Geostrophic circulation and heat flux across the Flemish Cap, 1988-2000

Abstract

Historical hydrographic data together with data from Spanish bottom trawl surveys are used to estimate geostrophic circulation over Flemish Cap and transport and heat fluxes across the 47°N line from 1988 to 2000. The data show a recurrence of anticyclonic circulation on Flemish Cap in July. We conclude that the topography plays a major role in determining the dynamics over the Cap. A coherent cold flow originating in the Labrador Current (LC) skirts around the northeastern flank with geostrophic velocities of ∼0.07 ms-1 and partly recirculates around the southern and southwestern flanks of the Cap with a mean flow of ∼0.03 ms-1, thereby isolating a central anticyclonic core. This core generally contains warmer and less saline waters than the surrounding waters. The most significant source of variability of the water masses over Flemish Cap is linked to the variability of the advective flows, principally the offshore branch of the LC and oscillations of the north wall of the North Atlantic Current (NAC). The estimated mean northward and southward geostrophic heat fluxes over the Cap across 47°N balance to within approximately 10%, although with suggestions of a long-term trend in the net heat flux from positive (northward) in the late-1980s to slightly negative (southward) in the second half of the 1990s. The latter is attributed to an increase in the offshore branch of the Labrador Current over the bank. Linkages between the geostrophic heat fluxes over Flemish Cap and the shift in the Coastal Slope Water System and the NAO are examined. Enhanced Labrador Current flow during 1995-2000 was observed to strengthen the anticyclonic gyre anchored to the topography of the Cap.