An ocean gyre is a large system of circular ocean currents formed by global wind patterns
and forces created by Earth’s rotation.
The world has five major ocean gyres which help to drive the “ocean conveyor belt.”
The ocean conveyor belt circulates ocean water around the entire planet.
It is essential for regulating temperature, salinity and nutrient flow throughout the ocean.
There are three major types of ocean gyres:
tropical (forming near the equator) subtropical (forming between polar and equatorial regions),
and subpolar (forming in polar regions).
It is in the subtropical gyres that ‘garbage patches’ exist; as the gyre turns in a circular motion,
it draws in plastic waste which has travelled from land via ocean currents or been dumped in the sea by ships.
The Indian Ocean, North Atlantic Ocean, and North Pacific Ocean all have significant garbage patches;
the North Pacific patch is currently known to be the largest, at twice the size of France.
Unfortunately, as these garbage patches generally accumulate far from any country’s coastline,
it is nearly impossible to track the origin of marine debris.
Consequently few countries have accepted the responsibility of cleaning up the ocean’s garbage patches.
The 5 gyres, where plastic accumulates
what are the effects?
Humans have been consuming plastics for over 50 years, with global production and consumption continuing to rise; plastic consumption is estimated to reach 25.3 million tonnes by the end of 2017*.
Land-based sources account for up to 80% of the world’s marine pollution; up to 95% of which is from plastic debris**. A staggering 8 million metric tons of plastic end up in our oceans every year***.
Plastic is very buoyant, and so can travel in ocean currents for thousands of miles, endangering marine ecosystems and wildlife along the way. A good example of this is the floating yellow ducks; in 1992, twenty containers full of plastic rubber ducks fell off a container ship travelling from China to Seattle in America. By 1994 some of these ducks had been found as far afield as Alaska, and Iceland (2000), and also in the Artic, Pacific and Atlantic Oceans (2003)****.
Plastics are also very good at absorbing harmful chemicals from the water they float in, both in their original and microscopic form. Plastics are essentially made from oil and so they have a oily and greasy quality, promoting the accumulation of hydrophobic contaminants (which repel rather than absorb water) from the surrounding water.
Plastic waste sucks up persistent organic pollutants (POPs) such as PCB’s (polychlorinated biphenyls), DDE and DDT (Dichlorodiphenyltrichloroethane) – the most toxic of all pesticides.
*'Global speciality plastics consumption', Smithers Rapra
**The United Nations Joint Group of Experts on the Scientific Aspects of Marine Pollution (GESAMP)
***NCEAS, Journal Science, 2015
Plastic pollution greatly affects the economies and inhabitants of coastal and waterside communities worldwide. Coastal communities are seriously affected by plastic pollution for several reasons:
Increased expenditure for beach cleaning, public health and waste disposal
Tourism (loss of income, bad publicity)
Fishing (reduced catch, damaged nets & gear, fouled propellers, contamination)
Shipping (frequent fouling of propellers, damaged engines, litter removal and waste management in harbours and marinas)
Although plastic is resistant to natural biodegradation processes, it does degrade by exposure to the sun, a process called ‘photodegeneration’. Photogeneration can continue down to the molecule level, resulting in plastic debris thinner than a human hair. Plastic can also be fragmented into smaller pieces due to wave, sand action and oxidation.
These plastic particles are not absorbed into the natural system as they do not biodegrade; ultimately, they are ingested by marine life and zooplankton, which forms the basis of the food chain.
These small plastic particles have been found on beaches and waters in Europe, the Americas, Australia, Africa and Antarctica. Once at a molecular level, plastics are very difficult to clean-up and can spread very quickly polluting the food chain.
It was previously thought that plastic waste would take hundreds of not thousands of years to decompose; but new findings suggest that plastic does in fact decompose as a surprising speed, and even as little as one year*.
*238th National meeting of the American Chemical Society (ACS), 2009, Katsuhiko Saido et al
When plastics decompose, they release toxins into the oceans, which subsequently become ingested and metabolised by marine life. This can cause global contamination.
Decomposing plastics release Bisphenol A (BPA), which is very toxic.
Polyethylene terephthalate (PET / PETE)
Used to make bottles and containers for mouthwash, detergent, food dressing and spreads. Leaches the toxic chemical antimony trioxide and (2ethylhexyl) phthalate otherwise known as DEHP.
DEHP may cause:
Asthma and allergies in children
Some types of cancer
And is known to effect:
The liver, kidney, spleen and bone formation
DEHP is so toxic that PET/PETE plastics have been banned for the use in children’s plastic toys since 1999.
Polyvinyl chloride (PVC)
Used to make toys, clear packaging (such as cling-film), shower curtains, medical tubing, watersports equipment (such as inflatable boats), food and detergent containers. Leaches the toxic chemical di (2-ethylhexyl) phthalate (DEHP) and butyl benzyl phthalate (BBzP).
Described as one of the most hazardous consumer products ever created and causes the same problems as mentioned above.
Used to make Styrofoam containers, egg cartons, disposable cups, take-away food containers, cutlery and compact disk cases. Leaches the toxin styrene.
Styrene can cause:
Reproductive and developmental problems
Brain and nervous system defects
Adverse effects on red blood cells and internal organs
Used to make plastic baby bottles, sports bottles, water storage containers, mobile phones, computers. Leaches the toxin Bisphenol A.
Bisphenol A can cause:
Chromosome damage in female ovaries
Decreased sperm production in males & erectile dysfunction
Early onset of puberty
Altered immune function
Associated with recurrent miscarriage
Thyroid disruption & resulting weight gain
Interferes with the reproductive systems of animals
*BPA can be metabolised and so is particularly dangerous.
All sea creatures, from the largest to the microscopic, are ingesting sea water instilled with toxic chemicals from plastic decomposition. Eventually, these toxins pass right through the food chain to us.
Entanglement and ingestion
Mistaken for food and causing entrapment, plastic debris can result in starvation, laceration, infection, choking and for animals which need to return to the surface to breathe, suffocation.
Plastic debris kills an estimated 100,000 marine mammals annually, as well as millions of birds and fishes*.
*National Oceanographic & Atmospheric Administration
Destruction of coral reefs
Derelict fishing gear, which is made from plastic, can be destructive to coral reefs. Corals are in fact animals, related to jellyfish and anemones.
Nets and lines become snagged on coral, and can break off coral heads with the movement of the waves. This is a continual process until the debris eventually sinks or is removed.
Plastic bags can also kill coral by covering and suffocating them, or by blocking sunlight which the coral need to survive.