Ocean Flux of CO2 debate

Last years (2010) World Development Report by the World Bank reported that oceans will become more acidic over the coming decades and centuries as a direct chemical consequence of the increasing atmospheric concentration of CO2. Most of which is considered to be produced by human activities. Oceanic water acts as a natural sponge, absorbing a large proportion of CO2, creating relatively dense CO2 rich waters that sink to the ocean bottom.

It has been proposed that absorption of approximately one-third of man-made emissions of CO2 over the past 200 years has decreased the pH of surface seawater by 0.1 units (which given that pH is measured on a logarithmic scale, is quite a lot). One of the most important implications of the changing acidity of the oceans is the problem that it may cause for the many of the marine photosynthetic organisms and animals, such as corals, bivalves, and some plankton that are very sensitive to acid because their shells and plates are made out of calcium carbonate, which cannot be formed in too acidic conditions.

Sea Butterfly
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If plankton, which form the base of the marine food chain and are a major food source for fish and marine mammals are unable to acclimatise or evolve in response to rapid changes in ocean acidity, whole marine ecosystems may collapse. Therefore no more tuna, salmon etc.

Ocean temperature increases in recent years have already pushed coral reefs to their limits with higher sea surface temperatures stressing corals and causing coral bleaching due to the death of the symbiotic algae, frequently resulting in large-scale mortality across regions of formerly pristine coral. What further effect will acidic conditions have? About 30 million of the world's poorest people directly rely on coral reef ecosystems for food, while they are exploited for goods and services of roughly $375 billion a year to nearly 500 million people. This includes food and tourism.

As with all such reports the World Bank report includes the statement that 

"research into the impacts of high concentrations of CO2 in the oceans is still in its infancy".

So it is not surprising that New Scientist reported contradictory evidence this week. Some scientists believe that as the world warms the oceans will emit more CO2 and studies of two independent sets of ice cores have shown evidence of this over the last 200 years.

Why is this? Well firstly melting sea ice, which produces very cold water that sinks to the bottom pushes CO2-rich deep ocean waters to the surface and increases the rate of ocean water mixing.

Secondly as anyone who has observed the bubbles forming on the base of a pan of water as it is heated on a stove knows - when you heat up water it releases gases it contains. Therefore warming of all this near surface CO2 rich water is thought likely to contribute to increasing atmospheric CO2.

Warmer oceans release CO2 faster than thought - environment - 25 April 2011 - New Scientist

The reality is that man made CO2 influences natural cycles in as yet unpredictable ways. This schematic shows clearly that while other aspects of the carbon cycle are offset by dynamic natural processes, there is as yet no dynamic offset capable of dealing with man's emissions.