Seasonal Ice loss in the Beaufort Sea: Toward Synchronicity and Prediction

Monday, 15 December 2014
Michael Steele, Suzanne Dickinson, Jinlun Zhang and Ronald W Lindsay, University of Washington, Seattle, WA, United States
The seasonal evolution of sea ice loss in the Beaufort Sea during 1979-2012 is examined, focusing on spatial differences between eastern and western sectors. Two stages in ice loss are identified: “opening” is defined as the spring decrease in ice concentration from its winter maximum below a value of 80% areal concentration; “retreat” is the summer decrease below 15% concentration. We consider three aspects of the problem, i.e. (i) the long-term mean, (ii) long-term linear trends, and (iii) year-to-year variability. We find that in the mean, ice opening occurs earliest in the southeast Beaufort Sea (SEB), forced by atmospheric heating acting on particularly thin ice relative to the southwestern Beaufort Sea (SWB). This thin SEB ice arises from divergence forced by easterly winds in fall and spring. There is no significant long-term trend in the date of SEB ice opening, although ice opening in the SWB is in fact trending toward earlier dates. This means that spatial differences in opening dates across the Beaufort Sea have been shrinking over the past 33 years, i.e., these dates are becoming more synchronous, a situation which may impact human and marine mammal activity in the area. Synchronicity in ice retreat dates is also increasing, although with no statistical significance at this time. Finally, we find that in any given year, an increase in monthly mean easterly winds of ~ 1 m/s during spring is associated with earlier summer retreat of 9-15 days, offering predictive capability with 1-2 months lead time.