User:Plutieye/Ross Gyre

The Ross Gyre is one of the two gyres that exists within the Southern Ocean around Antarctica, the other being the Weddell Gyre. The Ross Gyre is located north of the Ross Sea, and rotates clockwise. The gyre is formed by interactions between the Antarctic Circumpolar Current and the Antarctic Continental Shelf.

Geographic Boundaries
The Ross Gyre is a clockwise-rotating water mass that lies north of the Ross Sea. This gyre is bounded to the north by the Polar Front of the Antarctic Circumpolar Current (ACC) and Pacific-Antarctic Ridge bathymetry, and to the south by the Antarctic Slope Current (ASC) and the Antarctic continental shelf. The gyre is located between 160°E and 140°W with the eastern boundary associated with the eastern extension of the Pacific-Antarctic Ridge, but is highly variable. The Ross Gyre is bounded to the west by the presence of another gyre, the Balleny Gyre, associated with the Balleny Fracture Zone. The northeast boundary of the Ross Gyre expands and contracts semiannually due to reduced sea surface height (SSH) north of the gyre following deepening of the Amundsen Sea Low (ASL) to the east. The gyre is largest in area in May and November, and lowest following winter and in summer. The center of the gyre is located between 164°W, 68°S, and 150°W, 63°S, depending on 100/500m or 1500/3000m steric anomaly height maps, respectively.

Formation Processes
Physical formation processes for the Ross Gyre remain unclear and difficult to study, but current theories attribute wind forcing and zonal momentum conservation balanced by vorticity gradients and bottom frictional forces to its formation. Prevailing polar westerlies create an eastern flowing ACC that is balanced by the topography of the seafloor that drives this formation. The eastern boundary is closely linked to where the ACC crosses the Pacific-Antarctic Ridge, at the Udintsev Fracture Zone, with a southward deflection to conserve vorticity. Other theories of Southern Ocean gyre formation from blocked geostrophic flows on a western landmass have been challenged, as the Ross Gyre forms without any geostrophic contours being blocked. However, modeling simulations underline the importance of the northern ridge system in strengthening subpolar gyre circulation and shaping the stratification of the region.

Heat Exchange
The Ross Gyre plays an important role in exchanging polar water masses and heat in Antarctica, connecting the ACC to the Antarctic shelf. The undefined eastern boundary of the gyre entrains relatively warm Circumpolar Deep Water (CDW) that is transferred to the continental shelf and the Bellingshausen and Amundson Seas, which can effect sea ice melting rates. Eddy formation through gaps in the Pacific-Antarctic Ridge are hypothesized to facilitate this transport between the Antarctic Circumpolar Current and the Ross Gyre. The western limb of the gyre mediates the transfer of cold meltwater and newly formed Antarctic Bottom Water (AABW) originating in the Ross Sea towards the abyssal ocean. The presence of cold surface waters and warmer intermediate waters forms a double diffusive staircase within the Ross Gyre; this feature limits vertical heat exchange, and allows the development of ice in the gyre's center. It is estimated that the circulation of the Ross Gyre exports 20 ± 5 Sverdrup.