Methyl iodine over oceans from the Arctic Ocean to the maritime Antarctic

Abstract

Studies about methyl iodide (CH3I), an important atmospheric iodine species over oceans, had been conducted in some maritime regions, but the understanding of the spatial distribution of CH3I on a global scale is still limited. In this study, we reports atmospheric CH3I over oceans during the Chinese Arctic and Antarctic Research Expeditions. CH3I varied considerably with the range of 0.17 to 2.9 pptv with absent of ship emission. The concentration of CH3I generally decreased with increasing latitudes, except for higher levels in the middle latitudes of the Northern Hemisphere than in the low latitudes. For sea areas, the Norwegian Sea had the highest CH3I concentrations with a median of 0.91 pptv, while the Central Arctic Ocean had the lowest concentrations with all values below 0.5 pptv. CH3I concentration over oceans was affected by many parameters, including sea surface temperature, salinity, dissolved organic carbon, biogenic emissions and input from continents, with distinctive dominant factor in different regions, indicating complex biogeochemical processes of CH3I on a global scale.

Figure 1

Box-and-whisker plots of CH₃I concentrations in ocean origin (OO), land origin (LO) and Antarctic origin (AO) samples with CO concentration (a) below or equal to 150 ppbv and (b) above 150 ppbv during the CHINARE 11/12 and the CHINARE 12. The lower and upper boundaries of the box represent the 25th and the 75th percentiles, respectively; the whiskers below and above the box indicate the minimum and maximum, respectively; the line within the box marks the median; the dot represents the mean.

Figure 2. The spatial distribution of CH₃I concentrations in the marine boundary layer when the concentration of CO below 150 pptv during the CHINARE 11/12 and the CHINARE 12.

Base map is from ArcGIS 10.0 software (http://www.esri.com).