Mesoscale Features and Zooplankton Biomass Distribution: A Case of Study in the Eastern Pacific Tropical-Subtropical Transition Zone

Mesoscale eddies have a dominant role on the ocean’s kinetic energy. The zooplankton community has been known to respond to these physical processes. This research studies the life history, hydrography, and zooplankton biomass, of two mesoscale eddies (a Cyclone-Anticyclone dipole) situated South of Cabo San Lucas, Mexico, in spring 2012. OSTIA-GHRSST and COPERNICUS-SLA satellite images were processed to determine the eddies’ centers and perimeters throughout their life history. The CTD, dissolved oxygen and chlorophyll profiles of six hydrographic stations from an oceanographic cruise performed during early summer 2012 were analyzed to determine three zones: the Mixed layer (ML), the Thermocline and Chlorophyll maximum (TCM), and below the MaxChl to the 9 mmol/kg oxypleth (OMZ). Zooplankton net hauls were performed at these specific intervals to obtain the biomass (mg/m³) and species assemblage. Satellite images determine that the formation of eddies in this area depends on the latitudinal outreach of the California Current. When the California Current reaches the southern tip of the Baja California Peninsula, its cold and oxygenated waters are trapped and/or dispersed by eddies (mostly cyclonic ones), changing the structure of the water column and the equatorial outreach of subtropical waters. Zooplankton biomass was higher in the jet flow formed between the eddies, and in the periphery of the anticyclonic eddy. These mesoscale structures may cause strong variations on the biological processes in the area, indicated by the differential distribution of zooplankton biomass.