Scientists Warn: Darkening Oceans Endanger Marine Life and Ecosystems

Large areas of the world’s oceans have become darker over the past two decades, raising concerns for marine life globally. According to satellite data, over 21% of the ocean has experienced this darkening from 2003 to 2022, affecting an area roughly the size of Europe, Africa, China, and North America combined.

Dr. Thomas Davies, a marine conservationist from the University of Plymouth, noted that this trend could severely impact marine ecosystems, global fisheries, and the ocean’s ability to cycle carbon and nutrients. Most sea life thrives in the upper layers, known as photic zones, where sunlight penetrates. This area is crucial for tiny plants called phytoplankton, which are at the base of almost all marine food webs and produce nearly half of the world’s oxygen. These zones, however, are becoming less deep. In some parts of the ocean, photic zones are now 100 meters shallower.

The darkening occurs when water becomes less transparent due to factors like nutrient upwellings or increased runoff from land. Global warming and changes in ocean currents are believed to play a role here, particularly in the Southern Ocean and the Gulf Stream.

Interestingly, while most of the ocean has darkened, about 10% has actually become lighter. For instance, off the west coast of Ireland, some areas are brighter, though they are surrounded by darker waters.

Light is vital for marine organisms, influencing hunting, mating, and reproduction. As they are forced closer to the surface due to darkening, their habitat becomes limited. Prof. Oliver Zielinski from the Leibniz Institute for Baltic Sea Research expressed that such changes could disrupt food webs, alter species distributions, and weaken the ocean’s ability to support biodiversity. Coastal seas, close to human activity, are particularly at risk and need protection for both ecological health and human well-being.

The implications of ocean darkening are serious. It can affect fishing industries and even global oxygen levels. This issue highlights the urgent need to address climate change and its impact on our oceans.

For further reading, you can explore this Global Change Biology study on ocean darkening.

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