Monday, August 21, 2023

Europe's wild bird species are on the brink, but there are ways to bring them back

Almost two out of every five species of wild bird are of conservation concern across Europe, according to an updated and comprehensive assessment of their population status. That means these species are declining and becoming more scarce across the continent. Among the birds of conservation concern are some familiar species, including dunnock, goldcrest and meadow pipit.

Since the first assessment, which was carried out in 1994, the number of European bird species that are of global conservation concern has trebled. Snowy owl, northern lapwing, Eurasian curlew, steppe eagle and bearded vulture have all been unlucky enough to make this list.

The assessment used data collected on 546 bird species to estimate population sizes and trends throughout Europe. Species were then assigned one of five categories depending on their extinction risk, considering whether a species is of global or European conservation concern and whether its distribution is concentrated within Europe.

The number of species that are of conservation concern across the continent is worrying, but sadly not particularly surprising. Many of the species that are declining have been doing so for at least the past three decades—and this study highlights that not much has changed.

Which species are at risk?

Birds around the world are facing a multitude of threats. These include changes both to the climate and how land is used, but also over-exploitation, competition with invasive species and pollution. Habitat destruction and degradation, a key driver of bird population decline, affects 93% of globally threatened species.

Certain bird groups are being hit particularly hard. In the assessment, migratory birds, raptors, waders and duck species were noted as being of high conservation concern.

The recent assessment, along with many others, found that farmland birds are among those of highest concern. In fact, almost 60% of the species in the highest conservation concern category were associated with farmland habitats. These species include many that, in the not-too-distant past, were common.

The gentle coo of the European turtle dove, for example, was once a familiar sound across Europe's countryside. But since 1980, the species has declined by almost 80% across Europe. This decline is even more dire in the UK, where turtle doves have suffered a staggering 98% reduction in their population since the 1970s.

Research reveals that agricultural intensification, including the use of pesticides and inorganic fertilizers, is one of the key drivers of population decline in farmland birds across Europe.

The outlook is equally worrying for Europe's seabirds. Petrels, shearwaters, kittiwakes and—perhaps the most well-loved and recognizable seabird—puffins, are among the species that are noted as being of global conservation concern in the assessment.

Climate change is altering environmental conditions and industrial fishing practices are depleting stocks of the fish that these seabirds rely on. This means that food quality, quantity and availability are all changing, which carries serious consequences for the breeding performance and survival of these top predators.

A lack of prey near puffin colonies in the north-east Atlantic, for example, means adults are being forced to travel further to find food for their chicks. This comes with energy costs for adult puffins and also means that the chicks are fed less often.

The new strain of avian flu that is killing birds worldwide adds further and very urgent threats to this already vulnerable group.

What can be done?

The assessment suggests that current efforts to halt and reverse the loss of Europe's bird species are not sufficient. More and urgent action is needed if we want nature to have a fighting chance. But there are some promising measures that can be implemented both nationally and internationally.

In recent decades, there has been a focus on protecting sites for important bird populations. Natura 2000, for example, are designated areas within the EU that contain rare habitats and important breeding and resting sites. Currently, 18% of the EU's land surface area is designated as a Natura 2000 site, and the aim is to create a network of connected protected sites right across the continent.

Evidence on the effectiveness of protected areas is clear: when implemented appropriately, they work. Globally, the number of species is 10.6% higher within protected areas compared with unprotected areas.

But protecting existing habitats is not enough to reverse declines alone. Habitats need to be restored.

A compelling case emerges from Hungary's Hortobágy National Park, where areas of cropland have been converted into restored grassland. Over a three-year period after grassland restoration, the abundance and diversity of farmland bird species increased by 35% and 40% respectively.

We also need to consider the way we produce our food and fuel. Enforcing legislation on what kinds of chemicals, and how much of them, we use to control agricultural pests and diseases is crucial.

In 2018, EU member states banned the use of certain neonicotinoids (a class of insecticide) after mounting evidence of their widespread impact on insects—an important source of food for birds.

This is a promising start, but it will only be effective if implemented widely and not reversed. Unfortunately, the UK government has authorized the emergency application of neonicotinoids in each of the past three years.

There are ways to stop Europe's bird species from disappearing. We just need to make sure these ideas are put into action widely and in the right way.

Provided by The Conversation

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Bird study shows Europe's nature in 'dire straits'

Why researchers think that some extinct giant flying reptiles cared for their young

by Jason Gilchrist, The Conversation

Why we think that some extinct giant flying reptiles cared for their young — Pteranodon was a large-bodied pterosaur. Credit: YuRi Photolife / Shutterstock

Our understanding of animal behavior depends on observation. Researchers can study how animals are born, grow and develop. We can gather evidence of how they interact with each other and their environment.But how do we do this for extinct animals? In a recent scientific paper, paleontologist Zixiao Yang and colleagues compared the growth of small and giant pterosaurs.

These were flying reptiles that were alive between about 228 million years ago and 66 million years ago—sharing the Earth with dinosaurs. Yang and colleagues wanted to understand what, if anything, was different about how the giant animals got so big.

They looked at the limb bones, which are critical to locomotion: the forelimbs to flight, the hindlimbs to movement on the ground. With the smaller-bodied pterosaurs (the smallest in the study had a wingspan of 0.19–0.74 meters), they discovered that the limb bones that lay closest to the body—the "proximal" ones—grew more slowly relative to their total body size as the animals aged after hatching.

For large-bodied pterosaur species, such as Pteranodon, with a wingspan range of 3.91–6.37 meters, the limb bones that lay closest to the body grew faster than other elements of their skeleton after hatching.

In bird and mammal species alive today, this pattern is associated with particular developmental strategies. Present-day species showing a developmental pattern most similar to the smaller pterosaurs tend to move around independently from an early age.

While not necessarily lacking in parental care, such species tend to be less dependent on or demanding of their parents. By contrast, living species showing the developmental pattern seen in the larger Pteranodon tend to have young that are not capable of independent movement. In these animals, intensive parental care—including feeding the young—is the norm.

Wing development

Using data from fossils, Yang and colleagues used computers to model the body measurements of different pterosaur species as they grew.

Pteranodon's wing aspect ratio (the wing length relative to wing area) increased as the species grew, allowing it to develop a long, narrow wing, associated with soaring in modern birds. The smaller pterosaurs, however, showed a consistent or decreasing wing aspect ratio during growth, allowing more maneuverability.

These developmental differences between larger and smaller species of pterosaur indicate that Pteranodon's relatively greater proximal limb growth shortly after hatching, along with—perhaps—enhanced parental care, may have helped it reach a large adult size. Pterosaurs as a group encompassed the largest flying animals of all time. Hatzegopteryx thambema may have been the biggest, with a wingspan of up to 12 meters. But all pterosaurs started small.

Pterosaur hatchlings' size was limited by ultimately the size of their eggs, which was constrained by the size of the pelvic opening of female pterosaurs, and by the soft eggshell produced by pterosaurs. Compared to hard-shelled bird eggs, soft eggs are weaker and cannot support larger sizes. To grow big, pterosaurs had to do most of their growing after they hatched.

Parental care

A key difference between the small and large species may have been parental care. This may have released large pterosaurs from growth and size constraints. An extended maturation period where parents protected their young and fed them may have allowed a bending of developmental physics, resulting in a larger body size, a lighter skeleton and more robust joints. In contrast, small pterosaur species by the nature of their slower proximal limb growth may have been locked into maturity at smaller sizes.

It's also possible that baby pterosaurs from larger species with parental care were not capable of flight, whereas smaller species were flight-ready upon hatching.

To grow to such a large body size, the giant pterosaurs also needed two things from their environment: space and updrafts. Big pterosaurs would principally have been soarers, meaning that they used updrafts to stay aloft and economized on energy by minimizing flapping. Giant pterosaurs also needed a food supply to support their large size and fuel their metabolic requirements.

While competitors for food were likely in short supply for large adult pterosaurs, youngsters—being smaller—would be more likely to overlap in terms of food sources and habitats with smaller pterosaur species. Young giant pterosaurs probably did not compete for food with adult pterosaurs of the same species.

Predation on adult giant pterosaurs by other animals would have been limited. What dinosaurs (or other creatures) would have been big and hard enough to take on such an imposing sharp-beaked monster?

Future fossils

Incredible as it seems, we can infer the presence of parental care—and lack thereof—in long-dead species of flying reptile. The odds of a pterosaur being preserved in the act of unambiguous parental care seem incredibly slim. So evidence from fossils and understanding patterns from contemporary species are critical to our understanding.

At some point, someone will hopefully find juvenile giant pterosaurs, and their hatchlings, eggs and embryos. Otherwise, questions will remain regarding the development of baby pterosaurs.

These questions include: what was the nature of the parental care? Did parents keep eggs and young warm by sitting over them? Did they defend juveniles against predators, providing food for pterosaur babies? Did males and females share parental care equally? Did they care for young that were not their own?

To more fully re-imagine the early lives and parental behavior of giant pterosaurs, we need more fossils. Let's find them.

Provided by The Conversation

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Large pterosaurs were better parents than their smaller, earlier counterparts, study finds

First ever remains of a dicraeosaurid sauropod unearthed in India

A team of archaeologists from the Indian Institute of Technology and the Geological Survey of India, has unearthed the first ever remains of a dicraeosaurid sauropod in India. In their paper published in the journal Scientific Reports, the group describes the fossil, its condition and where it fits in with other dinosaurs of the Middle Jurassic.

The fossil (a partial dorsal vertebra) was dug up at a site in the Thar Desert near the city of Jaisalmer, in the state of Rajasthan. Prior research has shown that during the Mesozoic Era, the area was a shoreline along the Tethys Ocean. The newly found fossil has been dated to approximately 167 million years ago and identified as a member of the dicraeosaurids, which were a group of dinosaurs with long necks that fed on vegetation. It is the first member of the group to have ever been found in India—and the oldest in the world.

The team has named their new find Tharosaurus indicus. They note that dicraeosaurids, such as T. indicus, are all part of a larger group called diplodocoids, which all had long bodies and necks and spikes on the backs of their necks. T. indicus., the researchers note, has some slight differences from others in its group, such as a long depression on the side of its neck bones and neural spines that are believed to indicate it had uniquely facing spikes. It also had a frontal vertebra surface reminiscent of a heart near its tail bone.

The research team suggest their find is likely just the first of many to come, and together such fossils hint at the possibility that the area where the fossil was found likely played an important role in the emergence of neosauropods—also long-necked, vegetation eating dinosaurs.

They note that other fossils have been found in the area that also suggest the region played an evolutionary role in the development of many vertebrate groups. They conclude by noting that work such as theirs is still limited in India, due to an inadequate supply of resources—much more needs to be done to find out just how rich the country might be in dinosaur fossils.

More information: Sunil Bajpai et al, Fossils of the oldest diplodocoid dinosaur suggest India was a major centre for neosauropod radiation, Scientific Reports (2023). DOI: 10.1038/s41598-023-39759-2

Journal information: Scientific Reports

New dinosaur species discovered in Thailand

Researchers find 20,000-year-old refugium for orcas in the northern Pacific

by Birgitte Svennevig, University of Southern Denmark

Researchers find 20,000 years old refugium for orcas in the northern Pacific — Orcas in North Pacific. Credit: SDU/Olga Filatova

The northern Pacific near Japan and Russia is home for several different groups of orcas. They have no contact with each other, do not seek the same food, do not speak the same dialect, and do not mate with each other. How can this be when they live so close to each other and belong to the same species?

Whale biologist Olga Filatova, University of Southern Denmark, is interested in finding out how the northern Pacific has been colonized by orcas, and during her time at university in Moscow, she conducted several expeditions to the area. Today, she is with University of Southern Denmark's Marine Biological Research Center.

Now, some of her latest results have been published. In a recent paper published in Marine Mammal Science, she and colleagues explore the complex interaction between orca culture and post-glacial history of their colonization of the North Pacific, showing that the orca pods currently living near Nemuro Strait in northern Japan are descendants of orcas that settled there during the last ice age, around 20,000 years ago. The location was chosen as a refugium by distant ancestors, and their descendants have lived there ever since.

"Orcas are conservative and tradition-bound creatures who do not move or change their traditions unless there is a very good reason for it. We see that in this population," says Filatova.

This is the second time she has found an orca refugium from the Ice Age. The first one is near the Aleutian Islands, some 2500 km away. The pods there are just as conservative and tradition-bound as their Japanese conspecifics, and are also descendants of Ice Age ancestors who found refuge in ice-free waters.

"When the ice began to retreat again, and orcas and other whales could swim to new ice-free areas, some of them did not follow. They stayed in their [refugia], and they are still living there," says Filatova.

The studies are based on genetic analyses (the researchers took skin biopsies of the animals) and analyses of sounds made by the animals (recorded with underwater microphones).

"Orcas in the Nemuro Strait had unusually high genetic diversity, which is typical for glacial [refugia], and their vocal repertoire is very different from the dialects of orcas living to the north off the coast of Kamchatka. Kamchatkan orcas are most likely the descendants of the few pods that migrated west from the central Aleutian refugium; that's why they are so different," says Filatova.

Orcas' vocalizations are highly diverse, and no two pods make the same sounds. Therefore, these sounds can be used to identify individuals' affiliations to families and pods. Orcas are not genetically programmed to produce sound, for example, the way a cat is. A cat that grows up among other animals and has never heard another cat will still meow when opening its mouth. In contrast, orcas learn to communicate from their mother or other older family members. Each pod has its own dialect, not spoken by others.

"When we combine this with genetic analyses, we get a strong idea of how different orca communities relate to each other," says Filatova.

So far, two Ice Age refugia have been discovered, providing us with insight into how orcas may handle current and future climate changes: They will likely move northward as the ice melts, and this colonization may happen in small, individual families or pods rather than in large waves.

The discovery of the two Ice Age refugia not only contributes to knowledge about how orcas survived during the Ice Age, but it also paints a picture of orcas as very different animals that may not fit neatly into one species.

"Many believe that orcas should be divided into several species. I agree—at least into subspecies because they are so different that it doesn't make sense to talk about one species when discussing their place in the food chain or when allocating quotas to fishermen," says Filatova.

Some orcas eat fish, some only herring, some only mackerel, some only a specific type of salmon. Others only eat marine mammals such as seals, porpoises, and dolphins. Some take a little of everything, and still others live so far out in the open sea that we fundamentally know very little about them.

Whether a pod eats fish—and which fish—has a significant impact on the fishing that takes place in their habitat. When a country calculates fishing quotas, it must take into account how many fish are naturally hunted by predators, and since an orca can consume 50–100 kg of fish in a day, it greatly affects the quota calculation.

If pods eat marine mammals and do not touch fish, this matters if they are to be captured and sold to marine parks, where it is difficult to feed them marine mammals. While marine parks' popularity is declining worldwide, there is still a large market for orcas in Chinese marine parks.

Since there is only one scientifically recognized species of orcas, researchers have resorted to a different form of classification to distinguish between different types of orcas and categorize them into so-called ecotypes. In the northern Pacific, three ecotypes have been defined so far, and in the southern hemisphere, four or five have been described.

There are probably more—perhaps up to 20 different ecotypes, according to Filatova.

"We need to know the different ecotypes. Orcas are at the top of the food chain, and it affects the entire ecosystem around them what they eat and where they do it," she says.

In the Danish waters, Skagerrak and Kattegat, close to the SDU Marine Biological Research Center, orcas are occasionally seen. Yet, no one knows if they eat fish or marine mammals—and therefore, also, how they affect the food chain and fishing.

"I look forward to learning more about them. Maybe they turn out to belong to a new ecotype," says Filatova.

More information: Olga A. Filatova et al, Genetic and cultural evidence suggests a refugium for killer whales off Japan during the Last Glacial Maximum, Marine Mammal Science (2023). DOI: 10.1111/mms.13046

Journal information: Marine Mammal Science

Provided by University of Southern Denmark Killer whales teach each other how to steal fish from human fisheries

REBURN: A new tool to model wildfires in the Pacific Northwest and beyond

by James Urton, University of Washington

In 2006, the Tripod Complex Fire burned more than 175,000 acres in north-central Washington. The fire, which was within the Okanogan-Wenatchee National Forest, was more than three times the size of Seattle. Yet while considered severe at the time, even larger wildfires in 2014, 2015 and 2021 have since dwarfed Tripod.

Past research shows that large and severe wildfires like these were much rarer in the western U.S. and Canada prior to the late 20th century.

"Fire exclusion policies for much of the 20th century yielded many dense forests with largely uniform composition," said Susan Prichard, a research scientist with the UW School of Environmental and Forest Sciences. "By the turn of this century, we had mature and densely treed, multi-layered forests with high fuel content—and as a result, large, destructive wildfires can ignite and spread more easily. There's simply more to burn across large landscapes."

Prichard, along with colleagues from the U.S. Forest Service's Pacific Northwest Research Station—Paul Hessburg, Nicholas Povak and Brion Salter—and consulting fire ecologist Robert Gray, have created a modeling tool that will allow managers and policymakers to imagine and realize a different future: one where large, severe wildfires like Tripod are once again rare events, even under climate change.

The tool, known as REBURN, can simulate large forest landscapes and wildfire dynamics over decades or centuries under different wildfire management strategies. The model can simulate the consequences of extinguishing all wildfires regardless of size, which was done for much of the 20th century, or of allowing certain fires to return to uninhabited areas. REBURN can also simulate conditions where more benign forest landscape dynamics have fully recovered in an area.

In a pair of papers published in the journal Fire Ecology, the team applied REBURN to the region in north-central Washington where the 2006 Tripod Complex Fire burned. Simulations showed that setting prescribed burns and allowing smaller wildfires to burn can yield more varied and resilient forests over time.

Such forests are made up of forest condition "patches" of different sizes and shapes, and all at different stages of recovery from their most recent fire. Patches that recently burned acted as "fences" to the flow of fire for at least the next 5 to 15 years, preventing wildfires from spreading widely. REBURN simulations showed that a forest landscape comprised of 35 to 50% "fence" areas had far fewer large-scale and damaging wildfires.

"Landscapes had tipped to more 'benign' burning conditions," said Hessburg.

REBURN simulations showed that, when fence areas were less abundant across a region, larger and more severe wildfires tended to dominate how the landscape developed over time.

"The model allows us to simulate what can happen when different management scenarios are applied before the fact, including how small or medium-sized fires in uninhabited areas can reshape forest vulnerability to fires," said Prichard. "We found that having a more complex forest environment—in terms of tree age, composition, density, fuel content—makes it harder for large fires to spread and become severe."

"We also found that non-forest areas comprised of grasslands, shrublands, wet and dry meadows, and sparsely treed woodlands were key ingredients of wildfire-resilient forests," said Hessburg.

"REBURN showed us that our policy of extinguishing all wildfires created forests like those that exist today, with large, severe wildfires growing more prevalent. In addition to destroying homes and blanketing cities and towns with smoke, conflagrations like these displace wildlife, destroy habitats, and can burn large areas severely, sometimes making it difficult for forests to return."

Short intervals between forest reburns can be especially harmful for long-term recovery by destroying young trees that have not yet produced cones, they added.

From 1940 to 2005 in Washington's North Cascades, fire crews extinguished more than 300 fires in their early stages in the Tripod area—most triggered by lightning strikes. By the 1980s and 1990s, forests in the region had become high-density tinderboxes, loaded with older, dying trees and lots of dead wood and other fuel on the ground.

Research has shown that before large-scale European colonization of the area, smaller wildfires shaped forests in north-central Washington and elsewhere in the Pacific Northwest. The Methow people and other tribes in the region actively set fires through cultural burning practices. Aerial photos show that, as recently as the 1930s, forests in north-central Washington had a "patchwork quilt" structure that kept large wildfires from forming easily.

"Forests with more complex structure—including densely and lightly treed areas like meadows and grasslands, shrublands, and spare woodlands—also create a wider variety of habitats for wildlife," Hessburg said. "Recently burned areas can develop into wet or dry meadows that can host deer or moose. Other, younger tree-dense areas can host lynx and snowshoe hares."

REBURN can be adapted to other regions in the western U.S. and Canada. Prichard, Hessburg and their colleagues are currently adapting it to simulate forest development in the vast forests of southern British Columbia and northern California, including regions recently hit by wildfires and those culturally burned by Indigenous people.

But knowing when—or even whether—to allow a small fire to burn in an uninhabited region is no easy task, since fire managers must protect people, their homes and livelihoods. The team hopes ongoing research will help refine the model and the insight it can provide to modified forest management strategies.

"This is a new type of tool that couples forest and non-forest development models over time, fuel fall-down after fires, and a fire growth model," said Hessburg.

"We hope that it will help people who make major decisions about our forests understand the long-term consequences of different practices and policies when it comes to wildfires," said Prichard. "We hope it will make these conversations easier to have by grounding our predictions in sound forest science."

More information: Susan J. Prichard et al, The REBURN model: simulating system-level forest succession and wildfire dynamics, Fire Ecology (2023). DOI: 10.1186/s42408-023-00190-7

Nicholas A. Povak et al, System-level feedbacks of active fire regimes in large landscapes, Fire Ecology (2023). DOI: 10.1186/s42408-023-00197-0

Provided by University of Washington Research supports use of managed and prescribed fires to reduce fire severity

North Atlantic volcanic activity was a major driver of climate change 56 million years ago, study finds

The Paleocene–Eocene Thermal Maximum (PETM) is a period of global warming that occurred ~56 million years ago, lasting approximately 200,000 years, when the Earth experienced global surface temperature elevations of ~5°C.

Hypotheses for the cause of this hyperthermal (short-lived warming) event have included destabilization of methane hydrates (ice-like solids of methane and water) due to orbital forcing (changes in incoming solar radiation due to variation in the tilt of the Earth's axis and orbit) and uplift of the land causing weathering of marine rocks.

However, new research in Climate of the Past has suggested that volcanic activity within the North Atlantic contributed significant amounts of greenhouse gases to the atmosphere (it was active 63–54 million years ago but experienced peak volcanism 56–54 million years ago). Increased carbon emissions fall in line with a prominent spike in lighter carbon (12C) recorded in the shells of fossil microorganisms living in the oceans at the time, foraminifera. It enhances the greenhouse effect by trapping and absorbing heat radiating from the Earth's surface, causing a positive feedback loop of ever-increasing temperatures.

This volcanism spans a vast North Atlantic Igneous Province (NAIP) located between Greenland, north of the United Kingdom and west of Norway, with the total volume of magma thought to have been emplaced up to 1,000,000 km3, equating to a carbon reservoir of 35,000 gigatons.

To determine the contribution of the NAIP on PETM climate change, Dr. Morgan Jones from the University of Oslo and colleagues, turned to the sediment record preserved on the island of Fur, Denmark, where a complete section preceding the PETM through to after the event is present, having been uplifted from the seafloor over millennia.

Here, hundreds of ash layers (>1cm thick) derived from the NAIP can be found, which the scientists analyzed for particular elements to determine volcanic activity, changes in hydrology regimes and weathering. Such measurements are termed proxies, and provide an indication of past environmental conditions when direct measurements aren't available, unlike today when we can use instruments to measure emissions in real time.

Volcanic proxies include mercury and osmium that are released during eruptions and are deposited with organic matter. Their progressive enrichment through the succession indicates elevated NAIP activity leading up to the PETM, before a fairly prompt decline during the recovery phase post-event. This would have been comprised of basaltic eruptions and thermogenic degassing (removal of dissolved gases from liquids) due to contact with magma intrusions.

In the latter case, high levels of methane contributed significantly to global warming as it is a powerful greenhouse gas, 28 times more potent than carbon dioxide at trapping heat over a 100-year period. Dr. Jones suggests a distinct change in the activity of the NAIP from effusive (outpouring of lava onto the ground) to explosive (including ash clouds and volcanic bombs, for example) over this period.

Paleoclimate proxies include carbon, lithium and osmium, the latter two being tracers of silicate weathering. Lithium and osmium abundances increase during the peak and then post-PETM, highlighting enhanced silicate weathering and erosion resulting from a more intense hydrological cycle due to global warming. However, lithium measurements do not correspond fully to the palaeotemperature of the time, with Dr. Jones and colleagues suggesting that uplift of the NAIP would have contributed to providing more exposed rock for weathering and erosion to take place.

Post-PETM weathering of the silica-rich basaltic lava flows used carbon dioxide from the atmosphere to form carbonate and bicarbonate compounds that would sequester this greenhouse gas into the rock, helping to draw down carbon dioxide and therefore aid recovery from the climatic event. In addition, an enhanced hydrological cycle transported ash to the sea for burial, which would have helped create a negative feedback loop whereby more carbon was removed from the atmosphere and hydrosphere; thus, the greenhouse forcing reduced and global temperatures declined.

It is worth noting that not all of the volcanic record is preserved here, as only the most explosive eruptions would have had ash reach from the North Atlantic to Denmark to be preserved and discovered by scientists millions of years later. While there is still much more work to be conducted on climate change events over geological timescales, they are important to study as they offer a window into future global warming, understanding how both natural and anthropogenic-induced carbon dioxide will impact our world.

More information: Morgan T. Jones et al, Tracing North Atlantic volcanism and seaway connectivity across the Paleocene–Eocene Thermal Maximum (PETM), Climate of the Past (2023). DOI: 10.5194/cp-19-1623-2023.

Journal information: Climate of the Past

© 2023 Science X Network

Carbon emissions from volcanic rocks can create global warming: study

Physicists use a 350-year-old theorem to reveal new properties of light waves

by Stevens Institute of Technology

Want to know how light works? Try asking a mechanic — Physicists at Stevens Institute of Technology use a 350-year-old theorem that explains the workings of pendulums and planets to reveal new properties of light waves. Credit: Stevens Institute of Technology

Since the 17th century, when Isaac Newton and Christiaan Huygens first debated the nature of light, scientists have been puzzling over whether light is best viewed as a wave or a particle—or perhaps, at the quantum level, even both at once. Now, researchers at Stevens Institute of Technology have revealed a new connection between the two perspectives, using a 350-year-old mechanical theorem—ordinarily used to describe the movement of large, physical objects like pendulums and planets—to explain some of the most complex behaviors of light waves.

The work, led by Xiaofeng Qian, assistant professor of physics at Stevens and reported in the August 17 online issue of Physical Review Research, also proves for the first time that a light wave's degree of non-quantum entanglement exists in a direct and complementary relationship with its degree of polarization. As one rises, the other falls, enabling the level of entanglement to be inferred directly from the level of polarization, and vice versa. This means that hard-to-measure optical properties such as amplitudes, phases and correlations—perhaps even these of quantum wave systems—can be deduced from something a lot easier to measure: light intensity.

"We've known for over a century that light sometimes behaves like a wave, and sometimes like a particle, but reconciling those two frameworks has proven extremely difficult," said Qian "Our work doesn't solve that problem—but it does show that there are profound connections between wave and particle concepts not just at the quantum level, but at the level of classical light-waves and point-mass systems."

Qian's team used a mechanical theorem, originally developed by Huygens in a 1673 book on pendulums, that explains how the energy required to rotate an object varies depending on the object's mass and the axis around which it turns. "This is a well-established mechanical theorem that explains the workings of physical systems like clocks or prosthetic limbs," Qian explained. "But we were able to show that it can offer new insights into how light works, too."

This 350-year-old theorem describes relationships between masses and their rotational momentum, so how could it be applied to light where there is no mass to measure? Qian's team interpreted the intensity of a light as the equivalent of a physical object's mass, then mapped those measurements onto a coordinate system that could be interpreted using Huygens' mechanical theorem. "Essentially, we found a way to translate an optical system so we could visualize it as a mechanical system, then describe it using well-established physical equations," explained Qian.

Once the team visualized a light wave as part of a mechanical system, new connections between the wave's properties immediately became apparent—including the fact that entanglement and polarization stood in a clear relationship with one another.

"This was something that hadn't been shown before, but that becomes very clear once you map light's properties onto a mechanical system," said Qian. "What was once abstract becomes concrete: using mechanical equations, you can literally measure the distance between 'center of mass' and other mechanical points to show how different properties of light relate to one another."

Clarifying these relationships could have important practical implications, allowing subtle and hard-to-measure properties of optical systems—or even quantum systems—to be deduced from simpler and more robust measurements of light intensity, Qian explained. More speculatively, the team's findings suggest the possibility of using mechanical systems to simulate and better-understand the strange and complex behaviors of quantum wave systems.

"That still lies ahead of us, but with this first study we've shown clearly that by applying mechanical concepts, it's possible to understand optical systems in an entirely new way," Qian said. "Ultimately, this research is helping to simplify the way we understand the world, by allowing us to recognize the intrinsic underlying connections between apparently unrelated physical laws."

More information: Xiao-Feng Qian et al, Bridging coherence optics and classical mechanics: A generic light polarization-entanglement complementary relation, Physical Review Research (2023). DOI: 10.1103/PhysRevResearch.5.033110

Journal information: Physical Review Research

Provided by Stevens Institute of Technology Breakthrough in dynamical localization transitions and Berry curvature-induced transport

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