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Immediate report of Victoria University of Wellington Antarctic Expedition 1989-90: VUWAE 34

Scientific Endeavours and Achievements

Scientific Endeavours and Achievements

Bottom Currents Mooring.

Thirteen spot bathymetry measurements were made to define the mooring site in an area centred 7 km northeast from Discovery Bluff. Coring by S-216 (R. Dunbar, Rice University, Texas) in 1988 suggested that the sill defined by Macpherson (1986) which separated the inner and outer basins may not exist in this area. This year's bathymetry results have defined a 750 to 800 m deep channel trending north east mat joins the inner basin at Avalanche Bay to me outer basin in the centre of the harbour mouth. The mooring site was in the centre of me channel at 775 m depth and was chosen to test if the channel is a conduit for sediment entering the inner harbour from the Ross Sea.

The mooring deployed on 16 November consisted of an S4 electromagnetic current meter set 1 m above me sea floor and seven small sediment traps (collecting area 400 cm2) spaced through the water column (Table 1). The mooring was recovered on 24 November, redeployed and finally recovered on 5 January. A continuous record of 50 days duration was recorded by the current meter.

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Table 1. Granite Harbour Mooring 1989/09.
Instrument/equipment Depth below sea level Height above sea floor
Float package (4 floats)
(44 kg buoyancy)
12 m 760 m
Trap# I 45 m 730 m
Trap # II 165 m 610 m
Float package (4 floats)
(11 kg buoyancy)
272 m 507 m
Trap # III 370 m 405 m
Float package (4 floats)
(11 kg buoyancy)
477 m 302 m
Trap # IV 575 m 200 m
Trap # V 695 m 80 m
Trap # VI 747 m 28 m
Trap # VII 768 m 7 m
S4 Current Meter 774 m 1 m
Sea floor 775m 0 m

Sediment from the seven traps will be analysed at Rice University but initial observations show the expected higher flux rates in the tower part of the water column which suggests a nephetoid layer is also present within the channel.

Cape Roberts Tide Gauge.
Introduction.

A tide gauge was established on a rocky promontory at Cape Roberts on 19 November 1988, by K042 with assistance from the NZARP surveyors. We hoped that the gauge was sufficiently well secured to function continuously throughout the year (Pyne & Woolfe 1989, pp. 2-6). Data was first retrieved from the tide gauge on 8 January 1989. At this time we observed that the toe foot through which the transducer pipe passed had not melted and we then had doubts as to whether the transducer would survive the sea toe breakout.

1989/90 Season.

Cape Roberts was revisited this season by K042 on 12 November 1989. The transducer pipe had been broken away and the transducer presumably lost. The data logger, however, had functioned throughout the winter and we recovered a further 13 days of record between 24 January and when the toe foot breakout occurred on 5 February 1989. We now have 64 days of tidal record from Cape Roberts, with a 14 day gap (9 January to 24 January) lost because of memory storage limitations.

This season we intended to move the tide gauge recording station and power supply to higher ground and establish a meteorological station at the same site coupled to the tide gauge data recording system. A 4 metre mast was erected on the eastern end of Cape Roberts within 2 metres of Cape Roberts No.2 survey point on 17-18 November. As of 26 November 1989 the Met mast was measuring wind speed and direction at both 2 m and 4 m above local ground, temperature at 2 m and incoming solar radiation. On 5 January further Met. data was recovered and we attempted to correct the operation of the wind direction sensors. Unfortunately a computer malfunction due to the cold and tight helicopter scheduling has meant the Met. programme is not currently operating. The system is designed so that another tide recording transducer could be installed in the future. We did not Install a temporary tidal sensor this season because it would have only duplicated last seasons measurements which were sufficient for an initial hourly tidal prediction programme.

Installation of a transducer this season would have only been temporary and likely to result in the loss of the transducer also. We believe that the establishment of a permanent page 6 recording tide gauge on M continent at Capo Roberts is possible but will require better sit. preparation for the transducer than was achieved in 1900.

The present experiment and instrumentation at Cape Roberts is jointly sponsored by Antarctic Research Centre, University of Wellington, the N.Z Meteorological Service, and the Department of Survey and Land Information (DOSLI).

The Antarctic Research Centre (ARC) has thus far been responsible for the installation of equipment at Cape Roberts. We are interested in:
1.Short term tidal data for correlation with our bottom current measurements in Granite Harbour.
2.Permanent tidal recording for possible drill sites offshore of Cape Roberts (mid 1990's) and general tectonic/sea level information.
3.Meteorological records from the Cape Roberts area for planning of drilling in this area and a general interest for future work in this area.

The ARC owns the CR10 data logger, solar panel, mounting frame and battery with a further transducer and interface available for a permanent tide gauge installation.

The N.Z. Meteorological Service is responsible for archiving the meteorological data with interests in:
1.Establishing the natural variability of climate within the McMurdo Sound Area especially for comparison with Scott Base.
2.Testing instrumentation for year round remote station measurements for future proposals (see Granite Harbour Weather and Climate 1990/91 proposal to RDRC).

The Meteorological Service owns the Met. Instrumentation, data logger box, SM 192 storage module and mast.

DOSLI are responsible for archiving the tide data which has been analysed thus far to provide tidal predictions for K042 bottom current studies. DOSLI has a continued interest in:
1.Tidal data from Cape Roberts, to refine the mean sea level elevations of the geodetic network in the area. Cape Roberts is the origin for the network in this area.
2.Long term tidal records from the continent (Cape Roberts) for eustatic sea level comparison with the Scott Base tide gauge (K193).
Establishing a Permanent Installation.
Our experience has shown that it will be possible to establish a permanent tide gauge at Cape Roberts with sufficient site preparation for the sea level measuring transducer. A permanent tide gauge installation requires access to the transducer for checking or replacement if a fault occurs during several years of use. Two possible installations are envisaged for the transducer to avoid destruction of the transducer during sea ice breakout and are discussed briefly below.
1.A hole drilled through the coastal rock below the sea ice toot would provide the best protection for the transducer installation. The hole required could be up to 10 m long about 50 mm in diameter and could be drilled with Antarctic Divisions Winkie drill using a diamond coring bit: The drilling operation would use a sea water/salt drilling fluid, and so would be non-polluting. Detailed inspection of the seafloor below the ice foot would be required to establish the site and angle for drilling. This could be done either by a diver or by a special visual means through access holes in the ice foot.page 7
2.The second method would use divers to determine a suitable crevice in the rock extending below the ice foot. A hole in the ice foot against the rock would be made by chainsaw and melting techniques so that a diver could connect the transducer pipe to pitons fixed into the rock joint. Cementing the pipe within the rock crevice may work and provide protection, however, the technique is presently unproven. This method is less favoured because it requires a significant diver component based at Cape Roberts and would still not fully protect the transducer Pipe.
Testing Vibrocorer Components

On 19 November in central Granite Harbour, we pressure tested to 850 m depth the vibrator head and motor housing for a vibrocorer currently under development at VUW. The USARP group S-216 kindly allowed us to use their winch for these tests. The vibrocorer is being developed specifically to core sea floor sediments for the Holocene Marine Glacial programme which will be resubmitted for the 1991/92 season.

Terrestrial evidence of glacial expansion in Granite Harbour.

During the sea ice phase of this field season in Granite Harbour we visited several coastal sites looking for indicators of previous ice levels in the harbour.

Table 2. Coastal features In Granite Harbour
Coastal Site Features & Processes
Cape Roberts: Well developed boulder/gravel beach ridge system on the northern side. Ice planned rocks (glacial or sea ice?) on southern side, especially "Hut Cove".
Botany Bay: Poorly developed, moderately steep boulder beach. Hint of 2 beaches at the eastern end. Abundant moss and lichen.
Caps Geology: moss and lichen. Basement outcrop dominated by NE trending jointing/structure. Abundant
New Glacier Terminus: Steep talus slops extending from the terminus. Partly glacial retreat and slope adjustment of (ice cored?) talus. Undefinitive and undatable?
Devils Punchbowl: Gravelly "beach" of low slope Fluvial transport of fins gravel from the stops above in combination with tide crack ice.
Finger Point: Very indistinct steep local boulder beach.
Cuff Cape: Moraine ridges with high sand content associated with small hanging glacier/ice fall.
North side MGT: Talus slope process against glacier ice near the grounding line of MGT (north armpit).
Point Retreat: Single poorly developed boulder beach, 15-20 m high lichen abundant on sheltered parts of large rocks.

The features we observed (Table 2) are unlikely to give datable evidence of previous ice levels in this area. Generally, the beaches in the harbour are poorly developed which reflects a relatively sheltered aspect in comparison to Cape Roberts which is more exposed and where several beaches are developed.

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A detailed survey of the moraine ridges at Cuff Cape was carried out by our Swedish guest scientist Per Möller. Pat Sole (K191 - Survey Assistance) contributed to this work by surveying the ridge system and taking aerial photographs later in the season. The moraine ridge system at Cuff Cape is associated with a small hanging glacier to the south of the cape rather than the MGT.

We had also intended to study the glacial features on the side of the MacKay Glacier at the Flatiron. Mt Suess and Pegtop Mountain. The Hagglund (H26) was used to drive up New Glacier successfully but broke though into a crevasse at the top of the glacier in a gently sloped snow covered area. We concluded that the Hagglund was too heavy for the snow conditions in this area and had to cancel this part of the programme. We have operated without incident in this area in the past with toboggans and a USARP group using toboggans this season travelled up New Glacier to Pegtop Mountain also without incident.