Sea Ice Thickness - Mass Balance

The Arctic sea ice extent and thickness have undergone dramatic changes in the past decades: The summer sea ice extent is declining at an annual rate of approximately 12.7 % per decade over the satellite record (1978 – 2015) and its mean thickness is decreasing by 0.58 +/- 0.07 m per decade over the period 2000 - 2012. The thinning of sea ice is accompanied by an increase of ice drift velocity, deformation and a decrease of net ice growth rates. Climate model simulations indicate that ice extent and thickness will further decline through the 21st century in response to atmospheric greenhouse gas loading scenarios. The mass balance of Arctic sea ice is therefore determined not only by changes in the energy balance of the coupled ice-ocean-atmosphere system but also by the increasing influence of dynamic effects. One aspect of the mass balance of Arctic sea ice are changes of ice volume export rates through major gates of the Arctic, such as Fram Strait.

The Sea Ice Physics group investigates to what extent ice volume loss through major export gates is changing.  By combining sea ice concentration and drift data from satellites with thickness information derived from CryoSat-2 and aircraft data the Sea Ice Physics Section determines the sea ice volume flux in Fram Strait region and other key areas. Results are used to quantify whether coupled sea ice ocean models are capable of reproducing Fram Strait sea ice volume fluxes correctly.

Electromagnetic-induction (EM)

Electromagnetic-induction (EM) sounding is the main took of the Sea Ice Physics group to measure the thickness of sea ice in the Arctic and Antarctic. EM ice thickness measurements are based on the contrast of electrical conductivity between sea water and sea ice to determine the distance of the EM instrument to the ice-water interface. The method can be applied with ground-based and airborne sensors.

Ground-based EM surveys usually include hand-held sensors that are pulled on a sledge across the ice. Airborne EM (AEM) systems include custom-built instruments that are towed 12 to 20 meters above the ice surface using helicopters from land or from RV Polarstern. Since 2009, AEM measurements are also conducted with the research aircraft Polar 5 operating from different Arctic Research Stations, such as the Danish Station Nord in nord-east Greenland or Station Alert, in Canada. The fixed-wing based flight pattern follow straight lines of several hundreds of kilometers, while helicopter flights are typically performed along a triangular track with a side length of 40 to 80 km.

More information on the method can be found on

GEM Sea Ice Thickness Sensor

Towing the GEM sea ice thickness sensor on a blue sledge behind a snow scooter and 2 Nansen sledges across the sea ice of Atka Bay
Towing the GEM sea ice thickness sensor on a blue sledge behind a snow scooter and 2 Nansen sledges across the sea ice of Atka Bay (Photo: M. Nicolaus, AWI)

Helicopter EM Sensor

Helicopter EM sensor measuring sea ice thickness
Helicopter EM sensor measuring sea ice thickness (Photo: S. Hendricks, AWI)

AEM measurement by Polar 5