A vast concentration of floating garbage in the North Pacific appears to contain enough microplastics to alter how the ocean looks in satellite observations. Waters around the Great Pacific Garbage Patch are becoming noticeably more cyan in ocean color data.

That apparent shift could offer researchers a new way to estimate the scale and distribution of microplastic pollution from orbit. Current monitoring largely depends on physically sampling ocean water with a trawler.

Microplastics have been detected in locations ranging from the deepest ocean trenches to the human body, but their distribution across the ocean remains difficult to track. Satellite observations could help estimate their spread and predict how much plastic is entering marine food chains.

“We were able to say that we have this specific spectrum of light, this color that microplastics tend to produce,” study author Shea Cheatham, a PhD candidate at the University of Bergen in Norway, told CNN.

Cheatham cautioned that additional research is necessary to determine whether the observed color “is directly and exclusively caused by plastics.” Other particles and biological changes can also affect how light is reflected from the ocean.

The Great Pacific Garbage Patch is the largest accumulation of plastic waste in the world. The Dutch nonprofit The Ocean Cleanup estimates that it contains more than 1.8 trillion pieces of plastic weighing about 100,000 tonnes.

That debris is scattered across an area roughly twice the size of Texas. Although its precise location changes over time, the patch is generally found about halfway between California and Hawai'i.

The North Pacific Gyre, a vast rotating system of ocean currents, holds the accumulation in place and draws in additional debris. Much of the plastic is associated with waste from the fishing industry.

Despite its name, the patch is not a solid island of garbage. It is an expanse of water containing a substantially greater concentration of floating plastic than surrounding areas.

About 8% of the plastic by mass consists of microplastics measuring between 0.05 and 0.5 centimeters across. Surface water in the patch contains more than 17 milligrams of larger microplastic particles per cubic meter.

Cheatham and colleagues investigated whether satellites that monitor ocean color could detect those particles. They simulated how light reflects from contaminated seawater and identified a distinct change associated with relatively small concentrations of microplastics.

Just 5 milligrams of particles measuring 300 micrometers per cubic meter produced a notable increase in reflected cyan light. The wavelength associated with that increase was 490 nanometers.

The team then searched for that signature in three extensive satellite records of ocean color. These included MODIS, an imaging instrument aboard NASA’s Aqua satellite, and two initiatives that combine observations from multiple satellites.

To varying degrees, all three records showed areas within and around the garbage patch becoming brighter in the blue and green portions of the spectrum. However, microplastics are not the only possible explanation for changing ocean color.

NASA had reported earlier that month that the year’s El Niño had turned parts of the equatorial Pacific a deeper blue. That shift followed a mass die off of photosynthesizing phytoplankton, requiring the researchers to examine whether biological changes could explain the cyan signal.

The researchers conducted another 1,000 simulations. In 500, they randomly changed concentrations of phytoplankton and particles other than plastic, while the remaining 500 simulations also included microplastics.

Without plastic, only 3% of scenarios involving a brighter ocean produced a cyan tint, and each required a dramatic change in the local plankton community. When microplastics were included, the share increased to 13%.

The researchers described “a plausible scenario in which both moderate ecosystem shifts and the aggregation of microplastics contribute to the brightening spectra.” The results therefore indicate that plastics could contribute to the observed color without necessarily being the only factor.

The Ocean Cleanup is already removing larger debris from the garbage patch. However, the researchers said extracting particles this small at scale would be “difficult, if not impossible.”

The team’s next step is to collect direct measurements from waters around the patch. Those samples could help determine whether the cyan tint detected by satellites is genuinely associated with microplastic concentrations.

The study was published in the journal Communications Earth & Environment. Its findings present a possible route toward remotely estimating ocean microplastics while highlighting the need to confirm the signal through direct sampling.