Labrador Sea Water exported through Flemish Pass: Hydrographic trends and transport variability inducing processes

This study investigates the deep flow through the 1200 m deep Flemish Pass, located at the western subpolar margin, constrained by the Grand Banks and the underwater plateau Flemish Cap. In addition to the Deep Western Boundary Current (DWBC) pathway offshore of Flemish Cap, Flemish Pass represents another southward export pathway for Labrador Sea Water (LSW), a main component of the climate modulating Atlantic Meridional Overturning Circulation. Hydrographic measurements show a significant warming of 0.3 degree/decade and a salinification of 0.03/decade of the Upper LSW in Flemish Pass between 1993 and 2013. Ship-based velocity measurements between 2009 and 2013 in Flemish Pass and in the DWBC east of Flemish Cap revealed a considerable southward transport of Upper LSW through Flemish Pass (15 - 27%). Mooring based transport time series revealed an average southward LSW transport of -1.9 Sv (-1.4 Sv) and a range of -3.5 Sv to 0.7 Sv (-5 Sv to 3 Sv) in Flemish Pass in 2012 - 2013 (2013 - 2014). The dominant LSW transport variability was observed on intra-seasonal time scales of 20 - 50 days and related to topographic Rossby waves trapped at the western slope of Flemish Pass.