Impact of Wave-Induced Drift Amplification on the Dispersal of Plastics in the Great Pacific Garbage Patch

Abstract The Great Pacific Garbage Patch (GPGP) constitutes the largest area of floating plastic accumulation in the oceans. Dispersal models are created to understand better the surface and vertical distribution of plastics in the oceans to optimize the cleanup operation. These models account primarily for the sources of plastics (location and quantity) and their Lagrangian transport. The transport models include the sea-surface current, wind, and wave-induced drift contributions. As a first approximation, the contribution of the waves on the plastic transport is the Stokes drift, which corresponds to the wave-induced drift of a neutrally buoyant, infinitely small object. However, recent studies have shown that plastics size, shape, and density can impact their wave-induced drift, often amplifying this drift compared to the Stokes drift. To model this amplification, empirical correlations have been found in experimental and numerical studies. The present study aims to first implement such correlations in the WAVEWATCH III® (WW3) wave model by modifying the Stokes drift formulation using the directional wave energy spectrum components. This gives access to the wave-induced drift velocity components for different plastic characteristics and the nominal Stokes drift. As a second step, a multi-year regional wave model of the North-East Pacific Ocean bounding the GPGP is run, allowing for a first comparison of the impact of the wave-induced drift amplification on the velocity magnitudes and resulting circulation. Finally, the resulting drifts from the regional wave model can be used in the ADVECT plastic dispersal model to compare the influence of the different resulting wave-induced drifts on regional plastic accumulation.