Award: OCE-1220600

We have developed a new technique for measuring the dissolution rate of calcium carbonate in seawater under a wide variety of aqueous conditions. Our method uses highly 13C labeled solids and monitors the appearance of 13C atoms in the solution. In this way we are directly measuring the rate of mass loss. Inorganic calcite has a strongly non-linear dependence of dissolution rate on the degree of undersaturation. This curved behavior means that there are multiple mechanisms working at the solid-solution interface and the dominant one changes with the thermodynamic state of the system. We discovered that the enzyme Carbonic Anhydrase catalyzes the dissolution of calcite at all pH values, including those lower than the normal range for seawater. This result implies that carbonic acid is directly attacking the calcite surface and that we need to rethink the rate law for carbonate dissolution in seawater which currently only includes the activity of calcium and carbonate ions. Given our new, very sensitive, reactor for monitoring the progress of carbonate dissolution, we have begun to explore the rateÆs dependence on pressure and temperature as well as testing other carbonate materials. There is a strong increase in rate with increasing pressure that goes beyond the effect of pressure on the saturation value alone. Temperature experiments are ongoing, but we see a clear increase in rate with higher temperature and potentially different activation energies at different temperatures. We have also cultured planktonic and benthic foraminifera, cocoliths, and soft corals in the presence of 13C to then use the resulting shells in our reactor. At pH values close to equilibrium cocoliths behave the same as inorganic calcite. However, beyond a critical saturation value the biogenic materials are slower to dissolve than calcite, on a per area basis. Bleached and unbleached cocoliths show the same rate dependence on saturation and foraminifera lie between cocoliths and inorganic calcite. Our discovery of catalysis by carbonic anhydrase puts safe and efficient storage of human CO2 emissions in seawater back on the table as a viable climate mitigation solution. By reacting limestone at the surface of the earth, rather than at the bottom of the ocean where it will happen naturally, we can bypass many of the slow steps in the earthÆs natural process that will take up anthropogenic CO2. Given that we can also make the reaction of CO2 and limestone go nearly 1,000 times faster with the catalyst, a series of factories that processed limestone in seawater could greatly mitigate anthropogenic CO2 without changing the oceanÆs pH, pCO2 or carbonate ion concentration. Last Modified: 03/18/2016 Submitted by: Jess F Adkins