A mathematical model of ocean currents has proven successful in predicting the location of the previously known Great Floating Garbage Patch, an area between Hawaii and California with large amounts of degraded plastic debris. This model also shows a mini-gyre that theoretically would accumulate plastic and nets in the area between Panamá and the Galapagos islands, part of which is in Costa Rican waters.
Another recent at-sea study has shown there is indeed a concentration of floating plastic in the area of the north Atlantic predicted by the models. Plastic degrades in sunlight, so most of the samples are of small particles picked up by fine nets. Theoretically this degradation continues to the molecular level, making more of a poison soup on the surface than accumulated debris, though obviously highly diluted. Also, lost ghost nets that keep fishing would accumulate in these productive areas.
University of Hawaii researcher Nikolai Maximenko first developed models of surface currents using the movements of about 12,000 free floating buoys tracked by satellite as part of larger projects. Despite the uneven distribution of the release points of the research buoys, Maximenko used measurements over fairly short periods of time to provide the overview needed.
Extensive computer modeling then filled in empty areas to simulate an even distribution of release points. Real life data shows most of the drifters stayed at sea, with only 30 percent lost in 10 years by being washed ashore. That suggests most debris stays out also.
What the sea current modeling showed is that five large circular gyres which should accumulate floating debris, the
largest being in the North Pacific. Others are in the North Atlantic, South Atlantic, South Pacific, and a smaller one in the southern Indian ocean. The southern Pacific patch would be centered around Easter Island and would be the most concentrated, but has not been documented.
Closer to Costa Rica, the model shows that hypothetical drifters would tend to accumulate near the Pacific coast of Colombia after three years of movement, before dispersing somewhat as do the vast majority of sample points as they move out of the tropics. That means any given item, say a fishing net lost off El Salvador, would travel to that area in about three years and then perhaps move elsewhere.
Most sources would be local, with garbage washed into the ocean by rivers or from coastal settlements. The río Tárcoles, which drains the Central Valley, does have a substantial load of plastic. This in any case is tiny compared to that put out by northern developed countries where at-sea dumping of garbage was commonplace until recently. Also, at the level of development of Costa Rica and other southern hemisphere countries like Chile, local studies have shown how plastic still isn’t a large component of the solid waste stream.
Other sources would have to be nearby also, as in the cities on the Pacific slope of Central America and Colombia. The largest potential source of plastic in the area is Guayaquil, but it is on the edge of the predicted gyre. Maximenko did indicate in an e-mail that his theory suggested that in an extreme El Niño year some circulation to this area could come from California or Mexico.
The impact on fish and wildlife of the larger garbage patches is unknown, and the smaller one here might develop without effect. It is the potential reach of larger sources of plastic and nets that could affect Costa Rica’s turtles and other sea life.