Oceans are important natural resources and ecosystems where a whole life cycle undergoes and ensures the sustainability of human food chain supply. Oceans constitute by themselves 70% of earth’s surface and contain about 97% of the planet water. They serve many functions, from earth’s temperature moderation by absorbing solar radiation, to natural CO2 sinks. Today, oceans are being threatened by plastic pollution. Plastic being ditched in marine water, it survives in oceans and accumulates in gyres before it is degraded into microplastic, small particles with high toxicity.
In the last 80 years, plastic has invaded our world. Plastic resin global production peaked from 1.5 million tonnes in 1950 to 322 million tonnes in 2015 (Patricia Villarrubia-Gòmez, 2017). It has become essential in everyday applications, and humans consume and dispose of a huge amount of utensils, materials made out of plastic without bearing the consequences of their action. Plastics, that is a polymer synthesized material, present high resistance and lifespan, making it durable and most of the time non-biodegradable. After using it, humans end up ditching it to garbage where eventually it reaches landfills and oceans. As cited in (Patricia Villarrubia-Gòmez, 2017), 7.9 million tonnes of mismanaged land-based plastic waste has entered the oceans by 2010.The real quantity of plastic within ocean waters is a function of different factors and transport pathways, which makes it impossible to calculate the absolute drifted amount. However, marine plastic pollution (MPP) has become ubiquitous, and growing concerns about its impact on ecosystems, human well-being, and socio-economic sectors such as tourism, aquaculture, and navigation have been highlighted in recent studies.
Within oceanology course scope, this project underlines the sources and dispersion of plastic in the ocean, its fate and effects on the ecosystem. In the same context, attention is given to the formation of garbage patches especially the great pacific garbage patch (vortex), and the project concludes by shading light on the Ocean Cleanup initiative currently in action to reverse MPP in the Pacific Ocean.
I. MPP sources
Plastic pollution is driven by rivers, beaches and maritime activities and illegal dumping at sea into the marine environment. (Marcus Eriksen, 2013). We can categorize marine litter sources into 2 main groups: sea fisheries and shipping flotsam and the land-based inputs. So most of the litter encountered in oceanic water has been dispersed from coastal areas. (Ryan, 2014).
If we wish to estimate the plastic pollution that can result from the total conversion of oil resources on the same current rate basis till the global cumulative oil production is reached, an increase of marine plastic debris of 2.3x than actual pollution is for the future. (Patricia Villarrubia-Gòmez, 2017).
II. MPP dispersion
This pollution travels from coastal sources to subtropical gyres where it accumulates under its smallest form “microplastic particles”, this mechanism is known as weathering of macroplastics. There are 5 subtropical gyres that constitute accumulation zones for marine plastic debris, far away from original sources. These gyres are formed due to a combination of surface currents, mainly Ekman currents driven by local wind and geostrophic currents caused by sea level gradients balancing Coriolis force. In early 1970’s, floating plastic fragments have been detected in the Northern hemisphere subtropical gyre in the North Atlantic and North Pacific (Marcus Eriksen, 2013) , however, it was until 1997 that Charles Moore discovered the garbage patch in the Pacific Ocean while captaining a Yacht race.
Figure 1: The distribution of ocean garbage patches among subtropical gyres. Photo retrieved from (Greenhost, 2017)
III. MPP weathering
Plastic loses its elastic properties under the effect of UV degradation, hydrolysis, biofouling and biological degradation, then progressively starts to fragment into smaller particles under the power of wind and waves but never degrades totally. Hence, this debris will survive in oceanic water many years because of their chemical composition and slow rate of degradation. (Evan A. Howell, 2012)
This decomposition of plastic into micro-sized particles makes its substantial removal from marine environment almost unfeasible, meaning that plastic exposure is made irreversible. This stated, oceans have to deal with an estimated average of 4 million tons of plastic debris (Patricia Villarrubia-Gòmez, 2017), where this number still does not account for all the marine plastic because of the uncertainty about actual pathways and the fraction of onshore deposition.
IV. MPP effect on ecosystems
Plastic debris is important viruses and microbial communities’ host, as well as a platform for the growth of harmful algal bloom species, constituting what is today known as “Plastisphere”. It is considered as a transport vector of alien invasive species and of POPs, hence each plastic particle holds within it the ability to drive living organisms and redistribute toxic substances. This can result in modifying ecosystem composition and substances concentrations, and impact genetic diversity negatively. (Patricia Villarrubia-Gòmez, 2017)
Figure 2: Illustrative example of the effect of plastic debris on marine life, photography by Chris Jordan, U.S Fish, and Wildlife Service. (Caryl-Sue, 2014)
Besides its indirect effects as pollutants carrier, plastic has direct effects on organisms and systemic effects that come across multiple spatiotemporal scales.
The harmful effect of plastic debris can be explained through plastic additives high toxicity (plasticizers, flame-retardants, dyes, and others), and chemical composition of substances present in seawater that can be sorbed onto plastic surfaces. Examples of these effects are adverse rates of fecundity and reproduction in oysters and copepods in case of a high intake of microplastic. (Patricia Villarrubia-Gòmez, 2017). To this extent, it is important to highlight the role of copepods in trophic chains and carbon cycle, since they feed on phytoplankton and are preys to larger organisms, their plastic ingestion can thus impact higher trophic organisms and result in further accumulation in the marine food chain, including at the end Humans.
Marine debris can also alter biota physical environment, by changing their physical properties such as permeability, nutrients and water flows, and subsurface temperature, impacting among others marine turtles sex determination which is highly temperature- dependent, and devastating seabirds like albatross and other marine organisms. Fig. 2 illustrates the stomach contents of an unfortunate albatross including plastic marine debris fed to the chick by its parents.
V. The great pacific garbage patch
Oceanographers estimate that 5 garbage patches exist globally in subtropical gyres and Highs and that they are located in the North and South Pacific Ocean, North and South Atlantic Ocean and the Indian Ocean, highlighted in Figure 1. (Sesini, 2011)
Figure 3: Pacific garbage patch bounded by massive North Pacific Subtropical Gyre. Map by National Oceanic and Atmospheric Administration (NOAA)
Yet, only 2 garbage patches were explored by marine expeditions as for the remaining are estimated with mathematical models and simulation based on the amount of plastic drifted in the marine water. The greatest garbage patch of them all being the north Pacific patch also known as Trash Vortex, located between Hawaii and California (Figure 3). It is an accumulation of plastic concentration rendered in the subtropical gyre and degraded into microparticles under the effect of mechanical waves and wind transport of this zone. Although this patch is usually imagined as physical islands of plastic that can be detected in the naked eye, the reality differs from expectations. Since the patch is more a soup like a medium of small/ microscopic plastic debris, and form a “Smog” as Dr. Marcus Eriksen calls it. (Moore, 2016)
Figure 4: The plastic retrieved from Moore’s expedition of the south pacific garbage patch in 2017. Photo copyrights Algalita (Desantis, 2017)
While Moore reported in his study of 11 random sites in the North Pacific Subtropical High zone (NPSH), back to 2001, a large mean abundance (334,271 pieces/Km2) and weight (5114 g/ Km2) of plastic pieces (Evan A. Howell, 2012), whose size classes ranges from 0.355 mm to less than 1 mm (0.999 mm) (Marcus Eriksen, 2013), recent model studies and ocean explorations show greater plastic concentration in this region. As a matter of fact, Scientists have collected up to 750,000 bits of microplastic in a single square kilometer of the Great Pacific up to 2014 (Caryl-Sue, 2014). This increase can be explained by the increased reliance on disposable plastic or single-use plastic and production peaks. In fact, the plastic encountered in marine debris, if it still has not been fragmented, compromises packaging items (bottles, cups, bags, polystyrene food wrapping), fishery-related plastic articles accidentally or on purpose abandoned (ropes, nets, fishing gears and trays) and other plastic items (bucket, shoes, gloves…)
These estimates of plastic in the oceans urge a crucial cleanup and intervention from communities and countries. However, none of the concerned neighboring countries will consider garbage patch as one of its responsibilities and start an action plan to clean ocean trash since the already sinking pollution has the potential to cause government bankruptcy if conventional nets are to be used.
Figure 5: Cumulative plastic waste generation and disposal (in million metric tons) (Roland Geyer, 2017)
VI. The Ocean Cleanup initiative
Among the efforts made to clean the ocean from trapped plastic, Ocean Cleanup initiative is the 1st claimed feasible method to rid oceans of plastic. Ocean Cleanup is a concept founded by the Dutch inventor Boyan Slat.
Since using vessels and nets will be extremely costly, time-consuming, labor intensive and lead to vast amounts of carbon emission, the Ocean Cleanup has developed a passive system that relies on the ocean currents to catch floating plastic. Their system is comprised of a floater with a solid screen underneath, concentrating the debris and leading it to a collection system. It is slowed down by a drift anchor suspended at an approximate depth of 600 meters, making the system move slower than the plastic and therefore catching it. This project estimates to clean up to 50% of ocean plastic within 5 years and concentrated plastic will be brought to the shore, recycle and sold, in order to fund the cleanup expansion to the rest of trash vortexes. The first cleanup system deployment in the Great Pacific Garbage Patch is scheduled to take place in May 2018 (Greenhost, 2017).
The rise in plastic production, the great amount of mismanaged plastic debris entering the oceans and the barely significant impact of cleanup efforts worldwide indicates a situation of ignorance about the disruptive effects that pollutants may have on Earth-system processes. Marine plastic pollution is a real threat to living ecosystems, it can affect marine life and break natural balance. And the need for a precaution strategy is hence one of the major concerns.
While the elaboration of international convention on marine plastic debris is being discussed, individuals are encouraged to take action and be more aware of their own behavior on the environment. The Refuse campaign #4R’s launched since 2010 by TEDx great pacific garbage patch is one of the worthy plans to adapt to combat human addiction to plastic. It can be summarized with 4 actions: Refuse, Reduce, Reuse, and Recycle.
Each individual playing an important role in ecosystems conservation, the ocean cleanup project can see the light and plastic debris shall not only be removed from marine water but also reduced from the source, which will allow a more sustainable perspective of marine resources.