Development of an instrument package for quantifying sediment gas in JOIDES Resolution advanced piston cores
Lead Scientist: Charles Paull
Lead Engineer: Duane Edgington
Project Manager: Bill Ussler

We propose to develop and test a methodology jointly with the Ocean Drilling Program (ODP) to measure temperature, pressure, and electrical conductivity (TPC) within the standard ODP advanced piston corer (APC) core barrel during core recovery. Our objective is to investigate the spatial variation in the amount of gas contained in continental margin sediments. Almost nothing is known about the volumes of gas that occur in gassy marine sediments because most of the gas escapes during core recovery and currently there is no way to monitor this gas loss. However, variations in temperature, pressure, and electrical conductivity during core recovery between different cores at individual ODP drill sites are caused by differences in the amount of gas contained in the sediment. Gas expansion, endothermic decomposition of gas hydrates, and the formation of a gas phase by exsolution during core ascent will cool areas within the cores, produce time dependent pressure anomalies, and cause changes in the conductivity of the fluids at the end of the APC piston assembly in response to the formation of a free gas phase within cores. Thus, TPC sensors placed at the cutting shoe for the APC will measure changes in temperature, pressure, and conductivity, allowing gas content stratigraphies to be developed at individual drill sites. Moreover, the variation in the TPC records from various areas around the world will provide a basis to assess the global biogenic gas inventory in continental margin sediments.

Many observations of anomalously cold temperatures have been made on freshly-recovered, gas-rich cores from DSDP/ODP drilling legs. Attempts on recent ODP Legs (e.g., 146, 161, 164, 170) were made to document the temperature of core material on the catwalk of the JOIDES Resolution largely because of the interest in gas hydrates. To date core temperatures have only been measured on the catwalk using thermistors inserted several minutes after the core retrieval. These catwalk temperatures show that many core sections arrived on deck at distinctly lower temperatures (5-10° C lower) than other cores recovered from the same site. The interstitial water in some sections of freshly recovered core was actually frozen when they arrived on deck. Clearly there are significant thermal differences between various cores, however, the exact cause and magnitude of individual thermal effects cannot be determined with the data we are now able to collect. Catwalk temperature measurements are strongly affected by core ascent history and an unambiguous interpretation of their significance has not been possible. Because we know so little about the temperature, pressure, and gas exsolution history during core recovery, we are propose to develop a collection of sensors that can routinely monitor the TPC ascent history for ODP APC cores. The TPC sensors will be on the face of the APC piston, while the control electronics and data logger are embedded within the piston’s deadspace. The system will operate passively and require no attention by the drillers or science staff while the drilling is occurring. By establishing families of ascent curves, the stratigraphic variations in the amounts of gas stored in sediments can be determined at individual sites and variations between sites can be assessed.

This project is also supported by funding from the National Science Foundation.