Arctic Ocean

The Arctic Ocean is the smallest and shallowest of the world's oceans, centered on the North Pole and largely enclosed by North America, Greenland, Europe and Asia, and forms an ecosystem built around its seasonal sea ice rather than in spite of it. For much of the year, floating sea ice covers most of the ocean's surface, and algae growing on and beneath the ice form the base of a food web that runs upward through zooplankton to fish, seals, narwhals, beluga whales and, at the top, polar bears, which depend on the ice itself as a platform for hunting seals. The ecosystem experiences extreme seasonal swings in light, with months of continuous winter darkness followed by months of continuous summer daylight, a rhythm every part of the food web is adapted to. The Arctic Ocean is also warming and losing its summer sea ice cover faster than almost anywhere else on the planet, a change already reshaping the ecosystem's food web and the ranges of the species that depend on it, and making the Arctic one of the most closely watched systems for the effects of a warming climate anywhere in the world.