Formation and development of surface scattering layers on Arctic sea ice

Interactions between Arctic sea ice and incident shortwave radiation dominate the surface heat and mass budgets of the ice pack during the melt season. Once the snow melts, the physical state of the upper 25 50 cm of bare ice exerts primary control on the fraction of incident radiation reflected, absorbed and transmitted by the ice, affecting ice-albedo feedback, internal melting, heating of the upper ocean, and photosynthesis within and beneath the ice. In particular, the development and maintenance of a surface scattering layer is responsible for the relatively large and approximately constant albedo of bare, melting sea ice. While the physical depth of this layer typically varies between a few centimeters and a few tens of centimeters, it can have optical depth in excess of the optical depth of the entire rest of the ice column. This scattering layer persists on bare, melting ice despite extensive ablation of ice mass at the surface, and can be annihilated quickly if the ice becomes flooded or ponded. Measurements, modeling results, and analysis are presented on the development, maintenance and radiation budget of surface scattering layers occurring on melting first-year sea ice in the Arctic. The analysis traces the evolution of the surface scattering layer with the progression of melt and the effect of this layer on the properties of the interior ice. Key questions about the robustness of this layer under conditions of reduced ice thickness are also addressed.