Variability in upwelling along the Pacific shelf of Panamá and implications for the distribution of nutrients and chlorophyll

Abstract

Seasonal dynamics of dissolved inorganic nutrients (NO3-, PO43-, and Si(OH)4) and chlorophyll a were investigated in the Pacific shelf of Panama. The shelf is divided into two large semi-open areas, namely the non-upwelling Gulf of Chiriquí and the upwelling Gulf of Panama. Four research cruises sampled the water column in cross-shelf transects during wet and dry seasons at each region. Hydrological measures varied spatially between regions and also varied temporally on a seasonal basis. Low concentrations of NO3- (0.5 mg m-3) typically developed close to the usually shallow thermocline during non-upwelling conditions. We found no evidence of significant nutrient input from freshwater runoff. The position of the thermocline is considered to be the main source of nutrients to the euphotic zone in both regions.