Sea ice Our northernmost sea areas are covered by ice. The sea ice plays an important role in the climate by reflecting sunlight back into space, and prevents the exchange of heat, moisture and gases between the sea and the atmosphere. In recent decades, the extent of the ice has decreased significantly. This makes the Arctic more accessible to human activity, but also increases the pressure on a vulnerable ecosystem. Movement, distribution, and thicknessSea ice is affected by what happens both in the air above and in the water below and is a good indicator of how the climate is changing. The ice cover has been declining drastically in recent decades, and the trend towards an increasingly blue Arctic is expected to continue. Studies of the sea ice are important in order to understand the rapid climate changes in the Arctic, and to manage risks associated with increasing human activity in the region. Air-sea-ice interactionsThe sea ice in the Arctic functions as an insulating cover between the cold air above the ice and the relatively warm water below the ice. When the ice breaks up, the air above the sea will heat up and the water in the sea will cool down. The interaction between air, sea, and ice affects weather, climate, and life both below and above the sea surface. Sound as measuring instrumentThe Arctic Ocean – the water masses under the sea ice in the Arctic – is one of the least explored areas in the world. It is both time- and cost-consuming to make measurements in these inhospitable waters. One technique that enables data acquisition in these areas is to make measurements using sound. Sound can spread over great distances in the sea and can be recorded several thousand kilometers away from the source. This makes sound waves a valuable tool. Waves and iceWaves occur when wind creates ripples on the sea surface, and when wind persists, the ripples will grow into waves. Waves will not be able to occur where there is sea ice. Where the sea ice meets open water, waves will cause the ice to break up, and a zone of small and large ice floes is created between open water and dense ice. This is called the marginal ice zone. Waves in this zone can also spread into ice-covered areas.