The annual cycle of landfast ice in the eastern Bering Sea

Abstract

Seasonal sea ice – ice which freezes in late fall and melts completely the following summer – is a central feature in the ecology, geomorphology, and climatology of the eastern Bering Sea. In this region's coastal zones, sea ice becomes locked in a stationary position against coastlines and influences interactions among land, ocean, and atmospheric processes. A thorough understanding of how this stationary ice, known as landfast ice, affects unique biogeophysical processes in the eastern Bering Sea region is limited by a lack of data on its areal coverage and seasonal duration. Here, we present the most comprehensive landfast ice dataset created to date for the Alaska Bering Sea region, derived using satellite imagery dated 1996–2008. This study provides a baseline set of observations regarding the landfast ice regime by identifying patterns in spatial distribution and interannual change. Our results show that spatial distribution and interannual change vary by regional geography in the eastern Bering Sea. Landfast ice widths averaged approximately 4.2 km on Northern Section, 18.8 km on the Central Section coastlines, and 8.9 km on the Yukon-Kuskokwim Delta. Modal water depths at the landfast ice edge varied by the Northern Northern, Central, and Southern Section coastlines as well, with respective modal values of −13 m, −7 m, and − 8.5 m. We attribute these regional variations in width and water depth to differing conditions in near-shore bathymetry and coastal morphology. On an interannual basis, landfast ice formed 5 days later in the year, and broke up 4 days earlier on average in the eastern Bering Sea region from 1996 to 2008. Notably, ice-free conditions occurred 15 days later on the Central Section coastlines. The spatial distribution and interannual change of landfast ice is of importance to associated environmental changes in the eastern Bering Sea region, including accelerated coastal erosion, difficulties surrounding subsistence activities, diminishing wildlife habitat, and seasonal shifts in sediment transport into marine food webs from rivers.