A group of 19 scientists from five research organizations have conducted the broadest field study of ocean acidification to date using sensors developed at Scripps Institution of Oceanography, UC San Diego.
It is an important step toward understanding how specific ecosystems are responding to the change in seawater chemistry that is being caused as the oceans take up extra carbon dioxide produced by human greenhouse gas emissions, said its authors. "These data represent a critical step in understanding the consequences of ocean change: the linkage of present-day pH exposures to organismal tolerance and how this translates into ecological change in marine ecosystems," the authors wrote.
"These pH time series create a compelling argument for the collection of more continuous data of this kind." Ocean acidification research is a relatively new study topic as scientists have only appreciated the potential extent of acidification within the last decade. As greenhouse gas emissions have accelerated in the past century, the oceans have taken up about a third of the carbon dioxide produced by human activities. That excess beyond natural levels increases amounts of carbonic acid in seawater. Acidification also limits the amount of carbonate forms that are needed by marine invertebrates such as coral and shelled organisms to form their skeletons. Though many lab simulations of this effect have been performed recently, including at a new acidification laboratory in development at Scripps, there have been few comparable field studies. Using sensors recently developed at Scripps, the researchers surveyed marine ecosystems ranging from coral reefs in the South Pacific Ocean to volcanic CO2 vent communities in the Mediterranean Sea.
They found that in some places, such as Antarctica and the Line Islands of the south Pacific, the range of pH variance is much more limited than in areas of the California coast subject to large vertical movements of water known as upwellings. In some of their study areas, they found that the decrease in seawater pH being caused by greenhouse gas emissions is still within the bounds of natural pH fluctuation. Some areas already experience daily acidity levels that scientists had expected would only be reached at the end of the 21st Century.
"This study is important for identifying the complexity of the ocean acidification problem around the globe," said Scripps marine biologist Jennifer Smith. "Our data show such huge variability in seawater pH both within and across marine ecosystems making global predictions of the impacts of ocean acidification a big challenge. Some ecosystems such as coral reefs experience a daily range in pH that exceeds the predicted decrease in pH over the next century. While these data suggest that marine organisms may be more adapted to fluctuations in pH than previously thought much more research is needed to determine how individual species will respond over time. Importantly, these new sensors allow us continuously and autonomously monitor pH from remote parts of the world and thus provide us with important baselines from which we can monitor future changes caused by ocean acidification."
Because many in the marine chemistry community have expressed concerns that ocean acidification could happen too rapidly for some organisms to adapt, the researchers said that this finding is an important step toward identifying the mechanisms some marine organisms have developed in order to cope. They also said that knowledge of actual pH ranges in various ecosystems should improve assumptions about future pH levels that can only rely on broad generalizations about seawater chemistry. Furthermore it could guide future lab and field studies that investigate the limits of resistance and resilience in various marine communities.