GLOBAL WARMING, OCEAN ACIDIFICATION AND THE FUTURE OF THE PLANET.Connecting the Dots

• Main Author: Bruce Steele
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Ocean acidification
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.560.9514; http://switchboard.nrdc.org/blogs/kwing/media/Steele_OceanAcidification.pdf

In the past 200 years the oceans have absorbed about 525 billion tons of carbon dioxide (CO2), almost half of the amount produced by human activities. (Sabine and Feely, 2007). As CO2 dissolves in seawater, it acts to make the ocean more acidic. The pH of global oceans has already dropped 0.1, on average, but this seemingly small change has increased acidity by about 30 percent. Ocean acidification amplifies the negative impacts caused by climate change – one condition exacerbates the other. Seawater pH is a critical variable in the marine environment. Today’s surface ocean is slightly alkaline, and it is saturated with calcium carbonate, an essential organic molecule for organisms such as corals, echinoderms, mollusks and crustaceans that make shells. As CO2 reacts with seawater, it lowers the pH and releases hydrogen ions. These ions bind strongly with carbonate, preventing it from forming calcium carbonate molecules. If the pH of global oceans drops 0.4 by 2100, as predicted, the levels of calcium carbonate available for use by shellfish could decrease by some 45-50 percent. (Orr, 2005). To put this in historical perspective, surface ocean pH would decrease to a level not seen for more than 20 million years. (Feely et al, 2004). The ocean has mechanisms to buffer surface acidification. In fact, physical mixing of ocean water and the biological process that transports calcite shells of surface dwelling animals to the ocean depths as they die have been responsible for balancing the acidifying effects of CO2 for the last 750+ million years. (Knoll, 2003). Calcifiers span the food chain, including organisms such as echinoderms, crustaceans and mollusks. Today calcium carbonate and silica leave the ocean largely as skeletons. (Knoll, 2003). However, due to the combustion of hydrocarbons since the beginning of the Industrial Revolution and the resultant increases of atmospheric CO2, largely human-induced atmospheric changes have exceeded the ocean’s ability to absorb the increasing CO2 levels.