Mikayla Clark: UMaine MARINE Seed Grant Recipient

Living in coastal Alaska for the majority of my life let me work and play on the ocean from a young age. Like a lot of budding marine biologists, I loved tidepooling, snorkeling, and getting out on boats as much as possible. My interests began to shift when I went off to college to get my degree in biology. Through classes and independent research I realized that what I really wanted to study was the impacts that we as a society were having on our oceans. I started looking into changing fjord temperatures and potential impacts on glacial melt and finished my undergraduate studies at the University of Alaska Southeast. I went on to aid in collecting samples in the Arctic for a project focused on biogeochemical cycling of trace metals.

My transition to studying marine plastics began when I moved to Maine. It was a new and exciting combination of my interests in biogeochemical cycling and the human effects on our oceans. The NASA EXPORTs project launched a cruise in 2021 in the North Atlantic to help quantify the amount of carbon sinking as the result of the spring phytoplankton bloom. As these plankton die, they begin to sink and this causes a large export of carbon from the surface layer of the ocean to deeper depths. This is a large part of what’s known as the biological carbon pump. One of the tools used to measure the amount of sinking carbon in the ocean is called a sediment trap, which acts as a large funnel similar to a rain catch, and captures sinking material at depth. They found large amounts of sinking microfibers, providing a unique opportunity to study the amount of sinking fibers alongside sinking carbon.

Sediment trap readying for deployment.

This project is fascinating because the microplastics that were captured were specifically the sinking ones, allowing us to see if those types of buoyant plastics that are unusually found at the surface are actively sinking. Additionally, at the base of these sediment traps, there are gels in addition to filters. The gels let us capture clear images of the plastics and any substances adhering to them that might contribute to their sinking, such as dead phytoplankton. 

Microscope images of fibers found at 330 meters (>1000ft) in the North Atlantic Ocean. The scale bar is at 1000µm (1 mm).

We know microplastics are found in every ocean at all depths in the ocean. Previous research has shown that certain plastics which normally float in seawater are commonly found deep in the ocean, yet there was never a definitive understanding of how they sank. One theory is that the microplastics get stuck to these sinking plankton cells (and anything else that makes up marine snow) and essentially hitch a ride to the deep ocean. Because microplastics are usually collected by filtering or trawling with a net, it’s hard to differentiate between what’s sinking, what’s neutrally buoyant, and what’s rising back towards the surface. The gel trap method allowed us to only capture sinking particles and also preserve sinking marine snow to determine if that was the method that was causing the plastic to sink.

My work as a Master’s student in Oceanography was to find out how much plastic was sinking during the spring bloom and compare that to the amount of sinking carbon, measured by Dr. Margaret Estapa. Additionally, I worked in the lab to verify this new method of microplastic collection. I made marine snow in the lab with different types of plastic and different types of phytoplankton and tested how the particles sank into the gels. Additionally, I’ve been able to work with undergraduate students at the University of Maine to sample for plastics locally in the Damariscotta River Estuary here in Maine and look at how the concentrations of surface plastics changes throughout the river and throughout the seasons. While this is a spatial distribution rather than a vertical distribution, it can help us understand seasonal cycles of how plastics move downriver from our coastal towns into the Gulf of Maine.

As we as scientists and a society in general are looking to the ocean to help uptake more carbon, the biological carbon pump has become a topic of interest. Increasing the amount of carbon sinking from the surface to the deep ocean, increases the amount of carbon the surface ocean can pull from the atmosphere. Therefore processes to “speed up” the biological carbon pump have been proposed. As the biological carbon pump is driven by these sinking marine snow particles, it’s important to understand potential relationships between sinking aggregates and marine pollutants like plastic. This project is allowing us to study this relationship in ways that haven’t yet been explored and we’ll be adding to basic knowledge of the transport and fate of microplastics in the open ocean.