Attempted Recovery of Vibracorer

Within 4 hours we were in contact with Dr Ross Powell, Northern Illinois University, USAP event S027, whose group had deployed their ROV (remotely operated vehicle) at the site the previous day (23 November). The next day their ROV was back and searching by late afternoon. The vibracorer was located and recorded on video about 20 m to one side of a point on the sea floor directly below the access hole and was sitting upright on the sea floor which sloped between 15 and 25°. The corer appeared intact with no visible structural damage. The feet were penetrating up to 15 cm into a surficial mud blanket over harder sea floor, indicated by scattered boulders covered with mud and encrusting organisms. The air compensator water trap appeared to be clear of water, though it probably would not stay like this for long because of pressure cycling due to tidal action and because once the air bottle pressure is equal to the water pressure the system is then open to the sea.

These observations suggest that the corer spiralled to the sea floor and landed on its feet without external damage. Internal damage within the four battery housings, air compensated electric motor and vibrator, and data logger instruments could not be determined.

Two further attempts were made to recover the corer with the ROV through the access hole in the fast ice on November 25 and 26. A hook and line were devised for the ROV to carry down and attach to the corer using a hook from the chain hoist and the winch rope. The hook was held by a release mechanism so that if the corer could be caught the ROV could detach itself and return to the surface before the corer was hauled up. The hook and winch line were partly buoyed with 3 kg net floats.

On both recovery dives the ROV reached the sea floor but could not swim and turn properly because the drag of the winch rope was too great for the propulsion unit. The corer was not seen on the first dive, On the second dive the ROV sonar picked up an object behind it and thought to be the corer. However attempts to turn the ROV and swim towards the object caused the ROV umbilical and the winch line to become intertwined, endangering the ROV. At this point attempted recovery was abandoned.