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Victoria University Antarctic Research Expedition Science and Logistics Reports 1996-97: VUWAE 41

SEA ICE REPORT

page 4

SEA ICE REPORT

19.The sea ice reconnaissance of 07 November concentrated on finding a safe route from MPt to CR. Much of the ice to be traversed was extremely broken and rough. The largest crack encountered trended southeast from Dunlop Island and was almost certainly the line along which the July breakout occurred. It was 10 metres wide, snow filled and the ice only 1 metre thick compared to the surrounding ice which was 1.5 metre plus. At the time we didn't have the time or helicopter resources to confirm it but we suspected that much of the sea ice along the coast was a mosaic of plates joined by thinner and weaker snow-filled cracks. As expected, on the return traverse to SB on 11 December we encountered about six significant cracks that were becoming quite active.
20.On 25 November a helicopter-supported sea ice reconnaissance was made over the proposed drill sites. Nine holes were drilled in the area of the proposed drill holes. Ice thickness was between 1.6 and 1.8 meters. This thickness exceeded the Project's minimum operational requirement but it is unlikely that it would have been thick enough to operate on in early October. A feature of approximately half the holes drilled was that there was a weak wet zone in the ice at just over 1 meter which suggested late formation. (Refer attached sea ice report by Pyne).
21.The ice edge this season in the vicinity of Cape Roberts was indeterminate and clearly thin, 'watery' and well broken up. The 'Cape Roberts crack' was, as expected, clearly in evidence about 1.5 kilometres off the Cape. It was the probable boundary of the July breakout and this season appeared to be very active, wider than usual with lots of water exposed and longer than usual, extending much further south than in the last three seasons. Associated with it was a large pressure ridge system. Given the state of the ice edge, the extent of the annual Cape Roberts crack and the uncertain strength of the cracks joining the large ice platelets, we doubt that a ship off-load operation of the type done in January of the previous two seasons could have been undertaken in November let alone later.
22.When we returned to CR on 11 January 1997 the transition had collapsed and the sea ice inland of the Cape Roberts crack had broken up exposing watery cracks and small areas of open water. Vehicle operations on the sea ice were impossible yet in the previous year and a week later we had carried out a major ship offload nearly 20 kilometres from land. The longer term affect of the mid-winter breakout and the ensuing instability probably played a significant part in the early breakup of the sea ice both to the north and south of CR.