fCO2 dynamics in the Atlantic, South Pacific and South Indian oceans

Subsurface fugacities of CO2 (fCO2(20)) can be used in combination with total dissolved inorganic carbon (DIC) to precisely calculate total alkalinity. Thus it can be used to determine dissolution of calcium carbonate (hard tissue) and remineralization of organic material (soft tissue), to quantify saturation constants of calcite and aragonite in seawater, and to characterize water masses. fCO2(20) is a good tracer of biological transformation since it is thermodynamically related to the other inorganic carbon system parameters and it has a dynamic range from 200 to 2000 μatm in the worldʹs ocean. Precision of fCO2 measurements is 0.3% and the values are well calibrated using compressed gas reference standards. Increases of fCO2(20) are observed as the water masses age during movement from the Atlantic to the Indian and South Pacific oceans. As an example of the determination of the ratio of soft tissue remineralization to hard tissue dissolution from fCO2(20) and DIC, the trends along the 27.2 isopycnal for the subtropical gyres of the three basins are investigated. Little CaCO3 dissolves along this isopycnal in the Atlantic and the South Pacific while the soft tissue remineralization to hard tissue dissolution ratio in Indian Ocean is 4.5:1. The difference in this ratio along the 27.2 isopycnal appears to be a combination of the calcite and aragonite saturation levels and the supply of aragonite tests.