BIOGENIC VOLATILE ORGANOIODINE AND ORGANOBROMINE HYDROCARBONS IN THE ATLANTIC-OCEAN FROM 42-DEGREES-N TO 72-DEGREES-S

During the cruise ANT X/1 and 2 of the research vessel Polarstern from November 1991 to March 1992, 39 surface water samples of the Atlantic Ocean from 42 degrees N to 72.5 degrees S were collected and analysed for their concentration of volatile iodinated and brominated hydrocar bons. The concentration of chlorophyll-a was used as an indicator for phytoplankton, which is one of the main producers of iodinated and bro minated compounds in the ocean. For determination of chlorophyll-a, fl uorescence spectroscopy was applied, whereas the measurement of haloge nated volatile hydrocarbons was carried out by a purge and trap system with subsequent gas chromatographic separation and detection by an el ectron capture detector. With this technique the brominated substances CHBr3, CH2Br2, CHBr2Cl and CHBrCl2 have been detected in the range of < 0.03 ng/L to 15 ng/L. For these volatile bromomethanes a distinct c oncentration profile was found. CHBr3 was always found to be the subst ance with the highest concentration followed by CH2Br2, CHBr2Cl and CH BrCl2. It could also be shown that in addition to CH3I, which for a lo ng time was believed to be the only volatile iodinated substance in th e marine environment, other iodinated substances like CH2ClI, CH2I2 an d CH3CH2CH2I exist in the range of < 0.01 ng/L to 2.2 ng/L in surface water of the Atlantic Ocean. Although it is improbable that chlorophyl l-a is directly involved in the marine production of halogenated hydro carbons, it was found that it could be used as an indicator for the bi ogenic formation of brominated compounds, whereas the correlation betw een chlorophyll-a and the iodinated substances was not of the same qua lity. The positive correlation between bromoform and dibromomethane pr oves the same biogenic origin and mechanism of formation, which could not be found for the different iodinated compounds.