Gas hydrates in the Ginsburg and Yuma mud volcano sediments (Moroccan Margin): results of chemical and isotopic studies of pore water

Two active mud volcanoes on the Atlantic continental margin of Morocco were sampled during a 1999 expedition on the R/V Professor Logachev. The active mud volcanoes (named Yuma and Ginsburg) are each about 4 km in diameter, rise 150–250 m above the seafloor and are the first active methane-related mud volcanoes identified in this region. Gravity cores from the crest of the active mud volcanoes recovered methane hydrates (clathrates). Thirty-five pore water samples were extracted and analyzed from seven gravity cores taken in and around the active mud volcanoes. Estimated gas hydrate content in mud volcano sediments is 2–11% by volume and 4–19% by pore space. Chloride ion concentrations of the original mud volcano water are similar to those of surrounding seawater, but are isotopically different. The water is very high in oxygen (to +35‰) and light in hydrogen (to −70‰). Pore water with these features has not been previously described in the published literature.