Latest news with #oceanDarkening
Yahoo
2 days ago
- Science
- Yahoo
Why the world's oceans are getting darker
A recent worldwide study led by researchers from the University of Plymouth and Plymouth Marine Laboratory finds that more than 20 per cent of the world's oceans, equating to about 75 million square kilometres, have gotten darker in the past two decades, a phenomenon known as ocean darkening. Ocean darkening refers to changes in water clarity that reduce the depth of the photic zone, i.e., the sunlit layer of the ocean where 90 per cent of marine life lives and where sunlight and moonlight trigger ecological interactions. For their paper, scientists used satellite and numerical data to track changes in the photic zone between 2003 and 2022. They found that 21 per cent of the global ocean has darkened, and more than 9 per cent -- or 32 million sq km -- saw the photic zone shrink by more than 50 metres. In 2.6 per cent of the world's oceans, the depth of the photic zone was reduced by 100 metres. Significant darkening was found in both coastal waters and major open-ocean areas, particularly, the Gulf Stream, Arctic and Antarctic regions, and coastal and enclosed seas like the Baltic Sea, where agricultural runoff is high. But not everything is getting dark. Around 10 per cent of the area studied, which is about 37 million sq km, got lighter. A map focused on the UK and North Atlantic Ocean showing changes identified through this project – red areas indicate regions where the oceans are getting darker, while blues indicate regions where they are getting lighter. Image and caption courtesy of the University of Plymouth SEE ALSO: The paper outlines several factors that may be causing oceans to darken. Near coastlines, runoff from agriculture, increased rainfall, and sediment flow bring nutrients and organic materials into the water. This encourages plankton growth and reduces water clarity. In the open ocean, algal blooms and rising sea surface temperatures are likely driving ocean darkening. 'There has been research showing how the surface of the ocean has changed colour over the last 20 years, potentially as a result of changes in plankton communities,' Dr. Thomas Davies, Associate Professor of Marine Conservation at the University of Plymouth, says in a statement. 'But our results provide evidence that such changes cause widespread darkening that reduces the amount of ocean available for animals that rely on the sun and the moon for their survival and reproduction. We also rely on the ocean and its photic zones for the air we breathe, the fish we eat, our ability to fight climate change, and for the general health and well-being of the planet. Taking all of that into account, our findings represent genuine cause for concern.' A 50-metre reduction in a photic zone means animals that need light will be forced to congregate closer to the surface, which could result in more competition for food and resources. "That could bring about fundamental changes in the entire marine ecosystem,' says Professor Tim Smyth, Head of Science for Marine Biogeochemistry and Observations at the Plymouth Marine Laboratory. The study offers new insight into how our oceans are changing over time, and what that could mean for marine ecosystems. While the full ecological impact of ocean darkening is unknown, the findings highlight the importance of continued monitoring and research into the connections between ocean light, climate change, and human activity. Click here to view the video
BBC News
28-05-2025
- Health
- BBC News
University of Plymouth research finds 20% of ocean now darker
More than a fifth of the global ocean has become darker over the past two decades, according to University of Plymouth process, known as "ocean darkening", occurs when changes to the ocean's upper most level reduce the depth at which sunlight can study, published in Global Change Biology, found 21% of the global ocean had become darker between 2003 and for ocean darkening were believed to be down to factors such as changes in algal bloom dynamics, shifts in sea surface temperatures and artificial light, researchers said. The study found more than 9% of the ocean - an area similar in size of Africa - had seen a reduction in light by more than 164ft (50m).A further 2.6% of the ocean saw a reduction of more than 328ft (100m), it said. While the precise implications of the changes were not wholly clear, researchers said large numbers of the planet's marine species and ecosystem services could be Thomas Davies, associate professor of Marine Conservation at the university, said: "There has been research showing how the surface of the ocean has changed colour over the last 20 years, potentially as a result of changes in plankton communities."But our results provide evidence that such changes cause widespread darkening that reduces the amount of ocean available for animals that rely on the sun and the moon for their survival and reproduction." 'Fundamental changes' Dr Davies said ocean darkening could have an impact on the air humans breathe, the fish they eat and the world's ability to fight climate change."Our findings represent genuine cause for concern," he Tim Smyth, head of Science for Marine Biogeochemistry and Observations at the Plymouth Marine Laboratory, said some marine animals that need light could come closer to the surface as a result of the would cause increased competition for food and the other resources, he warned."That could bring about fundamental changes in the entire marine ecosystem," he said.
The Guardian
27-05-2025
- Science
- The Guardian
Planet's darkening oceans pose threat to marine life, scientists say
Great swathes of the planet's oceans have become darker in the past two decades, according to researchers who fear the trend will have a severe impact on marine life around the world. Satellite data and numerical modelling revealed that more than a fifth of the global ocean darkened between 2003 and 2022, reducing the band of water that life reliant on sunlight and moonlight can thrive in. The effect is evident across 75m sq km (30m sq miles) of ocean, equivalent to the land area of Europe, Africa, China and North America combined, and disturbs the upper layer of water where 90% of marine species live. Dr Thomas Davies, a marine conservationist at the University of Plymouth, said the findings were a 'genuine cause for concern', with potentially severe implications for marine ecosystems, global fisheries and the critical turnover of carbon and nutrients in the oceans. Most marine life thrives in the photic zones of the world's oceans, the surface layers that allow sufficient light through for organisms to exploit. While sunlight can reach a kilometre beneath the waves, in practice there is little below 200 metres. This upper band of water is where microscopic plant-like organisms called phytoplankton photosynthesise. The organisms underpin virtually all marine food webs and generate nearly half the planet's oxygen. Many fish, marine mammals and other creatures hunt, feed and reproduce in the warmer waters of the photic zones where food is most abundant. Davies and his colleagues drew on satellite data and an algorithm used to measure light in sea water to calculate the depths of photic zones around the world. Darkening affected 21% of the global ocean in the 20 years to 2022. In 9% of the ocean, this led to photic zones being 50 metres shallower, while in 2.6% of the ocean, the zones were 100 metres shallower. Details of this study appear in Global Change Biology. The oceans darken when light finds it harder to penetrate the water. It is often seen along coastlines where upwellings of cold, nutrient rich water rise to the surface, and where rainfall sweeps nutrients and sediments from the land into the water. The drivers for darkening far offshore are less clear, but global heating and changes in ocean currents are thought to be involved. 'The areas where there are major changes in ocean circulation, or ocean warming driven by climate change, seem to be darkening, such as the Southern Ocean and up through the Gulf Stream past Greenland,' Davies said. Despite an overall darkening, about 10% of the ocean, or 37 million sq km, became lighter over the past 20 years, the study found. Off the west coast of Ireland, for example, a very large area of ocean has brightened, but further out it has darkened. 'Marine organisms use light for a whole variety of purposes. They use it for hunting, for mating, for timing reproductive events. They use it for basically every single part of their biology,' said Davies. 'With ocean darkening, they have to move up the water column, and there is less space, they're all being squished up towards the surface.' Prof Oliver Zielinski, the director of the Leibniz Institute for Baltic Sea Research in Germany, said the darkening of vast ocean areas was a 'worrying trend'. 'Such changes can disrupt marine food webs, alter species distributions, and weaken the ocean's capacity to support biodiversity and regulate climate,' he said. 'Coastal seas, being closest to human activity, are particularly vulnerable, and their resilience is crucial for both ecological health and human wellbeing.'
