Latest news with #photicZone
Yahoo
3 days ago
- Health
- Yahoo
The Ocean Is Getting Darker, Threatening All That Lives Within
Almost all life in the ocean depends on the upper waters where sunlight filters in, known as the photic zone – but new research suggests this narrow window of valuable marine light is shrinking in oceans worldwide. In the past 20 years, marine scientists have found, more than a fifth of our oceans have been growing darker. Thomas Davies, a marine biologist from the University of Plymouth, and Tim Smyth, a marine biogeochemist from the University of Exeter, noticed that despite growing concerns from scientists about ocean darkening, nobody had really quantified its extent. "There has been research showing how the surface of the ocean has changed color over the last 20 years, potentially as a result of changes in plankton communities," Davies says. "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." Pairing NASA satellite data from 2003 to 2022 with numerical modeling, the duo has uncovered a pattern of the photic zone depth – which inherently constrains the habitat for most ocean life – shrinking across the years. The photic zone is the topmost layer of the ocean, where light from the Sun (including that reflected off the Moon) permeates the water. All marine organisms that photosynthesize – seagrasses, kelps, and most essential of all, phytoplanktons – must live in the shallower parts of this layer to harness the Sun's energy. So the many other organisms that depend on these primary producers – like corals, crustaceans, fish, and marine mammals – hang out in the photic zone too. The study found in nearly 10 percent of the world's oceans, the depth of the photic zone has shrunk by more than 50 meters (164 feet). This means that three-dimensional habitat has become a lot smaller, which leads to greater competition for resources. Even worse, in 2.6 percent of the ocean, the photic zone has reduced by more than 100 meters. "The ocean is far more dynamic than it is often given credit for. For example, we know the light levels within the water column vary massively over any 24-hour period, and animals whose behavior is directly influenced by light are far more sensitive to its processes and change," says Smyth. "If the photic zone is reducing by around 50 meters in large swathes of the ocean, animals that need light will be forced closer to the surface, where they will have to compete for food and the other resources they need. That could bring about fundamental changes in the entire marine ecosystem." A few factors affect the depth of the photic zone. Light that hits the ocean in a vertical nosedive, like equatorial rays shining in the middle of the day, can penetrate further into the water, with fewer photons reflecting off the surface. And the less resistance those plunging photons encounter, in the form of suspended sediment and organic matter, the further they can dive. That's why, in clear tropical waters, light can penetrate up to 80 meters deep. When entering the water at an angle, however, more light reflects off the surface, and photons that do break the surface have to travel farther on their way down. This results in a much narrower photic zone at the poles – less than 10 meters deep in some places. This may partially explain why some of the most prominent changes were seen in the photic zones of the Arctic and Antarctic. But sediment and other suspended matter, like algal blooms, make the water more opaque, affecting the depths that light can reach. This is what Davies and Smyth suspect is darkening the world's waters in recent decades. "A combination of nutrient, organic material, and sediment loading near the coasts and changes in global ocean circulation are probable causes of increases in primary and secondary productivity that have reduced light penetration into surface waters," they write in their research paper. In extreme cases, like the recent algal blooms across Australia's Great Southern Reef, a lack of light can lead to mass mortality events. But the world's photic zones aren't only shrinking near the coast, where we would expect excess runoff from human activities to cloud the waters, as is evident in the Baltic Sea and the eastern coasts of England and Scotland. Darkening was also prominent in the Gulf Stream and the poles, where climate change is rapidly changing the natural systems. "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 wellbeing of the planet," Davies says. "Taking all of that into account, our findings represent genuine cause for concern." This research was published in Global Change Biology. Your Salad Could Be Carrying Microplastics From Soil Into Your Body UN Warns: High Odds We'll Exceed 1.5°C Temp Rise by 2029 Earth's Crust Is Hiding Vast Reserves of Hydrogen – Here's How We Can Find It
The Independent
5 days ago
- Health
- The Independent
The ocean is getting even darker
The ocean is darkening. Researchers say more than a fifth of the planet's ocean — which makes up 70 percent of the surface of the Earth — has been subject to the darkening process over the course of the past two decades. It occurs following changes in the optical properties of the ocean that reduce the depth of its photic zones, the surface layers of the ocean that receive sunlight and moonlight, where 90 percent of marine life live. The consequences of continued shifts could be concerning — both for sea creatures and humans alike. Although there's much we don't know. A stunning 80 percent of the ocean remains unobserved and unexplored. 'If the photic zone is reducing by around 50 meters [55 yards} in large swathes of the ocean, animals that need light will be forced closer to the surface where they will have to compete for food and the other resources they need. That could bring about fundamental changes in the entire marine ecosystem,' Tim Smyth, the head of science for marine biogeochemistry and observations at the Plymouth Marine Laboratory, warned in a statement. Smyth was one of the co-authors of the study, which was published recently in the journal Global Change Biology. Possible ecosystem changes and animals moving closer to the surface could also be worrying for humans, who rely on the ocean for recreation, transport, and food. The change could also upset the availability of smaller prey, including brown shrimp, tuna, and other pelagic fish. In addition, it could send predators into new waters that are closer to shore, and potentially to swimmers. That's already happening thanks to climate change, as sharks follow schools of menhaden along the East Coast. The precise implications of changes, however, are 'not wholly clear' at this point, and 10 percent of the ocean has become lighter during the same time period. Using data from NASA's Ocean Color Web satellite, which breaks the global ocean down into a series of nine kilometer (5.5 mile) pixels, they were able to see changes on the ocean's surface. The authors developed an algorithm to measure light in seawater and tell them the depth of the photic zone in each location. They also relied on models to look closer at changes during daylight and moonlight conditions, determining that changes in photic zone depth at night were small compared to the daytime. The researchers found that more than nine percent of the ocean had seen its lit zones reduced by more than 50 meters, and just under three percent saw them reduced by more than 100 meters (109 yards). Coastal changes are likely due to multiple factors, including nutrients entering the water because of increased rainfall and agricultural runoff. Climate change is also leading to heavier rain events. In the open ocean, harmful algal blooms spurred by climate-change-driven sea surface temperatures have helped to block light. The most prominent changes were observed around the poles and the top of the Gulf Stream near Florida. Florida has seen multiple major harmful algae blooms in recent years, and a record bloom is headed for South Florida this summer. The most prominent changes in photic zone depth in the open ocean were observed at the top of the Gulf Stream, and around both the Arctic and Antarctic, areas of the planet experiencing the most pronounced shifts as a result of climate change. Darkening was also widespread in the Baltic Sea, which borders northern Europe and where rainfall on land brings sediment and nutrients into the sea, stimulating phytoplankton growth. Phytoplankton are microscopic marine algae and the base of several food webs. 'There has been research showing how the surface of the ocean has changed color 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,' said Dr. Thomas Davies, an associate professor of marine conservation at the University of Plymouth. '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 wellbeing of the planet. Taking all of that into account, our findings represent genuine cause for concern,' he added.
Fox News
5 days ago
- Health
- Fox News
Earth's oceans are growing darker, threatening marine life worldwide: study
Oceans around the globe have become darker over the last two decades, leaving researchers fearful for their marine inhabitants, according to a new study. Professor Thomas Davies of the University of Plymouth said in a study published in the Global Change Biology journal there is growing concern for the marine ecosystem. Satellite data from NASA's Ocean Color Web data portal showed 21% of the planet's oceans had darkened between 2003 and 2022. According to Davies, the majority of marine life lives in the photic zones of the ocean, which is where sufficient light penetrates to stimulate photobiological processes. The photic zone, which is 200 meters deep, is where global nutrients and carbon budgets sustain the planetary fish markets. This is the area where light reaches marine life that lives closer to the surface of the ocean. These ocean inhabitants rely on both the moonlight and sunlight for hunting, mating, reproduction and other important milestones. The upper level of the ocean is where microscopic organisms and different types of plankton live. With the oceans beginning to darken, it will cause creatures that rely on light to begin moving closer to the surface, potentially creating a cramped living space. Using satellite data and an algorithm-derived measure of the attenuation of light in seawater, Davis was able to measure how deep each photic zone was around the world. Among the darker oceans, 9% of their photic zones were 50 meters more shallow, and 3% of the oceans' photic zones were 100 meters more shallow. The reasoning behind the darkening of oceans far offshore is less clear. Global warming and changes in ocean currents are thought to be involved in this phenomenon, according to the study. Despite an overall darkening, about 10% of oceans, or 37 million square kilometers, have become lighter over the past 20 years, the study found. It also found that most coastal areas have seen an increase in light. However, the study found that this does not translate into a net reduction in photic zone depth near shorelines. Davies predicts the implications of ocean darkening could be severe for marine food webs, global fisheries and carbon and nutrient budgets.
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.'
