Pacific drought brings
environmental changes
A prolonged drought over the North Pacific Ocean has created a saltier sea surface, reducing the ocean's ability to absorb carbon dioxide and potentially contributing to global warming.
This was the surprising finding of University of Hawaii oceanographers John Dore, Dave Karl and Roger Lukas in a study of 15 years of measurements at an ocean site called Station Aloha about 60 miles north of Oahu.
Scientists led by Karl and Lukas have been collecting rainfall, salinity and carbon dioxide data monthly at that spot in a Hawaii Ocean Time-series Program.
Dore was lead author of a paper by the scientists in the British journal Nature this week on the effects of drought in the North Pacific.
Although the impacts of drought on land are well recognized, he said, they tend to go unnoticed on the ocean.
But the team found the effect on ocean salinity "is significant, and that was really unexpected," he said.
"We never really thought an actual change in saltiness of the ocean is important to the carbon cycle," said Dore, "but what we're finding is, it is important. And we need to take that into account when we try to model the carbon cycle and how it may change in the future."
Increased carbon dioxide in the atmosphere, attributed mostly to fossil fuel burning, is believed to be causing global warming and changes in climate.
Dore said the ocean is one of the major "natural sinks" to absorb atmospheric carbon dioxide, so it is important in regulating increase of the gas.
He said the strength of the sink can vary tremendously from year to year because of temperature, circulation and biology. But Station Aloha data show carbon dioxide taken up in the Central North Pacific decreased dramatically because of drought from 1998 to 2001, he said.
"It doesn't seem to have gotten better in the last couple years," he said.
The saltier ocean surface prevents further uptake of carbon dioxide from the atmosphere, Dore said.
"If the trend continues," he said, "it could completely eliminate the sink. The good news is, the opposite effect would hold true, too. If we have several years with above-average rainfall, the situation could be turned about."
Karl said the Nature paper is about "things we never knew existed, and even if they did exist, the possibility was that you'd never get a data set accurate enough to see small things like this. We've proven ourselves wrong again, which is great."
Dore credited Dan Sadler, a technician in Karl's lab and one of the paper's co-authors, with providing the precise measurements needed to reach their conclusions.
The 15-year record of biogeochemical and physical measurements at Station Aloha and at an affiliated station in Bermuda is the longest in the world, the scientists said.
Lukas and Karl are looking to even more exciting discoveries at Station Aloha with the recent award of another five years of funding by the National Science Foundation.
The oceanographers and UH geophysicist Fred Duennebier also have received funding to install an abandoned fiber-optic telephone cable at Station Aloha in 2005 for dozens of automated instruments.
Lukas said researchers will be able to make and observe measurements in real time from their desks on the Manoa campus. They will also be able to order changes in observations as oceanographic events occur, he said.
The UH scientists also hope to benefit from a foundation proposal to Congress for a $200 million ocean observation program. Lukas was on a National Academy of Sciences committee that defined requirements for the new program.
University of Hawaii
