|The shelled pteropod—an important food source for fish—is a small planktonic marine snail that may be unable to sustain its populations as the oceans become less alkaline. (Photo: Victoria Fabry, California State University, San Marcos).|
A new report finds that worldwide emissions of carbon dioxide from the combustion of fossil fuels are dramatically altering ocean chemistry and threatening marine organisms—including corals—that secrete skeletal structures and support oceanic biodiversity.
The report—Impacts of Ocean Acidification on Coral Reefs and Other Marine Calcifiers—released today summarizes the known effects of increased atmospheric carbon dioxide on these organisms, known as marine calcifiers, and recommends future research for determining the extent of the impacts.
The report follows a workshop funded by the National Science Foundation and the National Oceanic and Atmospheric Administration, and hosted by the US Geological Survey Integrated Science Center in St. Petersburg, Florida.
Oceans act as a sink for atmospheric carbon dioxide. During the 1980s and 1990s, only about half of the anthropogenic CO2 remained in the atmosphere, with the oceans having taken up about 30% and the terrestrial biosphere 20%.
Researchers have determined that with emissions of anthropogenic carbon dioxide continuing to rise, the partial pressure of CO2 (pCO2) dissolved in the surface ocean is likely to double its pre-industrial value within the next 50 years. Oceans are naturally alkaline, and they are expected to remain so, but the interaction with carbon dioxide is making them less alkaline and more acidic.
Increasing the amount of CO2 dissolved in the ocean lowers the pH, decreases the availability of carbonate (CO32-) ions, and lowers the saturation state of the major shell-forming carbonate minerals. Carbonate ions are building blocks for the calcium carbonate that many marine organisms use to grow their skeletons and create coral reef structures.
Tripling the pre-industrial atmospheric CO2 concentration will cause a reduction in surface ocean pH that is almost three times greater than that experienced during transitions from glacial to interglacial periods. This is often termed “ocean acidification”because it describes the process of decreasing pH.—“Impacts of Ocean Acidification”
Measurements of carbonate chemistry worldwide are showing shifts in the carbonate equilibrium consistent with increases in atmospheric CO2. Other studies have determined that the calcification rates of most calcifying organisms studied to date decrease in response to decreased carbonate ion concentration.
Although there have yet to be detailed studies on the effects of reduced calcification on individual organisms and on ecosystems, researchers are inferring that decreased calcification in marine organisms is likely to impact marine food webs and, combined with other climatic changes in temperature, salinity, and nutrients, could substantially alter the biodiversity and productivity of the ocean.
Many calcifying organisms—including marine plankton such as pteropods, a planktonic marine snail—are affected by the chemistry changes. Shelled pteropods are an important food source for salmon, mackerel, herring, and cod. If calcifying organisms such as pteropods are unable to sustain their populations, many other species may be affected.
It is clear that seawater chemistry will change in coming decades and centuries in ways that will dramatically alter marine life. But we are only beginning to understand the complex interactions between large-scale chemistry changes and marine ecology. It is vital to develop research strategies to better understand the long-term vulnerabilities of sensitive marine organisms to these changes.—Joan Kleypas, National Center for Atmospheric Research (NCAR), and lead author
This is leading to the most dramatic changes in marine chemistry in at least the past 650,000 years.—Richard Feely, NOAA Pacific Marine Environmental Laboratory (PMEL)
Several other major ecosystems that are supported by marine calcifiers may be particularly threatened by ocean acidification. These include cold-water reefs, which are extensive structures that provide habitat for many important fish species, particularly in the coastal waters of Alaska.
The report outlines future research to understand this consequence of climate change. While scientists cannot yet fully predict how much marine calcification rates will change in the future, the report warns that the more critical question is: “What does this mean in terms of organism fitness and the future of marine ecosystems?”