This project will make the first direct measurements of a low altitude atmospheric plume that has been observed in satellite imagery as rising from the sea ice in the vicinity of Bennett Island in the Arctic Ocean. It has been hypothesized that the plume consists of rapidly escaping methane released from the melting and vaporization of methane hydrates along a fault structure, but to date there has been no direct confirmation of this conjecture. This work will be supported under the Small Grants for Exploratory Research Program (SGER), which includes in its objectives the support of research that is risky and has severe urgency with regard to availablity of facilities. In this instance the field work will be a month-long deployment of a Russian AN-2 aircraft to the vicinity of Bennett Island following the already scheduled Arctic Gas and Aerosol Sampling Program (AGASP-4), sponsored by NOAA, in March and April of 1992. This will take advantage of the fact that the aircraft will already have been equipped with a suite of atmospheric chemistry instrumentation, and will only require the installation of a separate sample inlet line. The work will identify the composition of the Bennett Island plume, and if it is in fact largely methane, will allow a determination of the age of the source hydrates. This in turn will promote the construction of a global methane budget, and assess its effect as a radiatively important trace species on the global radiation budget.