When there’s an oil spill, companies and governments run oil spill models to predict where the oil is likely to go and how it will behave in the environment. There has been a lot of work done on how oil interacts with soil and groundwater, the mechanics of the marine environment are different. The models for what oil does in the marine environment and where it goes once it reaches the sediment aren’t very well developed, especially when it comes to how oil interacts with the seabed. University of Aberdeen PhD student Luis Perez-Calderon is trying to add a piece to that puzzle by studying how oil moves through marine sediment.
There were a lot of unknowns about the oil-sediment interaction in the aftermath of the Deepwater Horizon oil spill in 2010. Deepwater Horizon was the largest accidental marine oil spill in the world, spilling 4.9 million barrels of oil into the Gulf of Mexico. Experts are still unsure how much oil ended up in the seabed and where it might have gone from there. To ensure something similar doesn’t happen in the North Sea, Luis is focusing on the marine environment of northeast Scotland where there are over 400 oil drilling platforms. Although the rigs and pipelines are starting to be decommissioned, there’s still a risk of a spill. Once the oil settles into the seabed, it can either go into the sediment or through the sediment, affecting the microbial communities there. Along the way, the oil sticks to the sediment which can be spread by a strong current or weather event. The lessons learned from oil-sediment interaction from Deepwater Horizon may not necessarily be applicable to the colder environment of the North Sea which is why Luis’ work is so crucial.
To examine oil spills in the marine environment without causing an environmental disaster, Luis does oil spill simulations in the lab. He looks at how a commercial dispersant (which breaks the oil up and keep it from reaching shore) changes the way oil moves and interacts with the sediments. One of his experiments was on advective transport in sediments, or how the water carries the oil with it as it moves through the seabed. In this experiment, Luis observed a phenomenon called the Tea Leaf Paradox that was first described in 1926 by good old Albert Einstein. When you stir tea leaves in a cup, the friction on the side of the cup decreases its velocity and the tea leaves aggregate at the bottom of the cup in the middle. And the same thing happened in Luis’ simulation. “I could see in the top of my sediments that there was an accumulation of hydrocarbons in the centre of the chamber as opposed to homogeneously on the sides. The amount that accumulates in the centre is proportional to the size of the hydrocarbon with heavier hydrocarbons accumulating more in the centre. It gives a new dimension to the tea leaf paradox,” he says. He hasn’t done this experiment in the field yet, but he expects he will observe a similar effect.
Besides citing Albert Einstein, one of the coolest moments of Luis’ PhD happened outside of the lab. “I got to go offshore which was pretty cool. I went on a boat for a couple of weeks to get sediments from the Faroe-Shetland channel.” The sediment samples that he collected will serve as a baseline for sediment composition and microbial levels in case there is ever an oil spill. “That was a big problem in Deepwater Horizon because there wasn’t much background information so it was very difficult to say these were conditions before in terms of pollution,” Luis explains.
Luis’ research has shown that using a dispersant to break up the oil slick causes the oil to contaminate the sediment far more than if no dispersant is used. Dispersants are therefore bad for the sediment, but since they prevent oil from contaminating the shoreline are they bad in the bigger picture? Luis isn’t sure. “My research is a piece of the puzzle. You’ve got to weigh out social, economic, and environmental factors. And within the environmental factors, the coast, the fisheries, the seabed, and others. Among this one factor, my work is just a small piece. If you take all the other pieces into account, then you can make a decision.”