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Meteor-Blog 24. July 2008: Muddy adventures

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Besides the dive robot ROV QUEST several other technical equipment is deployed on the cruise. Geologist Jens Gröger reports from the first gravity corer station.

Planetearth  Blog

Does the biodiversity of deep-sea organisms play a role for the climate on Planet Earth? Questions all about marine research will be answered directly aboard of the German research vessel Meteor by cruise leader Prof. Antje Boetius and her crew. In cooperation with the geoportal from 17.07.08 to 24.08.08 they contribute a Science-Blog of METEOR expedition M76/3 GUINECO – MARUM research of fluid and gas seeps on the Westafrican continental margin. Technical highlight of the cruise is the remote-controlled under water robot QUEST4000 by MARUM that will be deployed for taking fauna and sediments samples and conduction of in situ experiments. Go on a dive down to places no other human being has ever seen before: explore the fascinating deep-sea fauna and watch the scientists’ work at gas and fluid seeps deep down on the ocean bottom.

Expedition M76/3b is a collaboration of MARUM – Center for Marine Environmental Sciences at Bremen University and its associated institutes MPI and AWI as well as the French research institute IFREMER and the University of Paris.

Mehr Informationen über das aktuelle Meteor-Logbuch und Expedition M76/3B

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24. July 2008 (Author: Jens Gröger)

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Present Position

Today's blog is contributed by:

Jens Gröger“Hi! I’m Jens Gröger (picture 1). I am working as a PhD student in the department of Geochemistry and Hydrogeology at the University of Bremen. My thesis deals with the assessment of environmental impacts by excavations of soils. There are a variety of soils, which contain high amounts of natural iron-sulphur compounds (pyrite). Upon excavation these compounds can release high amounts of acid to the surrounding environment.

24. Juli: ShiptrackThe goal of my work is the development and improvement of methods for safely assessing the possible impacts of these so called acid sulphate soils. On this cruise I am working on a slightly different topic, although we come across a lot of sulphur too (See below). Together with three colleagues I perform sampling and geochemical analyses of pore water and sediments.”

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Picture 1: Jens Gröger at work with the gravity corer

Muddy adventures

After a night of steaming we finally reached our main target site called REGAB. The ROV was still out of order after the last dive and is currently getting repaired. Therefore, we used the time to deploy a series of gravity corers. The gravity corer (picture 2) is a geological device to sample the seafloor. Basically, a gravity corer is a long steel pipe with an attached weight on top. A plastic tube, a so-called ‘liner’, is inserted in to the steel pipe. Then the core is lowered to the seafloor where it penetrates the sediments by its own weight. After recovery the liner is removed from the steel pipe, cut into segments and sampled by us geochemists.

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Picture 2: The gravity core is set up for deployment

The first core already contained lots of gas hydrate (a methane-water-ice). Several pieces of gas hydrate were collected and frozen in liquid nitrogen. This has to be done very quickly, since gas hydrate decomposes rapidly at the high temperature and low pressure on deck, compared to the deep sea floor.

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Picture 3: Black silver rings – the costs of coring as a result of the chemical reaction of silver and sulphide gas

In addition to methane, the cores include a lot of the very smelly sulphide gas. Sulphide reacts with silver, so several colleagues who helped with sampling of sediments saw their jewelry turn black (picture 3). The second core was sampled in the cold room below deck. We use rhizone-syringe sampling (picture 4) to extract the pore waters from the sediments. The most sensitive chemical parameters were analyzed instantly in the ship’s laboratory. The rest of the core was sealed and stored in our cooling room. At home they will be stored in the huge core archive of MARUM.

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Picture  4: Porewater subsampling using rhizones in the cold room

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Picture 5: A sign showing the way to the geochemistry lab on board (Artist: Jens Gröger)