the arctic ocean is one of the Earth's environments that will be most affected by climate change. As the Earth continues to warm, the Arctic Ocean will evolve into an environment that is much different from what is recognized today. Most of the animals currently living there will not be able to survive if this region warms too much. In addition, warming Arctic waters could affect ocean circulation elsewhere in the world.
The Arctic Ocean is unique in its physical properties. It has both the narrowest and the widest shelves on Earth due to glacial erosion, marine abrasion, and progradational clastics. It is a tectonically active region in which the closed-off basin of today developed in the Cretaceous (90 million years ago). The seafloor forming at the mid-ocean ridge in the Arctic is the slowest ridge system of any on Earth today.
The Lomonosov Ridge divides the ocean in half, creating the younger and deeper Eurasian (Eastern) basin and the older and larger Amerasian (Western) basin. The Amerasian Basin is divided by the Alpha Ridge into the Makarov Basin to the north, and the Canadian Basin to the south. The Alpha Ridge connects to the Mendeleev Ridge to the north. The Arctic Ocean is approximately 50 percent continental shelf, resulting in much of the sea floor being only 1,640-6,562 ft. (500-2,000 m.) below sea level.
The Arctic Ocean is the most extreme region on Earth in terms of climate and seasonality because of light and ice cover. The ocean covers an area of approximately 14,056,000 km2 and extends below the Arctic Circle in some locations. The average depth is just over 3,280 ft. (1,000 m.), with the deepest location in the Eurasian Basin at 17,881 ft. (5,450 m.) The Arctic Ocean is surrounded on all sides by land except for narrow connections to the Atlantic and Pacific Oceans. The Atlantic water flows through the Fram Strait (8,530 ft. [2,600 m.] deep), where the largest amount of water flows into the Arctic. The other is from the Pacific Ocean through the Bering Strait, a shallow connection (164 ft. [50 m.]) that has intermittently closed during glacial periods over the past few million years.
The Arctic water column is strongly stratified into three layers: the shallow, relatively fresh surface layer; the intermediate layer; and the deep salty layer. The shallow layer obtains its water predominantly from melting ice sheets, icebergs, and river runoff. Because of its low density, this layer, approximately 9.8 ft. (3 m.) deep, creates a relatively fresh water film that easily freezes. It is because of this film and the freezing temperatures that the center of the Arctic Ocean is frozen year-round. The intermediate layer receives its water from the salty waters of the North Atlantic. The deep water forms through convection and has a very slow exchange with a residence time of 450-500 years (about half that of the world ocean residence time of 1,000 years).
Large amounts of freshwater come from rivers, specifically from the Russian rivers Yenisei, Ob, and Lena, and the Canadian MacKenzie River. Together, these rivers contribute 2,000 km.3 a year of water. This influx of freshwater into an environment that is so cold creates a film of water on the surface because of the density difference and hence freezes solid. During the winter, there is 14x106 km.2 of sea ice, and about half of that in the summer. This number has decreased over the past several years, causing detrimental effects on the climate and resident species. The ice is critical for the heat exchange budget in the Arctic, as well as for sustaining life, from viruses, to polar bears, and subsistence hunters.
Because ice forms and leaves behind salt, during glacial periods the water is more saline due to an increased volume of sea ice. As the ice melts during interglacial periods, the surface layer becomes increasingly fresh, creating a deeper film of fresh water that does not mix with the rest of the water column. During this warmer period, there is more productivity in the surface layer, which allows more food and nutrients to sink to the bottom. It is this relationship between the surface layers and the deep sea that is recorded in the fossil record. The dominant surface productivity is from the phytoplankton that thrive in the summers due to 24 hours of light, and struggle to survive during the winter when there is 24-hour darkness.
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