Aluminium distributions in Central East Atlantic waters (Canary Islands)

Abstract

DASA-reactive aluminium and nutrients have been determined on a grid located in Central East Atlantic waters (Canary Islands) during early spring. The sample area shows major features of biogeochemical interest, such as elevated aeolian (dust) inputs from the Sahara desert, proximity to upwelling areas (150–200 km) and mesoscale features induced by the effect of the islands on the course of the Canary Current. The aluminium distributions show a marked latitudinal E-W gradient. The low values towards the east are explained by the intrusion of cold waters originated in the upwelling region off northwest Africa, where aluminium is scavenged by organic matter. High values towards the west suggest aeolian inputs that may stretch to below the seasonal thermocline. Nutrients are shown to be inefficient to trace these features, as they are quickly used by biological uptake. The mesoscale circulation south of the islands produces cyclonic and anticyclonic eddies that, respectively, rise and sink the thermocline over 60 m. Aluminium appears to be a useful tracer for this mixing process as well as for the intrusion of cold waters coming from the eastern boundary.