The findings, led by scientists at the University of Bristol and the cover story of the journal Nature, mean plants and shallow soil layers are likely removing around one gigatonne more CO2 each year from the atmosphere to counteract this, emphasising their pivotal and greater part in combating climate change.

Lead author Dr Josh Dean, Associate Professor in Biogeochemistry and UKRI Future Leaders Fellow at the University of Bristol, said: “The results took us by surprise because it turns out that old carbon stores are leaking out much more into the atmosphere then previous estimates suggested.

“The implications are potentially huge for our understanding of global carbon emissions. Plants and trees take up CO₂ from the atmosphere and can then lock this carbon away in soils for thousands of years.

“Our findings show some of this old carbon, as well as ancient carbon from rocks, is leaking sideways into rivers and making its way back to the atmosphere. We don’t yet know how humans are affecting this flow of ancient carbon, but we do know plants and trees must be taking up more carbon from the atmosphere today to account for this unrecognised release of old carbon.”

Rivers transport and release methane and carbon dioxide as part of the global carbon cycle. Until now, scientists believed the majority of this was a quick turnover derived from the recycling of recent plant growth – organic material broken down and carried into the river system in the past 70 years or so. This new study indicates the opposite, with more than half – some 60% – of emissions being attributed to long-term carbon stores accumulated over hundreds to thousands of years ago, or even longer.

The international research team, led by scientists at the University of Bristol, University of Oxford and the UK Centre for Ecology and Hydrology, studied more than 700 river reaches from 26 different countries across the world.

They took detailed radiocarbon measurements of carbon dioxide and methane from the rivers. By comparing the levels of carbon-14 in the river samples with a standard reference for modern atmospheric CO₂, the team was able to date the river carbon.

Co-author Prof Bob Hilton, Professor of Sedimentary Geography at the University of Oxford, explained: “We discovered that around half of the emissions are young, while the other half are much older, released from deep soil layers and rock weathering that were formed thousands and even millions of years ago.”

The research was supported by funding from UK Research and Innovation (UKRI) Natural Environment Research Council (NERC).

Co-author Dr Gemma Coxon, Associate Professor in Hydrology and UKRI Future Leaders Fellow at the University of Bristol, said: “Rivers globally release about two gigatonnes of carbon each year, compared to human activity that results in between 10-15 gigatonnes of carbon emissions. These river emissions are significant at a global scale, and we’re showing that over half of these emissions may be coming from carbon stores we considered relatively stable. This means we need to re-evaluate these crucial parts of the global carbon cycle.”

Further building on these findings, the researchers plan to explore how the age of river carbon emissions varies across rivers the study was not able to capture, as well as investigating how the age of these emissions may have changed through time.

The development, published today (June 11) in Nature, represents a major leap toward the realization of thinner, faster and more energy-efficient electronics, the researchers said. They created a complementary metal-oxide semiconductor (CMOS) computer — technology at the heart of nearly every modern electronic device — without relying on silicon. Instead, they used two different 2D materials to develop both types of transistors needed to control the electric current flow in CMOS computers: molybdenum disulfide for n-type transistors and tungsten diselenide for p-type transistors.

“Silicon has driven remarkable advances in electronics for decades by enabling continuous miniaturization of field-effect transistors (FETs),” said Saptarshi Das, the Ackley Professor of Engineering and professor of engineering science and mechanics at Penn State, who led the research. FETs control current flow using an electric field, which is produced when a voltage is applied. “However, as silicon devices shrink, their performance begins to degrade. Two-dimensional materials, by contrast, maintain their exceptional electronic properties at atomic thickness, offering a promising path forward.”

Das explained that CMOS technology requires both n-type and p-type semiconductors working together to achieve high performance at low power consumption — a key challenge that has stymied efforts to move beyond silicon. Although previous studies demonstrated small circuits based on 2D materials, scaling to complex, functional computers had remained elusive, Das said.

“That’s the key advancement of our work,” Das said. “We have demonstrated, for the first time, a CMOS computer built entirely from 2D materials, combining large area grown molybdenum disulfide and tungsten diselenide transistors.”

The team used metal-organic chemical vapor deposition (MOCVD) — a fabrication process that involves vaporizing ingredients, forcing a chemical reaction and depositing the products onto a substrate — to grow large sheets of molybdenum disulfide and tungsten diselenide and fabricate over 1,000 of each type of transistor. By carefully tuning the device fabrication and post-processing steps, they were able to adjust the threshold voltages of both n- and p-type transistors, enabling the construction of fully functional CMOS logic circuits.

“Our 2D CMOS computer operates at low-supply voltages with minimal power consumption and can perform simple logic operations at frequencies up to 25 kilohertz,” said first author Subir Ghosh, a doctoral student pursuing a degree in engineering science and mechanics under Das’s mentorship.

Ghosh noted that the operating frequency is low compared to conventional silicon CMOS circuits, but their computer — known as a one instruction set computer — can still perform simple logic operations.

“We also developed a computational model, calibrated using experimental data and incorporating variations between devices, to project the performance of our 2D CMOS computer and benchmark it against state-of-the-art silicon technology,” Ghosh said. “Although there remains scope for further optimization, this work marks a significant milestone in harnessing 2D materials to advance the field of electronics.”

Das agreed, explaining that more work is needed to further develop the 2D CMOS computer approach for broad use, but also emphasizing that the field is moving quickly when compared to the development of silicon technology.

“Silicon technology has been under development for about 80 years, but research into 2D materials is relatively recent, only really arising around 2010,” Das said. “We expect that the development of 2D material computers is going to be a gradual process, too, but this is a leap forward compared to the trajectory of silicon.”

Ghosh and Das credited the 2D Crystal Consortium Materials Innovation Platform (2DCC-MIP) at Penn State with providing the facilities and tools needed to demonstrate their approach. Das is also affiliated with the Materials Research Institute, the 2DCC-MIP and the Departments of Electrical Engineering and of Materials Science and Engineering, all at Penn State. Other contributors from the Penn State Department of Engineering Science and Mechanics include graduate students Yikai Zheng, Najam U. Sakib, Harikrishnan Ravichandran, Yongwen Sun, Andrew L. Pannone, Muhtasim Ul Karim Sadaf and Samriddha Ray; and Yang Yang, assistant professor. Yang is also affiliated with the Materials Research Institute and the Ken and Mary Alice Lindquist Department of Nuclear Engineering at Penn State. Joan Redwing, director of the 2DCC-MIP and distinguished professor of materials science and engineering and of electrical engineering, and Chen Chen, assistant research professor, also co-authored the paper. Other contributors include Musaib Rafiq and Subham Sahay, Indian Institute of Technology; and Mrinmoy Goswami, Jadavpur University.

The U.S. National Science Foundation, the Army Research Office and the Office of Naval Research supported this work in part.

But aside from skincare benefits, what role might busy cleaner fish stations play in spreading microbes and bacteria — for good or ill — throughout the reef?

A study published in the journal Marine Ecology Progress Series is the first to investigate the influence of cleaner fish stations on reef microbial diversity. It is led by scientists from the University of California, Davis, and Woods Hole Oceanographic Institute (WHOI) in collaboration with the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science.

Could busy cleaning stations, like some medical clinics, be hotspots for spreading bacteria and pathogens? Conversely, could they help spread beneficial microbes among reef communities? Such questions carry important implications for protecting and restoring coral reefs.

“How pathogens or microbes are moving around a reef could be critically important to understanding how individuals will be affected,” said lead author Anya Brown, an assistant professor with the UC Davis Bodega Marine Laboratory and a National Geographic Explorer who conducted the study while at WHOI. “We know microbes play a role in coral bleaching, for example. This study really lays a foundation for using cleaner fish stations as a way to study movement of microbes around the reef environment.”

Cleaner fish and reef health

One hardworking fish is the cleaning goby, a pinky-sized fish with a boldly colored stripe running along its length. To understand how the presence of cleaner fish stations influence microbial diversity, the researchers experimentally removed cleaning gobies from cleaner stations on two Caribbean reefs in Puerto Rico and St. Croix in June 2021. They compared water nutrients and microbial communities of the surrounding reef area with and without gobies. This also included resident damselfish, frequent clients of cleaner gobies.

They found that more fish visited sites where cleaner fish were present compared to where they were removed in both Puerto Rico and St. Croix. They also found that cleaner fish do influence damselfish and reef microbial diversity, but the extent of their role depends on substrate type and the specific reef environment, as each reef carries a unique microbial signature. In the study, client fish, nutrient concentrations and water bacterial cell densities varied throughout the sites.

The authors say the results highlight yet another potential impact of cleaner fish and the need to further demystify their role in shaping reef microbial diversity and transmission.

Tiny fish can have big impact

“While larger organisms on coral reefs attract the most attention, the study underscores the huge impact tiny organisms such as these fish can have and how important they are to helping healthy reef ecosystems function,” said coauthor Paul Sikkel, a research professor at the Rosenstiel School’s Department of Marine Biology and Ecology. “While cleaner fish are well-known for their role in consuming parasites and reducing stress in other fish, this is the first field study to quantify their effects on microbes of other fish and the surrounding coral reef environment.”

Additional coauthors include Amy Apprill and Jeanne Bloomberg of Woods Hole Oceanographic Institution (WHOI), Gina Hendrick and Matthew Nicholson of the University of Miami Rosenstiel School, and Marta Soares and Raquel Xavier of the University of Porto in Portugal.

The study was funded by the National Science Foundation, WHOI, and The Foundation for Science and Technology in Portugal.