Dissolved CO2 in Oceans Lowers pH and Decreases Aragonite Concentrations

The consumption of fossil fuels since the industrial revolution has dramatically increased the amount of CO2 dissolved in the oceans, the effects of which have only recently fallen under the lens of scientific research. The Earth’s oceanic ecosystems are dependent on the balance between pH levels and dissolved carbonic compounds such as CO32-, aragonite and calcite, all of which are drastically effected by CO2 dissolution. Studies indicate that pH levels have dropped by about 0.1, (Feely et al., 2009) since the industrial era and will continue to drop in conjunction with a decrease in carbonic compounds in the decades to come. This change may eventually disable marine organisms’ ability to produce calcium carbonate shells.— Julia Levy

Feely R., Doney S., Cooley S. (2009). Present Conditions and Future Changes in a High-CO2 World. Oceanography 22, 36-47

Richard A. Feely and associates at the World Ocean Circulation Experiment/Joint Global Ocean Flux Study spent nine years conducting cruises to measure different carbon parameters in oceans throughout the world. Carbonate ion, aragonite, calcite, and pH are among the parameters that the researchers measured. They then used the National Center for Atmospheric Research to predict future changes in the aforementioned parameters.
Their findings indicate that the current pH of the oceans is 8.1 but will drop to 7.8 by the end of this century. Concentrations of CO32- are also projected to decrease drastically before the turn of the century. They are projected to drop low enough that the concentrations of aragonite and calcite in the oceans will become undersaturated (anticipated to occur 2020 and 2050 respectively). It is this decrease in carbon compounds that will make it difficult if not completely impossible for aquatic creatures to form calcium carbonate shells.
The mechanism by which the inability to form carbonate shells occurs through a series of chemical reactions. After CO2 in the atmosphere is dissolved into the ocean, it reacts with water to produces more H+ ions (decreasing the pH of the ocean). The newly available H+ ions react with CO32-, decreasing the concentration of CO32-.  As mentioned before, this decreases aragonite and calcite concentrations, inhibiting the formation of calcium carbonate shells. The projections made by Feely and his colleagues indicate that this century is a pivotal time for humankind to decrease their CO2 emissions, or else marine ecosystems will be in danger as early as the year 2020.— Julia Levy