IODINE OVERABUNDANCES MEASURED IN THE SURFACE-LAYERS OF AN ANTARCTIC STONY AND IRON METEORITE

The surface layer and an interior sample of a large Antarctic H5 chrondite and of a IIIA iron meteorite were analysed with isotope dilution mass spectrometry for chlorine, bromine, and iodine. In addition, the evaporites of the stony meteorite and the surface layer of two different cracks in the iron meteorite were investigated. An evident iodine overabundance was found in the surface layer and in the evaporites of the chondrite specimen (enrichment factors of 11 and 6, respectively, compared with the iodine concentration in the interior). An even much higher iodine enrichment (factor 60-130) was observed in the corroded surface layers of the exterior and the two cracks of the iron meteorite. This result clearly confirms our previous hypothesis that an iodine concentration profile with depth has to be expected in Antarctic meteorites since we had also found it in Antarctic rocks. In some of the analysed meteorite surface layers low bromine enrichment could also be detected, but no significant chlorine enrichment was found. In the marine atmosphere near the Antarctic Peninsula an average methyl iodide concentration of 2.4 pptv was determined with gas chromatography using a halogen-sensitive electron capture detector. The corresponding surface sea water samples showed a mean of 2.6 ng/1 of this biogenic iodine compound. The existence of methyl iodide in the Antarctic atmosphere confirms our previous hypothesis that this compound influences the iodine content of Antarctic meteorites and rocks. © 1990.