Leibniz-Institut für Meereswissenschaften, Düsternbrooker Weg 20, 24105 Kiel, Germany.
Nature. 2009 Nov 26;462(7272):495-8. doi: 10.1038/nature08519.
The transport of warm and salty Indian Ocean waters into the Atlantic Ocean-the Agulhas leakage-has a crucial role in the global oceanic circulation and thus the evolution of future climate. At present these waters provide the main source of heat and salt for the surface branch of the Atlantic meridional overturning circulation (MOC). There is evidence from past glacial-to-interglacial variations in foraminiferal assemblages and model studies that the amount of Agulhas leakage and its corresponding effect on the MOC has been subject to substantial change, potentially linked to latitudinal shifts in the Southern Hemisphere westerlies. A progressive poleward migration of the westerlies has been observed during the past two to three decades and linked to anthropogenic forcing, but because of the sparse observational records it has not been possible to determine whether there has been a concomitant response of Agulhas leakage. Here we present the results of a high-resolution ocean general circulation model to show that the transport of Indian Ocean waters into the South Atlantic via the Agulhas leakage has increased during the past decades in response to the change in wind forcing. The increased leakage has contributed to the observed salinification of South Atlantic thermocline waters. Both model and historic measurements off South America suggest that the additional Indian Ocean waters have begun to invade the North Atlantic, with potential implications for the future evolution of the MOC.
温暖而咸的印度洋海水向大西洋的输送——阿古拉斯海流漏——在全球海洋环流中起着至关重要的作用，从而影响未来气候的演变。目前，这些海水为大西洋经向翻转环流（MOC）的表层分支提供了主要的热量和盐分来源。有证据表明，过去冰川间冰期的有孔虫组合和模型研究表明，阿古拉斯海流漏的数量及其对 MOC 的相应影响已经发生了实质性的变化，这可能与南半球西风的纬向位移有关。在过去的二三十年中，观测到西风呈渐进的向北迁移，并与人为强迫有关，但由于观测记录稀疏，无法确定阿古拉斯海流漏是否有相应的响应。在这里，我们展示了一个高分辨率海洋环流模型的结果，表明在过去几十年里，由于风强迫的变化，印度洋的海水通过阿古拉斯海流漏向大西洋南部的输送增加了。增加的泄漏导致了南大西洋温跃层海水的盐度增加。模型和南美的历史观测都表明，额外的印度洋海水已经开始入侵北大西洋，这可能对未来 MOC 的演变产生影响。
