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doi:10.2204/iodp.proc.329.204.2017

Results

Table T1 presents the detection limits (in nanograms PFT), drilling fluid equivalents (microliters), and nonindigenous cells equivalents (cells) for each of the Expedition 329 sites. The PFT detection limits reported for Expedition 329 sites were in the range of 1.03 × 10^–3 to 2.17 × 10^–3 ng PFT or 1.16 × 10^–3 to 2.44 × 10^–3 µL potential seawater intrusion. Variations in detection limit were driven by variations in the instrument calibration obtained for each site during the course of the analysis. Tables T2, T3, T4, T5, T6, T7, and T8 contain the measured PFT content (interior and exterior sample pairs), derived drilling fluid intrusion, and nonindigenous cell entrainment for all analyzed samples, sorted by site and hole. These tables also report sample location, lithology, and degree of sediment disturbance for each analyzed sample. Samples that produced a peak area below their hole’s detection limit are denoted as “BD.” Downhole variations in PFT content at Expedition 329 sites are shown in Figures F3, F4, F5, F6, F7, F8, and F9 on a logarithmic scale. In these figures, intervals characterized by slight to severe coring disturbance intensity are annotated with shaded areas.

The centers of the sediment cores contain generally less PFT than the core margins. Detection of the tracer in exterior core samples confirms successful delivery, whereas lower concentrations within the interior samples generally demonstrate lower contamination potential in core interiors. Despite these general patterns, PFT concentrations in interior-exterior sample pairs did not always follow a predictable gradient, with maxima at the core liner and minima in the center of the core. More than 50% of sample pairs in Holes U1365B and U1369C showed elevated PFT content in the center of the core compared to the core margins. These unexpected reversals of the expected pattern might be artifacts of (1) sample mislabeling, (2) differential PFT loss during relatively long sample storage times (months), or (3) advection of drilling fluid through microfissures (Lever et al., 2006). Lever et al. (2006) found relatively higher contamination potential in fine-grained samples (clay) compared to fine sand sediment, possibly due to preferential cracking of clays and resultant advection of drilling fluid through the core interior.

Different degrees of contamination potential characterize the PFT records of different sites. Sites U1370 and U1371 exhibit minimal contamination potential with PFT measurements in 71%, 99%, 99%, and 100% of the interior samples below detection for Holes U1370E, U1370F, U1371E, and U1371F, respectively. For above detection samples at Sites U1370 and U1371, the detected PFT concentration is relatively low, averaging 8.86 × 10^–4 ng_PFT/g_sediment. PFT concentrations were generally above detection levels at Sites U1365–U1369. Intermediate contamination levels (i.e., 7.28 × 10^–3 ng_PFT/g_sediment or 6.98 × 10^–2 µL_DF/g_sediment on average) were measured at Sites U1365–U1367. Finally, Sites U1368 and U1369 showed contamination potential averaging 9.87 × 10^–2 and 1.09 × 10^–2 ng_PFT/g_sediment, respectively. A large fraction of the sediment from Hole U1368C was reported as slightly disturbed by the shipboard scientific party, which may partly explain the elevated PFT content observed for that hole.

To understand the large variation in measured PFT content throughout Expedition 329 sites, we looked for relationships between observed PFT concentration and other parameters, including core section number, core depth, porosity, sediment lithology, and degree of coring disturbance. We found elevated PFT content in 55% of the samples from sedimentary intervals characterized by shipboard sedimentologists as heavily disturbed. We observed no relationship between lithology (e.g., abyssal clay, carbonate ooze, and siliceous ooze) and PFT content. However, because PFT extraction may have been incomplete at 70°C, we cannot fully preclude the possibility of a relationship between contamination potential and lithology.

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