Gas samples for hydrogen analyses were retrieved from the pressure core sampling (PCS) device. The workings and deployment of this device are described in detail in Tréhu, Bohrmann, Rack, Torres, et al. (2003). The use of the PCS allowed for the collection of the best possible in situ gas samples.
The PCS cores were degassed for periods of 450–2999 min onboard the ship (Milkov et al., 2003). Evolved gas was collected in a series of sample increments by allowing gas to bubble through a water bath and captured in an inverted plastic graduated cylinder. Gas was removed from the graduated cylinder by a syringe. Gas aliquots were then placed into 30-mL serum vials by water displacement. The vials were sealed and stored at 4°C until analysis.
Samples destined for acetate concentration measurement were collected in conjunction with other interstitial water (IW) samples. The majority of shipboard IW samples were obtained on 5- to 20-cm-long whole-round cores that were cut according to two general procedures described in Tréhu, Bohrmann, Rack, Torres, et al. (2003). Uncontaminated sediment (~150–300 cm3) was placed into a titanium squeezer (modified after the stainless steel squeezer of Manheim and Sayles [1974]), filtered through a 0.45-µm Gelman polysulfone disposable filter, and collected in a plastic syringe over the course of 20–40 min. The fluids were then filtered again through a 0.2-µm inline filter, and ~3-mL subsamples of this pore water were stored in glass vials for analyses of dissolved volatile fatty acids. The samples were kept frozen until analyzed.