ALBERT

Description: Between 14.03.2006 and 25.04.2006, bathymetric data based on the KONGSBERG EM710 system (MBES) was acquired in the Gulf of Mexico during the R/V METEOR cruise M67/2. The main research goal was the investigation of asphalt volcanoes in the Campeche Bay and related sedimentary structures. The leg was split into two parts. During the first sub-leg 2a geophysical and especially hydroacoustic methods were used to explore the distribution of these asphalt volcanoes and to map knolls as well as other structures like mass wasting and asphalt flows. Using reflection seismic, sedimentary structures related to the volcanoes were also investigated. Further mapping but also sampling of vent fluids and asphalt was the research interest of sub-leg 2b. Therefore the Remotely Operating Vehicle (ROV) QUEST (Marum) as well as a TV-MUC were used. Bathymetry mapping was done using the EM120 for deeper and the EM710 for shallower regions. CI Citation: Paul Wintersteller (seafloor-imaging@marum.de) as responsible party for bathymetry raw data ingest and approval. Description of the data source: During the M67/2 cruise, the hull-mounted multibeam echosounder (MBES) KONGSBERG EM710 was utilized to perform bathymetric mapping in shallower areas. It allows to conduct surveys in water depths of up to 2,000 m, however it operates best in shallower water depths under 500 m. Two transducer arrays transmit frequency coded acoustic signals (70 to 100 kHz). Data acquisition is based on continuous wave pulses in shallower depths and FM (chirp) pulses in greater depths. The beam footprint has a dimension of 1° by 1°. For further information on the system, consult: https://www.km.kongsberg.com/ Due to the water depth of the research area the EM120 was permanently used, while the EM710 was only used in few parts of the research area. To convert the recorded travel times into water depth, several sound velocity profiles were obtained with the shipboard CTD, providing a correction for ray bending for each beam. Depth is estimated from each beam by using the two-way travel time and the known beam angle known, and taking into account the ray bending due to refraction in the water column by sound speed variations. Responsible person during this cruise / PI: Volkhard Spieß (vspiess uni-bremen.de), Gerhard Bohrmann (gbohrmann@marum.de) Chief Scientist: : Volkhard Spieß (vspiess uni-bremen.de), Gerhard Bohrmann (gbohrmann@marum.de) CR: https://www.tib.eu/de/suchen/id/awi%3Adoi~10.2312%252Fcr_m67/ CSR: https://www2.bsh.de/aktdat/dod/fahrtergebnis/2006/20060077.htm

Description: Between 14.03.2006 and 25.04.2006, bathymetric data based on the KONGSBERG EM120 system (MBES) was acquired in the Gulf of Mexico during the R/V METEOR cruise M67/2. The main research goal was the investigation of asphalt volcanoes in the Campeche Bay and related sedimentary structures. The leg was split into two parts. During the first sub-leg 2a geophysical and especially hydroacoustic methods were used to explore the distribution of these asphalt volcanoes and to map knolls as well as other structures like mass wasting and asphalt flows. Using reflection seismic, sedimentary structures related to the volcanoes were also investigated. Further mapping but also sampling of vent fluids and asphalt was the research interest of sub-leg 2b. Therefore the Remotely Operating Vehicle (ROV) QUEST (Marum) as well as a TV-MUC were used. Bathymetry mapping was done using the EM120 for deeper and the EM710 for shallower regions. CI Citation: Paul Wintersteller (seafloor-imaging@marum.de) as responsible party for bathymetry raw data ingest and approval. Description of the data source: During the M67/2 cruise, the hull-mounted multibeam echosounder (MBES) KONGSBERG EM120 was utilized to perform bathymetric mapping. It allows to conduct surveys in water depths of up to 11,000 m. Two transducer arrays transmit frequency coded acoustic signals (11.25 to 12.6 kHz). While the emission beam has a dimension of 150° across and 2° along track, the reception is obtained from 191 overlapping beams with widths of 2° across and 20° along track. The beam footprint has a dimension of 2° by 2°. For further information on the system, consult: https://www.km.kongsberg.com/ Due to the water depth of the research area the EM120 was permanently used. Only for shallower regions the EM710 was used too. To convert the recorded travel times into water depth, several sound velocity profiles were obtained with the shipboard CTD, providing a correction for ray bending for each beam. Depth is estimated from each beam by using the two-way travel time and the known beam angle known, and taking into account the ray bending due to refraction in the water column by sound speed variations. Responsible person during this cruise / PI: Volkhard Spieß (vspiess uni-bremen.de), Gerhard Bohrmann (gbohrmann@marum.de) Chief Scientist: : Volkhard Spieß (vspiess uni-bremen.de), Gerhard Bohrmann (gbohrmann@marum.de) CR: https://www.tib.eu/de/suchen/id/awi%3Adoi~10.2312%252Fcr_m67/ CSR: https://www2.bsh.de/aktdat/dod/fahrtergebnis/2006/20060077.htm

Description: This study investigates the geometry and temporal variation of a prominent gas bubble stream from a seafloor pockmark in the Lower Congo Basin. We present results of a 3D gridding approach of singlebeam echosounder water column data (Parasound 18 kHz) that increases the lateral resolution and improves the localization of anomalies beyond the inherent depth-dependent footprint size of the sonar system. This allows a detailed reconstruction of gas bubble trajectories through the water column, revealing a stable gas bubble stream for the deepest 1000 m. The bubbles are shifted laterally by ∼200 m in the transition zone between North Atlantic Deep Water and Antarctic Intermediate Water with a reconstructed current velocity of ∼4 cm/s. The direction of lateral shift varies throughout the ∼15 h survey possibly because of internal waves and small-scale eddies at the water mass boundary. Furthermore, a stacking of SBES water column data acquired during sampling stations showed a periodic variation in seepage intensity with periods of 6 and 8 min, which are likely related to temporally modulated gas supply to the sea floor. Singlebeam echosounder are commonly limited by their small coverage of the survey area during individual passes and their footprint size in detailed imaging of individual seep sites, especially in the deep sea. The presented gridding method for singlebeam echosounder data may facilitate the use of such data in deep water gas bubble stream identification and localization.