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The implications of plastic pollution as seen by oceanographer and Changing Streams Co-Founder and Director Professor Jonathan Sharples

todayJuly 16, 2021


A healthy ocean is fundamental to our existence. That is not hyperbole – life on our planet is fundamentally dependent on having a healthy ocean.

Jonathan Sharples
Professor Jonathan Sharples

When we think about what a healthy ocean provides for us, the focus is understandably on fish. Certainly, fish are a vital source of food for people, but a healthy ocean does much more for us than provide fish. The ocean also absorbs CO2 from the atmosphere – in fact currently the ocean removes about one third of the carbon we emit via fossil fuel burning each year. So, the ocean is vital to the functioning of Earth’s climate. Part of the CO2-absorbing capacity of the ocean is controlled by the tiny plankton, so if we put enough plastic into the ocean to disrupt the plankton food chain (because we know that plankton will ingest plastic) then we could alter how the ocean deals with CO2.

As an oceanographer the focus of my research is particularly on the physics of coastal seas. So, I am interested in the fate of river inputs to the sea, in the circulation and transport of pollutants, and in the supply of coastal pollutants out into the open ocean. The physics of coastal ocean currents will help us understand the sources and distribution of plastics. For instance, plastics on the beaches along NW England could be supplied by the River Mersey – the water from the Mersey tends to flow northwards along the coast once it has left the mouth of the river. We have prevailing westerly winds on this coastline, so beach plastics will be blown ashore from the Mersey outflow and be transported ashore from further out in the Irish Sea. Ideally, we need to quantify what the plastics are that we see on the beaches and in the sea, understand the products that the plastics were originally used in, and finally determine the most likely sources of those plastics to the sea.

My own direct experience with the impact is plastic having on the marine environment is anecdotal, rather than based on any research, specifically on plastics. I recently led a research expedition in the subtropical North Atlantic, a region that I had last sailed through as a teenager with my father on merchant ships (my dad was the 1st mate). To me there is clearly more floating plastic debris in the open ocean now compared to when I was younger. This is borne out by research that has quantified the plastics in the ocean over time.

From years of experience as an oceanographer I am not convinced that it is possible to remove plastics from the ocean. We tend to get a distorted view from media reports of plastic in the ocean. For instance, the “Great Pacific Garbage Patch is often reported alongside images that look like floating landfill. But the density of plastic in the middle of the patch is about 100 kg per square kilometre (and that decreases quickly as you move out of the patch centre). That does sound a lot, but how much would be in one cubic metre of water? If we assume the plastic occurs in the top 10 metres of the ocean, then one square kilometre x 10 metres gives us 10 million cubic metres of water. So, 100 kg of plastic distributed through 10 million cubic metres means about 0.01 grams of plastic per cubic metre. That tells us that, even in a region where plastic has accumulated in the ocean, plastic debris is very dispersed – which means that removing it from the ocean is inordinately difficult.

Most of the plastic in the ocean is in the form of “microplastics”, which are plastic particles less than 5 mm in size – whatever plastic we put into the ocean gets broken down into these tiny particles. Pictures that we see in the media tend to focus on the larger plastic rubbish (e.g., plastic bags, fishing lines) which are a big problem when they are eaten or entangled by the larger animals that we easily recognise in the sea (fish, turtles, whales, seabirds). There is also a complex ecosystem of plankton in the upper ocean, and there is good evidence that the plankton eat the very tiny plastic particles (called “nano plastics”). These plankton are of similar sizes to the plastic particles in the ocean, so an additional problem with removing plastics is that any method of hoovering up the particles would also remove the plankton: so, trying to remove plastics from the ocean could potentially disrupt ocean ecosystems more than the plastic pollution does.

The solution is to stop putting plastics into the ocean in the first place. In order of priority I would say (1) stop using plastics (i.e. use alternative materials) wherever possible, and where we might think it is not possible do the R&D needed to make it possible, (2) recycle far more than we currently do, and (3) develop strategies to clean up the sources of the plastic to the ocean (e.g. rivers and beaches – these sources are where the plastic can be found in much greater concentrations than in the open ocean, so it is easier to collect).

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