Facing the Deepening Crisis: How Ocean Darkness Endangers Marine Life and Our Planet

Most ocean life thrives in the upper waters, known as the photic zone, where sunlight penetrates. But recent research shows that this vital area is getting darker. Over the past 20 years, scientists have discovered that more than 20% of our oceans are experiencing reduced light levels.

Thomas Davies, a marine biologist from the University of Plymouth, and Tim Smyth, a marine biogeochemist at the University of Exeter, recognized a gap in this research. Although many have expressed concern about ocean darkening, few had measured how severe it had become.

“Studies have shown changes in the ocean’s surface color, likely due to shifting plankton populations,” Davies noted. “Our findings show that this leads to significant darkening, limiting the habitat for marine animals that depend on the Sun and Moon for survival.”

By combining NASA satellite data from 2003 to 2022 with advanced modeling, they tracked the depth of the photic zone. This area, critical for photosynthesizing organisms like seagrasses, kelp, and phytoplankton, is essential for many marine life forms.

In nearly 10% of the world’s oceans, the depth of the photic zone has decreased by over 50 meters (164 feet). Even more alarming, in 2.6% of the oceans, it has shrunk by more than 100 meters. This change reduces living space and increases competition for resources among marine species.

“The ocean is more dynamic than often realized,” said Smyth. “Light levels change drastically even within a single day. Animals sensitive to light are affected by these changes.” As available light decreases, creatures that rely on it will be pushed closer to the surface, leading to a shift in the entire marine ecosystem.

Several factors influence the photic zone’s depth. Direct sunlight at midday can penetrate deeper into clear waters—up to 80 meters. In contrast, near the poles, light struggles to penetrate more than 10 meters due to reflection and other natural barriers.

The Arctic and Antarctic have seen some of the most significant changes. “Factors like nutrient overloads and altered ocean circulation are likely making waters darker,” Davies and Smyth wrote in their study. High levels of sediment and organic material can block light, which can lead to severe consequences, such as the recent algal blooms affecting Australia’s Great Southern Reef.

Interestingly, darkening isn’t limited to coastal areas where runoff from human activity is common. The Gulf Stream and polar regions are also heavily impacted. Climate change is rapidly affecting these marine environments.

Davies emphasized the broader implications: “The ocean’s photic zone is crucial for the air we breathe, the fish we eat, and our fight against climate change. This is a genuine cause for concern.” The study was published in Global Change Biology.

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