The latest research on the effects of increasing atmospheric CO₂ on ocean chemistry and its detrimental consequences for marine organisms will be presented in a special session on “ocean acidification”. New findings indicate that changes in ocean chemistry due to acidification over just the last 10 years are measurable even in the deep ocean. Such changes may become dramatic over the next 50 to 100 years, and they will likely have a major impact on ocean biota.

The oceans have so far absorbed about a third of human-caused CO₂ emissions, but this uptake has consequences for ocean chemistry. Adding CO₂ to seawater reduces pH, which is referred to as acidification. The average pH of the surface ocean has decreased from about 8.2 to 8.1 over the past century, and by the end of this century, pH is likely to become lower than it has been for millions of years.

Ocean acidification cannot be reversed over the span of a human lifetime, because the same processes that make the oceans an effective sponge for CO₂ also guarantee that the gas will remain in the oceans for centuries. Because ocean pH affects many chemical, sedimentological, and biological processes, its continuing decrease is expected to fundamentally change the biogeochemical and ecological balance in the ocean. Most research on biological consequences focuses on organisms that secrete calcium carbonate to form skeletons, such as corals and other reef organisms as well as some major planktonic groups of the open ocean.

New data confirms that skeletal formation in these organisms is depressed at lower pH, and sheds new light on how this long-ignored control on marine calcification may be shaping ecosystems. For example, both modeling and field measurements indicate that within this century, the rate of dissolution will exceed calcification in coral reef ecosystems.

In addition, several researchers will present data that shows other biological effects of decreased pH, such as a large increase in the production of dimethyl sulfide (a major source of cloud condensation nuclei) during plankton blooms, and a reduction in the fertilization success of some marine invertebrates. Many of these new findings stem from the Pelagic Ecosystem CO₂ Enrichment (PeECE-III) experiments conducted in floating mesocosms in Norway, which involve an international team of some fifty scientists.

Session: BG6.02 Ocean acidification: chemistry, paleo-analogues, response of organisms and ecosystems, and modelling | >>programme
Relevant publications for this subject: http://www.obs-vlfr.fr/~gattuso/papers.php

Jean-Pierre Gattuso gattuso@obs-vlfr.fr
Joan Kleypas kleypas@ucar.edu
Ulf Riebesell uriebesell@ifm-geomar.de
James Orr orr@cea.fr