Dr. Mary-Louise Timmermans
July 30, 2011
Mooring A was re-deployed today, beginning with the 4500-pound anchor, Bottom Pressure Recorder (BPR), and releases, followed by a string of 50 buoyant glass spheres (protected by yellow hardhats), and the instruments placed in-line on the wire at various stages. The glass spheres serve as backup buoyancy so that the mooring can be recovered from the deep end if the upper portion gets snarled in the ice during recovery.
The anchor-first deployment of the BGOS moorings differs from standard procedure in the mid-latitude ice-free oceans where moorings are typically deployed by stringing the top float and line of instruments off the ship (most often from the stern) and releasing the anchor last. In this case, as the anchor sinks, it pulls the components to rest in a vertical line above the sea floor. The anchor-last method, requiring a large open-water area, is not feasible in ice-covered waters. Fortunately, seas are generally calm here in the pack ice and there is very little ship heave so having a large load suspended over the side for the duration of the deployment is less risky than it would be in rougher seas. For these BGOS moorings heavier wire rope and hardware is used because of the extra tension during the deployment.
Release of the top flotation sphere (with the ULS and ADCP as described in yesterday's dispatch) completed the deployment about 5 hours after the beginning of the operation. The anchor probably took less than a minute to settle to the bottom, and the mooring is in place to measure water-column properties until next year.