The ocean surface is the dominant source of atmospheric iodine. Volatile organic iodine compounds (VOIs) such as methyl iodide (CH
3I) contribute to 20–40% of supply of the reactive iodine in the upper troposphere and lower stratosphere. In the ocean the dominant producers of VOIs have been thought to be marine plants such as macro algae, micro algae(phytoplankton). Most previous studies have focused on the production of VOIs in the upper euphotic zone, where marine plants grow. Recent studies have shown high concentrations of C
2H
5I in bottom water of the polar Chukchi Sea and northern Bering Sea, and subpolar Funka Bay, Japan. Therefore, we inferred that there is a source of organic iodine gas on the seafloor surface. Therefore, to elucidate the phenomenon of high C
2H
5I concentrations near the seafloor, we conducted time-series oceanographic observations of seawater and sediment samples in Funka-Bay, Hokkaido, and single oceanographic observations in the northern Bering Sea and southern Chukchi Sea. We also conducted laboratory incubations to test the hypothesis that diatom aggregates settled on the sea floor emit VOIs in darkness.
