Imminent ocean acidification in the Arctic projected with the NCAR global coupled carbon cycle-climate model M. Steinacher1, F. Joos1,2, T. L. Frölicher1, G.-K. Plattner1,*, and S. C. Doney3 1Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland 2Oeschger Centre for Climate Change Research, University of Bern, Erlachstrasse 9a, 3012 Bern, Switzerland 3Dept. of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543-1543, USA *now at: Environmental Physics, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Universitätstrasse 16, 8092 Zürich, Switzerland
Abstract. Ocean acidification from the uptake of anthropogenic carbon is simulated for
the industrial period and IPCC SRES emission scenarios A2 and B1 with a
global coupled carbon cycle-climate model. Earlier studies identified
seawater saturation state with respect to aragonite, a mineral phase of
calcium carbonate, as a key variable governing impacts on corals and other
shell-forming organisms. Globally in the A2 scenario, water saturated by more
than 300%, considered suitable for coral growth, vanishes by 2070 AD
(CO2≈630 ppm), and the ocean volume fraction occupied by
saturated water decreases from 42% to 25% over this century. The largest
simulated pH changes worldwide occur in Arctic surface waters, where hydrogen
ion concentration increases by up to 185% (ΔpH=−0.45). Projected
climate change amplifies the decrease in Arctic surface mean saturation and
pH by more than 20%, mainly due to freshening and increased carbon uptake in
response to sea ice retreat. Modeled saturation compares well with
observation-based estimates along an Arctic transect and simulated changes
have been corrected for remaining model-data differences in this region.
Aragonite undersaturation in Arctic surface waters is projected to occur
locally within a decade and to become more widespread as atmospheric CO2
continues to grow. The results imply that surface waters in the Arctic Ocean
will become corrosive to aragonite, with potentially large implications for
the marine ecosystem, if anthropogenic carbon emissions are not reduced and
atmospheric CO2 not kept below 450 ppm.
Citation: Steinacher, M., Joos, F., Frölicher, T. L., Plattner, G.-K., and Doney, S. C.: Imminent ocean acidification in the Arctic projected with the NCAR global coupled carbon cycle-climate model, Biogeosciences, 6, 515-533, doi:10.5194/bg-6-515-2009, 2009.