Currents, fronts and eddy fluxes in the Canary Basin

Abstract

-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 Warmwassersphdre. 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 × 500km 2) 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 westeast 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 term s and cooling by the eddy flux divergence.

A quasi‐synoptic survey of the thermocline circulation and water mass distribution within the Canary Basin

“…The th ree possible states are best recognized in the temperature record from the 1660-m-level. The "mean" state at that depth is 5.4 C , which is found in the beginning and during the final 2 months as well as for some interim periods in January, March, and attached and isolated vortices of cold or warm waters at several depth Ievels [Käse and Siedler, 1982;Käse et al, 1985; Amu ancl : Zenk, 1984]. There is also significant temporal variability at some locations in the Canary Basin.…”

“…A characteristic feature above 200-m depth is the thermostad in the 16 19 C range, wh1ch is often found in this region in connecuon wuh the Azores Current (stations 9-12). This is believed to be the remainder of locaJ wintertime convection in the northcrn Canary Basin similar to the 18 water of the Sargasso Sea [Worthington, 1976;Gou/d, 1985;Käse et a/., 1985]. Except in the Azores Current region, isotberms in the Central Water are rather flat between Stations 3 and II.…”

“…Th1s pattcrn of the relati-.e topograph) is associatcd w1th thc meandering of the Azores Current, first described by Käse et al [ 1985] for a different mesoscale case study 1n thc same region in spnng 1982. In contrast to th!S "Pose1don" bo>.…”

“…This current undergoes large amplitude north-south meandering [Käse et al .. 1985] with occasional eddy detachCopynght 1986 by the Amencan Geophysical Umon.…”

The distribution and biochemical composition of biogenic particles across the subtropical Front in June 1993 (Azores-Madeira region, Northeast Atlantic)

“…The mixed layer is maximum (~200 m depth) in winter and minimum (~50 m depth) in summer (Levitus, 1982). Below this layer, the North Atlantic Central Water (NACW) occurs at ~500-600 m, NACW is underlain by intermediate waters (Worthington, 1976;Kase et al, 1985) with the Mediterranean waters, characterised by higher temperature and salinity between ~ 800-1300 m. Middle NADW occurs at ~2000 m depth and below 3000 m there is the Lower NADW that arises from the mixing of the waters of the Norwegian Sea and the Denmark Strait (Kawase and Sarmiento, 1986).…”