2. Proposed Programme

This project was designed both to investigate the little explored sub-ice shelf environment and to provide essential site data for coring 1000 m into the sea floor by ANDRILL (Lacy et al., 2003) for a history of the McMurdo-Ross Ice Shelf (MRIS). Ross Island has been depressing the crust under its own weight for at least the last million years, and at the same time has been acting as the western pinning point for the MRIS. As a result sediment has been accumulating in a sea floor depression over 900 m deep to the south of Ross Island in Windless Bight (Fig. 2). These sediments record the presence and possible past absence of the MRIS, and the movement of Ross Sea Shelf Water behind Ross Island between McMurdo Sound and the central Ross Sea.

We proposed to occupy 4 sites, first melting a 50-cm-wide hole through the ice shelf (70 to 150 m thick). We then proposed to measure water depth (expected to be over 800 m) and water column properties through a tidal cycle (conductivity, temperature, current speed, current direction) before sampling the sea floor by grab and gravity corer. The access hole was to be melted by a Hot Water Drilling system provided by the Alfred Wegener Institute for Polar and Marine Research, which had been delivered by ship the previous summer.

The project ran extremely well with access holes drilled and kept open through the ice shelf for up to 9 days (for a full account see the Logistics Report). This was critical for the success of the project. All instruments and sampling devices deployed through the access holes functioned and were recovered. The two most central of the 4 proposed sites were occupied, and a third site at the edge of the ice shelf monitored over a period of three weeks for currents in the upper 2/3 of the water column.

System specification

Hot water capacity: 90 l/min from 6 JP8 fueled burners

Water temperature: 95°C

Working pressure: 80 bar (1200 psi)

Drilling rate:

• Pilot hole (~150 mm diameter) 30 m/hr
• Reamer hole (>600 mm diameter) 20 m/hr
• Bottom reamer (>600 mm diameter 5 m/hr

Fig 3. The system uses a combination of melted snow and re-circulated melt-water to produce a jet of hot (95°C) water to melt through the ice shelf. Firstly a vertical pilot hole (~15 cm) is made through the ice shelf. This is then widened to >600 mm using a reamer. Additional reaming is needed at the bottom of the hole as hot water is lost to the ocean beneath the ice shelf.