Keel Morphology Analysis on Winter Sea Ice in Northwestern Weddell Sea, Antarctica

  Objectives  Morphology of polar sea ice changes continuously under the influences of external driving forces, e.g., wind, flow and waves. Observations and change regularity analysis on morphology of polar sea ice not only is helpful for the optimization of sea ice thermodynamics numerical simulation and the inversion of sea ice thickness based on roughness parameters, but also provide distinct importance for understanding the response of polar sea ice morphology to climate change.

  Methods  Based on the undulations profiles of sea ice bottom in Northwestern Weddell Sea measured by the helicopter-borne electromagneticinduction bird(EM-bird) system during the winter of 2006, this paper establishes a nonlinear statistical optimal model with the cutoff draft as the identified variable to separate the ridge keels and local undulations on sea ice bottom. Then, the keel morphology parameters and correlation between the keel draft and frequency are statistically analyzed. Finally, a new parameter T is hatched to assess the correlation between the ridge sail height and keel draft.

  Results  The results suggest that the optimal cutoff draft is 3.8 m and the keel spacing is the main factor affecting the ridging intensity. Despite marked sea ice deformation in different regions in Northwestern Weddell Sea, morphology changes of the keel are not evident. There is a good log correlation between draft and frequency of the keel, which vividly describes morphology and distribution of the keel. The newly hatched parameter T has a significant linear correlation with keel depth(r=0.93).

  Conclusions  The newly proposed modeling method can separate the keel from sea ice bottom undulations more accurately, which provides a new theoretical reference for morphological correlation analysis between surface and bottom of sea ice, and the inversion of sea ice thickness and bottom draft from its surface height.