Cruise history and location of data

Most of the study area was covered by the permanent polar ice pack even during the brief period of maximum shrinkage in late summer. Acquisition of the data therefore required use of a Polar class icebreaker, the U.S. Coast Guard Cutter Polar Star (WAGB-10), and a specially designed air gun and hydrophone streamer seismic package capable of deployment and towing through multiyear pack ice. The Polar Star (Fig. 3) is 121.6 m long, 26.2 m broad, with a draft of 9.5 m and is diesel-electric driven. Details and further description of the Polar Star may be found at:

http://www.uscg.mil/pacarea/pstar/pstar.html

The relative amounts of seismic data acquired in 1988, 1992, and 1993 was largely a function of sea ice conditions, but improvements in the equipment used in 1992 and 1993 and increased experience in deploying and towing seismic arrays in sea ice on the part of both Coast Guard personnel and the scientific party also contributed to the significant increases in the amount of data collected each successive year:

• 1988: Severe sea ice conditions in the late summer limited data acquisition mainly to a few WNW-ESE-trending leads; 155 km of reflection profiles (Fig. 4) and eight useable sonobuoy refraction profiles (Fig. 5) were acquired.
  
  
• 1992: Sea ice conditions were somewhat improved over 1988, but sea ice covered 8/10 to 10/10 of the study area, and thick multiyear floes constituted 60% or more of the ice pack over large areas. As a result, the seismic profiles collected in 1992 are commonly circuitous and short; 500 km of reflection profiles (Fig. 4) and 23 sonobuoys (Fig. 5) were acquired.
  
  
• 1993: Sea ice conditions in the study area in were relatively favorable for seismic profiling, with only moderate concentrations of sea ice present over most of Northwind Ridge and the southwestern Canada Basin. Coverage of up to 7/10 sea ice over Northwind Ridge as far as 79° N latitude permitted the acquisition of 1,900 km of reflection profiles (Fig. 4) and 24 sonobuoy refractions profiles (Fig. 5). Heavy concentrations of multiyear sea ice in the southeastern Canada Basin prevented acquisition of a complete seismic reflection profile across the basin in 1993.