Scientific Drilling with the Sea Floor Drill rig MeBo
Introduction In March 2007 the sea floor drill rig MeBo (short for "Meeresboden-Bohrgerät", 'sea floor drill rig' in German) returned from a 17-day scientific cruise with the new German research vessel Maria S. Merian. Four sites between 350 m and 1700 m water depth were sampled at the continental slope off Morocco by push coring and rotary drilling. Up to 41.5-m-long sediment cores were recovered from Miocene, Pliocene, and Pleistocene marls. MeBo bridges the gap between conventional sampling
... ventional sampling methods from standard multipurpose research vessels (gravity corer, piston corer, dredges) and drill ships. Most bigger research vessels will be able to support deployment of the MeBo. Since the drill system can be easily transported within 20-ft containers, worldwide operation from vessels of opportunity is possible. With the MeBo a new system is available for marine geosciences that allows the recovery of high quality samples from soft sediments and hard rock from the deep sea without relying on the services of expensive drilling vessels. Rationale A variety of research targets in marine sciences-including gas hydrates, mud mounds and mud volcanoes, ore formation, and paleoclimate-can be addressed by shallow drilling (30-100 m below sea floor) in the deep sea (Quinn and Mountain, 2000; Sager et al., 2003; Herzig et al., 2003) . In general, standard sampling tools like gravity corers or dredges only allow recovery of fairly short cores from soft sediments or fragments of bedrock lying on the sea surface. Drill ships providing deeper penetration are expensive and typically booked far in advance, if available at all; therefore at the Marum Center for Marine Environmental Sciences (Marum) at the University of Bremen we developed the drill rig MeBo that can be deployed from standard research vessels. System Concept The MeBo is deployed on the sea bed and is remotely controlled from the vessel (Fig.1) . The rig is lowered to the sea bed using a steel-armored umbilical with a diameter of 32 mm. The deployment depth is currently limited to a maximum of 2000 m below sea level by the length and strength of the umbilical. Four legs are extended before landing to increase the stability of the rig (Fig. 2) . Copper wires and fiber optic cables within the umbilical are used for energy supply from the vessel and for communication between the MeBo and the control unit on the deck of the vessel, respectively. The drill rig is powered by four hydraulic pumps that are driven with electric motors. A variety of sensors, video cameras, and lights are used for monitoring the drill performance. The mast with the feeding system forms the central part of the drill rig (Fig. 2) . The drill head provides the required torque and rotary speed for rock drilling; it is mounted on a guide carriage that moves up and down the mast with a maximum push force of 4 tons. A water pump provides sea water for flushing the drill string, for cooling of the drill bit, and for removing the drill cuttings. The system utilizes commercial rotary core barrels with diamond or tungsten carbide bits. In addition it can push core barrels into soft formations, and case the boreholes. The MeBo stores drilling rods, casing tubes, and pushcoring and rotary barrels on two rotating magazines that Figure 1. Schematic deployment scheme of the sea floor drill rig MeBo exemplified for RV Maria S. Merian.