Geological setting, pore water chemistry, sediment chemistry, and metagenomics of hydrothermal systems in the Tyrrhenian Sea - Cruise No. M86/4 - February 06 - February 20, 2012 - Dubrovnik (Croatia) - Palma de Mallorca (Spain) (English)

The investigation of submarine hydrothermal systems in the Tyrrhenian Sea is generally aimed at a better understanding of the formation of submarine mineral deposits in island arcs where the shallow water depth (usually < 1000 m) and the influence of the subducting plate result in enrichments of gases, precious metals as well as abundant toxic elements at the seafloor. This cruise aimed at at a detailed mapping of known seafloor hydrothermal systems in an island arc setting using the autonomous underwater vehicle AUV "ABYSS". Due to the late arrival of the AUV in Europe from a previous cruise in the western Pacific, however, the AUV was not available for the cruise. This drastically affected the planned research. Instead of high-resolution AUV surveys, we used gravity coring along several transects over and beyond the mineralized area in order to sample the vertical extent of seafloor mineralization and to investigate the chemical variability of the overlying sediment. Overall 13 sediment cores were taken. The majority (N=10) was collected at Palinuro and many of these showed elevated temperatures within the core (up to 58°C) indicating that high-temperature fluids are far more widespread at Palinuro thean previously thought. The patchy distribution of these "hot" cores indicates that upwelling of these fluids is likely fault-controlled in the subseafloor. The influence of magmatic degassing and microbial processes on pore water chemistry and its sulfur isotopic composition will be investigated on-shore using sediment cores with and without hydrothermal influence. Geological sampling focused on two main areas, namely a known sulfide occurrence at the Palinuro volcanic complex and shallow marine sulfate deposits forming offshore Panarea Island. The study is continuing previous geological, geochemical, and biological work at these sites in the past couple of years using remotely operated vehicles (ROV's) and lander-type mobile drilling platforms during Poseidon cruises P340 and P412 as well as METEOR cruise M73/2. Additional sediment cores were collected from Glabro in order to evaluate the geochemical signature in this easternmost part of the Island Arc and to possibly detect geochemical signals of past hydrothermal influence away from the known vent sites. Part of the shiptime was spent on collecting water column samples with the CTD-multirosette for analyzing the stoichiogenomics of microbial communities in seawater in order to trace the limiting effect of nitrogen on the genetic material of marine microbial communities along water depth gradients. This sampling program was complemented by an extensive ship-based bathymetric mapping survey covering some 4700 km2 that were mapped using the Kongsberg Simrad EM122 multibeam system now providing a high-resolution map of the entire estern and northen part of the Aeolean Island Arc. We mainly used the EM120 to map volcanic edifices in the eastern part of the Aeolean Arc, however, the EM710 was used to map selected areas at the western summit of Palinuro in higher-resolution (10 m grid). A water column survey was obtained near Panarea in order to detect gas outlets associated with seafloor mineralization in the area.