The Faroe-Shetland Channel Jet: Structure, Variability, and Driving Mechanisms

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The Faroe-Bank Channel (FBC) is a key gateway through which dense overflow water of the Nordic Seas supplies the lower limb of the Atlantic Meridional Overturning Circulation. Most recently, it was discovered that a deep jet through the Faroe-Shetland Channel carries the bulk of this overflow water, but numerous questions regarding its structure, seasonality, and interannual variability as well as its linkage to atmospheric forcing remain poorly understood. A realistic high-resolution ocean reanalysis (GLORYS12; 1993–2018) is, therefore, employed to address these questions. We first confirm that the Faroe-Shetland Channel Jet is a permanent feature in GLORYS12 as well as in an ensemble of low-resolution reanalyses. On seasonal time scales, we find a strong transport covariability between this deep jet and the observed FBC overflow. On interannual time scales, the strength of this deep jet is governed by the wind-forced circulation in the Nordic Seas. Due to the largely barotropic structure of these flows, they have a signature detectable in satellite sea-surface heights. Further, we suggest that the structure of the deep jet is qualitatively consistent with a geostrophic dynamical model that accounts for along-isobath density variations. This study indicates that GLORYS12 is a promising product to study the dense water pathways and dynamics in the Nordic Seas.

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Journal of Geophysical Research: Oceans