Research shows oceans becoming more acidicThe world’s oceans are absorbing an unprecedented amount of carbon dioxide (CO2), which is increasing their acidity and possibly threatening the long-term survival of many marine species, especially calcifying organisms including corals, shellfish and phytoplankton. According to research presented recently at a symposium organized by UNESCO’s Intergovernmental Oceanographic Commission and the International Council for Science’s Committee on Oceanic Research (SCOR), this in turn could disrupt marine food chains and alter ocean biogeochemistry in ways that are not yet understood or predictable.
The symposium brought together scientists from the world’s leading oceanographic institutions to discuss how the ocean might be affected by higher levels of atmospheric carbon dioxide, and to develop research priorities to study these future effects. They were also called upon to discuss potential environmental consequences of proposals to use the ocean to sequester excess atmospheric CO2, which is one of the most important greenhouse gases.
A report on the meeting’s conclusions, now available online*, points out that the ocean is one of the Earth’s largest natural reservoirs of carbon and each year absorbs approximately one third of the carbon dioxide emitted by human activities. According to research** led by Christopher Sabine of the National Oceanographic and Atmospheric Administration in the United States (NOAA, an IOC Member State Agency)* the ocean has taken up approximately 120 billion metric tons of carbon generated by human activities since 1800. The IOC reports that some 20-25 million tons of CO2 are being are being added to the oceans each day.
The absorption of carbon dioxide by the oceans is considered a beneficial process that reduces the concentration of CO2 in the atmosphere and mitigates its impact on global temperatures. However there is growing concern over the price of this service. For the symposium participants, it is now well established that by the middle of this century, the accumulating burden of CO2 entering the ocean will lead to changes in pH or acidity of the upper layers that are three times greater in magnitude and 100 times faster than those experienced between ice ages. Such dramatic changes in the CO2 system in open-ocean surface waters have not been observed for more than 20 million years of earth’s history, concluded the meeting.
The initial findings of limited observation, research and modeling conducted to date and presented to the symposium indicate that in a high CO2 world:
· the ocean would be more acidic globally, and would also be more stratifed in the high latitudes. In addition nutrient concentrations in surface waters of high-latitude regions would be lower, subsurface waters would be less oxygenated, and phytoplankton would experience increased exposure to sunlight. These changes would affect many species and change the composition of biological communities in ways that are not yet understood or predictable.
· many calcifying organisms, including certain species of plankton and corals, and also non-calcifying organisms, would be unable to grow and reproduce effectively at higher CO2 and lower pH levels. Rising temperatures – combined with elevated CO2 and decreasing pH – pose a serious threat to coral reefs, possibly leading to the elimination of some reefs by the end of this century.
Participants at the symposium stressed that although the impact of climate change on the ocean has been much debated, the direct chemical and biological impact of CO2 itself has largely been neglected. However, they concluded, changes are clearly underway and their effects may be large and may seriously destabilize marine ecosystems. Their report signals the need for more research and identifies research priorities, in a bid to increase understanding of the changes taking place and their consequences, and to allow for more informed policy decisions in this area.
*The report is accessible on the internet at http://ioc.unesco.org/iocweb/co2panel/HighOceanCO2.htm
** A report on Dr. Sabine’s research and findings appears in the July 15 edition of Science magazine, along with a report from fellow NOAA scientist and participant at the UNESCO meeting, Dr. Richard Feely (http://www.sciencemag.org)
Caption: Gephyrocapsa Oceanica, a calcareous marine phytoplankton, normally round like a football, experiences difficulties growing its shell at CO2 levels expected by the end of this century (Riebesell et al., 2000). Reprinted with the permission of Nature (http://www.nature.com/)