Patterns of chlorophyll-a distribution linked to mesoscale structures in two contrasting areas Campeche Canyon and Bank, Southern Gulf of Mexico

Abstract

The chlorophyll-a (Chl-a) distribution in Campeche Canyon and Campeche Bank, at the Southern Gulf of Mexico, as well as its relationship with hydrographic structure were analyzed. The results show the existence of the Gulf Common Water (GCW), the Caribbean Tropical Surface Water (CTSW) and the Caribbean Subtropical Underwater (CSUW) in the 120m upper layer at the Campeche Canyon. While at the Campeche Bank only the Caribbean Tropical Surface Water (CTSW) was found. The 15°C and 18.5°C isotherms topography depict the presence of a mesoscale anticyclone-cyclone dipole. The nutrient pumping mechanism fertilizes the eutrophic zone promoted by the cyclonic eddy. Submesoscale processes in the border of an anticyclone and a cyclone results in maximum of nitrate concentration and vertically integrated Chl-a at the frontal zone. Two Chl-a vertical distribution patterns were found, a deep maximum at the base of the euphotic layer not associated to the thermocline over the Campeche Canyon and a peak associated to the thermocline related to the shallow bottom at the Campeche Bank. Oligotrophic conditions were observed in the 50m upper layer and mesotrophic conditions were found below this layer. The differences between the Campeche Bank and Campeche Canyon are that: in the canyon, the nutrient and Chl-a peaks were linked with the cyclone, and the submesoscale processes in the border of an anticyclone and a cyclone, respectively. In the vertical the maximum Chl-a was associated to the base of the euphotic layer and dominated by coccolithophores. In the Campeche Bank the nutrient and Chl-a peaks were influenced by the shelf break in the vertical the maximum Chl-a was associated with the thermocline and the silicoflagellate was identified as the dominant species.