Primary productivity in the northern Canary Islands region as inferred from SeaWiFS imagery

A 19-month record from September 1997 to March 1999 is presented of the productivity gradient at 3 stations that fall along a quasi-zonal 29°N transect through the Canary Islands using the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) chlorophyll data and the primary production method of Antoine and Morel (Global Biogeochem. Cycles 10(1) (1996) 43). These stations correspond to 3 fixed sediments traps positioned during the same period east of the island of Fuerteventura (Eastern Boundary Current, EBC) and north of the islands of Gran Canaria (European Station for Time-Series in the Ocean, Canary Islands, ESTOC) and La Palma (LP). The mean annual productivity during the 19-month period was observed to decrease steeply westwards along the quasi-zonal 29°N transect, from 237 g C m-2 yr-1 at EBC to 164 and 145 g C m-2 yr-1 at ESTOC and LP, respectively. The high productivity at EBC indicates that this station is strongly influenced by the seasonal coastal upwelling off the adjacent Moroccan coast. This is confirmed by SeaWiFS chlorophyll images showing incursions of the Cape Yubi filament over the EBC station in March, July and October 1998 and January 1999, coincident with a decrease in sea-surface temperature (SST) of up to 1.5°C as observed by satellite. In comparison it was observed that although some cooler upwelled water does reach the ESTOC and LP stations in summer 1997 and summer/autumn 1998, there was no corresponding increase in productivity, indicating that the water was nutrient depleted. It is concluded that the ESTOC and LP stations are more characteristic of oligotrophic ocean, with minimal influence of coastal upwelling in near-surface waters. Comparison of SeaWiFS chlorophyll values with in situ data at the ESTOC station show that in the SeaWiFS generally provided good-quality data (within the ±35\% accuracy goal targeted for this instrument) for the Canary Island region except for period December 1997-April 1998. Comparison of model productivity estimates with in situ 14C uptake measurements shows good agreement for oligotrophic water, but model usage in upwelling regions, in particular filaments, may be problematic. This investigation suggests that the application of the Antoine and Morel model with a limited dataset of satellite images can provide a good insight into relative primary production in the Canary Islands region.