Terrawatch: plastic-rich canyons forming in the deep ocean

Kate Ravilious
·1-min read
<span>Photograph: Education Images/UIG via Getty Images</span>
Photograph: Education Images/UIG via Getty Images

The Earth’s oceans are the graveyard for almost everything eventually. Fragments of rock, twigs and old leaves are carried there by glaciers and streams; desert sands hitch a ride on the wind and tiny plankton die, decay and settle to the ocean floor. Last year a survey of ocean floors, using seismic reflection data, revealed that the oceans contain a whopping 3.37 x 108 cubic kilometres of sediment – approximately enough to cover Earth’s continents in a 2km thick layer. However, the sediment is thicker in some places than in others, and now a new study shows how a very modern form of sediment – plastic – is forming plastic-rich channels on the deep ocean floor.

Using a flume tank, scientists mimicked what happens to a mix of sand and microplastic pieces when they emerge from a river mouth and enter the sea. Microplastic fragments tended to get stuck among the sand grains, and travelled with them as they fell in an avalanche off a mock ocean shelf. The results suggest that in the real world around 99% of the plastic arriving in the ocean is being whisked down to the far depths by underwater avalanches, potentially travelling thousands of kilometres across the ocean floor, and accumulating in deep sea canyons.