Drift Velocities of Ice Floes in Alaska's Northern Chukchi Sea Flaw Zone: Determinants of Success by Spring Subsistence Whalers in 2000 and 2001

By March each year, coast-influenced sea ice in Alaska's northern Chukchi Sea consists of the shorefast ice itself plus ice floes moving in a zone that extends from immediately beyond the shorefast ice to coherent pack ice, some 100 km farther offshore. Because westward-drifting polar pack ice encounters fewer landmasses (and less resistance from them) once it passes Point Barrow, a semipermanent polynya or flaw zone dominates coastal ice in this region. Iñupiat residents use open water in flaw leads to hunt migrating bowhead whales from mid-April to early June. Although Iñupiat hunters grasp the nature and importance of ice in motion beyond their horizon, the flaw zone has received less scientific attention than either shorefast ice or polar pack ice farther offshore. Synthetic aperture radar (SAR) satellite imagery is a form of remote sensing recently made available that allows us to address ice movement at a spatial scale familiar to traditional hunters. SAR-tracked ice movements differed between 2000 and 2001, illustrating contrasts between adverse and optimal conditions for spring whaling at Barrow. Case studies of icefloe accelerations in the two contrasting seasons suggest that many variables influence ice motion. These include weather, seafloor topography, currents, sea-level changes, and events that occurred earlier during an annual accretion of ice. Adequate prediction of threats to ice integrity in the northern Chukchi Sea will require adjustments of our current concepts, including 1) recognizing the pervasive influence of the flaw zone; 2) replacing a focus on vessel safety in ice-dominated waters with an emphasis on ice integrity in high-energy environments; and 3) chronicling ice motions through coordinated ground observation and remote sensing of March-June events in future field studies. /// Quand arrive mars chaque année, la banquise soumise à l'influence de la côte dans la partie nord de la mer des Tchouktches de l'Alaska est formée de la glace côtière elle-même plus des floes en mouvement dans une zone qui s'étend de la lisière de la glace côtière au pack cohérent, à quelque 100 km plus au large. Vu que, une fois passée la pointe Barrow, le pack polaire dérivant vers l'ouest se heurte à moins de masses continentales (et donc moins de résistance), une polynie ou zone de séparation semi-permanente domine la banquise côtière dans cette région. Les résidents Iñupiat utilisent l'eau libre des zones de séparation pour chasser la baleine boréal