Freeze-Up Processes in the Alaskan Beaufort and Chukchi Seas

Abstract

This paper characterizes the processes that presently occur during freeze-up in the Alaskan Beaufort and Chukchi Seas, based on joint-industry investigations conducted in 2009-10, 2010-11, and 2011-12. The studies were designed to address five specific objectives: (1) describe the ice conditions that evolve during the freeze-up and early winter seasons; (2) locate and map features of potential importance for offshore exploration and production activities, including ice movement lines, leads, polynyas, first-year ridges and rubble fields, and multi-year floes; (3) locate and quantify ice pile-ups on natural shorelines and man-made structures; (4) correlate significant changes in the ice cover with the corresponding meteorological conditions; and (5) compare present-day freeze-up processes with those that occurred in the 1980s. Each study included an analysis of meteorological data, ice charts, and satellite imagery in concert with a series of aerial reconnaissance missions. The study findings are presented in seven categories: (1) air temperatures, (2) first-year ice growth, (3) the timing of freeze-up, (4) landfast ice, (5) multi-year ice, (6) ice pile-ups, and (7) extraordinary ice features discovered off the Chukchi Sea coast.

Multi-Year Ice Incursions into the Chukchi Sea

“…Based on the data acquired in support of recent freeze-up studies (Leidersdorf, et al, 2012), the probability of large multi-year ice floes invading the nearshore portion of the Alaskan Beaufort Sea has declined substantially since the 1980s. This trend has resulted in part from the location of the pack ice, which has retreated farther to the north in recent summers (National Snow and Ice Data Center, 2013), and in part from warmer air temperatures and increased storm frequencies, which have decreased the likelihood that remnants of the Beaufort Sea shear zone will survive the summer melt season to become second-year floes.…”

“…During the winter of 2011-12, multi-year ice floes entered the Alaskan Chukchi Sea to the south and west of Point Barrow on multiple occasions (Leidersdorf, et al, 2012). In each instance, the invasion occurred when the flaw lead that typically forms off the coast in response to easterly winds extended north and east of Point Barrow until it intersected the southern boundary of multi-year ice in the permanent polar pack.…”