Abstract

To quantify the potential for biological contamination associated with the coring process, we conducted perfluorocarbon tracer (PFT) analysis on 556 sediment samples from Integrated Ocean Drilling Program (IODP) Expedition 329. The expedition cored deep-sea sediment at seven sites in the South Pacific Gyre (Sites U1365–U1371). We analyzed two types of sediment samples: (1) samples taken in the central part of the core (i.e., interior samples) and (2) samples taken near the core edge (i.e., exterior samples). We calculated the amount of potential drilling fluid intrusion from the mass of PFT that we measured in each sample. For the seven Expedition 329 sites (15 holes analyzed), PFT content ranges from below detection to levels where contamination is extremely apparent. The centers of the sediment cores (interior samples) contained generally less PFT than the core margins (exterior samples) and thus have lower potential drilling fluid (DF) contamination. The majority of sediment samples (interior) at Sites U1370 and U1371 have a contamination potential close to or below detection levels (i.e., 1.19 × 10–4 ngPFT/gsediment or 1.78 × 10–3 µLDF/gsediment on average). We observed higher contamination values (i.e., 7.28 × 10–3 ngPFT/gsediment or 6.98 × 10–2 µLDF/gsediment on average) at Sites U1365, U1366, and U1367. Finally, we measured much higher PFT concentrations throughout the sediment of Sites U1368 and U1369 (i.e., 5.48 × 10–2 ngPFT/gsediment or 6.60 × 10–1 µLDF/gsediment on average). We observe no apparent correlation of sample PFT content to sediment lithology, degree of sediment disturbance, core section number, or porosity.

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