Drifting Along: A Global Validation of Climatologies of Numerical Dispersal Over the Continental Shelf Using Trajectories From the Global Drifter Program

Abstract

The distance over which planktonic larvae are dispersed and the variability within that dispersal distance are important for understanding gene flow and species persistence in the coastal ocean. The breadth of spatial and temporal scales that are important to dispersal in shelf seas makes direct observations difficult—instead, we often use numerical simulations of circulation to estimate the statistics of larval dispersal. However, meroplanktonic life histories are most common in coastal regions where drifter-based estimates of circulation are sparsely distributed, making validation of these numerical simulations quite difficult. We use a novel technique to validate climatological mean and standard deviation of dispersal distance at a global scale by drawing on the tens of thousands of sparsely distributed drifter observations on the shelf. Numerical dispersal estimates were made using Lagrangian particle trajectories calculated with circulation fields from a 1/12° global physical model and were validated against data from the Global Drifter Program (GDP), an international program that observes ocean circulation using drifters. The median dispersal distance of a climatological ensemble of numerical drifters released from a single location were found to match GDP drifter estimates quite well (with a mean deviation of 0.2%), whereas model estimates of dispersal were shown to underestimate the diffusivity of GDP drifters by 30%–50%. Our results indicate that although global numerical estimates of dispersal statistics provide a close approximation of median dispersal distance in the coastal ocean, these numerical simulations underestimate the overall variation in dispersal distance of drifters in the coastal ocean.