Summary
Three satellite ocean-colour records show blue and green reflectance increasing in areas near the Great Pacific Garbage Patch between 2002 and 2022. Optical simulations suggest suspended microplastics could contribute to the pattern.
Three satellite records show statistically significant increases in blue and green ocean reflectance in areas near the Great Pacific Garbage Patch between August 2002 and September 2022, researchers report in Communications Earth & Environment. Radiative-transfer simulations suggest that suspended microplastics could contribute to the cyan-tinted brightening pattern. The satellite analysis records a change in ocean colour; the proposed microplastic link comes from modelling, not direct satellite counts of plastic particles.
A shared colour shift across three records
The researchers analysed monthly reflectance data from NASA’s MODIS-Aqua instrument and two merged records, GlobColour and the European Space Agency’s Ocean Colour Climate Change Initiative (OC-CCI). They divided the eastern North Pacific study area into broad grid cells and compared trends across the same 20-year period.
All three records showed areas in and near the Great Pacific Garbage Patch where reflectance increased in both blue and green spectral bands. Together, those increases produce a cyan-coloured signal in the study’s maps. The pattern was not uniform across the region, and the datasets differed in how much brightening they showed. OC-CCI produced the most conservative trends, while the authors point to sensor drift and differences in atmospheric correction and data-merging methods as factors that can affect comparisons.
Ocean-colour satellites measure light reflected from the water, which is shaped by suspended particles and dissolved substances as well as by the atmosphere. Small microplastics—defined in the study as particles under 300 micrometres—are difficult to detect directly because they are dispersed in the water column and occupy little of a satellite pixel. Their possible signal is instead a change in the combined spectrum of light leaving the ocean.
How the microplastic explanation was tested
The team used radiative-transfer models to simulate how light travels through the atmosphere and ocean under different conditions. In simulations of typical open-ocean waters, adding microplastics brightened the spectrum, with the largest effect around 490 nanometres, in the blue-green part of the visible spectrum. The modelled effect at that wavelength exceeded median background variation at a microplastic concentration of about 5 milligrams per cubic metre.
The researchers also generated reflectance scenarios that varied natural ocean-colour contributors, including dissolved organic matter and suspended particles, with and without microplastics. Cyan brightening made up 3% of the simulated brightening spectra when only natural variables were varied, compared with 13% when microplastic concentration was included. This is a comparison within the modelled scenarios, not a measured probability that microplastics caused the satellite-observed change.
The results make the cyan pattern a possible indicator for future satellite monitoring of microplastic accumulation. But the satellite records show colour trends, while the attribution to plastics rests on optical simulations. The authors identify in-water measurements of particle and optical properties near the patch as an important next step in testing that interpretation.