By studying cores drilled out of the ice, scientists can detect temperature changes over the centuries. Trapped air bubbles record changes in the concentration of carbon dioxide in the atmosphere, essential to our understanding of global warming. Ice cores have shown how radioactivity and lead pollution have increased in the atmosphere since 1945. However, the seas around this frozen continent are among the world's most fertile and productive, supporting a wealth of seabirds, marine mammals, and fish. These support vast numbers of krill, particularly Antarctic krill, a 70 mm long shrimp-like creature.
Antarctic krill forms dense concentrations, called swarms, during the Antarctic summer.
These can be several kilometres across and 20 metres deep. At night these swarms light up and the sea becomes a mass of living, blue-green light. These animals feed at different stages of the krill's life-cycle, at different times of the year, in different places and at different depths, thus achieving a delicate balance of supply and demand. Most of the region's fish contain anti-freeze molecules which prevent their body fluids from freezing. During the winter months, Weddell seals live permanently under the ice, using sonar to locate their food and find their way back to their breathing holes.