THE CARBON DIOXIDE SYSTEM AND ITS ROLE ON TRACE METAL CHEMISTRY IN THE MARINE ENVIRONMENT

Abstract

This thesis consists of a study of the relationship between trace metal chemistry and the carbon dioxide system in the marine environment. The distribution and speciation of several metals with an emphasis on manganese were studied to evaluate the effect of carbon dioxide system, water composition and biological processes. Seawater samples collected in January 1984 along the continental shelf and slope off Peru between latitude 10 to 11°S and longtitude 78 to 79°W were used for this study. An equilibrium model was used to predict the changes of inorganic speciation of trace metals in the marine environment due to changes in water properties. The ionic strength dependence of stoichiometric association constants for both major ions and trace metal complexes was based on a Pitzer-type function. Calculations were made for oceanic and estuarine waters based on thermodynamic data at 25°C and 1 atmosphere pressure. The range of speciation in near-surface ocean waters was based on the chemical characteristics of a highly productive region off Peru. The salinity of these waters was nearly constant at about 35 o/oo. The only significant chemical property that would affect the speciation of trace metals in the region off Peru was pH which ranged from 7.75. to 8.37 in the upper 30 meters. Hydroxy complexes were the major forms of iron(III). Changes in pH were important for the speciation of Pb(II) and Cu(II) for which carbonate complexes were the major species. For Mn(II) and Fe(II), free ions and their chloro complexes contributed more than 90% of the total species. Changes composition of seawater play an important role in Mn(II) and Fe(II) speciation. The chemical speciation of Mn(II) at various salinities was also examined. The amount of MnCl+ complexes increased from less than 0.1% in world-average river water to about 30% in seawater of salinity 35 o/oo. Measurements were made of pH, alkalinity and related biologically active chemicals in the waters off Peru. These data were used to calculate the inorganic carbon species concentrations and the degree of calcite and aragonite saturation in these waters. The total carbon dioxide and oxygen data indicated an upwelling location at about 6.5 km offshore. The water was upwelled along sq of 26.1 at a depth not greater than 100 meters. The recently upwelled water had low pH of less than 7.8 which corresponded to the low oxygen and high nutrient concentrations in this region. The highest biological activity was found