| Summary: | The Rockall Trough (RT), a deep channel in the northeast North Atlantic (NA), hosts water masses of subpolar and subtropical origins. Large-scale atmospheric (North Atlantic oscillation, Eastern Atlantic pattern) and oceanic (NA subpolar gyre) settings have been noted as the major drivers of water masses presence in the region, their properties, thus impacting heat and salinity inputs into the RT and higher northern latitudes. Intermediate water masses are known to retain their characteristics long distance away from their places of origin, thus their presence and impact on water properties further afield notable. To detect/discern large-scale driver(s) of intermediate water masses presence in the RT, empirical orthogonal function (EOF) analysis was used. Water masses metrics, used in the EOF analysis, are fractions based on a mixing triangle approach and derived from high-resolution ship-board conductivity-temperature-depth (CTD) and delayed mode processed Argo (ISAS15) in-situ datasets. The large-scale atmospheric and oceanic signals did not emerge as the main drivers. The EOF analysis pointed to intermediate water masses presence within the RT, southern and central domains in particular, to be most likely influenced by locally induced interior (sub)mesoscale processes and features, and possible consequent mixing. These results brought forward the role of interior water masses pathways, i.e., intermediate water currents, notably the deep, Mediterranean Overflow Water (MOW)-rich slope current, and interior (sub)mesoscale dynamics. The use of ship-board in-situ CTD, Coastal and Regional Ocean COmmunity (CROCO) model output and altimetry absolute dynamic topography datasets permitted the identification of a deep, recurrent, non-stationary anticyclone, centred at ~12 °W, 55 °N, named here the RT anticyclone. The above datasets were further used to perform analysis of RT anticyclone generating mechanism and core water masses origin. The analysis shows that the RT anticyclone is the result of the merging of, and ...
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