The aim of Maria S. MERIAN voyage MSM35 was to conduct marine controlled source electromagnetic (CSEM) measurements in the Danube Delta, Black Sea, to identify suitable gas hydrate deposits for a future MEBO drilling test site for methane production and CO2 sequestration in hydrate form. Marine CSEM is a geophysical exploration method to derive the electrical properties, i.e. resistivity of the seafloor. Gas hydrates and free gas are electrically insulating and replace conductive pore fluid.

During the MSM35 cruise the Kongsberg EM122 multi-beam echo sounder was used. The EM122 uses a nominal sounding frequency of 12 kHz. 288 beams or 432 soundings, with a 2°/2° footprint are formed for each ping while the seafloor is detected using amplitude and phase information for each beam sounding. For further information consult https://www.km.kongsberg.com/. Due to bad weather conditions during MSM35 the quality of the bathymetric data set is between fair and poor; the ship rolled more than the system set maximum roll compensation angle. Information gathered from the CR, responsible person during this cruise / PI: Udo Barkhausen (udo.barckhausen@bgr.de) Postprocessing and creation of products were conducted by the Seafloor-Imaging group of MARUM, responsible contact person: Paul Wintersteller (seafloor-imaging@marum.de). The open source software MB-system (Caress, D.W., and D.N. Chayes, MB-System Version 5, Open source software distributed from the MBARI and L-DEO web sites, 2000-2012.) was utilized for this purpose. A tide correction was applied, based on the Oregon State University (OSU) tidal prediction software (OTPS) that is retrievable through MB-System. In general, there is a tide differences of less than 20 cm in the Black Sea. Due to the fact that no sound velocity profiles (SVP) were obtained during the cruise, SVPs from MSM34-2 were applied for acquisition. In some areas this was not sufficient. The later correction of sound velocity is based on various SVP/CTD measurements throughout different cruises in the Black Sea within the last 15-20 years. In addition, the NATO Black Sea data base (http://sfp1.ims.metu.edu.tr/ODBMSDB/ODBMSDB.dll/querydb) was consulted for further CTD profiles in the given season/period of the year and in close position to the data set. The CTD data has then been used to calculate SVP by the usage of the UNESCO formula (G.S.K. Wong and S Zhu, Speed of sound in seawater as a function of salinity, temperature and pressure (1995) J. Acoust. Soc. Am. 97(3) pp 1732-1736). The changes in SVP were applied with the mbset function within mbsystem. Motion, lever-arm or offset corrections e.g. for roll, pitch or heading were not necessary. Bathymetric data has been manually cleaned for existing artefacts with mbeditviz. NetCDF (GMT) grids of the product and the statistics were created using mbgrid. Quality assurance was furthermore proven by visual and statistical comparison of crossing survey-lines from different cruises throughout the Black Sea. No total propagated uncertainty (TPU) has been calculated to gather vertical or horizontal accuracy. The currently published bathymetric grid of the cruise has a resolution of 125 m. A higher resolution is, at least partly, achievable.