Revealing the deep sea's underlying secrets
The remoteness of deep sea has led to a heavy reliance on technology to provide information needed for the study of the subsurface biosphere and its energy resources. For investigations of the sediment structures, autoclave sampling tools are continuously being developed to obtain undisturbed cores and to carry out subsampling with minimum distortion of sediments containing gas hydrates. The Autoclave Piston Corer-Anaximander (APC-A) is a coring tool equipped with a pressure chamber for sampling seafloor sediments at water depths of up to 2,000m. Specifically designed for retrieval of sediment cores (up to 2.5m in length) under ambient pressure, it allows in-situ determination of methane concentrations and gas hydrate volumes. On the other hand, the Multi Autoclave Corer-Anaximander (MAC-A) is able to secure up to four pristine cores (up to 1m in length) for subsequent geoscientific and microbiological laboratory investigations. After retraction of the cores into the lab transfer chamber (LTC), non-destructive analytical methods such as Computed Tomography can be applied before core subsampling by pressurised rod gauging. Originally developed within the German project OMEGA, the system concepts were upgraded and adapted to sample gas hydrate-bearing near-surface sediments in the Eastern Mediterranean. In autumn 2004, they were deployed on Anaximander mud volcanoes at depths close to the upper boundary of the hydrate stability zone and recovered gas hydrates from gravity cores. Either stored in steel vessels or in gas-tight bottles filled with brine solution where gas from dissolving hydrates was captured, gas hydrates-bearing cores laid the base for extensive analyses. The solid picture drawn of methane and hydrate occurrence at the specific sites was further refined by geological studies and microbiological description of the bacterial and archaeabacterial communities.
