Particle Accumulation in Stratified Ocean

BÁRBARA C. FRANCO; ELBIO D. PALMA

San Francisco

Conferencia; American Geophysical Union, Fall Meeting 2011; 2011

Vertical fine-structures and thin layers, from centimeters to ~3-5 m of thickness, which concentrate particulate, passive aggregates (marine snow), phytoplankton, and zooplankton species, have been broadly observed in the ocean. However, the mechanisms related with the formation, maintenance, and dispersal of thin layers in stratified oceans remain poorly understood. In this study we used a Random Displacement Model (RDM) approach to track particles dispersed vertically in 1D idealized mixed and stratified layers in order to inquire how the stochastic dynamics of turbulent flows could condition accumulation of particles in the ocean. Our preliminary results show that accumulations of particles in regions with high gradients of diffusivity, i.e. the boundaries of the pycnocline, are limited by the Lagrangian timescale and the timescale of turbulence to relax towards an isotropic state. Furthermore, our results suggest that a reasonable (although not perfect) well-mixed condition can be found when the solutions are analyzed statistically and a restricted time step is used. The numerical results also show the importance of a correct parameterization of the eddy diapycnal diffusivity and related Lagrangian properties of the turbulent flow by turbulence closure schemes; improved interpolation/smoothing schemes for the nonhomogeneous diffusivity field; and higher order numerical methods to solve the model stochastic behavior. Particularly, our results highlight that the numerical scheme accuracy in modeling individual trajectories in mixed layers can eventually affect 3-D displacements and contribute to crucial differences in biophysical models where individual particle behavior is important.