Seafloor microplastic hotspots controlled by deep-sea circulation

By I. Kane, M. Clare, E. Miramontes, R. Wogelius, J. Rothwell, P. Garreau, F. Pohl. Science, 2020

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Not just settling What controls the distribution of microplastics on the deep seafloor? Kane et al. show that the answer to that question is more complicated than particles simply settling from where they are found on the sea surface (see the Perspective by Mohrig). Using data that they collected off the coast of Corsica, the authors show that thermohaline-driven currents can control the distribution of microplastics by creating hotspots of accumulation, analogous to their role in causing focused areas of seafloor sediment deposition. Such currents also supply oxygen and nutrients to deep-sea benthos, so deepsea biodiversity hotspots are also likely to be microplastic hotspots. Science, this issue p. 1140; see also p. 1055 Microplastic distribution on the seafloor depends on more than surface accumulation patterns. Although microplastics are known to pervade the global seafloor, the processes that control their dispersal and concentration in the deep sea remain largely unknown. Here, we show that thermohaline-driven currents, which build extensive seafloor sediment accumulations, can control the distribution of microplastics and create hotspots with the highest concentrations reported for any seafloor setting (190 pieces per 50 grams). Previous studies propose that microplastics are transported to the seafloor by vertical settling from surface accumulations; here, we demonstrate that the spatial distribution and ultimate fate of microplastics are strongly controlled by near-bed thermohaline currents (bottom currents). These currents are known to supply oxygen and nutrients to deep-sea benthos, suggesting that deep-sea biodiversity hotspots are also likely to be microplastic hotspots.

Subfields: Ocean Engineering, Pollution

View Paper: https://www.semanticscholar.org/paper/4b9c094f6dbb63eaf18fae5c74316b75553cf20a