Scientists have found large amounts of a gas linked to global warming in the Pacific Ocean’s shallow waters, suggesting that increased El Nino activity could stoke even greater production of the gas.
The University of Hawaii researchers sampled seawater at a site about 60 miles north of Hawaii that’s considered representative of the deep-ocean waters that border the Pacific’s tropical zone.
They found three times more nitrous oxide than global models had predicted--and at relatively shallow depths that are influenced by El Nino, the periodic warming of the Pacific.
“This is really a double whammy. It’s both a greenhouse gas and an ozone-depleting gas,” said John E. Dore, a former University of Hawaii oceanic researcher who co-wrote the study.
Atmospheric levels of nitrous oxide, a byproduct of the burning of fossil fuels, are on the rise. The gas prevents the Earth from radiating heat back to space and also depletes its protective ozone layer.
In the Nov. 5 issue of the journal Nature, Dore and co-author David Karl of the University of Hawaii report that they found high nitrous oxide concentrations at about 900 feet of water, the murky zone where sunlight gives way to oceanic blackness.
Previous research suggested that the Pacific subtropical region, which covers about 8 million square miles, produces about 130,000 tons of nitrous oxide annually. But that was based on the assumption that the gas was percolating upward from much deeper waters--about 2,500 feet--where nitrous oxide readings are highest but static.
Dore said that 400,000 tons of the gas --three times the earlier estimate--is likely reaching the atmosphere.
If the University of Hawaii’s research is extrapolated worldwide, it suggests that Earth’s subtropical oceans produce 6 million tons of nitrous oxide each year--not the forecast 2 million tons.
Oceanic bacteria that consume organic nitrogen in search of ammonia appear to be producing the nitrous oxide, also known as laughing gas, as a byproduct of their feeding habits, the researchers suggest.