Estimation of vertical mixing in the upper ocean at Station P from chlorofluorocarbons

Vertical mixing (K-v) in the upper ocean is estimated from chlorofluorocarbons (CFC's) F-11 and F-12 data collected on 5 cruises (1982, 1985, 1992, 1993, 1995) near Station P (50N, 145W). A one-dimensional advection-diffusion model was fitted to the data from each cruise to estimate vertical mixing (K-v) and upwelling velocity (w). With constant K-v and w, the average value of K-v and w was 0.4 +/- 0.1 cm(2) s(-1) and 1.2 +/- 0.4 m yr(-1) respectively for the depth range 0-900 m below the base of the mixed layer. This case produced K-v values that increased with time, and modeled CFC concentrations that were higher than observed in the upper 200 m and lower than observed in the deeper water (200-900 m). Both of these conditions are consistent with K-v values that increased with depth. Fitting the one-dimensional advection-diffusion model to the data with K-v inversely related to the buoyancy frequency reduced the model-data misfit by 40%, produced consistent estimates of K-v for all cruises and reduced the systematic differences in the model data misfits. From this model K-v and w at the base of the mixed layer were 0.15 +/- .04 cm(2) s(-1) and 0.5 +/- 0.15 m yr(-1), respectively. The results strongly supported a K-v that increased with depth. Modeled anthropogenic CO2 penetration at Station P with the inverse buoyancy frequency scaling of K-v, produced results consistent with the observed anthropogenic CO2 penetration inferred from Sigma CO2, alkalinity and apparent oxygen utilization measurements.