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Plastic Pollution in the Coastal Oceans: Characterization and Modeling

Lermusiaux, P.F.J., A. Gupta, C.S. Kulkarni, G.R. Flierl, J. Marshall, and T. Peacock, 2019. Plastic Pollution in the Coastal Oceans: Characterization and Modeling. In: OCEANS '19 MTS/IEEE Seattle, 27-31 October 2019, in press.

Since the 19th and early-20th century, plastics have become ubiquitous in every walk of human life. Plastics have outgrown most man-made materials: their global volume production has surpassed that of steel production in the late 1980s. As plastic production continues to rise, its undesirable impacts have become significant throughout the world: from lands to rivers and oceans, from wildlife to livestock and consumables. Solving the global plastic pollution crisis is vital. This task can be broken into two constituent problems: engineering more sustainable alternative materials, and the environmental cleanup of the existing plastic contamination on a global scale, especially in global marine systems. The latter problem is of high importance mainly due to the long decay times of almost all polymeric materials in nature, and thus lies at the core of this work.

Ocean currents and dynamics are required to understand the influx, transport, dispersion, and accumulation of plastic waste in marine systems. Rigorous Lagrangian analyses are essential to understand and predict such transport characteristics. Further, understanding the origins and the prominent sources of the plastics entering the world’s oceans is needed for planning and implementing source mitigation strategies. Identifying regions where plastics are prone to be mixed with the surrounding ecosystems and regions where plastics remain contained is of direct use in planning management and cleanup operations. Finally, it is also ideal to be capable of performing such studies in fully three-dimensional domains as subduction zones and vertical mixing may have key impacts on marine plastic transport.

We first complete a literature survey to review the status of modeling and observing plastics in the oceans. To showcase our capabilities, we then focus on coastal plastic pollution, including the example of Massachusetts Bay, along the New England coast. One of the main objective is to characterize and locate the regions of attraction of plastic pollution originating both from offshore inflows and from river and sewage discharges in the region. We employ the MSEAS primitive equation ocean modeling system to capture the complex oceanic phenomenon in the region of interest, and apply the recently developed method of composition to efficiently and accurately compute the transport of plastic in 3D+time domains. Such study can be most useful in optimizing clean-up efforts in the region.

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Forecasting synoptic transients in the Eastern Ligurian Sea

Robinson, A.R., J. Sellschopp, W.G. Leslie, A. Alvarez, G. Baldasserini, P.J. Haley, P.F.J. Lermusiaux, C.J. Lozano, E. Nacini, R. Onken, R. Stoner, P. Zanasca, 2003. Forecasting synoptic transients in the Eastern Ligurian Sea. In "Rapid Environmental Assessment", Bovio, E., R. Tyce and H. Schmidt (Editors), SACLANTCEN Conference Proceedings Series CP-46, Saclantcen, La Spezia, Italy.

Oceanographic conditions in the Gulf of Procchio, along the northern Elba coast, are influenced by the circulation in the Corsica channel and the southeastern Ligurian Sea. In order to support ocean prediction by nested models, an initial 4-day CTD survey provided initial ocean conditions. The purposes of the forecasts were threefold: i) in support of AUV exercises; ii) as an experiment in the development of rapid environmental assessment (REA) methodology; and, iii) as a rigorous real time test of a distributed ocean ocean prediction system technology. The Harvard Ocean Prediction System (HOPS) was set up around Elba in a very high resolution domain (225 m horizontally) which was two-way nested in a high resolution domain (675 m) in the channel between Italy and Corsica. The HOPS channel domain was physically interfaced with a one-way nest to the CU-POM model run in a larger Ligurian Sea domain. Eleven nowcasts and 2-3 day forecasts were issued during the period 26 September to 10 October, 2000 for the channel domain and for a Procchio Bay operational sub-domain of the Elba domain.

After initialization with the NRV Alliance, CTD survey data adaptive sampling patterns for nightly excursions of the Alliance were designed on the basis of forecasts to obtain data for assimilation which would most efficiently maintain the structures and variability of the flow in future dynamical forecasts. Images of satellite sea surface temperature were regularly processed and used for track planning and also for model verification. Rapid environmental assessment (REA) techniques were used for data processing and transmission from ship to shore and vice versa for model results. ADCP data validated well the flow in the channel. Additionally and importantly, the direction and strength of the flow in Procchio Bay were correctly forecast by dynamics supported only by external observations. CU-POM model hydrographic and geostrophic flow data was assimilated successfully on boundary strips of the HOPS domain. Flow fields with/without CU-POM nesting were qualitatively similar and a quantitative analysis of differences is under study. A significant result was the demonstration of a powerful and efficient distributed ocean observing and prediction system with in situ data collected in the Ligurian Sea, satellite data collected at SACLANTCEN, forecast modeling at Harvard University and the University of Colorado, and adaptive sampling tracks designed at Harvard. The distributed system functioned smoothly and effectively and coped with the adverse six-hour time difference between Massachusetts and Italy.

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