Methods for Quantifying Potential Microbial Contamination during Deep Ocean Coring

INTRODUCTION The Ocean Drilling Program (ODP) is committed to deep-biosphere research and has constructed a new microbiological laboratory on board the JOIDES Resolution. The use of the JOIDES Resolution as a platform for deep-biosphere research requires that the recovered cores are suitable for microbiological study. The major concern is whether microbes from the drilling fluid are introduced into the recovered core material during coring. Therefore, it is critical to verify whether recovered cores are contaminated. Here we present details of two tracer methods used to quantify the amount of contamination. These methods were modified from land-based drilling operations for use on the JOIDES Resolution (see review by Griffin et al., 1997). Tracer experiments were first conducted during ODP Leg 185 (Plank, Ludden, Escutia, et al., in press) and involve the delivery of both chemical and particulate trac-ers during drilling and their quantification in the ODP cores. These tracers were introduced while drilling unconsolidated sediments using the advanced hydraulic piston corer (APC), sedimentary rock using the extended core barrel and rotary core barrel (RCB), and igneous rock using the RCB and diamond core barrel. This technical note presents details on the characteristics, preparation, and delivery of the tracers and their quantification in cores. Suggestions are made regarding sample handling with the goal of minimizing sample contamination. It is strongly recommended that these contamination tests be routinely conducted when coring for microbiological studies. Characteristics Perfluorocarbon tracers (PFT) have been used extensively in land-because they are inert and can be detected with high sensitivity. Perfluoro(methylcyclohexane) is the tracer that has been tested on the JOIDES Resolution. This perfluorocarbon (Aldrich 30293-7) has a molecular weight of 350.05, a boiling point of 76°C, and a density of 1.76 g/mL. Its solubility is ~1 mg/L in water and is 10 g/L in methanol (Colwell et al., 1992). The low solubility in water facilitates gas phase partitioning and quantitative headspace analysis. The stock PFT is shipped in sealed ampoules, and it is not necessary to dilute it prior to use. Because the PFT is volatile and can be detected at extremely low concentrations, it is necessary to open the ampoules and transfer the PFT to the carboy used for delivery in a ventilated area well away from the core handling and PFT detection areas. Gloves should be worn during this process and discarded afterward. It is recommended that this transfer be performed on the helicopter deck while …