Contact: Barbara McGehan FOR IMMEDIATE RELEASE
(303) 497-6286 2/17/95
Dr. Jim Butler
(303) 497-6898
Dr. Jurgen Lobert
(303) 497-7006
The ocean, up to now believed to be a main source of an ozone- depleting chemical, methyl bromide, also consumes the compound, effectively removing a significant amount from the atmosphere, according to a new study conducted by scientists at the National Oceanic and Atmospheric Administration.
The investigators, working with NOAA's Climate Monitoring and Diagnostics Laboratory in Boulder, Colo., have found that the ocean is largely undersaturated in methyl bromide, thus representing a significant mechanism for its removal from the atmosphere.
Up to this time, the ocean was believed to be a main source of atmospheric methyl bromide, contributing about 30% of the methyl bromide in the atmosphere. Other major sources of this gas include biomass burning and fumigation of soils, produce and buildings.
Methyl bromide is a strong ozone-depleting chemical that may ultimately contribute as much as 10% to global stratospheric ozone destruction. Unlike the chlorofluorocarbons (CFC's) and halons, which are entirely man-made, methyl bromide has both natural and anthropogenic sources.
According to the study by J. Lobert and co-authors, published in the Feb. 17 issue of Science, surface waters in the open oceanic regions of the east Pacific had much less methyl bromide than anticipated, indicating that the amount of methyl bromide being destroyed in the ocean exceeds the amount being produced. This destruction is driven mainly by reaction of methyl bromide with water and salt dissolved in seawater.
Project scientist and co-author, James Butler, said, "The results suggest that 30-40% of the methyl bromide in the atmosphere is destroyed in the ocean and that, consequently, its lifetime in the atmosphere is 30-40% shorter than previously believed."
Measurements were taken during January and February 1994 along a cruise track from Seattle, Wash., to Punta Arenas, Chile, as part of a scientific expedition aboard the NOAA Ship Discoverer. These analyses of methyl bromide in both the atmosphere and surface water show that it was highly undersaturated in the central part of the open ocean, which represents 80-90% of the global oceanic coverage. At the same time, coastal waters and other upwelling regions were supersaturated in methyl bromide, but represent a much smaller global coverage.
This is the most comprehensive data set on oceanic methyl bromide published to date. Although the study was limited to the eastern Pacific Ocean, the authors noted that more recent, preliminary results from another expedition last fall in the Atlantic Ocean are consistent with these findings.