Vertical advection Particles with radius <10 μm are more sensitive to the currents vertical velocity than to their gravitational settling (Figure 4). We compare transport simulation results when taking into account the vertical velocity (VZ) of the currents, or not, in the particle’s path computation. Their final positions can change by up to 600 m of meters vertically position and up to 120 km horizontally (Figure 5). Figure 5: A) Horizontal B) Vertical positions differences for particles exported from the coast, at 45 m depth, in January or July 2002 and advected until December 2011. C) Histograms of the total location offset. Conclusions and Perspectives Vertical sea currents can significantly mix plastic particles in the water column and thus change their lateral distribution, especially for particles with radius <10 μm. Advection simulations will be completed with beaching and plankton interaction studies. We shall also compare our simulations results with remote sensing data (Figure 6). Figure 6: Transport simulations results (left) and MODIS reflectance at 645 nm over the North Pacific gyre. Do MODIS data actually see plastic concentrations? References - Law, K L, et al. 2010. “Plastic Accumulation in the North Atlantic Subtropical Gyre.” Science 329 - Menemenlis, D. et al. 2008. “ECCO2: High Resolution Global Ocean and Sea Ice Data Synthesis.” Mercator Ocean Quarterly Newsletter 31. Figure 2: Three advection simulations (2002-2011) with increasing input depths (normalized color bar, increase from blue to red). Figure 3: Amount of particles in gyres (defined by the red squares in the upper panel of Figure 2) as a function of depth. Introduction In situ global quantifications underestimate the actual mass of plastic debris that must have entered the ocean since its earliest production (Law et al., 2010). Here we use velocity fields from the ECCO2 global circulation model (Menemenlis et al., 2008, Figure 1), to infer the 3D redistribution of plastic particles in the ocean. Figure 1: Example of the horizontal and vertical velocity fields of the sea currents on 03/01/2002 (no data at depth means seafloor). Spatial resolution = 0.25°. Velocity fields are updated every 3 days. Transport simulation Principle: Particles are injected from global coasts at t=03/01/2002 and the advection simulation runs until t=31/12/2011 using velocity fields that change every 3 days. We first neglect vertical velocities and inject particles at increasing depths. Surface currents concentrates the particles in the main gyres while deeper currents let them span wider oceanic areas (Figure 2). As a result, below 200 m the amount of particles in gyres is twice less than at the surface (Figure 3). Assuming plastic particles are released from the rivers at rather shallow depths, processes that may redistribute these particles in the water column are: 1. Sea currents vertical velocity 2. Particle settling velocity 3. Particle diffusion 4. Waves and turbulence across the water column. In the following we focus on the eea currents vertical velocity. Background image credit: https://marinedebris.noaa.gov/discover-issue Modelling of plastic nanoparticles redistribution in the ocean Maxime Mouyen 1 ( maxime.mouyen@univ - rennes1.fr), Philippe Steer 1 , Julien Gigault 1 , Laurent Jeanneau 1 , Hervé Tabuteau 2 1: Univ Rennes, CNRS, Géosciences Rennes - UMR 6118, F-35000 Rennes, France. 2: Univ Rennes, CNRS, Institut de Physique de Rennes - UMR 6251, F-35000 Rennes, France. A B C Figure 4: Settling velocities for three plastic materials (PS: polystyrene, PET: polyethylene) compared to the averaged vertical velocities of sea currents.

Modelling of plastic nanoparticles redistribution in the oceaninternationalmarinedebrisconference.org/wp-content/... · - Menemenlis, D. et al. 2008. “ECCO2: High Resolution Global

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Page 1: Modelling of plastic nanoparticles redistribution in the oceaninternationalmarinedebrisconference.org/wp-content/... · - Menemenlis, D. et al. 2008. “ECCO2: High Resolution Global

Vertical advectionParticles with radius <10 µm are more sensitive to the currents vertical velocity thanto their gravitational settling (Figure 4).

We compare transport simulation results when taking into account the verticalvelocity (VZ) of the currents, or not, in the particle’s path computation. Their finalpositions can change by up to 600 m of meters vertically position and up to 120 kmhorizontally (Figure 5).

Figure 5: A) Horizontal B) Vertical positions differences for particles exported from thecoast, at 45 m depth, in January or July 2002 and advected until December 2011. C)Histograms of the total location offset.

Conclusions and PerspectivesVertical sea currents can significantly mix plastic particles in the water column andthus change their lateral distribution, especially for particles with radius <10 µm.Advection simulations will be completed with beaching and plankton interactionstudies. We shall also compare our simulations results with remote sensing data(Figure 6).

Figure 6: Transport simulations results (left) and MODIS reflectance at 645 nm over theNorth Pacific gyre. Do MODIS data actually see plastic concentrations?

References- Law, K L, et al. 2010. “Plastic Accumulation in the North Atlantic Subtropical Gyre.” Science 329- Menemenlis, D. et al. 2008. “ECCO2: High Resolution Global Ocean and Sea Ice Data Synthesis.”

Mercator Ocean Quarterly Newsletter 31.

Figure 2: Three advection simulations (2002-2011) with increasing input depths(normalized color bar, increase from blue to red).

Figure 3: Amount of particles in gyres (defined by the red squares in the upper panel ofFigure 2) as a function of depth.

IntroductionIn situ global quantifications underestimate the actual mass of plastic debris that musthave entered the ocean since its earliest production (Law et al., 2010). Here we usevelocity fields from the ECCO2 global circulation model (Menemenlis et al., 2008,Figure 1), to infer the 3D redistribution of plastic particles in the ocean.

Figure 1: Example of the horizontal and vertical velocity fields of the sea currents on03/01/2002 (no data at depth means seafloor). Spatial resolution = 0.25°. Velocityfields are updated every 3 days.

Transport simulation

Principle: Particles are injected from global coasts at t=03/01/2002 and the advectionsimulation runs until t=31/12/2011 using velocity fields that change every 3 days.

We first neglect vertical velocities and inject particles at increasing depths. Surfacecurrents concentrates the particles in the main gyres while deeper currents let themspan wider oceanic areas (Figure 2).

As a result, below 200 m the amount of particles in gyres is twice less than at thesurface (Figure 3).

Assuming plastic particles are released from the rivers at rather shallow depths,processes that may redistribute these particles in the water column are:1. Sea currents vertical velocity2. Particle settling velocity3. Particle diffusion4. Waves and turbulence across the water column.

In the following we focus on the eea currents vertical velocity.Background image credit: https://marinedebris.noaa.gov/discover-issue

Modelling of plastic nanoparticles redistribution in the oceanMaxime Mouyen1 ([email protected]), Philippe Steer1, Julien Gigault1, Laurent Jeanneau1, Hervé Tabuteau2

1: Univ Rennes, CNRS, Géosciences Rennes - UMR 6118, F-35000 Rennes, France.2: Univ Rennes, CNRS, Institut de Physique de Rennes - UMR 6251, F-35000 Rennes, France.

Figure 4: Settling velocities for three plastic materials (PS: polystyrene, PET: polyethylene) compared to the averaged vertical velocities of sea currents.