Amundsen Basin

Amundsen Basin lies in the Arctic Ocean between Lomonosov and Gakkel ridges (see the bathymetric map in Arctic Ocean). Named in honor of Norwegian polar traveler and investigator Roald Amundsen, it is also called Fram Basin according to some sources. The Amundsen and Nansen basins, separated by the Gakkel Ridge, together are often referred to as the Eurasian Basin. Knowledge about the basin structure and about the deep structure of the whole of the Arctic Basin is based on observations from more than 30 years of drifting ice stations such as North Pole 1, and high-latitude air expeditions. Seismic refraction results from the drifting ice stations characterized the main regions and structures of the deep Arctic Basin, including Amundsen Basin. In spring 1979, an ice camp Fram-1 carried out further seismic studies above Amundsen Basin. In the 1980s and 1990s, further geophysical investigations were conducted on the icebreakers Polarstern (Germany) and Oden (Sweden), and the submarine SCICEX.

Amundsen Basin is a deep, linear basin with a length of about 2000 km and a width of 200-400 km. The basin floor is almost flat, at an average depth of about 4300 m. Due to an increased thickness of sediments in the Nansen Basin (which is closer to a sediment source, the Barents Sea shelf), its depth is 500 m less than the Amundsen Basin everywhere.

At the border of the Amundsen Basin with the continental margins of Eurasia, the continental shelf is represented by a gently sloping inclined plain. At the opposite end, in the region of the Greenland and Eurasian (Svalbard archipelago) continental margins, the shelf is developed in a relatively narrow strip (up to 50 km) at depths from 3800 to 4200 m. Low-frequency relief characterizes the eastern part of the basin, and higher frequency relief describes the western part of the basin and Gakkel Ridge, which rises rapidly from the abyssal plain. The slope of Lomonosov Ridge in Amundsen Basin has a stepped profile, complicated by numerous terraces at depths from 2200 to 3200 m, with valleys of up to 600 m relative depth.

Crustal structure in the basin is determined by its age, the oldest sediments furthest from Gakkel Ridge being about 60 million years old. In the eastern part of Amundsen Basin, the basement structures beneath the sediments appear to have a highly irregular relief. In the west part, such a phenomenon is not observed. The bottom of the basin is covered by loose sediments (mainly silts or clay) and sedimentary rocks reaching a thickness of not less than 2000 m, the thickness of sediment decreasing toward Gakkel Ridge. The thickness of oceanic crust in the basin as measured by seismic refraction experiments is 5-6° km in the center. Magnetic anomalies in Amundsen Basin are low gradient and linear, following the typical oceanic type magnetic field of the spreading Gakkel Ridge. The crustal structure of Amundsen Basin has much in common with the crustal structure of the western part of the abyssal valley of Iberia according to dynamics of the wave field and irregularity of its basement.

Water circulation in Amundsen Basin is determined by the inflow of Atlantic waters. Circulation of surface waters, as in the Arctic Ocean in general, is determined by surplus fresh-water balance, atmospheric circulation, and basin topography. The warm waters of Atlantic origin, because of their high salinity, are denser than the surface fresh waters, and thus descend deep into the basin and cannot play a significant role in the circulation of surface waters. Water of Atlantic origin enters the basin through the eastern part of Fram Strait with the West Spitsbergen current. It flows round the Arctic basins in boundary currents, flowing eastward along the Eurasian continental slope. One branch turns north to flow along the Lomonosov Ridge inside the Amundsen Basin, returning to the North European basin through

Fram Strait, leaving the Arctic Ocean. Another branch crosses the Lomonosov Ridge and penetrates into Amerasian Basin, before recrossing the Lomosonov Ridge to return to the Fram Strait. Cold bottom waters at depths of about 2000-3000 m, which enter the basin from the Barents Sea North European basin, move very slowly. This, together with insignificant horizontal and vertical thermohaline gradients, makes it difficult to track the circulation of these waters.

Valery Mit'ko See also Lomonosov Ridge; Nansen Basin

Further Reading

Gorbatskiy, G.V., Physicogeographical Zoning of Arctic, Volume 3, Arctic Basin, Leningrad: Leningrad University Publishing House, 1973 Gramberg, I.S. (editor), Orographic Map of Arctic Basin.

1:5,000,000, Helsinki: Karttaneskus, 1995 Gramberg, I.S. & G.D. Naryshkin, Peculiarities of the Arctic Deep-Water Basin's Ground. SPb, VNII Okenologiya, 2000 Sweeney, J.F., J.R. Weber & S.M. Blasco,"Continental ridges in the Arctic Ocean: Lorex constraints." Tectonophysics, 89 (1982): 217-238 Weigelt, E. & W. Jokat, "Peculiarities of roughness and thickness of oceanic crust in the Eurasian Basin, Arctic Ocean." Geophysical Journal International, 145 (2001): 505-516

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