The Weddell Gyre is one of the two gyres that exist within the

Southern Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-small ...

. The gyre is formed by interactions between the

Antarctic Circumpolar Current The Antarctic Circumpolar Current (ACC) is an ocean current that flows clockwise (as seen from the South Pole) from west to east around Antarctica. An alternative name for the ACC is the West Wind Drift. The ACC is the dominant circulation feat ...

(ACC) and the

Antarctic Continental Shelf The Antarctic continental shelf is a submerged piece of the Antarctic continent that underlies a portion of the Southern Ocean — the ocean which surrounds Antarctica. The shelf is generally narrow and unusually deep, its edge lying at depths aver ...

. The gyre is located in the

Weddell Sea The Weddell Sea is part of the Southern Ocean and contains the Weddell Gyre. Its land boundaries are defined by the bay formed from the coasts of Coats Land and the Antarctic Peninsula. The easternmost point is Cape Norvegia at Princess Martha ...

, and rotates clockwise. South of the ACC and spreading northeast from the

Antarctic Peninsula The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martín in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctic ...

, the gyre is an extended large cyclone. Where the northeastern end ends at 30°E, which is marked by the southward turn of the ACC, the northern part of the gyre spreads over the Southern

Scotia Sea The Scotia Sea is a sea located at the northern edge of the Southern Ocean at its boundary with the South Atlantic Ocean. It is bounded on the west by the Drake Passage and on the north, east, and south by the Scotia Arc, an undersea ridge and i ...

and goes northward to the South Sandwich Arc. Axis of the gyre is over the southern flanks of the South Scotia, America-Antarctic, and Southwest Indian Ridges. In the southern part of the gyre, the westward return flow is about 66

sverdrup In oceanography, the sverdrup (symbol: Sv) is a non- SI metric unit of volumetric flow rate, with equal to . It is equivalent to the SI derived unit cubic hectometer per second (symbol: hm3/s or hm3⋅s−1): 1 Sv is equal to 1 hm3/s. It is used ...

(Sv), while in the northern rim current, there is an eastward flow of 61Sv.

Physical oceanography

Due to the

Coriolis force In physics, the Coriolis force is an inertial or fictitious force that acts on objects in motion within a frame of reference that rotates with respect to an inertial frame. In a reference frame with clockwise rotation, the force acts to the ...

acting to the left in the Southern Hemisphere and the resulting

Ekman transport Ekman transport is part of Ekman motion theory, first investigated in 1902 by Vagn Walfrid Ekman. Winds are the main source of energy for ocean circulation, and Ekman Transport is a component of wind-driven ocean current. Ekman transport occurs w ...

away from the centers of the gyre, these regions are very productive due to upwelling of cold, nutrient rich water. Strong upwelling in the gyre is shown where the deep-water isotherms curve upwards. The Weddell front, which is identical to the Southern Antarctic Circumpolar Current Front, separates the Weddell gyre from the Antarctic Circumpolar Current. The flow is cyclonic, although the cavity flow is anticyclonic. This is because the new dense shelf ocean waters come in from the west, then modify under the Ronne Ice Shelf, then evolving in the east with colder and fresher water. The Weddell Sea Bottom Water gets its dense shelf water from the outflow of the east from under the Filchner Ice Shelf. In the northern part of the gyre, shelf water influence is traced continuously at 22°E from the top of the Antarctic Peninsula. To the north of the gyre, the ridge system confines the

Weddell Sea Bottom Water Weddell Sea Bottom Water (WSBW) is a subset of Antarctic Bottom Water (AABW) that is at a temperature of -0.7 °C or colder. It consists of a higher salinity branch and a lower salinity branch. It originates in the Weddell Sea and closely fol ...

formation in the western continental margins with the Weddell Abyssal Plain. Some of the bottom water spreads through a gap to fill the

South Sandwich Trench The South Sandwich Trench is a deep volcanic arc, arcuate ocean trench, trench in the South Atlantic Ocean lying to the east of the South Sandwich Islands. It is the deepest oceanic trench, trench of the Southern Atlantic Ocean, and the second d ...

. Because of upwelling the new Weddell Sea Bottom Water turns clockwise west of 20°W and are a mixture of shelf water and a part of the Circumpolar Deep Water that follows the southern part of the gyre to the west. East, another part of the Circumpolar Deep Water mixes with shelf water and may establish a particular source of Weddell Sea Deep Water. In the Weddell Sea Deep Water, there is a 2 gyre cyclonic system inferred and is able to spill over the South Scotia Ridge. Overlying circumpolar Deep Water of Antarctic Circumpolar Current and the Weddell Sea Deep Water mix and can be traced back to the Weddell Abyssal Plain revealing the western gyre. Geographically speaking, the Antarctic Peninsula contains the western end of the gyre. In these bottom and deep layers of the gyre, it is completed by a southward movement. where the currents at the bottom of the gyre flow in an opposite direction than the water column above. At the eastern and western sides of the basin, the transect circulation pattern is controlled by stable boundary currents, which are warm, deep, narrow and fast flowing currents forming on either the east or west side of ocean basins. These currents are several hundred kilometers in width and provide 90% of volume transport of the gyre. This equals out to 29.5Sv. The intensity of the boundary currents are controlled by the seasonal fluctuations, but the time-scale, days to weeks dominates the interior. The Antarctic divergence is the boundary region between the east and west winds. This location is between 65 and 70°S.

References

{{Ocean Geography of the Southern Ocean Filchner-Ronne Ice Shelf Oceanic gyres

Physical oceanography

See also

References