Degree of saturation of CaCO3in the oceans

Abstract

The degree of saturation of CaCO2 in the Pacific and Atlantic oceans has been calculated from measurements of the partial pressure of CO2 gas and of the total content of dissolved inorganic CO2. Lyman's apparent dissociation constants for carbonic and boric acid at 1 bar, MacIntyre's apparent solubility product of CaCO3 in sea water at 1 bar, and the Disteches' determinations of the pressure dependence of these parameters were used for the calculation. The results indicate that the crossover from supersaturation to undersaturation for CaCO3 occurs at a water depth between 500 and 3000 meters for calcite and at about 300 meters for aragonite in the Pacifiic, and between 4000 and 5000 meters for calcite and between 1000 and 2500 meters for aragonite in the North Atlantic Ocean. This difference between the Pacific and Atlantic oceans may be attributed to a difference in the amount of CO2 dissolved in these waters. Such a difference may, in turn, be caused by a difference in the residence times in these waters. The marked decrease of CaCO3 content in the ocean bottom sediments observed at water depths greater than 3500 meters in the Pacific and 4500 meters in the Atlantic appears to reflect a transition of the sea water from saturation to undersaturation with respect to calcite.