Estimation of total C02 concentration throughout the water column

We use total C02 data sets measured on the recent Joint Global Ocean Flux Study (JGOFS) and World Ocean Circulation Experiment (WOCE) cruises to investigate potential parameterizations of TC02 data sets. The observed temporal variations of TC02 in surface seawater were large (4% of the signal within a month) compared to the relatively small spatial variations (< 2% over 10 degree latitude). Yet the result of our study suggests that a single sigmoid function of the form TCO2(x) = a1 − b1[1 + e−(c1(x−d1))]e1 + b1 can be used to fit, parameterize, and interpolate closely (within the accuracy of the measurement) each upper ocean (< 250 m) TCO2-depth profile of the temporal and spatial data sets from the North Atlantic and Equatorial Pacific Oceans that we examined. This sigmoid function is not specific to TCO2 data sets, and it could probably be used over most (if not all) of the upper ocean to fit, parameterize, and interpolate physical and chemical oceanic data sets. the upper layer (depth > 250 m) TCO2 can be parameterized by the relationship TCO2 = a + bΘ + c AOU + dS where Θ, AOU, and S represents potential temperature, apparent oxygen utilization and salinity, respectively. The coefficients a, b, c, and d are experimentally determined by multiple linear regression using discrete bottle data from depths below the wintertime mixed layer depth. Densely sampled CTD data of temperature, salinity, and oxygen can then be used to interpolate TCO2 data at non-sampled depths. The two parameterized functions describing TCO2 in and below the upper ocean can further be blended at the wintertime mixed layer depth to yield a continuous estimate of TCO2 concentration throughout the water column.