Plastic in the ocean
The Great Pacific Garbage Patch. Perhaps you’ve heard of it? It’s plastic, essentially. Out in the ocean.
Wait, what? What would plastic be doing out in the ocean??? Let’s take a brief look...
The Great Pacific Garbage Patch was predicted in 1988 by the National Oceanic and Atmospheric Administration (NOAA) of the United States. It was first discovered by Charles Moore in 1997 as he sailed back across the Pacific after competing in the Transpacific Yacht Race. After being somewhat puzzled by the amount of plastic he encountered, he began to perform studies on it. It turned out to be an area approximately 2,200 km long and 800 km wide.
People often mistake the Great Pacific Garbage Patch as a large island of rubbish, twice the size of Texas or three times the size of France. It’s actually more like a plastic soup than a landfill-style rubbish site. It is a region of the ocean where there are pieces of plastic suspended at or near the ocean surface, to a depth of about 10 m. However, even just a few pieces of plastic per square metre amounts to a lot of plastic when you add it up over the enormous area of the ocean.
So where did the plastic come from in the first place? The United Nations Environment Programme (UNEP) reports that 80 % of the plastic comes from land, brought by sewer systems and rivers to the sea. 20 % comes from ships and ocean sources like nets or fishing gear, or from containers that have fallen into the sea during severe storms. UNEP also estimated in 2006 that every square kilometre of the ocean contained about 18,000 pieces of plastic.
Where, actually, is all this plastic? In the middle of the gyres. The five main gyres are the North Pacific, South Pacific, North Atlantic, South Atlantic, and Indian Ocean. A gyre is formed by a set of currents encircling a region. The North Pacific gyre is formed by the North Equatorial current, the Kuroshio current, the North Pacific current and the California current. Due to Ekman transport (the fact that when winds blow across the surface of the ocean, the net water movement is actually at 90 degrees to the surface movement due to the Ekman spiral), these currents cause a net movement of water in towards the middle of the gyre. Any floating pieces of plastic are simply carried along with the water movement to end up in the same region. So the Great Pacific Garbage Patch is found within the North Pacific gyre, but similar garbage patches have since been found in all five of the main gyres.
Now remember, plastic never biodegrades – it doesn’t break down into natural substances. Also, because plastics are a fairly new invention microbes haven’t evolved to feed on them like they do on natural polymers. What plastic does is photodegrade. Light causes it to be broken down into smaller and smaller pieces – but all of these smaller pieces are still plastic. As it breaks apart, the plastic ultimately becomes small enough to be ingested by aquatic organisms which reside near the ocean’s surface. The plastic waste then enters the food chain.
In the North Pacific gyre, most of the plastic comes from four sources:
Low density polyethylene (plastic bags)
Polypropylene (bottle caps)
Polyethylene terephthalate, or PET (plastic water bottles)
Expanded styrene (Styrofoam)
Plastics in the water absorb floating chemicals which are attracted to the plastics’ oil base. Many of these chemicals are known as persistent organic pollutants (POP) which never leave the environment or break down, and include pesticides such as DDT, polycyclic aromatic hydrocarbons (PAHs) that are carcinogenic and mutagenic, and dioxins that are toxic industrial waste.
So plastic particles have been entering the food chain, and they could potentially contain nasty chemicals. But there’s more to the story. According to the Monterey Bay Aquarium, up to 1,000,000 seabirds and 100,000 marine mammals and sea turtles die each year from eating plastic. Just check out the photo of an albatross chick from Midway Atoll. Look at all that plastic it had consumed. Tragic.
And that’s a brief introduction to the huge issue of plastic in the ocean. Let’s see what future science can do to fix the issue...
(Let's hear it for Boyan Slat!!!)