VOLATILE COMPOUNDS IN MEROMICTIC ANTARCTIC LAKES AND BASINS

Thirteen meromictic Antarctic lakes and basins were sampled for volatile compounds throughout 1991. Their physical characteristics varied widely in surface density(1.01 to 1.16 kg L(-1)), bottom density (1.03 to 1.19 kg L(-1)), bottom temperatures (-7.5 to +14.0 degrees C), bottom redox potential (-420 to +84 mV), maximum depth (7 to 110 m) and depth of oxycline (4 to 47 m). Nineteen compounds were identified and a further eight were tentatively identified using a Gas Chromatograph-Mass Selective Detector(GC-MSD). Volatile compounds detected identified included CS2 dimethylsulfide, polysulfides, substituted benzenes, thiophenes, octane and 6-methyl 5-hepten-2-one. In general the concentration of volatile compounds increased with depth in the water column with a further increase in concentration was observed in the sediment. The speciation of volatiles in each site was correlated with its physical characteristics. The predominant environmental factor that influenced the distribution of volatile compounds was density. However, this was modified by the temperature of the water column in heliorhermal lakes, Alkyl benzenes were restricted to sites with a bottom density less than or equal to 1.08 kg L(-1). CS2 and thiophenes occurred in sites with bottom densities less than or equal to 1.15 kg L(-1), whereas DMS and the polysulfides occurred in sites with a bottom density greater than or equal to 1.07 kg L(-1). CS2, thiophenes, DMS and the polysulfides were all found in lakes of intermediate density (1.07-1.14 kg L(-1)). Some potential sources of the compounds were discussed in relation to the physical nature of the lakes.