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Yes: a 2025 study found that sunlight penetrated less deeply across substantial parts of the ocean between 2003 and 2022. The change is called ocean darkening, but it does not mean every ocean visibly changed color. Researchers measured how quickly light fades through seawater using satellite data, then modeled changes in the depth of the ocean’s light-penetrated zone. The study found darkening across 21% of global ocean area, while about 10% showed lightening.
What “ocean darkening” means
Marine scientists use the term to describe reduced penetration of light into the water—not necessarily a darker-looking sea surface. Sunlight and moonlight are important to organisms in the ocean’s photic zone, the layer where enough light is available for photosynthesis and other biological processes.
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The study measured the diffuse attenuation coefficient at 490 nanometers, known as Kd(490). In simple terms, a higher value means downwelling light at that wavelength is attenuated more quickly as it travels through the water. The researchers used changes in this satellite-derived measure to estimate changes in photic-zone depth.
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Thomas W. Davies and Tim Smyth’s study, “Darkening of the Global Ocean,” was published in Global Change Biology in 2025. It analyzed an annual MODIS Aqua satellite record at 9-kilometer resolution for 2003–2022. The authors report the following global areas:
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| Finding | Area | Share of global ocean |
|---|---|---|
| Increased Kd(490), indicating greater light attenuation | 75,341,181 km² | 21% |
| Estimated photic-zone depth decline greater than 50 m | 32,449,129 km² | 9% |
| Estimated photic-zone depth decline greater than 100 m | 9,392,219 km² | 2.6% |
| Decreased Kd(490), indicating lightening | 37,269,515 km² | 10% |
The area figures describe changes across the study period; they are not a claim that the entire ocean darkened uniformly. The photic-depth figures are model estimates derived from attenuation data, rather than direct measurements of every location’s biological boundary.
Where the change was found
The reported pattern extends beyond coastal waters. Davies and Smyth identify broad open-ocean areas, including polar regions, the northeast Atlantic and the northwest Pacific. The finding is therefore not limited to water near shore, though the study also points to coastal processes as one possible contributor.
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Darkening was not universal: about 10% of global ocean area showed decreased attenuation, which indicates lightening. Including this counter-pattern is important; the headline percentage describes the area with increased attenuation, not a single direction of change everywhere.
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What may be causing it
The authors suggest more than one likely driver, without establishing a definitive cause for each region. Near coasts, increased inputs of nutrients, organic material and sediment can change water properties and biological productivity, reducing how far light travels. Changes in global ocean circulation may also contribute by shifting conditions that affect productivity and light attenuation.
These are probable explanations offered by the authors, not a complete causal accounting. The satellite record documents spatial changes in attenuation; it does not by itself identify the cause of every local change.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the study does—and does not—show
What it establishes
- A satellite-derived measure of light attenuation increased across 21% of global ocean area during 2003–2022.
- Using Beer’s law, the researchers estimated substantial declines in photic-zone depth in portions of the ocean.
- Changes occurred in open-ocean as well as coastal regions, and some areas became clearer to light rather than darker.
What remains unknown
- The study does not count affected marine organisms or measure resulting changes in fish stocks.
- It does not demonstrate a measured decline in ocean oxygen production or carbon uptake.
- It does not quantify ecosystem impacts or establish what the changes mean for particular species or communities.
Davies said the ecological and ecosystem-service implications are “currently unknown, but likely to be severe.” That is the authors’ qualified assessment of potential significance, not a measured estimate of damage. The study establishes a large-scale physical change in light conditions; its biological consequences remain unquantified.
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Study and further reading
- Davies and Smyth, “Darkening of the Global Ocean,” Global Change Biology (2025)
- University of Plymouth: Ocean darkening
- Futurism’s coverage of the finding
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