Pending recovery in the strength of the meridional overturning circulation at 26° N
Pending recovery in the strength of the meridional overturning circulation at 26° N
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DOI：
10.5194/os-2019-134
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发表时间：
2020-01
期刊：
影响因子：
3.2
通讯作者：
B. Moat;D. Smeed;E. Frajka‐Williams;D. Desbruyères;C. Beaulieu;W. Johns;D. Rayner;A. Sanchez‐Franks;M. Baringer;D. Volkov;L. Jackson;H. Bryden
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文献类型：
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作者：
B. Moat;D. Smeed;E. Frajka‐Williams;D. Desbruyères;C. Beaulieu;W. Johns;D. Rayner;A. Sanchez‐Franks;M. Baringer;D. Volkov;L. Jackson;H. Bryden
抽象的。2004年4月至2018年9月期间，RAPID阵列连续测量了26 ° N处大西洋纬向翻转环流（AMOC）的强度。这一记录提供了独特的洞察大规模的海洋环流的变化，以前只测量了零星的快照流域范围内的运输从水文剖面。连续的测量揭示了在几天到十年的时间尺度上惊人的变化，主要是由风力驱动的，与之前关于缓慢变化的浮力迫使大规模海洋环流的预期形成对比。然而，这些测量结果主要是在大西洋多年变化（AMV）的温暖状态下观察到的，自2008-2010年的峰值以来一直在稳步下降。在2013-2015年期间，大气的强浮力迫使在副极地北大西洋强烈的水团转变，并提供了一个独特的机会来研究大规模海洋环流对浮力强迫的反应。模拟研究表明，在亚热带的AMOC响应这样的事件，增加翻转输送后，滞后3-9年。在45 ° N，观测表明AMOC可能已经在增加。通过对26 ° N的分析，我们发现尽管近期的输送并不高于长期平均值，但AMOC已不再减弱。通过GloSea 5的海洋再分析，将记录向后延伸到26 ° N，26 ° N的输送波动与45 ° N的输送波动有0至2年的滞后，尽管幅度较低。由于副极地环流到副热带环流的信号时间跨度很短，而且预计会出现延迟，因此目前还无法确定副热带AMOC的强度是否正在恢复，也无法确定26 ° N的AMOC如何对强烈的浮力强迫作出反应。
Abstract. The strength of the Atlantic meridional overturning circulation (AMOC) at 26∘ N has now been continuously measured by the RAPID array over the period April 2004–September 2018. This record provides unique insight into the variability of the large-scale ocean circulation, previously only measured by sporadic snapshots of basin-wide transport from hydrographic sections. The continuous measurements have unveiled striking variability on timescales of days to a decade, driven largely by wind forcing, contrasting with previous expectations about a slowly varying buoyancy-forced large-scale ocean circulation. However, these measurements were primarily observed during a warm state of the Atlantic multidecadal variability (AMV) which has been steadily declining since a peak in 2008–2010. In 2013–2015, a period of strong buoyancy forcing by the atmosphere drove intense water-mass transformation in the subpolar North Atlantic and provides a unique opportunity to investigate the response of the large-scale ocean circulation to buoyancy forcing. Modelling studies suggest that the AMOC in the subtropics responds to such events with an increase in overturning transport, after a lag of 3–9 years. At 45∘ N, observations suggest that the AMOC may already be increasing. Examining 26∘ N, we find that the AMOC is no longer weakening, though the recent transport is not above the long-term mean. Extending the record backwards in time at 26∘ N with ocean reanalysis from GloSea5, the transport fluctuations at 26∘ N are consistent with a 0- to 2-year lag from those at 45∘ N, albeit with lower magnitude. Given the short span of time and anticipated delays in the signal from the subpolar to subtropical gyres, it is not yet possible to determine whether the subtropical AMOC strength is recovering nor how the AMOC at 26∘ N responds to intense buoyancy forcing.