A TRANSATLANTIC SECTION AT 14.5N - MERIDIONAL VOLUME AND HEAT FLUXES

Two high-resolution hydrographic sections occupied during February, Ma rch 1989 in the western and eastern basins of the North Atlantic at 14 .5N are combined to study the water mass structure and meridional mass and heat transports. Absolute velocities were determined using these data and an earlier section at 8N in a linear inverse analysis. Mass b alance for several layers representing the main water masses in the re gion and a zero net divergence for the sum of geostrophic and Ekman tr ansport between the two sections are assumed. Using the annual mean of Ekman transports (13.6 Sv, 14.5N), (15.2 Sv, 8N) based on the climato logy by Isemer and Hasse (1985) the annual average fluxes for the sect ions at 8N and 14.5N have been calculated. For the annual mean the str ength of the meridional overturning cell at 14.5N amounts to 15.9 Sv w ith an associated heat transport of 1.22 PW. A similar value can be ob tained at 8N where the annual mean heat transport reaches 1.18 PW and the overturning cell measures 15 Sv. The total northward heat transpor t is strongly dominated by the wind-driven Ekman heat transport. 'In-s itu' values of heat transport using the actual wind-driven transports for the respective months yield even higher estimates. Heat transport at 14.5N rises to 1.37 +/- 0.42 PW (February) and the maximum is now a t the 8N section, 1.69 +/- 0.52 PW (May). Comparisons of our results w ith another tropical section at 11N occupied concurrently demonstrate the large variability in heat transport related to changes in the wind field. Due to extremely weak winds in the eastern Atlantic and a resu lting low Ekman transport, the 'in-situ' value of heat transport throu gh this section ranged between 0.30 +/- 0.18 PW and 0.59 +/- 0.18 PW d epending on the value chosen for the Ekman transport. The lower of the two heat transport estimates results from calculations with the actua l observed winds and the other using a monthly climatological mean. Th at even the computations with the climatological monthly mean give suc h a low heat transport points to additional changes in the baroclinic structures between 11N and 14.5N.