Marine Litter Vital Graphics

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39 Marine Litter Vital Graphics
GEOGRAPHICAL DISTRIBUTION
enhanced vertical dispersion of near-neutrally buoyant
plastic particles and debris; further research is required.
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).
Particle dynamics and the role of
organisms
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
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).