The global ocean has already taken up half of the atmospheric carbon dioxide produced by humans over the last 200 years, so the ongoing effects of climate change are dampened. That’s right, you can thank the ocean for saving the planet so far. Without the ocean, what we would have? A place that looks a lot like Mars.
Ocean chemistry is changing, though, ever so slightly. The global ocean pH is about 8.2, slightly basic, but pH is falling (~0.1) due to an increased concentration of hydrogen ions resulting from the chemical reaction of water molecules and carbon dioxide at the ocean surface. Ocean pH is expected to fall even more, between 0.3 and 0.4 by the year 2100, if we continue burning fossil fuels at current rates. Note the values are still basic, so the oceans are not really “turning to acid”, but the change in pH could have important consequences for ocean animals.
Many ocean animals use calcium carbonate in their skeletons including corals, mollusks, and crustaceans. Single celled algae like the coccolithopores also have calcified plates. Will they adapt? During the Paleocene-Eocene thermal maximum many benthic calcifiers went extinct.
A recent paper in Coral Reefs by Turley et al (2007) anticipates that many species will not escape the effects of climate change, and even the deep reef forming corals will be in jeopardy from increasing atmospheric CO2. This perspective piece calls attention to the problem, but no new data is provided. Instead there is a call for information exchange and collaboration between warm water coral scientists and cold water coral scientists. Few could dispute the value of this exchange.
To be fair, caveats to the argument that pH is changing faster than corals can adapt might include the long fossil record of the Anthozoa, the phylogeny of the Cnidaria, the existence and survival of scleractinian forms below the carbonate compensation depth, and contrasting aquarium experiments that show these animals can be either 1) doomed to dissolution or 2) remarkably adaptable. What’s your guess?
Tune in to Coral Week this April for five full days on deep-sea corals, and more on this controversy.
Turley, CM, JM Roberts, JM Guinotte. 2007. Corals in deep-water: will the unseen hand of ocean acidification destroy cold-water ecosystems? Coral Reefs 26:445-448. doi 10.1007/s00338-007-0247-5