Galiomar III - Cruise No. M84/4 - May 01 - May 28, 2011 - Vigo (Spain) - Vigo (Spain) (English)

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The study of complex interactions governing sedimentary processes, transport routes and deposition dynamics at a continental margin are easier to understand where the system is simplified by the dominance of one external force. Off Northwest Spain, the sedimentary record on the Galician Shelf is controlled by a strong storm regime whilst contour-parallel currents seem to dominate at the continental slope. Intention of this cruise M84/4 GALIOMAR III was to a) trace the modes and routes of sediment transport from shallow to deep waters, b) understand the role of the shelf break and back-cutting gully systems for the sediment export dynamics, c) analyze the different modes and pathways of material downslope processes, and d) use locally confined depocenters at the lower continental slope, inside the gullies as well as on the outer and middle shelf as archives for reconstructing modern and past environmental conditions. Research groups from Bremen (MARUM) and Spain/Portugal (Vigo, Granada, Lisbon) with strong seismic, sedimentological, magnetic, geochemical and palae-oceanographic expertise have participated in this cruise utilizing a large number of complementary research devices. Extensive bathymetric mapping, PARASOUND and seismic profiling, during the first leg of this cruise, have shown how locally divers the sedimentary system in this study area is developed. On the slope, contouritic deposits seem to be the dominant feature indicating that current interactions with the morphology are omni-present. A surprising discovery along the margin is the manifold partitioning, with series of slope gullies, sporadic large canyon/channels systems draining deeply into the basin, and structural elements such as ridges and isolated mounts. Consequently, the sediment cores show a large variety of hemipelagic, contouritic, debritic and turbiditic successions. During the second leg on the associated shelf, coast-parallel and coast-perpendicular profiles were recorded, using PARASOUND and the new electro-magnetic sled NERIDIS III, to map individual depocenters (e.g., mud belts, outer-shelf ridge fields, pathway depressions). Special focus, in combination with an extended sampling/coring program was given to the character of depositional boundaries and the stratigraphic history of depocenters. The cruise M84/4 GALIOMAR III was, despite frequent rough weather conditions and heavy fishery activity, very successful. A complete bathymetry of the slope, 1500 km PARASOUND, 500 km seismic, and 130 km electromagnetic profiling, as well as coring (Rumohr, gravity, vibro) at not less than 108 stations were collected. With the analysis of this impressively large data set we expect to gain detailed insight into mechanisms and dynamics of sedimentary shelf-slope systems on different sub-modern to geological times scales.