Visualising physical oceanography
The image above shows the altimetry of the sea surface in the region surrounding the Kerguelen Islands (approximately in the centre of the image) and the Heard and McDonald islands (to the south-west). (The region shown covers 50°E—100°E and 60°S—30°S.)
The topography of the surface represents the sea surface height anomaly (data from AVISO). The vertical scale of the surface has been greatly exaggerated. The colours represent the sea surface temperature anomaly (data from NOAA), such that blue indicates surface water that is colder than normal, and red indicates warmer. The arrows represent the surface geostrophic current flow (data also from AVISO).
The topography shows a series of eddies to the north of the Kerguelen Islands. These eddies are created where the Antarctic Circumpolar Current crosses the South-West Indian Ridge, to the west of the region shown here (Nel et al. 2001).
In the southern hemisphere, the Coriolis force causes water to diverge from the centre of a clockwise-rotating eddy, causing a negative sea surface height anomaly. This divergence allows the colder subsurface water to upwell, and so we can see cold sea surface temperature anomalies associated with these eddies.
Mesoscale eddies can form "hotspots" of biological productivity and higher predators such as seabirds and seals have been observed to forage in their vicinities (e.g. Campagna et al. 2006, Nel et al. 2001).
References
- Campagna, C. et al. (2006) Southern elephant seal trajectories, fronts and eddies in the Brazil/Malvinas Confluence. Deep-sea research I 53(12):1907—1924.
- Nel, D.C. et al. (2001) Exploitation of mesoscale oceanographic features by grey-headed albatross Thalassarche chrysostoma in the southern Indian Ocean. Marine Ecology Progress Series 217:15—26. PDF from MEPS
