Long-term trends of surface ocean acidification in the Southern Ocean

Time: Sometime between Friday 11 June 16:00 and 17:30
theme: Theme 1. Linkages between Polar Regions and global systems
session: T1-6 Arctic and Antarctic marine chemistry: The role of the polar oceans in global carbon cycling and acidification
event: Poster session PS3 – Section B
location: Hall C

The Southern Ocean is considered to have a significant impact on global air-to-sea CO2 fluxes because of the large cold surface area, regional wind velocity and high export production. The long-term increase in the partial pressure of CO2 in surface waters (pCO2sea) was found in the extensive region north of the seasonal sea ice zone, i.e., from the subtropical to polar zone (Inoue and Ishii, 2005). The uptake of anthropogenic carbon by the ocean has given rise to changes in chemical equilibrium in the surface ocean CO2 system, resulting in a reduction of seawater pH, i.e., the ocean acidification. Model simulations have indicated that anthropogenic ocean acidification might impact calcifying organisms at high latitudes, particularly in the Southern Ocean, within the next few decades (Orr et al., 2005).

We estimated long-term trends of surface ocean acidification in the western Pacific sector and the Indian sector of the Southern Ocean. Estimates were based on the observational data of surface carbonate parameters from five cruises in Austral summer for 1994 to 2009. The pH values were calculated from sea surface temperature (SST), salinity, pCO2sea and dissolved inorganic carbon (or total alkalinity) by the methods of Dickson et al. (2007) using a solubility constant for CO2 in seawater given by Weiss (1974) and dissociation constants of carbonic acid given by Lueker et al. (2000).

The computed pH in surface waters exhibited significant decreasing trends for 15 years in the representative zones between oceanographic fronts by taking into account the contributions of long-term SST trends as well as the changes in the seasonal variations of carbonate parameters. It is concluded that the invasion of anthropogenic CO2 is responsible for the acidification. The characteristics of acidification in the Southern Ocean will be discussed, compared with that in the subtropical region.


Dickson, A. G., Sabine, C. L. and Christian, J. R. (Eds.) 2007. Guide to best practices for ocean CO2 measurements. PICES Special Publication 3, 191 pp.

Inoue, H. Y. and Ishii, M. 2005. Variations and trends of CO2 in the surface seawater in the Southern Ocean south of Australia between 1969 and 2002. Tellus, 57B, 58-69.

Lueker, T. J., Dickson, A. G. and Keeling, C. D. 2000. Ocean pCO2 calculated from dissolved inorganic carbon, alkalinity, and equations for K1 and K2: validation based on laboratory measurements of CO2 in gas and seawater at equilibrium. Mar. Chem., 70, 105-119.

Orr, J. C., et al. 2005. Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature, 437, 681-686.

Weiss, R. F. 1974. Carbon dioxide in water and seawater: the solubility of a non-ideal gas. Mar. Chem., 2, 203–215.

T. Midorikawa, H. Y. Inoue, M. Ishii, D. Sasano, G. Hashida, S. Nakaoka, Oslo Science Conference, Article.

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