The study comes from Shea Cheatham, a PhD candidate and the lead author, along with Daniel Koestner and Børge Hamre, all at the University of Bergen in Norway. They analyzed three satellite-derived ocean-color datasets, each about 20 years long, covering August 2002 to September 2022. The patch sits in the eastern North Pacific between Hawaii and California. The brightening appeared in the waters around it and was absent from more distant parts of the ocean. Blue wavelengths rose by about 10% and green by 2 to 4%.

Microplastics are a plausible explanation because of how they handle light. Experiments and computer simulations indicate that they scatter light strongly and absorb very little, which leaves a distinctive optical signature. Particles smaller than 300 micrometers scatter sunlight at about 490 nanometers, a fingerprint that could in principle be picked up from space. In the lab work, 5 milligrams of 300-micrometer particles per cubic meter of seawater produced a notable increase in reflected cyan light at that wavelength.

The team ran simulations to test whether natural changes could produce the same result. The brightening matched suspended microplastics in 13% of simulations, compared with 3% of those involving only natural change, which makes microplastics roughly four times as likely an explanation. The number of simulations is given differently across accounts of the work. The simulations were designed to rule out other influences, including phytoplankton die-offs linked to El Niño.

Those natural influences remain the central caveat. Phytoplankton and mineral particles can also alter the color of seawater, and the authors say satellite imagery cannot settle which one is responsible here. Cheatham has said seawater samples from the region are needed to test the hypothesis. The team plans direct water measurements to check whether the satellite signal lines up with actual plastic concentrations.

If the link holds, ocean-color satellites could become a way to monitor plastic accumulation across large stretches of open sea. The patch is about twice the size of Texas, according to the US National Oceanic and Atmospheric Administration, and is made up of fragmented debris spread too thinly to be seen from space. The Ocean Cleanup estimates it holds more than 1.8 trillion pieces of plastic weighing 100,000 tonnes, and a 2018 study put microplastics at 94% of the pieces by count. The study notes that removing particles this small from the open ocean is technically challenging at scale.