A CONTINUUM MIXTURE MODEL OF ICE STREAM THERMOMECHANICS IN THE LAURENTIDE ICE-SHEET .2. APPLICATION TO THE HUDSON STRAIT ICE STREAM

Episodic exportations of ice-rafted debris to the North Atlantic in th e late Pleistocene suggest quasiperiodic ice streaming or surging acti vity on the northeastern margin of the Laurentide Ice Sheet. Much of t his efflux of ice may originate from an ice stream issuing from Hudson Strait and tapping into core regions of the Laurentide in Hudson Bay, Labrador, and the Fore Basin. Applying the continuum mixture theory o utlined by Marshall and Clarke [this issue], we model the thermomechan ical evolution of the Hudson Strait Ice Stream in a three-dimensional finite difference model of the Laurentide Ice Sheet. Our simulations f ocus on internal dynamics of the ice stream. Under thermal regulation of basal flow we find surge cycles of stream activity interspersed wit h quiescent periods where the ice stream is frozen to the bed. Modeled surge durations vary from 105 to 3260 years, while surge periodicitie s range from 585 to 22,410 years. With pervasively warm or cold intern al temperature distributions in the ice, ice streams can also establis h modes of permanent activity or inactivity under thermal regulation. Our most vigorous ice streams produce peak values of approximately 0.0 3 Sv of freshwater flux to the North Atlantic from basal meltwater and iceberg production. Associated ice stream velocities in this maximum case approach 6700 m yr(-1). The total ice volume mobilized in a singl e surge event is equivalent to a global sea level rise of 0.04 m in th e most tranquil surge and almost 0.6 m in the most extreme case. These velocities and sea level impacts are an order of magnitude less than those predicted by MacAyeal [1993a,b], and only our most exuberant str eams approach the iceberg flux estimates of Dowdeswell et al. [1995]. We propose that the sediment load of icebergs emanating from Hudson St rait in a surge event may exceed expectations from contemporary iceber gs.