Microrelief Produced by Sea Ice Grounding in the Chukchi Sea near Barrow, Alaska

Abstract

In the summer of 1954 the writer studied the microrelief off Barrow, Alaska, to determine the effective range of grounding of the polar pack ice. ... The microrelief studied here is not the same as that described by Carsola (1954) for deeper waters of the outer continental shelf to the northwest of the Barrow area. ... The traverses generally showed irregular depth fluctuations of 8 feet or less over distances of 25 to 50 feet, superimposed on a very gently sloping bottom. ... Microrelief is best developed between depths of 20 to 80 feet, where it is often 6 feet, and in one case reached 12 feet. Moderate microrelief usually extends to a depth of 100 feet ... Before accepting the hypothesis of pack ice grounding to explain the microrelief a number of alternate hypotheses were considered. These were: residual features of thawed permafrost, slump topography, current scouring, and sand waves. ... Pack ice grounding could cause the development of microrelief in a way that explains all the observed features. ... The sharpness of the microrelief and the scale are what one would expect if an average ice floe (4-6 feet thick and 20-100 feet in diameter) were up-ended by the pressure of other floes and driven into the bottom. The abrupt end of microrelief at 100 feet can be explained as the maximum depth at which pack ice grounds. ... It is suggested that, on the basis of the sharpness of the microrelief, grounding is most frequent between 20 and 80 feet. Grounding below this depth is probably less frequent and occurs with less bottom gouging than grounding within this depth range. ... Subsequent to the completion of this paper MacGinite (1955) has made a number of comments on sea ice grounding. His observations agree with those of this writer, but are of a more general nature. MacGinitie's winter observations are of special interest ....