The dependence on temperature and salinity of dissolved inorganic carbon in East Atlantic surface waters

Recurring latitudinal patterns of the dissolved inorganic carbon (DIC) content and the fugacity of CO2 (fCO(2)) were observed in East Atlantic surface waters with strong gradients at hydrographic fronts. The dissolved inorganic carbon chemistry clearly displayed the effects of oceanic circulation and of persistent surface water processes. In two cases inorganic carbon components could be used as an indicator of the origin of hydrographic features. Surface water fCO(2) below the atmospheric value, low DIC and low salinity north of the equator were ascribed to a combination of high rainfall and low wind speed in the Intertropical Convergence Zone and of biological uptake of CO2. Low surface water DIC and salinity delineated the Congo outflow. Along the cruise tracks calculated titration alkalinity (TA) had an almost linear relationship with salinity, while DIC had an apparent dependence on temperature and salinity. The latter dependence was tested by comparing observed DIC to DIC estimated from fCO(2) and a reference value of TA normalised to salinity. Different scenarios of temperature, salinity, fCO(2) and nutrient contents were applied. Changes of DIC were found to be indeed related to both temperature and salinity. The latitudinal distribution of DIC could be inferred with an accuracy of 17 mu mol kg(-1) and a standard deviation of 13 mu mol kg(-1) from in situ salinity, in situ temperature and the reference values of TA and nutrient contents normalised to in situ salinity (scenario D). The applied technique of estimating DIC from temperature and salinity is a powerful diagnostic tool to evaluate the spatial distribution of DIG. (C) 1999 Elsevier Science B.V. All rights reserved.