Gridded bathymetry is based on data recorded during HE450 between 25.08.2015 and 08.09.2015 in the Norwegian Sea. The aim of the cruise was to explore gas emissions using the echosounders of the ship along the slope of the Barents Sea up to Svalbard to find more evidence for dynamic changes of gas hydrates and emissions of free gas. CI Citation: Paul Wintersteller (seafloor-imaging@marum.de) as responsible party for bathymetry post-processing and its products.

Description of processed data sources: During the cruise HE450 the Kongsberg EM710 shallow multibeam echosounder with a nominal sounding frequency of 70-100 kHz was utilized. 256 beams (and up to 800 soundings with equidistant and dual swath mode) are formed for each ping with a 1°(Tx)/2°(Rx) footprint while the seafloor is detected using amplitude and phase information for each beam sounding. For further information consult: http://epic.awi.de/26726/1/Kon2007b.pdf. During the surveys the EM710 experienced a few crashes (acquisition software and/or processing unit) but was otherwise stable during the cruise. The wobbling problem detected during the HE387 cruise (Sahling, 2012) is still present over the EM710 data. Responsible person during this cruise / PI: Christian dos Santos Ferreira (cferreira@marum.de) and Paul Wintersteller (pwintersteller@marum.de).Description of data processing: Postprocessing and products were conducted by the Seafloor-Imaging & Mapping group of MARUM, responsible person: Paul Wintersteller (seafloor-imaging@marum.de). The open source software MB-System suite (Caress, D.W., and D.N. Chayes, MB-System Version 5.5, 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. Though CTD measurements were taken during the HE450 cruise, these were not sufficient to represent the changes in the sound velocity (SVP) throughout the study area, therefore a correction had to be applied. The corrections in sound velocity are based on the mblevitus option, which generates annual mean water SVPs for a specified location using temperature and salinity data from the 1982 Climatological Atlas of the World Ocean (Levitus, S., Climatological Atlas of the World Ocean, NOAA Professional Paper 13, U.S. Government Printing Office, Washington D.C., 173pp, 1982). The SVP values are calculated using the DelGrosso equations (Dusha, B. D., Worcester P. F., Cornuelle B. D. and Howe, B. M., "On equations for the speed of sound in seawater", J. Acoust. Soc. Am., 93, 255-275, 1993). Changes in SVP were therefore applied (mbset), while further roll, pitch and heave corrections were not necessary for the HE450 data. But not all changes could be corrected this way and may still occur as artefact. The Bathymetric data has been manually cleaned for existing artefacts with mbeditviz. NetCDF (GMT) grids of the product and the statistics were created using mbgrid. 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 about 70 m. A higher resolution is, at least partly, achievable. The grid extended with _num represents a raster dataset with the statistical number of beams/depths taken into account to create the depth of the cell. The extended _sd -grid contains the standard deviation for each cell. All grids produced are retrievable through the PANGAEA database (www.pangaea.de).Chief Scientist: G. Bohrmann (gbohrmann@marum.de) CR: not available CSR: https://www2.bsh.de/aktdat/dod/fahrtergebnis/2015/20150037.htmA special thanks goes to the watch keeper of the hydroacoustic systems during HE450: Chieh-Wie Hsu and Markus Loher.