Seasonal measurements of volatile iodocabons at a coastal site

Volatile iodinated organic compounds produced in the oceans may be the major source of iodine oxide radicals that play an important role in tropospheric and stratospheric chemistry. In addition, precipitation of iodine derived from the oceans is essential to terrestrial organisms. Little is known about the relative contribution of individual organic iodine compounds to the sea-to-air flux of iodine or about the sources, considered to be biological, of these compounds in the oceans. We will report the results of a seasonal study to quantify the concentrations of CH3I, CH2I2, CH3CH2I, CH2ClI and CHBr3 in seawater in the Western English Channel. In an attempt to identify the source of these compounds, their concentrations are compared to a number of biological paramaters including phytoplankton biomass and taxonomic composition, bacterial abundance and primary productivity. The concentrations of each compound were measured at varying distances from shore and relative to CHBr3 in order to estimate the relative influence of marcoalgal and planktonic production on seawater standing stocks. Sea surface concentrations are used to estimate the magnitude and seasonal trends in the sea-to-air flux of iodine and the relative contribution of each organic iodine compound to the total flux.