Site Surveys für IODP-Bohrungen im subtropischen Nordatlantik (Koordination der MARIA S. MERIAN Reise 11)

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MARIA S. MERIAN Cruise MSM 11 comprises two legs to the subtropical North Atlantic. Aim of the first leg is to investigate the North Pond sedimentary basin at the western flank of the Mid Atlantic Ridge at 23'N. Main objectives of the second leg are the seismic survey and sediment geology investigations ofthe continental slope off NW Afnca. Both legs are dedicated to the preparation of lODP drilling expeditions. North Pond, an isolated sediment pond located on the Western flank ofthe mid-Atlantic Ridge, offers the opportunity to study microbial communities and their activities in deeply-buried sediments and the underlying basement. One important argument for choosing North Pond is that the geochemistry, hydrology, and geologic setting of North Pond have been previously studied by a series of DSDP and ODP dnil holes and seafloor observatories. However the existing site survey data are not sufficient for the approved North Pond lODP drilling expedition, scheduled to take place not before FY 2010. The goal ofthe proposed investigations on MSM 11/1 is therefore to map North pond in a detailed way in order to be able to position planned lODP holes precisely. These surveys compromise a detailed seismic mapping of the sediment-basement interface of North Pond, additional heat flow data and geochemical and microbial sampling of the sediments. In addition dredging of the upper crust, surrounding North Pond, will help to better define the petrological setting of North Pond. The proposed MERIAN cruise together with the planned lODP drilling project will provide a unique comprehensive geophysical, (bio)geochemical and microbial data set for the study of the deep biosphere. Main topic of the proposed MSM 11/2 is the preparation of an lODP expedition entitled Neogene Paleoclimate and sediment transport at the continental margin of NW Africa. Between Cap Bojador, southeast of the Canary Islands, and the deltas of rivers Senegal and Gambia we intend to collect seismic data in five different areas as presite survey. 4 out of 10 sites should cover at least the last 10 to 15 Ma to reconstruct the Neogene development of the Afncan monsoon and to document the early Pliocene aridification of the north African continent. Further 6 sites should explore sediments in high accumulation areas for a high resolution study of rapid climate changes in the subtropics and related sediment transport. Another topic of the proposed cruise will be the investigation of particle transport and charactenstics off Cap Blanc. Longterm moorings of sediment traps, oceanographic and optical sensors at stations CB (since 1988) and CBi (since 2002) will be renewed. Additional samples of particles in the water column and at the sediment surface wil! be taken by water samplers, in-situ pumps, and multicorers.