Arctic Ocean ecosystem

• Category: Marine and Oceanic Biomes.
• Geographic Location: Arctic.
• Summary: The Arctic Ocean holds a multitude of unique life forms that are highly adapted in their life history, ecology, and physiology to the extreme and seasonal conditions of this most-northern of environments.

The Arctic Ocean is unique among the world's oceans for many reasons. It is the most extreme ocean in regard to the seasonality of light and its year-round existing ice cover. Knowledge of what lives in the Arctic Ocean is limited due to the logistical challenges imposed by its many years of ice buildup and its inhospitable climate. Covering about 3 percent of the Earth's total surface area, the Arctic Ocean is the smallest of the world's five ocean regions (after the Pacific, Atlantic, Indian, and Southern/Antarctic). Most of this nearly landlocked ocean region is north of the Arctic Circle. The Arctic Ocean is connected to the Atlantic Ocean by the Greenland Sea, and to the Pacific Ocean via the Bering Strait. The Northwest Passage (between the United States and Canada) and the Northern Sea Route (between Norway and Russia) are two important seasonal waterways.

The center of the Arctic Ocean is covered by a drifting, persistent ice pack that has an average thickness of about 10 feet (3 meters). During the winter months, this sea ice covers much of the Arctic Ocean's surface. Higher temperatures in the summer months cause the ice pack to shrink in extent by about 50 percent. In the late twentieth and early twenty-first centuries, this polar ice pack thinned, and its summer extent contracted, allowing for increased navigation and raising the possibility of future undersea resource claims by neighboring countries and shipping disputes among countries bordering the region.

The Arctic Ocean has the widest continental shelf of any ocean, extending 750 miles (1,207 kilometers) from the coast of Siberia, but also has areas that are quite deep. The shallowest ocean region overall, it has an average depth of 3,450 feet (1,052 meters). The maximum depth is 17,850 feet (5,450 meters). The Chukchi Sea provides a connection with the Pacific Ocean via the Bering Strait, but this channel is very narrow and shallow, so most water exchange is with the Atlantic Ocean via the Greenland Sea. The Arctic Ocean connects to or envelops numerous other smaller seas and bays, including Baffin Bay, Barents Sea, Beaufort Sea, Chukchi Sea, East Siberian Sea, Hudson Bay, Hudson Strait, Kara Sea, and the Laptev Sea.

The polar climate is characterized by persistent cold and relatively narrow annual temperature ranges. The winters are characterized by near-continuous darkness, cold and stable weather conditions, and clear skies; the summers by continuous daylight, damp and foggy weather, and weak cyclones with rain or snow.

Seamounts and Submarine Ridges

The floor of the Arctic Ocean is divided by three submarine ridges—Alpha Ridge, Lomonosov Ridge, and Gakkel Ridge—of which the Lomonosov separates the two great basin deeps, the Amerasian and Eurasian. A further division of the Amerasian deep is the relatively isolated Canadian Basin; this area is particularly interesting to scientists because its isolation could mean that it contains life forms found nowhere else on Earth. The Lomonosov Ridge is an underwater mountain chain that averages 10,000 feet (3,048 meters) above the seafloor plain and in places comes to within 3,000 feet (914 meters) of the sea's surface.

Biodiversity

Researchers have only begun to scratch the surface of biodiversity in the Arctic Ocean, which has at least three distinct biological communities. The Sea-Ice Realm includes plants and animals that live on, in, and just under the surface ice. Because only 50 percent of this ice melts in the summer, ice flows can exist for many years and can reach a thickness of more than 6 feet (2 meters). Sea ice usually is not solid like an ice cube, but is riddled with a network of tunnels called brine channels that range in size from microscopic to more than 1 inch (25 millimeters) in diameter. Diatoms and algae inhabit these channels and obtain energy from sunlight to produce biological material through photosynthesis. Bacteria, viruses, and fungi also inhabit the channels, and together with diatoms and algae, they provide food for flatworms, crustaceans, and other animals. This community of organisms is called sympagic, which means “ice-associated.”

Partial melting of sea ice during the summer months produces ponds on the ice surface that contain their own communities of organisms. Melting ice also releases organisms and nutrients that interact with the ocean water below the ice. Also, the ice in the Arctic can contain natural history information about what the world was like thousands of years ago. Much history must be hidden in the Arctic ice, including information regarding historical weather patterns, carbon dioxide levels from the Stone Age, and what organisms were alive thousands of years ago.

The Pelagic Realm includes organisms that live in the water column between the ocean surface and the bottom. Melting sea ice allows more light to enter the sea, and algae grow rapidly because the sun shines twenty-four hours a day during the summer. These algae and phytoplankton provide energy for a variety of floating animals (zooplankton), including crustaceans and jellyfish. Zooplankton, in turn, are the main energy source for larger pelagic animals, including fishes, squids, seals, and whales.

When pelagic organisms die, they settle to the ocean bottom and become food for inhabitants of the Benthic Realm. A variety of sponges, bivalves, crustaceans, polychaete worms, sea anemones, bryozoans, tunicates, and ascidians are common members of Arctic benthic (floor-dwelling) communities. These animals provide energy for bottom-feeding fishes, whales, and seals.

Seawater Density and Salinity

Ocean currents are caused by winds and changes in seawater density. Density can be changed by evaporation or freshwater input (which raises or lowers the salinity), as well as by temperature changes. Near the equator, for example, evaporation causes seawater salinity and temperature to increase. The density of seawater increases as salinity rises and decreases as temperature rises. So even though the water is saltier, the higher temperature keeps the surface water from sinking. But as the water flows toward the poles (driven partly by wind), it becomes cooler and sinks due to the increased density.

Currents

The main ocean current flowing into the Arctic Ocean is the West Spitsbergen Current, a northward extension of the Norwegian Atlantic Current, passing through the Fram Strait and then following a deep trench leading to the Arctic Ocean. The access via the Barents Sea is partially obstructed by shallows. The water in this current is warm, above 37 Fahrenheit (F) (3 Celsius [C]); and relatively salty, with a salinity greater than 34.9 parts per million (ppm). The amount of water transported is uncertain, but it is possible that as much as half of it circulates in the vicinity of the Fram Strait without entering the Arctic Ocean.

Alongside the West Spitsbergen Current is the East Greenland Current. This is the main current out of the Arctic Ocean, carrying cold—below 32 F (0 C)—and relatively fresh (less than 34.4 ppm salinity) water southward. The Bering Strait is narrow at 53 miles (85 kilometers) and shallow, reaching just 164 feet (50 meters) in depth, allowing only a small northerly flow.

The Transpolar Drift, a surface current, flows from the Siberian to the Greenland side of the Arctic Ocean, where it feeds into the East Greenland Current. Explorer Fridtjof Nansen trusted this current to carry his ship, the Fram, across the Arctic Ocean in the 1890s into the vicinity of the North Pole. A less heroic demonstration of the Transpolar Drift is being provided by a consignment of 29,000 floating plastic bath toys (including ducks, frogs, and turtles) that were lost from a container ship in the North Pacific in October 1992. It was proposed that the floating toys would be transported by the pack ice across the Arctic Ocean into the North Atlantic.

The pack ice, up to 39 feet (12 meters) thick, plays an important part in conserving heat. The seawater, with a mean depth of about 3,937 feet (1,200 meters) and a volume of about four million cubic miles (17 million cubic kilometers), provides an immense heat reservoir. The ice cover reduces heat transfer to the atmosphere by one or two orders of magnitude compared with that from open water. Furthermore, largely because of the inflow of river waters and Bering Strait waters, a layer of low-salinity water floats on top of the denser water in the Arctic basin, producing a marked halocline (a vertical zone in the oceanic water column in which salinity changes rapidly with depth) at 98 to 197 feet (30 to 60 meters), which limits the convection that would otherwise mix the whole water column and promote heat loss. The deepwater consequently remains at 30 to 31 F (minus 0.5 to minus 0.9 C), above its freezing point of 28 F (minus 2 C). These various factors contribute to the generally higher temperatures of the Arctic Ocean compared with the Antarctic Ocean.

Plans to divert the southward part of the flow of some Siberian rivers to alleviate water shortages farther inland perhaps need not create too much alarm. On present evidence, it seems unlikely that such diversions would have major effects on circulation or sea-ice distribution in the Arctic Ocean.

This complex circulation system in the Arctic, which affects the entire food web, is however, in a delicate balance. Scientists have documented changes in the Arctic systems, including a dramatic reduction in sea-ice cover and a weakening of some of the circulation systems that are attributed to—and perhaps accelerating—climate change. The Arctic Ocean affects not only the Indigenous peoples living in the Arctic, but also those living farther south in Europe and North America. As a result, the Arctic Ocean and the effects of changes that occur here are the focus of intense study by many nations.

Climate change has had devastating effects on the ecosystem of the Arctic Ocean. Global warming and ocean acidification in the Arctic have occurred twice as fast as the global average. Among the many changes caused by climate change are a reduction in sea ice at a rate of about 13 percent each decade, changes in permafrost, and rising sea levels. The melting of sea ice has negatively affected polar bears, who depend on the ice to travel, hunt, and rest. It has also affected seals, walruses, and narwhals, which need sea ice to raise their young. It has also altered the typical ranges of indigenous fish and the migration habits of whales. The food chain in the Arctic Ocean has also been disrupted. Atlantic cod have increasingly replaced the polar cod, an essential link in the Arctic food chain. As the ice melts and the sun's light penetrates deeper into the Arctic waters, the fat phytoplankton naturally produce has become less nutritious, and krill populations have declined. According to scientists, even with a reduction in global emissions, by 2100, ice in the Arctic Ocean may disappear completely during summers.

Bibliography

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"Arctic Ecosystems." National Ocean Economics Program, 2017, www.oceaneconomics.org/NOEP/Arctic/ecosystems. Accessed 15 Dec. 2024.

"Biodiversity and Nature." WWF's Global Arctic Programme, www.arcticwwf.org/our-priorities/biodiversity-and-nature. Accessed 15 Dec. 2024.

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