Separation Timescales of Vertically Migrating Zooplankton and Other (a)Biotic Materials in the Benguela System

Abstract

Plankton, plastics, nutrients, and other materials in the ocean can exhibit different dispersion patterns depending on their individual transport properties. These dispersion patterns can provide information on the effective timescales of interaction between different types of materials in a highly dynamic ocean environment, such as the Benguela system in the southeast Atlantic Ocean. In this study, we compare the timescales and spatial distribution of separation for zooplankton performing Diel Vertical Migration (DVM) while drifting with currents to those of other materials: (a) positively buoyant plastics or planktonic organisms passively floating near the ocean's surface; (b) nutrients or pollutants passively advecting in the three-dimensional flow; and (c) sinking biogenic particulate matter. We apply the drift properties of each material type in Lagrangian flow modeling to simulate the movement of virtual particles across the Benguela system. Our results indicate faster separation between zooplankton performing DVM and the other particle types during the upwelling season in the austral spring and summer. We also observe a decrease in the separation timescales between zooplankton performing DVM and other particle types as the zooplankton migration depth increases. Despite the differences in separation timescales across seasons, different particle types can become trapped in coherent features such as eddies, fronts, and filaments, indicating prolonged exposure of zooplankton to prey and pollutants in these coherent ocean features.