Paper: Lavender Law, K.; Morét-Ferguson, S. E.; Goodwin, D. S.; Zettler, E. R.; DeForce, E.; Kukulka, T.; Proskuroski, G. Distribution of Surface Plastic Debris in the Eastern Pacific Ocean from an 11-Year Data Set. Environ. Sci. Technol. 2014. DOI: 10.1021/es4053076
There’s been a lot of news floating around about “The Great Pacific Garbage Patch”, the region of the Pacific Ocean where all of our long-lasting plastic products accumulate (Read Zoe’s post about the South Pacific Garbage Patch here). While you may have seen photos showing large pieces of plastic trash floating in the ocean, most plastic pollution comes in the form of small plastic shards and beads.
Marine microplastics, small plastic pieces on the millimeter scale, are still a very new area of research; we are just beginning to understand how these materials behave, where they go, and how they impact marine species. Many plastics, like industrial pellets (nurdles) and microbeads from soaps, enter the ocean as small pieces. Others are broken down into small pieces as larger plastic debris becomes brittle and is broken down by the Sun, wind, and waves. Small plastic pieces accumulating in the ocean can harm birds and marine wildlife that ingest the plastic and suffer internal injuries. Researchers have also discovered that the plastic can host and transport invasive species or absorb and leach toxic compounds. You can read more about how microplastics interact with the environment here, here, and here).
While scientists are well aware that the Garbage Patch exists and is made up primarily of microplastics, several questions remain. For example: How big is the Garbage Patch? How much plastic does it contain? Is the Garbage Patch growing over time? How long do plastics remain in the Garbage Patch – do they degrade or eventually sink? Global plastic production increased 41% from 2002 – 2012 and every year we depend on plastic more and more in our daily lives. It is crucial that researchers find answers to the above questions and develop ways for us to minimize the release of plastics to our oceans.
http://youtu.be/g3dq07GXhxQ Kara Lavender Law and other scientists worked along with undergraduate students as part of the Sea Education Association (SEA) Semester Program to collect samples and analyze data from more than 2500 net tows taken on 97 research cruises from 2001 – 2012. 95 of these cruises were part of the . The 97th was the Plastics at Sea Cruise, which was aimed at sampling regions in the convergence zone expected to contain elevated concentrations of plastic debris. Samples were collected by dragging a mesh net along the sea surface, a method originally intended for sampling plankton. The “tow area”, the amount of sea surface skimmed by the net, was determined from the net’s width and the tow distance. After samples were collected, any plastic pieces visible to the naked eye were picked out, counted, and archived. For samples that contained very large amounts of plastic, a portion was counted and the data was extrapolated to find out about how much plastic was in the entire sample.
The authors found that 93% of plastic found in all 2500 net tows was from the “accumulation zone” outlined in the box within Figure 1. Concentrations in some locations exceeded 1,000,000 pieces/km2 (1 piece per square meter). The researchers used average plastic particle mass (0.014 g) and the concentrations they measured to estimate that there are 21,290 tons of microplastic floating in the eastern Pacific Ocean – 10 times more than estimates for the North Atlantic gyre.
To understand the distribution of plastics observed in their data, the authors needed to understand how the surface ocean water circulates. The areas of highest accumulation were associated with the subtropical convergence zones, which occur in the central regions of oceanic gyres. The major gyres in the Pacific Ocean are shown in Figure 2. The North Pacific gyre is separated into an eastern and western gyre – here, researchers were sampling the eastern gyre. In convergence zones, surface currents from distant regions come together – anything buoyant floating along with the currents will accumulate in this region and presumably remain until they degrade or sink.
The authors highlighted and discussed many difficulties that have plagued scientists studying microplastics:
(1) Lack of temporal trends:
This study and many others have not been able to measure any change in the concentrations of plastics over time even though we know plastic production is increasing. Theoretically, concentrations should be increasing over time. We don’t yet understand why temporal trends aren’t readily observable. One reason might be due to small-scale variability: the exact location of maximum accumulation changes over time due to changes in wind patterns, and concentrations of plastics can change drastically over small distances, so it is difficult to track changes in concentration over time.
(2) Poor spatial coverage:
Even though the North Pacific gyre has been intensively studied for plastic accumulation and this study used the most extensive data set to date, the authors noted that spatial coverage is still poor because the region is so vast. The full extent of the subtropical accumulation zones is still unknown.
(3) Plastics come in all sizes and shapes:
The plastics counted here don’t include very small microplastics that pass through the net or rare, larger pieces of plastic debris, so researchers don’t know what percentage of total plastic debris they are sampling. This is a problem many researchers have encountered, and requires more standardized methods of plastics sampling to be developed.
What Can I Do to Help?
All of this talk about marine pollution may have you wondering: “What can I do to help”? While the problem is vast and cleaning up mid-ocean gyres would be an inconceivably huge undertaking, there are things we can do to slow continued accumulation of marine debris.
The best place to start is reducing your own plastic use. Bringing your own grocery bags to the store or your own coffee cup to the cafe are two simple ways to get started. If you want to do more, organizing or joining a beach cleanup is another way to contribute. You can find out more about beach cleanups from the Ocean Conservancy and Save the Bay. You can even contribute to scientific research by sending nurdles you find on the beach to the International Pellet Watch!