Detailed Snow Characterisation

 

Rob Massom, Takenobu Toyota, Katie Leonard, Ted Maksym, Barry Giles, Ernesto Trujillo-Gomez, and Olivier Lecomte

Most sea ice older than a few days is covered with snow. Understanding not only the thickness but also the characteristics of this snow cover, and its spatial and temporal variability, is important for a number of reasons.

Snow cover significantly modifies and regulates the physical, optical and thermal properties of the sea-ice. This is due to snow’s 1.) superb insulative properties, 2.) high albedo (spectral-albedo-of-young-sea-ice-types); and 3.) a direct relationship with the growth of underlying sea ice (role-of-snow-distribution-processes-on-antarctic-sea-ice-mass-balance),  For example, the presence of snow cover typically enhances the temperature of underlying ice and thus affects the microstructure, salinity and permeability of sea ice (spectral-albedo-of-young-sea-ice-types). By this mechanism, snow cover affects space for algal colonisation and nutrient transport within the ice.  In addition, snow plays a crucial part in the mass balance of Antarctic sea ice cover, via its roles in regulating the ice thermodynamics and “snow-ice formation”. Depression of the ice surface (involving the loading effect of a snow cover and/or ice deformation processes) can lead to flooding of the lower snow layers, which subsequently freeze to form ice on the surface of the underlying sea ice.

As a result of these factors, snow is of major climatic significance as an integral component in polar atmosphere-ice-ocean interactions, and also plays a key role in biological and biogeochemical processes involving the ice. Moreover, it forms an important source of freshwater to the ocean when it melts, and its presence complicates the interpretation of satellite data and the retrieval of sea ice geophysical parameters from these data.  From a human perspective, snow can greatly reduce the ice-breaking efficiency of icebreakers, depending upon its characteristics.

The aim of this programme is to provide a detailed characterization of the snow cover observed during SIPEX-2. This will involve measurements within snowpits dug along the snow and ice thickness transects (in-situ-ice-and-snow-thickness-transects), and in support of other projects requiring detailed snow information.

Snow parameters to be measured include vertical profiles of density, temperature, salinity, hardness, grain size and grain shape. Snow type within distinct snow layers (stratigraphy) will be identified and classified using a standardised international snow classification scheme. Taken together, these data provide information on the overall impact of the snow cover and its temporal evolution. We shall also be recording the distribution of surface flooding and snow-ice formation, in concert with the snow and ice thickness transect work (ice-floe-survey), associated ice coring work (in-situ-ice-and-snow-thickness-transects), and the snow distribution and sea ice mass balance project (role-of-snow-distribution-processes-on-antarctic-sea-ice-mass-balance). A major motivation for measuring snow density is to provide crucially important information to help interpret sea ice freeboard and draft measurements obtained by the in situ, airborne and underwater measurement programmes (R-APPLSAUV, ROV), and ultimately to derive improved large-scale sea ice (and snow cover) thickness distributions from satellite data.