Impacts of climate change on air-sea exchanges of CO2
Totterdell, I. (2013) Impacts of climate change on air-sea exchanges of CO2, MCCIP Science Review 2013, 91-97, doi:10.14465/2013.arc11.091-097
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The oceans are a significant sink for anthropogenic carbon dioxide (CO2), taking up 2.3±0.5 petagrammes of carbon per year from the atmosphere (about one quarter of anthropogenic emissions) as CO2 naturally dissolves in the water.
This net air-to-sea anthropogenic flux is in addition to an approximately globally-balanced natural cycle of CO2 between the atmosphere and ocean
Some of the in-gassed anthropogenic CO2 remains in the surface ocean, increasing the partial pressure there, while the rest is mixed or carried into the deep ocean.
The ocean uptake of CO2 is expected to decrease during the 21st Century due to a number of factors:
- the additional CO2 will increase the proportion present as dissolved gas rather than as bicarbonate and carbonate ions;
- rising sea-surface temperatures will reduce the solubility of CO2 in sea-water;
- slowing ocean circulation will reduce the transport to depth;
- reduction in biological activity may reduce the sinking flux of particulate organic carbon
Reductions in the uptake flux have been seen in recent decades in two regions with large net air-to-sea fluxes of anthropogenic CO2 (the North Atlantic and the Southern Ocean) but it is not clear if these are long-term trends or short-term variability.
The continental shelves are very important in the natural carbon cycle, but it is not clear what role they will play in the future uptake of anthropogenic CO2.
Increased monitoring, using automated sensors on moored buoys, drifting floats and commercial shipping, is essential to better understand the ocean uptake of anthropogenic CO2.