACC flow with future climate warming.
南极环极流（ACC）是世界上最大的海洋流系统，它影响着全球海洋循环、气候和南极冰盖的稳定性。如今，ACC 的动力由大气强迫、海洋密度梯度和旋涡活动控制。虽然古海洋重建显示，在更新世冰期-间冰期旋回中，ACC 的位置和强度存在区域异质性，但对 ACC 的长期演化知之甚少。本文作者通过南大洋太平洋的沉积岩芯记录，记录了 ACC 强度的变化。结果显示，自 530 万年前以来，ACC 流量没有线性的长期趋势，与全球变冷和全球冰量增加形成对比。相反，作者观察到了一个百万年的时间尺度上的反转，从上新世全球变冷期间 ACC 强度的增加，到随后随着早更新世进一步变冷而减少。这种 ACC 格局的转变与南大洋的重新配置相吻合，改变了 ACC 对大气和海洋强迫的敏感性。作者发现，ACC 强度的变化与 40 万年的偏心率周期密切相关，可能源于与热带太平洋温度变化相关的南太平洋射流进动变化的调制。在中更新世过渡期（MPT），首次出现了较弱的 ACC 流、向南偏移的蛋白石沉积和大气 CO2 减少之间的持续联系，这种联系出现在冰川期。最强的 ACC 流发生在更新世-全新世暖期，这为未来气候变暖可能导致 ACC 流量增加提供了证据。
