Interrelationships among primary production, chlorophyll, and environmental conditions in frontal regions of the western Mediterranean Sea

In May 1986, we investigated processes contributing to the unique characteristics of oceanic fronts in the western Mediterranean Sea. Simulated in situ measurements of 14C-based primary production were made in conjunction with precise chemical, physical and optical analyses coordinated with remote sensing. Eight transects consisting of 4–7 vertical stations were made across density fronts associated with the Almeria Gyre and the Algerian Current. A model was developed to describe the relationship between chlorophyll-specific primary production (mg C mg Chl −1h −1) and depth in the water column. Model regressions for Modified Atlantic Water (MAW, salinity = 36.5–36.8), Mediterranean water (37.6–38.0), and intermediate frontal water were not significantly different, and a single equation based on the pooled data was used to estimate regional production. East of 0° longitude, primary production integrated over the upper 100 m (ΣP) in Mediterranean water was 0.47 g C m −2 d −1 (range0.33–0.60) and 0.88 g C m −2 d −1 (range 0.50–1.30) in MAW and frontal regions. higher ΣP in MAW and frontal regions could be attributed partially to higher integrated chlorophyll, although locationof the chlorophyll maximum higher in the water column was also an important contributing factor. The chlorophyll maximum was shallower in MAW than in Mediterranean-type water. The depth of chlorophyll maxima generally coincided with the nitracline rahter than isopycnal surfaces, supporting the view that chlorophyll distributions and primary production were primarily influenced by nutrient supply.