Some Parts of the Ocean Are Turning a Weird Shade of Blue-Green. Scientists Suspect It’s Plastic

This change in ocean colour, while not ideal, could help us to track microplastics.

Something strange is happening to the Pacific Ocean. Near the Great Pacific Garbage Patch, the water has been reflecting more blue and green light over the past two decades.

Scientists now suspect that some of the ocean’s tiniest pollutants may be responsible.

A new study suggests that microscopic plastic particles accumulating in the water could be scattering enough sunlight to leave a detectable signature from space. If confirmed, it could give scientists a new way to track an almost invisible form of pollution.

An ocean-sized optical mystery

Despite its name, the Great Pacific Garbage Patch isn’t a floating island of trash. It’s an enormous accumulation zone between Hawaii and California, where circulating ocean currents concentrate discarded fishing gear, bottles, fragments, and countless microscopic particles.

A landmark 2018 study estimated that the patch contained around 1.8 trillion pieces of plastic spread across 1.6 million square kilometers (around 1 million square miles). Microplastics accounted for approximately 94% of those pieces, although larger debris made up most of the mass.

Much of this pollution is almost impossible to see directly.

The smallest particles drift through the water column, carried by currents and mixed beneath the surface. Some are smaller than plankton, making them extraordinarily difficult to collect and measure across vast stretches of ocean.

But even particles too small to see can interact with sunlight. And that interaction may be giving them away.

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Satellites spotting plastic

Researchers Shea Cheatham, Daniel Koestner, and Børge Hamre, from the University of Bergen in Norway, wondered whether accumulating microplastics might leave a detectable optical fingerprint.

They examined three satellite-derived ocean-color datasets covering August 2002 through September 2022. The records included measurements from NASA’s MODIS instrument aboard the Aqua satellite, along with two multi-satellite ocean-color products, ESA’s Ocean Colour Climate Change Initiative and Copernicus GlobColour.

All three revealed areas near the Great Pacific Garbage Patch where reflected blue and green light had increased together, creating an unusual cyan-colored signature in the researchers’ visualizations.

Still, something had changed in the light escaping the water. And the researchers wanted to know whether plastic could explain it.

How plastic changes the ocean’s color

Using satellites to hunt for ocean plastic isn’t entirely new. In 2021, scientists used NASA satellite measurements of ocean surface roughness to estimate where microplastics might be accumulating.

But the new study takes a different approach. Instead of looking for changes in the waves, researchers examined the light reflected by the water itself.

The idea builds on earlier laboratory experiments showing that tiny plastic particles scatter blue-green light in distinctive ways. Now, for the first time in this line of research, they’ve identified a matching pattern in decades of satellite observations near the Great Pacific Garbage Patch.

The ocean looks blue largely because water absorbs longer wavelengths of visible light more strongly than shorter blue wavelengths. But its appearance also depends on everything suspended or dissolved within it.

Phytoplankton, for example, absorb light for photosynthesis, influencing the ocean’s green and blue tones. Dissolved organic matter and other particles also affect which wavelengths escape back toward the sky.

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Microplastics behave differently.

Many tiny plastic particles absorb relatively little visible light but scatter it efficiently, sending some of the incoming sunlight back toward the surface. Earlier laboratory experiments found that this scattering can be especially pronounced around 490 nanometers, near the boundary between blue and green light.

That gave the researchers a testable idea. If concentrations of suspended microplastics were increasing, the ocean might become brighter at particular wavelengths, producing a distinctive pattern that satellite instruments could detect.

The blue-green brightening they found near the garbage patch was consistent with that prediction. But consistency isn’t proof. Natural changes in the ocean can also alter its color, so the team needed to investigate other possible explanations.

Weeding out false positives

The researchers turned to computer simulations, testing how the ocean’s optical signature might change as different materials increased or decreased in concentration.

They modeled changes in phytoplankton communities, natural suspended particles, dissolved organic matter, and microplastics, generating more than 50,000 scenarios that produced some degree of brightening.

They simulated tens of thousands of scenarios involving changes in phytoplankton communities, suspended particles, dissolved organic matter, and microplastics.

The difference was striking.

When the models included only natural changes, approximately 3% of brightening scenarios produced the cyan signature. When microplastics were included, that figure climbed to approximately 13% — more than four times as often.

In other words, the observed blue-green brightening was much easier to reproduce when the models allowed microplastic concentrations to change.

This means that the unusual color change is much easier to explain when microplastics are factored in. It doesn’t prove that plastic pollution is responsible, but it strengthens the case that accumulating microplastics may be contributing to the ocean’s changing appearance.

The plastic that’s hard to remove

The discovery matters because the smallest plastics are among the most difficult to monitor, and virtually impossible to clean up at the scale of an ocean.

Large debris, such as fishing nets and plastic containers, can sometimes be collected. But the smaller plastics become, the harder they are to remove; and these microplastics are pervasive.

A 2025 study published in Nature, drawing on measurements from 1,885 ocean sampling stations, found that microplastics are distributed throughout the water column, with smaller particles often extending more evenly into deeper waters than larger fragments.

The new research focuses specifically on particles smaller than 300 micrometers — a fraction of a millimeter. Such particles can remain suspended in seawater, beyond the reach of conventional floating-debris cleanup methods.

That makes monitoring them extraordinarily challenging.

Scientists can collect water samples, filter particles, and analyze them in laboratories, but these measurements cover only tiny portions of the ocean. Satellites, meanwhile, repeatedly observe enormous areas of water.

The attraction of this approach is that scientists might eventually be able to identify regions of microscopic plastic accumulation without having to sample every stretch of water.

But there’s still a critical step missing: matching the satellite signal with direct measurements of plastic concentrations in the ocean itself. The researchers say further fieldwork is needed to establish whether the signature can reliably distinguish microplastics from natural particles and biological changes.

If researchers can do that, they might eventually track the accumulation of microscopic pollution across entire ocean basins.

For now, the changing color of the Pacific remains something of a mystery. But scientists have identified a possible clue, hiding in plain sight in 20 years of satellite observations.

The study was published in Communications Earth & Environment.