First evidence of plastic fallout from the North Pacific Garbage Patch

Abstract

The infamous garbage patches on the surface of subtropical oceanic gyres are proof that plastic is polluting the ocean on an unprecedented scale. The fate of floating plastic debris 'trapped' in these gyres, however, remains largely unknown. Here, we provide the first evidence for the vertical transfer of plastic debris from the North Pacific Garbage Patch (NPGP) into the underlying deep sea. The numerical and mass concentrations of plastic fragments (500 µm to 5 cm in size) suspended in the water column below the NPGP follow a power law decline with water depth, reaching values <0.001 pieces/m 3 and <0.1 µg/m 3 in the deep sea. The plastic particles in the NPGP water column are mostly in the size range of particles that are apparently missing from the ocean surface and the polymer composition of plastic in the NPGP water column is similar to that of floating debris circulating in its surface waters (i.e. dominated by polyethylene and polypropylene). Our results further reveal a positive correlation between the amount of plastic debris at the sea surface and the depth-integrated concentrations of plastic fragments in the water column. We therefore conclude that the presence of plastics in the water column below the NPGP is the result of 'fallout' of small plastic fragments from its surface waters.

The global biological microplastic particle sink

“…All members of the 14-simulation subset contain total MP particle inventories that roughly agree with an independently calculated MP inventory at year 2010 3 . Four of the simulations also produce power law-shaped "free" MP particle profiles that generally agree with new observations from the North Pacific Gyre 32 . Local surface or sub-surface particle minima in the unattached MP compartment are also present in 12 of the simulations, which is broadly consistent with the findings of widespread "missing" microplastic in surface sampling 1,3 .…”

“…Local surface or sub-surface particle minima in the unattached MP compartment are also present in 12 of the simulations, which is broadly consistent with the findings of widespread “missing” microplastic in surface sampling 1 , 3 . Our simulations furthermore simulate observed local sub-surface particle maxima 16 , 32 in 9 samples, which are produced as marine snow-aggregated microplastic particles ( ) and zooplankton faecal pellet-bound plastic particles ( ) release MP back into the free MP compartment. However, note the data compilation 32 included sizes of MP within the larger end of the size range than are typically thought to aggregate with marine snow 33 or that are ingested by small zooplankton 34 .…”

“…Our simulations furthermore simulate observed local sub-surface particle maxima 16 , 32 in 9 samples, which are produced as marine snow-aggregated microplastic particles ( ) and zooplankton faecal pellet-bound plastic particles ( ) release MP back into the free MP compartment. However, note the data compilation 32 included sizes of MP within the larger end of the size range than are typically thought to aggregate with marine snow 33 or that are ingested by small zooplankton 34 . Comparison to data obtained from manta trawls, such as used by 32 biases the comparison away from what might be the most biologically-active size range (although, our model does not simulate size classes).…”

“…• are numerically stable and constrained to total MP inventories at or below the time-integrated global ocean pollution rate at year 2010 • are roughly constrained to an independently calculated plastic annual ocean pollution rate 30 • are generously constrained to independently calculated marine snow aggregation rates 31 • roughly agree with an independently calculated total ocean MP inventory for year 2010 3 • produce subsurface MP particle maxima 16 below local minima 32 • quantitatively simulate the "missing" surface MP 3 .…”

The Way of Macroplastic through the Environment

“…Regarding temporary sinks of MaP, different areas need to be mentioned. During transport, MaP may deposit in peripheral areas [67], on floodplain areas of rivers [21], on shorelines of lakes [91], and in coastal zones [164], and in addition, it may stay temporarily on the water surface of lakes [135] and oceans [176] before it is transported to the shorelines and coasts or sinks to the sea floor.…”