Structural biases in marine microplastics research: the underrepresentation of deep ocean and full water column studies

Abstract The distribution and fate of marine microplastics have become central concerns in ocean science, yet the literature remains strongly biased toward coastal and surface environments. This review presents a systematic analysis of over 40 000 peer-reviewed articles indexed in Scopus and Web of Science between 1980 and 2024, classified according to their disciplinary scope, marine environment, and climate-inspired framing (diagnosis, mitigation, adaptation). Our results reveal persistent structural imbalances: biology dominates thematically, beaches and coastlines dominate spatially, and diagnostic efforts far outnumber mitigation or adaptation studies. Crucially, the deep ocean—despite comprising the majority of marine volume and likely acting as a long-term reservoir for microplastics—remains severely underrepresented. Studies that include sampling below 1000 m are rare, and most lack specific geographic metadata. While the growth in microplastics literature is robust, its conceptual and spatial coverage remains narrow. We argue for a strategic expansion of research to include the full depth and breadth of the ocean, and for increased interdisciplinarity to reduce current uncertainties in global plastic budgets and support evidence-based mitigation efforts.