Project Team Member

LT Scott Boedeker, USN
 
 

Major Findings

• The East Australia current is the Western Boundary Current for the South Pacific Ocean. It originates in the tropics and flows south along the East Coast of Australia to the vicinity of 32deg S where a retroflection occurs and the current turns to the east towards New Zealand. It then flows south along the East Coast of New Zealand. Where the current flows eastward it forms the Tasman Front, separating the Coral and Tasman Seas. Meanders in the current along this front propagate westward as baroclinic Rossby waves until they reach the Australian Coast where they pinch off the retroflection and form a warm core ring.
• These rings, or eddies, when formed have a relatively warm, shallow mixed layer indicative of their source water in the Coral Sea. As these eddies age over the course of a winter in the Tasman Sea their mixed layer will change dramatically. An eddy observed in 1977-78 had an initial mixed layer of 22.7deg C and ~75m depth at formation in March 1977 (equivalent to September in the Northern Hemisphere). By July of the same year the mixed layer had deepened to ~350m depth and cooled to 17.3deg C through heat loss to the atmosphere and entrainment of deeper water. After summer warming, the eddy was observed to have a mixed layer of ~80m and 23.1deg C in February 1978. The eddy had however retained an isothermal layer of 16.2deg C water between 250 and 320m.
• East Australian Current Eddies form at the rate of about two per year. Most are reabsorbed by a Southern excursion of the EAC. If not, they are estimated to last 650 ± 150 days and slowly decay in the Tasman Sea SE of Sydney, Australia or possibly swept away south of Tasmania.

References

Nilsson, C.S., and G.R. Cresswell, 1981: "The Formation and Evolution of East Australia Current Warm-Core Eddies." Prog. Oceanog.., Vol. 9, 133-183.

Cresswell, G.R., and R. Legeckis, 1986: "Eddies off Southeastern Australia." Deep-Sea Res., Vol. 33, 1527-1562.
 

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