Biogenic volatile organoiodine and organobromine hydrocarbons in the Atlantic Ocean from 42°N to 72°S

Abstract

 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°N to 72.5°S were collected and analysed for their concentration of volatile iodinated and brominated hydrocarbons. The concentration of chlorophyll-a was used as an indicator for phytoplankton, which is one of the main producers of iodinated and brominated compounds in the ocean. For determination of chlorophyll-a, fluorescence spectroscopy was applied, whereas the measurement of halogenated volatile hydrocarbons was carried out by a purge and trap system with subsequent gas chromatographic separation and detection by an electron 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 concentration profile was found. CHBr₃ was always found to be the substance with the highest concentration followed by CH₂Br₂, CHBr₂Cl and CHBrCl₂. It could also be shown that in addition to CH₃I, which for a long time was believed to be the only volatile iodinated substance in the marine environment, other iodinated substances like CH₂ClI, CH₂I₂ and 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 chlorophyll-a is directly involved in the marine production of halogenated hydrocarbons, it was found that it could be used as an indicator for the biogenic formation of brominated compounds, whereas the correlation between chlorophyll-a and the iodinated substances was not of the same quality. The positive correlation between bromoform and dibromomethane proves the same biogenic origin and mechanism of formation, which could not be found for the different iodinated compounds.