Saltier seas in drought raise alarm
By Jan TenBruggencate
Advertiser Science Writer
The drought that has affected the Hawaiian Islands in recent years is making the ocean saltier than normal, cutting its ability to absorb carbon dioxide, which could have implications for the global climate.
"This enormous drought that has been happening on land in Hawai'i is also happening in the ocean," said University of Hawai'i scientist Dave Karl, co-author of a paper published today in the journal Nature.
Karl and fellow UH scientists John Dore and Roger Lukas studied data from the university's Hawai'i Ocean Time-Series program, which has collected detailed oceanographic data for 15 years at a spot in the ocean about 100 miles north of O'ahu's Kahuku Point.
Every month, a ship goes to Station Aloha to take temperature, salinity and other measurements. In the next few years, researchers hope to have sampling gear permanently moored at the site.
"Along with a sister station in Bermuda, Station Aloha has the longest records of comprehensive biogeochemical and physical measurements in the world," Lukas said.
Studies of the data showed that less rainfall and more evaporation have made surface waters saltier — from 34.5 parts salt per thousand parts water to 35.5 parts. That's not enough that a swimmer could taste the difference, but it is enough to have significant impacts on the interaction between sea and air.
Dore explained that oceans play an important role in the carbon cycle — the movement of carbon from the ground through plants, into the atmosphere, into the oceans and so on. Some areas of ocean suck up carbon dioxide, and some release it, but for the most part the oceans are a "carbon sink," meaning they take up more of the gas than they release.
That's an important factor, as carbon dioxide levels are increasing steadily in the Earth's atmosphere.
Lukas said most experts agree that human activity — mainly the burning of fossil fuels — is behind rising carbon dioxide levels. And while fewer experts are completely convinced the phenomenon is causing global warming, many are concerned it could be associated with worldwide climate changes.
Saltier ocean water is taking up less carbon dioxide than before, and if the drought continues, in two or three years "the ocean will be at equilibrium and will take up none," Karl said.
The drought appears to be associated with long-term climate cycles in the Pacific, including both the El Niño-La Niña cycle, which occurs every three to five years, and the Pacific Decadal Oscillation, lasting several decades. The coincidence of the two cycles appears to be associated with a drought that has lasted since 1998, Lukas said.
It is not clear what the new information means, and when or whether the cycles will revert to wetter conditions. It is clear there's a lot left to learn. Scientists knew ocean temperatures could affect carbon dioxide uptake, but did not know until now that salinity also had that effect.
"This shows that the rate at which the ocean can take up carbon dioxide is controlled by factors that we don't understand," Dore said, and which need to be studied.
Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808) 245-3074.
