Anisotropic internal thermal stress in sea ice from the Canadian Arctic Archipelago

Abstract

Results from an ice stress buoy deployed near the center of a multi‐year floe in the Viscount Melville Sound of the Canadian Arctic Archipelago between 10 October 2010 and 17 August 2011 are presented. The position record indicates the landlocked season was approximately 5 months, from 18 January to 22 June, when the sea ice was fast to Melville Island and Victoria Island. Thermal stresses (ranging from −84 to 66 kPa) dominate the internal stress record, with only a few dynamic stress events (∼50 kPa) recorded before the landlocked season. Intriguingly, the thermal stresses are isotropic before the landlocked ice onset and anisotropic during the landlocked season. Two possible causes to explain anisotropy in thermal stresses are considered: preferred c axis alignment of the ice crystal, and land confinement associated with the nearby coastline. The orientation of the principal stresses indicates that land confinement is responsible for the anisotropy. The stress record also clearly shows the presence of residual compressive stresses at the melt onset, suggesting a viscous creep relaxation time constant of several days. Finally, results show an interesting reversal in the sign of the correlation (from negative to positive) between surface air temperature and thermal stress after the onset of surface melt. We attribute this to the onset of water infiltration within sea ice after which colder night temperature leads to refreezing and compressive stresses. To the best of the authors' knowledge, this is the first time that anisotropic thermal stresses have been reported in sea ice.

A 1.5‐D anisotropic sigma‐coordinate thermal stress model of landlocked sea ice in the Canadian Arctic Archipelago

“… (a) Time series of major ( σ 1 : red line) and minor ( σ 2 : blue line) principal stresses, and (b) 1 m air (blue line) and wire (red line) temperatures. The gray shading and white area below each figures indicate the drift and landlocked seasons, as per the GPS and compass angle records from the buoy [see Hata and Tremblay , ].…”

“…The thermal stress record during the landlocked ice season, however, is not isotropic. Analysis of the internal stress record suggests that land confinement in the north‐south direction is responsible for the anisotropy—with smaller effects from the c axis alignment in sea ice if at all present [ Hata and Tremblay , ]. In fact, the proximity of the land prevents thermal expansion (or contraction) of the sea ice in the direction perpendicular to the coastline.…”

“…The internal stress time series also show a residual compressive stress at the end of the winter season (beginning of the melt season) that relaxes to zero after approximately 20 days. This suggests a relaxation time constant ( τ ) of several days [ Hata and Tremblay , ].…”

“…In section 2, we develop the governing equations for the 1.5‐D anisotropic thermal stress model. The atmospheric fields used to force the thermal stress model are presented in section 3. In section 4, we give a general description of the internal stress data collected in the Viscount Melville Sound of the CAA [ Hata and Tremblay , ] that are used to validate the thermal stress model. Results from the thermal stress model forced with a simple linear and a full nonlinear internal sea‐ice temperature profiles are presented in section 5. Sensitivity studies of the anisotropic thermal stress model to the vertical resolution of the internal temperature profile, the snow depth, and the parameterizations of viscous creep and Young's Modulus are presented in section 6. The conclusions are summarized in section 7. Finally, an analytical solution for the thermal stress model forced with a linear internal temperature profile is presented in Appendix .…”

“…The atmospheric fields used to force the thermal stress model are presented in section 3. In section 4, we give a general description of the internal stress data collected in the Viscount Melville Sound of the CAA [Hata and Tremblay, 2015] that are used to validate the thermal stress model. Results from the thermal stress model forced with a simple linear and a full nonlinear internal seaice temperature profiles are presented in section 5.…”