The North Atlantic Current (NAC) supplies the subpolar gyre with warm and saline water from the subtropics as part of the upper branch of the Atlantic Meridional Overturning Circulation (AMOC). In the context of climate changes, the North Atlantic Ocean is one of the key regions to investigate the variability of the overturning circulation in which salinity and freshwater variability are playing a central role. Through the gravest empirical mode (GEM) method, we reconstructed salinity and velocity fields in the same spatiotemporal resolution as the sea surface height (SSH) product. The time series of salinity, freshwater, and volume transport are characterized by strong interannual variability related to most of the recently developed subpolar gyre indices. The variability of the freshwater transport in the study area is as high or even higher than the freshwater fluxes from the Arctic Ocean and thus needs to be considered for the impact of freshwater on the subpolar North Atlantic. Our analysis also revealed that the NAC import into the subpolar gyre is not only occurring in the western Atlantic close to the western boundary current. One o the NAC branches that forms at the Mann Eddy contributes about 15% of the volume transport and 28% of the freshwater transport crossing from the western into the eastern Atlantic north of 45°N. This branch has not been subject to the strong lateral mixing with freshwater at the western boundary, and thus, the salinity of this NAC pathway is higher than the one at the western boundary.

中文翻译：

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1993-2016年，北大西洋次极地带的北大西洋洋流及其流量和淡水运输

北大西洋洋流（NAC）向亚极回旋区提供来自亚热带的温盐水和咸水，这是大西洋子午倾覆环流（AMOC）上部分支的一部分。在气候变化的背景下，北大西洋是研究倾覆环流变化的关键区域之一，其中盐度和淡水的变化起着核心作用。通过最严重的经验模式（GEM）方法，我们以与海平面高度（SSH）产品相同的时空分辨率重建了盐度和速度场。盐度，淡水和体积输运的时间序列的特征是与大多数最新开发的亚极回旋指数相关的强烈年际变化。研究区域内淡水运输的变异性高于或什至高于来自北冰洋的淡水通量，因此需要考虑淡水对北极次极地的影响。我们的分析还显示，NAC不仅进入西极边界流附近的西大西洋，而且还进入次极回旋。从Mann Eddy形成的NAC分支中，约有15％的体积是输水，而淡水的28％则是从西部到45°N以北的大西洋东部。该分支没有在西部边界与淡水进行强烈的横向混合，因此，该NAC途径的盐度高于在西部边界的盐度。