Description: Two newly developed coring devices, the Multi-Autoclave-Corer and the Dynamic Autoclave Piston Corer were deployed in shallow gas hydrate-bearing sediments in the northern Gulf of Mexico during research cruise SO174 (Oct-Nov 2003). For the first time, they enable the retrieval of near-surface sediment cores under ambient pressure. This enables the determination of in situ methane concentrations and amounts of gas hydrate in sediment depths where bottom water temperature and pressure changes most strongly influence gas/hydrate relationships. At seep sites of GC185 (Bush Hill) and the newly discovered sites at GC415, we determined the volume of low-weight hydrocarbons (C1 through C5) from nine pressurized cores via controlled degassing. The resulting in situ methane concentrations vary by two orders of magnitudes between 0.031 and 0.985 mol kg**-1 pore water below the zone of sulfate depletion. This includes dissolved, free, and hydrate-bound CH4. Combined with results from conventional cores, this establishes a variability of methane concentrations in close proximity to seep sites of five orders of magnitude. In total four out of nine pressure cores had CH4 concentrations above equilibrium with gas hydrates. Two of them contain gas hydrate volumes of 15% (GC185) and 18% (GC415) of pore space. The measurements prove that the highest methane concentrations are not necessarily related to the highest advection rates. Brine advection inhibits gas hydrate stability a few centimeters below the sediment surface at the depth of anaerobic oxidation of methane and thus inhibits the storage of enhanced methane volumes. Here, computerized tomography (CT) of the pressure cores detected small amounts of free gas. This finding has major implications for methane distribution, possible consumption, and escape into the bottom water in fluid flow systems related to halokinesis.

Description: During the RV Maria S. Merian cruise 98, which took place between 08.01.2021 to 23.01.2021 bathymetry data based on multibeam echosounder (MBES) was recorded. The main objective of the cruise was focused on the hydrocarbon fluid emissions in the German North Sea and focused on the 'Entenschnabel'- area. In total, 43 CTDs were deployed, mainly to sample the methane content in the water column and to observe the stratigraphy of the water column. Oceanographic data as well as water samples have been collected at every CTD station. At the borehole locations of B11-2 and B18-1 but also at the DOK1-X Thor-1 and D1 well 4 CTDS per site have been deployed.Detailed information about the temperature, conductivity and oxygen of the water column have been carried out with a Seabird CTD/Rosette SBE911 with SBE-32 water sampler, equipped with 24 OTE bottles (10L).