Causes and effects of composition changes in the ocean

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For more than a century the assumption that the dissolved matter in seawater has a fixed relative composition, and hence can be characterized by a single variable (the "salinity"), has dominated ALL practical aspects of oceanographic science. However, although measurements of salinity using electrical conductivity can be made routinely to a precision of +/-2 mg/kg (on the new Reference Composition Salinity Scale), the true salinities of real seawater may differ by from these estimates by up to 30 mg/kg in the open ocean, 90 mg/kg in the Baltic, and potentially much more in near-coastal areas. These errors arise due to the effects of changes in the chemical composition of seawater. These composition changes are in fact the largest source of uncertainty in estimates of the thermodynamic properties of seawater (e.g., density) when using standard equations that relate them to conductivity. Although I have proposed some techniques for estimating the necessary corrections based on fundamental physical/chemical factors, these techniques are relatively immature. This is partly due to inadequacies in our knowledge of the actual composition variations and the physical, biological, and chemical processes that control them, and partly due to uncertainties in our fundamental knowledge of the theory governing conductivity/salinity/density relationships in all natural waters.