That suggests that the coastal ocean may have its own mechanism for holding carbon dioxide something Cai first suspected in 2005 on a cruise off the coast of Georgia. There he was surprised to see that sea surface carbon dioxide levels were about the same as 10 years prior, even though there were significantly greater amounts of the greenhouse gas in the atmosphere.
Conventional wisdom would hold that sea surface carbon dioxide should rise in tandem with levels in the atmosphere, as is the case in most of the ocean basin.
"However, if the coastal ocean has its own way to hold sea surface carbon dioxide and atmospheric carbon dioxide keeps increasing, that makes the coastal ocean more important as a carbon dioxide sink in the future as the rate of carbon dioxide uptake by the ocean is determined by the concentration difference between the atmosphere and the ocean, which is increasing," Cai said. "The global carbon cycling model should take this additional carbon dioxide sink into account."
In the Nature paper, Cai and his co-authors posit that an increased physical uptake of atmospheric carbon dioxide explains the continental shelf switching from a carbon dioxide source to a sink or repository over the industrial age. They also provided a mechanism to explain the slower carbon dioxide increase in the coastal ocean. Others have suggested that agricultural fertilizers feeding extra nutrients into water caused the shift.
New instrumentation allows scientists to generate new best estimates of carbon cycling in coastal areas. Using the latest measures available, Cai and his colleagues created a model estimating that coastal areas released, on average, about 150 million metric tons of carbon per year a century ago. Now, these same waters are estimated to absorb approximate
|Contact: Andrea Boyle Tippett|
University of Delaware