An international research team investigated the sinking of tiny plastic particles, which have long been considered “missing” worldwide, in the Southern Ocean off South Georgia for the first time. In Cumberland East Bay near Grytviken, which is heavily frequented by ships, the team contributed to clarifying their whereabouts as part of their case study.
Microplastics in the Southern Ocean have been detected so far on the surface, in and on the seabed and in organisms. To find out how and where the small plastic particles occur in the water column, an international research team led by Clara Manno from the British Antarctic Survey BAS investigated the sinking of particles smaller than one millimetre in the current case study. The authors published the results of the study in the journal Marine Pollution Bulletin.
The research team deployed a sediment trap at the entrance of Cumberland East Bay in South Georgia for the first time in the Southern Ocean over a rather short 24-hour period in January 2019, capturing sinking particles at depths of 50 m, 100 m and 150 m. Analysis showed that most microplastic particles entered the trap at 50 m depth (306 particles per square metre per day), while less than a third marde it down to 150 m depth (94 particles per square metre per day).
The scientists found mostly fibres at all three depths, accounting for 92% of the total material, and these were mostly made up of polyester, which is often used in fishing but is also often a component of outdoor clothing.
In an earlier study published last year, a research team led by Jack Buckingham, a scientist at the University of Hull, found the highest concentrations of microplastics to date in the Southern Ocean in the same area at the water surface near the King Edward Point research station, with an average of 0.6 particles per litre.
Both studies link these comparatively high concentrations of microplastic in Cumberland East Bay primarily to the numerous human activities in the region. On one hand, shipping traffic, especially from passenger, fishing and research vessels as well as private yachts, is quite high: in 2019, for example, 105 vessels came to the bay to register at the office of the South Georgia and South Sandwich Islands administrative authorities. On the other hand, the BAS research station King Edward Point is manned all year round.
The extent to which the input of microplastics by currents from other regions plays a role or microplastics travel from the bay into the open ocean will be the subject of future research. It is also not yet known which small-scale currents in the bay have an influence on the distribution of microplastic particles.
The study also provides the first general indication of the fate of microplastics in the ocean. The small particles, less than one millimetre in size, were hardly represented in samples collected from the water surface in previous studies in different oceans. This led to the assumption that 99 % of microplastics were “missing”. Only recently has the sinking of these particles also been studied and now for the first time in the Southern Ocean. The current study contributes to a better understanding of the impact of the presence of microplastics on marine organisms and the extent to which it interacts with the marine ecosystem.
Julia Hager, PolarJournal
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