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New research shows over 21% of the ocean has become darker between 2003 and 2022, covering 75 million sq km.
It’s when light penetration reduces in ocean waters, shrinking photic zones — the sunlit layers that support 90% of marine life.
Over 9% of ocean areas lost more than 50m in photic zone depth; Around 2.6% of oceans saw over 100m loss in sunlit depth.
About 10% of the ocean — around 37 million sq km — actually became brighter over the past 20 years.
Using NASA satellite data and custom algorithms, researchers analyzed photic zone depths in 9km ocean pixels globally.
Darkening is driven by sediment, runoff, and climate-linked algal shifts.
The Gulf Stream, Arctic, and Antarctic experienced the most prominent photic zone changes due to climate change.
Animals that depend on light for survival are being pushed toward the surface, where they face greater competition and stress.
Photic zones support oxygen, food chains, and climate regulation.
“These findings are a genuine cause for concern,” says Dr. Thomas Davies.