Fine thermohaline structure and gas-exchange in the near-surface layer of the ocean during GasEx-98

During the GasEx-98 field campaign, observations of the upper ocean structure were performed to identify relationships between the fine thermohaline structure, turbulence, and gas exchange in the near-surface layer of the ocean. The upper ocean dynamics were then simulated using a 1-D mixed layer model with the mixing parameterization developed during TOGA Coupled Ocean-Atmosphere Response Experiment (COARE). The model was initialized with the temperature, salinity, and velocity profiles in the upper 50 m thick layer of the ocean obtained from the Conductivity-Temperature-Depth (CTD) and Acoustic Doppler Current Profiler (ADCP) measurements and was forced with the air-sea heat and momentum fluxes measured by Edson et al. [1999]. The model produced a set of parameters including the time and depth dependent mixing coefficient and the depth of the mixed layer. The simulated mixed layer depth is consistent with the depth of the actively mixed layer determined from the turbulence profiles taken occasionally during GasEx-98 leg 2 with a free-rising profiler. Moderate wind speed conditions prevailed during GasEx-98 leg 2 with several storms and a few periods of calm weather. Both the modeling and experimental results demonstrate that under conditions of low wind speed, the surface-generated turbulence is constrained within a relatively thin surface layer of the ocean. In the near-surface layer, appreciable temperature, salinity, and gas concentration differences are formed because of diurnal warming or precipitation effects. These results are applied to the estimation of the effect of mixed layer processes on the bulk-flux formulation for the air-sea exchange of gases.