Differences in coastal and oceanic SST trends due to the strengthening of coastal upwelling along the Benguela current system

Abstract

Coastal and oceanic sea surface temperature (SST) trends were analyzed in the Benguela upwelling ecosystem from the seventies on. Monthly SST data were obtained from the UK Meteorological Office, Hadley Center at two transects in front of the Namibia coast and the western coast of South Africa. A positive SST trend (0.06 °C dec−1) is observed at open sea locations and a negative one (−0.13 °C dec−1) near shore. The observed negative ΔSST (SSTcoast−SSTocean) trend (−0.18 °C dec−1) is linked to the strengthening of upwelling (87 m3 s−1 km−1 dec−1) during the same period. For this purpose, Ekman transport was directly obtained from the Pacific Fisheries Environmental Laboratory in the area under study and calculated from reanalysis wind data from NCEP/NCAR at six locations in front of the Namibia coast and the western coast of South Africa. This coastal upwelling enhancement is in good agreement with changes in the intensity and location of the South Atlantic High, which are also reflected in the Southern Annular Mode (SAM) index.