Woods Hole (Bernd F. Laeschke – 19.08.2010): Scientists are still trying to figure out how large amounts of marine debris accumulate in certain parts of the ocean and end up floating within the North Atlantic and North Pacific Gyre. The North Atlantic Gyre is estimated to be hundreds of miles (kilometers) across in size, with a density of several hundred thousand pieces of debris per square mile (kilometer). The Sea Education Society (SEA) has conducted extensive research on the Atlantic Garbage Patch. Over a 22 year period, nearly 7,000 students dragged 6,100 fine meshed nets through the Atlantic to collect and study the debris.
Based on the data collected since 1988, a team of researchers from SEA, the Woods Hole Oceanographic Institution (WHOI), and the University of Hawaii (UH) published a scientific paper. A previously undefined expanse of the western North Atlantic has been found to contain high concentrations of plastic debris, comparable to those observed in the region of the Pacific commonly referred to as the "Great Pacific Garbage Patch."
More than 64,000 individual plastic pieces were collected at 6,100 locations sampled every year over the course of the study. The scientists and volunteers used surface plankton nets to collect plastic debris as well as biological organisms at each station. The highest concentrations of plastic were observed in a region centered roughly at the latitude of Atlanta, GA. Numerical model simulations by Nikolai Maximenko (UH) explain why surface currents cause the plastic to accumulate in this region.
“Not only does this important data set provide the first rigorous scientific estimate of the extent and amount of floating plastic at an ocean-basin scale, but the data also confirm that basic ocean physics explains why the plastic accumulates in this region so far from shore,” said SEA scientist Kara Lavender Law, the Science paper's lead author.
One surprising finding is that the concentration of floating plastic debris has not increased during the 22-year period of the study, despite the fact that the plastic disposal has increased substantially. The whereabouts of the ‘missing plastic’ is unknown.
“The analysis presented in this Science article provides a robust scientific description of the extent of plastic pollution to date, which can be used to make better management and policy decisions, and to inform popular perceptions of this issue,” said SEA Dean Paul Joyce.
A companion study published this week in Marine Pollution Bulletin details the characteristics of the plastic debris collected in these tows. Most of the plastic is millimeters in size and consists of polyethylene or polypropylene, materials that float in seawater. There is evidence that biological growth may alter the physical characteristics of the plastic over time, perhaps causing it to sink.
“I think some of the big questions are colonization: who actually lives on these pieces of plastic?” said Chris Reddy of WHOI, who was co-author on both papers. “To what extent are ocean currents moving the small life on these plastic particles around the ocean?”