Geodynamik und Vulkanismus im tropischen/subtropischen Atlantik (Koordinatorantrag M64)

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M64/1 (FL Haase) The overall goals of the investigation are (1) to obtain insight into the volcanic and tectonic dynamics of the slow-spreading Mid-Atlantic Ridge (MAR) and geochemical and biological processes at active hydrothermal vent areas with emphasis on variations in time and space, and (2) to link the hydrothermal processes to the volcanic activity on the axis. The MAR between 4 and 11°S is highly variable in morphology, melt production and magma composition and an ideal region to study magma transport in the crust and mantle as well as volcanic eruption processes. The evolution of rift propagation, dyke intrusion, and volcanic activity will be investigated which will provide a basis to understand the formation and evolution of the hydrothermal vents and associated biological processes. The southern MAR is geologically and biologically much less well investigated than the northern MAR. However, indications for the occurrence of hydrothermal venting of hot and gas-rich fluids have been found. On the basis of these data, our research group will select two hydrothermally active sites and characterize them volcanologically, geochemically and biologically. Discrete aims for the fluid geochemistry and microbiology are the comparison with northern MAR systems and the investigation of water-depth dependant phase separation of the fluids in relation to the associated microorganisms and fauna. From the zoological perspective, the role of the southern MAR for biogeography and evolution of hydrothermal fauna as a possible link between the Indian and Pacific Ocean is of special interest. The interdisciplinary approach of this project will provide new insight into the coupled processes and dynamics on a slow-spreading axis. M64/2 (FL Villinger) The investigations of this cruise are a continuation of the program started at 15°N on the Mid-Atlantic Ridge in 2004 (cruise M60/3 and respective proposals). While in the 2004 cruise basic geochemical and biological studies were carried out in the Logatchev field at 15°N, the emphasis of the 2005 cruise lies on the temporal variability of fluid emanations, fluid temperature and chemistry, microbial activities and associated fauna at selected hydrothermal vent sites. In order to assess longterm variations in hydrothermal activity of the Logatchev Hydrothermal Field, a number of environmental monitoring stations will be installed which will be recovered in 2006. The fluids sampled at the Logatchev field in 2004 are probably of supercritical (>300 bar, >400°C) origin, showed high iron, methane and hydrogen concentrations, but low sulfide contents, thus providing a very special environment for hydrothermal habitats. The geochemical changes at different vent emanation sites and their consequences for the hydrothermal ecosystem will be in the focus of the studies in 2005. As little is known so far about the medium-term variability of complex hydrothermal systems, it is planned to continue these time-dependant studies in the following years. The strength of this interdisciplinary project is the intense interaction of the different working groups of geochemistry, biology and microbiology, which address the different levels of the hydrothermal ecosystem (from the inorganic material of the fluids to the different life forms) and the interfaces between these levels.