MEASURED AND MODELED CFC DISTRIBUTION OF LOWER NORTH-ATLANTIC DEEP-WATER IN THE GUIANA BASIN

The circulation of the Overflow Lower North Atlantic Deep Water (OLNAD W) in the Guiana Basin is studied by the measured and modeled distribu tion of the chlorofluorocarbon component CFC-11. The OLNADW is formed in the northern Atlantic and transported south to the equatorial,regio n as the densest part of the Deep Western Boundary Current (DWBC), cha racterized by CFC and oxygen maxima. Some former studies proposed a no rthwestward recirculation of the boundary current in the Guiana Basin, because the measured southeastward DWBC transport was larger than the calculated net transport across the entire width of the basin. Despit e the variability of the DWBC reported recently, this discrepancy seem s to hold. An advective-diffusive model is presented, which includes r ecirculation in the northern Guiana Basin as well as horizontal diffus ion, and the results are compared with a CFC survey in March 1994. Bec ause of high CFC concentration in the boundary current one would expec t to find a high CFC signal in the recirculated water mass near the Mi d-Atlantic Ridge as well. However, this was not observed. Modeled CFC distributions and observations only agree if the presumed recirculatio n is located in the center of the northern Guiana Basin or if no westw ard recirculation exists at all. It was found that the strength of the recirculation is about 3 +/- 1.5 Sv, which is smaller than previously supposed.