Plastic carbon in the ocean

The annual influx of ∼11 million metric tons of plastic debris into the ocean poses a significant and growing threat to the marine environment globally. Additionally, plastic debris serves as a source of allochthonous carbon to marine ecosystems — a factor that has only drawn scientific attention recently. Herein, we synthesize recent evidence about this new form of plastic carbon in the ocean by addressing it as three components: particulate organic carbon of plastic (pPOC), dissolved organic carbon leaching from plastic (pDOC), and biogenic organic carbon of plastic-attached biofilm (pBOC). Current estimates of pPOC and pDOC account for only a modest fraction of natural carbon pool in the ocean, but their portions are expected to increase. pDOC is highly heterogenous, varying by polymer types, and has been shown to influence seawater biogeochemistry as well as the structure and function of microbial communities. Furthermore, biofilm biomass colonizing on plastic debris can utilize the pPOC and pDOC as carbon sources. Current evidences proved the incorporation of plastic carbon into microbial biomass, which consequently affects the carbon and nitrogen cycling. Given these emerging insights, we further suggest specific research questions aimed at stimulating research on the nature, dynamics, and role of plastic carbon in the ocean.