Deep sea sediments of the Arctic Central Basin: A potential sink for microplastics
Introduction
Microplastics are pervasive, persistent contaminants in the world's oceans that warrant concern due to the potential threat they pose to marine organisms. Traditionally, microplastic sampling has been conducted in surface and near-surface waters due to the presumption that the majority of microplastics would be present in that layer of the water column. However, when plastic production and projected plastic input to the ocean was considered, there was an evident mismatch between reported and expected plastic concentrations in surface oceanic waters (Cózar et al., 2014, Eriksen et al., 2014). It was therefore apparent that apart from surface waters, microplastics were present in various environmental compartments in the world's oceans (water column, sea ice, sediments, biota) and that some of these potentially functioned as sinks (Obbard et al., 2014, Woodall et al., 2014). Deep sea sediments have recently been identified as a potential sink for microplastics (Woodall et al., 2014, Bergmann et al., 2017). To date, only a few studies have reported on microplastics in deep sea sediments in various oceanic basins (Van Cauwenberghe et al., 2013, Woodall et al., 2014, Fischer et al., 2015, Bergmann et al., 2017). Despite the fact that each of these studies employed different sampling equipment, extraction techniques and reported microplastic abundance in different units, the consensus was that microplastics have made it to the deep-sea and that they are pervasive in its sediments. Presently, uncertainty still exists regarding the exact mechanisms that are responsible for the vertical transport of microplastics out of surface oceanic waters and into deep sea sediments.
The Arctic Ocean, though one of the most remote oceanic basins in the world, has been subject to the entry of plastic debris into its ecosystem. It has been suggested that this plastic debris, in particular microplastics, could have entered the Arctic ecosystem via a combination of (i) long-range transport processes, e.g. via oceanic currents (Zarfl and Matthies, 2010, Van Sebille et al., 2012), biotransport (Mallory, 2008, Provencher et al., 2012) and riverine input (Obbard et al., 2014) and, (ii) local anthropogenic activities, e.g. shipping (Tekman et al., 2017). Specifically, microplastics were discovered in the surface/sub-surface waters and sediments (Lusher et al., 2015, Bergmann et al., 2017, Cózar et al., 2017, Mu et al., 2019) of the Arctic. Further north, in the Arctic Central Basin (ACB), microplastics were recorded in sea ice, biota, such as juvenile polar cod (Boreogadus saida) and benthic organisms, and sub-surface waters (Obbard et al., 2014, Kanhai et al., 2018, Kuhn et al., 2018, Peeken et al., 2018, Fang et al., 2018). The fact that microplastics have been reported in the various water layers of the ACB, in particular its deep waters, suggests that these particles are pervasive in the water column and that they are being transported out of its surface waters (Kanhai et al., 2018). It was therefore hypothesized that microplastics would be present in deep sea sediments in the ACB. To our knowledge, the present study sought for the first time to determine whether microplastics were present in surficial sediments of the Arctic Central Basin (ACB) and to establish whether the deep sea in this oceanic basin is possibly acting as a sink for microplastics.
Section snippets
Material and methods
The Arctic Ocean, the world's smallest ocean, is comprised of a deep central basin surrounded by extensive continental shelves. The bathymetry of the Arctic Ocean is such that the Lomonosov Ridge divides the central basin into the Canadian (Amerasian) and Eurasian sub-basins (Jakobsson et al., 2004). Within each of the sub-basins, there are further divisions as well as the existence of Abyssal Plains (APs) which are deep water areas of low relief. In the Amerasian basin, the Alpha-Mendeleev
Results
In the present study, the following plastic materials made direct contact with the sediment samples either during collection or processing (i) plastic film – low-density polyethylene (LDPE), (ii) core liner – polyvinyl chloride (PVC) or polycarbonate (PC), (iii) scraper – polypropylene (PP), (iv) sediment collection scoop – polypropylene (PP) and, (v) sample bag – low-density polyethylene (LDPE). In the surficial sediment samples, no polyethylene particles were recovered. However, in two
Discussion
Elucidation of the transport and fate of microplastics in the marine environment is a critical step towards assessing the threat that these contaminants potentially pose to organisms inhabiting different compartments of an ecosystem. In the Arctic Central Basin (ACB), only a few studies have reported on microplastic presence in the sea ice, biota and water column (Obbard et al., 2014, Kuhn et al., 2018, Kanhai et al., 2018, Peeken et al., 2018). Based on these studies, the key suggestions
Conclusion
To our knowledge, this is the first study to present preliminary information regarding microplastics in surficial sediments of the Arctic Central Basin (ACB). The potential discovery of these particles in the sediment phase of this seemingly remote oceanic basin emphasizes the pervasiveness of microplastics in the marine environment. The possible presence of microplastics, specifically low-density polymers such as polypropylene (PP) and polystyrene (PS), in the sediment phase of the ACB
Acknowledgements
The authors acknowledge the invaluable support of the staff of the Swedish Polar Research Secretariat (especially Jeanette Axelsson, Robert Holden, Lars Lehnert, Asa Lindgren, Axel Meiton and Per Salo) and the crew of icebreaker Oden with the Arctic Ocean 2016 expedition. The expert guidance of Mr. Andrew Tonkin (University of Plymouth) during FT-IR analyses is also acknowledged. The authors acknowledge the support of the coring technicians (Draupnir Einarsson, Markus Karasti), fellow early
Funding
Sampling in the Arctic Ocean was funded by the Swedish Polar Research Secretariat (SPRS) under the Early Career Scientist (ECS) Programme in which the first author was a participant. This work was also co-funded through a MARES Grant. MARES is a Joint Doctorate programme selected under Erasmus Mundus and coordinated by Ghent University (FPA 2011-0016). The funders had no role in study design, data collection, analysis and interpretation, decision to publish, or preparation of the manuscript.
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