Geochemistry of carbon dioxide in seawater at the Hawaii Ocean Time Series Station, ALOHA

Abstract

This paper examines the fundamental biological and physical processes controlling the distribution of the inorganic carbon species throughout the water column at the Hawaii Ocean Time series station, ALOHA. Profiles of alkalinity and calcium are strongly influenced by the distribution and movement of the six water masses at this location. The semiconservative behavior of these parameters can be useful in identifying water masses. The dissolution of carbonate particles, however, contributes up to 21% (49 μmol C kg−1) of the dissolved inorganic carbon added to the intermediate waters between the time the waters enter the Pacific and the time they reach Station ALOHA. A sharp increase in carbonate‐derived carbon observed between 800 and 2200 m is due to the dissolution of the more soluble forms of carbonate such as aragonite. The distribution of TCO2 and pH at this site are significantly affected by biological processes as indicated by the apparent nonlinear mixing curves between water masses, the similarity of the measured ratios of C:N and C:P to the Redfield ratios in the upper 700 m of the water column, and the results of a carbon system model. The nonconservative nature of these properties demonstrates that both physical and biological factors must be considered when evaluating temporal variability. The carbon system evaluation techniques presented here are similar to those used on several previous trans‐Pacific cruises allowing the results from this station to be compared to the results of other cruises in this area.