Volatiles and Fluids in Subduction Zones

at Sea at 8°30´N/85°10´W

From 19th to 22nd April, the change-over from leg 1 to leg 2 of cruise SO163 was taking place in Caldera, Costa Rica. The agenda was extensive during these days since, apart from all usual work of unloading/ loading (four containers on board) RV SONNE was being QSU-certified. In addition, a reception and a press conference with 50 persons participating were held aboard on Saturday, 20st April. On this occasion, we collaborated with the German Embassy in San José and with our Costa Rican partner ICE (Instituto Costaricense de Electricidad). Our reports met with great interest when we were introducing the results of leg 1 as well as the aims of the current cruise and of SFB 574 in general.

On 22nd April at 11.40 a.m., RV SONNE departed to reach the first station very soon at 14.00 p.m. At first, six OBH/s were deployed throughout the seismological net; 15 units had been completely installed ashore in the preceding week. One of the two new tiltmeters was launched to take test measurements. In the evening we checked the function of 16 acoustic releasers by means of geology cable at a depth of 3000 m.

On 23rd April, we reached the location of a fluid vent above which 10 OBH/S had been deployed during leg 1 to record any microseismicity. Two further units were deployed and some airgun profiles were shot by the 32 l gun. Then we took samples from the first 4 CTD/ rosette stations situated along a long profile from the coast to the deep sea. 2 of the rosette stations had been provided with multicorers.

On 25. 4., two further profiles were shot above the seismic net using a G-gun cluster, and all 12 stations could be successfully recovered. The stations were then deployed above the gas hydrate area at the foot of the Nicoya slide, and shot with two long airgun profiles; both the bolt airgun and the two G-gun clusters were used. After having successfully recovered 14 stations, including a new ‚flat-design' OBS work was completed by sampling two further CTD/KW stations (CTD 05 and 06, one of these with MUC) along the northern regional profile. Presently, we are in transit to Jaco Scar to recover the tiltmeter and to deploy another five stations for the seismological net.

All aboard are fine, the weather is excellent (27° air temperature, 30° water temperature). Air conditioning failed temporarily just when the first tropical rain of this cruise poured down. We have all noted the change in the color of the seas from green off Nicoya peninsula to blue further south. All laboratories are busily processing samples and data collected, and we hope to be able to communicate first results soon.

Best regards to all at home,
E. Flüh