Emission of methyl iodide from the Southern Ocean

The first full year record of methyl iodide measurements has been collected at Cape Grim, Tasmania, and provides important insights into flux of this gas from the Southern Ocean. Methyl iodide is a primary vector for transport of iodine from oceans to the land and to the atmosphere, where it may play a significant role in destruction of tropospheric ozone. Though oceans are thought to be the dominant source of atmospheric methyl iodide, poor understanding of the flux, particularly from the Southern Ocean, has hindered attempts to compute global budgets of the gas.

Based on the Cape Grim observations and a 3-box model, we estimate flux rates of methyl iodide from the Southern Ocean to the atmosphere. The flux is shown to vary strongly with latitude and season, raising doubts about previous attempts to deduce fluxes from field campaigns of limited scope and duration. Back trajectories are used to help identify regions of particularly strong marine emission, and to investigate whether continental sources substantially influence methyl iodide concentrations at Cape Grim. Correlations of methyl iodide with other halocarbons measured at Cape Grim will also be discussed.