FATTY-ACIDS AND STEROLS AS SOURCE MARKERS OF ORGANIC-MATTER IN SEDIMENTS OF THE NORTH-CAROLINA CONTINENTAL-SLOPE

To estimate the source and diagenetic state of organic matter reaching bottom sediments, fatty acids and sterols were measured in unconsolid ated surface material (Aocs) at 12 sites ranging from 600 to 2000 m ac ross the mid-Atlantic continental slope off Cape Hatteras, North Carol ina. Total free and esterified fatty acids were similar in distributio n and concentration to other coastal systems, with values ranging from 0.64 to 46.52, mu g mg(-1) organic carbon (1.10-68.85 mu g g(-1) dry sediment). Although shallow (600 m) stations contained significantly g reater fatty acid concentrations than deep (>1400 m) stations, high va riability observed at mid-depth (800 m) collections precluded a consis tent relationship between total fatty acid concentration and station d epth. At three sites where underlying sediments we re also collected, decreases in total fatty acids, reduced amounts of polyenoic acids and significant presence oi bacterial fatty acids suggest rapid reworking of labile organic material that reaches the sediment surface. The dis tribution of sterols was remarkably consistent among all sites even th ough there were large variations in concentrations (1.8-20.7 mu g mg(- 1) organic carbon). Sterol composition indicated phytoplankton, princi pally diatoms and dinoflagellates, as the principal source of labile o rganic matter to sediments, together with a significant input of chole st-5-en-3 beta-ol typical of zooplankton and their feeding activity. A minor but widespread terrigenous input was also evident based upon si gnificant concentrations of sterols dominant in vascular plants.