Anthropogenic Ocean Osteoporosis I - The Chemistry

Dear readers,

Now that you know what causes ocean acidification, this entry will focus on one of the consequences of ocean acidification. In nature, there are many delicate equilibriums. For example, in the oceans, there is a balance between the addition of minerals, such as calcium carbonate, to the oceans, which occurs through the slow weathering of land and stone, and the absorption of carbon dioxide (CO2) into the water. Today, the oceans are absorbing CO2 at a rate of 22 million tons a day, which is overloading this delicate balance and changing the chemistry of the marine system.

Due to the important chemical equilibrium in the oceans between CO2, carbonate ions (CO₃^2-), water, and carbonic acid (H2CO3), an increase in CO2 means a decrease in the available carbonate ions in a marine system. Basically, the available carbonate ions get used up to decrease the elevated concentration of CO2 and form carbonic acid. This process returns the system to a chemical equilibrium. However, on a biological level this has two profoundly negative consequences. One we have already touched on: ocean acidification. As the concentration of carbonic acid increases, the oceans become more acidic. The second consequence is that the availability of carbonate ions decreases.

Carbonate ions are extremely important because, when they react with calcium ions (Ca+2), they form calcium carbonate (CaCO3). Calcium carbonate is the substance of every single shell and coral skeleton in the ocean. As the concentration of carbonate ions decreases, so does the ability of a plethora of marine organisms to build their skeletons and shells. Basically, the anthropogenic input of CO2 into the atmosphere is inadvertently causing a case of ocean osteoporosis.

-N. Gallo

Over thousands of years, the ocean reclaims sediments and minerals by weathering the land. The ions from this weathering process naturally balance the amount of CO2 the oceans absorb. However, the rate of industrial CO2 production has overwhelmed this delicate balance, leading to ocean acidification and decreased carbonate availability. (Photo credit: http://www.alaska-in-pictures.com/data/media/6/crashing-waves_4710.jpg)

For a longer explanation about the chemistry of carbonate loss, check out this great blog entry: http://www.realclimate.org/index.php/archives/2005/07/the-acid-ocean-the-other-problem-with-cosub2sub-emission/