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.

Density-dependent changes in the spatial distributions of Atlantic Cod (Gadus morhua), American Plaice (Hippoglossoides platessoides), and Greenland Halibut (Reinhardtius hippoglossoides) on the Flemish Cap during 1988-2002

“…A seasonal thermocline is present on the Cap during May through late August (Gil et al, 2004). There is no seasonal cycle in temperature or salinity at depths below 100 m (Colburne and Foote, 2000), and at depths below 200 m, average temperature and salinity values recorded during the 1988-2000 EU surveys exhibited little interannual variability (Gil et al, 2004). These trends suggest that factors other than changes in thermohaline conditions are the primary reason for the persistence of the observed distributional changes.…”

“…In either case, the distributional shifts of cod and plaice have persisted across years during the summer, when thermohaline conditions near the bottom of the water column are fairly constant on the Flemish Cap. A seasonal thermocline is present on the Cap during May through late August (Gil et al, 2004). There is no seasonal cycle in temperature or salinity at depths below 100 m (Colburne and Foote, 2000), and at depths below 200 m, average temperature and salinity values recorded during the 1988-2000 EU surveys exhibited little interannual variability (Gil et al, 2004).…”

“…The most obvious is the potential for increased vulnerability of aggregations to trawl fisheries (Kulka et al, 1995). In addition, geographic fragmentation of the spawning stock, whereby spawners are concentrated in small patches located further apart, may hinder stock recovery due to: a) reduced demo- gyre present in 1998 (Gil et al, 2004). Presence of the gyre affects thermal and salinity conditions on the Cap whereby the core contains warmer, less saline waters.…”

Aglaopheniid hydroids (Cnidaria: Hydrozoa: Aglaopheniidae) from bathyal waters of the Flemish Cap, Flemish Pass, and Grand Banks of Newfoundland (NW Atlantic)

“…Compared with the Grand Banks, the Flemish Cap supports higher primary and secondary productivity due to its hydrodynamic conditions (Maillet et al 2005). The mix of different currents in the area (Gil et al 2004), a highly oxygenated environment rich in nutrients (Stein 2007), and greater substratum heterogeneity on the Flemish Cap compared with adjacent areas may explain differences in its faunal composition. It is a poorly studied area, and one in which rare and seldom-recorded species of other animal groups, such as deepsea corals (Murillo et al 2011), are not uncommon.…”

“…Situated eastward of the Grand Banks of Newfoundland, it is separated from those banks by the approximately 1200 m deep Flemish Pass (Figure 1). The Flemish Cap is located within an area of transition between cold subpolar waters and is influenced by fluctuations in the Labrador Current and in the North Atlantic Current (Gil et al 2004). Compared with the Grand Banks, the Flemish Cap supports higher primary and secondary productivity due to its hydrodynamic conditions (Maillet et al 2005).…”