As part of a study supported by both NASA and NOAA, scientists from two NOAA laboratories, three universities and CSIRO participated in a research cruise aboard the R/V Ronald H. Brown. The cruise departed Kwajalein, Republic of the Marshall Islands on 14 September 1999 and arrived in Seattle, Washington on 23 October 1999 with stops in Honolulu, Hawaii, Dutch Harbor, Alaska, and Kodiak, Alaska. The objective of this research effort was to obtain reliable measurements of the uptake and emission of methyl bromide and other climatically important halocarbons in tropical to temperate regions of the North Pacific Ocean.

Atmospheric methyl bromide (CH3Br), which is of both natural and anthropogenic origin, has been identified as a Class I ozone-depleting substance in the amended and adjusted Montreal Protocol on Substances that Deplete Stratospheric Ozone. The role of the ocean in regulating the atmospheric burden of this gas is still somewhat uncertain. Methyl bromide is both produced and destroyed in the ocean through chemical and biological processes. The organisms or reactions that produce CH₃Br at rates sufficient to explain its observed concentrations are not known. Degradation has been shown to occur at rates that are faster than can be explained by known chemical degradation reactions, and evidence suggests that this additional degradation is bacterial consumption of CH₃Br. While recent measurements have shown that, on the whole, the ocean is a net sink for CH₃Br, measurement coverage to date has been limited and sporadic, which restricts our ability to map the spatial and temporal variations that are necessary for understanding how the system will respond to perturbations (e.g. Global Warming).

The measurements made during this cruise are designed to help improve our understanding of the role that the oceans play in the cycling of CH₃Br. The program involved instrumentation from two NOAA laboratories and two universities. Measurements were made of the concentrations of CH₃Br and a suite of natural and anthropogenic halocarbons in the air and surface water, degradation rates of CH₃Br in the surface water, production rates of CH₃Br and other natural halocarbons in the surface water, and depth profiles of CH₃Br and other halocarbons. The combined results from these measurements will be used to constrain the budget of CH₃Br in these waters at this time of year. The relative importance of the biological and chemical processes will be examined for tropical and high latitudes. Attempts will also be made to extract relationships between the rates and concentrations measured and satellite measurements in order to develop proxies that can provide global coverage on shorter time scales. At this time, there is insufficient data to examine seasonal and long-term trends in net flux, production, or degradation. Until satellite measurable proxies can be found, additional research cruises are needed to reduce the uncertainty in the global net flux estimate and to map the spatial and temporal variations in the net fluxes, production rates, and degradation rates of CH₃Br and other climatically important halocarbons.

Figure 1. Cruise Track.

Figure 2. Scientists collecting water samples for production and degradation incubations.

Last updated 09/21/2001 by the OCD Webmaster.