Currents, fronts and eddy fluxes in the Canary Basin

Hydrographic data from two cruises in the Canary Basin (Meteor 57, July 1981; Poseidon 86, April 1982) are analysed with respect to current distribution and lateral heat flux in the Azores-Madeira region. The first part of the data base consists of long transects of XBT and G.E.K. measurements between Cape Finisterre (North West Spain) and the northern Canary Basin, where several year-long current meter records exist. Further information is obtained by thermosalinograph surface data and by expendable current profilers (XCP). Geostrophic currents are derived from XBT profiles, using the tight temperature-salinity relationship in the depth range of the Warmwassersphäre. The results compare well with the G.E.K. and XCP current observations. The second part consists of CTD data from an eddy resolving, box-shaped CTD survey (500 × 500 km2) centered at the mooring location (33°N, 22°W), The observations are supplemented by satellite-buoy trajectories. Horizontal parameter distribution is shown in terms of objectively contoured maps. Bands of spatially enhanced energetic structures, seen in the long transects are further resolved by the box survey as a deep jet-like current system cross the Canary Basin in a west-east direction. Associated with this Azores Current is a frontal zone with near-surface temperature and salinity steps of order 2 K and 0.3 practical salinity units. The dynamic topography field can be decomposed into a linear background field, a Rossby wave and a mesoscale eddy field. We find that major contributions to the meridional eddy heat flux are confined to the vicinity of the Azores current frontal zone. It is shown that the principal balance in the temperature equation is between heating by the mean horizontal advection terms and cooling by the eddy flux divergence