[A-CG44] Biogeochemical linkages between the surface ocean and atmosphere

[ACG44-04] Iodomethane and Iodoethane distributions in coastal seawater of subarctic Pacific and Northern Bering sea

*Atsushi Ooki¹, Keita Minamikawa¹, Fanxing Meng¹ (1.Hokkaido University)

Keywords:haloarbon, Volatile Organic Compounds (VOCs), Iodine

Volatile organic iodine compounds (VOIs) such as iodomethane (CH₃I), iodoethane (C₂H₅I), diiodomethane (CH₂I₂) and chloroiodomethane (CH₂ClI) carry iodine from the ocean into the atmosphere (Chameides and Davis, 1980). These VOIs have the potential to deplete ozone in boundary layer air on a wide scale (e.g., Carpenter et al., 1999) via the catalytic ozone destruction of iodine atom released from VOIs. Marine organisms are the dominant producers of VOIs. Many studies have reported the productions of VOIs from marine organisms of macro algae, micro algae, photosynthetic bacteria, and heterotrophic bacteria (e.g. Schall et al. 1994; Tokarczyk and Moore 1994; Hughes et al. 2008). The vertical distributions of VOIs in water column have been measured in many ocean areas, however, VOIs in ocean sediment have not ever measured so far. In this study, we have firstly measured VOIs in coastal ocean sediment of Chukchi Sea, northern Bering Sea, and Funka bay, Japan. We found that iodoethane (C₂H₅I), which is a minor VOIs anywhere in the air and ocean water, becomes overwhelming majority of VOIs in the surface of ocean sediment on the sea floor of Arctic and subarctic coastal area. The iodoethane concentrations in the sediment drastically increased soon after the diatom spring bloom in water column above the sediment. We verified that the aggregates of dead diatom cells in a dark incubation bottle produced large amounts of iodoethane as well as small amounts of iodomethane (CH₃I) within 7 days. Live marine algae have been thought to drive sea-air cycle of iodine via. biogenic CH₃I, CH₂ClI, and CH₂I₂ productions. Dead marine algae (diatom) drive sea-sediment cycle of iodine via. biogenic C₂H₅I production. Iodoethane in the ocean sediment will give us a key to understand global iodine cycle.