Summary for Field Activity Number 81022

Area of Operations : Lydonia Canyon, Georges Bank, United States, North America, North Atlantic

Dates: June 30, 1981 to July 2, 1981

Chief scientist: Brad Butman
   

Objectives: The WHITEFOOT/LULU-ALVIN joint cruise was to recover a subsurface mooring in Lydonia Canyon (Figs 1,2,3). The release failed in April 1981 on OCEANUS 95 (#81009) when recovery was planned. We dragged for the mooring, severed the wire below the second current meter, recovered the upper portion. We were unable to recover the deep instrumentation package after dragging for about 2 days. The near-bottom instrument was a key instrument in the Lydonia Canyon moored array. ALVIN was planning a certification dive near Lydonia Canyon and agreed to try to release the mooring on this dive. A hydraulic chain cutter was mounted on the sample basket of ALVIN, the hand pump was operated by the arm. Because LULU could not easily retrieve the heavy mooring on the surface and because of a tight schedule, WHITEFOOT was chartered to pickup the mooring, once ALVIN cut it loose.

Type of Activity: Mooring work

Information to be derived: Time series data

Summary: Mooring recovered: 1 (#211 deployed #80034 OCEANUS OC90 Nov. 24 - Dec. 3, 1980.) The deep instrument package was recovered! ALVIN had little trouble locating the package with guidance from LULU. We could still transpond to the release on the mooring, fortunately all flotation was intact. Backup recovery scheme using a rope canister dropped from WHITEFOOT was not needed. Chain was cut relatively easily with hydraulic cutter. One VACM was lost on mooring 211. Apparently we cut mooring in 2 places while dragging on OCEANUS 95, and intermediate flotation was insufficient to bring VACM (V111P,Fig 3) to surface. We were extremely fortunate to be able to use ALVIN. It was a textbook yet remarkable recovery due to the skill of ALVIN crew. Mooring could not have been recovered otherwise.Cruise was delayed for about a month while cradle for ALVIN aboard LULU was repaired.

USGS Project Number:

Contact: Brad Butman (bbutman@usgs.gov)