Super ocean current pathway discovered: Tasman Outflow

By William Atkins
Thursday, 16 August 2007 21:16

Science - Climate

A major underwater current called the Tasman Outflow has been discovered by Australian scientists. It helps to regulate the Earth’s climate by providing water flow between three oceans in the southern hemisphere.

Two scientists, K. R. (Ken) Ridgway and J. R. (Jeff) Dunn, both from the Commonwealth Scientific and Industrial Research Organization (CSIRO), collected information and data that has been accumulating for over fifty years from satellites, ships, and various ocean monitors that have been making observations between the latitude of 60 degrees south and the equator.

They found a large and deep ocean pathway, what is called a supergyre, which connects smaller water pathways (gyres) in the southern hemisphere between the Indian, Pacific, and Atlantic Oceans. The Tasman Outflow travels south of Australia, dips further south past Tasmania, and then flows north along Australia’s eastern coast. It occurs at an average depth of about 0.5 to 0.6 miles (800 to 1,000 meters) below the surface of the water.

The abstract of their paper states: “A high-resolution hydrographic atlas resolves the narrow boundary flow of the western Pacific gyre and its pathway around Tasmania, southern Australia and into the Indian Ocean basin. This confirms recent model descriptions of a Southern Hemisphere ‘supergyre’, a nested system of subtropical gyres. The observations show that the gyre flow is squeezed into a narrow band between Tasmania and the Antarctic Circumpolar Current. The residue of East Australian Current transport turns westward around Tasmania and ‘leaks’ into the Indian Ocean. While there is also a limited form of gyre connection between the Indian and Atlantic systems south of Africa, with a mean outflow of Agulhas Current water into the Atlantic basin, these gyre circulations remain far more discrete. The gyre coupling and the East Australian Current in particular, provide the mechanism by which Sub Antarctic Mode Water and Antarctic Intermediate Water are distributed between the ocean basins.”

The water within an ocean moves in pockets of counterclockwise motion, forming pathways (or gyres) that provide passageways for ocean life and nutrients. For the global climate, such gyres help to transfer heat from the hot tropical areas to the cold polar regions. Earlier, it was thought that these gyres were connected to one another, however, no proof had yet been found. The research performed by both researchers shows definitive proof about how these gyres are connected by a supergyre, the Tasman Outflow.

The article (“Observational evidence for a Southern Hemisphere oceanic supergyre”), which describes the discovery of the Tasman Outflow, appears in Geophysical Research Letters (volume 34, L13612).