Chemical speciation of the CO2 system in seawater off Coquimbo, Chile

CO2 occupies a major place in the biosphere, and its exchange between the a tmosphere and ocean plays an important role in global climate control. The ocean is able to absorb large quantities of CO2, due to its solubility in w ater; the solubility is increased by the buffering action of the carbonate- bicarbonate system in sea water. In order to study the vertical distribution of the different chemical speci es in the dissolved CO2 system of water off the Chilean coast, seawater sam ples were taken at two oceanographic stations near Coquimbo, down to 2,800 m depth. Precise measurements of dissolved oxygen, pH and total alkalinity (A(T)) at 25 degrees C were made. Knowing the in situ salinity and temperat ure, it is possible to estimate the apparent dissociation constants require d to describe the CO2 system equilibrium, in a complex matrix such as seawa ter, in which high ionic strength and large temperature differences exist.