Impact of climate change on Antarctic krill

Ocean acidification

The ecosystems of the Southern Ocean are expected

to be some of those most severely affected by ocean

acidification (OA) because of the higher solubilities

of CO

2

and CaCO

3

in cold waters, and because of

regional upwelling of hypercapnic deep-sea water

(Sabine et al. 2004, Doney et al. 2009). Atmospheric

CO

2

concentration has risen from 280 ppm in the

preindustrial period to presently ~380 ppm (Orr et al.

2005). Although future projections for atmospheric

CO

2

level are highly variable among the scenarios

discussed by the Intergovernmental Panel on Cli-

mate Change (IPCC), atmospheric CO

2

concentra-

tions are projected to increase throughout the 21st

century according to all scenarios. The IPCC marker

scenarios project atmospheric CO

2

concentrations

ranging from 535 to 983 ppm by 2100 (IPCC 2007).

Recent studies based on in situ time series provide

evidence of OA already progressing in extensive

regions of the Southern Ocean (Midorikawa et al.

2012). In the Southern Ocean, model-based projec-

tions of CO

2

concentrations in seawater expressed as