Isle scientists find
source of nitrous oxide
in North Central Pacific

By Helen Altonn
Star-Bulletin

You know it as laughing gas or as the stuff in whipped cream cans.

It's nitrous oxide, used in anesthesia and aerosols and of great interest to scientists as a greenhouse gas in the atmosphere.

"Molecule for molecule, it's about 200 times more potent than CO-2 (carbon dioxide)," said John Dore, researcher with Aqua Search Inc., at Keahole, on the Big Island.

"It's also an ozone-depleting gas, so it's the real double whammy there. It does both bad things," he said.

Nitrous oxide is increasing in the atmosphere, so it's a good idea to know where it's coming from and where it goes in the atmosphere, Dore said.

Dore and three colleagues have found a large source of atmospheric nitrous oxide in shallow Central North Pacific waters. Their findings were published in this month's Nature magazine.

Working with Dore, who was the principal investigator, were University of Hawaii scientists Brian N. Popp, David Karl and Francis Sansone.

Dore began the research while earning a doctorate degree at UH. He had worked with Karl a number of years on cycling of nitrogen in the North Pacific Ocean. He was doing post-doctoral research with Popp when he had an idea how to modify Popp's mass spectrometer to make sensitive isotopic measurements of nitrous oxide.

Gas concentrations can be measured relatively easily, he said. "But the isotopic signature of the gas -- a very powerful tool for tracing where it comes from -- is the difficult part. That's the part we refined."

They were never really funded for nitrous oxide research but Popp "put the nuts and bolts together" and they plunged ahead in their spare time, Dore said.

Karl allowed them to collect samples during some of his cruises and they made some measurements "with intriguing results," he said.

The oceans have long been known as a source of nitrous oxide flowing to the atmosphere, Dore said. But it was thought the gas was being formed in deep ocean waters with little oxygen concentration, he said.

They found, however, that nitrous oxide in the Central North Pacific is being formed in much shallower waters and at a greater rate than was expected.

This has significant implications, Dore pointed out. "It means instead of there being a rather constant, slow diffusion of this gas upwards out the ocean, its production and flux to the atmosphere is going to be highly variable and can be affected strongly by climate."

The source of the gas is a natural part of the ecosystem -- a by-product of the way bacteria recycle nitrogen in the oceans, Dore explained.

Noting that the Central North Pacific covers more than 8 million square miles, he said, "It's a very large circulation feature on our planet ... and there's reason to believe the other open ocean areas would behave similarly."

So it's possible there are similar sources of atmospheric nitrous oxide over vast ocean areas, he said, "which is why it's so important.

"We're not looking at something that can be abated. ... However, if we can at least accurately quantify this source, and others, then we can get a better handle on where all the nitrous oxide is coming from and make better predictions as to how it's going to accumulate in the atmosphere in the future."

Any climactic phenomenon that affects winds over the ocean, such as El Nino, will affect movement of the gas from the upper ocean into the atmosphere, he said.

Scripps Institution of Oceanography scientists Kyung-ryul Kim and Harmon Craig in 1993 suggested nitrous oxide might be found in surface ocean waters, but they didn't have methods sensitive enough to obtain the information, Dore said.

He said Popp and Sansone have received National Science Foundation funding to use the method developed by the UH group to do research on sources of the gas from other parts of the world.

They also will study how the gas cycles vary over seasons and years to determine if it is influenced by climate, as they expect, he said.

Dore said they also can use their method to measure production rates of the gas in the ocean. "That's something that's never successfully been done before."