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Victoria University Antarctic Research Expedition Science and Logistics Reports 1991-92: VUWAE 36

[introduction and objectives]

This season we had proposed to run two programmes together; 1.,vibrocorer sampling of the sea floor in Granite Harbour and 2., the study of the Mackay Glacier Tongue grounding line with a remotely operated submersible vehicle (ROV). At the end of September we postponed the vibrocorer programme because the equipment was not ready and satisfactorily tested but received RDRC permission to continue with the ROV-grounding line study.

Mackay Glacier forms a 3 km wide, 300 m thick, "floating" glacier tongue that moves seaward at 250 ma"1 when it enters Granite Harbour, an embayment up to 900 metres deep on the Victoria Land coast. The project is to observe and describe, for the first time, the interaction between a polar glacier tongue, sediment and sea water at the detachment point (grounding line) using a remotely operated submersible vehicle (ROV).

We propose to study the subglacial delta presumbed to have formed as basal debris carried in the glacial tongue melts out. (Macpherson 1987, Alley et al. 1989). The existence of subglacial deltas and sedimentation processes requires testing to provide better models to compare with seismic data from the Antarctic continental shelf where a number of page break examples of delta like sedimentary bodies have been observed (Cooper et al. 1990).

The principal objectives for this seasons research are;
1.Determine the character and thickness of the basa! debris layer in the glaciers.
2.Evaluate grounding line processes including debris meltout, sediment deformation, meltwater production (if any) and grounding line stability.
3.To check if a subglacial delta exists.

Scientific Endeavours & Achievements

Mackay Glacier Tongue

Ten days were spent working around the Mackay Glacier Tongue (23 November - 2 December) at three dive sites, site 1 on the southside of the tongue, and Sites 2 & 3 on the north side (Figure 1).

Access holes (1.8 m × 1.2 m minimum) were made in the sea ice for the ROV by a combination of drilling with the 0.6 m auger on the NSF nodwell and explosives. In each case holes were made in existing ice cracks. Near the ice tongue several platelett cubic metres of platlett ice was cleared from holes at sites 2 & 3 especially before the holes were clear for the ROV.

The Phantom DHD2 ROV which belongs to Dr Ross Powell is equipped with colour and low light black and white video cameras. A sea bird CTD, an electromagnetic current meter, a optical back scatter sensor and still stereo photography comprise the instruments which were on the vehicle. In addition we designed and built a 5 bucket min-dredge at Victoria University to sample the sea floor for the ROV.

A total of 10 dives were made at the Mackay Glacier Tonge sites.