Likely Condition of the Corer on Retrieval

The ROV has shown that the exterior structure of the corer was intact about 24 hours after impacting the sea floor. We have no idea of the internal damage caused by the impact but expect that the 288 kg of sealed lead acid batteries will be damaged, although they are contained within high tensile steel housings(< 6 mm thick) designed for water depths of 1000 m. The electro-hydraulic motor housings and vibrator are pressure compensated with air which is likely to leak in the short term and allow sea water ingress.

The vibracorer is made primarily of mild and high tensile steel, coated with industrial grade paints, 316 and 304 stainless steel, marine grade aluminium alloy and high tensile aluminium alloys. These metals are in contact with each other and no sacrificial anode protection was installed because planned immersions were for only a few hours duration for each deployment. The sea water in the Ross Sea is well oxygenated at depth and we expect that corrosion will occur at normal or accelerated rates especially where electrolytic action can occur between dissimilar metals. The presence of any electrical change remaining in the battery packs is likely to enhance corrosion.

We believe that all the electrical components will suffer irrevocable damage in the short term. The main battery packs were probably damaged internally on impact. Instruments in a stainless steel pressure housing with anodised high tensile aluminium (Alumec 79) closures will become damaged in the longer term when the housing is corroded through. Part of the main lifting structure is built of 3 aluminium tubes (100 mm OD, 6 mm wall), which will corrode and weaken the structure with time.