Modes of upwelling variability in the Benguela Current System and how they relate to ecosystem productivity
Marisol Garcia Reyes1, Tarron Lamont2, Steven James Bograd3, Bryan Black4, Robert J.M. Crawford5, Carl Van Der Lingen6, Sarah Ann Thompson1, Ryan R Rykaczewski7 and William J Sydeman8, (1)Farallon Institute, Petaluma, CA, United States, (2)Department of Environmental Affairs, Oceans & Coasts Research Branch, Cape Town 8012, South Africa, (3)NOAA Southwest Fisheries Science Center, Environmental Research Division, Monterey, CA, United States, (4)University of Texas at Austin, Austin, TX, United States, (5)Department of Environmental Affairs, South Africa, (6)Department of Agriculture, Forestry and Fisheries, South Africa, (7)University of South Carolina, Columbia, SC, United States, (8)Farallon Institute for Advanced Ecosystem Research, Petaluma, CA, United States
Abstract:
In the central California Current, coastal upwelling varies in two independent seasonal modes with contrasting atmospheric drivers, frequencies of variability, and influences on the marine ecosystem. Summer upwelling is most intense, supplies the large amount of nutrient required for the ecosystem during this productive season, and has relatively low interannual variability but with an increasing trend in mean over the latter 20
th. In contrast, winter upwelling has greater interannual variability and correspondingly greater impacts on variability in ecosystem productivity.
In this work, we consider if upwelling modes such as these and their differential biological impacts occur in other Eastern Boundary Upwelling Systems, particularly, the Benguela Current along the west coast of Africa. We analyzed upwelling (Ekman transport calculated from alongshore wind) and sea surface temperature data from the northern and southern Benguela, as well as the South Coast of South Africa, and calculated modes of variability through a principal component analysis. We identified two modes of upwelling variability: one during the summer season and another in winter, resembling the modes found in the California Current. The summer mode shows a trend towards more intense upwelling in the southern Benguela region (western coast) since the early 90’s. This shift in environmental conditions might help explain some of the observed disturbances of fish and seabirds as well as trends and southern redistribution of fish and lobster catches.
