Country：Japan

Deans Award for excellence in research awarded at Interdisciplinary Graduate School of Engineering Sciences

Award type：Award from international society, conference, symposium, etc. 

Charles James Moore Best Student Presentation Award for presentation in ocean plastics session

Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Outstanding Student Presentation Award in Ocean plastic Session

Language：English  

Southeast Asian countries are widely acknowledged as major sources of plastic waste entering the ocean. The seasonality of floating marine debris abundance in the Gulf of Thailand (GoT) was investigated through visual observations in situ and a particle tracking model (PTM). The observations documented the highest concentration of floating debris (3329 pieces) during the northeasterly monsoon (dry season), characterized by offshore-ward winds on the beaches along the eastern coast. A PTM representing riverine plastic debris was developed to reproduce these observations by incorporating ocean surface currents, horizontal diffusion, Stokes drift, windage, and beaching/re-drifting processes. Two re-drifting processes were examined in the PTM experiments: one where re-drifting occurs on a timescale assigned to each particle with an average of 200 days and another where modeled particles were re-drifting after the onset of offshore-ward winds above the beaches. The latter experiment successfully reproduced the seasonal patterns observed in reality, although re-drifting should occur after 10–60 days from the onset of offshore-ward winds, suggesting that plastic beach litter is prevented from re-drifting immediately due to various obstructions such as beach vegetation. The results indicate that the floating plastic debris observed visually in the GoT does not directly come from rivers but from the beaches where plastic debris accumulates during the onshore-ward winds. This information will support evidence-based measures, such as beach cleanup campaigns, to effectively reduce plastic debris impact in the GoT.

DOI： 10.1016/j.rsma.2025.104718

Authorship：Lead author   Language：English  

Although the Indian Ocean receives a large amount of land-based plastic waste, the studies on pathways of riverine plastic debris are limited to date. Therefore, a particle tracking model that included ocean surface currents, horizontal diffusion, Stokes drift, windage, and beaching/re-drifting processes was developed to reproduce the behavior of riverine plastic debris in the Indian Ocean. The modeled particles were released in the model domain based on riverine plastic debris database. The maximum abundance of beached particles occurred during the southwesterly monsoon season, particularly in the Bay of Bengal. The particles released from the rivers were trapped in the northern Indian Ocean unless both Stokes drift and windage were excluded from transportation velocity. These results suggest that the riverine plastic debris was trapped in the northern Indian Ocean until it fragmented into less buoyant small microplastics drifting in the subsurface layer, free from windage and Stokes drift at increasing depths.

DOI： 10.1016/j.marpolbul.2023.115985

Event date： 2026.5

Country：Japan  

Large amounts of mismanaged plastic wastes enter the world`s oceans every year. Indian Ocean also receives a large amount of mismanaged plastic waste from the countries bordering it coastlines. The previous study by Irfan et al. (2024, Mar. Pollut., Bull.) suggested the riverine macroplastic debris trapped in the northern Indian Ocean due to windage and Stokes drift. However, microplastics traveling in the subsurface layer, free from windage and Stokes drift, may be free from the trapping. To date, our knowledge is limited about the transport pathway of macro- and microplastics in the Indian Ocean. Therefore, this research aims to understand the transport pathway of both riverine macroplastics and fragmented microplastics concurrently in the Indian Ocean using a particle tracking model (PTM), after validating it with observation data.

In PTM the macroplastic particles were input from river mouths based on the riverine debris database by Lebreton et al. (2017). The macroplastic particles were fragmented into microplastic particles over the timescales assigned to each particle at their generation. The macroplastics were carried by ocean surface currents from HYCOM, Stokes drift, and horizontal diffusivity in the same fashion as microplastics except including windage. The model incorporated the exchange processes between ocean and beaches as well as the removal processes of microplastic debris from the surface layer representing settling via biological processes such as biofouling. The modeling started in the ocean free of plastics and continued for 10 years during which the daily averaged HyCOM currents over 10 years (1993 to 2017) were repeatedly used in the computation.
In the PTM experiments, we demonstrate that the microplastic particles, free from windage and Stokes drift, spread over Indian Ocean including the southern area unlike macroplastics. Nonetheless, a majority of microplastics remain in the Indian Ocean, but almost 5% of microplastic particle generated in the Indian Ocean escaped eastward to the South Pacific through the Ombai Strait and Timor Sea.

Event date： 2024.12

Language：English   Presentation type：Oral presentation (general)  

Country：United States  

Large amounts of mismanaged plastic wastes enter the world`s oceans every year. Indian Ocean also receives a large amount of mismanaged plastic waste from the countries bordering it coastlines. The previous study by Irfan et al. (2024, Mar. Pollut., Bull.) suggested the riverine macroplastic debris trapped in the northern Indian Ocean due to windage and Stokes drift. However, microplastics traveling in the subsurface layer, free from windage and Stokes drift, may be free from the trapping. To date, our knowledge is limited about the transport pathway of macro- and microplastics in the Indian Ocean. Therefore, this research aims to understand the transport pathway of both riverine macroplastics and fragmented microplastics concurrently in the Indian Ocean using a particle tracking model (PTM), after validating it with observation data.

In PTM the macroplastic particles were input from river mouths based on the riverine debris database by Lebreton et al. (2017). The macroplastic particles were fragmented into microplastic particles over the timescales assigned to each particle at their generation. The macroplastics were carried by ocean surface currents from HYCOM, Stokes drift, and horizontal diffusivity in the same fashion as microplastics except including windage. The model incorporated the exchange processes between ocean and beaches as well as the removal processes of microplastic debris from the surface layer representing settling via biological processes such as biofouling. The modeling started in the ocean free of plastics and continued for 10 years during which the daily averaged HyCOM currents over 10 years (1993 to 2017) were repeatedly used in the computation.
In the PTM experiments, we demonstrate that the microplastic particles, free from windage and Stokes drift, spread over Indian Ocean including the southern area unlike macroplastics. Nonetheless, a majority of microplastics remain in the Indian Ocean, but almost 5% of microplastic particle generated in the Indian Ocean escaped eastward to the South Pacific through the Ombai Strait and Timor Sea.

Event date： 2024.5

Language：English   Presentation type：Poster presentation  

Country：Japan  

Large amounts of mismanaged plastic wastes enter the world`s oceans every year. Indian Ocean also receives a large amount of mismanaged plastic waste from the countries bordering it coastlines. The previous study by Irfan et al. (2024, Mar. Pollut., Bull.) suggested the riverine macroplastic debris trapped in the northern Indian Ocean due to windage and Stokes drift. However, microplastics traveling in the subsurface layer, free from windage and Stokes drift, may be free from the trapping. To date, our knowledge is limited about the transport pathway of macro- and microplastics in the Indian Ocean. Therefore, this research aims to understand the transport pathway of both riverine macroplastics and fragmented microplastics concurrently in the Indian Ocean using a particle tracking model (PTM), after validating it with observation data.

In PTM the macroplastic particles were input from river mouths based on the riverine debris database by Lebreton et al. (2017). The macroplastic particles were fragmented into microplastic particles over the timescales assigned to each particle at their generation. The macroplastics were carried by ocean surface currents from HYCOM, Stokes drift, and horizontal diffusivity in the same fashion as microplastics except including windage. The model incorporated the exchange processes between ocean and beaches as well as the removal processes of microplastic debris from the surface layer representing settling via biological processes such as biofouling. The modeling started in the ocean free of plastics and continued for 10 years during which the daily averaged HyCOM currents over 10 years (1993 to 2017) were repeatedly used in the computation.
In the PTM experiments, we demonstrate that the microplastic particles, free from windage and Stokes drift, spread over Indian Ocean including the southern area unlike macroplastics. Nonetheless, a majority of microplastics remain in the Indian Ocean, but almost 5% of microplastic particle generated in the Indian Ocean escaped eastward to the South Pacific through the Ombai Strait and Timor Sea.

Mismanaged plastic wastes accounting for 70% of marine debris remain persistently in the marine environment, even if they are being degraded and fragmentized to tiny microplastics. To date, it is far from answering how this anthropogenic, buoyant, and persistent matter which was first appeared in the earth history, contaminates (or is incorporated into) the earth system. The ocean plastic study requires the insight and methodology of a variety of earth sciences such as the oceanography, geology, and paleontology. We welcome studies on the plastic circulation from the land/atmosphere to upper oceans and bottom sediments, studies on microplastics as a proxy of the "Anthropocene", and studies to establish procedures in monitoring and analyzing macro/microplastics.

Mismanaged plastic wastes accounting for 70% of marine debris remain persistently in the marine environment, even if they are being degraded and fragmentized to tiny microplastics. To date, it is far from answering how this anthropogenic, buoyant, and persistent matter which was first appeared in the earth history, contaminates (or is incorporated into) the earth system. The ocean plastic study requires the insight and methodology of a variety of earth sciences such as the oceanography, geology, and paleontology. We welcome studies on the plastic circulation from the land/atmosphere to upper oceans and bottom sediments, studies on microplastics as a proxy of the "Anthropocene", and studies to establish procedures in monitoring and analyzing macro/microplastics.