Mapping Plastic Pollution
GIS Maps of Plastic Density in the North Pacific Subtropical Gyre (NPSG)
Learn about AMRF plastic pollution sampling methods >>
Below you will find links to a series of maps created by the Algalita research team using GIS (Geographical Information Systems) which represent 10 years of research in the North Pacific Subtropical Gyre. While data is collected and analyzed in various ways, the following maps focus on representing the the count density of plastic per cubic meter of water for Manta trawl samples only. Select a tab below to access the maps for a specific year or range of years.
Sampling in the North Pacific Gyre: Background
Since 1999 Algalita has been collecting data on plastic pollution in the NPSG. Originally Algalita suspected the "Eastern Garbage Patch" as the area of highest debris accumulation. As more data is collected we are discovering that the boundaries of the original Eastern Garbage Patch are likely an underestimation of the prevalence of plastic pollution in the NPSG. It is important to note that not one sample collected during any of our six research expeditions has been free of plastic!
In attempt to understand the scope of the plastic pollution, the ORV Alguita has both resampled the same locations within the NPSG and extended our sample range. By resampling the same area we can compare the repeated sample locations to try and figure out the rate of plastic accumulation in the area. By extending our sample range we are gaining a better perspective on the pervasiveness of this problem (see map below.)
Sampling Methods
Step 1: Sample Collection
Method 1: Surface samples with the Manta trawl
Surface data is collected using a Manta trawl, a device that captures surface debris in a fine mesh net. The manta trawl skims the ocean surface and can trap particles as small as 1/3 of a millimeter. The Manta trawl has two angled wings that keep it floating on the ocean surface, as well as a hood that directs surface splash back into the trawl.
The trawl has an opening which is 90cm wide and 30cm tall, called an aperture. At the end of
the aperture a 333 micron (or .333mm) mesh net is attached which terminates in a small collection sock called the cod end (see right).
After several miles of trawling (trawl length depends on volume of debris and zooplankton filling the trawl) the Manta trawl is lifted out of the ocean. The inside of the mesh net is washed into the cod end, which is then removed, strained, and preserved in a collection jar for land-based analysis. Each sample is labeled and stored with a corresponding data sheet which includes the start and stop time and location of the trawl, start and stop numbers on the flow meter (the flow meter measures the distance trawled), time of day, and any other miscellaneous notable information about the trawl.
Method 2: Sub-surface samples with the Bongo Nets
A Bongo net is a paired net device which can take samples throughout the water column. The net openings are 61cm in diameter with 3m long, 333 micron nets and 30x10cm2 collecting bags. Bongo samples are taken at depths of 10, 30, 50, and 100 meters.
Step 2: Sample analysis
Sorting
At the lab samples are placed in fresh water and floating plastic debris is removed. A dissecting scope is then used to remove and sort the remaining debris and plankton. Debris is sorted in to following categories: plastics, tar, rust, paint chips, carbon fragments, and feathers. The plastics are further categorized as: fragments, styrofoam, pellets, polypropylene/monofilament line, thin plastic films, and resin. Each category was sorted into size classes using Tyler sieves of 4.75, 2.80, 1.00, 0.71, 0.50, 0.35mm and then counted.
Weighing
In order to figure out how plastic and zooplankton compare, the dry weight of each sample group is taken. Plastics are oven dried at 65°C for 1 hour and the plankton and other plant material are oven fried at 65°C for 24 hours, then weighed.
