Session Chairs: Erik van Sebille, Utrecht University; Kara Lavendar Law, Sea Education Association

This session focuses on how ocean waves and ocean currents move around the world. It also looks how does this transport impact the fate and transport of marine debris in the ocean.

After plastic debris enters the ocean, its distribution is to a large extent determined by the ocean circulation; in particular waves and current. Knowing how and where marine debris is transported by the ocean is key to understanding its fate and impact on marine ecosystems. Oceanographic phenomena that impact the transport and dispersion of marine debris occur on a large range of scales, from thousands of kilometers for the Ekman convergence in the subtropical gyres to a few centimeters for the Stokes drift by individual surface waves. The way that these different phenomena affect the dispersion of marine debris, and how this leads to the emergence of patchy accumulation regions and ‘hotspots’, is a major knowledge gap.

In this session, we invite presentations on advances in the theory and modelling, possibly supported by observations, of marine debris of all sizes and materials. Topics include but are not limited to:

-The stirring of buoyant debris due to turbulence, in particular in the mixed layer.

-The transport of plastic in coastal seas, from the surf zone to the open ocean.

-The effects of Stokes drift, Langmuir circulation, and other (nonlinear) wind effects on the transport of debris.

-The effects of fragmentation, degradation, bio aggregation and biofouling on the evolution of the buoyancy of debris particles.

-The movement and transport of debris in the water column and/or on the sea floor.

-Development of and comparison between tools and software to simulate the dispersion of debris.




A journey into the Great Pacific Garbage Patch

presenting: Laurent Lebreton (The Ocean Cleanup, New Zealand); authors: Laurent Lebreton (The Ocean Cleanup, New Zealand), Julia Reisser (The Ocean Cleanup), Boyan Slat (The Ocean Cleanup)

In 2015, the Ocean Cleanup Foundation conducted a multi-vessel expedition in the subtropical oceanic waters between the Hawaiian Archipelago and the Californian coast, sampling for buoyant ocean plastics in the Great Pacific Garbage Patch (GPGP). The expedition was followed a year later by an aerial survey to collect imagery of the same area. We assessed the validity of several sampling methods regarding debris sizes to quantify ocean plastic pollution at the sea surface. We report numerical and mass concentration for microplastics (0.05 – 0.5 cm) and mesoplastics (0.5 – 5 cm) using Manta trawls (0.5 mm mesh, 90 cm x 15 cm, n = 501 net tows), macroplastics (5 – 50 cm) using Mega trawls (1.5 cm mesh, 6 m x 1.5 m mouth, n = 151 net tows) and finally, megaplastics (> 50 cm) using aerial RGB imagery (~ 360 m x 240 m frame size, 0.1 m resolution, n = 7,298 frames). Our observations were used to calibrate a multi-forcing and multi-source global Lagrangian dispersal model able to predict the spatio-temporal distribution of ocean plastic concentrations within the GPGP area. Here, we present mass and count load estimates of ocean plastic in the GPGP with confidence intervals that account for uncertainties related to both monitoring and modelling. Using our calibrated model, we discuss seasonal and inter-annual variability of the GPGP position. Finally, we assess whether previous samplings reported in the literature were conducted inside or outside the GPGP, allowing us to draw a decadal trend of plastic pollution in the area from early monitoring in the 1970s to present.


An estimate of future spread of pelagic microplastics based on a transoceanic survey and numerical modeling over the Pacific Ocean

presenting: Atsuhiko Isobe (Research Institute for Applied Mechanics, Japan); authors: Atsuhiko Isobe (Research Institute for Applied Mechanics, Japan), Shinsuke Iwasaki (Research Institute for Applied Mechanics), Keiich Uchida (Tokyo University of Maritime Science and Technology), Tadashi Tokai (Tokyo University of Maritime Science and Technology)

As a part of microplastic research project granted by the Ministry of Environment, Japan, a transoceanic survey of pelagic microplastics (0.3< size <5 mm) was conducted from the Southern Ocean to Tokyo from January to March in 2016 (see figure for stations). The concentrations of microplastics (pieces/m3) were vertically integrated (pieces/km2) to reduce influences of oceanic turbulence owing to winds/waves during the surveys. It is found that the concentrations in the Northern Hemisphere (~100,000 pieces/km2) are one order of magnitude larger (smaller) than those in the Southern Hemisphere (East Asian seas). A numerical particle tracking model (PTM) was established using the HYCOM (ocean currents) and a wave model (Stokes drift) to hindcast/forecast the concentration of pelagic microplastics over the Pacific from 1950s to 2060s. The microplastic concentrations observed in the transoceanic surveys were used for model validation. Our PTM includes simplified source & sink terms to express the generation and disappearance of pelagic microplastics in the upper ocean. The source term is based on the recent estimate of mismanaged plastic wastes over the world, and on the time series of gross domestic product in regions. The sink term was required to reproduce the observed concentrations of pelagic microplastics; otherwise the numerical model overestimated microplastic concentrations in the actual ocean.


Source to Sea Transport of Microplastics: Modeling Fate and Transport in San Francisco Bay and the Coastal Ocean

presenting: Rusty Holleman (San Francisco Estuary Institute, United States); authors: Rusty Holleman (San Francisco Estuary Institute, United States), Emma Nuss (San Francisco Estuary Institute), Lawrence Sim (San Francisco Estuary Institute), Meg Sedlak (San Francisco Estuary Institute), Diana Lin (San Francisco Estuary Institute), Carolynn Box (5 Gyres), Rebecca Sutton (San Francisco Estuary Institute)

Microplastics enter the environment from a variety of sources, with varying morphologies, size and composition. These characteristics affect the transport and fate of such particles, with an impact on whether plastics enter the aquatic food web, wash ashore, deposit on the bed, or even become entrained in one of the five global gyres.


We present a process-based modeling study intended to predict the trajectories of microplastics from potential sources, through San Francisco Bay, and to the coastal ocean and beyond. The Bay portion of the domain requires a robust treatment of tidal transport and mixing, complex geometry and wetting and drying. Modeled transport in the coastal ocean, including three National Marine Sanctuaries, draws on HF radar data as well as regional ROMS models. We investigate the sensitivity of the predictions to particle characteristics and source location. The modeling study complements a field-based study of the Bay and coastal ocean, with the ultimate goal of assessing the feasibility and model skill for predicting microplastic transport and fate.


Coastal accumulation mapping of microplastic particles emitted from the Po River, Italy: Integrating remote sensing, in situ sample collections and ocean current modelling

presenting: Elizabeth C. Atwood (RSS Remote Sensing Solutions GmbH, Germany); authors: Elizabeth C. Atwood (RSS Remote Sensing Solutions GmbH, Germany), Francesco M. Falcieri (CNR – ISMAR), Sarah Piehl (University Bayreuth, Dept. Animal Ecology I), Mathias Bochow (University Bayreuth, Dept. Animal Ecology I), Michael Matthies (University of Osnabrück, Institute of Environmental Systems Research), Jonas Franke (RSS Remote Sensing Solutions GmbH), Sandro Carniel (CNR – ISMAR), Mauro Sclavo (CNR – ISMAR), Christian Laforsch (University Bayreuth, Dept. Animal Ecology I), Florian Siegert (RSS Remote Sensing Solutions GmbH)

Plastic pollution in inland waters and the open ocean is a long recognized problem for marine wildlife, coral reefs, the fishing industry and shipping transport safety. Microplastics (particles < 5 mm) can be ingested by planktonic animals, thus potentially introducing accumulated persistent organic pollutants (POPs) or carcinogenic plastic additives into the base of the food chain. Research has mainly concentrated on marine systems, while river plumes as an important influencing factor for the input and distribution of microplastics into coastal ocean areas have to date received less attention. Here we present a study of the accumulation of microplastic particles emitted by the Po River along the Adriatic coastline in northern Italy. We posit that river-induced coastal microplastic accumulation can be predicted using a hydrodynamic model, supported by remote sensing data from Landsat-8 and Sentinel-2A. Model accumulation maps were validated against in situ sampling at 9 beaches (sampled particle size range: 1-5 mm). Hydrodynamic modelling suggests that the amount of discharged particles is only semi-coupled to beaching rates. Object tracking revealed that beaching of emitted particles was strongly mouth dependent and relatively low (less than 25%), primarily occurring within the first five days. The southernmost Po River mouth posed an exception, where more released particles (94%) were found to beach over an extended period of time and along a longer stretch of coastline. Comparison with remote sensing based accumulation maps and validation against in situ beach samples are discussed. The presented methodology lays groundwork for developing an operational monitoring system to assess microplastic pollution being emitted by a major river and its distribution along adjacent coastlines.


Predicting accumulation zones of marine debris at management relevant scales

presenting: Kay Critchell (James Cook University, Australia); authors: Kay Critchell (James Cook University, Australia)

Models that predict the movement of marine debris are generally conducted at broad scales with relatively coarse resolution. To be useful to environmental managers, predictive models of marine debris dispersal need to be conducted at a finer spatial scales and resolution. In this study, I compare field data to predictive models of marine debris dispersal in a small (approximately 10,000 km2) management jurisdiction within the Great Barrier Reef, Queensland, Australia. I compared the model outputs to the field data in two ways. First, I assessed whether the field site was correctly categorised by the model as an accumulation “hot spot” or as an area of low accumulation (“cold spot”). Secondly, I assessed the magnitude of accumulation predicted by the modelling. I found that the predictability of a site varied based on the physical characteristics of the site. Understanding the characteristics of a correctly categorised site could explain what makes a site a “hot spot”. An accurate understanding of where debris accumulates is needed to inform many levels of marine spatial management, from risk assessments to debris removal efforts. My study shows the utility of fine spatial scale predictive models of marine debris dispersal.


Understanding wind-driven vertical mixing of microplastics

presenting: Jessica Donohue (Sea Education Association, United States); authors: Jessica Donohue (Sea Education Association, United States), Kara Lavender Law (Sea Education Association), Ethan Edson (Northeastern University), Kathryn Tremblay (University of Massachusetts Dartmouth, School for Marine Science and Technology)

How initially buoyant microplastics move vertically in the water column remains poorly understood. The amount of floating microplastics measured at the sea surface varies depending on the wind speed (Kukulka et al. 2012). The energy from the wind mixes buoyant microplastics down to depths out of reach of the nets used to measure them. Using measured wind speed and sea surface plastic concentrations, numerical models can predict the amount of plastic that has been mixed to depth. A key parameter in these models is the particle rise velocity – the speed at which a submerged particle would rise back to the surface if released at depth.


Utilizing a custom built rise velocity chamber, we carried out laboratory experiments measuring the rise velocity of individual microplastics collected at variable depths by Sea Education Association. We measured more than 200 particles of various forms, shapes and sizes, and evaluated the relationship between these particle characteristics and rise velocity. We also measured the mass of each particle, numerous 2-D size parameters using high-resolution scanned images, and polymer type using Raman spectroscopy. These results can advance our understanding of the depth distribution of microplastics in the upper ocean, improve existing numerical models, and lead to better predictions of surface microplastic concentrations in variable wind conditions.


Use of NOAA’s Trajectory Analysis Planner (TAP) for Marine Debris Transport Studies

presenting: Dylan Righi (Genwest Systems, Inc., United States); authors: Dylan Righi (Genwest Systems, Inc., United States), Sherry Lippiatt (NOAA Marine Debris Program), Peter Murphy (Genwest Systems, Inc), Glen Watabayashi (NOAA Office of Response and Restoration, Emergency Response Division)

NOAA’s Office of Response and Restoration has developed the Trajectory Analysis Planner (TAP) tool to prepare contingency plans for oil spill response. TAP graphically presents the results of thousands of simulated oil spills to help understand and anticipate many possible spill outcomes and potential habitat damage.

We have applied this tool to marine debris release scenario modelling in the Southern California Bight region. Using water velocity and wind forcing data from a 10 year Regional Ocean Model (ROMS) study, we predict marine debris trajectories from numerous sources in the area. At each source location a large number of trajectories are computed, each with random start times over the 10 year forcing record. Combining these trajectories gives a statistical view of debris fate. We are also able to vary marine debris characteristics, such as windage, to study how different debris types are distributed. We will present results from this study and discuss its applicability as a marine debris planning tool.


Beneath the waves: a deep dive into the transport and fate of microplastics in pelagic ecosystems

presenting: Anela Choy (Monterey Bay Aquarium Research Institute, United States); authors: Anela Choy (Monterey Bay Aquarium Research Institute, United States), Bruce Robison (monterey Bay Aquarium Research Institute), Kyle Van Houtan (monterey Bay Aquarium)

While plastic waste has been documented in all aquatic ecosystems (terrestrial, freshwater, and marine), little is known about the transport and fate of microplastics within Earth’s largest habitat, the deep sea. Using targeted sampling and instrumentation on remotely operated vehicles, we present a comprehensive dataset on the counts and types of microplastics found throughout the upper kilometer of the oceanic water column of monterey Bay. Large volumes comprising approximately a thousand liters of seawater were sampled from discrete depths, filtered for potential plastics, and identified using microscopy and Raman spectroscopy. Microplastics (primarily microfibers) were identified across all depth horizons, comprising a diversity of plastic types (e.g., polycarbonate, polyamide, polyethylene) of varying degraded states. Further, we examine the ecological fate of microplastics in the monterey Bay food web by identifying them in the bodies of representative ecological vectors that ingest and transport microplastics through marine ecosystems. Pelagic red crabs (Pleuroncodes planipes) are key prey of numerous predators (tuna, sea birds, marine mammals), and as particle-feeding detritivores would effectively deliver microplastics into pelagic food webs following ingestion. Giant larvaceans (Bathochordaeus spp.) are filter-feeders that contribute to the vertical flux of microplastics through the rapid sinking of fecal pellets and discarded mucus feeding filters. We present a comprehensive deep water survey of microplastics, providing empirical data on key biological vectors linking surface waters with the seafloor. Our findings point to the need for an urgent consideration of plastic pollution and its attendant chemical burdens within pelagic food webs, as these ecosystems are intimately tied to global human societies.


From the sea surface to the deep seafloor: microplastics prevail at all ocean depths of the HAUSGARTEN observatory (Arctic)

presenting: Mine B. Tekman (HGF-MPG Group for Deep-Sea Ecology and Technology, Alfred-Wegener-Institut Helmholtz-Zentrum fü r Polar- und Meeresforschung, Germany); authors: Mine B. Tekman (HGF-MPG Group for Deep-Sea Ecology and Technology, Alfred-Wegener-Institut Helmholtz-Zentrum fü r Polar- und Meeresforschung, Germany), Gunnar Gerdts (Department of Microbial Ecology, Biologische Anstalt Helgoland, Alfred-Wegener-Institut Helmholtz-Zentrum fü r Polar- und Meeresforschung), Claudia Lorenz (Department of Microbial Ecology, Biologische Anstalt Helgoland, Alfred-Wegener-Institut Helmholtz-Zentrum fü r Polar- und Meeresforschung), Sebastian Primpke (Department of Microbial Ecology, Biologische Anstalt Helgoland, Alfred-Wegener-Institut Helmholtz-Zentrum fü r Polar- und Meeresforschung), Melanie Bergmann (HGF-MPG Group for Deep-Sea Ecology and Technology, Alfred-Wegener-Institut Helmholtz-Zentrum fü r Polar- und Meeresforschung)

Although recent research indicates that microplastic (MP) has spread to all marine ecosystem compartments from the sea surface to the deep sea, our understanding of transport pathways is still limited. Currently, our knowledge of MP concentrations throughout the water column is largely based on model runs. To fill this gap, we deployed in-situ pumps at four different depths (sea surface, ~300m, ~1000m, near seafloor) at five stations of the HAUSGARTEN observatory (west of Svalbard). These pumps filtered 218–560 litres of seawater (> 10µm). Our analyses using µFTIR spectroscopy resulted in 16–8,750 MP m-3, comprising 16 different polymer types. The highest concentration was detected at the sea surface near the coast of Svalbard. Rubber was the dominant polymer in this sample. Of the four deep stations (2500m depth), the northernmost station, which is located in the marginal ice zone, harboured the highest concentration (1,927 MP m-3) throughout the water column, and polyamide accounted for the largest proportion (28%). The surface waters had the highest MP concentrations at all stations with a decrease throughout the water column. Our results will be compared with trends in the vertical distribution of organic particles and discussed in the context of prevailing water masses and sea ice coverage. Still, our preliminary results highlight that noticeable amounts of MP are present throughout the water column, Earth’s largest biome, which has been largely neglected in previous estimates of plastic in the world’s oceans.


Generation of secondary microplastics in the sea swash zone

presenting: Irina Chubarenko (P.P.Shirshov Institute of Oceanology of Russian Academy of Sciences, Russia); authors: Irina Chubarenko (P.P.Shirshov Institute of Oceanology of Russian Academy of Sciences, Russia), Irina Efimova (P.P.Shirshov Institute of Oceanology of Russian Academy of Sciences), Margarita Bagaeva (P.P.Shirshov Institute of Oceanology of Russian Academy of Sciences)

Mechanical fragmentation of plastics in the sea swash zone is one of the major mechanisms of generation of marine microplastics (MPs). Reproducing the process of repeated wave breaking, the series of experiments in a rotating laboratory mixer with an inclined axis of rotation were carried out, with the goal to disclose (i) qualitative features of the process of fragmentation and of the particles generated, (ii) increase in mass of MPs with time, (iii) variation of size distribution of MPs with time, and (iv) distribution of mass of MPs versus their size. Samples made of the world’s most common plastics were used: Low Density Polyethylene (LDPE, garbage bags), polystyrene (PS, disposable dishes), polypropylene (PP, disposable cups), and foamed polystyrene (PSfoam, sheets for building heat protection). The results indicate that the mass of MPs generated from macro-samples increases exponentially for LDPE, PS, and PP samples, while foamed PS first shows linear mass increase due to its initial break-down to individual spherules (also regarded as MPs) and only then – breaking of the very spherules to smaller MPs. Time of complete disintegration of the PP / LDPE / PS macro-samples into MPs, recalculated from the number of rotating circles using typical surface wave period for the Baltic Sea of about 5 s, is estimated to be about 1 month (for PP samples) / 2 weeks (LDPE) / 1 week (PS) for the swash zone with coarse bottom sediments (cobbles) under rather moderate wind-wave conditions. Log-log presentation of the number of generated MPs particles versus their size shows a clear linear trend, allowing for suggestion that the right wing of the oceanic size-distribution of floating MPs (Cózar et al., 2017) resembles mechanical fragmentation of larger debris on the oceanic coasts.


Making virtual particles behave like plastic: developing the OceanParcels Lagrangian Ocean Analysis framework

presenting: Erik van Sebille (Utrecht University, Netherlands); authors: Erik van Sebille (Utrecht University, Netherlands), Michael Lange (Imperial College London), Philippe Delandmeter (Utrecht University)

Most of our understanding about plastic debris movement in the ocean comes from observations of drifting buoys or numerical simulations of passive virtual particles in ocean general circulation models. However, neither of those represent the fragmentation, sinking, beaching and other processes that affect the movement of real plastic items in the ocean.


In order to facilitate the simulation of virtual particles that ‘behave’ like plastic, we’re developing the new Parcels framework. Parcels is primarily written in Python, utilising the wide range of tools available in the scientific Python ecosystem, while generating low-level C-code and using Just-In-Time compilation for performance-critical computation.


Here, we will demonstrate the ease of use of this code in simulating particles as plastic. This will aid studies into the global distribution and fate of plastic particulates; not only at the ocean surface but also in the abyss, on beaches and in marine animals. We will discuss the code’s current limitations and future development plan. We will also highlight some of the other applications of the OceanParcels framework, including the simulation of plankton and fish.