20% Of Planet's Oceans Have Darkened In Past 20 Years, Light No Longer Penetrates As Deeply Into Key Zones For Life
Great swathes of the planet’s oceans have become darker in the past two decades, according to researchers who fear the trend will have a severe impact on marine life around the world. Satellite data and numerical modelling revealed that more than a fifth of the global ocean darkened between 2003 and 2022, reducing the band of water that life reliant on sunlight and moonlight can thrive in.
The effect is evident across 75m sq km (30m sq miles) of ocean, equivalent to the land area of Europe, Africa, China and North America combined, and disturbs the upper layer of water where 90% of marine species live. Dr Thomas Davies, a marine conservationist at the University of Plymouth, said the findings were a “genuine cause for concern”, with potentially severe implications for marine ecosystems, global fisheries and the critical turnover of carbon and nutrients in the oceans.
Most marine life thrives in the photic zones of the world’s oceans, the surface layers that allow sufficient light through for organisms to exploit. While sunlight can reach a kilometre beneath the waves, in practice there is little below 200 metres.
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“Marine organisms use light for a whole variety of purposes. They use it for hunting, for mating, for timing reproductive events. They use it for basically every single part of their biology,” said Davies. “With ocean darkening, they have to move up the water column, and there is less space, they’re all being squished up towards the surface.” Prof Oliver Zielinski, the director of the Leibniz Institute for Baltic Sea Research in Germany, said the darkening of vast ocean areas was a “worrying trend”.
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https://www.theguardian.com/environment/2025/may/27/planets-darkening-oceans-pose-threat-marine-life-scientists-say