Marine Litter Windrows: A Strategic Target to Understand and Manage the Ocean Plastic Pollution

Abstract

Windrow is a long-established term for the aggregations of seafoam, seaweeds, plankton and natural debris that appear on the ocean surface. Here, we define a “litter windrow” as any aggregation of floating litter at the submesoscale domain (<10 km horizontally), regardless of the force inducing the surface convergence, be it wind or other forces such as tides or density-driven currents. The marine litter windrows observed to date usually form stripes from tens up to thousands of meters long, with litter densities often exceeding 10 small items (<2 cm) per m2 or 1 large item (>2 cm) per 10 m2. Litter windrows are generally overlooked in research due to their dispersion, small size and ephemeral nature. However, applied research on windrows offers unique possibilities to advance on the knowledge and management of marine litter pollution. Litter windrows are hot spots of interaction with marine life. In addition, since the formation of dense litter windrows requires especially high loads of floating litter in the environment, their detection from space-borne sensors, aerial surveys or other platforms might be used to flag areas and periods of severe pollution. Monitoring and assessing of management plans, identification of pollution sources, or impact prevention are identified as some of the most promising fields of application for the marine litter windrows. In the present Perspective, we develop a conceptual framework and point out the main obstacles, opportunities and methodological approaches to address the study of litter windrows.

Distribution Patterns of Floating Microplastics in Open and Coastal Waters of the Eastern Mediterranean Sea (Ionian, Aegean, and Levantine Seas)

“…It is important to specify that the sampling design of this study was not arranged according to the presence of slicks, i.e., concentrations may have been even higher if trawls were conducted 100% inside the slicks, suggesting that this finding is worthy for further investigation. The importance of windrows in understanding marine litter and MPs pollution and the need for targeted windrow research has been acknowledged very recently by Cózar et al (2021), in their relative perspective article.…”

Observational Evidence and Open Questions on the Role of Internal Tidal Waves on the Concentration and Transport of Floating Plastic Debris

“…These waves travel over hundreds of kilometers of ocean and could conceivably accumulate a tremendous amount of plastic. Videos posted on YouTube show dense patches of plastic debris in the coastal waters off Honduras 2, 3 (see also Figure 1A in Cozar et al, 2021). The plastic patches were in the shape of long bands.…”

“…This limited set of observations begs the question: we have demonstrated that the convergence over tidally generated internal waves can concentrate and transport plastic surface drifters, but how much floating plastic does one find in internal wave convergences and is this a regular occurrence? If internal waves regularly concentrate plastic debris, could this be exploited; could one "fish" internal wave slicks to remove plastic debris (Ruiz et al, 2020;Cozar et al, 2021)?…”

Sea-Surface Slicks and Their Effect on the Concentration of Plastics and Zooplankton in the Coastal Waters of Rapa Nui (Easter Island)

“…On the other hand, the mesoscale (10-200 km) circulation in form of eddies and fronts influences the horizontal movements of particles in the open ocean (Pichel et al, 2007;Howell et al, 2012;Frère et al, 2017;Brach et al, 2018). Spatial variability of particle abundance and distribution at smaller scales (<10 km) may be due to water movements resulting from processes such as internal waves, Langmuir cells, submesoscale fronts and other related roll-like instabilities with surface convergence (Hamner and Schneider, 1986;van Sebille et al, 2020;Cózar et al, 2021;Shanks, 2021).…”