Sinking microplastics at a deep-sea seamount in the North Atlantic: a year-long flux study

Abstract The deep sea is now known to accumulate a significant fraction of the ocean's microplastics, yet the mechanisms by which these particles are transported down to the seafloor are still poorly quantified. Here, we quantify the annual and seasonal pattern of microplastic sinking fluxes on the summit of Condor seamount located on the mid-Atlantic Ridge. A sediment trap was deployed at 230 m depth and collected sinking particles over 20-day intervals for a year. A total of 32 microplastics ranging from 80 to 2675 μm were detected, which equates to an average annual sinking flux of 0.18 microplastics m −2 d −1 . No significant seasonal pattern in sinking rates was observed but an increase was observed in spring. Similar proportions of fragments and fibres were found in each sample, with polyethylene, polypropylene, and cellulose being the dominant polymer types. Based on our annual sinking flux, we extrapolated that up to 444 million microplastics could be reaching the summit of Condor seamount each year, assuming uniform deposition across the area. The development of comprehensive and long-term monitoring of sinking fluxes of microplastics will be crucial to better understand the role of the deep sea as a repository of microplastics and to help predict its consequences for this relatively unexplored ecosystem.