Sea ice thickness and dynamics

Changes in the Arctic become very obvious in the sea ice cover: over the past decades, the summer sea ice cover has shrunk both in extent and thickness. A better knowledge of the ice thickness distribution will help the assessment of changes in ice dynamics and vice versa. The snow cover is likely to play an increasingly important role regarding the seasonal development of the sea ice.

Helicopter takes off with EM-bird

Take off of the helicopter with the EM-bird. With this instrument, we can measure the combined snow and ice thickness over several kilometers, making use of the different salt content in the ice and the sea water underneath. Photo: Angelika Renner / Norwegian Polar Institute

Scientist working a EM31, a small version of the EM-bird, on the sea ice

On the sea ice, the EM31, a small version of the EM-bird, is used to get higher resolution sea ice thickness data. The EM31 is mounted on a sledge so that it can be easily pulled along transects of several hundreds of meters length. Photo: Ella Darlington

The Arctic summer sea ice cover has shrunk dramatically over the last three decades both regarding its extent and thickness. Old ice that has survived for multiple years has been lost, and young first-year ice is becoming dominant. Sea ice thickness, however, is still difficult to measure and data covering larger scales both in space and in time are needed. We are using a helicopter-borne instrument based on an electromagnetic induction method, the EM-bird, as well as autonomous ice mass balance buoys and sonars on moorings to cover large spatial and temporal scales, respectively. This will contribute to the validation of satellite measurements and sea ice models.

We anticipate a continuation of the thinning of the Arctic sea ice cover with a larger fraction of first-year ice. This in turn will lead to a further decrease of sea ice volume, especially in summer. The thinning will also affect the ice dynamics. With our observations we aim to understand whether changes in the ice thickness distribution are due primarily to thermodynamic (i.e. temperature forced) or dynamic (i.e. wind and ocean current forced) deformations.

With a change in the Arctic climate, precipitation is likely to increase and the snow cover may play an increasingly important role. Thinner ice is more susceptible to flooding and the effect of insulation by the snow cover is bigger compared to thick ice. Snow cover on sea ice also affects the transmission of light through the ice as more sunlight is reflected by snow than by bare ice, and snow is the base for melt ponds forming in summer months. Observations of snow thickness and the physical properties of the snow pack are sparse though and not necessarily spatially representative. During the ICE Fluxes field campaigns, we will therefore collect data on snow thickness and other parameters.