Global-Scale Dynamics of Ocean Plastics

Abstract

This study reviews the literature on the dynamics of ocean plastics and outlines the historical development, current status, and future prospects of this research field. Prior to the 2010s, most studies focused on reporting the abundance of ocean plastics. Since the mid-2010s, however, research has increasingly emphasized the dynamics of ocean plastics, particularly their transport processes. A major driver of this shift has been the so-called “missing plastics paradox,” which highlights the striking discrepancy between the total mass of plastic waste historically entering the ocean and the small amount of ocean plastics observed globally. As observational and analytical methods have become standardized and guidelines established, the accumulation of data has enabled an increasingly clear understanding of the overall dynamics of ocean plastics, including their emission to the ocean, stranding on coastlines, and subsequent redrifting, degradation, and fragmentation processes, as well as mass increase and sinking mediated by biological activity. In the 2020s, an international database of floating microplastics, the Atlas of Ocean Microplastics (AOMI), was developed, accompanied by significant advances in numerical studies using particle-tracking models. Through numerical simulations, age analyses of floating microplastics, and the quantification of microplastics in sediment cores, the fate of missing plastics has been examined from multiple perspectives. Recently, observations of microplastics fragmented to sizes below several hundred micrometers, together with numerical studies coupled with ecosystem models, have further advanced the field. Consequently, research on the dynamics of ocean plastics has expanded beyond the surface ocean to encompass subsurface layers and the vertical structure of ocean plastics within the water column.