Exploring Microplastic Concentrations and the Sedimentology of San Diego's Offshore Benthic Environments

Marine pollution studies are showing infiltration of plastic debris in remote parts of oceans including the deep sea. Microplastics (MPs) are being discovered not only in the ocean’s water column but also benthic sediments reaching thousands of meters in depth. This is the first study to analyze MP concentrations in conjunction with sedimentary characteristics from varying deep-sea environments (coastal, deep ocean, offshore terrace) in the Southern California Continental Borderland (CCB). Our goal for this study was to observe how the concentration and type (morphology, color, size) of microplastics varied with distance from shore, with water depth, and between different submarine environments (deep basins, shallow shelves, and slopes/submarine canyons). We also investigated how MP concentrations varied with sedimentary characteristics (biogenic, terrigenous, grain size, organic matter, microfossils etc.) to explore if we could infer the source and transport pathways for MPs to these environments. Density separation methods were utilized to extract the plastic particles from the sediment samples. Measurable amounts of MPs (comprising predominantly fibers) were found in every sample yet varied within each environment as well as with sedimentary parameters (organic matter, grain size, etc.). Though there was not a clear pattern showing MP concentration variation with depth, distance offshore, or sediment type, we found that when MP accumulation rates were calculated using previously published regional sedimentation rates, there was a negative correlation between MPs/year and depth. These findings can be a foundation for measuring and managing plastic pollution in our oceans.