The production of volatile iodocarbons by biogenic marine aggregates

We present the first reported measurements of volatile iodocarbon production by biogenic marine aggregates. Iodomethane (CH3I), iodoethane (C2H5I), 2-iodopropane (CH3CHICH3), and 1-iodopropane (CH3CH2CH2I) concentrations were determined in incubations of aggregates formed by concentrating the >53 mu m fraction of the plankton during a field campaign in the Celtic Sea. All four iodocarbons increased significantly in concentration in the aggregate incubations relative to filtered seawater controls. Maximum production rates ranged from 0.01 pmol L-1 h(-1) for CH3CHICH3 to 0.31 pmol L-1 h(-1) for C2H5I. Accompanying pheopigment and bacterial heterotrophic production suggest that the processes taking place on the aggregates studied were a good representation of those known to occur on natural marine particles. We also report iodocarbon production rates observed in natural marine aggregates, including a diatom mucilage collected in the Celtic Sea and phytodetritus sampled from Kongsfjord in the Arctic. Detrital particles could be hotspots of iodocarbon production in the marine environment.