近日，德国赫姆霍兹极地和海洋研究中心Lamy Frank团队，分析了500万年的南极环极流强度变化。该项研究成果发表在2024年3月27日出版的《自然》上。

据了解，南极环极流(ACC)是世界上最大的洋流系统，影响着全球海洋环流、气候和南极冰盖的稳定性。今天，ACC动态受大气作用力、海洋密度梯度和涡旋活动的控制。在更新世冰期—间冰期旋回期间，研究人员利用古海洋学重建出ACC的位置和强度的区域异质性，但对ACC的长期演变仍知之甚少。

研究人员记录了南太平洋沉积物岩芯中ACC强度的变化。研究发现，自5.3个百万年(Ma)前以来，ACC流量没有线性的长期趋势，这与全球变冷和全球冰量增加形成鲜明对比。相反，研究观察到了百万年的时间尺度上的逆转，从上新世全球变冷期间ACC强度增加到，到随后随着早更新世进一步变冷而下降。ACC的这种变化与南大洋的重构相吻合，南大洋的重构改变了ACC对大气和海洋作用力的敏感性。

研究人员发现ACC强度的变化与40万年的偏心周期密切相关，可能源于与热带太平洋温度变化相关的南太平洋急流的岁差变化调制。在更新世中期过渡时期(MPT)，冰川期间较弱的ACC流、向赤道移动的蛋白石沉积和大气CO₂减少之间的持续联系首次出现。最强的ACC流发生在比现在更暖的上新世-更新世期间，这为未来气候变暖可能增加ACC流量提供了证据。

附：英文原文

Title: Five million years of Antarctic Circumpolar Current strength variability

Author: Lamy, Frank, Winckler, Gisela, Arz, Helge W., Farmer, Jesse R., Gottschalk, Julia, Lembke-Jene, Lester, Middleton, Jennifer L., van der Does, Michlle, Tiedemann, Ralf, Alvarez Zarikian, Carlos, Basak, Chandranath, Brombacher, Anieke, Dumm, Levin, Esper, Oliver M., Herbert, Lisa C., Iwasaki, Shinya, Kreps, Gaston, Lawson, Vera J., Lo, Li, Malinverno, Elisa, Martinez-Garcia, Alfredo, Michel, Elisabeth, Moretti, Simone, Moy, Christopher M., Ravelo, Ana Christina, Riesselman, Christina R., Saavedra-Pellitero, Mariem, Sadatzki, Henrik, Seo, Inah, Singh, Raj K., Smith, Rebecca A., Souza, Alexandre L., Stoner, Joseph S., Toyos, Maria, de Oliveira, Igor M. Venancio P., Wan, Sui, Wu, Shuzhuang, Zhao, Xiangyu

Issue&Volume: 2024-03-27

Abstract: 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 5.3million 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 CO2 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.

DOI: 10.1038/s41586-024-07143-3

Source: https://www.nature.com/articles/s41586-024-07143-3