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SO173-1, 1st weekly report, July 13, 2003

Cruise SO173-1, with RV SONNE at the Pacific coast offshore Costa Rica and Nicaragua, has set out to perform work necessary for reaching the goals of SFB 574 at the Christian-Albrechts-Universität Kiel: "Volatiles and Fluids in Subduction Zones: Climate Feedback and Trigger Mechanisms for Natural Disasters". We left Balboa on 9th July at 10:00 p.m. to start the cruise. Captain M. Kull and his crew welcomed the scientific team comprising 17 scientists of SFB574, GEOMAR, from Costa Rica, and the USA.

The day before, the German Embassy had organized a reception on board. In spite of pouring rain, journalists arrived as well as about 70 guests from embassies, public authorities, scientific institutions, industry and commerce, to be informed about the research vessel and scientific work. All guests were very impressed, and the reception met with a very good response of the press.

Unfortunately, we had to leave Balboa without having received an urgently needed air freight consignment containing the positioning system Posidonia required for the side-scan sonar and the deep-towed seismic system. Posidonia, which had been used on RV METEOR, was still stored in Caracas. We will try to ship this system when riding at anchor in Costa Rica. Prior to departure we had loaded three containers and several air freight consignments containing scientific equipment that we could now install in the relevant laboratories. Some of the air freight consignments bore their name very rightly since the outer appearance of these aluminium boxes led us to the assumption that they might have had several meters of free flight through the air. However, except for one computer, no damage had been caused to any of the parts stored in the boxes.

During the transit of approx. 450 nm to our first working area off Quepos we continued providing the laboratories with instruments. At the same time we were recording bathymetric data by means of the SIMRAD System, and we added another magnetic profile to our data basis that had been established during previous cruises.

Our first task was the recovery of the marine seimological network consisting of 23 stations that had been deployed more than nine months ago, i.e. at the beginning of October 2002 during cruise M54-3B. We recorded two short air gun profiles for each station in order to accurately locate the instruments at the ocean floor. The position of the instruments, the orientation of the seismometers, and the polarity of the hydrophones can be determined by analysing the water sound arrival times. The first instrument was back on deck on 11th July at 05:00 a.m. Depending upon the depth of the stations, we recovered one instrument every three to four hours, except for one that unfortunately did not respond - all our attempts were in vain. This instrument (OBH302), deployed at a depth of more than 300 m, was the station nearest to the coast. Although we fear that it may have been destroyed or towed away by trawling activities, there is still hope that it may be found some day. The long period of deployment has obviously caused corrosion damage to the instruments. However, their are still in proper operating condition.

In the meantime, we made a CTD survey (SIMRAD probe) down to a depth of 2000 m in order to calibrate the SIMRAD system. For this purpose, we also recorded a short profile in two opposite directions across Jaco Scar. This work was finished on Sunday, 13th July at 03:00 p.m.

Presently, we are in transit off Nicoya Peninsula, where we are going to record the first seismic depth profile. The weather is changeable, first it rains and then the sun shines, while the sea is mostly calm.
All aboard are fine and are sending their regards to those at home.

At sea, 13.07.03

E. Flüh

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