As we covered in Lecture 8 and more recently in Lecture 24 the oceans act as a carbon dioxide sink. Increased atmospheric carbon dioxide dissolves into the ocean water increasing dissolved carbon dioxide but also increasing the formation of carbonic acid. The carbonate complex consists of the following reactions:
H2CO3 (carbonic acid) ←→ H+ + HCO3- (bicarbonate)
HCO3- ←→ H+ + CO32- (carbonate)
As the carbonic acid levels increase, more H+ donates to the ocean, in aggregate, making the ocean more acidic. CO2 becomes corrosive to shells and skeletons of ocean organisms. Although worsening conditions for marine life, the carbonate complex also helps to keep atmospheric CO2 levels lower. According to a recent New York Times article, Dr. Samar Khatiwala, a professor at Georgia Institute of Technology, suggests the absorption rate grows less effective as the acidity increases. “It’s a small change in absolute terms. What I think is fairly clear an important in the long term is the trend toward lower values, which implies that more of the emissions will remain in the atmosphere.”
Dr. Khatiwala uses a model to calculate the oceans’ uptake rate growth, which seems to drop by 10 percent from 2000 to 2007. Dr. Christopher Sabine used a different study, published in Science 2004 to confirm global uptake rates in 1994, measuring CO2 levels on more than 100 cruise ships.
Although, the evidence remains mostly within a model, this trend could mean that marine life may not experience a simple exponential growth in acidity. Unfortunately, the uptake loss would only further atmospheric CO2 accumulation acting as a positive feedback loop as explained in Lecture 6.