Large expanses of the planet’s oceans have become darker in the past two decades, according to researchers who fear that the trend has a serious impact on marine life in the world.
Satellite data and digital modeling have revealed that more than a fifth of the world ocean darkened between 2003 and 2022, reducing the water strip that life depends on the sun and the moonlight can prosper.
The effect is obvious on 75 m squares (30 m square m) of Ocean, equivalent to the terrestrial area of Europe, Africa, China and Combined North America, and disrupts the upper layer of water where 90% of sea species live.
Dr. Thomas Davies, a marine environmentalist at Plymouth University, said the results were a “real concern”, with potentially serious implications for marine ecosystems, world fisheries and critical carbon and nutrient renewal in the oceans.
Most of the marine life prosperously in the photical areas of the world’s oceans, the surface layers that allow sufficient light for organisms to exploit. While sunlight can reach a kilometer under the waves, in practice, there are just under 200 meters.
This upper water strip is the place where microscopic organisms similar to plants called phytoplankton photosynthesis. Organizations underlie practically all marine food networks and generate almost half of the planet’s oxygen. Many fish, marine mammals and other creatures hunt, feed and reproduce in the warmer waters of the Photic areas where food is the most abundant.
Davies and her colleagues were based on satellite data and an algorithm used to measure light in seawater to calculate the depths of the social areas of the whole world. The darkening affected 21% of the global ocean during the 20 years to 2022. In 9% of the ocean, this led to philotic areas at 50 meters deep, while in 2.6% of the ocean, the areas were 100 meters in lower. The details of this study appear in World change biology.
The oceans darken when light finds more difficult to penetrate the water. We often see it along the ribs where the increases in cold water and rich in nutrients rise on the surface and where precipitation swept away nutrients and sediments of the earth in water.
The drivers for offshore distant darkening are less clear, but global heating and changes in ocean currents would be involved. “The areas where there are major changes in the circulation of the oceans or the warming of the oceans driven by climate change, seems to darken, like the South Ocean and through the Gulf Stream after Greenland,” said Davies.
Despite an overall darkening, around 10% of the ocean, or 37 million kilometers, have become lighter in the past 20 years, the study has revealed. Off the coast of the west coast of Ireland, for example, a very large area of Ocean was raised, but further darkened.
“Marine organisms use light for purposes. They use it for hunting, for coupling, for timing of reproductive events. They use it essentially for all parts of their biology, ”said Davies. “With the darkening of the ocean, they must go up the water column, and there is less space, they are all crushed towards the surface.”
Professor Oliver Zielinski, director of the Leibniz Institute for Research in Baltic Sea in Germany, said that the darkening of large ocean areas was a “disturbing trend”.
“Such changes can disrupt marine food networks, modify species distributions and weaken the ocean capacity to support biodiversity and regulate the climate,” he said. “The coastal seas, being the closest to human activity, are particularly vulnerable and their resilience is crucial both for ecological health and human well-being.”