In gas hydrate areas seafloor sediments may contain high concentration of gas, specifically CH4. A pressure piston corer (PPC) is designed for collecting the gases which would otherwise escape during sampling. With gravity as the only driven force, the corer can penetrate into 10 meters' sediments. The core tube is also used as pressure container, attached with a pair of accumulators to maintain internal pressure. The PPC is 12 meters long, less than 1500 kg in net weight. The maximum working depth is 4000 meters, suitable for sampling all over the South China Sea.
Dissolved gas components, specially CH4, are rather important for understanding microbial activities in associated with cold seep on seafloor (Dickens et al., 2003). Traditionally, dissolved gas is extracted by headspace technique from sediments sampled with piston corer or gravity corer. This approach may work in near shore where in situ pressure of the core is low (Fossing et al., 2000; Hoehler et al., 2000). It does not work when in situ pressure is high (Dickens et al., 1997; Paull et al., 2000). In these cases, significant amounts of gas can escape from cores during recovery when the drop in pressure or increase in temperature lowers CH4 saturation (Dickens et al., 2000a). Sealing the sediment core at in situ pressure is essential for collecting the gases which would otherwise escape due to decreasing pressure or increasing temperature during recovery the samples from depth. In previous work PCS (Pressure Core Sampler) was deployed for ODP Legs in gas hydrate areas. The PCS is a downhole tool designed to recover a cylindrical sediment core, including gas and interstitial water, at in-situ pressure (Pettigrew, 1992). For that seafloor drilling is rather expensive, pressure corer independent from drilling machine is highly desired for gas hydrate