Session MG Poster Raum: Kármán-Auditorium Katrin Schwalenberg (BGR Hannover) , Carsten Scholl , Ele Willoughby , Nigel Edwards Marine Controlled Source Electromagnetic Experiments for Sediment Characterization Email: k.schwalenberg@bgr.<strong>de</strong> In the last 5 years marine controlled source electromagnetic experiments (CSEM) have been conducted on the West Coast of Vancouver Island, B.C. to investigate the electrical signature of submarine gas hydrate accumulations using a bottom-towed electric dipole-dipole system. Potential targets of the method are hydrocarbon <strong>de</strong>posits such as oil, gas and gas hydrates which have a much lower electrical conductivity than seawater which commonly occupies the marine sediment pore space. On the Cascadia Margin off Vancouver Island, gas hydrates have been i<strong>de</strong>ntified through the occurrence of bottom simulating reflectors (BSR) in several seismic data sets. They have been inferred during ODP leg 146 and directly i<strong>de</strong>ntified during IODP 311. Of particular interest is a 10km x 5km area which is characterized by a series of seismic blank zones interpreted as cold vents. Pressure coring, LWD and wireline logs into the largest of the vents called “Bullseye” during IODP 311 revealed massive gas hydrates in the upper 40mbsf. Data from 4 profiles show clearly very high resistivity anomalies over the vents which support the presence of massive hydrates within the vents in contrast to a probably mo<strong>de</strong>rate to low hydrate concentration outsi<strong>de</strong> the vents, even though BSRs are clearly visible. More resistivity anomalies have been <strong>de</strong>tected in Cascadia close to other IODP drill sites. However, the nature of these anomalies is not fully un<strong>de</strong>rstood, yet, but they have been verified through repeated measurements within a year. In January 2007, the system will be used to explore gas hydrates and gas venting on the Hiku- 297 rangi Margin on the NE coast of New Zealand. Joint interpretation of CSEM and <strong>de</strong>ep-towed seismic data will enhance the significance of the mo<strong>de</strong>ls <strong>de</strong>rived.
Session MG Poster Raum: Kármán-Auditorium Marcus Fabian (Universität Bremen, Fachbereich Geowissenschaften, Meerestechnik/Sensorik) , Heinrich Villinger The Bremen Ocean Bottom Accelerometer -OBA- Email: marcus.fabian@uni-bremen.<strong>de</strong> The Bremen Ocean Bottom Accelerometer (OBA) is a new scientific tool to monitor local ocean bottom acceleration in three directions with high resolution in time and amplitu<strong>de</strong>. The instrument has six accelerometers of MEMStype (micro electro mechanical systems), which have a nominal resolution of 10 −5 m/s 2 and a bandwidth from DC to 300 Hz. As their resolution is in the range of ocean floor background noise and the sensors are of small physical dimensions 27 mm x 27 mm x 16 mm) and have low current-consumption (≈ 17 mA, ± 6.2 V), they are best suited for long-time autonomous operation in <strong>de</strong>ep sea instruments like the OBA (Fabian & Villinger, in press). A newly <strong>de</strong>signed digitizer continuously samples and filters the acceleration data from all six sensors at 5Hz and writes the data to a CompactFlash card. The powerconsumption of the complete system is 996 mW. A 304 D-cell lithium battery pack powers the instrument for more than a year. Maximum operation <strong>de</strong>pth of the OBA is 6000 m. The OBA will be <strong>de</strong>ployed in autumn of 2007 by means of the new ROV (remotely operated vehicle) ‘Kiel 6000‘ in the Logatchev Hydothermal Vent field (LHF), 14°N on the Mid-Atlantic Ridge in a <strong>de</strong>pth of 3000 m. Its position will be nearby the OBT (Ocean Bottom Tiltmeter), which was installed in May 2005 by the ROV ‘Quest‘ (Fabian & Heesemann, 2006, Fabian & Villinger, in press) and was recovered and replaced by the ROV ‘Jason II‘ in February 2007 during cruise MSM04/3 of the new german research vessel ‘Maria S. Merian‘. The OBA will record until January 2009 simultaneously to the OBT. The 3-axis acceleration data from the OBA will complete long-time data tilt data of the OBT. Both instruments provi<strong>de</strong> data of local seismicity and tilt related to hydrothermal activity and crustal growth. Activity-phases in the LHF like enhanced seismicity or ocean floor <strong>de</strong>formations will be <strong>de</strong>termined and correlated with the data of co-workers in our research program (temperature, ocean bottom water pressure, test-sequences of local smoker-fluid chemistry and vent-fauna during the visits of the LHF between 2005 and 2009). The long-time data will be used as a proxy for changes in energy flux from the earth‘s mantle to the ocean and for variations and diversifications in local life cycles. The OBA is a part of the monitoring system of project LOLEM (Logatchev Longtime Environmental Monitoring) which is supported by the Deutsche Forschungsgemeinschaft (DFG) in the frame of Schwerpunktprogramm 1144: ‘Vom Mantel zum Ozean: Energie-, Stoff- und Lebenszyklen an Spreizungsachsen‘. References: Fabian, M., Villinger, H. (in press). The Bremen Ocean Bottom Tiltmeter, OBT,- a technical article on a new instrument to monitor seafloor tilt and local seismicity, Marine Geophysical Researches. Fabian, M., Heesemann, B. (2006). Neigungswaage für Unterwasser- und Hochdruckanwendungen (<strong>de</strong>ep sea level), Gebrauchsmusterschrift (registered <strong>de</strong>sign) DE 20.2006.013066 U1 - Universtät Bremen, Deutsches Patent- und Markenamt. 298