The physical oceanography of the transport of floating marine debris

Marine plastic debris floating on the ocean surface is a major environmental problem. However, its distribution in the ocean is poorly mapped, and most of the plastic waste estimated to have entered the ocean from land is unaccounted for. Better understanding of how plastic debris is transported from coastal and marine sources is crucial to quantify and close the global inventory of marine plastics, which in turn represents critical information for mitigation or policy strategies. At the same time, plastic is a unique tracer that provides an opportunity to learn more about the physics and dynamics of our ocean across multiple scales, from the Ekman convergence in basin-scale gyres to individual waves in the surfzone. In this review, we comprehensively discuss what is known about the different processes that govern the transport of floating marine plastic debris in both the open ocean and the coastal zones, based on the published literature and referring to insights from neighbouring fields such as oil spill dispersion, marine safety recovery, plankton connectivity, and others. We discuss how measurements of marine plastics (both in situ and in the laboratory), remote sensing, and numerical simulations can elucidate these processes and their interactions across spatio-temporal scales

Discontinuous Galerkin finite element modelling of geophysical and environmental flows

Numerical models are essential tools in modern oceanography and limnology. They are used in various domains, from climate change studies to forecasting of storm surge or contaminant transport. Over the last decade, unstructured mesh models have proved their efficiency in simulating multiscale hydrodynamics in complex topographies. However, numerous challenges and limitations still need to be addressed. This thesis focuses on the development of the unstructured mesh Second-generation Louvain-la-Neuve Ice-ocean Model (SLIM, www.climate.be/slim), based on the discontinuous Galerkin finite element method, and especially its three-dimensional version, SLIM 3D. Two key aspects of the model development are tackled: model validation and the improvement of SLIM 3D accuracy and stability. High-resolution models such as SLIM can resolve flow features with a length scale of the order of a hundred metres but how accurate are those results? Using new stereo high-resolution satellite imagery, which is used to measure the water velocity with an unprecedented resolution, SLIM modelling of tidal eddies in the wake of coral islands in the Great Barrier Reef, Australia, is validated. To study complex hydrodynamics, SLIM 3D stability is increased by modifying the pressure gradient computation and by handling a discrete bathymetry. Moreover, its accuracy is greatly improved with a new vertically adaptive mesh as well as a conservative and consistent formulation of the tracer, salinity and temperature equations. The improved model is used to simulate thermocline oscillations in Lake Tanganyika, East African Rift, and the transport of the sediment exported by the Burdekin River, Australia.(FSA - Sciences de l'ingénieur) -- UCL, 201

The Parcels v2.0 Lagrangian framework : New field interpolation schemes

With the increasing number of data produced by numerical ocean models, so increases the need for efficient tools to analyse these data. One of these tools is Lagrangian ocean analysis, where a set of virtual particles is released and their dynamics are integrated in time based on fields defining the ocean state, including the hydrodynamics and biogeochemistry if available. This popular methodology needs to adapt to the large variety of models producing these fields at different formats. This is precisely the aim of Parcels, a Lagrangian ocean analysis framework designed to combine (1) a wide flexibility to model particles of different natures and (2) an efficient implementation in accordance with modern computing infrastructure. In the new Parcels v2.0, we implement a set of interpolation schemes to read various types of discretized fields, from rectilinear to curvilinear grids in the horizontal direction, from z to s levels in the vertical direction and using grid staggering with the Arakawa A, B and C grids. In particular, we develop a new interpolation scheme for a threedimensional curvilinear C grid and analyse its properties. Parcels v2.0 capabilities, including a suite of meta-field objects, are then illustrated in a brief study of the distribution of floating microplastic in the northwest European continental shelf and its sensitivity to various physical processes

Influence of Near-Surface Currents on the Global Dispersal of Marine Microplastic

Buoyant microplastic in the ocean can be submerged to deeper layers through biofouling and the consequent loss of buoyancy or by wind-induced turbulent mixing at the ocean surface. Yet the fact that particles in deeper layers are transported by currents that are different from those at the surface has not been explored so far. We compute 10-year trajectories of 1 million virtual particles with the Parcels framework for different particle advection scenarios to investigate the effect of near-surface currents on global particle dispersal. We simulate the global-scale transport of passive microplastic for (i) particles constrained to different depths from the surface to 120-m depth, (ii) particles that are randomly displaced in the vertical with uniform distribution, (iii) particles subject to surface mixing, and (iv) for a 3-D passive advection model. Our results show that the so called “garbage patches” become more “leaky” in deeper layers and completely disappear at about 60-m depth. At the same time, subsurface currents can transport significant amounts of microplastic from subtropical and subpolar regions to polar regions, providing a possible mechanism to explain why plastic is found in these remote areas. Finally, we show that the final distribution in the surface turbulent mixing scenario with particle rise speed wr = 0.003 m/s is very similar to the distribution of plastic at the surface. This demonstrates that it is not necessary to incorporate surface mixing for global long-term simulations, although this might change on more local scales and for particles with lower rise speeds

Influence of Barotropic Tidal Currents on Transport and Accumulation of Floating Microplastics in the Global Open Ocean

Floating plastic debris is an increasing source of pollution in the world's oceans. Numerical simulations using models of ocean currents give insight into the transport and distribution of microplastics in the oceans, but most simulations do not account for the oscillating flow caused by global barotropic tides. Here, we investigate the influence of barotropic tidal currents on the transport and accumulation of floating microplastics, by numerically simulating the advection of virtual plastic particles released all over the world's oceans and tracking these for 13 years. We use geostrophic and surface Ekman currents from GlobCurrent and the currents caused by the four main tidal constituents (M (Formula presented.), S (Formula presented.), K (Formula presented.), and O (Formula presented.)) from the FES model. We analyze the differences between the simulations with and without the barotropic tidal currents included, focusing on the open ocean. In each of the simulations, we see that microplastic accumulates in regions in the subtropical gyres, which is in agreement with observations. The formation and location of these accumulation regions remain unaffected by the barotropic tidal currents. However, there are a number of coastal regions where we see differences when the barotropic tidal currents are included. Due to uncertainties of the model in coastal regions, further investigation is required in order to draw conclusions in these areas. Our results suggest that, in the global open ocean, barotropic tidal currents have little impact on the transport and accumulation of floating microplastic and can thus be neglected in simulations aimed at studying microplastic transport in the open ocean

Influence of Barotropic Tidal Currents on Transport and Accumulation of Floating Microplastics in the Global Open Ocean

Floating plastic debris is an increasing source of pollution in the world's oceans. Numerical simulations using models of ocean currents give insight into the transport and distribution of microplastics in the oceans, but most simulations do not account for the oscillating flow caused by global barotropic tides. Here, we investigate the influence of barotropic tidal currents on the transport and accumulation of floating microplastics, by numerically simulating the advection of virtual plastic particles released all over the world's oceans and tracking these for 13 years. We use geostrophic and surface Ekman currents from GlobCurrent and the currents caused by the four main tidal constituents (M (Formula presented.), S (Formula presented.), K (Formula presented.), and O (Formula presented.)) from the FES model. We analyze the differences between the simulations with and without the barotropic tidal currents included, focusing on the open ocean. In each of the simulations, we see that microplastic accumulates in regions in the subtropical gyres, which is in agreement with observations. The formation and location of these accumulation regions remain unaffected by the barotropic tidal currents. However, there are a number of coastal regions where we see differences when the barotropic tidal currents are included. Due to uncertainties of the model in coastal regions, further investigation is required in order to draw conclusions in these areas. Our results suggest that, in the global open ocean, barotropic tidal currents have little impact on the transport and accumulation of floating microplastic and can thus be neglected in simulations aimed at studying microplastic transport in the open ocean

Parcels

<p>This is a minor update to Parcels with mostly bugfixes; in preparation for a new v2.4.0 in a few weeks with support for writing directly to zarr.</p> What's Changed <p>Most relevant for users:</p> <ul> <li>Adding option to silence xarray decodewarnings (<a href="https://github.com/OceanParcels/parcels/pull/1208">https://github.com/OceanParcels/parcels/pull/1208</a>)</li> <li>Updating the structure and particle-particle interaction tutorial (by @pdnooteboom, <a href="https://github.com/OceanParcels/parcels/pull/1197">https://github.com/OceanParcels/parcels/pull/1197</a>)</li> <li>Clarification on the <code>show_time</code> parameter (by @VeckoTheGecko, <a href="https://github.com/OceanParcels/parcels/pull/1215">https://github.com/OceanParcels/parcels/pull/1215</a>)</li> <li>Adding section to delaystart tutorial on adding particles during execution (<a href="https://github.com/OceanParcels/parcels/pull/1223">https://github.com/OceanParcels/parcels/pull/1223</a>)</li> <li>Implementing fieldset.UV.eval for SummedVectorFields too (<a href="https://github.com/OceanParcels/parcels/pull/1200">https://github.com/OceanParcels/parcels/pull/1200</a>)</li> </ul> <p>Other fixes</p> <ul> <li>Bugfix for ParticleSet.add() in mpi mode (<a href="https://github.com/OceanParcels/parcels/pull/1194">https://github.com/OceanParcels/parcels/pull/1194</a>)</li> <li>Fixing the <code>sh: None: command not found warning</code> (<a href="https://github.com/OceanParcels/parcels/pull/1201">https://github.com/OceanParcels/parcels/pull/1201</a>)</li> <li>Fixing pipy upload script (<a href="https://github.com/OceanParcels/parcels/pull/1202">https://github.com/OceanParcels/parcels/pull/1202</a>)</li> <li>Adding hint for export CC=gcc in compilation error message (<a href="https://github.com/OceanParcels/parcels/pull/1203">https://github.com/OceanParcels/parcels/pull/1203</a>)</li> <li>Fixing new flake8 requirements (<a href="https://github.com/OceanParcels/parcels/pull/1206">https://github.com/OceanParcels/parcels/pull/1206</a>)</li> <li>Fixing numpy DeprecationWarning in timeslices concatenation (<a href="https://github.com/OceanParcels/parcels/pull/1207">https://github.com/OceanParcels/parcels/pull/1207</a>)</li> <li>Fixing DeprecationWarning on elementwise comparison in converters (in <a href="https://github.com/OceanParcels/parcels/pull/1125">https://github.com/OceanParcels/parcels/pull/1125</a>)</li> <li>Fix broken ipynb link (by @VeckoTheGecko, <a href="https://github.com/OceanParcels/parcels/pull/1219">https://github.com/OceanParcels/parcels/pull/1219</a>)</li> <li>Using f-string in logger info for plotting (<a href="https://github.com/OceanParcels/parcels/pull/1222">https://github.com/OceanParcels/parcels/pull/1222</a>)</li> <li>Throwing explicit error in codegenerator when using random() in JIT Kernel (<a href="https://github.com/OceanParcels/parcels/pull/1230">https://github.com/OceanParcels/parcels/pull/1230</a>)</li> </ul> New Contributors <ul> <li>@VeckoTheGecko made their first contribution in <a href="https://github.com/OceanParcels/parcels/pull/1215">https://github.com/OceanParcels/parcels/pull/1215</a></li> </ul> <p><strong>Full Changelog</strong>: <a href="https://github.com/OceanParcels/parcels/compare/v2.3.1...v2.3.2">https://github.com/OceanParcels/parcels/compare/v2.3.1...v2.3.2</a></p>If you use this software, please cite it as below

The Parcels v2.0 Lagrangian framework: New field interpolation schemes

With the increasing number of data produced by numerical ocean models, so increases the need for efficient tools to analyse these data. One of these tools is Lagrangian ocean analysis, where a set of virtual particles is released and their dynamics are integrated in time based on fields defining the ocean state, including the hydrodynamics and biogeochemistry if available. This popular methodology needs to adapt to the large variety of models producing these fields at different formats. This is precisely the aim of Parcels, a Lagrangian ocean analysis framework designed to combine (1) a wide flexibility to model particles of different natures and (2) an efficient implementation in accordance with modern computing infrastructure. In the new Parcels v2.0, we implement a set of interpolation schemes to read various types of discretized fields, from rectilinear to curvilinear grids in the horizontal direction, from z to s levels in the vertical direction and using grid staggering with the Arakawa A, B and C grids. In particular, we develop a new interpolation scheme for a threedimensional curvilinear C grid and analyse its properties. Parcels v2.0 capabilities, including a suite of meta-field objects, are then illustrated in a brief study of the distribution of floating microplastic in the northwest European continental shelf and its sensitivity to various physical processes

Parcels

<p>Parcels v2.4.2 is a minor update to the v2.4.1 release of February 2023; focussing mostly on a redesign of the documentation, notebooks and tutorial structure at <a href="https://docs.oceanparcels.org/en/latest/">docs.oceanparcels.org</a>, using ReadTheDocs. This change was a fantastic effort by @VeckoTheGecko.</p> What's Changed Documentation changes <ul> <li>Cleaning the documentation and moving to ReadTheDocs in <a href="https://github.com/OceanParcels/parcels/pull/1321">https://github.com/OceanParcels/parcels/pull/1321</a>, <a href="https://github.com/OceanParcels/parcels/pull/1341">https://github.com/OceanParcels/parcels/pull/1341</a>, <a href="https://github.com/OceanParcels/parcels/pull/1342">https://github.com/OceanParcels/parcels/pull/1342</a>, <a href="https://github.com/OceanParcels/parcels/pull/1346">https://github.com/OceanParcels/parcels/pull/1346</a>, <a href="https://github.com/OceanParcels/parcels/pull/1355">https://github.com/OceanParcels/parcels/pull/1355</a> and <a href="https://github.com/OceanParcels/parcels/pull/1371">https://github.com/OceanParcels/parcels/pull/1371</a> (by @VeckoTheGecko)</li> <li>A new tutorial on how to use Parcels output in geospatial datatypes and software <a href="https://github.com/OceanParcels/parcels/pull/1359">https://github.com/OceanParcels/parcels/pull/1359</a> (by @VeckoTheGecko)</li> </ul> Code changes <ul> <li>Create combined kernel from kernel function list in <a href="https://github.com/OceanParcels/parcels/pull/1351">https://github.com/OceanParcels/parcels/pull/1351</a> (by @VeckoTheGecko)</li> <li>Speedup C-contiguous arrays in <a href="https://github.com/OceanParcels/parcels/pull/1074">https://github.com/OceanParcels/parcels/pull/1074</a></li> <li><code>isort</code> support in <a href="https://github.com/OceanParcels/parcels/pull/1323">https://github.com/OceanParcels/parcels/pull/1323</a> (by @VeckoTheGecko)</li> <li>Upgrade syntax to Python 3.8 in <a href="https://github.com/OceanParcels/parcels/pull/1328">https://github.com/OceanParcels/parcels/pull/1328</a> (by @VeckoTheGecko)</li> </ul> GitHub Continuous Integration changes <ul> <li>Add <code>black</code> as dev dependency and intialise .git-blame-ignore-revs in <a href="https://github.com/OceanParcels/parcels/pull/1327">https://github.com/OceanParcels/parcels/pull/1327</a> (by @VeckoTheGecko)</li> <li>Configure pre-commit and pre-commit CI in <a href="https://github.com/OceanParcels/parcels/pull/1286">https://github.com/OceanParcels/parcels/pull/1286</a> (by @VeckoTheGecko)</li> <li>Update to use mamba in <a href="https://github.com/OceanParcels/parcels/pull/1337">https://github.com/OceanParcels/parcels/pull/1337</a> (by @VeckoTheGecko)</li> <li>Issue templates in <a href="https://github.com/OceanParcels/parcels/pull/1361">https://github.com/OceanParcels/parcels/pull/1361</a> (by @VeckoTheGecko)</li> </ul> <p><strong>Full Changelog</strong>: <a href="https://github.com/OceanParcels/parcels/compare/v2.4.1...v2.4.2">https://github.com/OceanParcels/parcels/compare/v2.4.1...v2.4.2</a></p>If you use this software, please cite it as below