IMPACT OF SEASONAL HYPOXIA ON DIAGENESIS OF PHYTOL AND ITS DERIVATIVES IN LONG-ISLAND SOUND

Isoprenoid compound distributions were measured in sediment at two sit es in Long Island Sound, one with oxygenated overlying water throughou t the year, the other seasonally variable with hypoxia in summer. A co mparison of these two sites showed that the initial rate and pathway o f phytol degradation were strongly influenced by benthic faunal activi ty and environmental redox conditions. Solvent-extractable phytol (in detritus of phytoplankton origin) was rapidly converted into highly-bo und phytol (in sediment matrix) after deposition. Paradoxically, dihyd rophytol, a product of phytol reduction, was produced under oxic envir onmental conditions, apparently by macrofaunal digestion, Tn contrast, the 6,10,14-trimethylpentadecan-2-one and 4,8,12-trimethyltridecanoic acid, products of phytol oxidation, were formed under hypoxic environ mental conditions during suboxic or sulfidic microbial metabolism. Inc ubation of planktonic material further revealed the difference in degr adation pathway between oxic and anoxic conditions. Degradation proces ses of phytol and its derivatives were quantified based on a conceptua l model and incubation data. Relatively greater preservation of isopre noid compounds at the periodically low oxygen site may result from the higher input of planktonic detritus and slower degradation rate than at the continuously oxic site. (C) 1998 Elsevier Science B.V. All nigh ts reserved.