Jerry Miller, Assistant Director,Â Ocean Sciences, and
Tom Armstrong, Executive Director,Â U.S. Global Change Research Program,
Office of Science and Technology Policy, Executive Office of the President
A new study concludes that the current rate of ocean acidification is higher than at any time in at least the last 300 million years and attributes this ecosystem-threatening change to the huge quantities of carbon dioxide being released into the atmosphere from fossil-fuel burning and deforestation. The studyâ€™s investigators, at Columbia University and other institutions, scrutinized Earthâ€™s geologic record for times in ancient history when natural events such as intensive volcanic activity may have similarly led to CO2 releases or ocean acidification. Although none of those ancient chemical changes appear to have been as extreme as those occurring today, there is nonetheless evidence that they contributed to serious ecological disruptions. That suggests that current trends similarly pose serious threats to marine ecosystems, the researchers conclude in the journal Science.
Oceans are major storage depots for carbon dioxide (CO2), with levels naturally remaining in rough equilibrium with carbon dioxide levels in the air above. Thus, as human activities like fossil-fuel burning have driven up carbon content in the atmosphere, the worldâ€™s oceans have taken up more and more of that carbon. In fact, more than a quarter of the CO2 released into the atmosphere each year is absorbed by oceans, causing changes in natural seawater chemistry. Among the most significant of these chemical changes has been a gradual increase in the concentrations of carbonic acid and other chemicalsâ€”a Â process called acidification. This shift, which is already being observed around the world, lowers the concentration and availability of ocean carbonatesâ€”a class of chemicals that many marine organisms need to build their skeletons and shells.
Whether and to what extent a more acidic ocean environment is impacting or will impact marine ecosystems is a question that scientists have sought to answer for decades. Nailing down specific impacts is difficult because the complexity of ocean ecosystems far exceeds that which can be fully replicated and analyzed in a laboratory. Just consider the elaborate system of ocean currents, weather patterns, atmospheric conditions, food webs, ocean chemistry, and other factors that play a dynamic role in shaping the marine environment.
In the new study, scientists sought to address that problem by analyzing evidence of ancient changes in marine organisms that correspond to periods in history when the rate of change in atmospheric CO2 concentration and ocean acidity were particularly high. The study is careful to point out that while no historic event perfectly compares to the current state of our climate and oceans, valuable lessons may still lurk in the geologic record.Â
The study found a correlation between periods of rapid acidification and periods when the shell-like plates that cover certain types of algae and plankton shrunk in size.The study also found that at the boundary between Paleocene and Eocene periods (about 55 million years ago), a large release of carbon caused temperatures and ocean acidity to rise, leading to mass extinctions of deep-sea foraminifersâ€”one of the most common marine plankton speciesâ€”as well as the collapse of coral reefs in shallow waters. Â Â
Because a variety of co-occurring environmental changes may have contributed to these marine ecosystem changes, scientists canâ€™t directly or fully attribute them to ocean acidification. However, they still provide clues about possible causes and consequences of changes to the marine environmentâ€”information that is critical not only to scientists, but to communities and local economies that depend on ocean resources for food and income.
For example, studies and monitoring in the Arctic Ocean, the Puget Sound, shellfish hatcheries in the Pacific Northwest and elsewhere have concluded that acidification is already having impacts on marine life, such as compromising the ability of oysters and other organisms to build the protective shells they need to survive. Other reports, such as the U.S. Global Change Research Programâ€™s most recent National Climate Assessment have found that ocean acidification poses a significant threat to coral reefs and the rich ecosystems, local fishing industries, and tourism economies they support.
These threats are among the reasons why the Obama Administrationâ€™s National Ocean Council lists among its nine priority objectives strengthening theâ€œresiliency of coastal communities and marine and Great Lakes environments and their abilities to adapt to climate change impacts and ocean acidification.â€