Methyl iodide in the NW Atlantic: Spatial and seasonal variation

Abstract

While the global ocean is an important source of atmospheric methyl iodide (CH3I), the major producers of CH3I within the ocean remain unclear. During a seasonal study in the NW Atlantic, the relationship between CH3I and some characteristic phytoplankton pigments was examined in order to identify possible phytoplankton producers of CH 3I. Although no characteristic pigments exhibited a strong positive correlation with CH3I, in the surface mixed layer, there was a weak correlation (R = 0.35, n = 70, p = 0.003) between the concentrations of CH3I and zeaxanthin, a pigment characteristic of cyanobacteria in the open ocean. In this study, a moderate correlation was observed between the surface mixed layer CH3I concentration and depth-averaged daily radiant exposure (R = 0.61, n = 15, p = 0.02), which indicates a positive influence of solar radiation on CH3I production. However, the results from this study do not conclusively show whether the influence was exerted through photochemistry or other pathways. A positive correlation between the CH3I concentration and sea surface temperature was also observed (R = 0.61, n = 79, p « 0.001). Copyright 2009 by the American Geophysical Union.