Marine Litter Vital Graphics

GEOGRAPHICAL DISTRIBUTION

enhanced vertical dispersion of near-neutrally buoyant plastic particles and debris; further research is required.

again in other areas of the ocean when organisms shift location – even outside the marine environment, for example when seabirds bring debris to land. Vertical downward migration of organisms in the water column following night-day cycles has been shown to play a crucial role in exporting carbon away from surface waters (Ducklow et al., 2001) and this could well be the case for microplastics too (Cózar et al., 2014). Fouling by algae and other colonising organisms such as molluscs also plays a role in the redistribution of plastic particles, as it can increase the density of particles and make them sink towards the sea floor. Remineralization, the reverse process due to degradation of the colonising organisms during sinking, can also affect the particle’s buoyancy and cause it to float towards the surface again (Wang et al., 2016). Finally, several mechanical processes influence the size spectrum of marine plastic items, which affects their interaction with the physical and biological processes. Plastic objects exposed to solar UV radiation and oxidation are progressively eroded and fragmented by wind, wave or biological action. On the other hand, plastic debris can be aggregated with other natural or artificial substances, ultimately leading to sedimentation or shore deposition (Wang et al., 2016).

The transfer of plastic debris and microplastics towards deeper parts of theoceanhas alsobeendocumentedacross continental margins. Here, near-bottom transfer, especially throughdeep sea canyons, has been linked toaccumulation of debris andmicroplastics along these submarine canyons and adjacent deep sea areas (Pham et al., 2014). In addition to flows triggered by gravity, another efficient mechanism for debris transfer is the enhanced downwards circulation caused by overcooling and evaporation of surface waters on the continental shelf, and their cascading along deep sea canyons (Woodall et al., 2014, Tubau et al., 2015). In addition to physical redistribution linked to wind, waves, and surface and deep currents, a whole other suite of biological and mechanical processes influences the distribution of plastic debris andmicroplastics in the ocean. Among biological processes, ingestion by all kinds of organisms plays a role in the redistribution of plastic particles within the ocean, as particles may be released Particle dynamics and the role of organisms

Natural processes a ecting the distribution and fate of plastics

Weathering from UV action

Mechanical degradation from wave action

Biofouling* and biological degradation

Sinking

Resuspension in faeces

Ingestion by zooplankton and sh

Aggregation and sedimentation

Plastics

Bioturbation

Secondary microplastics

Sedimentation via faeces

*Biofouling is the gradual accumulation of waterborne organisms on the surfaces of plastics in water that contributes to its corrosion and degradation

Marine Litter Vital Graphics

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