This blog post is written by Mike Clare, Ian Kane and Elda Miramontes. Mike is a researcher at the National Oceanography Centre (UK) who measures deep-sea currents to find out how they affect natural and human systems. Ian is a researcher at Manchester University (UK) who studies microplastics transport across a range of natural environments; from mountains to the deep-sea. Elda is a researcher at the University of Bremen (Germany) who uses ocean science data to understand the effects of seafloor currents in the modern day and over geological timescales.
Plastic can be fantastic
Since mass-production of plastic started in the 1950s, it has been used for so many things: for packaging to keep food fresh; to make affordable syringes for vaccinations; and probably much of the computer or mobile device on which you are reading this blog right now! In fact, it is hard to think of many items we use in our day-to-day lives that don’t include plastic in some way.
In recent years, plastic pollution in natural environments has gained a lot of attention in the media. However, how it gets there, where it will end up, and how much we should be worried about it remains unclear. Geoscientists have an important part to play in addressing these challenges.
A disposable way of life
Plastic has become so widely used because it is lightweight, hardwearing, waterproof and relatively cheap to produce for a range of applications. Unfortunately, these same benefits also explain why plastic pollution has become a global issue. The widespread use of plastic, often to make disposable products such as drinks bottles, means that enormous quantities have been created. It is estimated that more than 8.3 billion tonnes of plastic have been produced in the last 65 years – the same weight as 55 million jumbo jets (or 8,433 billion pints of beer). Much of that plastic gets thrown away and either ends up in landfill or enters the natural environment, where it can be harmful for wildlife and potentially for human health.
Microscope photographs of microplastics commonly found in the deep sea, including microfibres (A) and tiny fragments of plastic (B). Figure from Kane and Clare (2019)
Plastic pollution all over the planet
Expeditions have found plastic everywhere scientists have looked for it: from the top of Mount Everest to the deepest trenches at the bottom of the ocean. Much of the plastic litter that has been found in these natural environments occurs as fragments and fibres, some of which are as thin as a human hair. These tiny particles are known as microplastics, and due to their small dimensions are often accidentally eaten by animals of all sizes.
Microplastics are either created from the breakdown of larger pieces of plastic as they are worn down, or are created intentionally – like the tiny fibres used to make clothes. Just one washing machine load can generate hundreds of thousands of fibres that make their way into the natural environment. Their lightweight and durable nature means microplastics (fibres in particular) can be easily transported over very large distances. But, precisely how these microplastics are transported across the land and into and across the ocean is not well understood.
Going with the flow, but where does it go?
Rivers play an important role in transporting plastic to the ocean. Waves and currents on the sea surface then transport that plastic across the oceans, locally swirling around to create a concentrated ‘soup’ of floating plastic. However, more than half of all plastics sink, with the plastic floating on the surface accounting for less than 1% of all of the plastic in the ocean. So, the missing 99% of plastics must be somewhere else in the ocean- but where? Recent studies have shown that deep-sea currents also transport plastics, carrying much of this pollution deep below the ocean surface to its final resting place on the seafloor where it can become buried.
High concentrations of microplastics have been found in some parts of the deep sea, such as in underwater canyons and vast piles of sediment created by oceanic circulation. Sadly, these sites are also important sites for vulnerable wildlife, such as corals that provide important habitats for a host of other marine life. It is therefore important to map and predict the likely trails of plastic pollution around the world, to understand which ecosystems are likely to come into contact with it, and to what extent.
The role of geoscientists in tackling plastic pollution
Geoscientists study deep-sea currents, rivers on land, and other processes like wind, to explain how other types of tiny particles (called sediments, like sand, mud and dust) are transported, how they break down and where they end up. Plastic, due to its abundance, has effectively become a new type of modern day sediment that can be tracked through the natural environment by geoscientists using existing and new tools.
Some of the processes that transport microplastics in the deep ocean, including deep-sea currents that flow down underwater canyons and bottom currents that flow along the seafloor. Sadly, these currents can concentrate microplastics in the same locations (such as submarine canyons and sediment drifts) where deep sea organisms live. Figure from Kane et al. 2020.
Out of sight, but not out of mind
Plastics have only been around in large quantities since the 1950s. We don’t know for certain how long plastic will last in the environment, but its durability means that some plastics will likely last for hundreds or thousands of years without degrading significantly. For that reason, geoscientists are now finding plastics in sediment deposits all around the world, sometimes providing a record of how human activity and waste production has changed over time.
Efforts are now needed to reduce our reliance on plastics, promote recycling, and stem the flow of mismanaged waste into the natural environment. Hopefully in hundreds of years’ time, geoscientists will see evidence of a more responsible attitude to waste disposal when they look back at the deposits that we left behind.
Feature image: Unsplash Ishan @seefromthesky