Solar radiation

Melt ponds on sea ice affect the albedo and thus the amount of heat through solar radiation that is taken up by the ice. The ponds vary in area and depth depending on the ice type. Melt ponds, snow coverage, and particles in the sea ice are also crucial to how much light will get through the ice and reach the upper ocean, where it can be used for biological activity and production.

Albedo measurements on sea ice

Albedo measurements on sea ice. The instruments on the right measure the incoming radiation from the sun and the reflected light from the ice surface. Photo: Angelika Renner / Norwegian Polar Institute

Research vessel Lance seen from a helicopter above

R/V Lance in a lead north of Svalbard. The sea ice is covered by melt ponds and very little snow, typical for the end of the summer melting season. Photo: Angelika Renner / Norwegian Polar Institute

In addition to regular seasonal changes, the Arctic sea ice is shifting from thick old ice to thinner young ice. With this, the seasonal progression of surface albedo, the amount of sunlight that is reflected by the sea ice, the snow, and the ocean surface, is changing as well. During summer, heat from the sunlight changes and finally melts the snow and the surface of the sea ice. The melt water runs together into so-called melt ponds on the ice surface. These have a significantly lower albedo than snow or ice, so that with increasing melt pond coverage, more heat will be taken up and lead to more snow and ice melt. On thin young ice, melt ponds are commonly shallow but cover large areas while on old ice, they are deeper, smaller, but more numerous. Our aim is to assess the evolution, extent and optical properties of melt ponds and other surface types and estimate mean albedos at larger scales. Our results will be used to develop new techniques for specifying the albedo of sea ice in climate models, which is crucial for predicting the future evolution of sea ice in a changing climate.

Transmission of light through the sea ice is important for organisms living in or directly under the ice and in the upper ocean, and also provides energy for melting sea ice from the underside. The amount of light that gets through to the underside of the ice depends on the presence of snow and melt ponds and on the properties of the sea ice – e.g. whether it is very salty, includes a lot of air bubbles or pockets of highly saline water, has had dust or soot deposited on it, or has algae living within it. With reduced ice coverage, the optical properties of the sea water in the Arctic Ocean are becoming more important both for the heat uptake by the ocean and the light availability for biological productivity. The main factors controlling the transmission of light through the water are sediments from river input and suspended organic material. Observations of both the amount of light getting through the ice and snow cover and through the water column are sparse and we are gathering new data to validate models and improve the description of these processes in them. Our studies will provide methods for including the factors controlling the transparency of water in the Arctic Ocean and the exposure of the ocean to sunlight in ocean and climate models.