A recent scientific study has found that microplastic pollution in the world’s oceans may be significantly distorting scientists’ understanding of the marine carbon cycle, with potential implications for climate change research and environmental modelling.

The oceanic carbon cycle plays a critical role in regulating Earth’s climate by absorbing and storing large amounts of atmospheric carbon dioxide. Accurate measurement of this process is essential for understanding how oceans mitigate global warming. However, the new research shows that the presence of microplastics can interfere with standard carbon measurement methods, leading to misleading results.

The study, published in the peer-reviewed journal PLOS One, demonstrates that when microplastics are unintentionally collected alongside natural organic particles in ocean water and sediment samples, the carbon released from plastic fragments during laboratory combustion is often mistakenly recorded as natural organic carbon. This misclassification can lead to overestimation or distortion of particulate organic carbon levels in marine environments.

Microplastics — tiny plastic fragments formed from the breakdown of larger plastic waste, as well as microbeads used in industrial and consumer products — are now widespread throughout coastal and open-ocean waters. These particles enter marine systems through rivers, wastewater discharge, stormwater runoff and industrial effluents, and persist in the environment due to their resistance to natural degradation.

In the study, researchers used commonly applied analytical techniques to compare carbon yields from microplastics and natural sedimentary organic matter. Their findings showed that existing tools used by marine scientists are unable to effectively distinguish between carbon derived from plastic materials and carbon originating from living organisms.

This limitation poses a serious challenge for marine biogeochemistry. Carbon measurements are fundamental to building climate and ecosystem models that predict how environmental systems respond to rising greenhouse gas emissions. Even small inaccuracies in baseline carbon data can introduce significant uncertainty into long-term projections.

The study further highlighted that contamination can occur at multiple stages of sample collection and processing. Microfibers from synthetic clothing, airborne plastic dust, and plastic components of sampling equipment can all inadvertently enter samples, further complicating accurate measurement. These contaminants often go undetected and are incorporated into carbon inventories used in scientific assessments.

While some discrepancies between microplastic-derived carbon and natural organic carbon were found to be relatively minor in individual samples, the authors warn that the cumulative impact could be substantial. Over time, such contamination may have quietly influenced decades of marine carbon data, potentially skewing climate models and scientific understanding of ocean carbon storage.

The researchers emphasise that their work represents one of the first quantitative demonstrations of how plastic contamination affects environmental organic carbon analysis. They argue that current laboratory protocols must be re-evaluated and updated to address this growing source of error, including improved contamination controls, revised processing methods and more precise analytical techniques.

The research was partially funded through grants from the National Science Foundation (NSF), underscoring the strategic importance of improving the accuracy of climate-critical measurements in the face of expanding global plastic pollution.