Influence of snow depth and surface flooding on light transmittance through Antarctic pack ice

Snow on sea ice alters the properties of the underlying ice cover as well as associated physical and biological processes at the interfaces between atmosphere, sea ice and ocean. The Antarctic snow cover persists during most of the year and contributes significantly to the sea-ice mass due to the widespread surface flooding and related snow-ice formation. Snow also enhances the sea-ice surface reflectivity of incoming shortwave radiation and determines therefore the amount of light being reflected, absorbed, and transmitted to the upper ocean. Here, we present results of a case study of spectral solar radiation measurements under Antarctic pack ice with an instrumented Remotely Operated Vehicle in the Weddell Sea in 2013. In order to identify the key variables controlling the spatial distribution of the under-ice light regime, we exploit under-ice optical measurements in combination with simultaneous characterization of surface properties, such as sea-ice thickness and snow depth. Our results reveal how the distinction between flooded and non-flooded sea-ice regimes dominates the spatial scales of under-ice light variability for areas smaller than 100m-by-100m. However, the heterogeneous and widely metamorphous snow on Antarctic pack ice prevents a direct correlation between surface properties and the under-ice light field. Compared with Arctic sea ice, light levels under Antarctic pack ice are extremely low during spring (< 0.1%). This is mostly a result of the distinctly different dominant sea ice and snow properties with seasonal snow cover (including strong melt and summer melt ponds) in the Arctic and a year-round snow cover and strong surface flooding in the Southern Ocean