19 August 2010

Where did all the ocean plastic go?

By
Cosmos Online
Humans are dumping more plastic than ever, but not all of it is accumulating in the garbage patches of the Atlantic as expected, scientists reported.
plastic collection

During the study, more than 64,000 pieces of plastic were collected in nets towed along the ocean’s surface between Newfoundland, Canada and the Caribbean Sea. Credit: SEA/Skye Moret

Plastic pieces

Plastic pieces collected in a surface plankton net tow. Pieces are typically millimetre-sized fragments of once-larger items.
Credit: SEA/Giora Proskurowski

SYDNEY: Humans are dumping more plastic than ever, but not all of it is accumulating in the garbage patches of the Atlantic as expected, scientists reported.

Of the millions of metric tons of plastic produced annually, an enormous proportion ends up as tiny debris in the open ocean. The currents loosely gather it together in vast, swirling ‘garbage patches’ near the surface.

But the amount of floating plastic accumulating in the Atlantic Ocean has remained curiously static over the last two decades, in spite of the fact that plastic waste by humans has increased significantly over the same timeframe, according to a new study published in the journal Science.

Study took 22 years

“Surprisingly, over the 22-year period of the study (1986-2008) we did not observe an increase in the amount of plastic floating in the western Atlantic in the region where it is most highly concentrated,” said Kara Lavender Law of the Sea Education Association and lead author of the study.

Plastic debris has been accumulating in the world’s oceans for decades, but until recently we have had only a peripheral understanding of its extent.

A major pollutant, plastics have far reaching environmental impacts in the ocean, including entanglement of marine fauna, particle ingestion by seabirds and other organisms, dispersal of invasive species to non-native waters and the transport of organic contaminants.

Manually counted 64,000 plastic pieces

The researchers discovered that while highest concentrations of plastic debris occurred in an area where ocean-surface currents converge – the North Atlantic Subtropical Gyre – over the last two decades there has not been a substantial increase in the overall amount.

During the study, more than 64,000 pieces of plastic were collected in nets towed along the ocean’s surface between Newfoundland, Canada and the Caribbean Sea.

Researchers used tweezers to pick the small plastic bits out of the algae and other collected material, and then manually counted the plastic particles: 88% were less than 10 millimetres, and there were likely to be many smaller pieces of plastic that passed through the mesh net used in the study.

Where did all that plastic go?

Although most plastic enters the ocean from land, owing to surface current patterns, the highest concentrations of plastic debris were found far offshore. However, there were no strong trends in plastic concentrations in the data-set over-time.

The absence of a substantial increase in the extent of plastic pollution in the Atlantic Ocean presents scientists with a puzzle: where has the additional plastic gone?

It is possible that it may break up into pieces too small to be collected by nets, or that much of it is sinking below the surface. It is even plausible that the smaller particles are being consumed my marine organisms, but further research is needed to determine the role of each variable.

Deep sea and Antarctica accumulating plastic

Marine scientist Richard Thompson of the University of Plymouth – an expert on plastic debris in the marine environment – warns that “while the study clearly shows no consistent trend in the abundance of debris in the North Atlantic subtropical Gyre we should not extrapolate this to other regions.”

“Over the same time period there are reports of plastic accumulating in remote regions including the Antarctic and in substantial quantities in the deep sea.”

“As indicated by Lavender Law and colleagues, we need more work to establish rates of accumulation in remote regions and in particular rates of accumulation of very small microscopic fragments. Meanwhile we all need to work much harder to dispose of end of life plastics properly.”

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