Estimation of vertical mixing in the upper ocean at Station P from chlorofluorcarbons
Vertical mixing (Kv) 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 (Kv) and upwelling velocity (w). With constant Kv and w, the average value of Kv and w was 0.4 ± 0.1 cm2 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 Kv 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 Kv values that increased with depth. Fitting the one-dimensional advection-diffusion model to the data with Kv inversely related to the buoyancy frequency reduced the model-data misfit by 40%, produced consistent estimates of Kv for all cruises and reduced the systematic differences in the model data misfits. From this model Kv and w at the base of the mixed layer were 0.15 ± 0.4 cm2 s−1 and 0.5 ± 0.15 m yr−1, respectively. The results strongly supported a Kv that increased with depth. Modeled anthropogenic CO2 penetration at Station P with the inverse buoyancy frequency scaling of Kv, produced results consistent with the observed anthropogenic CO2 penetration inferred from Σ CO2, alkalinity and apparent oxygen utilization measurements.
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Document Type: Research Article
Publication date: May 1, 1997
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