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Methods and materials

Interstitial water samples were collected from whole-round sections ranging from 5 to 20 cm in length, which were cut on the catwalk, capped, and taken to the laboratory for immediate processing. In the laboratory, samples were extruded from the core liner and the outside ~1 cm was removed to minimize the potential for contamination. Samples were cut in half to allow examination of the core interior, and any visible outsized clasts and fossil debris >1 cm in diameter were removed. The samples were then placed in a titanium squeezer, which was modified after the standard stainless steel squeezer of Manheim and Sayles (1974). Interstitial water was passed through a prewashed Whatman number 1 filter fitted above a titanium screen, filtered through a 0.45 µm Gelman polysulfone disposable filter, and subsequently extruded into a precleaned (10% HCl) 50 mL plastic syringe attached to the bottom of the squeezer assembly. Splits (1–2 mL) of samples were placed into clean glass vials with polyseal caps in preparation for analysis of δ13CDIC. Approximately 10 mg of mercuric chloride (HgCl) was added to each sample to prevent microbial growth. Samples were stored at 4°–10°C until analysis.

Isotopic analyses were performed at the Environmental Isotope Laboratory at the University of Arizona in Phoenix, Arizona (USA). Samples were analyzed using an automated headspace sampler (Finnigan GasBench) connected to a continuous-flow gas-ratio mass spectrometer (Finnigan Delta PlusXL). Samples were acidified with concentrated phosphoric acid, and a minimum of 30 min was allowed for degassing of the water sample. Carbon isotope ratios are reported in parts per thousand (‰) relative to the Vienna Peedee belemnite (VPDB) standard. Precision is ±0.2‰, as monitored through multiple analyses of an in-house sodium bicarbonate standard solution that was calibrated against National Bureau of Standards (NBS)-18 and NBS-19.