Kinematics and planktonic ecosystem dynamics of a coastal cyclonic eddy in the Southern California Bight

Abstract:

The highly productive Californian eastern boundary upwelling system exhibits high mesoscale eddy activity. Eddies that are formed at the coast move offshore, entraining and redistributing nearshore nutrients and planktonic organisms. High planktonic biomass can be found in these eddies months after detaching from the coast. The mechanisms driving these patterns, and their ecological impacts are still poorly understood. To characterize and understand the influence of mesoscale eddies on planktonic ecosystems in the California Current System (CCS) we use a numerical approach coupling the Regional Ocean Modeling system (ROMS), at 5 km horizontal resolution, with a multiple size class planktonic ecosystem model (NEMURO). Combining Eulerian and Lagrangian analyses, we were able to follow one specific cyclonic eddy formed in the Southern California Bight as it detached from the coast and migrated offshore. Lagrangian particle tracking allowed us to identify the eddy core where high concentrations of coastal nutrients are found. The Eulerian calculations allowed us to quantify ecosystem properties and dynamics along the particle tracks. We highlight the role of this eddy in altering local planktonic ecosystem dynamics, and contrast those dynamics with the coastal upwelling source waters, and the waters encircling the eddy.