Science to Share

Plastic Pollution

The new North Pole is made of plastic: How ocean currents spread and hide plastic unseen

“Plastic has no boundaries,” Chloe Dubois of Ocean Legacy said in an interview with The Guardian about plastic that ends up in the sea. All seas and oceans are connected to each other and most rivers eventually flow into it. Ocean currents, wind, waves and the rotation of the earth all affect floating plastic, causing it to end up everywhere. Even on the North Pole, where it is so cold that plastic does not decompose and can freeze in the ice. When researchers examine pieces of ice from the Arctic, they find plastic in every piece. And when they check under the North Pole, the bottom is full of plastic. So, who knows, maybe all icebergs of the future will just be frozen plastic.

If you throw away a plastic bottle, where will it end up? “In the trash,” my 14-year-old nephews said when I asked them. But what if that bottle ends up in a river? “Then it ends up in the sea or the Atlantic Ocean. There it floats for a long time, breaks down very slowly or is eaten by a marine animal, “they said. I also learned this myself. But is this always the case? The sea and the ocean are very large, together about 72% of the surface of the earth. We all know the images of large plastic islands floating around in the sea. A lot of plastic ends up here, due to sea currents that go around and round here like a kind of whirlpool. As a result, the plastic cannot escape, and it piles up. But sometimes such a bottle makes a much longer journey. More and more research shows that floating plastic such as a bottle is hidden in ice or deep underwater because ocean currents bring it there.

The currents that carry a plastic bottle spread over all seas and oceans. They can increase floating plastic practically anywhere. If you are standing on the beach here in the summer and your Coke bottle blows out of your hand, straight into the sea, you see it slowly drifting away. At the moment, it is most driven by the ebb or flow of the beach. And by the wind and waves. These create currents in the water, causing the bottle to float further and further away. If it is far enough from the beach, the ebb and flow will not have much of an effect. But other, larger movements are now taking over. These currents arise, for example, by the wind or the rotation of the earth. There are many of them and they all pull and push your bottle.

After weeks or even months of floating in the current in the blazing sun, the label has broken. Plastic can break into smaller pieces and this is very dependent on the temperature: The warmer and the more, the faster it breaks down. The label, damaged by the sun, peels off from the bottle. It floats in the same current. The further these pieces of plastic travel, the longer they will float in the sun. They all lose small parts of themselves, but do not break apart further. These kinds of very small pieces of plastic are also called microplastics and for the time being they float nicely with the bottle.

Our Coke bottle is now slowly drifting north on one of these currents. The bottle has missed the great circular movement of currents that most plastic ends up in and does not become part of a plastic island in the “plastic soup”. This bottle is taken to the North Pole. The water around the bottle cools down and therefore becomes heavier. It slowly begins to sink under the even warmer water that continues to be supplied by the current. The current is now going down. Some pieces of plastic float and end up in the ice. The cold, sinking water pulls down other things that float in the current, including our Coke bottle.

Along the way, the plastic bottle has slowly lost parts: first its label and later all small pieces of microplastic. And they have descended just like the bottle with the cold current. When that current reaches the bottom of the sea, the water is at its coldest and heaviest. The bottle and the small particles are pushed against the sea floor. The bottle bounces and stays against it or gets caught on something. However, the pieces of microplastic fit between the sand grains and settle in the sand. Because the current continues to go down here, they can stay stuck here for a long time. The bottle itself no longer decays, stuck at the bottom of the ocean. The pieces of microplastic in the sand do not decay any further. The sun does not come here, and it is not warm enough for the plastic to decay. Tidy is neat, right?

A current that goes down and then flows through, also rises again. This can be because something is in the way or because the water heats up slowly. The ocean current that the label took with it does not suddenly stop there. These kinds of cold currents run across the sea floor until they rise somewhere. The label of our bottle is also in such a flow, just like other particles of microplastics. These could rise in the Indian or the Pacific Ocean, for example. Or at the South Pole. Even though it is cold there, the water flows upwards by bumping into the pool. And what is in that flow goes up with it. This also applies to the label, microplastics and many other plastics. The plastic drifts somewhere else here, falls apart further or freezes into the ice. For example, a bottle can spread over all seas and oceans, and hide under the water or in the ice for years.

A crab that has taken up residence in washed up plastic. (Photo: Shawn Miller, 2014)

But is plastic cleaned up if it is stuck to the bottom of the sea? Or if it is frozen in ice at the North or South Pole? Small pieces of plastic can come loose again, and our bottle can also be taken further. They don’t decay so they stay there. Maybe a crab will live in it temporarily. The plastic is therefore not gone, but only hidden. And if it rises again at the South Pole or does not sink fast enough in the north, it will freeze in the ice. When the ice of the North Pole has melted, is the only white in there still the plastic that came with it?
And what happened to the label? It floats further around, somewhere in the sea. There it breaks down very slowly or a marine animal eats it, as my nephews predicted. Because plastic has no boundaries.