Abstract
AbstractDuring the 2018/19 Antarctic field season, the British Antarctic Survey (BAS) Basal conditions on Rutford Ice Stream: BEd Access, Monitoring and Ice Sheet History’ (BEAMISH) project drilled three holes through the Rutford Ice Stream, West Antarctica. At up to 2154 m, these are the deepest hot water drilled subglacial access holes yet created, enabling the recovery of sediment from the subglacial environment, and instrumenting the ice stream and its bed. The BEAMISH hot-water drill system was built on extensive experience with the BAS ice shelf hot-water drill and utilises many identical components. With up to 1 MW of heating power available, the hot water drill produces 140 L min−1of water at 85°C to create a 300 mm diameter access hole to the base of the ice stream. New systems and processes were developed for BEAMISH to aid critical aspects of deep access drilling, most notably the creation of cavities interlinking boreholes at 230 m below the surface and enabling water recirculation throughout the deep drilling operations. The modular design of the BEAMISH drill offers many benefits in its adaptability, redundancy, and minimal logistical footprint. These design features can easily accommodate the modifications needed for future deep, clean access hole creation in the exploration of subglacial environments.
Highlights
Ice sheets play a major role in controlling the Earth’s sea level
Smith (2020) provides further details of the scientific program and an overview of the BEAMISH project and fieldwork; here we present the BEAMISH hot-water drilling (HWD) system that was used to provide the required subglacial access holes and give details of its design, the drill equipment and subsystems and its field operation
The access holes created allowed the recovery of sediment samples from the ice stream using samplers on the drill nozzle or from the bed using a simple sediment corer (Makinson, 2021) as well as the in-ice installation of a range of monitoring instrumentation to aid in describing ice-sheet dynamics (Smith, 2020)
Summary
Ice sheets play a major role in controlling the Earth’s sea level. Our ability to predict future change is limited by our lack of understanding of ice sheet physics and uncertainty over how ice sheets behaved during past climate cycles (IPCC, 2019). An additional 100 m umbilical with a 5.5 kW borehole pump was used to recover water from Return Hole A (Fig. 14) and establish the first water recirculation system as per normal shallow drilling HWD operations (Makinson and Anker, 2014). A HWD calculation script has been developed within BAS, and utilised in all previous drilling projects, to determine the drilling speed needed to provide the required hole diameter profile It follows a simple energy-balance model which is iterated along the estimated depth of the ice column (Humphrey and Echelmeyer, 1990). By increasing the borehole pump speeds, abstraction rates exceeded flow through the drill nozzle, lowering water levels as the nozzle approached the ice base. With hole operation periods of up to 6 days, a shift pattern ensured at least three individuals were always available to monitor the operation of the drill
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