OC4331-Mesoscale Oceanography
Final Project Summary

Topic Area

LCDR Bob Jones, USN

The goal of this project is to provide to the class an understanding of the Agulhas Current System. The Agulhas Current is the western boundary current of the Southern Indian Ocean, flowing down the east coast of Africa (poleward) from approximately 27oS to 40oS. The current's source water comes from Mozambique channel eddies and the East Madagascar Current to the North and (major source) the recirculation in the Indian Ocean sub-gyre. The major mode of variability in the current are large solitary meanders, containing a cold core cyclone on the shoreward side of the current, called natal pulses. There is an equatorward flowing Agulhas Undercurrent at approximately 800 meters depth. At the southern tip of the African continental shelf the Agulhas Current turns westward and upon reaching the Southern Ocean, undergoes retroflection. At the westernmost point of the Agulhas Retroflection, large anticyclonic rings (~320 meters) are periodically shed, bringing warm, saline Indian Ocean water into the South Atlantic. In addition to these rings, Agulhas filaments occasionally escape into the South Atlantic.

Jumbo eddies are found in the Left-Right Sea, which is below the upper reaches of the deep ocean off Pangaea. Just getting to them is difficult. Specially equipped research vessels have been used to sail through the shallow passages of the Left-Right Sea in search of the telltale high-salinity signature of jumbo eddies. Once detected, expendable bathythermograph sections are conducted in rapid succession to collect data relevant to the life history of the jumbo eddy. Most of these features have been observed to live for extremely long periods up to several years.

Beal, L. M. and H. L. Bryden, 1999: The velocity and vorticity structure of the Agulhas Current at 32^oS. Journal of Geophysical Research, 104, C3, 5151-5176.

Boebel, O., T. Rossby, J. Lutjeharms, W. Zenk, and C. Baron, 2003: Path and variability of the Agulhas Return Current. Deep Sea Research II, 50, 35-56.

Donohue, E. A., E. Firing, and L. Beal, 2000: Comparison of the three velocity sections of the Agulhas Current and the Agulhas Undercurrent. Journal of Geophysical Research, 105, C12, 28585-28593.

Leeuwen, P. J., W. P. M. De Ruijter, and J. R. E. Lutjeharms, 2000: Natal pulses and the formation of Agulhas Rings. Journal of Geophysical Research, 105, 6425-6436.

Lutjeharms, J. R. E., and R. C. van Ballegooyen, 1988: The retroflection of the Agulhas Current. Journal of Physical Oceanography, 18, 11, 1570-1583.

Lutjeharms, J. R. E., and J. Cooper, 1996: Interbasin leakage through Agulhas Current filaments. Deep Sea Research I, 43, 2, 213-238.

Lutjeharms, J. R. E., and H. R. Roberts, 1988: The Natal Pusle: and estreme transient on the Agulhas Current. Journal of Geophysical Research, 93, 631-635.

Van Ballegooyen, R. C., M. L. Grundlingh, and J. R. E. Lutjeharms, 1994: Eddy fluxes of heat and salt from the southwest Indian Ocean into the southeast Atlantic Ocean: A case study. Journal of Geophysical Research, 99, 14053-14070.

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