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
drifting 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: (i) positively buoyant plastics or planktonic
organisms passively floating near the ocean's surface; (ii) nutrients
or pollutants passively advecting in the three-dimensional flow; and
(iii) 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.