Using Numerical Model Simulations to Improve the Understanding of Micro-plastic Distribution and Pathways in the Marine Environment

Abstract

Numerical modeling is one of the key tools with which we can gain insight into the distribution of marine litter, especially micro-plastics. Over the past decade, a series of numerical simulations have been constructed that specifically target floating marine litter, based on ocean models of various complexity. Some of these models include the effects of currents, waves, and wind as well as a series of processes that impact how particles interact with ocean currents, including fragmentation and degradation. Here, we give an overview of these models, including their spatial and temporal resolution, limitations, availability, and what we have learned from them. Then we focus on floating marine micro-plastics (<5 mm diameter) and we make recommendations for experimental research efforts that can improve the skill of the models by increasing our understanding of the processes that govern the dispersion of marine litter. In addition, we highlight the importance of knowing accurately the sources or entry points of marine plastic debris, including potential sources that have not been incorporated in previous studies (e.g., atmospheric contributions). Finally, we identify information gaps and priority work areas for research. We also highlight the need for appreciating and acknowledging the uncertainty that persists regarding the movement, transportation and accumulation of anthropogenic litter in the marine environment.

Modeling the Fate and Distribution of Floating Litter Particles in the Aegean Sea (E. Mediterranean)

“…Fourth, floating litter particles have been considered here as passive drifters advected exclusively by surface currents. So, we did not include other particle properties related to buoyancy (Yoon et al, 2010;Carlson et al, 2017), windage (Neumann et al, 2014), subsurface movement, and sinking (Hardesty et al, 2017). All these properties need to be better understood and taken into account in further modeling.…”

A Surface “Superconvergence” Pathway Connecting the South Indian Ocean to the Subtropical South Pacific Gyre

“…This result is clearly consistent with the accumulation of the numerical particles and the "superconvergence pathway" that our study has disclosed, but a direct application of our results to the global plastic issue remains challenging. Future progress in tackling the ubiquitous and growing plastic and litter problem in the global ocean should consider the usefulness of ocean models, as already been stated by several studies and international reports (i.e., Hardesty et al, 2017;Williamson et al, 2016) and, in particular, should take into account the mesoscale and submesoscale variabilities in the simulation of ocean dynamics. Another limitation is the difficulty of a direct comparison with the trajectories of actual drifters.…”

“…Ongoing efforts with these models incorporate more physical processes such as waves, tides, vertical displacements, and specific behaviors related to the nature of the pollutants including the rates of fragmentation and the frequency of active biofouling (e.g., Hardesty et al, 2017). Ongoing efforts with these models incorporate more physical processes such as waves, tides, vertical displacements, and specific behaviors related to the nature of the pollutants including the rates of fragmentation and the frequency of active biofouling (e.g., Hardesty et al, 2017).…”

Combining Litter Observations with a Regional Ocean Model to Identify Sources and Sinks of Floating Debris in a Semi-enclosed Basin: The Adriatic Sea

“…As the transport of marine debris is inherently a Lagrangian problem, both ocean models and debris transport models should be evaluated more extensively using Lagrangian observations (Hardesty et al, 2017). Lagrangian assessments typically compare surface or drogued drifter trajectories to virtual particle trajectories (Liu and Weisberg, 2011;Carlson et al, 2016), yet quantitative comparisons between drifter and AMD trajectories over large distances in oceanic environments have not yet been reported.…”