Wintersteller, Paul; dos Santos Ferreira, Christian (2016): Gridded bathymetry from multibeam echosounder EM120 data of the cruise M72/2 (2007) [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.860086

Bathymetry based on data recorded during M72-2 between 23.02.2007 and 13.03.2007 in the Black Sea. The main focus of the cruise was to study the fluxes and turnover of methane and sulphur in the Black Sea hydrocarbon seep systems and investigating the microbial diversity in two contrasting permanently anoxic settings associated with fluid flow and gas seepage: the methane seeps at the shelf break of the Palaeo-Dnepr area and the hydrocarbon seeps of the mud volcanoes in the 2000 m deep Sorokin trough east of Crimea.

Detailed description:

During the cruise M72-2 the Kongsberg EM120 multi-beam-echo sounder was used. The EM120 uses a nominal sounding frequency of 12 kHz. 191 beams with a 1°/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://epic.awi.de/26725/1/Kon2007a.pdf. The EM120 multibeam was used continuously during M72-2. The vessel's speed was 5 kn during surveys and 10 kn during the transits. Responsible person during this cruise / PI: Steffen Gauger (info@fielax.de).

Description of data processing:

Postprocessing and products were conducted by the Seafloor-Imaging group of MARUM, responsible 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. Though CTD measurements were taken during the M72-2 cruise, these were not sufficient to represent the changes in the sound velocity profile throughout the study area, therefore a sound velocity correction had to be applied. The corrections of sound velocity profiles (SVP) are 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). Changes in SVP were set with the mbset function within mbsystem. Further roll, pitch and heave corrections were not applied for the M72-2 data. 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.

Objectives of Cruise:

This cruise leg combines activities of the 6th EU framework project HERMES and the German 'Geotechnologien' project MUMM II and investigates seep systems of the NW and NE Crimean margin. These consist of numerous fluid- and gas-escape structures outcropping in water depths between 200 and 2100 m which include actively gas emitting mud volcanoes and microbial reefs associated with gas seeps. The rising fluids carry hydrocarbons, mostly methane, to the seabed surface, which build the basis for rich and abundant microbial life. On the basis of geophysical, geochemical and microbiological data from various seep structures collected during M 72/2 we aim at gaining a better understanding of the distribution and functions of the anoxic seep ecosystems. The objectives are to understand the controls and mechanisms of chemical element transport and breakdown by seep microbiota, and to obtain insight in the element cycling and export from the seabed into the water column at different types of fluid seeps in the Black Sea. These goals will be achieved by detailed near-field mapping of selected habitats using the French autonomous underwater vehicle (AUV) ASTERX (IFREMER) followed by detailed geochemical in-situ measurements and specific sampling of mud, fluids, carbonates and biota along geochemical gradients. Sampling and in-situ measurements will be performed with the German ROV QUEST (MARUM).