Severe bleaching events are hitting coral reefs five times as often as in 1980, researchers report in the Jan. 5 Science.
Scientists surveyed 100 coral reef locations in tropical zones around the world, tracking each spot’s fate from 1980 to 2016. At first, only a few of the locations had experienced bleaching. But by 2016, all had been hit by at least one bleaching event, and all but six had suffered a severe event — defined as affecting more than 30 percent of corals in an area. The median time between pairs of severe bleaching events has also decreased, the researchers found — it’s now just under six years, versus 25 to 30 years in the early 1980s. That’s not enough time for corals to fully bounce back before getting hit again.
Consistently higher tropical water temperatures, the result of climate change, are in part to blame for the increase in bleaching, researchers say. Warm water stresses corals and strips away their symbiotic algae — their main source of food and the reason they’re colorful. Bleaching episodes can be fatal, especially if corals can’t recover between events.
In the past, major bleaching events were most likely to happen when El Niño brought bands of warmer water to the tropics. But sea surface temperatures in tropical areas are now warmer during today’s La Niña years (when the water is typically cooler) than during El Niño events 40 years ago, says study coauthor Terry Hughes, a coral researcher at James Cook University in Townsville, Australia. Because those temperatures continue to rise, “we have a narrowing window of opportunity to save reefs,” he says.
It was one of the flashiest mysteries in the news about a decade ago — honeybee workers were vanishing fast for no clear reason. To this day, that puzzle has never been entirely solved, researchers acknowledge.
And maybe it never will be. Colony collapse disorder, or CCD, as the sudden mass honeybee losses were called, has faded in recent years as mysteriously as it began. It’s possible the disappearances could start up again, but meanwhile bees are facing other problems. CCD probably peaked around 2007 and faded since, says Jeff Pettis, who during the heights of national curiosity was running the Beltsville, Md., honeybee lab for the U.S. Department of Agriculture’s research wing. And five years have passed since Dennis vanEngelsdorp, who studies bee health at the University of Maryland in College Park, has seen a “credible case” of colony collapse.
Beekeepers still report some cases, but Pettis and vanEngelsdorp aren’t convinced such cases really are colony collapse disorder, a term that now gets used for a slew of things that are bad for bees. To specialists, colony collapse is a specific phenomenon. An apparently healthy colony over the course of days or a few weeks loses much of its workforce, while eggs and larvae, and often the queen herself, remain alive. Also food stores in collapsing colonies don’t get raided by other bees as a failing colony’s treasures usually do.
“I think I know what happened,” says Pettis, now in Salisbury, Md., consulting on pollinator health. His proposed scenario for CCD, like those of some other veterans of the furor, is complex and doesn’t rest on a single exotic killer. But so far, no experiment has nailed the proof. Looking back, Pettis realizes he had heard about what might have been early cases of CCD, described as colonies “just falling apart,” for several years before the phenomenon made headlines. Then in November 2006, Pennsylvania beekeeper David Hackenberg, as usual, sent his colonies to Florida for the winter. They arrived in fine shape. Soon after, however, many buzzing colonies had shrunk to stragglers. Yet there were no dire parasite infestations and no dead bee bodies in sight.
“It was, ‘OK, something weird just happened,’ ” remembers Jay Evans of the USDA’s honeybee lab in Beltsville. “It looked like a ‘flu,’ something that kind of swept through miraculously fast.”
No single menace, however, could be tightly linked to every sick colony, or only to sick colonies. Varroa mites, small hive beetles, Nosema fungi, deformed wing virus, unusual signs of pesticide exposure, for instance —screening techniques at the time just weren’t picking up a clear pattern in any of these bee bedevilments.
“People were following this story like crazy,” Pettis says. The bees’ unexplained plight prompted a national outbreak of amateur entomology. “There were people saying, ‘Why aren’t you doing more with jet contrails?’ There were ‘alien abductions.’ And the rapture — the bees were being called home.”
Entomologists were hounded by the press, not to mention leaned on by politicians and pursued by would-be entrepreneurs. “For me, what made it rewarding,” Pettis says, “was that people were learning about the value of pollination.” A Columbia University researcher who had identified pathogens in mysterious human disease outbreaks took a crack at the problem. Ian Lipkin had never worked with bees, but he and his lab collaborated with entomologists and other bee specialists to search for any genetic signature of a pathogen appearing only in collapsing colonies. The approach of searching through mass samples, with their messy traces of gut microbes and random parasites, is now familiar as metagenomics. At the time, this way of searching for pathogens was groundbreaking, says collaborator Diana Cox-Foster, then at Penn State. The resulting paper, in Science , pointed to several viruses, especially the previously obscure Israeli Acute Paralysis Virus , or IAPV ( SN: 9/8/07, p. 147 ). That emphasis on IAPV, which got a lot of attention at the time, hasn’t held up well. “It’s not 100 percent ruled out,” Evans says. But the explanation’s main problem is shared by other threats proposed as a single cause of CCD. After finding IAPV or another presumed single menace in sick bees in one place, he says, “you could go to other apiaries that were collapsing and not find it, or you could find it in healthier colonies.”
As an apiary inspector for Pennsylvania at the time, vanEngelsdorp monitored for signs of collapse in over 200 hives. “We tried to watch it happen but we couldn’t,” he says. None collapsed. Even finding the sickest bees in collapsing colonies was a challenge. Doomed bees presumably flew off in multiple directions, and birds or other scavengers usually found the bees before scientists could.
A gang of killers Pettis now sees the disaster as a two-step process. Various stressors such as poor nutrition and pesticide exposure weakened bees so much that a virus, maybe IAPV, could quickly kill them in droves. Evans, too, sees various stressors mixing and matching. When pressed for his best guess, he says “all of the above.”
Cox-Foster has managed to re-create part of the process, the vanishing effect that marked the end for stressed bees. When she infected honeybee colonies in a greenhouse with a virus, the sick bees left the hive but were trapped by the greenhouse walls before dispersing too far to be found. (Of course, this experiment doesn’t demonstrate how colonies with no sign of a virus died.)
That tendency for sick bees to leave hives, vanEngelsdorp proposes, could have developed as a hygiene benefit. “Altruistic suicide,” as social-insect biologists call it. Flying away from the colony could minimize a sick bee’s tendency to pass disease to the rest of the family. Today, hive losses remain high even with CCD waning or gone, according to national surveys by the Bee Informed Partnership, a nonprofit bee health collaboration. Beekeepers typically note that they either expect or can tolerate annual losses between 15 and 20 percent of their total number of colonies. Yet from April 2016 until March 2017, losses across the United States ran at about a third of hives. And that was a so-called good year, the second-lowest loss in the seven years with data on annual losses.
Classic CCD may not be much threat these days, but the “four p’s” — poor nutrition, pesticides, pathogens and parasites — are, says Cox-Foster, now at a USDA lab for pollinating insects in Logan, Utah. While honeybees aren’t likely to go extinct, these threats to the beekeeping industry boost pollination costs, which could affect food prices.
Coping with the four p’s may not fire the imaginations of armchair entomologists. But it’s more than enough of a challenge for the bees.
Orlando Brown Jr.'s first order of business as a member of the Bengals? Partner with Cincinnati's mayor in a humorous trailer for the team's Week 17 clash vs. Brown's old squad, the Chiefs.
Brown showed off his acting chops alongside the head of his new hometown.
Check it out here: The full NFL 2023 schedule will be announced Thursday, May 11.
Pureval famously got into a war of words with Kansas City stars Patrick Mahomes and Travis Kelce when the two sides battled in January for a berth in the Super Bowl. It seemed his words helped to light a fire under KC; Mahomes threw for three touchdowns as the Chiefs sent the Bengals home and marched toward another Super Bowl triumph.
MORE: Chiefs among teams facing hardest schedules in 2023
Back then, Brown was protecting Mahomes' blind side. He switched sides during the offseason, signing a four-year, $64 million deal with Cincinnati to keep rushers from putting Joe Burrow on his back. As such, his loyalties have changed, and in a show of goodwill, he offered Pureval some advice.
"Yeah, I think that was better than last time," Brown said after recording Pureval's vanilla reveal of the New Year's Eve game scheduled to be played in Kansas City. The mayor was far less fiery than when he declared Arrowhead Stadium "Burrowhead" ahead of the AFC championship game.
MORE: Best games on 2023 NFL schedule by team
Suffice to say, Mahomes and Kelce got the last laugh then. Not only did they vanquish their AFC rivals, they also were loud about it, hopping on the microphone to dish dirt.
"Know your role and shut your mouth, you jabroni," Kelce said, mimicking The Rock.
MORE: Ranking all 16 AFC QBs as Aaron Rodgers joins loaded conference
Revenge is a dish best served cold. But it's always nice to see someone laugh at themselves after getting caught with their foot in their mouth. Brown's cameo should add intrigue to what is certain to be one of the most-watched games of the 2023 regular season.
With the Eastern Conference Semifinals tied at 2-2 heading back to Boston for a "Pivotal Game 5," the Celtics were completely routed by the 76ers on their home floor.
It was clear from the opening tip that Philadelphia simply wanted it more. Boston had no answer for Philadelphia's star duo, as Joel Embiid and James Harden pick-and-rolled the Celtics' defense to death while Tyrese Maxey delivered dagger after dagger whenever his number was called.
Embiid finished with a game-high 33 points, torturing Boston's drop coverage with a barrage of midrange jumpers. The MVP didn't score a single point at the rim — all 10 of his made field goals came in the soft spots of the Celtics' defensive gameplan.
Harden teed him up perfectly, dishing out 10 assists, while Maxey poured in 30 points with six 3-pointers. Star forward Jayson Tatum finally found his groove after another field-goalless first quarter, catching fire in the second and third quarters to keep Boston in it. He finished with 36 points, 10 rebounds and five assists, and Jaylen Brown chipped in 24 points, but the Celtics couldn't overcome poor shooting nights from Al Horford (0-7 3PT), Marcus Smart (2-7 FG), Malcolm Brogdon (3-9 FG) and Derrick White (2-6 FG).
MORE: Breaking down Celtics' major clutch problems in NBA Playoffs
Now, trailing 3-2 in the series and in need of a road win to keep their season alive, the Celtics find themselves in the exact same position as their NBA Finals run a season ago.
Celtics in familiar territory after dropping Game 5 to 76ers In the 2022 Eastern Conference Semifinals, the Celtics had a complete meltdown in the final minutes of Game 5, losing to the Bucks on the TD Garden parquet to fall into a 3-2 hole.
With their backs against the wall as the series shifted to Milwaukee, Tatum delivered his signature performance of the postseason, erupting for 46 points to force a Game 7 in Boston. The Celtics carried that momentum back onto their home floor, destroying the Bucks by 28 points to advance to the Eastern Conference Finals.
After falling into the exact same position against the 76ers, Boston's leaders all gave their spin on how last year's experience prepared them for Game 6 on Thursday.
"It's easy, we've been there before," Smart began. "It's one game at a time. So you know they're feeling good. We got to go to a hostile environment and we got to go take it. it's not gonna be easy. It's gonna be a dog fight."
Smart elaborated further, specifically comparing this situation to Game 6 in Milwaukee last year.
"The brutality of it. It's a true dogfight, scratching and clawing, biting, blood, everything," he told the media. "And if you're not willing to pretty much get dirty, if you're not willing to bleed… If you’re not willing to break something, willing to tear something, going hard, then you shouldn’t be on that court because that's what it is.
"That's what the playoffs are about. Hopefully, you stay safe but that's the mentality. You gotta go, you gotta be willing to risk it all for these games. And that's the mentality we got to have.” Tatum wasn't as intense as Smart, but he offered some musings as to how Boston can approach Game 6 differently than Game 5.
"I think we were a little tight today, so go out there and relax. There's no secret answer. Go out there and play how we know we're capable of, and we'll see."
Brown, on the other hand, elected to keep last year in the past.
"Last year's over with. This year, we gotta come out and be better than we were tonight or we'll have a different ending. Obviously, we are still in this series and we gotta muster up what we got left to win Game 6," he told the media.
The Celtics will look to keep their championship hopes alive when they travel to Philadelphia to take on the Sixers in a win-or-go-home Game 6 on Thursday, May 11 at 7:30 p.m. ET on ESPN.
Meet Zhong Zhong and Hua Hua, the first primates cloned by reprogramming adult cells.
Two decades after Dolly the Sheep was successfully cloned (SN: 3/1/97, p. 132), Chinese researchers have used the same technique — somatic cell nuclear transfer — to clone two healthy baby macaque monkeys. The results, reported January 24 in Cell, could lead to more efficient cloning and a better way to study genetic diseases in primates.
“This could be it — the next step in cloning,” says Jose Cibelli, a geneticist at Michigan State University in East Lansing not involved with the study. Over 20 species of mammals have been cloned via somatic cell nuclear transfer — including cats, dogs, rats and even a camel (SN: 3/23/02, p. 189). This cloning technology has improved since Dolly’s birth in 1996. Back then, she was the only sheep born from 277 attempts. By 2014, the cloning technique had an 80 percent success rate in pigs. Despite these gradual advances (SN: 3/8/14, p. 7), cloning of nonhuman primates has long eluded researchers.
A rhesus monkey “clone” was created through embryo splitting, a technique that divides a single embryo into genetically identical embryos, in 1999. But this type of cloning has little in common with somatic cell nuclear transfer. In somatic cell nuclear transfer, a nucleus from a mature body cell is transplanted into an egg cell without a nucleus. The egg cell must then reprogram the nucleus’s DNA, basically stripping the body cell of its identity and returning it to an embryonic state. With no set identity, it can become any kind of cell in the body.
Story continues below video Previous failures in reprogramming primate cells probably happened because the egg ran into roadblocks — portions of the body cell’s DNA known as reprogramming-resistant regions, say study coauthor Mu-ming Poo, director of the Institute of Neuroscience at the Chinese Academy of Sciences in Shanghai, and his colleagues. In these regions, DNA is so tightly wrapped around proteins called histones that the egg can’t reprogram those bits. So the researchers added two molecules aimed at loosening the DNA’s packaging.
The team tried this method with two types of body cells: ovarian cells from an adult and connective tissue cells from a fetus. Although 22 out of 42 monkeys became pregnant with embryos cloned from ovarian cells, only two babies were born and neither survived long past birth. Efforts with embryos made with the fetal cells resulted in six pregnancies among 21 surrogate monkey moms and two healthy babies.
“After 20 years of trying from the most talented groups, and nothing working, finally this works,” Cibelli says. “This research is going to help cloning of all species.”
Cloned primates could help researchers better understand diseases in humans. Macaques are close genetic relatives to humans, making the monkeys better analogs than other lab animals. And clones make it easier to weed out the complications of different genetics when studying diseases or testing drugs.
The sisters are just a few weeks old, but they hold a lifetime of promise for researchers. Poo says the scientists will watch for any abnormalities as Zhong Zhong and Hua Hua grow and play.
“The monkeys are in good health and very active,” he says. “There are no signs they are unhealthy.”
More than 100 days after two neutron stars slammed together, merging into one, new telescope images have revealed that the collision’s lingering X-ray light show has gotten brighter. And scientists don’t fully understand why.
NASA’s orbiting X-ray telescope, Chandra, previously picked up the X-rays 15 days after gravitational waves from the cataclysm reached Earth on August 17, 2017 (SN: 11/11/17, p. 6). The merged remnant then spent several months too close to the sun for its X-rays to be seen.
When the remnant reemerged from the sun’s veil on December 4, it was about four times brighter than when it was last spotted, Daryl Haggard of McGill University in Montreal and her colleagues report January 18 in Astrophysical Journal Letters.
The glow may be tapering off. The XMM-Newton space telescope found on December 29 that the X-ray signal may be starting to weaken, according to a paper published January 18 at arXiv.org.
“The plot is about to thicken,” says Haggard. Chandra has collected new data to look for a drop in brightness.
Scientists are debating how to explain the enduring X-rays. Neutron star collisions are expected to emit bright jets of material, creating X-rays that fade quickly. The long-lasting X-rays might be explained by a “cocoon” of debris (SN Online: 12/20/17), among other possibilities.
Airborne particles smaller than 50 nanometers across can intensify storms, particularly over relatively pristine regions such as the Amazon rainforest or the oceans, new research suggests. In a simulation, a plume of these tiny particles increased a storm’s intensity by as much as 50 percent.
Called ultrafine aerosols, the particles are found in everything from auto emissions to wildfire smoke to printer toner. These aerosols were thought to be too small to affect cloud formation. But the new work suggests they can play a role in the water cycle of the Amazon Basin — which, in turn, has a profound effect on the planet’s hydrologic cycle, researchers report in the Jan. 26 Science. “I have studied aerosol interactions with storms for a decade,” says Jiwen Fan, an atmospheric scientist at the Pacific Northwest National Laboratory in Richland, Wash., who led the new study. “This is the first time I’ve seen such a huge impact” from these minute aerosols.
Larger aerosol particles greater than 100 nanometers, such as soot or black carbon, are known to help seed clouds. Water vapor in the atmosphere condenses onto these particles, called cloud condensation nuclei, and forms tiny droplets. But water vapor doesn’t condense easily around the tinier particles. For that to be possible, the air must contain even more water vapor than is usually required to form clouds, reaching a very high state of supersaturation.
Such a state is rare — larger aerosols are usually also present to form water droplets, removing that extra water from the atmosphere, Fan says. But in humid places with relatively low background air pollution levels, such as over the Amazon, supersaturation is common, she says. From 2014 to 2015, Brazilian and U.S. research agencies collaborated on a field experiment to collect data on weather and pollution conditions in the Amazon Basin. As part of the experiment, several observation sites tracked plumes of air pollution traveling from the city of Manaus out across the rainforest. During the warm, wet season, there is little difference day to day in most meteorological conditions over the rainforest, such as temperature, humidity and wind direction, Fan says. So a passing pollution plume represents a distinct, detectable perturbation to the system.
Story continues after image The international team examined vertical wind motion, or updrafts, and aerosol concentration data from one of these stations from March to May 2014. When a large plume of aerosols with an abundance of ultrafine particles passed by an observation station, the researchers observed a corresponding, more powerful vertical wind motion and heavier rain. Such updrafts intensify storms, helping to drive stronger circulation.
Next, the researchers conducted simulations of an actual storm that occurred on March 17, 2014, matching its temperature, wind and water vapor conditions, as well as a low level of background aerosols in the atmosphere. Then, the team introduced several pollution scenarios to interact with the storm, including no plume and a typical plume from the Manaus metropolis. The results suggested that the ultrafine aerosol particles, in particular, were not only acting as cloud condensation nuclei over the Amazon Basin, but also that the water droplets the aerosols created significantly strengthened the gathering storm.
If the conditions are right, the sheer abundance of the ultrafine particles in such a plume would rapidly create a very large number of cloud droplets. The formation of those droplets would also suddenly release a lot of latent heat — released from a substance as it changes from a vapor to a liquid — into the atmosphere. The heat would rise, creating updrafts and quickly strengthening the storm.
Aside from the Amazon, Fan notes that such pristine, humid conditions can also exist over large swaths of the oceans. One recent study in Geophysical Research Letters that she points to found a link between well-traveled shipping lanes, which would contain abundant exhaust including ultrafine aerosols, and an increase in lightning strikes. “This mechanism may have been at play there,” she says.
Atmospheric scientist Joel Thornton of the University of Washington in Seattle, who led the study on the shipping exhaust, says it’s possible that ultrafine particles play a role in that scenario. “What this paper does is raise the stakes in needing to develop a deeper, more accurate understanding of the sources and fates of atmospheric ultrafine particles,” Thornton says.
Meteorologist Johannes Quaas of the University of Leipzig in Germany, who was not involved in either study, agrees. “It’s a very interesting hypothesis.”
But the observations described in the new study don’t definitively demonstrate that ultrafine aerosols alone drive updrafts, Quaas adds. The weather conditions may appear highly consistent from day to day, but such systems are still highly chaotic. Everything from wind to temperature to how the land surface interacts with incoming solar radiation may be variable, he notes. “In reality, it’s not just the aerosols that change.”
The Golden State is at the vanguard in the United States in reducing auto emissions of nitrogen oxide gases, which help produce toxic smog and acid rain. But the NOx pollution problem isn’t limited to auto exhaust. California’s vast agricultural lands — particularly soils heavily treated with nitrogen fertilizers — are now responsible for as much as 51 percent of total NOx emissions across the state, researchers report January 31 in Science Advances. The catchall term “NOx gases” generally refers to two pollution-promoting gases: nitric oxide, or NO, and nitrogen dioxide, or NO2. Those gases react with incoming sunlight to produce ozone in the troposphere, the lowest layer of the atmosphere. At high levels, tropospheric ozone can cause respiratory problems from asthma to emphysema.
Between 2005 and 2008, regulations issued by the California Air Resources Board on transportation exhaust reduced NOx levels in cities such as Los Angeles, San Francisco and Sacramento by 9 percent per year. However, the U.S. Environmental Protection Agency has increasingly recognized nitrogen fertilizer use as a significant source of NOx gases to the atmosphere.
NOx gases are produced in oxygen-poor soils when microbes break apart nitrogen compounds in the fertilizer, a process called denitrification. The release of those gases from fertilized soils increases at high temperatures due to increased microbial activity, says Darrel Jenerette, an ecologist at the University of California, Riverside, who was not involved in the new study.
Jenerette and others have studied local NOx emissions from soils in California, but no statewide assessment existed. So Maya Almaraz, an ecologist at the University of California, Davis, and her colleagues designed a study to examine the question — both from above and below. Using a plane equipped with scientific instruments including a chemiluminescence analyzer to detect NOx gases in the atmosphere, the researchers measured the concentrations of the gases above the San Joaquin Valley, an area of California’s fertile Central Valley, over six days at the end of July and beginning of August. The team also simulated NOx emissions from soils across the state, using the San Joaquin Valley data to ensure that the simulations gave accurate results. Finally, the researchers compared those data with nitrogen fertilizer inputs, as estimated by crop type and U.S. Department of Agriculture fertilizer consumption data.
Story continues below maps Croplands are contributing 20 to 51 percent of the total NOx in California’s air, Almaraz’s team reports. In the simulations, those soil emissions were particularly sensitive to two factors: climate, especially temperature, and rates of nitrogen input. That findings suggests that regions with greater inputs of nitrogen fertilizer will also see greater soil emissions — and that the emission of NOx gases from the soils will also increase as temperatures rise in the region due to climate change.
Although food demands — and the need for fertilizer for crops — are likely to increase in the future, there are numerous possible ways to limit unwanted nitrogen fertilizer spillover, the researchers note. For example, farmers can use more efficient fertilization strategies such as adjusting how much fertilizer is used depending on specific growing stages, or planting what are called cover crops along with the target crops that enrich soils and consume the excess nitrogen.
Almaraz’s team has produced an important finding, Jenerette says. “The combination of bottom-up soil emission measurements and top-down airborne measurements provide strong evidence for their emission assessments,” he says. The finding that NOx emission rates will increase with warming temperatures also highlights the urgency of taking steps to better manage nitrogen fertilizer use in a warming world, he says.
Female polar bears prowling springtime sea ice have extreme weight swings, some losing more than 10 percent of their body mass in just over a week. And the beginnings of bear video blogging help explain why.
An ambitious study of polar bears (Ursus maritimus) in Alaska has found that their overall metabolic rate is 1.6 times greater than thought, says wildlife biologist Anthony Pagano of the U.S. Geological Survey in Anchorage. With bodies that burn energy fast, polar bears need to eat a blubbery adult ringed seal (or 19 newborn seals) every 10 to 12 days just to maintain weight, Pagano and his colleagues report in the Feb. 2 Science. Camera-collar vlogs, a bear’s-eye view of the carnivores’ diet and lifestyle secrets, show just how well individual bears are doing. The study puts the firmest numbers yet on basic needs of polar bears, whose lives are tied to the annual spread and shrinkage of Arctic sea ice, Pagano says. As the climate has warmed, the annual ice minimum has grown skimpier by some 14 percent per decade (SN Online: 9/19/16), raising worries about polar bear populations. These bears hunt the fat-rich seals that feed and breed around ice, and as seal habitat shrinks, so do the bears’ prospects. Pagano and colleagues used helicopters to search for polar bears on ice about off the Alaska coast in the Beaufort Sea. It’s “a lot of grueling hours looking out the window watching tracks and looking at whiteness,” he says. After tracking down female bears without cubs, the researchers fitted the animals with a camera collar. A full day’s doings of bears on the sea ice have been mostly a matter of speculation, Pagano says. Collar videos showed that 90 percent of seal hunts are ambushes, often by a bear lurking near a hole in the ice until a seal bursts up for a gulp of air. Videos also caught early glimpses of the breeding season and what passes for courtship among polar bears. Males, Pagano says, “pretty much harass the female until she’ll submit.”
The researchers also injected each bear with a dose of water with extra neutrons in both the hydrogen and oxygen atoms. Eight to 11 days later, the team caught the same bear to check what was left of the altered atoms. Lower traces of the special form of oxygen indicated that the bear’s body chemistry had been very active, and that the bear had exhaled lots of carbon dioxide. (The unusual form of hydrogen let scientists correct results for oxygen atoms lost in H2O, for instance when the bear urinated.)
Using CO₂ data from nine females, Pagano and his colleagues calculated the field metabolic rates for polar bears going about their springtime lives. The team found that female bears need to eat a bit more than 12,000 kilocalories (or what human dieters call calories) a day just to stay even. That estimate adds some 4,600 kilocalories a day to the old estimate. But merely maintaining weight isn’t enough for a polar lifestyle. To survive lean times, polar bears typically pack on extra weight in spring.
To get a broader view of the bears’ energy needs, similar metabolic measurements for other seasons would be useful, says physiological ecologist John Whiteman of the University of New Mexico in Albuquerque. That could help resolve whether and how much bear metabolism drops when there’s little food, a response that might protect bears during hard times. Using temperature loggers to estimate metabolic rates, he has seen only a gradual decline in metabolic rates in summer as food gets tougher to find. Winter metabolic rates remain a mystery.
Hunting success and bear activity are only part of the picture of polar bear health, says ecotoxicologist Sabrina Tartu, of the Norwegian Polar Institute, which is based in Tromsø. Tartu coauthored a 2017 paper showing that toxic pollutants such as polychlorinated biphenyls, or PCBs, can build up in bear fat. Such “pollutants could, by direct or indirect pathways, disrupt metabolic rates,” she says. So changing the climate is far from the only way humankind could affect polar bear energy and hunting dynamics.
Like sailors and spelunkers, physicists know the power of a sturdy knot.
Some physicists have tied their hopes for a new generation of data storage to minuscule knotlike structures called skyrmions, which can form in magnetic materials. Incredibly tiny and tough to undo, magnetic skyrmions could help feed humankind’s hunger for ever-smaller electronics.
On traditional hard drives, the magnetic regions that store data are about 10 times as large as the smallest skyrmions. Ranging from a nanometer to hundreds of nanometers in diameter, skyrmions “are probably the smallest magnetic systems … that can be imagined or that can be realized in nature,” says physicist Vincent Cros of Unité Mixte de Physique CNRS/Thales in Palaiseau, France. What’s more, skyrmions can easily move through a material, pushed along by an electric current. The magnetic knots’ nimble nature suggests that skyrmions storing data in a computer could be shuttled to a sensor that would read off the information as the skyrmions pass by. In contrast, traditional hard drives read and write data by moving a mechanical arm to the appropriate region on a spinning platter (SN: 10/19/13, p. 28). Those moving parts tend to be fragile, and the task slows down data recall. Scientists hope that skyrmions could one day make for more durable, faster, tinier gadgets.
One thing, however, has held skyrmions back: Until recently, they could be created and controlled only in the frigid cold. When solid-state physicist Christian Pfleiderer and colleagues first reported the detection of magnetic skyrmions, in Science in 2009, the knots were impractical to work with, requiring very low temperatures of about 30 kelvins (–243° Celsius). Those are “conditions where you’d say, ‘This is of no use for anybody,’ ” says Pfleiderer of the Technical University of Munich.
Skyrmions have finally come out of the cold, though they are finicky and difficult to control. Now, scientists are on the cusp of working out the kinks to create thawed-out skyrmions with all the desired characteristics. At the same time, researchers are chasing after new kinds of skyrmions, which may be an even better fit for data storage. The skyrmion field, Pfleiderer says, has “started to develop its own life.” In a magnetic material, such as iron, each atom acts like a tiny bar magnet with its own north and south poles. This magnetization arises from spin, a quantum property of the atom’s electrons. In a ferromagnet, a standard magnet like the one holding up the grocery list on your refrigerator, the atoms’ magnetic poles point in the same direction (SN Online: 5/14/12).
Skyrmions, which dwell within such magnetic habitats, are composed of groups of atoms with their magnetic poles oriented in whorls. Those spirals of magnetization disrupt the otherwise orderly alignment of atoms in the magnet, like a cowlick in freshly combed hair. Within a skyrmion, the direction of the atoms’ poles twists until the magnetization in the center points in the opposite direction of the magnetization outside. That twisting is difficult to undo, like a strong knot (SN Online: 10/31/08). So skyrmions won’t spontaneously disappear — a plus for long-term data storage.
Using knots of various kinds to store information has a long history. Ancient Incas used khipu, a system of knotted cord, to keep records or send messages (SN Online: 5/8/17). In a more modern example, Pfleiderer says, “if you don’t want to forget something then you put a knot in your handkerchief.” Skyrmions could continue that tradition. On the right track Skyrmions are a type of “quasiparticle,” a disturbance within a material that behaves like a single particle, despite being a collective of many individual particles. Although skyrmions are made up of atoms, which remain stationary within the material, skyrmions can move around like a true particle, by sliding from one group of atoms to another. “The magnetism just twists around, and thus the skyrmion travels,” says condensed matter physicist Kirsten von Bergmann of the University of Hamburg.
In fact, skyrmions were first proposed in the context of particles. British physicist Tony Skyrme, who lends his name to the knots, suggested about 60 years ago that particles such as neutrons and protons could be thought of as a kind of knot. In the late 1980s, physicists realized the math that supported Skyrme’s idea could also represent knots in the magnetization of solid materials.
Such skyrmions could be used in futuristic data storage schemes, researchers later proposed. A chain of skyrmions could encode bits within a computer, with the presence of a skyrmion representing 1 and the absence representing 0.
In particular, skyrmions might be ideal for what are known as “racetrack” memories, Cros and colleagues proposed in Nature Nanotechnology in 2013. In racetrack devices, information-holding skyrmions would speed along a magnetic nanoribbon, like cars on the Indianapolis Motor Speedway.
Solid-state physicist Stuart Parkin proposed a first version of the racetrack concept years earlier. In a 2008 paper in Science, Parkin and colleagues demonstrated the beginnings of a racetrack memory based not on skyrmions, but on magnetic features called domain walls, which separate regions with different directions of magnetization in a material. Those domain walls could be pushed along the track using electric currents to a sensor that would read out the data encoded within. To maximize the available space, the racetrack could loop straight up and back down (like a wild Mario Kart ride), allowing for 3-D memory that could pack in more data than a flat chip. “When I first proposed [racetrack memories] many years ago, I think people were very skeptical,” says Parkin, now at the Max Planck Institute of Microstructure Physics in Halle, Germany. Today, the idea — with and without skyrmions — has caught on. Racetrack memories are being tested in laboratories, though the technology is not yet available in computers.
To make such a system work with skyrmions, scientists need to make the knots easier to wrangle at room temperature. For skyrmion-based racetrack memories to compete with current technologies, skyrmions must be small and move quickly and easily through a material. And they should be easy to create and destroy, using something simple like an electric current. Those are lofty demands: A step forward on one requirement sometimes leads to a step backward on the others. But scientists are drawing closer to reining in the magnetic marvels.
Heating up Those first magnetic skyrmions found by Pfleiderer and colleagues appeared spontaneously in crystals with asymmetric structures that induce a twist between neighboring atoms. Only certain materials have that skyrmion-friendly asymmetric structure, limiting the possibilities for studying the quasiparticles or coaxing them to form under warmer conditions.
Soon, physicists developed a way to artificially create an asymmetric structure by depositing material in thin layers. Interactions between atoms in different layers can induce a twist in the atoms’ orientations. “Now, we can suddenly use ordinary magnetic materials, combine them in a clever way with other materials, and make them work at room temperature,” says materials scientist Axel Hoffmann of Argonne National Laboratory in Illinois.
Scientists produced such thin film skyrmions for the first time in a one-atom-thick layer of iron on top of iridium, but temperatures were still very low. Reported in Nature Physics in 2011, those thin film skyrmions required a chilly 11 kelvins (–262° C). That’s because the thin film of iron loses its magnetic properties above a certain temperature, says von Bergmann, who coauthored the study, along with nanoscientist Roland Wiesendanger of the University of Hamburg and colleagues. But thicker films can stay magnetic at higher temperatures. And so, “one important step was to increase the amount of magnetic material,” von Bergmann says.
To go thicker, scientists began stacking sheets of various magnetic and nonmagnetic materials, like a club sandwich with repeating layers of meat, cheese and bread. Stacking multiple layers of iridium, platinum and cobalt, Cros and colleagues created the first room-temperature skyrmions smaller than 100 nanometers, the researchers reported in May 2016 in Nature Nanotechnology.
By adjusting the types of materials, the number of layers and their thicknesses, scientists can fashion designer skyrmions with desirable properties. When condensed matter physicist Christos Panagopoulos of Nanyang Technological University in Singapore and colleagues fiddled with the composition of layers of iridium, iron, cobalt and platinum, a variety of skyrmions swirled into existence. The resulting knots came in different sizes, and some were more stable than others, the researchers reported in Nature Materials in September 2017.
Although scientists now know how to make room-temperature skyrmions, the heat-tolerant swirls, tens to hundreds of nanometers in diameter, tend to be too big to be very useful. “If we want to compete with current state-of-the-art technology, we have to go for skyrmionic objects [that] are much smaller in size than 100 nanometers,” Wiesendanger says. The aim is to bring warmed-up skyrmions down to a few nanometers. As some try to shrink room-temp skyrmions down, others are bringing them up to speed, to make for fast reading and writing of data. In a study reported in Nature Materials in 2016, skyrmions at room temperature reached top speeds of 100 meters per second (about 220 miles per hour). Fittingly, that’s right around the fastest speed NASCAR drivers achieve. The result showed that a skyrmion racetrack might actually work, says study coauthor Mathias Kläui, a condensed matter physicist at Johannes Gutenberg University Mainz in Germany. “Fundamentally, it’s feasible at room temperature.” But to compete against domain walls, which can reach speeds of over 700 m/s, skyrmions still need to hit the gas.
Despite progress, there are a few more challenges to work out. One possible issue: A skyrmion’s swirling pattern makes it behave like a rotating object. “When you have a rotating object moving, it may not want to move in a straight line,” Hoffmann says. “If you’re a bad golf player, you know this.” Skyrmions don’t move in the same direction as an electric current, but at an angle to it. On the racetrack, skyrmions might hit a wall instead of staying in their lanes. Now, researchers are seeking new kinds of skyrmions that stay on track.
A new twist Just as there’s more than one way to tie a knot, there are several different types of skyrmions, formed with various shapes of magnetic twists. The two best known types are Bloch and Néel. Bloch skyrmions are found in the thick, asymmetric crystals in which skyrmions were first detected, and Néel skyrmions tend to show up in thin films.
“The type of skyrmions you get is related to the crystal structure of the materials,” says physical chemist Claudia Felser of the Max Planck Institute for Chemical Physics of Solids in Dresden, Germany. Felser studies Heusler compounds, materials that have unusual properties particularly useful for manipulating magnetism. Felser, Parkin and colleagues detected a new kind of skyrmion, an antiskyrmion, in a thin layer of such a material. They reported the find in August 2017 in Nature.
Antiskyrmions might avoid some of the pitfalls that their relatives face, Parkin says. “Potentially, they can move in straight lines with currents, rather than moving to the side.” Such straight-shooting skyrmions may be better suited for racetrack schemes. And the observed antiskyrmions are stable at a wide range of temperatures, including room temperature. Antiskyrmions also might be able to shrink down smaller than other kinds of skyrmions.
Physicists are now on the hunt for skyrmions within a different realm: antiferromagnetic materials. Unlike in ferromagnetic materials — in which atoms all align their poles — in antiferromagnets, atoms’ poles point in alternating directions. If one atom points up, its neighbor points down. Like antiskyrmions, antiferromagnetic skyrmions wouldn’t zip off at an angle to an electric current, so they should be easier to control. Antiferromagnetic skyrmions might also move faster, Kläui says.
Materials scientists still need to find an antiferromagnetic material with the necessary properties to form skyrmions, Kläui says. “I would expect that this would be realized in the next couple of years.”
Finding the knots’ niche Once skyrmions behave as desired, creating a racetrack memory with them is an obvious next step. “It is a technology that combines the best of multiple worlds,” Kläui says — stability, easily accessible data and low energy requirements. But Kläui and others acknowledge the hurdles ahead for skyrmion racetrack memories. It will be difficult, these researchers say, to beat traditional magnetic hard drives — not to mention the flash memories available in newer computers — on storage density, speed and cost simultaneously.
“The racetrack idea, I’m skeptical about,” Hoffmann says. Instead, skyrmions might be useful in devices meant for performing calculations. Because only a small electric current is required to move skyrmions around, such devices might be used to create energy-efficient computer processors.
Another idea is to use skyrmions for biologically inspired computers, which attempt to mimic the human brain (SN: 9/6/14, p. 10). Brains consume about as much power as a lightbulb, yet can perform calculations that computers still can’t match, thanks to large interconnected networks of nerve cells. Skyrmions could help scientists achieve this kind of computation in the lab, without sapping much power. A single skyrmion could behave like a nerve cell , or neuron, electrical engineer Sai Li of Beihang University in Beijing and colleagues suggest. In the human body, a neuron can add up signals from its neighbors, gradually building up a voltage across its membrane. When that voltage reaches a certain threshold, ions begin shifting across the membrane in waves, generating an electric pulse. Skyrmions could imitate this behavior: An electric current would push a skyrmion along a track, with the distance traveled acting as an analog for the neuron’s increasing voltage. A skyrmion reaching a detector at the end would be equivalent to a firing neuron, the researchers proposed in July 2017 in Nanotechnology . By combining a large number of neuron-imitating skyrmions, the thinking goes, scientists could create a computer that operates something like a brain.
Additional ideas for how to use the magnetic whirls keep cropping up. “It’s still a growing field,” von Bergmann says. “There are several new ideas ahead.”
Whether or not skyrmions end up in future gadgets, the swirls are part of a burgeoning electronics ecosystem. Ever since electricity was discovered, researchers have focused on the motion of electric charges. But physicists are now fashioning a new parallel system called spintronics — of which skyrmions are a part — based on the motion of electron spin, that property that makes atoms magnetic (SN Online: 9/26/17). By studying skyrmions, researchers are expanding their understanding of how spins move through materials.
Like a kindergartner fumbling with shoelaces, studying how to tie spins up in knots is a learning process.
