Blue Carbon

Oceans are absorbing both heat and carbon from the atmosphere, therefore alleviating the impacts of global warming in the environ- ment. Covering more than two-thirds of the earth’s surface, the oceans store the sun’s energy that reaches earth’s surface in the form of heat, redistribute it, from the coast to the mid-ocean, shal- low to deep waters, polar to tropical, and then slowly release it back to the atmosphere. These storage and circulation processes prevent abrupt changes in temperature, making coastal weather mild and some high latitude areas of the globe habitable. However this huge heat storage capacity can have undesirable consequences with the advent of climate change. With global warming, the ocean is ab- sorbing a large portion of the excess heat present in the atmosphere (almost 90%), resulting in a measurable increase of surface water temperatures (an average of approximately 0.64 o C over the last 50 years) (Levitus et al. , 2000; IPCC, 2007b). As water warms, it ex-

 Figure 6: Carbon cycling in the world’s oceans. The flow of carbon dioxide across the air-sea interface is a function of CO 2 solubility in sea water (Solubility Pump). The amount of CO 2 dissolved in sea water is mainly influenced by physico-chemical conditions (sea water temperature, salinity, total alkalinity) and biological processes, e.g. primary production. The solubility pump and the biological pump enhance the uptake of CO 2 by the surface ocean influencing its val- ues for dissolved CO 2 and transferring carbon to deep waters. All these mechanisms are strongly connected, subtly balanced and influential to the ocean’s capacity to sink carbon. The net effect of the biological pump in itself is to keep the atmosphere concentration of CO 2 around 30% of what it would be in its absence (Siegenthaler and Sarmiento, 1993).

Oceans carbon fluxes

Mol of carbon per square metre

Net carbon release

1

0.5

-0.5

-1

Net carbon uptake

Source: Marine Institute, Ireland, 2009.

Figure 7: Carbon fluxes in the oceans. (Source: adapted from Takahashi et al ., 2009).

25