Coastal-ocean variability in primary production in the Canary Current upwelling region: comparison among in situ and satellite-derived estimates

Abstract

The Canary Current Eastern Boundary Upwelling Ecosystem (CanC-EBUE), unlike other EBUE, has been unabatedly warming, and decreasing (or at least not increasing) in wind intensity during the last 60 years. However, past trends in net primary production are uncertain, due to differences in the outputs of remote sensing models and the lack of in situ data to validate these models in the region. Here we compare four widely-used models – the Vertically Generalized Production Model (VGPM) and its variant based on Eppley’s description of the growth function (Eppley-VGPM), the Carbon-based Production Model (CbPM), and the Carbon, Absorption and Fluorescence Euphotic-resolving model (CAFE)- with in situ primary production (PP) data. Together with chlorophyll a concentration (Chl a) and phytoplankton biomass (B), we measured PP by 14C and 13C uptake, and oxygen evolution inside incubation bottles, along 11 stations across the transition zone expanding from the coastal upwelling to the open ocean waters at the Cape Verde Frontal Zone (17-23ºN; 16-26ºW). We compared in situ PP, Chl a and B with models’ outputs (NPP) and inputs (satellite derived Chl a and B), respectively. Although carbon and oxygen –based in situ PP estimates were frequently correlated, we found that only the Chl a-based VGPMs were significantly correlated with in situ estimates, yet these are among the the first-described models in the literature. Models based on B, however, did not correlate with in situ PP estimations, in spite that satellite-derived B presented better correlations than Chl a with the in situ data