Volatile und Fluide in Subduktionszonen

Last week we had to interrupt our research work to make a stopover in port of Caldera, Costa Rica. This stop became necessary as we had to arrange for the transport of a container with ocean bottom seismometers and for an urgent air freight to make sure for them to reach their next places of usage in time. At the same time, turnover of some members of the crew and of the scientific team took place. On Wednesday, 30th July, we departed on time at 08:00 a.m.; we reached the last area of survey off Nicaragua after a fast transit. Having recalibrated the Posidonia system (the antenna must be taken out of the sea when the vessel exceeds 8 kn), we used the deep tow system with the side-scan sonar system and the streamer on 31st July at 03:30 a.m. to start extensive high-resolution mapping of the continental margin off Nicaragua. Previous hydrosweep surveys made in this region covering 10 * 30 nm had revealed structures indicating the presence of mounds. We were to find out whether this supposition would prove true since particularly the upper area of the shelf had only been mapped incompletely so far. Our efforts of the last weeks for the maintenance of instruments have been worthwhile. To the present day, the deep tow system has been operating without any interruption so that there is good progress with regard to profiles - even the first ones reveale both larger and smaller mounds on the monitors of the side-scan sonar system and seismics. The SIMRAD map overview shows two very large mounds, "Nica-1" and "Nica-2", at the upper shelf margin. Nica-1, the larger one, rises to 300 m above the surrounding sea floor. Thus it is higher than Mound Culebra off Costa Rica. Further mound structures have already become visible in the lower area of the continental slope we are presently surveying, i.e. there is obviously a considerable number of such structures to be found here off Nicaragua. On Tuesday in the afternoon we will have to leave this exciting survey region as we are scheduled to reach Caldera - and the end of cruise SO173-1 - by 6th August.

We thank the captain and all crew members very much for the kind reception on board and for their extraordinary efforts. Without their enthusiasm and expert knowledge the results of our work could not have been reached. We look forward to the next year, trusting that we will then achieve further excellent results on research vessel SONNE.

The weather is still fine and all on board are well.

Best regards from all aboard,
Jörg Bialas (at sea, 10:56 N 86:59 W)