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Modeling submerged biofouled microplastics and their vertical trajectories
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Researchers modeled how biofouling — the growth of algae and microbes on plastic surfaces — affects the vertical movement of microplastic particles in the open ocean. Biofouling increased sinking rates, causing microplastics to accumulate at depth rather than floating at the surface. This has implications for understanding where microplastics end up in the water column and how they are ingested by deep-water organisms.
Abstract. The fate of (micro)plastic particles in the open ocean is controlled by physical and biological processes. Here, we model the effects of biofouling on the subsurface vertical distribution of spherical, virtual plastic particles with radii of 0.01–1 mm. For the physics, four vertical velocity terms are included: advection, wind-driven mixing, tidally induced mixing, and the sinking velocity of the biofouled particle. For the biology, we simulate the attachment, growth and loss of algae on particles. We track 10,000 particles for one year in three different regions with distinct biological and physical properties: the low productivity region of the North Pacific Subtropical Gyre, the high productivity region of the Equatorial Pacific and the high mixing region of the Southern Ocean. The growth of biofilm mass in the euphotic zone and loss of mass below the euphotic zone result in the oscillatory behaviour of particles, where the larger (0.1–1.0 mm) particles have much shorter average oscillation lengths (< 10 days; 90th percentile) than the smaller (0.01–0.1 mm) particles (up to 130 days; 90th percentile). A subsurface maximum concentration occurs just below the mixed layer depth (around 30 m) in the Equatorial Pacific, which is most pronounced for larger particles (0.1–1.0 mm). This occurs since particles become neutrally buoyant when the processes affecting the settling velocity of the particle and the motion of the ocean are in equilibrium. Seasonal effects in the subtropical gyre result in particles sinking below the mixed layer depth only during spring blooms, but otherwise remaining within the mixed layer. The strong winds and deepest average mixed layer depth in the Southern Ocean (400 m) result in the deepest redistribution of particles (> 5000 m). Our results show that the vertical movement of particles is mainly affected by physical (wind-induced mixing) processes within the mixed layer and biological (biofilm) dynamics below the mixed layer. Furthermore, positively buoyant particles with radii of 0.01–1.0 mm can sink far below the euphotic zone and mixed layer in regions with high near-surface mixing or high biological activity. This work can easily be coupled to other models to simulate open-ocean biofouling dynamics, in order to reach a better understanding of where ocean (micro)plastic ends up.
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Researchers experimentally measured how biofouling alters the settling velocity of microplastic particles, finding that biofilm growth on buoyant plastic fragments caused them to sink more rapidly. The results demonstrate that biological colonization of plastic surfaces is a key mechanism driving the vertical transport of microplastics from surface water to the seafloor.
Modelling submerged biofouled microplastics and their vertical trajectories
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Using an ocean circulation model, researchers simulated the vertical trajectories of biofouled microplastic particles of different sizes across three ocean regions with distinct biological and physical properties. Larger particles (0.1 to 1.0 mm) showed rapid oscillatory sinking and resurfacing behavior with cycles under 10 days, while smaller particles oscillated over up to 130 days, explaining how biofouling drives microplastic distribution through the water column.
Effect of Biofouling on Microplastic Transport in a 3-D Global Eulerian Model
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Scientists built a computer model showing that ocean germs growing on microplastic surfaces (a process called biofouling) cause larger plastic particles to sink hundreds of feet below the surface and spread out, rather than staying concentrated in the famous ocean "garbage patches." This matters because it means microplastics aren't just floating on top of the ocean where we can see and potentially clean them up—they're being carried deeper into marine ecosystems and food webs, which affects seafood safety and our understanding of where this pollution actually ends up.
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