Schmid, Florian , Peters, Maike, Walter, Maren, Devey, Colin and Sültenfuß, Jürgen and MSM25 Scientific Party (2018) Hydrothermal plumes and δ3He anomalies above the Southern Mid-Atlantic Ridge (13°-33°S) indicating previously unknown active vent sites. [Poster] In: GeoBonn 2018. , 02.09.-06.09.2018, Bonn, Germany .

Abstract

The Mid-Atlantic Ridge south of 13° S was entirely unexplored for hydrothermal activity until recently. In 2013 the expedition MSM-25 of the German research vessel Maria S. Merian set sail to systematically survey the axial region of the Southern Mid-Atlantic Ridge between 13° and 33° S for signs of active hydrothermal venting. Our shipboard sampling gear during the expedition included a typical conductivity-temperature-depth (CTD) probe with an additional turbidity sensor mounted to carousel water sampler and miniaturized plume recorders which were attached to the cable above the CTD system. Turbidity and oxidation-reduction-potential sensors were also mounted to the GEOMAR Abyss, the autonomous underwater vehicle (AUV) operated during the cruise. We intensely surveyed and sampled the water column above 16 separate ridge segments by conducting 65 CTD stations (including single dip casts and tow-yo stations) and 11 successful AUV dives. A total of 973 water samples collected at CTD stations for noble gas analysis were filled in gas-tight glass ampoules or copper tubes and later analysed for their isotopic composition in the Bremen helium isotope lab. About 800 of the samples were successfully analysed and yield meaningful δ3He results. Thus, we achieved a unique dataset of δ3He concentrations above the Southern Mid-Atlantic Ridge which is likely unprecedented in its extent along the spreading axis and density of sampling in particular in the bottom waters filling the axial rift valley. In summary, we identified 10 discrete plumes that are characterized by anomalies either in turbidity, oxidation-reduction-potential, δ3He or most frequently a combination of these parameters. Eight of the plume anomalies were previously unknown. Most of the identified hydrothermal plumes are located above the high-relief segment centres, where the axial morphology indicated robust magmatism. This contribution will give an overview of the hydrothermal plume discoveries made during the MSM-25 expedition which certainly represent promising targets for further exploration of active venting along the Southern Mid-Atlantic Ridge.

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