Low molecular weight hydrocarbon (LMWH) distributions were examined in sediments from Sites 1109 and 1115 in the western Woodlark Basin using purge-trap thermal adsorption/desorption gas analysis. A number of different hydrocarbon components >C1, which were not detected during shipboard gas analysis, were detected at both sites using the purge-trap procedure. Concentrations of ethane, propane, and butane remained relatively low (<100 pmol/g) throughout Site 1109 and had no consistent trend with depth. In contrast, the longer-chain components increased in concentration with depth. Hexane concentrations rose to 716 pmol/g at the base of the site with a concomitant increase in both 2-methyl- and 3-methylpentane. At Site 1115, concentrations of ethane, propane, butane, and isobutylene + 1-butene remained low (<60 pmol/g) throughout the site and again had no consistent trend with depth. 2-Methylpentane, 3-methylpentane, and hexane concentrations had a subsurface maximum that coincided with sediments containing abundant plant-rich material. The LMWH downhole profiles plus low in situ temperatures suggest that the LMWH components were formed in situ by low-temperature biological processes. Purge-trap analysis has indicated the presence of some unexpected deep low-temperature bacterial reactions, which demonstrates that further analysis of LMWH may provide valuable information at future Ocean Drilling Program sites.
1Mather,
I.D., Wellsbury, P., Parkes, R.J., and Maxwell, J.R., 2001. Purge-trap analysis
of sediments of the western Woodlark Basin, Sites 1109 and 1115. In
Huchon, P., Taylor, B., and Klaus, A. (Eds.), Proc. ODP, Sci. Results,
180 [Online]. Available from World Wide Web:
<http:// www-odp.tamu.edu/publications/180_SR/chap_171/171.htm>.
[Cited YYYY-MM-DD]
2Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, United Kingdom. Correspondence author: J.Parkes@bris.ac.uk
3School of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom.
Initial receipt:
19 December 2000
Acceptance: 10 June 2001
Web publication: 27 August 2001
Ms 180SR-171