Open AccessAgulhas Current Influence on the Shelf Dynamics of the KwaZulu-Natal Bight
Author(s) -
Tarron Lamont,
M.A. van den Berg,
Raymond G Barlow
Publication year - 2016
Publication title -
journal of physical oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.706
H-Index - 143
eISSN - 1520-0485
pISSN - 0022-3670
DOI - 10.1175/jpo-d-15-0152.1
Subject(s) - oceanography , hydrography , geology , geostrophic wind , ekman transport , geostrophic current , submarine pipeline , current (fluid) , temperature salinity diagrams , stratification (seeds) , salinity , water mass , boundary current , mixed layer , eddy , outflow , ocean current , climatology , thermohaline circulation , continental shelf , upwelling , geography , meteorology , seed dormancy , botany , germination , turbulence , dormancy , biology
The Agulhas Current is a fast western boundary current flowing along the South African east coast, strongly influencing oceanographic variability on the adjacent KwaZulu-Natal shelf. Hydrographic observations in January 2010, July 2010, and July 1989 have been used to describe variations in geostrophic currents and water masses and to elucidate mechanisms of change in circulation and thermohaline structure. Differences in wind forcing, precipitation, and solar insolation caused modifications in stratification and mixing that resulted in seasonal changes in surface temperature, salinity, and mixed layer depth Z MLD between the austral summer and winter surveys. During January 2010, surface temperatures were elevated and there was a large range in salinity as the upper 10 m was influenced by river outflow and rainfall. In July 2010 and 1989, surface temperatures were lower and the salinity range was significantly less. The Z MLD in January 2010 was much shallower, varying between 5 and 40 m, while deeper Z MLD , from 9 to 107 m, was found in July 2010 and 1989. Cross-shelf, alongshore, and vertical variations in water masses during July 2010 and July 1989 were driven by deviations in the position of the inshore edge of the Agulhas Current and the influence of offshore cyclonic eddies. In January 2010, the close proximity of the current to the coast and shelf break caused increased Ekman veering in the bottom layers along the shelf edge and slope in the north and recirculation in the south.