Ventilation of the Atlantic Ocean equatorial thermocline

Reverdin, G, Weiss RF, Jenkins WJ.  1993.  Ventilation of the Atlantic Ocean equatorial thermocline. Journal of Geophysical Research-Oceans. 98:16289-16310.

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circulation, geostrophic transport, guinea dome, gyre, he-3, isopycnal, north-atlantic, south-atlantic, surfaces, tritium, water


The ventilation of the lower equatorial Atlantic thermocline (100 m to 400 m) is investigated from the distributions of salinity, oxygen, the chlorofluoromethanes F-11 and F-12, tritium, and the excess helium 3; 1983 data suggest a correlation on isopycnal surfaces between oxygen, chlorofluoromethanes and to a lesser extent, with the apparent ages derived from F-11/F-12 and helium 3/tritium. The apparent ages increase with depth from 10 years on sigma(THETA)=26.5 to over 15 years near 400 m. The tracers are largely undersaturated with respect to the surface concentrations corresponding to the apparent ages. We investigate the ventilation processes responsible for these distributions with simple circulation models, where water from the subtropical gyres reaches isopycnally the equatorial thermocline. The few model parameters are determined by fitting the simulations to the chlorofluoromethane distributions in 1983. The sensitivity of these parameters to expected errors on the past surface concentrations and to vertical mixing is comparable and can result in an error of more than 20% in the model parameters. In 1983, model [H-3] and [He-3]* are too large, in particular when no diapycnal mixing is modeled, but the differences could have arisen from errors on past surface concentrations. During the 1980s, die model overestimates the increase in chlorofluoromethanes, in particular F-12. The fitted model inflow from the southern subtropical gyre between 110 m and 400 m is 14 x 10(6) m3 s-1, in the range of expected transports by the western boundary current near Brazil. The model oxygen utilization rate is on the order of 12 mmol kg-1 yr-1 at 100 m and 5 mmol kg-1 yr-1 at 400 m (below sigma(theta)=27.1).