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Victoria University Antarctic Research Expedition Science and Logistics Reports 1993-94: VUWAE 38

Summary

Summary

A specially designed battery powered vibracorer was developed and built at VUW over a period of 4 years to take cores up to 6 m long from the Antarctic continental shelf in water depths to 1000 m. The cores were to be used for research into the region's climate and glacial history over the last 20,000 years. The vibracorer, which weighed 1.5 tonnes, was designed to be deployed by a small mobile crane through 1.5 m diameter holes in the fast ice fringe around McMurdo Sound as well as from ships (Figure 1). For sea ice deployments a polyester winch line was chosen for lightness and ease of handling, with a breaking load of 6.75 tonnes, giving a safety factor of 4.5.

On 24 November 1993 the vibracorer was lost when the winch rope failed at the spliced eye used to connect winch rope to corer. Lowering into the water had just begun and the vibracorer free-fell 350 m to the sea floor. A remotely operated vehicle (ROV) operated by US colleagues nearby was used to look for the vibracorer, which was found upright on the first dive and with no visible damage. Two subsequent dives with a recovery line attached to the ROV did not find the corer because the ROV could not manoeuvre properly with the line attached and the dives were endangering the ROV. Further recovery attempts were abandoned. The site is located precisely using GPS at 76° 56.631′S and 162° 48.116′E, and a position surveyed independently to within 2 m will be available at a later date.

No reason for failure of the winch rope has been ascertained at this time. It had performed satisfactorily the previous season for 2 deployments in Antarctica and had been tested off Scott Base 7 days prior to 24 November with the full corer load lowered to a depth of 50 m.

The prospect of the corer's recovery from a ship in late January/February when the fast ice is weak or broken out is considered low. The option favoured in terms of least support requirements and most chance of success is to make another recovery attempt from new fast ice in October 1994 with the assistance of the US ROV, which will be working in the area, and a purpose built tool for attaching a cable to the corer.