RV METEOR Fahrtbericht / Cruise Report M127 Metal fluxes and Resource Potential at the Slow-spreading TAG Midocean Ridge Segment (26°N, MAR) – Blue Mining@Sea,Bridgetown (Barbados) – Ponta Delgada (Portugal), 25.05.-28.06.2016 (Extended Version)

Abstract

Cruise M127 is an integral part of the EU-FP7 project “Blue Mining: Breakthrough Solutions for the Sustainable Deep Sea Mining Value Chain” and is addressing research questions regarding the nature and resource potential of marine minerals, especially seafloor massive sulfides (SMS) along mid-ocean ridges. The cruise left from Bridgetown (Barbados) in the evening of May 25th and reached the working area at 26°N on the Mid-Atlantic Ridge on May 30th (Fig.1.1). One of the main tasks during the cruise was mapping of the TAG segment (26°N) in various resolutions. This included ship-based multibeam mapping over the entire length of the ridge segment as well as high-resolution mapping using an autonomous underwater vehicle (AUV) flying close to the seafloor (40-100 m altitude). The ship-based multibeam mapped along 710 nautical miles of profile lines covering approximately 7,000 km2 in the working area. Another 1,800 nautical miles of lines were mapped on the transit from Barbados to the working area and from there back to the Azores. The AUV was used on 19 missions, usually with survey times close to the seafloor of between 10 and 12 hours. Most dives provided maps with a resolution of 2 m and collected a number of other parameters with its sensors at the same time. Two dives were devoted to mapping points of interest in 50 cm resolution. Seismic work, as the 2nd important part of the cruise, included refraction and reflection seismics with airgun shots and multichannel seismic streamer records being compiled along 49 profiles on 8 survey runs (230 nautical miles in total length). Additionally, 22 ocean bottom seismometers (OBS) and 9 ocean bottom hydrophones (OBH) deployments were undertaken. The seismic work was hampered by problems with the compressor, for which the oil could not be cold enough at the beginning. This was later solved with the help of the ships crew. Deep-towed streamer work could also not be performed because of continued problems with the streamer that could not be resolved on board. A series of 6 ocean bottom electro-magnetic stations (OBEM) were deployed as preparation for the up-coming RRS James Cook cruise, which is also part of the Blue Mining project. A modular towed instrument platform (HYBIS) was used to deploy 10 of the (OBS) to the seafloor with high precision. Since this platform has built-in cameras and can be equipped with a sampling module we used this instrument later in the cruise to further visually inspect the seafloor and select locations for sampling. The final instrument being used was a short (3m) gravity corer for sediment sampling. In the course of the cruise 35 stations were attempted of which 22 stations successfully retrieved sediment for some of which ship-board analyses showed very high concentrations of copper. Rock fragments were recovered in 9 stations indicating the volcanic nature of those sampling stations. At the end of the cruise all Ocean Bottom Seismometers (OBS) were recovered. Only the six OBEM were intentionally left behind. Station work in the working area ended on 20:30 LT on June 23rd when the 5 day transit to Ponta Delgada was started. During the transits from and to the working area 3 ARGO floats were deployed and the ship-based multibeam and the 75-kHz ADCP collected data in international waters. The cruise ended 09:00 LT of June 28th with docking in Ponta Delgada. Overall on 1/3 of the cruise was used for the transit and 2/3 for stations work and transits within the working area (Fig. 1.2). Most of station time was devoted to geophysical work including seismic profiling and the deployment and recovery of the instruments.