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Abstract
The Agulhas Current system contains one of the world's strongest western boundary currents, and plays an important part in the warm water path of the global thermohaline circulation. However, there have been few surveys of the source regions of the Agulhas Current, and thus little in situ measurement of their variability. Utilizing the more than 5-year record of SeaWiFS data, we examine the eddy activity present in the southern portion of the Mozambique Channel. The two sources of Agulhas input from the central Indian Ocean (southward flow through the Mozambique Channel and westward flow around the southern limit of Madagascar) both show great temporal variability, with no clear seasonal signal. A number of large (∼200 km diameter) anticyclonic rings intermittently propagate poleward along the western edge of the channel, sweeping coastal waters into mid-channel. Their passage past Maputo appears to affect the circulation of the lee eddy in the Delagoa Bight. The eastern side of the channel is mainly characterized by cyclonic eddies. These are made manifest in the lee of the southern tip of Madagascar, although it is not clear whether many form there or just develop a visible presence due to entrainment of high-chlorophyll coastal waters. Several of these cyclonic eddies then appear to move in west-southwesterly direction. The chlorophyll data do reveal the apparent East Madagascar Retroflection on occasions, but do not show clear examples of the pinching off of anticyclonic eddies. However, surface waters from the East Madagascar Current may reach the African mainland on occasions when no retroflection is present.
Highlights
The southern end of the Mozambique Channel is the source region for the incipient Agulhas Current, the strongest western boundary current in the southern hemisphere
To overcome some of the sharper temporal changes in chlorophyll, and especially the occasional patches of cloud, the images in the animation have had further spatial and temporal smoothing applied. (We used a simple 3-point [0.25 0.5 0.25] smoothing filter in both spatial dimensions and in time.) The animation makes it easier to follow the evolution of some events, which are otherwise portrayed as a series of staccato scenes
We focus on selected features in turn, and discuss them with respect to other observations, such as those from hydrographic surveys and satellite sea surface temperature (SST) measurements
Summary
The southern end of the Mozambique Channel is the source region for the incipient Agulhas Current, the strongest western boundary current in the southern hemisphere. Contributions are believed to come southward through the Mozambique Channel and westward from the East Madagascar Current (EMC) and to involve recirculation within a gyre in the southwest of the Indian Ocean (Stramma and Lutjeharms, 1997). As there have been few hydrographic surveys in this region, there are few estimates of the mean transport from these sources, let alone reliable bounds on their variability, either short term or interannual.
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