Proposed Programme

The purpose of this project was to investigate mud-carrying bottom currents in Granite Harbour. Such currents have been suggested as the explanation for the deposits of mud flooring the deeper parts of McMurdo Sound and the basins/harbours along the southern Victoria Land Coast (Barrett et al. 1983, Kelly 1986, Macpherson 1987). There is no single obvious source or depositions! process for the mud deposits although Anderson et al. (1984) suggested impinging geostrophic currents and subglacial meitwater as potential sources.

Sediment trapping experiments in Granite Harbour show that there is a greater sediment flux near the sea floor than higher in the water column (Macpherson 1987, and Dunbar et al. 1986). The existence of a layer of sediment charged water at the sea floor (nepheloid layer) implies periodic resuspension of sea floor sediments. These sediments are a mixture of terrigenous and biogenic material. Some from budget considerations as derived from within the harbour, but some must come from the open Ross Sea (Macpherson 1987). This circumstantial evidence suggested that bottom current activity occurs in Granite Harbour.

The 1988/89 season's programme was designed to check on bottom currents originating from beneath the MacKay Glacier Tongue (MGT) in Granite Harbour. A current meter mooring with eight small (400 cm²) sediment traps was deployed in 702 m of water near the snout of the MacKay Glacier for 53 days between 15 November 1988 and 6 January 1989. The current velocities 1 m above sea floor average between 6.9 and 4.3 cm/s with intermittent speeds up to 10 cm/s. These speeds are considered capable of maintaining the suspension of fine sediment to form a near bottom nepheloid layer, and this is confirmed by much higher sediment fluxes below 520 m. The dominant flow direction at this site is towards the glacier tongue (240°-270°T) but "dally" swings occur towards the south which are most likely related to the diurnal tidal cycle.

This season's programme (1989-90) was to study the movement of sediment entering Granite Harbour from the Ross Sea by mooring the current meter and sediment traps on the sill the two main basins of the Harbour. The mooring was to be in place for about 2 months (November - January). We also planned to service the tide gauge at Cape Roberts established in November 1988, and if possible add meteorological instruments to record local climate data for future programmes. Inspection of the tide gauge in January 1989 has raised doubts about the permanence of the transducer installation which may not have survived ice foot breakout.

A further part of this season's work was related to a future proposal aimed at studying the Holocene Marine Glacial History in this area of the Ross Sea. We intended to carry out a reconnaissance survey of both coastal features in Granite Harbour and nunataks on the south side of the MacKay Glacier to find evidence of Holocene glacier expansion both at sea level and well above the present day MGT grounding line.

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.

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.

Publications

The two seasons of bottom current data will make up a major part of the paper on the current system and sedimentation in Granite Harbour to be prepared this year. We hope to also incorporate short current measurements made by ourselves and Rob Dunbar's Rice University group during out cooperative work on Granite Harbour sedimentation.

Per Möller will work on the data and sediment samples collected from the moraine ridges at Cuff Cape. A short paper will describe the process of ridge formation associated with the small hanging glacier on the south side of the cape.

Environmental Impact

Most of our operation is based on the sea ice and therefore has no lasting impact on the environment. The enlarged refuge hut facility at Cape Roberts was used by us and kept as clean as possible. The only additional impact is the meteorological instrumentation added to the tide gauge on the eastern end of Cape Roberts, this is a small relatively neat installation with minimal visual impact.

Management of Science in the Ross Dependency

The major concern we have for future programmes such as our sea ice based work is the continuation of NZARP survey assistance. This season the normal survey assistance was severely reduced because of funding considerations. The single surveyor was unable to operate independently at times. We found this placed an extra strain on our field programme even though our survey requirement was less than in previous years.

The survey assistance provided by DOSLI has been a very successful part of NZARP science support in the past and envied by several USARP programmes. It is important for many science groups to have accurate "high tech" surveying for their work in Antarctica that Is often beyond the means of individual groups.

References

Anderson, J.B., Brakes, C.F. and Myers, N.C. 1964. Sedimentation on the Ross continental shelf, Antarctica. Marine Geology, 57: 295-333.

Barrett, P.J., Pyne, A.R. and Wards, B.L. 1983. Modern sedimentation in McMurdo Sound. In R.L Oliver, P.R. James, and J.B. Jago (eds.), Antarctic Earth Sciences, Australian Academy of Science, Canberra: 550-554.

Dunbar, R.B. and Leventer A. 1987a. Diatom flux in McMurdo Sound, Antarctica. Marine Micropaleontology V:12, 49-64.

Dunbar, R.B. and Leventer A. 1987b. Sediment fluxes beneath fast ice: October 1986 through February 1987. Antarctic Journal of the United States, 22(5), 112-115.

Kelly, D.N. 1986. Sedimentation in Ferrar Fjord, western McMurdo Sound. B.Sc (Hons) project, victoria University of Wellington Library: 50 pp.

Macpherson, A.J. 1986. Glaciological, oceanographic and sedimentological data from Mackay Glacier and Granite Harbour, Antarctica. Victoria University of Wellington Antarctica Data Series Mo. 12: 81 pp.

Macpherson, A.J. 1987. The Mackay Glacier/Granite Harbour system (Ross Dependency, Antarctica) - a study in nearshore glacial marine sedimentation. PhD thesis, victoria University of Wellington Library: 173 pp.