Nearshore Lagrangian Connectivity: Submesoscale Influence and Resolution Sensitivity

Realistic simulation of nearshore (from the shoreline to approximately 10-km offshore) Lagrangian material transport is required for physical, biological, and ecological investigations of the coastal ocean. Recently, high-resolution simulations of the coastal ocean have revealed a shelf populated with small-scale, rapidly evolving currents that arise at resolutions ?100m. However, many historical and recent investigations of coastal connectivity utilize circulation models with approximate to 1-km resolution. Here we show a resolution sensitivity to simulated Lagrangian transport and coastal connectivity with a hierarchy of Regional Oceanic Modeling System simulations of the Santa Barbara Channel at Delta x=1, 0.3, 0.1, and 0.036km. At higher resolution ( Delta x?100m), rapid alongshore and vertical transport occurs in regions less than 1km from the shoreline due to submesoscale shelf currents that open up new transport pathways on the shelf: submesoscale fronts and filaments, topographic wakes, and narrow alongshore jets. Shallow-water fronts and filaments induce early time downwelling and subsequent dispersal at depth of surface material; this is not captured at coarser resolution (Delta x=1km). Differences in three-dimensional and two-dimensional transport are explored in a higher-resolution simulation: In general, three-dimensional trajectories are more dispersive than two-dimensional, due to a separation in their respective trajectories.