Computerized high-precision titrations of some major constituents of seawater on board the R.V. Dmitry Mendeleev

Abstract

Abstract Computerized high-precision titrations used on board the R.V. Dmitry Mendeleev on its 9th cruise in the Pacific are described. The methods give precise total concentrations in moles per kg seawater (M w ) of alkalinity ( A t ), carbonate ( C t ), calcium ([Ca] t ), calcium + magnesium ([Ca] t + [Mg] t ) and chlorinity (C1). Depth variations of A p C t and Ca t can be explained by the decomposition of photosynthetic matter and the dissolution of calcium carbonate below the photozone. The ratio [Mg] t /Cl varies within 2% and measurements close to 20°N show water masses with both high and low ratios (Fig. 11). The pH and carbonate speciation are calculated from the alkalinity titrations and Hansson's dissociation constants of carbonic acid. The concentration of CO 2 in the surface water is close to the saturation value. Seawater saturated with Globigerina ooze was analyzed for A t , C t and, [Ca 2+ ] t , and these values were used to obtain the saturation depths of calcium carbonate; values close to 200 to 400 m were found.