Acidification CO2

The rate of carbon dioxide (CO2) production has been continually increasing over the past century (Figure 9). Due to this rise in levels of atmospheric CO2, there has been a notable decrease in the pH of the global oceans through the process of acidification due to the CO2 dissolving into the water. The increased acidity of the oceans alters the chemistry of the water, which in turn affects life processes of many marine organisms (Doney et al., 2009).

Figure 10:
Figure 9: Showing the past and projected pH and dissolved carbon dioxide of the ocean.

The waters of the Southern Ocean are particularly susceptible to ocean acidification because of the higher level of solubility seen within compounds in the colder waters; for example CO2 and CaCO3.

Antarctic krill (Euphausia superba) are found in a variety of depths within the Southern Ocean. They are seen to spawn within the surface waters of the ocean, where the eggs then sink hundreds of meters before hatching; the larvae then ascend by swimming towards the surface. During this process the krill are naturally exposed to an increased CO2 at depth due to hypercapnic upwelling (heightened levels of CO2) (Pane & Barry 2007; Quentin & Ross, 1984).

E. superba have been found to be exceptionally susceptible to fluctuations in the ocean acidity. During a series of controlled investigations carried out on krill eggs, whereby the level of CO2 was gradually increased, it was found that disruption was evident on the krill embryos, as well as inhibition during periods of hatching at levels of considerably increased concentrations of CO2 (Kawaguchi et al., 2013).