R/V Professor Bogorov Cruise report: Cruise 37 POSETIV - Paramushir-Okhotsk Sea Expedition to Investigate Venting, Vladivostok - Vladivostok, September 23 - October 22, 1994

Abstract

Since the discovery of fluid venting in the late seventies the processes involved in the marine geochemical cycle, especially those of fluid and gas flux through the sediment-water interface have become a new and exciting area of interest and research. Today numerous vent fields have been discovered and described. Special benthic communities which include molluscs with bacterial symbiotes and polychaete worms are related to fluid discharge onto the sea-floor. The main scientific objectives have been to qualify and quantify the amount of water and gas discharge at the sea-floor in order to estimate the role of these sources to the global biogeochemical cycle of elements. Thus the mapping of vent fields and the description of related geological structures such as the bottom-simulating reflector (BSR) were among the first steps of investigation. The BSR is a acoustically detectable horizon in the sedimentary column. Above this horizon gas hydrates of methane (and sometimes higher order hydrocarbons) and water occur in varying amounts in an ice like condition. The depth of the BSR below the sea-floor depends on physico-chemical parameters such as temperature and pressure, as well as the chemical composition of the fluids. The BSR occurs widely in the area of investigation. To evaluate fully the nature and origin of vent phenomena, thought to be related to tectonic processes in the forearc and backarc region of island arcs, multidisciplinary research is necessary. From September 23 to October 22, 1994 a joint expedition with scientists from the Pacific Oceanological Institute (POI), Vladivostok/Russia, the Shirshov Institute of Oceanology, Moscow/ Russia, the Institute for Marine Geology and Geophysics (IMG&G), Yuzhno-Sakhalinsk/Russia, the Research Centre for Marine Geoscience (GEOMAR), Kiel/Germany and the Netherlands Institute for Marine Research (NIOZ), Texel/The Netherlands was carried out on board the Research Vessel Professor Bogorov during her 37th cruise. The Expedition was the principle part of the INTAS project 93-1881 - A Joint Russian-European Expedition to Paramushir Island: Reconnaissance Mapping of a Giant Deep Sea Vent in the Sea of Okhotsk - funded by the European Union. In order to evaluate the scale and nature of venting, a scientific party including geophysicists, sedimentologists, geochemists and micropalaeontologists worked closely together.