Is Plastic Changing the Ocean’s Color? What the Study Shows

What did the ocean colour study find?

Shea Cheatham, Daniel Koestner and Børge Hamre, physicists at the University of Bergen in Norway, published “The ocean’s color is changing near the Great Pacific Garbage Patch” in Communications Earth & Environment on November 5, 2026. It is open access. They looked at the eastern North Pacific between Hawaii and California, where ocean currents collect floating plastic into the accumulation zone known as the Great Pacific Garbage Patch. They chose it because the water there is clear and low in plankton, so a small extra signal from suspended particles should stand out more than it would in greener coastal seas.

Across three 20-year satellite records, they found grid cells in and near the patch where reflected blue light and reflected green light both increased over time, a combination that reads as a shift toward cyan. Much of the surrounding ocean either showed no significant brightening or brightened mainly in green. The cyan cells sat near the western edge of the patch as mapped by Lebreton and colleagues in 2018, which the authors suggest fits small particles drifting with the water rather than being pushed by wind like large debris.

News coverage followed the same day. CNN reported it on November 5 and Phys.org on November 6. Both carried the authors’ caution that direct measurements in the patch are still needed.

How can a satellite see microplastics?

Not by spotting pieces. A satellite ocean-colour sensor records how much sunlight bounces back out of the sea at several wavelengths, a quantity called remote-sensing reflectance. Everything in the top layer of water shapes that spectrum. Phytoplankton absorb blue and red light for photosynthesis. Dissolved organic matter absorbs blue. Pure water scatters blue, which is why the open ocean looks blue.

In earlier lab work, Koestner and colleagues (2024) made suspensions of small plastic particles and measured how they absorb and scatter light. Plastics turned out to absorb fairly evenly across the spectrum and to scatter a lot of light backwards, unlike most natural particles in the open ocean. Put that in a model of clear, nutrient-poor water and the result is extra brightness peaking around 490 nm, with blue and green bands rising together. Plankton changes tend to move blue and green in opposite directions instead.

The new study turned that idea into a test. For each grid cell, the team computed trends at five bands (412, 443, 490, 560 and 665–670 nm), kept only trends that were statistically significant and consistent across thousands of resampled versions of the record, and mapped them to a colour: blue for the shortest bands, green for 490 and 560 nm, red for 670 nm. A cell where blue and green both climbed shows up cyan.

Could plankton or dust explain the colour change instead?

This is the heart of the paper, and the authors are careful. They write that a colour shift consistent with plastic does not, by itself, show plastic is the cause. So they ran 500 simulations in which the amounts of natural particles, dissolved organic matter and microplastics, and the type of phytoplankton, were varied at random, then compared every pair of results. Of 124,750 simulated changes, 56,125 brightened the ocean in at least one colour channel.

Most brightening came out blue, which is what happens when the water simply loses some plankton or dissolved matter. Cyan was rare. With natural causes only, 3% of brightening cases turned cyan, and every one of them needed a large drop in particles and dissolved matter plus a wholesale switch from bigger to smaller phytoplankton. Adding microplastics as a variable lifted the cyan share to 13% with much smaller ecosystem changes.

They also considered other bright particles. Coccolithophores, chalk-plated algae that whiten water during blooms, have not been active in this region and reflect most strongly near 560 nm, which would push the colour greener. Records from Station ALOHA, north of Hawaii, show desert dust deposition following its normal seasonal pattern rather than rising. Their conclusion is that both a moderate ecosystem shift and accumulating microplastics may be contributing.

What are the limits of the ocean colour study?

• The datasets disagree in places. MODIS showed red brightening across much of the southern study area that the merged products did not; the authors link this to sensor drift and atmospheric correction. ESA’s CCI record found the fewest significant trends and, they argue, is least prone to false positives. All three still showed cyan cells near the patch.
• No ground truth yet. Concentrations of small microplastics under 300 µm have not been measured in the patch. The closest data are 2016 trawls suggesting larger microplastics (0.5–5 mm) may exceed 17 mg per cubic metre near the surface, under an assumption about how deep the nets rode.
• Borrowed optics. Complete optical measurements from the North Pacific gyre were not available, so the model used particle measurements from other waters and an assumed plastic mix.
• Coarse grid. Each cell spans 4° of latitude by 5° of longitude, hundreds of kilometres across, chosen to smooth out passing plankton blooms.
• Plausible, not proven, quantities. If all the 490 nm brightening at the brightest western cell came from plastic, it would imply an increase of 11 to 25 mg per cubic metre over 20 years, depending on the dataset. The authors call that reasonable, not confirmed.
• Ocean colour is changing almost everywhere. A 2023 analysis found significant 20-year colour trends across 56% of the global surface ocean, linked to climate-driven ecosystem change (Cael et al., 2023). Most colour change is not about plastic. This study’s claim rests on the specific cyan signature, not on change as such.

Why satellite monitoring of microplastics matters

Small microplastics are the hardest kind to study. Counting them means pumping or trawling water, filtering it and identifying particles one by one, which is slow and expensive and covers only the places a ship visits. The paper notes that particles below 300 µm are probably the most likely to enter marine food webs, and that cleaning them out of open water at scale would be difficult, if not impossible. Large-debris detection from space already exists, but it relies on infrared light reflected by floating litter, which does not work for specks mixed into the water column.

A colour signature could change that. If ship surveys confirm it, the same method could be run over other suspected accumulation zones using archives that already exist, and repeated every year. Richard Thompson, a marine biologist at the University of Plymouth who was not involved, told CNN that remote detection would be “faster and less costly than counting debris piece by piece.” For now it is a promising lead, and the authors say so.

The work is also easy to check, which matters for a claim this striking. All three satellite records are public, from NASA’s Ocean Biology archive, ESA’s Climate Change Initiative and the Copernicus Marine Service, and the authors published their simulation inputs, configuration files and outputs in open repositories. Other groups can rerun the trend analysis, try different colour-mapping choices (the authors report that alternatives did not change the result much) or test the same signature over the Atlantic and Indian Ocean gyres.

What would confirm it?

The paper names the test: measurements in the patch itself of the water’s optical properties and of the particles suspended through the upper water column. In practice that means a research vessel filtering water at several depths, counting and identifying small plastic particles, and measuring how the same water absorbs and scatters light. If the plastic concentrations line up with what the colour signal implies, the method gains a calibration point. If they come in far lower, natural ecosystem change becomes the leading explanation. CNN described that fieldwork as tricky and expensive, which is part of why a satellite proxy is attractive in the first place.

How to read ocean-plastic headlines

This study was reported accurately by the outlets we read, but ocean-plastic stories often blur what was found. A quick guide to the claims you will see:

Where does ocean microplastic come from?

The garbage patch itself is mostly big stuff by weight. Lebreton and colleagues estimated at least 79,000 tonnes (range 45,000 to 129,000) of plastic floating across 1.6 million square kilometres, with more than three-quarters of the mass in pieces larger than 5 cm and at least 46% from fishing nets. Microplastics were only 8% of the mass but 94% of the estimated 1.8 trillion pieces. Much of that small fraction is larger debris breaking apart in sunlight and waves.

Another stream starts small. A 2017 IUCN report modeled the release of “primary” microplastics, those that enter the sea already tiny, at about 1.5 million tonnes a year (range 0.8 to 2.5 million), 98% of it from land (Boucher and Friot, 2017). It is a global estimate with wide uncertainty, but the ranking of sources is useful.

The report found road runoff carried about 66% of these releases, wastewater 25% and wind 7%. The two biggest household-linked sources, laundry and tyres, have their own guides: microplastics from laundry and microplastics from car tyres.

Use the App

Which plastics are you sending down the drain?

Scan clothing labels, cosmetics and household products. The app shows the declared plastics in each one, such as polyester, nylon, acrylic or polyethylene terephthalate glitter, so you can see which items shed into wastewater.

What you can do about ocean microplastics

No one household changes the colour of the Pacific, and this study does not measure the effect of any personal choice. What the source data do show is that a large share of ocean microplastic begins as everyday wear: fabric in the wash, rubber on the road, packaging that escapes the bin. That is the part individuals touch.

• Wash synthetics less and gentler. Full loads, cooler cycles and air drying reduce fibre shedding. A washing-machine filter catches more; see the laundry filter guide. Know which clothes are plastic with our polyester explainer.
• Drive less, and gently. Hard braking and fast cornering wear tyres faster, and tyre makers advise keeping tyres at the recommended pressure. The tyre guide has the detail.
• Keep plastic out of drains and gutters. Wipe glitter and craft scraps into the bin, and pick up litter near storm drains, which lead to rivers.
• Choose fewer single-use plastics, especially packaging that blows away easily: films, bags and foam.
• Support better infrastructure. Wastewater upgrades, road-runoff treatment and fishing-gear recovery address the largest flows, which no shopping choice can.

For readers wondering what ocean plastic means for dinner, the seafood guide and the sea salt guide cover what has been measured in food, separately from the ocean-scale question here.