Eddy fluxes of heat and salt from the southwest Indian Ocean into the southeast Atlantic Ocean: A case study

Abstract

Hydrographic data collected during a dedicated research cruise in the Agulhas Retroflection region in February/March 1987 are analyzed in conjunction with Geosat altimetry from December 1986 to December 1988. Estimates of the heat and salt anomalies of eddies and rings observed in this hydrographic survey, are combined with the altimetric tracking of these features to provide insight into and quantification of the climatically important interbasin exchanges occurring in this region. Over the 2‐year period a total of 14 anticyclonic eddies were generated by the Agulhas Current, approximately 50% of these were observed in the satellite altimetry analysis not to migrate farther than 1500 km west or northwest of the Agulhas Retroflection region. Altimetry data show a number of eddies being shed south of the Agulhas Retroflection; all were observed ultimately to move westward rather than southward across the Subtropical Convergence. The estimated net heat fluxes (300 W m−2) and evaporative losses (1 cm day−1) to the atmosphere from eddies within the Agulhas Retroflection region in February–March 1987 were appreciably larger than the austral summer climatological means (25 to 100 W m−2 and 0.6 cm day−1, respectively) for this region. From the combined altimetric and hydrographic analyses, the volume flux of Indian Ocean water warmer than 10°C into the South Atlantic Ocean via the Agulhas eddy field is estimated to be 6.3 Sv (1 Sv = 106 m3 s−1) and 7.3 Sv for water warmer than 8°C. Similarly, estimated fluxes of heat and salt into the Atlantic Ocean via the Agulhas eddy field are 0.045 PW and 78×1012kg per annum, respectively.