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Immediate report of Victoria University of Wellington Antarctic Expedition 1988-89: VUWAE 33

Scientific Endeavours and Achievements

Scientific Endeavours and Achievements

1. Deployment of mooring and establishing the Cape Roberts Tide Gauge. (7 – 20 November, 1988).
Mackay Ice Tongue Site

A north-south bathymetry profile was measured across the north-eastern tip of the glacier tongue to determine the deepest part of the channel striking east from under the glacier tongue. Eight 250 mm diameter holes were drilled through 3 m thick second year sea ice and a 28 kHz echosounder transducer lowered through the holes to record water depth.

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The InterOcean S4 current meter was then set one metre off the bottom in about 702 m of water to check the mooring design and that the instrument was functioning correctly. Two days later on 15 November the current meter was recovered, checked, reprogrammed and redeployed on a mooring with 8 small (400 cm2) sediment traps (Figure 1).

Cape Roberts Tide Gauge

The fast ice on the eastern side of Cape Roberts forms a well developed ice foot each season with the tide crack between 8–12 m from the exposed rock on shore. Several sites were checked and the ice foot drilled to determine water depth profiles beneath the ice foot. We intended to install the tide gauge vibrating wire pressure transducer through the ice foot within a 2" galvanised pipe that would be bolted and possibly cemented to the shore rock face. Unfortunately a suitable site for cementing was not available and we had to be satisfied with terrier bolting 10 m of pipe to rock face (Figure 2). A 3 m deep hole was cut into the ice foot with a chain saw to install the transducer pipe, finally using a drill to break through to clear water below.

The data recording system consists of a Campbell CR10 data logger, 135 Ahr (C20) lead acid battery and 22W (GL125-M25) solar panel mounted on a tripod frame located about 10 m from the surface end of the transducer pipe. A tide gauge bench mark has been established by the NZARP surveyors and the height of this will be progressively refined as more tidal data is recorded.

We had also hoped to determine the tidal time lag between Cape Roberts and inner Granite Harbor by establishing a temporary tide station at Cuff Cape 22 km away. Unfortunately because of time constraints this was carried out during the neap part of the tide cycle (17–21 November), and the results have poor resolution.

Sea Ice and Surface Travel

This phase of our program was carried out using surface transport (ASV and trailer) on the sea ice. We were not subject to the poor flying weather this season and consequently the program went smoothly. The extent of fast sea ice along the Victoria Land Coast was much less this season than for the last 8 years but still suitable for safe surface travel to Granite Harbor from Scott Base. In Granite Harbor second year sea ice was present west of a line between First View Point to Cape Archer and this made travelling slower and more difficult than usual.

2. Recovery of mooring and Cape Roberts Tide Gauge data. (6–9 January, 1989).
Current meter mooring

The mooring was recovered during the evening of 6 January after flying by helo' to Granite Harbor from Scott Base. The mooring's sea ice anchor had melted about 30 cm into the sea ice and was partly refrozen. Melting of the sea ice around the site was less than expected and was probably due to a cloudier than normal summer in this area. Recovery of the mooring went smoothly once the subice line had been caught through a newly drilled 30 cm ice hole adjacent to the mooring line.

The Cape Roberts tide gauge was checked the following day after the helo move from the mooring site to Cape Roberts. The previous 50 days data was downloaded using a Zenith lap top computer at the tide gauge site. The data logger was then returned to the Cape Roberts hut where new power supply protection was installed and a new recording program downloaded into the logger. The following 36 hours were spent periodically levelling the sea surface to recalibrate the reinstalled logger. A swell surge with a range of up to 8 cm was measured with the ice edge still about 3 km to the east.

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Figure 1. Mooring configuration at the MacKay Glacier Tongue. F = floats, T = traps.

Figure 1. Mooring configuration at the MacKay Glacier Tongue. F = floats, T = traps.

Figure 2. Tide Gauge at Cape Roberts.

Figure 2. Tide Gauge at Cape Roberts.

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The tide gauge has now been programmed to record through the winter months to November 1989. The instrumentation is rated to −55°C and should theoretically continue to operate during the winter. However, we are less confident that the transducer pipe will remain it the ice foot floats off. By 9 January the bottom part of the pipe was still frozen solidly into the base of the ice and there was little evidence of basal ice melting around the pipe. We had expected basal melting would occur, thereby freeing the pipe before icefoot breakout. The life of the lead acid battery power supply is also of some concern during the winter months even though theoretically it should not freeze if it remains sufficiently charged during the winter.