Snow: the sea ice’s indispensible partner

Dr Stefanie Arndt, sea-ice physicist at the Alfred Wegener Institute.

Viewed from the above, the colour of the sea ice is largely determined by the snow covering it. Here white isn’t just white and snow isn’t just snow. There are clear differences if you compare, e.g., the Arctic and Antarctic. While the snow on the Arctic sea ice is completely melting over the course of the year, and so-called meltwater ponds form on the surface of the ice, the Antarctic sea ice is covered by snow all year round: a situation that could soon change as a result of ongoing global warming, which means that in the future, in the Southern Ocean, the snow cover might also start melting significantly during summer.

Today, we are already observing a seasonal change in the snow layer on the Antarctic sea ice; thus, e.g., melting and refreezing processes lead to the formation of ice lenses in the snow. These complex structures make our satellite-based measurements of the snow and ice properties more difficult and result in considerable uncertainties, which we are trying to minimise through our extensive fieldwork on site.

Overall, the snow layer is a key parameter in climate-relevant processes in the polar regions. On the one hand, snow is characterised by a high albedo. The reflection of short-wave solar radiation cools the snow and sea ice in the Arctic and Antarctic, which in turn has a significant impact on Earth’s energy balance. On the other hand, the thickness and properties of the snow layer on the sea ice are decisive factors in its thermodynamic growth. The thicker the snow layer, the more effectively it insulates, and as such reduces the transfer of heat from the ocean to the atmosphere. However, the less warmth the ocean gives off, the thinner the sea ice remains. Therefore the snow not only determines the colour of the sea ice; it also makes a major contribution to the processes and fluxes between the atmosphere, sea ice, ocean and ecosystem.