Floating plastics: a wide-reaching problem
Floating plastics provide an estimate of the abundance of floating litter in the ocean which can be used to work out the potential risk of harm to marine organisms, and to people using the sea for a living or for recreation. The abundance of floating plastic in the surface waters of the ocean has been measured in terms of items per square km. Two separate indicators were examined: microplastics (<5mm diameter) and macro-plastics (>5mm diameter).
Plastic enters the marine environment from a wide variety of land and sea based activities, but there are no reliable estimates of the nature and quantities of material involved
Smaller plastic particles, or "microplastics" (<5mm), were measured with towed nets fitted with a fine mesh. Larger floating items were detected by direct observation from ship.
The data were collected by many researchers over several decades. The first publication was in 1972, and described small fragments of floating plastic and expanded polystyrene spherules found in nets used for sampling plankton, off the eastern seaboard of the USA. Now all ocean basins have been sampled, including the Southern Ocean around Antarctica.
The majority of the floating plastic in the open ocean is likely to have originated from activities in coastal waters and on land
Findings
Once floating plastic reaches the open ocean, either by direct input or by transport from more coastal regions, the distribution becomes dominated by the surface ocean circulation, with highest relative concentrations found in the sub-tropical gyres of the North and South Pacific, the North and South Atlantic and the Indian Oceans. Overall concentrations are highest in the northern hemisphere, due to greater contributions from a wide variety of sources, for example: shipping, fisheries, aquaculture, urban population and coastal tourism.
The overall distribution of plastics in the open ocean is dominated by the influence of the general surface water circulation, with relatively high abundances confined to sub-tropical circulating currents or gyres
Long-distance transport mechanisms in the ocean result in plastic litter being found on remote mid-ocean islands, thousands of kilometres from the input point. Within the gyres there are large differences in concentrations due to wind events and smaller scale ocean circulation patterns. We were not able to distinguish any trend of increase or decrease over time in the available data.
Floating debris sampling in North Atlantic
Floating plastic debris sampling in the North Atlantic, by the Sea Education Association. Download data and get information, or following this link for an interactive map. Click here for a printable version (click to display, right-click to download).
Floating debris sampling in North Pacific
Floating plastic debris sampling in the North-East Pacific, by the Scripps Institution of Oceanography. Download data and get information, or following this link for an interactive map. Click here for a printable version (click to display, right-click to download).
| 0 | 0 – 500 | 500 – 1,000 | |||
| 1,000 – 2,000 | 2,000 – 5,000 | 5,000 – 10,000 | |||
| 10,000 – 20,000 | 20,000 – 50,000 | >50,000 |
Floating debris, global transect
Global sampling of floating plastic debris, by Malaspina. Download data and get information, or following this link for an interactive map. Click here for a printable version (click to display, right-click to download).
| 0 - 5 | 5 - 20 | 20 - 50 | 50 - 150 | 150 - 1600 |
Limitations and knowledge gaps
Despite an upsurge in interest, we still know little about floating plastic pollution in many regions of the ocean. Even in regions with relatively good coverage, such as the eastern North Pacific, a high degree of variability in distribution has been noted thanks to ocean circulation and wind and wave effects. This makes it difficult to provide reliable and representative estimates of abundance. The difficulty and expense of sampling in remote regions increases the level of uncertainty. It has proved very difficult to find trends over time, even with two datasets that extend over one or two decades.
Larger items of plastic debris can have a significant impact on many marine species, cause significant economic loss, and may pose a threat to navigation and human safety
