71% of the earth’s surface is covered by water and large areas of the land are covered by frozen water. Water and water vapour are also significant components of the atmosphere.
The atmosphere and its trace component of carbon dioxide is a very thin skin in close contact with the surface of all of this water. Carbon dioxide is very soluble in water and Henry’s Law says that as the temperature of water changes the quantity of carbon dioxide dissolved in that water will change.
Thus if the sea surface temperature increases, carbon dioxide will be expelled to the atmosphere just like carbon dioxide bubbles are expelled from a warming beer. And as sea surface temperature falls, carbon dioxide will dissolve in the cooling water and this reduces the carbon dioxide in the atmosphere.
This effect can be seen in seasonal, medium term and long term trends.
The seasonal variation in atmospheric content of carbon dioxide is well known, and the huge southern oceans are key players. See the short paper by Bob Beatty on the carbon dioxide cycle at : http://www.bosmin.com/HenrysLaw.pdf [PDF, 689 KB]
When it is winter in the southern hemisphere, the cold surface water of the oceans absorb carbon dioxide and the content of carbon dioxide in the air falls suddenly by about 4 ppm. This is reversed when the southern oceans warm in summer, and the carbon dioxide is expelled from the oceans. (The seasonal summer growth and winter fall of northern hemisphere vegetation adds to this seasonal fluctuation caused mainly by the southern oceans.)
On a medium time scale (21 year moving average) Professor Lance Endersbee published a short paper in August 2008 and he concluded that the oceans regulate the carbon dioxide in the atmosphere and the influence of human-generated carbon dioxide in the atmosphere is negligible. His paper included the following diagram:
See full article at: endersbee-co2-and-oceans.pdf [PDF, 490 KB; Source: ATSE No 151, August 2008.]
See also this paper by Alan MacRae: http://icecap.us/images/uploads/CO2vsTMacRae.pdf [PDF, 286 KB]
On longer time scales, ocean mixing caused by deep ocean currents causes long term changes in ocean temperatures. These changes also affect long term carbon dioxide trends. Carbon dioxide held in large quantities in cold deep ocean water is slowly released as ocean currents mix this cold water with warmer surface water. The reverse occurs as the sea surface cools, absorbs carbon dioxide and the cold dense water sinks to the ocean floor.
The most dramatic evidence of this lagged response comes from ice core data. These show that significant turning points in temperature precede the corresponding turning points in carbon dioxide content in air by between 650 and 1600 years.
Henry’s Law can and has been tested in laboratory experiments. The other data provides additional evidence for the conclusion that the major factor regulating carbon dioxide in the atmosphere, on all time scales, is the temperature of the oceans. Ocean temperature is controlled by solar cycles, cloud cover, ocean currents and undersea volcanism.
– Viv Forbes
[Originally published December 2010 at https://carbon-sense.com/2010/12/29/forbes-co2-and-oceans/]