Generation of biogenic hydrocarbons during a spring bloom in Newfoundland coastal (NW Atlantic) waters

The distribution and carbon isotopic composition of biogenic hydrocarbons in spring bloom plankton, bottom sediments, and benthic macrobiota in Conception Bay, Newfoundland (NW Atlantic) were determined by gas chromatography/mass spectrometry and gas chromatography/combustion/isotepe ratio mass spectrometry. Although individual hydrocarbons were generally depleted by at least 3 parts per thousand relative to bulk organic matter, significant variations and temporal fluctuations in compound-specific carbon isotopic compositions were documented in bloom samples and laboratory cultures. Marked C-13 depletions in a suite of eight C-25 highly branched isoprenoid alkenes, as well as a temporal shift in the C-13 composition of spring bloom n-alkanes are suggested to be related to changes in the growth rates of bloom organisms. The input of multiple sources of organic matter into deep bay sediments could be recognized in the isotopic compositions of sedimentary n-alkanes. Overall, the carbon isotopic composition appeared to be primarily a reflection of the carbon fixing pathway of source organisms, with superimposed variations caused by fluctuations in growth rates and [CO2(aq)]. These findings highlight the need for more study of contemporary biogenic hydrocarbons; specifically of the influence of growth rate and timing of synthesis on the carbon isotopic composition of biomarkers over the course of phytoplankton blooms. (C) 1997 Elsevier Science Ltd.