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From interannual to decadal: 17 years of boundary current transports at the exit of the L abrador S ea
Author(s) -
Zantopp R.,
Fischer J.,
Visbeck M.,
Karstensen J.
Publication year - 2017
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2016jc012271
Subject(s) - boundary current , current (fluid) , oceanography , north atlantic deep water , geology , baroclinity , submarine pipeline , water mass , ocean current , ocean gyre , gulf stream , climatology , deep water , subtropics , fishery , biology
Abstract Over the past 17 years, the western boundary current system of the Labrador Sea has been closely observed by maintaining the 53°N observatory (moorings and shipboard station data) measuring the top‐to‐bottom flow field offshore from the Labrador shelf break. Volume transports for the North Atlantic Deep Water (NADW) components were calculated using different methods, including gap filling procedures for deployment periods with suboptimal instrument coverage. On average the Deep Western Boundary Current (DWBC) carries 30.2 ± 6.6 Sv of NADW southward, which are almost equally partitioned between Labrador Sea Water (LSW, 14.9 ± 3.9 Sv) and Lower North Atlantic Deep Water (LNADW, 15.3 ± 3.8 Sv). The transport variability ranges from days to decades, with the most prominent multiyear fluctuations at interannual to near decadal time scales (±5 Sv) in the LNADW overflow water mass. These long‐term fluctuations appear to be in phase with the NAO‐modulated wind fluctuations. The boundary current system off Labrador occurs as a conglomerate of nearly independent components, namely, the shallow Labrador Current, the weakly sheared LSW range, and the deep baroclinic, bottom‐intensified current core of the LNADW, all of which are part of the cyclonic Labrador Sea circulation. This structure is relatively stable over time, and the 120 km wide boundary current is constrained seaward by a weak counterflow which reduces the deep water export by 10–15%.