RV Sonne Cruise Report / Fahrtbericht SO-236, Malé to Colombo, 9 to 29 August 2014 (English)

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Cruise 236 of the research vessel SONNE has provided data which are an important building block of the research by members of the Institute for Geology of Hamburg University, aimed to understand the interaction of paleoceanographic and climate change and evolution of the Maldives carbonate platform. The efforts undertaken to reach this goal encompass an earlier cruise with RV METEOR in 2007, a cruise with a smaller boat to analyze atoll anatomy in 2011, and IODP Expedition 359 with RV JOIDES RESOLUTION scheduled for October and November 2015. The specific goal of Cruise SO-236 was to acquire seismic, hydroacoustic, sedimentological, CTD and LISST data as well as current and sediment trap data in the area of the seven sites to be drilled during this expedition. A grid of seismic lines was therefore acquired in the dedicated working areas, which, after the corresponding post-cruise processing, will allow reconstructing the shape of the parts of the carbonate platform which underwent consecutive drowning steps during the Miocene and Pliocene. Seismic surveying was continuously accompanied by hydroacoustic measurements. Due to the bad state of the swath echosounder equipment, multibeam data were very noisy and no backscatter data could be acquired. Nevertheless, a careful and very time-consuming on-board processing of the multibeam data produced useful results with spectacular maps showing drowned banks at the sea floor of the Inner Sea. The new hydroacoustic and seismic data also allowed the discovery of sediment destabilization processes in the Inner Sea, a previously unknown process in the archipelago. Post-cruise research will address the question of the geohazard emanating from this process. Sediment sampling was successful at several localities using gravity and box corer as well as the video grab. Sediment cores will allow to reconstruct sedimentological and microfaunal variations thus providing insights into Holocene and late Pleistocene paleoceanographic and climatic variations. The video grab very successfully recovered rock samples from exposed parts of drowned banks and will allow a dating of the features using large benthic foraminifers. CTD and LISST data provided the first oceanographic data in a west to east transect of the archipelago. Preliminary results show the depth zonation of the water masses at the flanks of the archipelago and in the Inner Sea, and allows to show the occurrence of an oxygen minimum zone which probably corresponds to the eastern expansion of the oxygen minimum zone of the Arabian Sea. During the cruise, two moorings were set out in the Inner Sea. Mooring comprise current meters and sediment traps and will be retrieved after 12 months, i.e. after a full monsoon cycle. All of the strategic goals of the cruise were achieved with great success. A very good database was acquired, which forms a solid fundament for the post cruise analyses and research.

  • Title:
    RV Sonne Cruise Report / Fahrtbericht SO-236, Malé to Colombo, 9 to 29 August 2014
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    Institut für Geologie, Universität Hamburg
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    48 pages
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  • Type of material:
    Electronic Resource
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  • Classification:
    DDC:    550 Earth sciences and geology
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