MILLIMETER-SCALE PROFILING OF ABYSSAL MARINE-SEDIMENTS - ROLE OF BIOTURBATION IN EARLY STEROL DIAGENESIS

Near surface sediments from an abyssal northeast Atlantic site were sectioned using a newly designed Precision Core Extruder (PCE). Downcore profiles of excess Pb-210 and sterols showed pronounced millimeter-scale variability reflecting specific degradation and bioturbation processes. Excess Pb-210 and sterol concentrations decreased sharply in the uppermost 5 mm, and pronounced subsurface maxima were present. Stanol/stenol ratios, and the relative abundance of cholesterol, increased below 10 mm, indicating biodegradation involving Delta(5) double bond hydrogenation, C-24 dealkylation and/or de novo synthesis. Sterol profiles indicate that early diagenesis of labile compounds is dominated by processes operating near the sediment/water interface, and that the penetration of labile material into oxic sediments is largely controlled by advective processes, associated with infaunal feeding rather than diffusive-like mixing.