“We don’t know what happens to 99% of the plastic that ends up in the ocean”

On 1 April, Oceanographer Erik van Sebille will begin working as an Associate Professor at the IMAU, and he’s bringing a rich dowry with him: an ERC Starting Grant of 1.5 million Euros that he was awarded late last year. Van Sebille will use the grant to study the distribution of plastic in the ocean. “80% of all sea birds studied have plastic in their stomachs, and we don’t know how it got there.”

“It feels like coming home”, says Van Sebille. “I studied at Utrecht University for exactly 10 years, from the first day of my Bachelor’s to my PhD in 2009.” For the past seven years, Van Sebille has worked at several international universities: as a Postdoc in Miami and as Lecturer/Fellow in Sydney, and for the past few years as a Lecturer at Imperial College London. “Utrecht has always had a warm place in my heart, and I’ve always maintained contact with my colleagues here. The opening at the IMAU was a perfect fit, and I feel privileged to be able to come back here.”

Stuck in ice

When he enrolled in the Physics Bachelor’s programme, Van Sebille’s plan was to specialise in Meteorology. “I really wanted to be a weatherman. But then in the fourth year of my studies, I had the opportunity to join an expedition to the Canary Islands, which was awesome. Since then, I wanted to be an oceanographer and do exciting things with big boats and big instruments.” Has that dream come true? “After my studies, I went on several expeditions, especially ones based in Miami. While I was in Sydney, I travelled to Antarctica on a ship that got stuck in the ice. Although the expedition was a great scientific succes, I’ve kept closer to home since then.”

Data analysis

Has his passion for expeditions changed to something else instead? “My work had already gradually shifted towards data analysis, the simulation of ocean activities. Today, my research mainly focuses on the question of how ocean currents spread things around the ocean.” Van Sebille was awarded the ERC Starting Grant to study how plastic moves in the ocean. “For that, ocean currents alone are not enough; you also have to study the influence of waves and storms, how fast plastic can decompose into tiny pieces under different conditions, that kind of thing. You only get a good idea of what happens in the ocean when you include all of those factors.”

5 million tonnes of plastic

Researchers currently have a reasonably good understanding of how floating plastic moves around, Van Sebille explains. “But over the past year and a half, we’ve realised that you miss quite a bit if you focus only on floating plastic. There are an estimated 250,000 tonnes of plastic in the ocean, but each year, another 5 million washes into the ocean. That means more than 99% of all of the plastic that has been dumped in the ocean is no longer floating on the surface. So where is it then? Part of it is on the ocean floor – we can observe it in core samples and from submersibles – and some of it washes ashore on beaches and coastlines. But a far more worrisome concern is that a lot of it is consumed by animals. Biologists are finding more and more animals with plastic in their stomachs, for example 80% of all sea bird species. And we don’t know why that is.”

Algae and storms

Van Sebille plans on unleashing computer models on the problem. “In fact, we work with something like a reversed computer model. First we collect as many data points as possible from scientific literature – how much plastic is found at which locations? – and then we adjust our computer simulation so that the results correspond to the data. A lot of factors need to be taken into consideration, such as: how important are algae that grow on the plastic and make it heavier? How important are waves along the coast? How much plastic is washed ashore immediately with the next storm?” Van Sebille’s ERC project is not simply a computer project, however. “We will also conduct simulations using wave tanks. We’ll throw pieces of plastic in the water and watch what happens when we hit them with waves, currents and winds.”

Marine protected areas

In addition to plastic, Van Sebille will also continue studying other things that spread in the ocean, such as bacteria, fish, and larvae. “For that, I collaborate not only with other oceanographers, but also with biologists and geologists. For example, we are working on models of how organisms live in different parts of the ocean, and how that affects where you find these species. In this way, we’re for example trying to figure out the best way to set up marine protected areas that will still be in the same place in 50 years.”