A global‐scale map of isoprene and volatile organic iodine in surface seawater of the A rctic, N orthwest P acific, I ndian, and S outhern O ceans

Isoprene (C 5 H 8 ) and three volatile organic iodine compounds (VOIs: CH 3 I, C 2 H 5 I, and CH 2 ClI) in surface seawater were measured in the western Arctic, Northwest Pacific, Indian, and Southern Oceans during the period 2008–2012. These compounds are believed to play an important role in the marine atmospheric chemistry after their emission. The measurements were performed with high time‐resolution (1–6 h intervals) using an online equilibrator gas chromatography mass spectrometer. C 5 H 8 was most abundant in high‐productivity transitional waters and eutrophic tropical waters. The chlorophyll‐ a normalized production rates of C 5 H 8 were high in the warm subtropical and tropical waters, suggesting the existence of a high emitter of C 5 H 8 in the biological community of the warm waters. High concentrations of the three VOIs in highly productive transitional water were attributed to biological productions. For CH 3 I, the highest concentrations were widely distributed in the basin area of the oligotrophic subtropical NW Pacific, probably due to photochemical production and/or high emission rates from phytoplankton. In contrast, the lowest concentrations of C 2 H 5 I in subtropical waters were attributed to photochemical removal. Enhancement of CH 2 ClI concentrations in the shelf‐slope areas of the Chukchi Sea and the transitional waters of the NW Pacific in winter suggested that vertical mixing with subsurface waters by regional upwelling or winter cooling acts to increase the CH 2 ClI concentrations in surface layer. Sea‐air flux calculations revealed that the fluxes of CH 2 ClI were the highest among the three VOIs in shelf‐slope areas; the CH 3 I flux was highest in basin areas. Isoprene and volatile organic iodine were measured in ocean surface water High concentrations occur in highly productive waters CH 3 I sea‐to‐air flux was dominant in basin areas; CH 2 ClI in shelf‐slope areas