Drilling operations onboard the Aranda were carried out using the BGS Rockdrill. The BGS system is a compact seabed-drilling platform that is deployed from a standard A-frame by a cable and winch carrying power and data transmission lines. The drill kelly and retraction winch are powered hydraulically by a three-phase electric pump mounted on the platform. Additional electric pumps are used for flushing the drill bit. The standard BGS system is equipped with a 5-m-long core barrel; however, because of the small A-frame and aft deck layout of the Aranda this core barrel was reduced to 3 m (Fig. F3). Unlike the wireline diamond coring system on the Norskald, holes drilled by the BGS system are limited to a 3-m depth. Core is recovered only by raising the drilling platform to the surface. The drill collects a 49-mm-diameter core using a double-walled core barrel. The core in the inner barrel is retained by a spring forming a wedge between the core and the barrel wall. The most commonly used core bit was a surface-set diamond bit with a stepped profile on the outer diameter (Fig. F4). A steel rod (called the "Tasiilaq insert") was hung within the core barrel during drilling at some sites to keep stones from entering and jamming the bit throat (Fig. F5). Although the short penetration depth and inconvenience of raising the entire system to retrieve core are disadvantages of the BGS robotic seabed system, the ease and speed of deployment and recovery are distinct advantages for operating under Arctic conditions where weather and heavy ice can be serious impediments to conventional ocean drilling (Fig. F6).
Dynamic positioning of the Aranda was achieved by differential Global Positioning System and a multiple thruster system. This system was connected to the BGS Trac-C system that operated as a slave for monitoring vessel station and warning about position loss while the Rockdrill was on the seabed. On a number of occasions, the Rockdrill was deployed multiple times using the same set of navigation coordinates. This was done, for example, if we discovered that the bit had jammed or if we were unsure whether basement lithology was sampled. In these instances, we commonly redeployed the drilling platform using the same navigation coordinates. In other cases, inclement weather or threatening ice flow forced us to abandon a station. Once the danger had passed, we would reoccupy the position using the same set of navigation coordinates. Therefore, with the Aranda we define a site by a unique set of navigation coordinates. Using a new set of navigation coordinates constituted the establishment of a new site. If the navigation coordinates were identical, successive drilling at the same site was identified by a new hole, regardless of core recovery. This site and hole designation differs slightly from that adopted on the Norskald cruise.