Methane from overlooked sources higher than predicted in Osaka

Researchers found overlooked sources of greenhouse gas emissions in urban Osaka using mobile measurements

Osaka Metropolitan University

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Methane levels in Osaka and Sakai were analyzed using car- and bike-mounted mobile measuring devices.

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Credit: Osaka Metropolitan University

Methane is a greenhouse gas that is more than 25 times as potent as CO2 in warming the Earth. Reducing methane emissions is necessary to reduce the impact of global warming. In urban areas, evidence suggests that natural gas use and sewage treatment are responsible for generating methane. However, the extent of the contribution of other sources is unclear, especially in Japan.

A research group led by Associate Professor Masahito Ueyama at Osaka Metropolitan University’s Graduate School of Agriculture measured methane and ethane concentrations in Osaka by examining the eddies that transport the gas into the atmosphere as well as ‘mobile measurements’ consisting of bicycles and automobiles equipped with gas-measuring analyzers. The study focused on the urban areas of Osaka City and Sakai City.

By simultaneously measuring methane and ethane, the researchers were able to use gas ratios to distinguish between methane originating from fossil fuels, such as natural gas; methane originating from biological sources such as the microorganisms involved in sewage treatment; and combustion.

The group found a discrepancy between observed methane emissions and official estimates. Several areas of elevated methane concentrations were observed, which did not match methane emission inventories reported by local governments.

Researchers found that city gas was a major source, showing up at many sites in the study. There were also other often overlooked contributors ranging from industrial plants and restaurants to biological sources like sewage, reservoirs, dairy farms, and compost piles. Some specifically Japanese sources also stood out including the water-filled ditches around ancient kofun burial mounds and even the process of making the fermented foods commonly eaten in Japan.

“This research is expected to lead to concrete measures for reducing emissions from sources that have been overlooked until now,” Professor Ueyama said. “Going forward, we will increase reliability by repeating measurements and expand the system to multiple cities. We aim to establish evaluation methods and deepen our understanding of methane emissions in Japan's major cities.”

The findings were published in Atmospheric Chemistry and Physics.

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About OMU

Established in Osaka as one of the largest public universities in Japan, Osaka Metropolitan University is committed to shaping the future of society through the “Convergence of Knowledge” and the promotion of world-class research. For more research news, visit https://www.omu.ac.jp/en/ and follow us on social media: X, Facebook, Instagram, LinkedIn.

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Journal

Atmospheric Chemistry and Physics

DOI

10.5194/acp-25-12513-2025 

Method of Research

Observational study

Subject of Research

Not applicable

Article Title

Evaluating urban methane emissions and their attributes in a megacity, Osaka, Japan, via mobile and eddy covariance measurements

Article Publication Date

9-Oct-2025

 

Scientists uncover a new way to forecast eruptions at mid-ocean ridges through hydrothermal vent temperatures

Woods Hole Oceanographic Institution

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The human-occupied vehicle Alvin, during a dive on the East Pacific Rise, collected samples and recovered instruments placed at the vents during previous expeditions.

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Credit: (Photo courtesy of Jill McDermott, Lehigh Univ.; WHOI, NDSF, Alvin Team; Funder: National Science Foundation. © Woods Hole Oceanographic Institution)

Woods Hole, Mass (October 13, 2025) -- A new study published in the Proceedings of the National Academy of Sciences (PNAS) provides scientists with a powerful new tool for monitoring and predicting tectonic activity deep beneath the seafloor at mid-ocean ridges—vast underwater mountain chains that form where Earth’s tectonic plates diverge.

The study, titled “Hydrothermal vent temperatures track magmatic inflation and forecast eruptions at the East Pacific Rise, 9°50'N,” reveals that fluctuations in the temperature of fluids flowing from hydrothermal vents occurring over minutes to years indicate the effects of magmatic and tectonic processes that occur miles beneath the seafloor. The research offers the first evidence that these subtle but detectable temperature changes could offer the means to predict seafloor volcanic eruptions.

Led by Thibaut Barreyre of the French National Centre for Scientific Research (CNRS) and University of Brest, with collaborators from Woods Hole Oceanographic Institution (WHOI), Lehigh University, and Scripps Institution of Oceanography, the study presents a 35-year time-series of temperature measurements from five hydrothermal vents along the East Pacific Rise, one of the most active segments and well-studied of the global mid-ocean ridge system.

“Mid-ocean ridges are where much of Earth’s internal thermal energy is transferred to the ocean,” said Dan Fornari, scientist emeritus at WHOI and a co-author on the study. “Until now, we lacked a direct way to link what we can measure at the seafloor to what’s happening deep below, where magma accumulates and drives eruptions. Our results show that the two are intimately connected.”

Hydrothermal vents form when seawater seeps into oceanic crust, heats as it interacts with the underlying rock, and re-emerges at locations known as hydrothermal vents, often reaching temperatures above 350°C (660°F). These vents help maintain Earth’s thermal balance and support unique ecosystems that thrive in the absence of sunlight.

The long-term dataset used by the team—one of the most continuous and comprehensive of its kind ever assembled—revealed that vent temperatures at the East Pacific Rise rose steadily from around 350°C to nearly 390 °C in the years preceding two known eruptions, in 1991–1992 and 2005–2006. Following the latter event, temperatures dropped back to about 350°C but have been climbing ever since.

The authors suggest that this temperature increase is driven by rising pressure in the oceanic crust, itself caused by the gradual increase of magma located roughly one mile beneath the seafloor. As the magma body expands, it pressurizes surrounding rock as well as the hydrothermal fluids they contain, a process detectable as a slow but steady warming at the vent outlets.

“By combining these temperature measurements with analytical models and seafloor data, we found that vent heating correlates with the buildup of magmatic pressure,” said Barreyre. “That’s a clear signal that can help us anticipate eruptions before they occur.”

Indeed, the team’s analysis indicated conditions consistent with an imminent eruption in early 2025—a forecast that proved accurate when a mid-ocean ridge eruption was confirmed in April by a team using the human-occupied submersible Alvin that included many of the co-authors. This marks one of the first times scientists have successfully predicted a deep-sea volcanic event based on hydrothermal data.

The findings hold promise for advancing global ocean monitoring networks along mid-ocean ridges and for improving understanding of how Earth’s interior interacts with the ocean. With long-term autonomous instruments now capable of continuously tracking seafloor conditions, scientists are closer than ever to “listening” to the planet’s tectonic heartbeat in near-real time.

“This is an extraordinary step forward in submarine geophysics,” said Fornari. “Hydrothermal vents are not just biological oases—they are windows into the dynamic processes that shape our planet.”

Research funded by NSF Grants OCE-1834797, OCE-1949485, OCE-194893, OCE-1949938, OCE-1948936; the Agence Nationale de la Recherche (ANR) Grant ANR-24-CE56-6841-01 (Project OMENS); the Centre National de la Recherche Scientifique (CNRS); and the European Research Council (ERC) under Grant Agreement No. 10117070619 (Project SeaSALT).

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About Woods Hole Oceanographic Institution
Woods Hole Oceanographic Institution (WHOI) is a private, non-profit organization on Cape Cod, Massachusetts, dedicated to marine research, engineering, and higher education. Founded in 1930, its mission is to understand the ocean, its interactions with the Earth, and its role in a changing global environment. WHOI’s pioneering discoveries arise from a unique blend of science and engineering that has made it one of the world’s most trusted leaders in ocean research and exploration. Known for its multidisciplinary approach, advanced ship operations, and unmatched deep-sea robotics, WHOI also operates the most extensive suite of ocean data-gathering platforms worldwide. More than 800 concurrent projects—driven by top scientists, engineers, and students—push the boundaries of knowledge to inform people and policy for a healthier planet. Behind the scenes, ship captains, mates, craftsmen, marine operations, and other skilled professionals provide essential support that makes this work possible. Learn more at whoi.edu.

 

  

Data loggers deployed at hydrothermal vents on the East Pacific Rise record temperature ofvent fluids every ten minutes for up to a year.

Credit

Photo courtesy of Jill McDermott, Lehigh Univ.; WHOI, NDSF, Alvin Team; Funder: National Science Foundation. (© Woods Hole Oceanographic Institution)

Journal

Proceedings of the National Academy of Sciences

DOI

10.1073/pnas.2510245122 

Method of Research

Observational study

Subject of Research

Not applicable

Article Title

"Hydrothermal vent temperatures track magmatic inflation and forecast eruptions at the East Pacific Rise, 9{degree sign}50'N"

Article Publication Date

13-Oct-2025

 

North Atlantic dolphins are dying younger, new study shows

University of Colorado at Boulder

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The common dolphin is the most abundant cetacean in the world.

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Credit: Observatoire Pelagis - France

Common dolphins are among the ocean’s most abundant mammals, but they are living shorter lives in the North Atlantic, according to a new study published October 10 in Conservation Letters.

The  research team, led by the University of Colorado Boulder, discovered that the longevity of female common dolphins has declined by seven years since 1997, an alarming trend that the authors say threatens not only the species but also the marine ecosystem it helps maintain. 

“There is an urgent need to manage the population better,” said Etienne Rouby, a postdoctoral researcher in the Institute of Arctic and Alpine Research (INSTAAR). “Otherwise, there is a risk for decline and, ultimately, extinction.”

About 6 million common dolphins roam tropical and temperate oceans around the globe. They are the world’s most common cetaceans, a group that includes all whales, dolphins and porpoises. 

The Bay of Biscay in the Atlantic Ocean off the French coast is a popular destination for dolphins in winter, because its warmer, nutrient-rich waters attract smaller species of fish like anchovies and sardines that dolphins eat. But those same conditions also make it one of Europe’s fishing hotspots.

While dolphins are not the target of fishing, many of them end up in nets by accident, also known as “bycatch”. Most dolphins caught as bycatch die. Some studies estimate that in 2021, fishing bycatch was responsible for the death of 6,900 dolphins in the bay, from a winter population of 180,000.

Despite those numbers, traditional abundance monitoring methods previously suggested that the dolphin population in the bay was stable.

Conventionally, scientists have estimated dolphin numbers by tallying individuals spotted from survey ships and planes. Because dolphins are constantly moving in and out of a region, this approach can miss population changes until drastic shifts occur. For long-lived animals that only produce a few offspring in their lifetimes, such as dolphins, recovery may not be possible once population declines are significant enough to show up in general counts, Rouby said.

He and his team set out to reevaluate how well these cetaceans were surviving using a new approach they developed: counting and analyzing deceased dolphins stranded on beaches in the bay. 

Dolphins often come onto the shore because they are old, sick, injured or disoriented, and rarely any survives after being stranded. While stranded dolphins represent only about 10% of total dolphin deaths, changes in their mortality patterns over time can reveal broader population trends.

The team studied 759 common dolphins stranded on beaches along the Bay of Biscay between 1997 and 2019. 

“We wanted to capture changes in the population’s survival and fertility rates. These are more sensitive indicators of population health, and they enable us to identify the problems before they become irreversible,” he said. 

By analyzing dolphin teeth, the team determined the age at which these animals died. The team found that female dolphins’ longevity decreased from 24 years in the late 1990s to just 17 years two decades later. This decline has led to fewer calves born, the study suggests.

The researchers estimated that the dolphin population growth rate has declined by 2.4% from 1997 to 2019. In ideal conditions, a healthy common dolphin population grows ideally at about 4% per year. This means if the population was thriving perfectly in 1997, it was only growing at 1.6% annually by 2019. 

“The numbers are likely to be lower in reality,” Rouby said. If the trend continues, the growth rate could dip below zero, a threshold that would signal population decline, he added.

Since 2024, the French government has been closing the Bay of Biscay to fishing for one month every January to protect the dolphins. While some data has suggested the measure has been helpful, Rouby said a more flexible schedule could work better. 

Depending on ocean conditions, dolphins may arrive at the bay earlier or later than the set period in January, so timing fishing restrictions to match dolphin visits would better protect the animals.

Other cetaceans in the North Atlantic, including Harbor porpoise and bottlenose dolphins may also be experiencing similar declines. Studying how well their populations are doing could improve current conservation policies including the US Marine Mammal Protection Act and the European Marine Strategy Framework Directive, Rouby said.

“Dolphins are the top predators in the Bay of Biscay, and they play a very important role in the ecosystem. Without these predators, fish populations could become out of control, and they would in turn consume too much plankton and vegetation until the system collapses,” Rouby said. “As humans, we should make conscious decisions to protect the living and non-living things around us. Facing evidence of viability loss, we need to act before it is too late.” 

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Journal

Conservation Letters

DOI

10.1111/conl.13142 

Article Publication Date

10-Oct-2025