Sea Ice Measurements

This season the sea ice in McMurdo was expected to be significantly thinner than in most previous seasons. A major winter storm in early June caused the seaice to breakout nearly to the Mcmurdo Ice Shelf and Hut Point consequently it was expected by some people that the ice would be thin or absent later in the spring/summer. By the time we travelled to Granite Harbour on 18-20 November the seaice along our coastal route was between 1.68 and 2.0 m thick. Offshore of Cape Roberts in the area interest for drillsites ice thickness varied from a normal thickness of 2.3 m within Granite Harbour to 1.15 m thick about 18.3 km ENE offshore of Cape Roberts. At 21 km offshore pack ice had refrozen against a developed ice edge with about 300 mm of ice between floes.

Table 1 Ice thickness Granite Harbour and offshore Cape Roberts.

The sea ice surface was generally smooth within Granite Harbour and offshore north of the thickness measurement positions in Table 1. Immediately to the south however the ice was rough from winter breakout and refreezing and was likely to be thicker. The ice thickness was certainly a bit thinner than usual in areas affected by the early June breakout but of normal thickness in Granite Harbour. If this season had been a drilling season then it would have unlikely that heavy transport could have traversed to Cape Roberts until early October. One or 2 of the planned inshore drillsites could probably have been occupied this season especially along the Rice Seismic line PD90-10. The planned study of winter sea ice formation from satellite imagery is expected to confirm this.