Annual Cycles of Sea Ice Motion and Deformation Derived From Buoy Measurements in the Western Arctic Ocean Over Two Ice Seasons

Abstract

Data collected by two buoy arrays that operated during the ice seasons of 2014/2015 and 2016/2017 were used to characterize annual cycles of ice motion and deformation in the western Arctic Ocean. An anomalously strong and weak Beaufort Gyre in 2014/2015 and 2016/2017 induced generally anticyclonic and cyclonic sea ice drift during 2014/2015 and 2016/2017, respectively. Cyclonic ice motion resulted in higher contributions of ice divergence to total ice deformation in 2016/2017 than in 2014/2015. In 2014, the autumn ice concentration and multiyear ice coverage were higher than in 2016; consequently, the response of ice motion to wind forcing was weak, and less ice deformation was observed in autumn 2014. During the autumn‐winter transition, the ice‐wind speed ratio, ice deformation rate and its spatial and temporal scaling exponents, and localization of ice deformation decreased markedly in both 2014/2015 and 2016/2017 as a result of freeze‐up and consolidation of ice floes. Such dynamic behavior was maintained through to spring with the further thickening of ice cover. Ice deformation increased due to weakened ice strength as summer approached. The amplitude of the annual cycle of ice deformation rate in the western Arctic Ocean in 2014/2015 and especially in 2016/2017 was larger than that observed during the Surface Heat Budget of the Arctic Ocean (SHEBA) program in 1997/1998. We attribute this phenomenon to ice loss during the recent summers, especially of thick multiyear ice.

Arctic sea ice motion change and response to atmospheric forcing between 1979 and 2019

“…For all sub‐regions, the increase rates of ice drift speed in summer were generally lower than those in other seasons. It may be related to the fact that ice motion may approach a state of free drift in regions where ice concentration is low (Lei et al ., 2020). A similar mechanism may have been operating during the early phase of the study period, especially in the peripheral seas (Zhang et al ., 2012), which is responsible for relatively low increase rates.…”

“…The determination coefficient was the highest in summer ( R 2 = 56%), indicating that the wind speed increase was only able to explain a small portion of the variance in autumn ice drift speed. This is likely because, as the summer ice pack approaches a state of free drift, it responds more readily to wind forcing than in other seasons (Lei et al ., 2020). The coefficient of determination was the lowest in autumn ( R 2 = .17), indicating that a wind speed increase was unable to completely explain the variability in autumn ice speed.…”

“…In summer, the determination coefficient between ice drift speed and wind speed was relatively high ( R 2 > .5) in the NWCA (Figure 7b). Although ice concentration is high here, when ice concentration decreases from 100 to 80%, wind stress transfer into the ocean will increase, leading to enhanced ocean current and higher ice speed (Martin et al ., 2014; Lei et al ., 2020). Therefore, the response of ice speed to wind speed is relatively strong in the NWCA.…”

“…Such conditions, associated with, reduced ice thickness (e.g., Kwok, 2018) and ice pack strength (e.g., Oikkonen et al ., 2017), are likely to further increase sea ice mobility and deformation. Sea ice deformation exhibits high intermittence (Lei et al ., 2020), indicating that deformation mostly takes place during extreme events. Therefore, studies of sea ice dynamics need to include quantitative assessments of both the average modulus and extreme value of sea ice motion speed, with the latter being associated with extreme wind events.…”

Survival and abundance of polar bears in Alaska’s Beaufort Sea, 2001–2016

“…Climate warming has led to rapid reductions in sea ice extent, volume, and age (e.g., Kwok, 2018 ), and peripheral Arctic seas are either seasonally ice‐free or projected to become so within a decade (Onarheim et al., 2018 ). The loss of stabilizing sea ice cover has intensified geophysical processes that are expected to induce greater ice loss in the future (Post et al., 2019 ), including increased intrusion of warm sub‐Arctic waters (Barton et al., 2018 ; Pacini et al., 2019 ; Wang et al., 2020 ) and vertical mixing (Liang & Losch, 2018 ), greater absorption of solar radiation by ice‐free waters (Timmermans et al., 2018 ), and increased wind speed and wave height (Li et al., 2019 ; Liu et al., 2016 ) with corresponding ice deformation (Lei et al., 2020 ; Williams et al., 2013 ; Zhang et al., 2012 ).…”