Imminent danger for marine organisms due to ocean acidification
Unfortunately, as this CO2 combines with seawater, it forms an acid. Because this process reduces the naturally basic state of seawater, it is termed acidification, even though seawater remains basic (pH > 7). A new study by an international team of oceanographers that will be published in Nature magazine on September XX, reports that ocean acidification could result in chemical conditions that will be corrosive enough to force key polar marine organisms to disappear within 50 to 100 years, much sooner than previously thought. Most threatened are cold-water organisms that build their external skeletal material out of calcium carbonate, the basic building block of limestone. Such organisms include sea urchins, cold-water corals, and plankton known as pteropods—winged snails that flutter through surface waters. And because these organisms provide essential food and habitat to others, their demise could affect entire ocean ecosystems.
In the Nature study, a group of 27 marine chemists and biologists, from Europe, Japan, Australia, and the United States, combined recently compiled global ocean carbon data with numerical models to study potential future changes in the ocean CO2 system. The models project that the ocean's coldest surface waters, such as in the Weddell Sea of Antarctica, will become corrosive to pteropods much sooner than thought. In other words, shells of these marine organisms may simply dissolve as soon as atmospheric CO2 reaches the levels that are expected to occur in about 50 years under the IS92a business-as-usual CO2 emissions scenario. As atmospheric CO2 continues to rise, the projection is that by the end of this century the entire Southern Ocean and part of the North Pacific would become too corrosive for these organisms to grow their shells. The lead author of the study, ocean modeler James Orr from the Laboratoire des Sciences du Climat et de l'Environnement in France, says “Basic chemistry tells us that many folks alive today will live to see the polar oceans becoming inhospitable to key organisms, and unlike climate predictions, the uncertainties here are small.”
As a complement to model projections, one of the coauthors, Prof. Victoria Fabry from the Dept. of Biological Sciences at California State University San Marcos, set up experiments aboard the U.S. National Oceanographic and Atmospheric Administration’s (NOAA) research ship Discoverer that demonstrated how shells of live pteropods actually do dissolve under such corrosive conditions. With those results and more than two decades of experience scrutinizing pteropods, she says, “unfortunately, pteropods won’t suddenly learn to survive once they can’t grow the shells they need for protection and buoyancy control”. The demise of polar pteropods could provoke a chain reaction of events through complex ocean ecosystems. It is known for instance that pteropods are eaten by organisms ranging in size from zooplankton to whales and including fish. For instance, North Pacific salmon include pteropods as part of their diet..
The material that makes up pteropod shells is aragonite, a common mineral form of calcium carbonate, which is also secreted by other marine organisms to form external skeletal material. Such organisms include varieties of hard corals that grow throughout the cold, dark recesses of the ocean. Unlike their better-known tropical cousins, which grow in warm surface waters, these cold-water corals grow very slowly and can live to be hundreds of years old. In recent years, manned and remotely controlled submersibles have begun to provide us with photographs of their beautiful skeletal structures. These are made of aragonite and are essential not only for their survival, but also for providing the habitats for diverse ecosystems, including deep-sea fish, eels, crabs, and sea urchins. Cold-water corals are already threatened by practices of open-ocean trawling for bottom fish. Ocean acidification will add further pressure on cold-water corals, especially in areas such as the North Atlantic, where hard coral varieties are most abundant and where polar waters that now offer hospitable refuge down to depths of 3 km will become mostly corrosive by the end of the century due to invasion of CO2.
Other marine organisms that will be among the first to show signs of corrosion from ocean acidification are those that construct external skeletons out of a variety of calcium carbonate that is rich in magnesium. These organisms include sea urchins and ubiquitous coralline algae, which grow where corals cannot, providing essential foundation and repair material for reefs and releasing substances that encourage settlements of other organisms such as abalone.
Cold polar surface waters will start to become corrosive to these organisms once the atmospheric CO2 level reaches about 600 parts per million, which is 60% more than the current level but which could well be attained by the middle of this century.
Original paper:
Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms p681 by
J.C. Orr, V.J. Fabry, O. Aumont, L. Bopp, S.C. Doney, R.A. Feely, A. Gnanadesikan, N. Gruber, A. Ishida, F. Joos, R.M. Key, K. Lindsay, E. Maier-Reimer, R. Matear, P. Monfray, A. Mouchet, R.G. Najjar, G.-K. Plattner, K.B. Rodgers, C.L. Sabine, J.L. Sarmiento, R. Schlitzer, R.D. Slater, I.J. Totterdell, M.-F. Weirig, Y. Yamanaka and A.Yool
Paper
Contact Information:
Dr. James Orr (lead author)
LSCE/CEA Saclay, Bat. 712 L’Orme
F-91191 Gif-sur-Yvette, FRANCE
e-mail
Tel: +33 1 69 08 77 23 work
Dr. Ernst Maier-Reimer
Max Planck Institut für Meteorologie
D-20146 Hamburg, Germany
e-mail
Tel: +49 40 41173 233
October 6, 2005