Big oceans, big IT: Modelling plastic pollution in the ocean

Department of Physics undergraduate Thomas Stokes reflects on his recent research placement at the Grantham Institute.

Approaching a new project can be a daunting prospect. This is especially true when you’re trying to model real-world systems; given how mind-bogglingly complex the ‘real world’ can be, it is easy to feel dwarfed by the problem at hand. Oceanographers, however, can’t afford such anxieties – they deal only in the large scale.

As such, I began my summer research placement (as part of Imperial’s UROP scheme) in  Dr. Erik van Sebille’s group with an air of trepidation. My mission? To fine tune an ocean model capable of describing the spread of plastic pollution in the ocean. Although my knowledge of ocean physics is, relatively speaking, rather limited, I am not one to turn down a challenge. I set out to study the problem at hand and find out just how effectively I could apply my skills within a new context.

Plastics in our ocean

It is estimated that up to 8 million metric tonnes of plastic enter the oceans annually. Once in the ocean, the plastic can experience a range of fates.  Whilst much of it sinks to the seafloor or is washed ashore, the remainder of the floating plastic drifts into the open ocean, driven by oceanic currents. The plastic then accumulates within gyres (regions of convergence in ocean currents), all the while fragmenting into increasingly smaller pieces, known as ’microplastics’. It is thought that these very small plastic fragments, in particular, represent the greatest threat to wildlife. The potential harm to animals ingesting them is not yet fully understood.

Even more disconcerting is the fact that 99% of plastic residing in our oceans remains unaccounted for. This gaping hole in our knowledge necessitates a big modelling project to help understand and tackle the threat posed by the plastic debris; if we were able to catalogue precisely where the plastic ends up, more precise efforts could be made to target the waste. A sufficiently daunting task, I’m sure you’ll agree.

Doing physics the IT way

As physicists, we are taught how to break down a problem into its constituent parts. Even so, developing a program to simulate large systems comprised of many interacting components (currents, in this case) represents an enormous challenge – never before in my undergraduate studies had I been presented with a challenge of comparable complexity.

To tackle the problem, we draw on principles employed by professional software engineers. This means following the same standard practices by which software projects, such as applications, websites or databases, are built. For instance, unit tests are small programmes run during development on an individual part of the code that  are checked with each new update that is made. This ensures any new changes in one part of the model don’t incur errors in previously built parts of the system. Clarity in layout and design make collaboration easier by virtue of improved readability of the program itself since the structure will be universal across all of the program. Perhaps the most useful, though, is the version control system Git. This system allows multiple people to work on a project simultaneously and make changes to code incrementally.

This rigorous approach quickly transformed seemingly insurmountable challenges into  easily digestible tasks that I could carry out one at a time. I found that, through by working on these individual tasks, I acquired an understanding of both the existing model and the underlying physics at far quicker rate than during any project I’d previously attempted. With a computationally based Master’s project around the corner, I’ll certainly be looking to adopt a similar process.

Moving forward, it is the ambition of those working on the plastic tracking project (PARCELS) for it to be the next-generation particle tracking tool within the field of oceanography.

With Erik’s grand ambition of a global inventory for the world’s plastic pollution, there remains a substantial amount of hard work to be done. To have made any tangible contribution to the project is an enormous source of pride for me and I am thankful to have had the opportunity.

Beyond models

During my summer placement, I was also fortunate enough to participate in the Royal Society’s Summer Science Exhibition, engaging with the public and introducing them to the plastic pollution problem. Doing so underpinned the purpose that models serve in the scientific discipline and, on a more personal level, gave context to my summer work as a whole.

Models, while imperfect, enable a more comprehensive understanding of systems and how they may develop over time. It is ultimately imperative that environmental scientists disseminate this information in an effective manner; without public consensus driving pressure upon policy makers capable of implementing change, we cannot hope to solve the environmental problems our society currently faces.