A new source of volatile organoiodine compounds in surface seawater

Volatile organoiodine compounds (VOIs) are the main carrier of iodine from the oceans to the atmosphere. We have identified a novel, sea-surface source of the short-lived VOIs CH2I2, CHClI2 and CHI 3 in a series of laboratory experiments. These compounds were formed when seawater, collected during winter in the North Sea, was exposed to ambient levels of ozone. The VOIs are produced from the reaction of marine dissolved organic matter with hypoiodous acid/molecular iodine, which are formed at the sea surface when ozone reacts with dissolved iodide. The same three VOIs were formed when we incubated seawater of different productivity levels with molecular iodine during a cruise in the tropical Atlantic Ocean. We suggest that the presence of dissolved iodide, dissolved organic matter and ozone can lead to the sea-surface production of CH2I2, CHClI2 and CHI3. As such, this process could provide a ubiquitous source of iodine to the marine atmosphere.