The ocean’s color is changing near the Great Pacific Garbage Patch

Marine microplastic pollution has proven remarkably difficult to detect from satellite. However, decades of satellite ocean color measurements have revealed long-term changes in the ocean’s optical signature, which may be influenced by the aggregation of small suspended microplastics in some regions. Analyzing three 20-year records of satellite ocean color reflectance over the North Pacific, we find distinct brightening in both blue and green spectral bands near the Great Pacific Garbage Patch relative to the surrounding ocean. Using radiative transfer modeling, we show that the spectral shift observed corresponds to expectations for the accumulation of suspended microplastics beyond reasonable uncertainty. Finally, we utilize a Monte Carlo approach to generate over 50,000 ocean brightening spectra to determine the likelihood that the observed brightening is attributable to natural multidecadal biogeochemical changes. Microplastics in the water column correspond with a more than four-fold increase in likelihood of the ocean color changes observed near the Great Pacific Garbage Patch, indicating that the spectral shape of brightening caused by small microplastics is unlikely to be caused by natural shifts in ocean color variables and may be used as a diagnostic tool to assess microplastic accumulation from satellite ocean-color measurements.