Biodiversity in the Arctic Marine Environment

The Arctic marine environment is of extreme importance for many ecological processes in Arctic terrestrial ecosystems. The marine system functions as a base for many Arctic food webs. Arctic ocean currents also have a major impact on the Earth's climate, due to the high-energy exchange between polar and tropical areas. The marine region of the Arctic includes the Arctic Ocean and 13 adjacent seas and water bodies, and features a permanent ice cover of 5-8 million km2 during summer and approximately 12-13 km2 during winter.

Generally, sea water freezes at approximately -1.9°C, when the salinity is 33 parts per thousand. However, the freezing point of sea ice changes relative to the concentration of salt in the sea water. Remarkably, some water bodies within the Arctic stay open, even in the coldest periods of the winter. These ice-free areas appear where horizontal sea currents, upwellings (vertical sea currents), or winds form leads and polynyas (bodies of open sea water), and thus allow organisms access to primary production of phy-toplankton (free floating algae). The sea ice constitutes a thermal barrier against the cold winter atmosphere, with the result that the interface between the ice and the underlying sea water remains relatively high. During spring, when sunlight starts to become available for photosynthesis, a large biomass of unicellular ice algae develops within the lowermost section of the ice and coats the submerged surfaces of floating ice. Their population growth appears to be exponential when the polar day returns, doubling in biomass every five to ten days, depending upon snow cover and nutrient availability. These algae (mainly diatoms) feed the zooplankton preyed upon by higher organisms, for example, Arctic cod (Breogadus saida), as well as by birds and marine mammals. Ice algae are a very important part of the Arctic marine food web, and contribute on average over 50% to the total marine primary production in permanently ice-covered waters.

Areas of high productivity usually occur where nutrient-enriched Atlantic sea waters mix with Arctic water bodies. Generally, ice edges and associated waters are areas of exceptionally high productivity. Phytoplankton production begins when the ice cover disappears and the melting ice causes an increase in the stability of the water column. Phytoplankton contributes to almost 90% of plant photosynthesis in seasonally ice-covered waters. As in Arctic terrestrial ecosystems, increasing spatial heterogeneity in the marine biota results in an increased species diversity, even in the deep sea. The forces effecting such heterogeneity range from riverine influences and benthic storms to small-scale disturbances by grazers and bio-turbators in the water columns and on the sea bottom. Iceberg scours also play an important role in the spatiotemporal pattern of the seafloor fauna.

Larger, warm-blooded animals such as birds, seals, whales, and polar bears use the sea ice for migration routes, hunting grounds, and raising their young. Two groups of homoiothermic (warm-blooded) marine mammals, the cetaceans and pinnipeds, occur in Arctic waters. Cetaceans include baleen whales (suborder Mysticeti) and toothed whales (suborder Odontoceti). Pinnipeds include fur seals (Otariidae), hair seals (Phocidae), and walruses (Odobenidae). Among the marine mammals that inhabit Arctic waters all year round are the beluga or white whale (Delphinapterus leucas), narwhal (Monodon monocerus), and bowhead whale (Balaena mysticetus). All three rely upon open leads, polynyas, and areas of shifting ice where they have access to air. Of the three Arctic whales, belugas are the most numerous and widely distributed. Other whales such as orca (or killer whale, Orcinus orca), blue whale (Balaenoptera musculus), minke whale or lesser rorqual (Balaenoptera acutorostrata), fin whale (Balaenoptera physalus) and sperm whale (Physeter macrocephalus) appear in Arctic waters occasionally.

Two subspecies of walrus (Odobenus rosmarus) are recognized and live, respectively, in the Atlantic and the Pacific. Atlantic walruses live east of Sommerset Island in the Canadian Arctic, notably in Baffin Bay, Davis Strait, Foxe Basin, and the mouth of Hudson Bay. Pacific walruses are found along the Alaska coast and westward along the Arctic shore of Siberia. Five species of the seal family (Phocidae) spend at least part of the year in Arctic waters. Bearded seal (Erignathus barbatus) and ringed seal (Phoca hispida) remain in the Arctic all year round. Harp seal (Phoca groenlandica) and hooded seal (Cystophora cristata) overwinter farther south. With the exception of the orca, the polar bear is the top predator in the Arctic marine food chain. The polar bear can be considered marine rather than terrestrial, since it spends most of its life on annual sea ice in search of its major prey, seals. However, females still need to find suitable denning sites on the land which, in the case of the Hudson Bay population, extend their range far into the Subarctic woodland.

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