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Abstract:
Dissolution of fossil fuel CO 2 in seawater results in decreasing carbonate ion concentration and lowering of seawater pH with likely negative impacts for many marine organisms. We project detectable changes in carbonate dissolution and evaluate their potential to mitigate atmospheric CO 2 and ocean acidification with a global biogeochemistry model HAMOCC forced by different CO 2 emission scenarios. Our results suggest that as the anthropogenic CO 2 signal penetrates into ocean interior, the saturation state of carbonate minerals will drop drastically-with undersaturation extending from the ocean floor up to 100-150 m depth in the next century. This will induce massive dissolution of CaCO 3 in the water column as well as the sediment, increasing the Total Alkalinity (TA) by up to 180 mol kg -1 at the surface and in the ocean interior over the next 2500 years. Model results indicate an inhomogeneous response among different ocean basins: Atlantic carbonate chemistry responds faster and starts recovering two millennia after CO 2 emissions cease, which is not the case in the Pacific. CaCO 3 rain stops in the Pacific Ocean around 2230. Using an observation-derived detection threshold for TA, we project detectable dissolution-driven changes only by the year 2070 in the surface ocean and after 2230 and 2500 in the deep Atlantic and Pacific respectively. We show that different model assumptions regarding dissolution and calcification rates have little impact on future projections. Instead, anthropogenic CO 2 emissions overwhelmingly control the degree of perturbation in ocean chemistry. In conclusion, ocean carbonate dissolution has insignificant potential in mitigating atmospheric CO 2 and ocean acidification in the next millennia. Copyright 2012 by the American Geophysical Union.
