Latitudinal distribution of reactive iodine in the Eastern Pacific and its link to open ocean sources

摘要

Ship-based Multi-Axis Differential Optical Absorption Spectroscopymeasurements of iodine monoxide (IO) and atmospheric and seawater GasChromatography-Mass Spectrometer observations of methyl iodide (CH₃I)were made in the Eastern Pacific marine boundary layer during April 2010 asa part of the HaloCarbon Air Sea Transect-Pacific (HaloCAST-P) scientificcruise. The presence of IO in the open ocean environment was confirmed, witha maximum differential slant column density of 5 × 1013 molecules cm?2along the 1° elevation angle(corresponding to approximately 1 pptv) measured in the oligotrophic regionof the Southeastern Pacific. Such low IO mixing ratios and their observedgeographical distribution are inconsistent with satellite estimates and withprevious understanding of oceanic sources of iodine. A strong correlationwas observed between reactive iodine (defined as IO + I) and CH₃I,suggesting common sources. In situ measurements of meteorological parametersand physical ocean variables, along with satellite-based observations ofChlorophyll a (Chl a) and Chromophoric Dissolved Organic Matter (CDOM) wereused to gain insight into the possible sources of iodine in this remoteenvironment. Surprisingly, reactive iodine showed a negative correlation(> 99% confidence) to Chl a and CDOM across the cruisetransect. However, a significant positive correlation (> 99%confidence) with sea surface temperature (SST) and salinity instead suggestsa widespread abiotic source related to the availability of aqueous iodineand to temperature.