09 December 2010

Rising from the deep: Plastic!

Marcus Eriksen

The 5 Gyres crew arrived in Cape Town at 02h30 yesterday morning through thick fog. The crew has been conducting research into plastic pollution in the southern hemisphere. You can meet the 5 Gyres crew aboard the research vessel Sea Dragon tomorrow at the yacht marina next to the Aquarium. This article, written by 5 Gyres co-founder Marcus Eriksen, was originally published six days ago on the 5 Gyres blog.

A sea sample retrieved by the 5 Gyres team

We’re now on the southeastern edge of the South Atlantic Subtropical Gyre, on the home stretch to Cape Town, South Africa. We’ve had the joy of a week of spectacular weather, and even a minke whale travelled alongside our boat for a while today, breaching the surface to show its pointy dorsal fin. The sea surface is calm, relative to the storms we had a week ago. It almost looks glassy at times. We’re still trawling.

Every sample contains plastic, but it’s different. “What’s all that string in there?” a crew member chimes in, as the high-speed trawl comes in over the rail. The end of the net is heavy with slimy salps [underwater filter feeders].

Hovering in the net between them are dozens of plastic fragments, like confetti.

But also there are long pieces of coloured nylon and mono-filament fishing line. It is unusual. This has happened before, the way plastic in the trawl changes with the weather. But why?

When the wind and waves become calm, the plastic rises. In higher sea states plastic is churned below the surface. Larger fragments stay on top. In our trawls conducted during eight to 10 foot seas, we only found large, pea-sized fragments. There was no line and no small fragments.

Now, this has changed. Mono-filament line and nylon are relatively close to the density of seawater, so it doesn’t take much to drag them down. But after a few days of calm, these types of plastic slowly migrate to the surface.

One big question yet to be answered is, “What is the effect of sea state on the vertical distribution of plastic pollution?” Our experience sailing 4 000 miles across the South Atlantic Ocean is giving us a glimpse at the answer.

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