Investigating Microplastics and their Transport in the Atlantic Surface Ocean

Abstract

Microplastics are a serious threat to the marine environment. Understanding their characteristics and transport aids policy and mitigation efforts. The three primary aims of this study were to first contribute large-scale field samples of microplastics in the surface ocean to the research community, with focus on providing samples from the under-represented southern hemisphere. Best-practice guidelines were to be followed where possible and minimally processed data to be made open-access alongside clear methodological reporting. Then, the abundance characteristics of microplastics from these samples were to be analysed and discussed within the context of the literature. Samples were to be grouped by ocean current region as a means of exploring their transport. Finally, a two-dimensional Lagrangian particle tracking model was to be implemented with the aim of understanding the transport of these particles to the remote oceanic locations they were collected from, and their possible coastal sources.
Two transects of surface ocean microplastic samples were presented, one independently conducted, both with methods aligning closely to best practice and published/ in process of publishing under FAIR (Findable, Accessible, Interoperable, Reusable) principles. Two articles were prepared, the first focusing on abundance characteristics of microplastics from a single transect, and the second combining both transects and investigating microplastic assemblage by current region and transport pathways to collection sites via a Lagrangian particle tracking model.
The study showed that, in the 2021 transect, there was an abundance of 0.011 items/m3. The dominant polymer type was HD-PE (63.4%), shape was fragment (88.6%), and colour was white (59.1%). While comparison to the literature is complicated by methodological and reporting differences outlined in the Background, these findings align with findings from previous work. The paper concludes that one location cannot be used as a proxy for another, but that continued monitoring and reporting is necessary to understand the microplastic assemblage of a region.
In the second report, microplastic assemblages were compared between ocean current regions, finding that microplastics in the ECs (Equatorial Currents) are significantly less abundant and less diverse in particle colour, shape, and polymer type. Lagrangian particle backtracking reveals that very few (0.038% of 2-year trajectories and 0.0029% of 10-year) trajectories cross the Equator, but that particle leakage between ocean basins is otherwise ubiquitous. The paper concludes that the equatorial currents act as a physical barrier to surface ocean transport of plastics, and that while the nearest coastline is not necessarily responsible for the marine litter in a given area, within the Atlantic Ocean basins, the litter likely entered the marine environment in the same hemisphere.
I conclude that continued monitoring of surface ocean microplastics is important for optimising policy and mitigation efforts, but that this monitoring needs to closely comply with best-practice methodologies and reporting guidelines, and that one location cannot be used as a proxy for another. The Equatorial Currents are a barrier to transport between the North and South Atlantic, but that seepage between ocean basins is otherwise common. Effective policy and mitigation efforts therefore require inter-governmental co-operation to reduce the impacts of microplastics on the marine environment.

Date of Award	28 Apr 2026
Original language	English
Awarding Institution	Bangor University
Supervisor	Yueng-Djern Lenn (Supervisor) & Mattias Green (Supervisor)