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Methods and materials

Samples for interstitial waters were extracted from either (1) 5 cm long whole-round sediment sections that were cut and capped immediately after core retrieval on deck or (2) small plug sediment samples of ~10 cm3 taken with a syringe from the ends of cut sections, also immediately after core retrieval. In the shipboard laboratory, whole-round sediment samples were removed from the core liner and the outside surfaces of the samples were carefully scraped off with spatulas to minimize potential contamination with drill fluids. Plug sediment samples were expelled from the syringe directly into squeezers. Fluids were extracted from sediments in Manheim titanium squeezers at ambient temperature with a Carver hydraulic press (Manheim and Sayles, 1974). Interstitial water samples discharged from the squeezer were passed through 0.45 µm polyethersulfone membrane filters and collected in plastic syringes. Aliquots for shore-based inorganic carbon isotope analysis were poisoned with saturated mercuric chloride solution and stored in 2 cm3 glass vials sealed with butyl rubber septa and plastic screw caps. The glass vials were kept refrigerated until they were processed for isotopic analysis at a shore-based laboratory.

Interstitial water samples were analyzed for δ13C content of DIC at Oregon State University using the method described in Torres et al. (2005). In summary, this method loads ~0.15–0.7 mL of sample into a Thermo Fisher GasBench-II headspace sampler, which is online with Thermo Fisher Delta V Plus isotope ratio mass spectrometer. Replicate measurements during these analyses indicate precision to be better than ±0.15‰ (1σ).