Magazine article Oceanus

Life in the Arctic Ocean: Distinctive Species and Environmental Factors Combine to Create a Unique, Complex Food Web

Magazine article Oceanus

Life in the Arctic Ocean: Distinctive Species and Environmental Factors Combine to Create a Unique, Complex Food Web

Article excerpt

Capped with a formidable ice and snow cover, plunged into total darkness during the winter, buffeted by blizzard winds, and bitterly cold, the Arctic Ocean is one of the most inaccessible and yet beautiful environments on Earth. Life here endures some of the greatest extremes in light and temperature known to our planet. Yet despite these inhospitable conditions, the Arctic Ocean is teeming with life.

Great polar bears roam the ice and swim the seas. These top predators are supported by a complex ecosystem that includes plankton, fish, birds, seals, walruses, and even whales. At the center of this food web, supporting all of this life, are phytoplankton and algae that produce organic material using energy from the sun.

The Arctic's extreme environmental conditions have limited our opportunities to study this complex food web. Expeditions to the remote Arctic are difficult and expensive. When we can get there at all, it is usually only in summer. Such gaps in our observations have compromised our ability to understand the food web's intricacies and vulnerabilities--at a time when the ecosystem appears to be increasingly vulnerable.

Scientists now know that warming temperatures are affecting the Arctic Ocean, producing changes that may have cascading effects on the Arctic's inter-linked and delicately balanced food web. Changes in the food web not only threaten life in the Arctic region, they also could have impacts on Earth's climate. Populations of Arctic plankton, for example, not only provide food at the base of the food web, they also convert carbon dioxide from the atmosphere into organic matter that eventually sinks to the ocean bottom--effectively extracting a heat-trapping greenhouse gas from the atmosphere.

Life and light springs eternal

Every spring, after the long dark night of Arctic winter, the sun reappears over the horizon. Then, a cumulative sequence of events begins, and life in the Arctic springs into action.

With each day longer than the previous one, light begins to penetrate the thick cover of snow and ice to the undersurface of the ice, where ice algae begin to grow, like mold on a damp ceiling. One green, string-like form, Melosira, grows long, hanging under the ice like Spanish moss. It eventually detaches from the under-ice surface and sinks to the seafloor where it is consumed by the animals living there.

As days lengthen, light and warmth increase, and the winter snow cover that accumulated over the ice begins to melt. Once the snow melts, enough light can penetrate the ice to spur the growth of phytoplankton--very small, drifting, plantlike organisms that live in the water. They become available as food for higher organisms in the food web, the zooplankton--tiny marine animals that, in turn, are eaten by larger animals, from fish to jellyfish to whales.

A rich and vulnerable ecosystem

Nowhere are plankton ecosystems less understood than in the Arctic Ocean. Without more detailed knowledge about the workings of these ecosystems and the life histories of the individual life forms in them, we cannot predict how they will be affected by climate changes. But those changes already appear to be happening.

Scientists have documented dramatic shifts in Arctic ice cover, water temperature in the Arctic Ocean, and the atmosphere above it--all potentially due to the effects of a warming climate. Such changes are likely to affect, and may alter, the Arctic food web and ecosystem. They may change the amounts of water, nutrients, and plankton coming into the Arctic Basin, or change the timing of spring growth.

The great bowhead whale, for example, depends on plankton patches found along the northern coast of Alaska for food during its migrations between the summer feeding grounds off Arctic Canada and its overwintering grounds in the Pacific. Climate-induced changes in the availability of these plankton patches may have dramatic impacts on the whales, with either more or less food available along their migration route. …

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