THE IMPACT OF TURBULENCE ON PREDICTABILITY OF THE PLANKTON ECOSYSTEM

The predictability of the plankton ecosystem is defined by the inter-annual variation of environmental variables and of the demographies of each plankton population. We present the results of numerical experiments on a Virtual Plankton Ecosystem using the Woods-Barkmann model integrated at the Azores by the Lagrangian Ensemble method of individual-based modelling. We show that the ecosystem has long-term stability with inter-annual variation that can be attributed solely to small random fluctuations associated with the turbulent displacement of individual plankters. Tests with ensemble simulations confirm that these fluctuations are ergodic, apart from a tiny non-ergodic element caused by inheritence of biological properties through plankton lineages. Sensitivity studies reveal that there is no chaotic instability in these virtual plankton ecosystems. That result is explained in terms of the biofeedback process in Lagrangian Ensemble simulations. We conclude that the method offers useful predictability. However the predictability is limited by the influence of turbulence in the mixed layer.