Distribution and sea-air fluxes of biogenic trace gases in the eastern Atlantic Ocean

A number of atmospherically important trace gases (dimethyl sulphide (DMS), methyl iodide (CH3I), and nonmethane hydrocarbons (NMHCs)) were measured s imultaneously in the eastern Atlantic Ocean during May 1997. This investiga tion was part of the U.K. Atmospheric Chemistry Studies in the Oceanic Envi ronment (ACSOE) Community Research Program and covered a 200 by 200 nautica l mile (1 nautical mile is 1.852 km) area to the west of the Mace Head Atmo spheric Research Station on the coast of Ireland. Different spatial and tem poral patterns were observed for each of the gases, showing that distinct s ources dominate their production in this region: specific species of phytop lankton (DMS), macroalgae (CH3I), total phytoplankton biomass (isoprene), a nd photochemistry (ethene). Sea-to-air fluxes of the gases are calculated f or near and offshore domains, and their temporal variations are discussed. A simple photochemical box model has been used to assess the contributions of the gas fluxes to the levels of the gases observed at Mace Head. Results show that the area studied may constitute a substantial source of DMS, a w eak source of CH3I, a small source of ethene at night, and an insignificant source of isoprene to atmospheric levels of these gases measured at Mace H ead in western Ireland.