Microplastic pollution in the deep sea ecosystem

: a study from the Rockall Trough, North East Atlantic Ocean

Abstract

Over the last decade there has been growing environmental concern regarding microplastics. Despite the continued and increasing inputs of plastics into the environment, studies reveal lower than expected concentrations in surface waters. More recently reports have emerged documenting high concentrations of microplastics on the deep seafloor, indicating this may be a sink for microplastic pollution, however the residence times and distribution of microplastics within the deep ocean remains relatively poorly studied. The long-term fate of microplastics is considered using a repeat monitoring site located >2000 m deep in the Rockall Trough, North East Atlantic Ocean. The hypothesis that microplastics are present within this ecosystem is tested and their historical occurrence over different time-scales is investigated. Potential sources of the microplastics and their distribution pathways are considered with reverse Lagrangian hydrodynamic models. Firstly, due to the wide variety of methods used to isolate microplastics from environmental samples, a validation of a density-independent oil based method for sediment samples was undertaken and a rapid and non-destructive enzymatic appropriate for biota was developed. The results of this thesis indicate the potential for the widespread presence of microplastics within the deep sea ecosystem. Comparable quantities were enumerated from each of the matrices sampled (sediment, water and benthic invertebrates) as found in their nearshore counterparts. The chronology of plastics was investigated using sediment cores and an archival collection of invertebrates, the results of which alluded to the long-term occurrence of microplastics at this locality. Model simulations indicated that microplastics are exported relatively rapidly and therefore ocean-based sources may have a greater contribution to the overall load found on the deep seafloor than land-based inputs. Complex interactions between abiotic and biotic factors influence the transport of microplastics and their distribution within environmental reservoirs. The investigative work presented suggests that microplastics are a long-term and prevalent pollutant within the Rockall Trough deep sea ecosystem.

Date of Award	4 Jun 2019
Original language	English
Awarding Institution	University of the Highlands and Islands
Sponsors	SAMS Studentship & UHI Studentship
Supervisor	Bhavani Narayanaswamy (Supervisor), Stefan Gary (Supervisor) & Brian Quinn (Supervisor)