Local and mesoscale influences on nutrient variability in the northwest African upwelling region near Cabo Corbeiro

Abstract

Abstract During the JOINT-1 experiment nutrient concentrations were routinely determined in a portion of the northwest African upwelling system near Cabo Corbeiro. Analysis of the nitrate and ammonia distributions reveals that much of the nutrient variability can be related to data obtained within this region without reference to large-scale processes. There was a clear relationship between nutrient variations and the local wind. Some of the remaining variability could be related to temporal changes in primary production, to variations in the cross-shelf flow, and to the interaction of the advective field with a longshore nutrient gradient. Mesoscale observations made it possible to explain the occurence of anomalously high ammonia concentrations over the inner shelf. There may have been a net transport of organic material into this region, and high nearshore turbidities reduced primary production rates. These factors apparently enabled community catabolism to produce ammonia faster than it could be consumed.