Upwelling indices for comparative ecosystem studies: Variability in the Benguela Upwelling System

The influence of climate variability on Eastern Boundary Upwelling Ecosystems (EBUEs) is evident through changes in productivity and shifts in species' distributions, yet to date, metrics of upwelling variability appropriate for comparative ecosystem studies have yet to be implemented. Here, we present synoptic-scale upwelling indices to quantify inter-annual to decadal variations in Ekman transport, at temporal and spatial scales relevant to the biota of EBUEs, and apply them to the Benguela Upwelling System (BUS). From 1979 to 2015, interannual, decadal-scale, and unidirectional variability in upwelling was observed, including a significant recent decrease in upwelling in the northern BUS, and a significant increase on the Agulhas Bank. These trends are associated with changes in the number of upwelling days and events in these regions, and correspond to a shift in the meridional positioning of the South Atlantic High pressure system.