1991 Marine Biological Association (MBA) Witch Ground Basin RRS Challenger Cruise 82 sediment cores and gas sampling

The objectives of Leg 1 of this survey were: - To locate the source of hydrogen plumes in the Witch Ground Basin by taking water samples with the rosette sampler. - To take core samples from the 2 large pockmarks in UK Block 15/25 to obtain Astomonema and other samples needed to complete studies on these pockmarks. - To re-survey the extent of the shallow gas deposits mapped in 1990. Leg 2: - To map the distribution of shallow gas and gas seeps in the Skagerrak north of Hirtshals and to study the relationship of the seeps to bottom and sub-bottom topography. - To obtain sediment cores from methane-rich and methane-poor sediments in order to compare their biomass, species composition and geochemistry. - To collect fauna for stable isotope analysis, for biochemical studies and for electron microscopy. - To measure gas concentrations and bacterial activity in the sediments and in the water collumn.