Earth's oceans are losing light: Scientists warn of widespread, mysterious marine darkening

Oceans Are Losing Light: Study Warns of Widespread Marine Darkening (Image: Canva)

Deep under the waters, a silent change is taking place. Scientists now believe that the darkening of vast areas of the ocean during the last 20 years may alter marine life as we know it. There is cause for concern as the sunlight layers that support the majority of marine life are getting smaller.

More Than 75 Million Square Kilometres Affected

Researchers at the University of Plymouth and Plymouth Marine Laboratory examined between 2003 and 2022. The results indicate that more than 21% of the world's oceans are getting darker. This accounts for over 75 million square kilometres of water — a space bigger than most continents.

They tracked the way light travels through the ocean using satellite data and computer simulations. The photic zone, where sunlight penetrates and sea creatures survive, is considerably shallower in most places now. For 9% of the ocean, this zone has decreased more than 50 metres. In certain regions — about 2.6% — it's even declined by more than 100 metres.

Up to 10% of ocean areas have experienced minor brightening. The majority of waters are dimming, which becomes more difficult for sea creatures that depend on sunlight or moonlight. Such species utilise light to search for food, feed, and breed.

Farming Runoff and Warming Oceans to Blame

Experts think the causes vary by region. On coastlines, farm runoff and large rainfalls churn up sediment. This triggers plankton production that makes water cloudy, keeping sunlight from penetrating deeply.

In open waters, variable algal blooms and increasing sea temperatures could be responsible for the darkening. Both trends disrupt nature's equilibrium and shorten the depth of the sunlit zone.

Dr Thomas Davies, a marine conservation specialist, said that loss of light prevents many animals from surviving. As the lit area gets smaller, organisms are driven to the surface, where the food is more limited.

A Threat to the Ocean's Balance

Plymouth Marine Laboratory professor Tim Smyth cautioned that decreasing photic zones could damage the entire marine ecosystem. When animals are pushed up, they fight more for food and space. That would alter fish populations, shift the food web, and possibly affect how oceans absorb carbon.

The research identifies an increasing imperative to track and control this quiet change. Ocean darkening might not be seen from shore, but its impacts could stretch from our plates to the Earth's climate.

It is essential to know what causes these changes to safeguard marine — and human — life in the years to come.