Significance of carbon isotope discrimination between bulk carbon and extracted phospholipid fatty acids in selected terrestrial and marine environments

The development of compound-specific stable isotope analysis (CSIA) has led to many new environmental applications. One advantage of making isotopic m easurements of biomarkers over that of bulk carbon is that specific compone nts of:ln ecosystem can be defined isotopically. This approach has been use d recently with phospholipid fatty acids (PLFAs), which call be a plc,xy fo r bacteria. We conducted a comparison of bacterial PLFAs and bulk carbon is otope ratios in diverse terrestrial, estuarine and marine environments. The isotopic discrimination between bulk carbon and PLFA 16:0 varied from 10.1 to -11.4 parts per thousand and was greatest in environments that were lik ely anoxic and where methane was a potential carbon sourer. This approach w as used to estimate that methane accounted for about 15% of the carbon used by bacteria in a Gulf of Mexico cold seep site. (C) 2001 Published by Else vier Science Ltd.