Fast mechanisms linking the Labrador Sea with subtropical Atlantic overturning
Fast mechanisms linking the Labrador Sea with subtropical Atlantic overturning
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DOI：
10.1007/s00382-022-06459-y
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发表时间：
2022-08
期刊：
影响因子：
4.6
通讯作者：
Y. Kostov;M. Messias;H. Mercier;H. Johnson;D. Marshall
中科院分区：
文献类型：
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作者：
Y. Kostov;M. Messias;H. Mercier;H. Johnson;D. Marshall
我们使用的海洋环流模式及其伴随分析的因果链连接在拉布拉多海的海面浮力异常的变化在大西洋纬向翻转环流（AMOC）的深分支年际时间尺度上。我们的研究强调了北大西洋海流（NAC）在AMOC中的南北连通性和北大西洋深层水（LNADW）的纬向输送的重要性。我们确定了两种机制，使拉布拉多海影响LNADW层的速度。第一种机制涉及被动平流的表面浮力异常从拉布拉多海向东副极地环流的背景NAC。第二种机制起着主导作用，涉及的NAC的表面密度异常起源于拉布拉多海的动态响应; NAC的调整修改盐和热的向北输送，并施加了强烈的正反馈，放大上层海洋浮力异常。这两种机制在几年的时间尺度上使副极地环流向上/向下旋转，而边界捕获波迅速将此信号传达给副热带，并在几个月的时间尺度上触发LNADW运输的调整。NAC和东副极地环流在连接拉布拉多海与LNADW输送变率和副热带AMOC的机制中起着至关重要的作用。因此，我们调和两个明显矛盾的范式AMOC连接：（1）拉布拉多海浮力异常驱动AMOC的变化;（2）水团的改造是最大的在东副极地环流。
We use an ocean general circulation model and its adjoint to analyze the causal chain linking sea surface buoyancy anomalies in the Labrador Sea to variability in the deep branch of the Atlantic meridional overturning circulation (AMOC) on inter-annual timescales. Our study highlights the importance of the North Atlantic Current (NAC) for the north-to-south connectivity in the AMOC and for the meridional transport of Lower North Atlantic Deep Water (LNADW). We identify two mechanisms that allow the Labrador Sea to impact velocities in the LNADW layer. The first mechanism involves a passive advection of surface buoyancy anomalies from the Labrador Sea towards the eastern subpolar gyre by the background NAC. The second mechanism plays a dominant role and involves a dynamical response of the NAC to surface density anomalies originating in the Labrador Sea; the NAC adjustment modifies the northward transport of salt and heat and exerts a strong positive feedback, amplifying the upper ocean buoyancy anomalies. The two mechanisms spin up/down the subpolar gyre on a timescale of years, while boundary trapped waves rapidly communicate this signal to the subtropics and trigger an adjustment of LNADW transport on a timescale of months. The NAC and the eastern subpolar gyre play an essential role in both mechanisms linking the Labrador Sea with LNADW transport variability and the subtropical AMOC. We thus reconcile two apparently contradictory paradigms about AMOC connectivity: (1) Labrador Sea buoyancy anomalies drive AMOC variability; (2) water mass transformation is largest in the eastern subpolar gyre.