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The Blue-Cloud thematic Virtual Labs (VLabs) are the main test beds for users to get the hang of the Blue-Cloud framework, exploiting the 10+ million datasets available via the Data Discovery and Access Service (DD&AS), as well as the easy access to the collaborative VLabs via D4Science and the EOSC federated login. These collaborative workspaces hosted in the Blue-Cloud Virtual Research Environment (VRE) are serving more than 1,300 users in total spread across more than 20 countries. Five Virtual Labs were developed and deployed in the Blue-Cloud pilot project, making use of the analytical tools and generic services as provided through the VRE, and the data repositories, as made accessible via the DD&AS and through external data services. The Blue-Cloud VLabs are real-life demonstrators for web-based open science and are open and available for testing by different research communities. Each VLab comprises a series of applications for data processing, publishing of data results, and managing computation routines as well as services for collaboration, this way providing open science-friendly working environments for its users to analyse datasets and (re)generate research products. Zoo & Phytoplankton EOV Products Plankton Genomics Marine Environmental Indicators Fish, a matter of scales Aquaculture Monitor 12 thematic marine services are included in the VLabs and make extensive use of the Blue-Cloud framework and its rich set of resources. These services illustrate the wide range of subjects that can be addressed using such resources, from genomics to wildlife as well as environmental data coming from multiple disciplines and repositories, and all together demonstrate Blue-Cloud’s potential in different fields of marine research,ranging from biodiversity to environmental science, as well as fisheries and aquaculture. In addition to these, this document also features factsheets for the three top teams awarded at the Blue-Cloud Hackathon 2022, providing additional examples of applications for Blue-Cloud assets in the blue economy. Sea Clearly- A tool to assess ocean plastic impacts on and by aquaculture farms PerfeCt- Performance of Aquaculture under Climate change Wildlife Tracker for Oceans- MPA assessment with real-time wildlife tracking & ocean monitoring data

Plastic is one of the most commonly used materials in the world today, with polymers such as polypropylene and polyethylene used for applications such as packaging, textiles and commercial fishery. However, not all plastic objects are properly disposed of at the end of their useful lives, and today plastic pollution is ubiquitous throughout the environment and particularly in the ocean. Here plastic pollution can cause harm in a variety of ways, such as entangling marine wildlife, leaching chemical compounds into the water and causing economic damage by deterring tourism at commercial beaches. However, it is difficult to understand the full scope of these threats, in part because the fate of plastic once it enters the ocean is poorly understood. Plastic debris has been found everywhere from on coastlines to the open ocean, and from the ocean surface down to the deep ocean on the seafloor, but it is not always clear what physical processes contribute to the observed distribution of plastic objects. Numerical models can provide insight into plastic debris transport by modeling various transport scenarios, but physical processes such as plastic beaching and resuspension, vertical transport and fragmentation are not always completely represented or even included at all. This thesis investigates the transport of plastic debris in the global ocean by means of Lagrangian particle transport scenarios, where plastic debris is represented by virtual particles. Using circulation and other oceanographic data from oceanic general circulation model (OGCM) reanalysis products, particles trajectories are calculated that provide insight into the distribution and pathways of plastic debris in marine environments. By modifying the model setup in the various scenarios, the influence of di↵erent physical processes on plastic transport is investigated. Chapter 1 provides a general overview of marine plastic pollution, where this is broadly split into insights gained from the observational record and from modeling studies. The current understanding of the relative distribution of plastic debris on a global scale is described, as well as the current knowledge of how this is influenced by various physical processes. This also highlights current knowledge gaps such as the role of coastal and vertical transport processes, which are investigated in later chapters of this thesis. While the specific model frameworks are described in each subsequent chapter in this thesis, chapter 2 provides a general overview of Lagrangian ocean modeling and particularly the Parcels modeling framework. In addition, while all the details of OGCMs and ocean reanalysis products are beyond the scope of this thesis, a general overview is given of various OGCM features that are relevant to the work described in the following chapters. Chapter 3 investigates plastic debris beaching and resuspension on a global scale. The spatial and temporal resolutions of OGCMs are insufficient to resolve the physical processes that contribute to debris beaching and resuspension, and stochastic parametrizations are introduced to represent plastic beaching and resuspension within a large-scale modeling framework. Coastlines and coastal waters are globally shown to hold at least 77% of all positively buoyant plastic debris, with the spatial distribution of beached plastic being strongly influenced by the model input scenario. As such, coastal dynamics are shown to play a more prominent role in global-scale plastic transport than previously thought. Chapter 4 describes various parametrizations for modelling the wind-driven vertical turbulent mixing of buoyant particles within the surface mixed layer. Ocean reanalysis products generally do not provide turbulence data fields, but turbulent vertical transport is an important driving process in the full three-dimensional distribution of plastic in the ocean. The modeled vertical microplastic concentration profiles correspond reasonably well with field observations, and the parametrizations are numerically stable with an integration timestep #t = 30 seconds. This makes it computationally feasible to apply the paramatrizations in large-scale three-dimensional modeling frameworks. Chapter 5 examines the influence of particle size on the three-dimensional transport of microplastic debris in the Mediterranean Sea. The distribution of plastic in beached, coastal waters and open waters reservoirs is strongly a↵ected by the particle size, with smaller particles being more likely to reach open water. Smaller particles are also mixed farther below the ocean surface up to depths of 3000 m. Fragmentation is shown to be a slow process over timescales of years to decades, with ocean-based fragmentation likely being negligible compared with beach-based fragmentation processes. Therefore, while fragmentation was not shown to strongly influence the particle size distribution over the course of 3 years, over longer timescales it can play an important in the gradual plastic mass transfer to o↵shore and subsurface waters. Finally, chapter 6 provides a general overview and discussion of the main results described in chapters 3 - 5, and outlines future possible research directions.

The fate of (micro)plastic particles in the open ocean is controlled by biological and physical 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. The biological specifications include the attachment, growth and loss of algae on particles. The physical specifications include four vertical velocity terms: advection, wind-driven mixing, tidally induced mixing and the sinking velocity of the biofouled particle. We track 10 000 particles for 1 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 (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.

Turbulent mixing is a vital component of vertical particulate transport, but ocean global circulation models (OGCMs) generally have low-resolution representations of near-surface mixing. Furthermore, turbulence data are often not provided in OGCM model output. We present 1D parametrizations of wind-driven turbulent mixing in the ocean surface mixed layer that are designed to be easily included in 3D Lagrangian model experiments. Stochastic transport is computed by Markov-0 or Markov-1 models, and we discuss the advantages and disadvantages of two vertical profiles for the vertical diffusion coefficient Kz. All vertical diffusion profiles and stochastic transport models lead to stable concentration profiles for buoyant particles, which for particles with rise velocities of 0.03 and 0.003gmgs-1 agree relatively well with concentration profiles from field measurements of microplastics when Langmuir-circulation-driven turbulence is accounted for. Markov-0 models provide good model performance for integration time steps of "t≈30gs and can be readily applied when studying the behavior of buoyant particulates in the ocean. Markov-1 models do not consistently improve model performance relative to Markov-0 models and require an additional parameter that is poorly constrained.

Floating microplastic in the oceans is known to accumulate in the subtropical ocean gyres, but unclear is still what causes that accumulation. We investigate the role of various physical processes, such as surface Ekman and geostrophic currents, surface Stokes drift, and mesoscale eddy activity, on the global surface distribution of floating microplastic with Lagrangian particle tracking using GlobCurrent and WaveWatch III reanalysis products. Globally, the locations of microplastic accumulation (accumulation zones) are largely determined by the Ekman currents. Simulations of the North Pacific and North Atlantic show that the locations of the modeled accumulation zones using GlobCurrent Total (Ekman+Geostrophic) currents generally agree with observed microplastic distributions in the North Pacific and with the zonal distribution in the North Atlantic. Geostrophic currents and Stokes drift do not contribute to large‐scale microplastic accumulation in the subtropics, but Stokes drift leads to increased microplastic transport to Arctic regions. Since the WaveWatch III Stokes drift and GlobCurrent Ekman current data sets are not independent, combining Stokes drift with the other current components leads to an overestimation of Stokes drift effects and there is therefore a need for independent measurements of the different ocean circulation components. We investigate whether windage would be appropriate as a proxy for Stokes drift but find discrepancies in the modeled direction and magnitude. In the North Pacific, we find that microplastic tends to accumulate in regions of relatively low eddy kinetic energy, indicating low mesoscale eddy activity, but we do not see similar trends in the North Atlantic.

Global coastlines potentially contain significant amounts of plastic debris, with harmful implications for marine and coastal ecosystems, fisheries and tourism. However, the global amount, distribution and origin of plastic debris on beaches and in coastal waters is currently unknown. Here we analyze beaching and resuspension scenarios using a Lagrangian particle transport model. Throughout the first 5 years after entering the ocean, the model indicates that at least 77% ofpositively buoyant marine plastic debris (PBMPD) released from land-based sources is either beached or floating in coastal waters, assuming no further plastic removal from beaches or the ocean surface. The highest concentrations ofbeached PBMPD are found in Southeast Asia, caused by high plastic inputs from land and limited offshore transport, although the absolute concentrations are generally overestimates compared to field measurements. The modeled distribution on a global scale is only weakly influenced by local variations in resuspension rates due to coastal geomorphology. Furthermore, there are striking differences regarding the origin of the beached plastic debris. In some exclusive economic zones (EEZ), such as the Indonesian Archipelago, plastic originates almost entirely from within the EEZ while in other EEZs, particularly remote islands, almost all beached plastic debris arrives from remote sources. Our results highlight coastlines and coastal waters as important reservoirs ofmarine plastic debris and limited transport ofPBMPD between the coastal zone and the open ocean.