Mesoscale eddies and plastic dispersion

Abstract

It is widely accepted that floating plastic debris have a negative effect on the ocean environment. However, while the variability in plastic concentrations in the ocean is well understood on the gyre scale (Ekman dynamics), little is known about the variability on the mesoscale. For these reasons, it is important to gain a better understanding of the distribution of plastic in the ocean. Thus, the objectives of this work include exploring the possible relationship between the concentration of surface microplastic within mesoscale eddies and the flow direction of the eddies, the potential relationship of chlorophyll and eddy activity, as well as the ways in which mesoscale eddy dynamics may influence the transport of surface microplastic. To achieve this, plastic data from surface trawling nets was collected from multiple sources, and analyzed for the time period 1995-2019. The analysis was carried out with respect to eddy mechanisms in the ocean, with eddies identified by an eddy-tracking tool, using sea level anomaly data as the input. The relation to remote sensed chlorophyll-a concentration data at the surface of the ocean was also studied in the main areas of interest – the North Atlantic, the North Pacific and Worldwide. Anticyclonic eddies were observed to contain higher percentage of plastic concentrations in all areas of interest compared to cyclonic eddies. Except for the North Atlantic region, the highest percentage of plastic was found outside of eddies. Data in other regions was too sparse to support making similar conclusions, as more data will be necessary to fill in the gaps and being able to investigate on a global scale the relationship between plastic marine debris and eddy dynamics.