First results from a controlled deep sea CO2 perturbation experiment: Evidence for rapid equilibration of the oceanic CO2 system at depth

摘要

We have carried out series of remotely operated vehicle–controlled oceanic CO2 system perturbation experiments off the coast of California at depths down to 1000 m to observe reaction rates and pathways with both HCl and HCO3 - addition. The work was done to evaluate possible barriers to carrying out future Free Ocean CO2 Enrichment experiments to simulate the chemistry of the emerging high CO2–lower pH ocean. A looped 460 mL flow cell with a pH sensor was used to monitor the time to equilibrium for 900 μL additions of 0.008 N HCl and for small slugs of HCO3 ?enriched seawater. The results were compared to equivalent experiments at the same temperature and 1 atm pressure. In each case the experiments at depth showed significantly faster time to equilibrium than those at 1 atm. These results are consistent with the low partial molal volume of CO2 in seawater, favoring the hydration reaction rate. The results imply, but do not prove, a significant effect of pressure on the rate constants. The relatively rapid equilibration times observed in seawater of 4°C and at 10 MPa indicates that there are no fundamental physical chemistry limits for carrying out small-scale free-ocean CO2 enrichment experiments.