To further methods for monitoring seawater intrusion, we applied a water-soluble chemical tracer and deployed fluorescent microspheres to reveal the extent to which seawater or individual prokaryotic cells penetrate a sediment sample during drilling operations. In total, 154 subsamples from cores were investigated with an additional 6 cores studied by measuring chemical tracer in transects through the cross-sections of the cores. The averaged results show that the center of the sediment cores contain less perfluorocarbon tracer than the core margins and have lower potential seawater contamination by a factor of between 3.5 and 100. Samples obtained using the advanced piston corer were generally less contaminated than sediments obtained using the extended core barrel by a factor of between 3 (Site 1230) and 10 (Site 1226). The gradient between chemical tracer concentrations in the core center and the periphery was found to be steeper in sediment cores from the shallow-water sites (a factor of 65) than in cores from deepwater sites (a factor of 9), which may relate to core retrieval time. The method of microsphere deployment was improved to help eliminate failures by forcing cores to burst through the bead delivery bag. In 34 samples with a range of chemical tracer concentrations, the number of microspheres detected was compared with the level of chemical tracer found. This comparison demonstrated that in spite of the large number of microspheres deployed, the beads end up at a largely diluted concentration of ~1000 beads/mL seawater, which is similar to the abundance of prokaryotic cells in surface seawater. The relevance and importance of all of the tracer results to efforts aimed at studying the subsurface biosphere are discussed.
1House, C.H., Cragg, B.A., Teske, A., and the Leg 201 Scientific Party, 2003. Drilling contamination tests during ODP Leg 201 using chemical and particulate tracers. In D'Hondt, S.L., Jørgensen, B.B., Miller, D.J., et al. (Eds.), Proc. ODP, Init. Repts., 201 [Online]. Available from the World Wide Web: <http://www-odp.tamu.edu/publications/201_IR/chap_02/chap_02.htm>. [Cited
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2Department of Geosciences, Pennsylvania State University, 212 Deike Building, University Park PA 16803, USA. chouse@geosc.psu.edu
3Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, United Kingdom.
4Biology Department, Woods Hole Oceanographic Institution, Redfield Laboratory, MS 33, Water Street, Woods Hole MA 02543, USA. Present address: Department of Marine Sciences, University of North Carolina at Chapel Hill, CB 3300, Venable Hall, Chapel Hill NC 27599, USA.
5Shipboard Scientific Party addresses.
Ms 201IR-102