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Physical Background

How physical processes affect carbon dioxide uptake

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Figure 1: The difference between current ocean CO2 concentrations and preindustrial concentrations. Warm colors indicate surplus CO2 added by human activity. (Sabine et al., 2004)

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Figure 2: Ocean carbon dioxide data in the central Pacific (HOT) and Atlantic (BATS) Oceans. In both oceans, ocean pH (third plot down) has decreased measurably in the past decade. (Kleypas et al., 2005)

Carbon dioxide in the atmosphere enters the surface ocean by diffusion that depends on water temperature, salinity, and windspeed.  The gas is most soluble in cold, salty water, and greater wind speeds drive more gas into the water surface more quickly.  As a result, the upper oceans and the cold, polar oceans  will experience ocean acidification due to increased CO2 before the deep oceans.  Figure 1 shows the extent to which anthropogenic CO2 has invaded the ocean already, and the surface oceans are clearly most affected. 

The north Atlantic contains a greater share of anthropogenic CO2 in part due to ocean circulation.  The "solubility pump" moves cold surface seawater rich in anthropogenic CO2 towards the poles, where it cools further and sinks into the deep ocean.  Deep ocean water is then out of contact with the atmosphere for about 1000 years. At sites where deep ocean water upwells to the surface, ocean waters do not contain anthropogenically generated CO2, because they have been out of contact with the high-CO2 present-day atmosphere. 

Due to the large size of the ocean basin and the large capacity of deep seawater for carbon dioxide, models predict that the ocean can take up X amount of atmospheric CO2.  However, that will come at the cost of further decreasing ocean pH and injuring ocean ecosystems.

Ocean pH is changing throughout the worlds' oceans (figure 2) from ocean uptake of atmospheric CO2 (Kleypas et al., 2005).  Even though the ocean will not become neutral or even acidic due to OA, the pH decrease due to OA can still significantly influence ocean life. 

Last updated: January 26, 2009

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