Eriksen, M.; Maximenko, N.; Thiel, M.; Cummins, A.; Lattin, G.; Wilson, S.; Hafner, J.; Zellers, A.; Rifman, S. “Plastic pollution in the South Pacific subtropical gyre.” 2013. Marine Pollution Bulletin, 68, 71-76.
Some scientists are now referring to the human contribution to the geologic record as the anthropocene. This is the layer of earth currently being deposited, much like ancient layers of sediment, but defined by concrete, development, mining, and trash. One significant component of the anthropocene is plastic.
Petroleum-based plastic litter has become so ubiquitous on our home planet that it contaminates land and ocean habitats alike, even reaching some of the world’s most remote beaches. It is the dominant anthropogenic (man-made) debris in the marine environment, representing 60-80% of flotsam. As of 2007, more than 260 species of fish, seabirds, turtles, and marine mammals were found to ingest or become entangled in plastics. In addition to physical harm, microplastics (<5mm diameter) can absorb and transport organic contaminants, which can be toxic to wildlife (Teuten et al. 2007). Humans also feel the effects of a dirty ocean: trash on beaches and interference with boat navigation.
Plastic debris has been found in both the North Pacific and North Atlantic since the early 1970s. Plastics enter the ocean by several different avenues: river outflows, beaches, maritime activities, and illegal dumping at sea. They accumulate in naturally forming gyres located in the subtropical zones of the world’s oceans (Figure 1). These gyres are the result of the combined effects of currents formed by local winds and currents maintained by the rotation of the Earth.
Previously, large pieces of plastic pollution were documented in the South Pacific Subtropical Gyre (SPSG), but this study is the first of its kind to determine the presence and abundance of microplastics in that area. Exposure to sun and water weakens the elasticity of the plastics, causing them to break into smaller and smaller fragments. So, the image of a garbage patch being like an island of trash isn’t quite accurate. Some liken it more to a “plastic soup,” where tiny plastic particles are mixed through the water column. The depth of plastic distribution depends upon the turbulence of the water, as well as the size and type of plastic present.
South Pacific Subtropical Gyre (SPSG) Study
Eriksen et al. conducted a survey of the SPSG in March/April 2011 upon the S/V Sea Dragon. Towing a 333µm mesh net at 15cm depth, they collected 48 60-minute samples over a 2424 mile transect (Figure 2). Plastics were discovered in 46 samples; the two eastern-most sites did not yield any plastics. The research team used ocean currents and winds to predict patterns of plastic concentrations and to determine the sampling path. As hypothesized, their results showed that concentrations were greater within the gyre than in the areas surrounding the region, exhibiting an average of ~27,000 pieces of plastic per square kilometer, weighing in at ~71 grams of plastic per square kilometer. Moreover, nearly 90% of both the total count and total weight of plastic was found within the center third of the sample transect, meaning the center of the gyre had the highest plastic concentration (~400,000 particles per square kilometer).
Different types of plastic debris were identified and categorized during this study. The most abundant category was fragments, with 55% of the particles falling between 1.00-4.749mm in diameter. In particular, fragments of foamed polystyrene, along with plastic bags and food sacks were the most abundant plastic pollutants in the SPSG. These plastics are all associated with aquaculture (farming of fish, crabs, aquatic plants, etc.). Although low in count, pellets accounted for ~10% of the total weight of plastics collected. Also known as nurdles, pellets are the raw form of plastics transported for use in industry. The scarcity of smaller particles (0.335-1.00mm) may be indicative of their turbulent transport to depths below 15cm, reduced buoyancy due to biofouling (biological growth on the plastic’s surface), ingestion by marine organisms, or beach deposition.
The study by Eriksen et al. documents and confirms the existence of a plastic garbage patch in the SPSG. Although some transfer from the North Pacific and the Southern Ocean may occur, the main sources of plastic to this gyre are the coastal margins of the South Pacific. The garbage patch is similar to the better studied examples in the northern hemisphere, although it exhibits lower plastic concentrations due to fewer inputs from shipping and shore activities.
The negative environmental consequences of plastic pollution necessitate an understanding of the spatial distribution of plastic in the ocean. Ongoing and future expeditions to less studied regions that favor plastic accumulation will improve our understanding of global plastic dispersal and direct policy to mitigate this growing problem. In the meantime, we can all help with the effort by being conscious of our plastic use, reducing consumption, and recycling more. Whales shouldn’t be swimming in plastic soup.