ABSTRACT: Reduction in sea ice scour impact rates on the seabed 1979 to 2003, Canadian Beaufort Sea.

CGRG Bibliography of Canadian Geomorphology
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Abstract

The shallow Canadian Beaufort Shelf is dominated by the presence of sea ice for at least nine months of the year. Multi-year and first year pressure ridge keels that form in the Beaufort Sea's landfast, transition and polar pack ice zones can incise the seabed in water depths of 6 to 55 m. During the 1979 to 1990 time interval, the Canadian Beaufort oil industry and the Geological Survey of Canada conducted repetitive mapping surveys of the seabed. Using high-resolution sidescaning sonar and echo sounders a grid of regional survey lines was intermittently run on a 1 to 8 year repeat basis across the Canadian Beaufort Shelf in water depths ranging from 6 to 60 m. Comparison of consecutive survey profile data resulted in the identification of new ice scouring events on the seabed. A digital database incorporating the attributes of 5329 new ice scour events was created. This database was used to calculate ice scour impact rates across the Shelf. After an 11 to 13 year hiatus sections of the 1990 repetitive mapping grid were rerun in 2001 and 2003 and the historic database was augmented with the attributes of approximately 1900 new scour events. Preliminary comparison of ice scour impact rates for the 1990 to 2003 versus pre 1990 time interval resulted in an observed reduction in impact rates for ice scours with seabed incision depths equal to or greater than 0.5 m. In general, for these scour events, there was a 40 percent reduction in impact rates over the compared time interval. More specifically, in water depths of 24 m where seabed impact rates peak, the impact rate of extreme ice scouring events with incision depths equal to or greater than 2 m was reduced from 9.6 to 6 impacts per km per century. Questions remain as to whether these observed reductions in seabed impact rates are a function of natural cyclicity in the Beaufort's sea-ice regime or global warming or both. Decadal time scales for the ice scour impact rate observations suggest interannual variability would be averaged out and therefore not be a controlling factor.

Bibliography of Canadian Geomorphology