In Medieval Europe and the Middle East, merchants from faraway places traded in rare, precious commodities. One of the most popular commodities was ivory, which came from places few could have imagined.

Because when the Crusades temporarily prevented trade in ivory from elephants, walrus ivory became a popular commodity, and seeing as walruses only live in icy-cold parts of the world, it must have been brought to European markets from faraway places.

New research from the University of Copenhagen shows that the Vikings were (the first) part of a network that supplied not just Europe and the Middle East, but probably also East Asia with walrus ivory.

“Our study shows that the Vikings regularly travelled the around 6,000 kilometres to Pikialasorsuaq in Northwest Greenland, an area characterised by harsh climatic conditions. And they probably didn’t do it for the thrill of it, but to obtain this precious commodity, which they brought to Northern Europe and other parts of the world,” says Associate Professor Morten Tange Olsen from the Globe Institute at the University of Copenhagen, who is one of the authors of the new study.

The researchers conducted DNA analyses, which show that the Vikings covered a greater distance than previously believed in their search for walruses.

The study is a collaboration between researchers at the University of Copenhagen, the University of Lund in Sweden and the University of Groningen in the Netherlands and international partners from Greenland, Iceland and Canada.

Trade and exchange of hunting techniques

To prove that the Vikings did indeed cover such a great distance, the researchers studied fragments of walrus skulls mainly, obtained from excavations of Viking villages in Europe and settlements in Greenland and Canada.

“DNA sequences from these fragments provided us with a genetic map of the place of origin of various Arctic walrus populations at the time of the Vikings. This enabled us to show in which part of the Arctic the animals were caught,” says Morten Tange Olsen.

The study also demonstrates that the Vikings probably had more dealings with indigenous Arctic populations than previously assumed, including the Thule and Dorset cultures.

“Our research shows that the Vikings were extremely well-travelled and had a well-established network that covered a larger area than previously believed and which in time and place must have overlapped with early Greenlandic and Canadian cultures,” says Morten Tange Olsen, who is a marine mammal biologist and geneticist. He believes the cross-disciplinary collaboration between archaeologists, biologists and geneticists is what has made the study a success.

The new study once again shows that the Vikings had a remarkable ability to navigate and survive in harsh climatic conditions, and that they helped create a global trade network that reached beyond the borders of Europe.

“Now, for the first time ever, we have a clear genetic map of Arctic walrus populations, which tells us where the Norsemen went to obtain the precious commodity, ivory.”

Morten Tange Olsen and his colleagues hope the study will open our eyes to the Vikings’ complex and extensive trade network and interaction with other cultures.

The Princeton Plasma Physics Laboratory (PPPL) — a U.S. national laboratory funded by the Department of Energy (DOE) — is leading several efforts on this front, including collaborating on the design and development of a new fusion device at the University of Seville in Spain. The SMall Aspect Ratio Tokamak (SMART) strongly benefits from PPPL computer codes as well as the Lab’s expertise in magnetics and sensor systems.

“The SMART project is a great example of us all working together to solve the challenges presented by fusion and teaching the next generation what we have already learned,” said Jack Berkery, PPPL’s deputy director of research for the National Spherical Torus Experiment-Upgrade (NSTX-U) and principal investigator for the PPPL collaboration with SMART. “We have to all do this together or it’s not going to happen.”

Manuel Garcia-Munoz and Eleonora Viezzer, both professors at the Department of Atomic, Molecular and Nuclear Physics of the University of Seville as well as co-leaders of the Plasma Science and Fusion Technology Lab and the SMART tokamak project, said PPPL seemed like the ideal partner for their first tokamak experiment. The next step was deciding what kind of tokamak they should build. “It needed to be one that a university could afford but also one that could make a unique contribution to the fusion landscape at the university scale,” said Garcia-Munoz. “The idea was to put together technologies that were already established: a spherical tokamak and negative triangularity, making SMART the first of its kind. It turns out it was a fantastic idea.”

SMART should offer easy-to-manage fusion plasma

Triangularity refers to the shape of the plasma relative to the tokamak. The cross section of the plasma in a tokamak is typically shaped like the capital letter D. When the straight part of the D faces the center of the tokamak, it is said to have positive triangularity. When the curved part of the plasma faces the center, the plasma has negative triangularity.

Garcia-Munoz said negative triangularity should offer enhanced performance because it can suppress instabilities that expel particles and energy from the plasma, preventing damage to the tokamak wall. “It’s a potential game changer with attractive fusion performance and power handling for future compact fusion reactors,” he said. “Negative triangularity has a lower level of fluctuations inside the plasma, but it also has a larger divertor area to distribute the heat exhaust.”

The spherical shape of SMART should make it better at confining the plasma than it would be if it were doughnut shaped. The shape matters significantly in terms of plasma confinement. That is why NSTX-U, PPPL’s main fusion experiment, isn’t squat like some other tokamaks: the rounder shape makes it easier to confine the plasma. SMART will be the first spherical tokamak to fully explore the potential of a particular plasma shape known as negative triangularity.

PPPL’s expertise in computer codes proves essential

PPPL has a long history of leadership in spherical tokamak research. The University of Seville fusion team first contacted PPPL to implement SMART in TRANSP, a simulation software developed and maintained by the Lab. Dozens of facilities use TRANSP, including private ventures such as Tokamak Energy in England.

“PPPL is a world leader in many, many areas, including fusion simulation; TRANSP is a great example of their success,” said Garcia-Munoz.

Mario Podesta, formerly of PPPL, was integral to helping the University of Seville determine the configuration of the neutral beams used for heating the plasma. That work culminated in a paper published in the journal Plasma Physics and Controlled Fusion.

Stanley Kaye, director of research for NSTX-U, is now working with Diego Jose Cruz-Zabala, EUROfusion Bernard Bigot Researcher Fellow, from the SMART team, using TRANSP “to determine the shaping coil currents necessary for attaining their design plasma shapes of positive triangularity and negative triangularity at different phases of operation.” The first phase, Kaye said, will involve a “very basic” plasma. Phase two will have neutral beams heating the plasma.

Separately, other computer codes were used for assessing the stability of future SMART plasmas by Berkery, former undergraduate intern John Labbate, who is, now a grad student at Columbia University, and former University of Seville graduate student Jesús Domínguez-Palacios, who has now moved to an American company. A new paper in Nuclear Fusion by Domínguez-Palacios discusses this work.

Designing diagnostics for the long haul

The collaboration between SMART and PPPL also extended into and one of the Lab’s core areas of expertise: diagnostics, which are devices with sensors to assess the plasma. Several such diagnostics are being designed by PPPL researchers. PPPL Physicists Manjit Kaur and Ahmed Diallo, together with Viezzer, are leading the design of the SMART’s Thomson scattering diagnostic, for example. This diagnostic will precisely measure the plasma electron temperature and density during fusion reactions, as detailed in a new paper published in the journal Review of Scientific Instruments. These measurements will be complemented with ion temperature, rotation and density measurements provided by diagnostics known as the charge exchange recombination spectroscopy suite developed by Alfonso Rodriguez-Gonzalez, graduate student at University of Seville, Cruz-Zabala and Viezzer.

“These diagnostics can run for decades, so when we design the system, we keep that in mind,” said Kaur. When developing the designs, it was important the diagnostic can handle temperature ranges SMART might achieve in the next few decades and not just the initial, low values, she said.

Kaur designed the Thomson scattering diagnostic from the start of the project, selecting and procuring its different subparts, including the laser she felt best fits the job. She was thrilled to see how well the laser tests went when Gonzalo Jimenez and Viezzer sent her photos from Spain. The test involved setting up the laser on a bench and shooting it at a piece of special parchment that the researchers call “burn paper.” If the laser is designed just right, the burn marks will be circular with relatively smooth edges. “The initial laser test results were just gorgeous,” she said. “Now, we eagerly await receiving other parts to get the diagnostic up and running.”

James Clark, a PPPL research engineer whose doctoral thesis focused on Thomson scattering systems, was later brought on to work with Kaur. “I’ve been designing the laser path and related optics,” Clark explained. In addition to working on the engineering side of the project, Clark has also helped with logistics, deciding how and when things should be delivered, installed and calibrated.

PPPL’s Head of Advanced Projects Luis Delgado-Aparicio, together with Marie Skłodowska-Curie fellow Joaquin Galdon-Quiroga and University of Seville graduate student Jesus Salas-Barcenas, are leading efforts to add two other kinds of diagnostics to SMART: a multi-energy, soft X-ray (ME-SXR) diagnostic and spectrometers. The ME-SXR will also measure the plasma’s electron temperature and density but using a different approach than the Thomson scattering system. The ME-SXR will use sets of small electronic components called diodes to measure X-rays. Combined, the Thomson scattering diagnostic and the ME-SXR will comprehensively analyze the plasma’s electron temperature and density.

By looking at the different frequencies of light inside the tokamak, the spectrometers can provide information about impurities in the plasma, such as oxygen, carbon and nitrogen. “We are using off-the-shelf spectrometers and designing some tools to put them in the machine, incorporating some fiber optics,” Delgado-Aparicio said. Another new paper published in the Review of Scientific Instruments discusses the design of this diagnostic.

PPPL Research Physicist Stefano Munaretto worked on the magnetic diagnostic system for SMART with the field work led by University of Seville graduate student Fernando Puentes del Pozo Fernando. “The diagnostic itself is pretty simple,” said Munaretto. “It’s just a wire wound around something. Most of the work involves optimizing the sensor’s geometry by getting its size, shape and length correct, selecting where it should be located and all the signal conditioning and data analysis involved after that.” The design of SMART’s magnetics is detailed in a new paper.

Munaretto said working on SMART has been very fulfilling, with much of the team working on the magnetic diagnostics made up of young students with little previous experience in the field. “They are eager to learn, and they work a lot. I definitely see a bright future for them.”

Delgado-Aparicio agreed. “I enjoyed quite a lot working with Manuel Garcia-Munoz, Eleonora Viezzer and all of the other very seasoned scientists and professors at the University of Seville, but what I enjoyed most was working with the very vibrant pool of students they have there,” he said. “They are brilliant and have helped me quite a bit in understanding the challenges that we have and how to move forward toward obtaining first plasmas.”

Researchers at the University of Seville have already run a test in the tokamak, displaying the pink glow of argon when heated with microwaves. This process helps prepare the tokamak’s inner walls for a far denser plasma contained at a higher pressure. While technically, that pink glow is from a plasma, it’s at such a low pressure that the researchers don’t consider it their real first tokamak plasma. Garcia-Munoz says that will likely happen in the fall of 2024.

Support for this research comes from the DOE under contract number DE-AC02-09CH11466, European Research Council Grant Agreements 101142810 and 805162, the Euratom Research and Training Programme Grant Agreement 101052200 — EUROfusion, and the Junta de Andalucía Ayuda a Infraestructuras y Equipamiento de I+D+i IE17-5670 and Proyectos I+D+i FEDER Andalucía 2014-2020, US-15570.

At the start of the 20th century, northern elephant seals were on the brink of being wiped out by hunting. ‘Genetic analyses suggest that the population was likely reduced to fewer than 25 animals at that time,’ explains Professor Dr Joseph Hoffman, lead author of the study and head of the Evolutionary Population Genetics group at Bielefeld University. Such drastic population declines can squeeze out a species’ genetic diversity, increasing the risk of inbreeding and threatening its survival. The population of northern elephant seals has since recovered to around 225,000 individuals. The study published in the journal ‘Nature Ecology and Evolution’ examines how this near-extinction event impacted the species’ genetic diversity and health.

Adaptability at risk

For their analyses, the researchers combined genetic data, health records, modelling of population sizes and genetic simulations. Their findings suggest that the severe population decline led to the loss of many beneficial and harmful genes from the northern elephant seal’s gene pool. This pattern was not observed in the closely related southern elephant seal, which did not experience such a drastic decline.

‘The highly reduced genetic diversity, including the loss of beneficial gene copies, may impair the ability of northern elephant seals to cope with future environmental changes, including those caused by anthropogenic climate change, changes to the species’ habitat, or even natural threats such as disease outbreaks,’ warns Professor Dr Kanchon K. Dasmahapatra from the University of York, UK, who is the senior author of the study.

Surprising results on inbreeding

All individuals of a species carry some harmful mutations, though their effects are usually hidden. However, inbred individuals may face health issues as these mutations become exposed. ‘We looked at several key health traits in these seals, including body weight, blubber thickness and disease susceptibility. To our surprise, we found no signs of health problems related to inbreeding,’ Joseph Hoffman says. ‘We believe the severe population decline may have eliminated many harmful mutations.’

Significance for species conservation

‘Our study illustrates how a species’ unique population history shapes its genetic diversity,’ says Dasmahapatra. The findings offer important insights for species conservation and ecosystem management. Hoffman adds: ‘Our research underscores the importance of understanding a species’ history when planning conservation strategies. Each species responds differently to threats, so individualized approaches are essential.’

A team of researchers led by University of Maryland Atmospheric and Oceanic Science Professor Ning Zeng analyzed a 3,775-year-old log and the soil it was excavated from. Their analysis, published on September 27, 2024, revealed that the log had lost less than 5% carbon dioxide from its original state thanks to the low-permeability clay soil that covered it.

“The wood is nice and solid — you could probably make a piece of furniture out of it,” Zeng noted.

Understanding the unique environmental factors that kept that ancient log in mint condition could help researchers perfect an emerging climate solution known as “wood vaulting,” which involves taking wood that is not commercially viable — such as trees destroyed by disease or wildfires, old furniture or unused construction materials — and burying it to stop its decomposition.

Trees naturally sequester carbon dioxide — a potent planet-warming gas — for as long as they live, making tree-planting projects a popular method of mitigating climate change. But on the flip side, when trees die and decompose, that greenhouse gas is released back into the atmosphere, contributing to global warming.

“People tend to think, ‘Who doesn’t know how to dig a hole and bury some wood?'” Zeng said. “But think about how many wooden coffins were buried in human history. How many of them survived? For a timescale of hundreds or thousands of years, we need the right conditions.”

In 2013, while conducting a wood vaulting pilot project in Quebec, Canada, Zeng discovered the 3,775-year-old log that became the focus of the Science study — a chance encounter that for Zeng felt “kind of miraculous.” While digging a trench to bury fresh wood, Zeng and other researchers spotted the log about 6.5 feet below the surface.

“When the excavator pulled a log out of the ground and threw it over to us, the three ecologists that I had invited from McGill University immediately identified it as Eastern red cedar,” Zeng recalled. “You could tell how well it was preserved. I remember standing there thinking, ‘Wow, here’s the evidence that we need!'”

While past studies have analyzed old samples of preserved wood, they tended to overlook the surrounding soil conditions, according to Zeng.

“There is a lot of geological and archeological evidence of preserved wood from hundreds to millions of years ago, but the focus of those studies was not ‘How we can engineer a wood vault to preserve that wood?'” Zeng said. “And the problem with designing a new experiment is that we can’t wait 100 years for the results.”

Shortly after the Quebec dig, UMD’s collaborators at MAPAQ, a government ministry in Montreal, conducted carbon dating to determine the log’s age. Then, in 2021, Distinguished University Professor Liangbing Hu in UMD’s Department of Materials Science and Engineering helped Zeng analyze the 3,775-year-old sample’s microscopic structure, chemical composition, mechanical strength and density. They then compared those results to that of a freshly cut Eastern red cedar log, which revealed that the older sample had lost very little carbon dioxide.

The type of soil covering the log was the key reason for its remarkable preservation. The clay soil in that part of Quebec had an especially low permeability, meaning that it prevented or drastically slowed oxygen from reaching the log while also keeping out fungi and insects, the decomposers typically found in soil.

Because clay soil is common, wood vaulting could become a viable and low-cost option in many parts of the world. As a climate solution, Zeng noted that wood vaulting is best paired with other tactics to slow global warming, including reducing greenhouse gas emissions.

As he and his colleagues continue to optimize wood vaulting, he looks forward to putting what they’ve learned into practice to help curb climate change.

“It’s quite an exciting discovery,” Zeng said of this latest study. “The urgency of climate change has become such a prominent issue, so there was even more motivation to get this analysis going.”