Evidence of humanity’s “plastic footprint” continues to grow, with a new study in Science providing the first documentation of high concentrations of plastic waste in the Atlantic Ocean. Yet researchers say you might sail right through the most-polluted waters and never see much trash—most of the debris consists of small plastic fragments only a few millimeters in diameter.
The new study gathers data from over 6,100 plankton-net tows conducted on “semester at sea” educational cruises over a 22-year period and raises new questions about the ultimate fate of plastic debris in the open ocean. While 40 percent of the net tows found no plastic at all, plastic concentrations in some samples taken far offshore reached over 200,000 pieces per square kilometer. Debris densities in some areas rivaled those found in the better-known “Great Pacific Garbage Patch,” an enormous swath of the Pacific Ocean where circulating currents cause floating trash to accumulate.
The study also highlights a mystery. Researchers found no evidence that the amount of plastic in the Atlantic concentration zone has been increasing over time. Lead author Kara Lavender Law says plastic has probably been entering the ocean at an increasing rate corresponding to the four- to five-fold rise in plastic production and municipal waste disposal over the two-decade study period. But the debris is also being broken down and perhaps transported to deeper waters by processes still not well understood. Plastic fragments may be reduced by weathering and UV radiation to a size that allows them to escape sampling. Others may also become weighted down by algal films and sink to the bottom or be ingested by marine organisms. Researchers say any or all of these outcomes may pose serious threats to the marine environment, particularly if the chemical building blocks of all that plastic are eventually released into the sea. ❧
Law, K.L. et al. 2010. Plastic accumulation in the North Atlantic subtropical gyre. Science doi:10.1126/science.1192321.
image: ©SEA/Skye Moret (Plastic pieces collected in a surface plankton net tow. Pieces are typically millimeter-sized fragments of once-larger items.)