Ice and ocean velocity in the Arctic marginal ice zone: Ice roughness and momentum transfer

Abstract

Cole, ST, et al 2017 Ice and ocean velocity in the Arctic marginal ice zone: Ice roughness and momentum transfer. Elem Sci Anth, 5: 55, DOI: https://doi.org/10.1525/elementa.241 IntroductionThe canonical view of subinertial ocean currents immediately beneath sea ice consists of a logarithmic boundary layer, within which the stress is independent of depth, and an Ekman layer, where the influence of the Earth's rotation becomes important (Figure 1; McPhee, 2008). Together these layers are termed the ice-ocean boundary layer (IOBL), and encompass the upper tens of meters of the Arctic Ocean. The logarithmic boundary layer is typically a few meters thick at most, but within it currents vary logarithmically with depth. The Ekman layer under sea ice has currents that decay and rotate with depth. The specific details RESEARCH ARTICLEIce and ocean velocity in the Arctic marginal ice zone: Ice roughness and momentum transfer The interplay between sea ice concentration, sea ice roughness, ocean stratification, and momentum transfer to the ice and ocean is subject to seasonal and decadal variations that are crucial to understanding the present and future air-ice-ocean system in the Arctic. In this study, continuous observations in the Canada Basin from March through December 2014 were used to investigate spatial differences and temporal changes in under-ice roughness and momentum transfer as the ice cover evolved seasonally. Observations of wind, ice, and ocean properties from four clusters of drifting instrument systems were complemented by direct drill-hole measurements and instrumented overhead flights by NASA operation IceBridge in March, as well as satellite remote sensing imagery about the instrument clusters. Spatially, directly estimated ice-ocean drag coefficients varied by a factor of three with rougher ice associated with smaller multi-year ice floe sizes embedded within the first-year-ice/multi-year-ice conglomerate.Temporal differences in the ice-ocean drag coefficient of 20-30% were observed prior to the mixed layer shoaling in summer and were associated with ice concentrations falling below 100%. The ice-ocean drag coefficient parameterization was found to be invalid in September with low ice concentrations and small ice floe sizes. Maximum momentum transfer to the ice occurred for moderate ice concentrations, and transfer to the ocean for the lowest ice concentrations and shallowest stratification. Wind work and ocean work on the ice were the dominant terms in the kinetic energy budget of the ice throughout the melt season, consistent with free drift conditions. Overall, ice topography, ice concentration, and the shallow summer mixed layer all influenced mixed layer currents and the transfer of momentum within the air-ice-ocean system. The observed changes in momentum transfer show that care must be taken to determine appropriate parameterizations of momentum transfer, and imply that the future Arctic system could become increasingly seasonal.

Retrieving Sea Ice Drag Coefficients and Turning Angles From In Situ and Satellite Observations Using an Inverse Modeling Framework

“…As there is a strong correlation between the buoy and satellite winds and ice drift data, it is possible that this difference is due to the different nature of the geostrophic ocean current data or the deviation between buoy and satellite measured ice drift in Figure . The local buoy measurements of were subject to shorter time and length scale variations (Cole et al, ), whereas the satellite dynamic ocean topography in theory should be immune to short time and length scale flows. We suggest this as the reason for the improved resolution of the satellite 10‐day geostrophic only inversions.…”

Internal Waves in the Arctic: Influence of Ice Concentration, Ice Roughness, and Surface Layer Stratification

“…Ice concentrations were similar at C2–C4 through July with similar timing of, for example, melt pond drainage (late June to early July) and mixed layer depth shoaling (mid‐July). The smallest ice concentration was observed at C2 in September (Figure a), with ice remaining about C2 throughout the melt season (Figure 7 of Cole et al, ).…”

“…Evolution of the ice cover, upper ocean velocity, and surface layer stratification was largely coherent across C2–C4 due to the large scale of the wind forcing and solar heating (Cole et al, ; Gallaher et al, ). The ice began to break up with initial minor decreases in ice concentration (Figure a) due to wind events in late April and early May (Figure b).…”

“…Here we are interested in the monthly scale variations in drag coefficients that result from dynamic or thermodynamic changes to the ice cover. On this monthly timescale, the ice at C2 was a factor of 3 smoother during March–June due to larger multiyear ice floes embedded within the first‐year ice/multiyear ice conglomerate (Cole et al, ). The ice‐ocean drag coefficient increased at C3 during 15 May to 27 June due to rearrangement of the ice cover (Cole et al, ).…”

“…On this monthly timescale, the ice at C2 was a factor of 3 smoother during March–June due to larger multiyear ice floes embedded within the first‐year ice/multiyear ice conglomerate (Cole et al, ). The ice‐ocean drag coefficient increased at C3 during 15 May to 27 June due to rearrangement of the ice cover (Cole et al, ). All estimated ice‐ocean drag coefficients were smaller than the canonical value of 5.5 × 10 −3 (McPhee, ).…”