Background

The vibracorer was developed to recover a complete and undisturbed sample of the sea floor for glacial and climate history studies. This was difficult for the sea floor around Antarctica because sampling both soft mud in the upper metre or two and compact diamictite beneath, a mixture of mud, sand and stones deposited by the last expansion of the Antarctic ice sheet, can only be satisfactorily achieved with a vibrating tube. Existing vibracorers either were limited to water depths of 200 m (but most Antarctic sea floor is deeper, to 1000 m), or they were too large and heavy to move and operate from the fast ice, where at least part of the science goal could be met and where VUW had considerable operational experience. VUW decided then to build its own corer, which would also have sensors for recording tilt and orientation of the core, important for studying changes in past sedimentation and magnetic field directions.

The corer was successfully checked out in a series of tests in early October 1992, culminating with the recovery of a 3.7 m core from Petone Wharf on the northern margin of Wellington Harbour, and was first deployed in Antarctica a few weeks later. The first two Antarctic deployments were made in 700 m of water in Granite Harbour, outlet for the well-studied Mackay Glacier 150 km northwest of Scott Base. On both occasions the corer tilted on the soft sea floor mud as the core barrel was driven in, the barrel bending as retrieval was attempted. On its return to Wellington the corer was redesigned with larger feet and a lower centre of gravity, and successfully tested in the middle of Wellington Harbour (which is muddier than Granite Harbour). It should be noted that the mechanical and electrical systems in the corer have consistently performed well from the time of the recovery of the first core from Petone Wharf.