The Benguela Niño 1995 observed in Angolan waters

Abstract

During the cruise by R/V ''Dr. Fridtjof Nansen" in February-March 1995, we observed that the upper ocean layers were very warm and brackish. Comparing with a similar cruise performed in 1994, the water temperature was up to 8°C warmer, and the salinity some 5 psu lower. The maximum salinity differences was found at the surface, but the temperature deviations were maximum at typically 30 to 50m depth. The thermocline was found at 20 to 30m greater depths than usual. The horizontal and vertical distribution of the phenomenon is discussed, as well as the time-evolution. We believe this is an Benguela ''Niño", a phenomenon similar to the well known "El Niño" in the Southern Pacific. While the Pacific "El Niño" occurs up to several times per decade, the South Atlantic counterpart has been observed about once per decade. The former ''Niños" were also characterized by warm surface water, but in contrast to Niño-95 the surface salinity have usually been observed to be higher than normal. The Benguela Niños are believed to be caused by warm, saline water advected from north or north-west. The low salinity of the Niño-95 corresponds to an excess off-shore precipitation of the order of 3000 mm above normal. The significance of Benguela Niño-95 as a global climate perturbation is discussed. During the Niño-95 the abundance estimates of three important pelagic species were very low.