The Agulhas Current system is a vital part of the global thermohaline circulation. This global thermohaline overturning of the oceans has in turn an inextricable link to world climate. Although this current is so important, relatively little is known on its sources. One of these proposed sources of the Agulhas Current is the southern limb of the East Madagascar Current (EMC). Previously the EMC was primarily studied through the use of drifters, remote sensing and ships' drift methods. In an attempt to increase the understanding of this possible source region a first dedicated cruise was organised for the southern termination of the EMC. The cruise took place in March 2001. The hydrographic and other data from the cruise have the potential to describe the EMC termination in a seminal way. The EMC is shown to consist of Tropical Surface Water, Subtropical Surface Water and South Indian Central Water. In the region of the EMC Antarctic Intermediate Water, North Indian Deep Water and North Atlantic Deep Water/Circumpolar Deep Water were found. There is clear evidence of the presence of Red Sea Intermediate Water with salinities greater than 34.5 psu at temperatures between 4 and 6.5°C from 800-1250 m, inshore of the EMC. The width of the current during the cruise period was 100 km, the maximum speed of the current was 1.1 m/s and the depth of the current was 1000 m. The maximum transport of the EMC was calculated to be 39.3 Sv. An EMC undercurrent was found with a depth range of 1000-2000 m. The maximum speed of the undercurrent was seen to be 0.3 mis and the transport of the undercurrent was 0.8 Sv. No retroflection of the EMC emerges from this data set. Satellite geostrophics over a period of 13 years give evidence of eastward flow being associated with eddies in the region of the EMC termination. References have suggested that such eddies may give the appearance of a retroflection. From the observations there was ample evidence for the presence of a relatively weak upwelling cell inshore of the EMC. The temperature at the surface of the upwelling cell was 26°C (2 degrees less than the surrounding water) and the chlorophyll concentration was 0.63 mg Chl-a/m3 . Nitrate concentration was 6.4 µmol/kg at 100 m, phosphate 0.53 µmol/kg, silicate 5.69 µmol/kg and oxygen was 107.5 µmol/kg. At 45 km from the coast there was an average movement of water offshore down to a depth of 40 m. The maximum speed of the offshore flow was 0.5 m/s.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uct/oai:localhost:11427/38280 |
| Date | 21 August 2023 |
| Creators | Webb, Adrian Myles |
| Contributors | Lutjeharms, Johann |
| Publisher | Faculty of Science, Department of Oceanography |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Master Thesis, Masters, MSc |
| Format | application/pdf |
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