organic biological matter (a mechanism known as the “biological pump), with a net transfer of approximately 2 Gt of carbon (equivalent to about 7.5 Gt of CO2) to the ocean. Since the industrial revolution, the planet’s oceans have absorbed roughly one-third of all the anthropogenic carbon emissions. Given the its central role in the global carbon cycle, any feedback mechanism that negatively impacts the ocean’s ability to act as a carbon sink is likely to make an appreciable difference to the future of the climate in general. There are three primary positive warming feedbacks associated with a reduction in the oceans’ ability to sequester carbon:
(1) As anyone who has ever left a bottle of soda in a car on a very hot day (and ended up with an expensive cleaning bill) knows, liquid’s ability to store dissolved carbon dioxide decreases as the liquid’s temperature increases. As increased CO2 levels in the atmosphere lead to increased air temperatures, the oceans too will warm. This will decrease their ability to “scrub” excess CO2 from the atmosphere, leading to still more warming.
(2) This increased oceanic temperature will also potentially disrupt the action of the Atlantic Thermohaline Circulation. The thermohaline transports a tremendous amount of water--something in the neighborhood of 100 times the amount of water moved by the Amazon river--and is the mechanism by which the cold anoxic water of the deep oceans is circulated to the surface. This renders the thermohaline essential not just for deep ocean life (in virtue of oxygenating the depths), but also an important component in the carbon cycle, as the water carried up from the depths is capable of absorbing more CO2 than the warmer water near the surface. The thermohaline is driven primarily by differences in water density, which in turn is a
- Dawson and Spannagle (2007), p. 303-304