Biogeochemistry of sterols in plankton, settling particles and recent sediments in a cold ocean ecosystem (Trinity Bay, Newfoundland)

In the context of a multidisciplinary study to determine current and past e cosystem health and the relative contributions of sources of organic matter (marine vs. terrestrial and natural vs. anthropogenic input), sterols were determined in plankton, settling particles and sediments from Trinity Bay, Newfoundland, a sub-polar Atlantic Ocean ecosystem. The centric diatoms Ch aetoceros spp.. Thalassiosira spp. and Leptocylindrus danicus were all prom inent in the plankton samples, and centric diatoms predominated in the sett ling particles. Plankton samples contained 0.4 +/- 0.4 mg/g dw (1995) or 1. 4 +/- 1.3 mg/g dw (1996) total sterols, with cholesta-5,24-dien-3 beta -ol (mean 26% of total sterols), cholest-5-en-3 beta -ol (24%) and cholesta-5,2 2(E)-dien-3 beta -ol (13%) chief among these, denoting diatom and zooplankt on sources. In settling particles, the prominence of cholesta-5,24-dien-3 b eta -ol (24%), cholest-5-en-3 beta -ol (24%), cholesta-5,22(E)-dien-3 beta -ol (13%) and 24-methylcholesta-5,22(E)-dien-3 beta -ol (9%) again suggeste d mainly marine sources. The sterol composition of plankton and settling pa rticles from different sampling periods showed a high degree of consistency . Higher plant C-29 sterols (notably 24-ethylcholest-5-en-3 beta -ol, 9-26% ) were prominent in sediments from both inshore and offshore sites. No decr easing trend in total or individual sterols was observed down the 30-cm sed iment cores, suggesting good overall preservation. No 5 beta -stanols such as 5 beta -cholestan-3 beta -ol (coprostanol) were detected in offshore sed iments, plankton or settling particles, with only low levels (5 beta -chole stan-3 beta -ol max. 4.4%, 5 beta -cholestan-3 alpha -ol max. 5.1%) in cert ain inshore sediments. This suggests that raw sewage discharges in rural Ne wfoundland are being efficiently degraded or dispersed, or that inputs are highly localized. Source apportionation of organic matter in the sediment s amples based on sterol composition was attempted. This highlighted the larg e terrestrial contribution to the sterols in marine sediments (up to 58% of sterols inshore, 24% offshore) and suggests either degradation or effectiv e recycling of marine sterols. (C) 2001 Published by Elsevier Science B.V.