An in situ experiment of calcium carbonate dissolution in the central Pacific Ocean

We developed a new in situ experimental device and conducted a field experiment in the central Pacific Ocean to calculate with a high degree of accuracy a quantitative evaluation of the neutralizing effect and the CaCO3 dissolution rate of sinking particles for effective CO2 ocean sequestration. Devices utilizing a continuous flow system to avoid the effects of water stagnation were deployed in two layers, ca. 3800 and 5000 m deep, over a period of 23 days to measure the dissolution rate of CaCO3 particles that consisted of samples of planktonic foraminiferal tests and fragmental calcite and aragonite crystals. Furthermore, sample chambers (moored chambers) were attached to the same mooring system in 26 layers at intervals of 100 or 250 m below 1700 m deep to obtain the dissolution rate versus depth. Comparison of dissolution rates between experimental device and moored chambers showed the influence of the stagnation in ambient water of particles largely effects on dissolution rates. Foraminiferal tests showed higher dissolution rates than those of crystal fragments because of the larger surface reacting with water. It is concluded that the dissolution rate of foraminiferal tests increases notably with the decreasing degree of saturation with calcite (Ωc) value immediately less than ca. 0.8. In case of increasing the degree of undersaturation in mid-deep layer by CO2 injection, the dissolution rate of CaCO3 particles accelerate exponentially.