Global relationships of total inorganic carbon with temperature and nitrate in surface seawater

Abstract

High quality total inorganic carbon (CT) measurements made in the major ocean basins as part of the Joint Global Ocean Flux Study (JGOFS), the National Oceanic and Atmospheric Administration/Ocean Atmosphere Carbon Exchange Study (NOAA/OACES), and the Department of Energy/World Ocean Circulation Experiment (DOE/WOCE) programs are related to sea surface temperature (SST) and nitrate (NO3-). A simple two-parameter function with SST and NO3- of the form NCT = a + b SST + c SST2 + d NO3- fits salinity (S)-normalized surface CT (NCT = CT × 35/S) data for different parts of the oceans within an area-weighted error of ±7 μmol kg-1 (1σ). Estimated values of NCT using the derived algorithms with NO3- and SST are compared with values calculated from the surface partial pressure of CO2 (pCO2sw) [Takahashi et al.,1997] and total alkalinity (AT) [Millero et al., 1998] fields using thermodynamic models. Comparisons of the estimated values of NCT with measurements not used to derive the same algorithms, and comparisons with the values calculated from global AT and pCO2sw fields, give a realistic uncertainty of ±15 μmol kg-1 in estimated CT. The derived correlations of NCT with SST and NO3- presented here make it possible to estimate surface CT over the ocean from climatological SST, S, and NO3- fields.