Particle trajectories in an eastern boundary current using a regional ocean model at two horizontal resolutions

Abstract

Lagrangian particle tracking (LPT) models are used to study the transport and dispersal of marine organisms. In LPT studies, the accuracy of the circulation is essential for nearshore habitats of Eastern Boundary Current (EBC) regions that are areas of high productivity and economically important fisheries. We used the California Current System as an example of an EBC region, specifically the Oregon coast located in the northern California Current System because it has distinct upwelling and downwelling regimes and variable shelf width. More specifically, we developed and applied a LPT model to compare and contrast particle drift patterns during the spring transition as it is an important period for spawning. We contrasted years (2016–18) using Regional Ocean Modeling System (ROMS) with different horizontal spatial resolutions (2 km, 250 m). Lagrangian particles experience stronger downward velocities and displacements to greater depths in the 250 m ROMS simulations that used a finer resolution bathymetry. Consequently, retention along the Oregon coast increases in the 250 m ROMS compared to the 2 km ROMS. After 10 days, 37%–83% of particles forced with the 2 km ROMS remain in the model domain, compared to 61%–86% of particles remaining when using the 250 m ROMS. Particles in the 250 m ROMS are advected to depth at specific times and locations for each simulated year, coinciding with the location and timing of a strong and shallow alongshore undercurrent that is not present in the 2 km ROMS. Additionally, ageostrophic dynamics close to shore, in the bottom boundary layer, and around headlands emerge in the 250 m resolution model, while they are at best poorly resolved in the 2 km resolution case. We conclude that the higher horizontal model resolution and bathymetry used in the 250 m ROMS generates well-resolved mesoscale and submesoscale features (e.g., surface, subsurface, and nearshore jet) that vary annually. These physical features are significantly different than those modeled by the 2 km model and may be responsible for these differences in particle dispersal. These results have implications for modeling the dispersal, growth, and development of coastal organisms with dispersing early life stages.