Sea ice and a polar bear in the Fram Strait (Arctic Circle).

Sea ice is frozen seawater that floats on the ocean's surface.  It forms in the winter (in both the Arctic and Antarctic) and retreats in the summer, but does not completely disappear.

Ice crystals form on the surface of the ocean.  They expel salt, which increases the water salinity below them.  This cold salty water is dense, and it can sink to the ocean floor, whence it flows back towards the equator.

Sea ice has an important influence on polar environments (e.g. weather, regional climate and ocean circulation).  The sea ice layer restricts wind and wave movement near coastlines, which reduces coastal erosion and protects ice shelves.

It also creates an insulating “cap” on the ocean, reducing evaporation and heat loss to the atmosphere.  Because of this, the weather in ice-covered areas tends to be colder and drier than in areas not covered by ice.

When the ice melts in the summer, it releases nutrients into the water.  This stimulates the growth of phytoplankton, which are at the centre of the marine food web.  The melting ice exposes the ocean water to sunlight, which encourages photosynthesis in plankton.

When ice freezes and the saltier, denser water sinks, it mixes the water column and brings nutrients to the surface.  The sea ice is a habitat for animals including polar bears, seals, penguins and Arctic foxes.

Winner, Behaviour category

Respiro by Antonia Doncila. This photograph was taken while crossing the Fram Strait near the eastern Greenland coast. The polar bear found a portion of fast ice which rapidly became his home

Photograph: Antonia Doncila/PA

Spring ice chokes the Bering Strait (7th May, 2000).  Ice is flowing southwards from the Bering Strait to the Bering Sea.

There is no land at the North Pole.  The sea ice occupies an ocean basin that is mostly surrounded by land.

Because the North Pole has no land, the ice is subject to the most extreme oscillations between winter darkness and summer sunlight.  And because the ocean basin is surrounded by land, the ice has less freedom to drift to lower latitudes and melt.

The Arctic Oscillation is the main cause of atmospheric variability around the North Pole, causing fluctuations that can last from years to decades.  It is an atmospheric “see-saw” in which air masses shift between the polar regions and lower latitudes.  This shifting can intensify, weaken, of shift the location of semi-permanent low- and high-pressure systems. These changes influence the strength of the existing westerly winds, and also influence the track that storms tend to follow.

In a “positive phase”, the winds intensify, making leads (narrow linear openings) in the ice packs bigger.  The thin, young ice that forms in the leads is more likely to melt in the summer.  The strong winds flush more ice out of the Arctic through the Fram Strait, which means that more of it will melt at these lower latitudes.

In a “negative phase”, the winds are weaker.  Thicker, multiyear ice is less likely to be swept out of the Arctic Basin into lower latitudes, and thus more of it will last the summer.

The mid-1990s had a strong positive AO phase, which flushed thicker, older ice out of the Arctic, replacing it with first-year ice that is more prone to melting.  After that, the AO was often neutral or negative, but sea ice failed to recover.  A steep pattern of Arctic sea ice decline began in 2002.

Programmed multicopter flies through the Arctic autonomously

Researchers performed an independent multicopter trip in the Arctic using its own check UAV system which used a u-blox LEA-M8T GPS device. (Picture: Alfred-Wegener Institute)

how can you efficiently pilot a UAV in the distant areas of the Arctic Sea when the compass can’t supply reliable placement info? Technicians on-board the Alfred Wegener Institute’s (AWI’s) study icebreaker Polarstern…