Abstract The water masses exiting the Labrador Sea, and in particular the dense water mass formed by convection (i.e. Labrador Sea Water, LSW), are important components of the Atlantic Meridional Overturning Circulation (AMOC). Several studies have questioned the connection of the LSW production to the AMOC variability. This is partly due to the limited understanding of how this locally formed water mass leaves the interior of the Labrador Sea. In this study, the pathways and the timescales of the water masses exiting the Labrador Sea via the boundary current are investigated by Lagrangian particle tracking. This method is applied to the output of a strongly-eddying idealized model that is capable of representing the essential physical processes involved in the cycle of convection and restratification in the Labrador Sea. The Lagrangian trajectories reveal that prior to exiting the domain the water masses follow either a fast route within the boundary current or a slower route that involves boundary current-interior exchanges. The densest water masses exiting the Labrador Sea stem from this slow route, where particles experience strong water mass transformation while in the interior. In contrast, the particles that follow the fast route experience water mass transformation in the boundary current at the western side of the domain only, yielding a lighter product. Although both routes carry roughly the same transport, we show that 60% of the overturning in density space is associated with the volume transport carried by particles that follow the slow route. This study further highlights that the export of dense water masses, which is governed by the eddy activity in the basin, yields export timescales that are usually longer than a year. This underlines the necessity of resolving the mesoscale features required to capture the interior–boundary current exchange in order to correctly represent the export of the LSW.

中文翻译：

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离开拉布拉多海的水团路径：边界内部交换的重要性

摘要 离开拉布拉多海的水团，特别是对流形成的密集水团（即拉布拉多海水，LSW），是大西洋经向翻转环流（AMOC）的重要组成部分。几项研究质疑 LSW 生产与 AMOC 可变性之间的联系。这部分是由于对这种局部形成的水团如何离开拉布拉多海内部的了解有限。在这项研究中，通过拉格朗日粒子追踪研究了通过边界流离开拉布拉多海的水团的路径和时间尺度。该方法应用于强涡旋理想化模型的输出，该模型能够表示拉布拉多海对流和再分层循环中涉及的基本物理过程。拉格朗日轨迹表明，在离开域之前，水团沿着边界流内的快速路径或涉及边界流内部交换的较慢路径。离开拉布拉多海的最密集的水团源于这条缓慢的路线，其中粒子在内部经历了强烈的水团转变。相比之下，遵循快速路线的粒子仅在域西侧的边界流中经历水质量转换，从而产生更轻的产品。尽管两条路线携带的输运大致相同，但我们表明，密度空间中 60% 的翻转与沿慢速路线的粒子携带的体积输运有关。这项研究进一步强调，密集水团的出口，受盆地涡流活动支配，产生的出口时间尺度通常超过一年。这强调了解决捕获内部边界电流交换所需的中尺度特征的必要性，以便正确表示 LSW 的输出。