Coastal oceanic climate change and variability from 1982 to 2009 around South Africa
DOI: 10.2989/1814232X.2010.501563
Title: Coastal oceanic climate change and variability from 1982 to 2009 around South Africa
Journal Title: African Journal of Marine Science
Volume: Volume 32
Issue: Issue 2
Publication Date: November 2010
Start Page: 237
End Page: 246
Published online: 8 Nov 2010
ISSN: 1814-232X
Author: M Rouaulta, B Pohlb & P Penvenc
Affiliations:
a Department of Oceanography, Marine Research Institute , University of Cape Town , Rondebosch, 7701, South Africa
b Centre de Recherches de Climatologie , CNRS/Université de Bourgogne , 6 boulevard Gabriel, 21000, Dijon, France
c Laboratoire de Physique des Oceans , UBO, IRD and IFREMER, 29280, Plouzané, France
Abstract: Changes and fluctuations in sea surface temperature (SST) around the South African coast are analysed at a monthly scale from 1982 to 2009. There is a statistically significant negative trend of up to 0.5 °C per decade in the southern Benguela from January to August, and a cooling trend of lesser magnitude along the South Coast and in the Port Elizabeth/Port Alfred region from May to August. The cooling is due to an increase in upwelling-favourable south-easterly and easterly winds. There is a positive trend in SST of up to 0.55 °C per decade in most parts of the Agulhas Current system during all months of the year, except for KwaZulu-Natal where warming is in summer. The warming was attributed to an intensification of the Agulhas Current in response to a poleward shift of westerly winds and an increase in trade winds in the South Indian Ocean at relevant latitudes. This intensification of the Agulhas Current could also have contributed to the Coastal cooling in the Port Alfred dynamic upwelling region. The El Ni?o Southern Oscillation (ENSO) is significantly positively correlated at a 95% level with the southern Benguela and South Coast from February to May, and negatively correlated with the Agulhas Current system south of 36° S. The correlation with the Antarctic Annular Oscillation is weaker and less coherent. El Ni?o suppresses upwelling along the coast, whereas La Ni?a increases it. Although there does not seem to be a linear relationship between the strength of the ENSO and the magnitude of Coastal SST perturbation, El Ni?o and La Ni?a appear to be linked to major warm and cool events, respectively, at a seasonal scale in summer in the southern Benguela and along the South Coast. However, care must be taken in interpreting low-resolution reanalysed climate data (ERA40 and NCEP) and optimally interpolated Reynolds SST, such as used here.
Accepted: 1 Apr 2010

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