25
Figure 7: Carbon fluxes in the oceans.
(Source: adapted from Takahashi
et al
., 2009).
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).
Mol of carbon per square metre
Oceans carbon fluxes
-1
0.5
-0.5
1
Source: Marine Institute, Ireland, 2009.
Net carbon
release
Net carbon
uptake
