Thinning ice sheets may drive sharp rise in subglacial waters

Two Georgia Tech researchers, Alex Robel and Shi Joyce Sim, have collaborated on a new model for how water moves under glaciers. The new theory shows that up to twice the amount of subglacial water that was originally predicted might be draining into the ocean -- potentially increasing glacial melt, sea level rise, and biological disturbances.

The paper, published in Science Advances, "Contemporary Ice Sheet Thinning Drives Subglacial Groundwater Exfiltration with Potential Feedbacks on Glacier Flow," is co-authored by Colin Meyer (Dartmouth), Matthew Siegfried (Colorado School of Mines), and Chloe Gustafson (USGS).

While there are pre-existing methods to understand subglacial flow, these techniques involve time-consuming computations. In contrast, Robel and Sim developed a simple equation, which can predict how fast exfiltration, the discharge of groundwater from aquifers under ice sheets, using satellite measurements of Antarctica from the last two decades.

"In mathematical parlance, you would say we have a closed form solution," explains Robel, an assistant professor in the School of Earth and Atmospheric Sciences. "Previously, people would run a hydromechanical model, which would have to be applied at every point under Antarctica, and then run forward over a long time period." Since the researchers' new theory is a mathematically simple equation, rather than a model, "the entirety of our prediction can be done in a fraction of a second on a laptop," Robel says.

Robel adds that while there is precedence for developing these kinds of theories for similar kinds of models, this theory is specific in that it is for the particular boundary conditions and other conditions that exist underneath ice sheets. "This is, to our knowledge, the first mathematically simple theory which describes the exfiltration and infiltration underneath ice sheets."

"It's really nice whenever you can get a very simple model to describe a process -- and then be able to predict what might happen, especially using the rich data that we have today. It's incredible" adds Sim, a research scientist in the School of Earth and Atmospheric Sciences. "Seeing the results was pretty surprising."

One of the main arguments in the paper underscores the potentially large source of subglacial water -- possibly up to double the amount previously thought -- that could be affecting how quickly glacial ice flows and how quickly the ice melts at its base. Robel and Sim hope that the predictions made possible by this theory can be incorporated into ice sheet models that scientists use to predict future ice sheet change and sea level rise.

A dangerous feedback cycle

Aquifers are underground areas of porous rock or sediment rich in groundwater. "If you take weight off aquifers like there are under large parts of Antarctica, water will start flowing out of the sediment," Robel explains, referencing a diagram Sim created. While this process, known as exfiltration, has been studied previously, focus has been on the long time scales of interglacial cycles, which cover tens of thousands of years.

There has been less work on modern ice sheets, especially on how quickly exfiltration might be occurring under the thinning parts of the current-day Antarctic ice sheet. However, using recent satellite data and their new theory, the team has been able to predict what exfiltration might look like under those modern ice sheets.

"There's a wide range of possible predictions," Robel explains. "But within that range of predictions there is the very real possibility that groundwater may be flowing out of the aquifer at a speed that would make it a majority, or close to a majority of the water that is underneath the ice sheet."

If those parameters are correct, that would mean there's twice as much water coming into the subglacial interface than previous estimates assumed.

Ice sheets act like a blanket, sitting over the warm earth and trapping heat on the bottom, away from Antarctica's cold atmosphere -- and this means that the warmest place in the Antarctic ice sheet is at the bottom of a sheet, not on the surface. As an ice sheet thins, the warmer underground water can exfiltrate more readily, and this heat gradient can accelerate the melting that an ice sheet experiences.

"When the atmosphere warms up, it takes tens of thousands of years for that signal to diffuse through an ice sheet of the size of the thickness of the Antarctic ice sheet," Robel explains. "But this process of exfiltration is a response to the already-ongoing thinning of the ice sheet, and it's an immediate response right now."

Broad implications

Beyond sea level rise, this additional exfiltration and melt has other implications. Some of the places of richest marine productivity in the world occur off the coast of Antarctica, and being able to better predict exfiltration and melt could help marine biologists better understand where marine productivity is occurring, and how it might change in the future.

Robel also hopes this work will open the doorway to more collaborations with groundwater hydrologists who may be able to apply their expertise to ice sheet dynamics, while Sim underscores the need for more fieldwork.

"Getting the experimentalists and observationalists interested in trying to help us better constrain some of the properties of these water-laden sediments -- that would be very helpful," Sim says. "That's our largest unknown at this point, and it heavily influences the results."

"It's really interesting how there's a potential to draw heat from deeper in the system," she adds. "There's quite a lot of water that could be drawing more heat out, and I think that there's a heat budget there that could be interesting to look at."

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Did sabertooth tigers purr or roar?

When a sabertooth tiger called out, what noise did it make -- a mighty roar or a throaty purr? A new study from North Carolina State University examined the data behind the arguments for each vocalization and found that the answer was more nuanced than they thought -- and that it could depend on the shape of a few small bones.

Modern cats belong to one of two groups: either the pantherine "big cats," including the roaring lions, tigers and jaguars; or Felinae "little cats," which include purring cats like lynxes, cougars, ocelots and domestic cats.

"Evolutionarily speaking, sabertooths split off the cat family tree before these other modern groups did," says Adam Hartstone-Rose, professor of biological sciences at NC State and corresponding author of the research. "This means that lions are more closely related to housecats than either are to sabertooths.

"That's important because the debate over the kind of vocalization a sabertooth tiger would have made relies upon analyzing the anatomy of a handful of tiny bones located in the throat," Hartstone-Rose says. "And the size, shape and number of those bones differ between modern roaring and purring cats."

Although vocalization is driven by the larynx and soft tissue in the throat, not bones, anatomists noticed that the bones responsible for anchoring those tissues in place -- the hyoid bones -- differed in size and number between roaring and purring cats.

"While humans have only one hyoid bone, purring cats have nine bones linked together in a chain and roaring cats have seven," says Ashley Deutsch, a Ph.D. student at NC State and lead author of the research. "The missing bones are located toward the top of the hyoid structure near where it connects to the skull."

"Because sabertooth tigers only have seven bones in their hyoid structure, the argument has been that of course they roared," Hartstone-Rose says. "But when we looked at the anatomy of modern cats, we realized that there isn't really hard evidence to support this idea, since the bones themselves aren't responsible for the vocalization. That relationship between the number of bones and the sound produced hasn't ever really been proven."

The researchers looked at the hyoid structures of four species of roaring cats: lions, tigers, leopards and jaguars; and five species of purring cats: cougars, cheetahs, caracals, servals and ocelots. They compared these to 105 hyoid bones from the iconic sabertooth tiger Smilodon fatalis.

"You can argue that since the sabertooths only have seven bones they roared, but that's not the whole story," Hartstone-Rose says. "The anatomy is weird. They're missing extra bones that purring cats have, but the shape and size of the hyoid bones are distinct. Some of them are shaped more like those of purring cats, but much bigger."

According to the researchers, if the missing bones (called epihyoid bones) were key to different vocalizations, the bones most closely connected to them should look different between the two groups. However, those bones looked very similar in shape whether they came from purring or roaring cats.

In fact, the researchers saw more shape variation in the bones closer to the vocal apparatus; i.e., the thyrohyoid and basihyoid bones. The uniformity of the upper bones between the two groups suggests that if the hyoid structure plays a role in vocalization, the lower bones are more important than the upper ones. So having these key hyoid bones shaped like those of purring cats could indicate that they purred rather than roared.

"We found that despite what history has told us about the number of bones in the hyoid structure, no one has validated the significance of that difference," Hartstone-Rose says. "If vocalization is about the number of bones in the hyoid structure, then sabertooths roared. If it's about shape, they might have purred. Due to the fact that the sabertooths have things in common with both groups, there could even be a completely different vocalization."

"It is perhaps most likely that the size of the hyoids plays a role in the pitch of vocalization," says Deutsch. "Although Smilodon wasn't quite as big as the largest modern cats, its hyoid bones are substantially larger than those of any of their living relatives, so potentially they had even deeper vocalizations than the largest tigers and lions."

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Bronze Age family systems deciphered: Mainz palaeogeneticists analyse a 3,800-year-old extended family

The diversity of family systems in prehistoric societies has always fascinated scientists. A groundbreaking study by Mainz anthropologists and an international team of archaeologists now provides new insights into the origins and genetic structure of prehistoric family communities.

Researchers Jens Blöcher and Joachim Burger from Johannes Gutenberg University Mainz (JGU) have analysed the genomes of skeletons from an extended family from a Bronze Age necropolis in the Russian steppe. The 3,800-year-old "Nepluyevsky" burial mound was excavated several years ago and is located on the geographical border between Europe and Asia. Using statistical genomics, the family and marriage relationships of this society have now been deciphered. The study was carried out in cooperation with archaeologists from Ekaterinburg and Frankfurt a. M. and was partly financially supported by the German Research Foundation (DFG) and the Russian Science Foundation (RSCF).

The kurgan (burial mound) investigated was the grave of six brothers, their wives, children and grandchildren. The presumably oldest brother had eight children with two wives, one of whom came from the Asian steppe regions in the east. The other brothers showed no signs of polygamy and probably lived monogamously with far fewer children.

Fascinating snapshot of a prehistoric family

"The burial site provides a fascinating snapshot of a prehistoric family," explains Jens Blöcher, lead author of the study. "It is remarkable that the first-born brother apparently had a higher status and thus greater chances of reproduction. The right of the male firstborn seems familiar to us, it is known from the Old Testament, for example, but also from the aristocracy in historical Europe."

The genomic data reveal even more. Most women buried in the kurgan were immigrants. The sisters of the buried brothers, in turn, found new homes elsewhere. Joachim Burger, senior author of the study, explains: "Female marriage mobility is a common pattern that makes sense from an economic and evolutionary perspective. While one sex stays local and ensures the continuity of the family line and property, the other marries in from the outside to prevent inbreeding."

The genomic diversity of the prehistoric women was higher than that of the men

Accordingly, the Mainz population geneticists found that the genomic diversity of the prehistoric women was higher than that of the men. The women who married into the family thus came from a larger area and were not related to each other. In their new homeland, they followed their husbands into the grave. From this the authors conclude that in Nepluyevsky there was both "patrilineality", i.e. the transmission of local traditions through the male line, and "patrilocality", i.e. the place of residence of a family is the place of residence of the men.

"Archaeology shows that 3,800 years ago, the population in the southern Trans-Ural knew cattle breeding and metalworking and subsisted mainly on dairy and meat products," comments Svetlana Sharapova, archaeologist from Ekaterinburg and head of the excavation, adding, "the state of health of the family buried here must have been very poor. The average life expectancy of the women was 28 years, that of the men 36 years."

In the last generation, the use of the kurgan suddenly stopped and almost only infants and small children were found. Sharapova adds, "it is possible that the inhabitants were decimated by disease or that the remaining population went elsewhere in search of a better life."

Multiple partners and many children for the putative firstborn son

"There is a global connection between different family systems and certain forms of life-style and economy," says Blöcher. "Nevertheless, human societies are characterised by a high degree of flexibility." He adds, "in Nepluyevsky, we find evidence of a pattern of inequality typical of pastoralists: multiple partners and many children for the putative firstborn son and no or monogamous relationships for most others."

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Rewriting the past and future of the universe

New research has improved the accuracy of the parameters governing the expansion of the Universe. More accurate parameters will help astronomers determine how the Universe grew to its current state, and how it will evolve in the future.

It is well established that the Universe is expanding. But with no landmarks in space, it is difficult to accurately measure how fast it is expanding. So, astronomers search for reliable landmarks. The same way a candle looks fainter as it gets farther away, even though the candle itself hasn't changed, distant objects in the Universe look fainter. If we know the intrinsic (initial) brightness of an object, we can calculate its distance based on its observed brightness. Objects of known brightness in the Universe that allow us to calculate the distance are called "standard candles."

An international team led by Maria Giovanna Dainotti, Assistant Professor at the National Astronomical Observatory of Japan (NAOJ), and Giada Bargiacchi, PhD student at the Scuola Superiore Meridionale in Naples, with the aid of the supercomputing facilities at NAOJ run by Kazunari Iwasaki, Assistant Professor at NAOJ and member of the Center for Computational Astrophysics, ushered in a new research field by leveraging the use of a variety of new statistical methods to analyze data for various standard candles such as Supernovae, Quasars (powerful black holes consuming matter in the distant Universe), and Gamma Ray Bursts (sudden flashes of powerful radiation). Different standard candles are useful in different distant ranges, so combining multiple standard candles allowed the team to map larger areas of the Universe.

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World's deepest coral calcification rates measured off Hawaiian Islands

In the waters off the Hawaiian Islands, rates of calcification were measured in the deepest coral colonies and reported recently in a study led by a University of Hawai'i (UH) at Manoa oceanographer.

Reef building corals require light for photosynthesis to build the reef structure through calcification, but available light declines quickly with increasing water depth. Below about 200 feet, calcification rates for light-dependent corals had previously not been measured.

In the new study published in Coral Reefs, Samuel Kahng, lead author and graduate affiliate faculty of oceanography in the UH Manoa School of Ocean and Earth Science and Technology (SOEST), reported the first calcification rates from corals (Leptoseris spp.) in Hawai'i at depths of 230-360 feet.

"In addition to being from the deepest coral analyzed, these are by far the lowest calcification rates ever measured for healthy, light-dependent corals in their natural habitat," said Kahng. "These rates are 20-40 times slower than observed in shallow water corals."

Leptoseris spp. dominate the coral community in deep, low-light zones throughout the Indo-Pacific region. This species of coral exhibits a strategic approach to expanding the surface area with which it captures downwelling light -- they form very thin horizontal plate-like skeletons to maximize the area that can be built by their very low calcification rates. Kahng and colleagues published a previous study revealing that the lateral growth rates of these plate-like skeletons are unexpectedly high, given the low light availability.

"The corals' ability to quickly grow horizontal surface area is impressive, especially given the low calcification rates," said Kahng. "What this points to is the incredibly efficient use of calcification."

Because Hawai'i has such clear water, coral reef ecosystems extend offshore to extreme depths, with specialized light-dependent coral communities as deep as 500 feet.

"Hawai'i has much more vertical habitat compared to other coral reef ecosystems around the world," said Kahng. "These deep 'mesophotic' coral ecosystems can cover more habitat area than shallow water coral reefs. However, the general public rarely see them, so they present unique ecosystem management and conservation challenges."

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Cracking the code that relates brain and behavior in a simple animal

To understand the full relationship between brain activity and behavior, scientists have needed a way to map this relationship for all of the neurons across a whole brain -- a so far insurmountable challenge. But after inventing new technologies and methods for the purpose, a team of scientists in The Picower Institute for Learning and Memory at MIT has produced a rigorous accounting of the neurons in the tractably tiny brain of a humble C. elegans worm, mapping out how its brain cells encode almost all of its essential behaviors, such as movement and feeding.

In the journal Cell, the team presents new brain-wide recordings and a mathematical model that accurately predicts the versatile ways that neurons represent the worm's behaviors. Applying that model specifically to each cell, the team produced an atlas of how most cells, and the circuits they take part in, encode the animal's actions. The atlas therefore reveals the underlying "logic" of how the worm's brain produces a sophisticated and flexible repertoire of behaviors, even as its environmental circumstances change.

"This study provides a global map of how the animal's nervous system is organized to control behavior," said senior author Steven Flavell, Associate Professor in MIT's Department of Brain and Cognitive Sciences. "It shows how the many defined nodes that make up the animal's nervous system encode precise behavioral features, and how this depends on factors like the animal's recent experience and current state."

Graduate students Jungsoo Kim and Adam Atanas, who each earned their PhDs this spring for the research, are the study's co-lead authors. They've also made all their data, and the findings of their model and atlas, freely available to fellow researchers at a website called the WormWideWeb.

Microscopes to models

To make the measurements needed to develop their model, Flavell's lab invented a new microscope and software system that automatically tracks almost all behaviors of the worm (movement, feeding, sleeping, egg-laying, etc.) and the activity of every neuron in its head (cells are engineered to flash when calcium ions build up). Reliably distinguishing and tracking separate neurons as the worm wriggles around and bends required writing custom software, utilizing the latest tools from machine learning. It proved to be 99.7 percent accurate in sampling individual neuron's activities with greatly improved signal-to-noise compared to previous systems, the scientists report.

The team used the system to record simultaneous behavior and neural data from more than 60 worms as they roved about their dishes, doing whatever they wanted.

Data analysis revealed three novel observations about neural activity in the worm: Neurons track behavior not only of the present moment but also the recent past; they tune their encoding of behaviors, such as motion, based on a surprising variety of factors; and many neurons simultaneously encode multiple behaviors.

For example, while the behavior of wriggling around one's little laboratory dish might seem like a very simple act, neurons represented factors such as speed, steering, and whether the worm is eating or not. In some cases they represented the animal's motion spanning back in time by about a minute. By encoding recent, rather than just current motion, these neurons could help the worm compute how its past actions influenced its current outcome. Many neurons also combined behavioral information to execute more complex maneuvers. Much like a human driver must remember to steer the car in the opposite way when going in reverse versus going forward, certain neurons in the worm's brain integrated the animal's direction of motion and steering direction.

By carefully analyzing these kinds of patterns of how neural activity correlated with behaviors the scientists developed the C. elegans Probabilistic Neural Encoding Model. The model, encapsulated in a single equation, accounts for how each neuron represents various factors to accurately predict whether and how the neural activity reflects behavior. Nearly 60 percent of the neurons in the worm's head indeed accounted for at least one behavior.

In fitting the model, the research team used a probabilistic modeling approach that allowed them to understand how certain they were about each fit model parameter, an approach pioneered by co-author Vikash Mansinghka, a principal research scientist who leads MIT's Probabilistic Computing Project.

Making an atlas

In creating a model that could quantify and predict how any brain cell would represent behavior, the team initially gathered data from neurons without tracking the cells' specific identities. But a key goal of studying the worms is to understand how each cell and circuit contributes to behavior. So to apply the model's capability to each of the worm's specific neurons, which have all been previously mapped out, the team's next step was to relate neural activity and behavior for each cell on the map. Doing that required labeling each neuron with a unique color so that its activity could be associated with its identity. The team did this in dozens of freely-moving animals, which provided them with information of how almost all of the defined neurons in the worm's head related to the animal's behavior.

The atlas resulting from this work revealed many insights, more fully mapping out the neural circuits that control each of the animal's behaviors. These new findings will enable a more holistic understanding of how these behaviors are controlled, Flavell said.

"It allowed us to complete the circuits," he said. "Our hope is that as our colleagues study aspects of neural circuit function, they can refer to this atlas to obtain a fairly complete view of the key neurons involved."

Built for flexibility

Another major outcome of the team's work was the finding that while most neurons always obeyed the predictions of the model, a smaller set of neurons in the worm's brain -- about 30 percent of those that encode behavior -- was able to flexibly remap their behavior encoding, essentially taking on new jobs. The neurons in this group were reliably similar across animals, and were well connected with one another in the worm's synaptic wiring diagram.

Theoretically these remapping events could occur for any number of reasons, so the team ran further experiments to see if they could cause neurons to remap. As the worms wriggled around their dishes, the researchers applied a quick laser zap that heated the agar around the worm's head. The heat was harmless but enough to annoy the worms for a while, inducing a change in the animal's behavior state that lasted for minutes. From these recordings the team was able to see that many neurons remapped their behavioral encoding right as animals switched behavioral states.

"Behavioral information is richly expressed across the brain in many different forms -- with distinct tunings, timescales, and levels of flexibility -- that map onto the defined neuron classes of the C. elegans connectome," the authors wrote.

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Spear thrower weapon use by prehistoric females equalized the division of labor while hunting

A new study led by Archaeologist Michelle Bebber, Ph.D., an assistant professor in Kent State University's Department of Anthropology, has demonstrated that the atlatl (i.e. spear thrower) functions as an "equalizer," a finding which supports women's potential active role as prehistoric hunters.

Bebber co-authored an article "Atlatl use equalizes female and male projectile weapon velocity" which was published in the journal Nature: Scientific Reports. Her co-authors include Metin I. Eren and Dexter Zirkle (a recent Ph.D. graduate) also in the Department of Anthropology at Kent State, Briggs Buchanan of University of Tulsa, and Robert Walker of the University of Missouri.

The atlatl is a handheld, rod-shaped device that employs leverage to launch a dart, and represents a major human technological innovation used in hunting and warfare since the Stone Age. The first javelins are at least hundreds of thousands of years old; the first atlatls are likely at least tens of thousands of years old.

"One hypothesis for forager atlatl adoption over its presumed predecessor, the thrown javelin, is that a diverse array of people could achieve equal performance results, thereby facilitating inclusive participation of more people in hunting activities," Bebber said.

Bebber's study tested this hypothesis via a systematic assessment of 2,160 weapon launch events by 108 people, all novices, (many of which were Kent State students) who used both javelins and atlatls. The results are consistent with the "atlatl equalizer hypothesis," showing that the atlatl not only increases the velocity of projectile weapons relative to thrown javelins, but that the atlatl equalizes the velocity of female- and male-launched projectiles.

"This result indicates that a javelin to atlatl transition would have promoted a unification, rather than division, of labor," Bebber said. "Our results suggest that female and male interments with atlatl weaponry should be interpreted similarly, and in some archaeological contexts females could have been the atlatl's inventor."

"Many people tend to view women in the past as passive and that only males were hunters, but increasingly that does not seem to be the case," Bebber said. "Indeed, and perhaps most importantly, there seems to be a growing consilience among different fields -- archaeology, ethnography, and now modern experiments -- that women were likely active and successful hunters of game, big and small."

Since 2019, every semester Bebber takes her class outside to use the atlatl. She noticed that females picked it up very easily and could launch darts as far as the males with little effort.

"Often males became frustrated because they were trying too hard and attempting to use their strength to launch the darts," Bebber said. "However, since the atlatl functions as a simple lever, it reduces the advantage of male's generally greater muscle strength."

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Unprecedented look at what influences sea ice motion in the Arctic

A new study led by researchers at Brown offers fresh insights into the forces above and beneath the ocean surface that influence how sea ice moves and disperses in the Arctic Ocean, which is warming at over twice the rate of the global average.

The in-depth analysis reveals how local tidal currents strongly affect the movement of the ice along its journey and provides an unprecedented look at how the makeup of the seafloor is causing some of the most abrupt changes.

Data from the study can be applied to improve complex computer simulations used for forecasting Arctic sea ice conditions, and in the long-term, the results may help clarify how climate change is altering the Arctic and inform future climate predictions.

"The ice is clearly feeling the influence of the bottom of the ocean," said Daniel Watkins, a postdoctoral researcher at Brown and lead author of the new study published in Geophysical Research Letters. "The landscape at the ocean floor, like canyons and continental shelves, affects tides and other ocean currents. And as it drifts, the sea ice passes over many different undersea features. We see sharp changes in the dynamics of the sea ice as soon as it gets to those undersea features."

Using data from largest ever drifting sea-ice buoy array, along with 20 years of satellite images, the researchers examined sea ice motion as it drifted from the Arctic Ocean through a deep-water passage called the Fram Strait and eventually into the Greenland Sea. The analysis revealed the seafloor's impact on some of the most abrupt changes affecting the sea ice, like dramatic gains in speed or motions that force the ice to pack in close together or even break apart.

"What we see with this dataset is a transition from the central Arctic, where the ice is mostly moving as a whole and following wind patterns, to areas where we're seeing much stronger impacts of ocean currents," Watkins said.

The Arctic is the fastest warming part of the globe and it has long been understood that sea ice in the region plays an important role in the planet's climate. For instance, the ice acts like a reflective surface deflecting how much sunlight is absorbed by the Earth. As it disappears, more sunlight is absorbed, leading to a warmer planet. Many scientists also expect that as Arctic ice vanishes, weather across the Northern Hemisphere will be impacted, producing periods of bitter cold, punishing heat waves and disastrous floods.

With the study, the researchers wanted to delve deeper into the changes happening in this critically important part of the Earth. Much of the data for the study was gathered during the largest polar expedition in history -- the Multidisciplinary drifting Observatory for the Study of Arctic Climate.

Comprehensive research reveals sudden increases in ice speed

During the expedition, teams of researchers took turns spending a year drifting with the sea ice aboard a massive German icebreaker in the Arctic Ocean. Watkins was there for two weeks in October 2019 to help install a network of autonomous sensors around the base camp. While there, Watkins coordinated helicopter flights to remote patches of sea ice, worked with analysts to find suitable sites for instruments and buoys and deployed them on the ice.

Throughout the year-long expedition, a total of 214 buoys were deployed, including 51 during Watkins' tenure on the expedition. The study is based on GPS data transmitted from a set of 108 of the buoys that drifted from the central Arctic through the Fram Strait and into the Greenland Sea.

The major focus was on what are known as marginal ice zones in the Greenland Sea and Fram Strait, which is the transition zone between the open, ice-free ocean and the pack ice of the central arctic.

As part of their analysis, the group also analyzed satellite measurements taken from 2003 to 2020 to put the data the buoys gathered over the year adrift into historical context. The satellite data helped confirm sharp changes in ice velocity and ice motion that could only be explained by the seafloor's influence on the sea ice.

For instance, looking at the data from an area northeast of Svalbard, Norway, the researchers noticed the speed of the ice suddenly increased even though the wind hadn't changed. That meant the ice was getting pushed by the ocean currents, so the team delved deeper to find where this happens and how. They found that the sea ice speeds up where the Transpolar Drift Stream, one of the Arctic's Ocean major currents, ends and the fast-moving East Greenland Current, which forms due to a combination of the Earth's rotation and the edge of the continental shelf on the seafloor, begins. The analysis shows how the sea ice responds to different ocean currents and that the sea floor plays a role.

"In the beginning of this journey, there was almost no difference in the drift speed across the whole set of buoys," Watkins said. "Then there's essentially one day where the wind died down and the ice ran into the that boundary current and it just took off. It was like a one-day-to-the-next change in what was pushing the ice."

As next steps, the researchers plan to work with model developers to help implement the data from the study into forecasts of how the ice will move and where it will end up. They also plan to further develop an ice floe tracking tool to track the motion of individual pieces of ice. The tool would help researchers see details of ice motion that are invisible to standard approaches.

"We're hoping to understand the changing ice physics in a warming Arctic and use it to help make our models of those physics better," Watkins said.

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Scientists zero in on timing, causes of ice age mammal extinctions in southern California

The end of the last Ice Age also marked the end for more than three dozen genera of large mammals in North America, from mammoths and mastodons to bison and saber-toothed cats. Details concerning the precise timing and circumstances, however, have remained murky ever since.

A team of scientists that included Texas A&M University archaeologist Dr. Michael Waters recently focused on the well-known Rancho La Brea Tar Pits in southern California in their quest to provide answers to these questions, resulting in the most exact and detailed timeline for the extinctions that happened during the latter part of the Pleistocene period in North America, along with some foreboding insight into the area's present and future. Their work is featured on the cover of the current issue of Science.

Waters, a distinguished professor in the Department of Anthropology and director of the Center for the Study of the First Americans (CSFA), along with roughly a dozen fellow researchers, examined the timing and cause of the extinction of a variety of large mammals, known as megafauna, that got stuck in tar at Rancho La Brea, ensuring the preservation of their bones. The team used the radiocarbon dating method to date 169 bones from seven different animals -- bison, horse, camel and ground sloths as well as the carnivores that ate them, including the saber-toothed cat, dire wolf and American lion. They also compared those findings to regional pollen and charcoal records along with continent-wide data on human and large mammal populations.

Armed with their new data, the researchers subsequently used time-series modeling to produce the most detailed chronobiology to date, showing the relationships between climate and vegetation change, fire activity, human demographics and megafauna extinctions -- groundbreaking results they report in the Aug. 18 edition of the world-leading academic journal.

Waters says the team's findings reveal that Ice Age mammal populations in southern California were steady from 15,000 to around 13,250 years ago. Afterward, there was a sharp decline in the population of the seven animals studied, and they all became extinct between 13,070 to 12,900 years ago.

In an interesting modern-day parallel, this extinction event corresponds with a change in the environment from 13,300 to 12,900 years ago marked by warming and drying that made the land more vulnerable to fires in southern California. Charcoal records show that fires increased around 13,500 years ago and peaked between 13,200 and 12,900 years ago. Studies show that humans arrived in North America's Pacific coast 16,000 to 15,000 years ago and lived alongside the megafauna for 2,000 to 3,000 years before their extinction.

While humans hunted animals during this period, Waters says the impact of hunting on the demise of the megafauna likely was minor because of the low population of humans on the landscape. However, the fires would have been devastating, resulting in the loss of habitat causing the rapid decline and extinction of the megafauna in southern California. The study suggests these fires were ignited by humans, which had increased in number by that time.

"Fire is a way that small numbers of humans can have a large impact over a broad area," said Waters, who also cautions that climate changes observed in present-day California are similar to those of the late Pleistocene.

"This study has implications for the changes we see in southern California today," Waters added. "The temperatures are rising, and the area is drying. We also see a dramatic increase in fires. It appears that history may be repeating itself."

While Waters acknowledges that this is the story of extinction at Rancho La Brea, he says it has the potential to offer insights into when extinctions happened across all of North America.

"Mammoths and mastodons survived in many parts of North America until around 12,700 years ago," he added. "These animals were hunted by the Clovis people between about 13,000 and 12,700 years ago. We are now dating megafauna remains from other locations to give a broader understanding of the Rancho La Brea research in the context of North America."

The museum at La Brea Tar Pits holds the world's largest collection of fossils from the Ice Age and has been central to the study of animal and plant life at the end of the Pleistocene epoch for more than a century. Its naturally occurring asphalt pools entrapped and preserved the bones of thousands of individual animals representing dozens of megafaunal species during the last 60,000 years, enabling scientists to determine when different species disappeared from the ecosystem and why.

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Brain recordings capture musicality of speech -- with help from Pink Floyd

As the chords of Pink Floyd's "Another Brick in the Wall, Part 1," filled the surgery suite, neuroscientists at Albany Medical Center diligently recorded the activity of electrodes placed on the brains of patients undergoing epilepsy surgery.

The goal? To capture the electrical activity of brain regions tuned to attributes of the music -- tone, rhythm, harmony and words -- to see if they could reconstruct what the patient was hearing.

More than a decade later, after detailed analysis of data from 29 such patients by neuroscientists at the University of California, Berkeley, the answer is clearly yes.

The phrase "All in all it was just a brick in the wall" comes through recognizably in the reconstructed song, its rhythms intact, and the words muddy, but decipherable. This is the first time researchers have reconstructed a recognizable song from brain recordings.

The reconstruction shows the feasibility of recording and translating brain waves to capture the musical elements of speech, as well as the syllables. In humans, these musical elements, called prosody -- rhythm, stress, accent and intonation -- carry meaning that the words alone do not convey.

Because these intracranial electroencephalography (iEEG) recordings can be made only from the surface of the brain -- as close as you can get to the auditory centers -- no one will be eavesdropping on the songs in your head anytime soon.

But for people who have trouble communicating, whether because of stroke or paralysis, such recordings from electrodes on the brain surface could help reproduce the musicality of speech that's missing from today's robot-like reconstructions.

"It's a wonderful result," said Robert Knight, a neurologist and UC Berkeley professor of psychology in the Helen Wills Neuroscience Institute who conducted the study with postdoctoral fellow Ludovic Bellier. "One of the things for me about music is it has prosody and emotional content. As this whole field of brain machine interfaces progresses, this gives you a way to add musicality to future brain implants for people who need it, someone who's got ALS or some other disabling neurological or developmental disorder compromising speech output. It gives you an ability to decode not only the linguistic content, but some of the prosodic content of speech, some of the affect. I think that's what we've really begun to crack the code on."

As brain recording techniques improve, it may be possible someday to make such recordings without opening the brain, perhaps using sensitive electrodes attached to the scalp. Currently, scalp EEG can measure brain activity to detect an individual letter from a stream of letters, but the approach takes at least 20 seconds to identify a single letter, making communication effortful and difficult, Knight said.

"Noninvasive techniques are just not accurate enough today. Let's hope, for patients, that in the future we could, from just electrodes placed outside on the skull, read activity from deeper regions of the brain with a good signal quality. But we are far from there," Bellier said.

Bellier, Knight and their colleagues reported the results today in the journal PLOS Biology, noting that they have added "another brick in the wall of our understanding of music processing in the human brain."

Reading your mind? Not yet.

The brain machine interfaces used today to help people communicate when they're unable to speak can decode words, but the sentences produced have a robotic quality akin to how the late Stephen Hawking sounded when he used a speech-generating device.

"Right now, the technology is more like a keyboard for the mind," Bellier said. "You can't read your thoughts from a keyboard. You need to push the buttons. And it makes kind of a robotic voice; for sure there's less of what I call expressive freedom."

Bellier should know. He has played music since childhood -- drums, classical guitar, piano and bass, at one point performing in a heavy metal band. When Knight asked him to work on the musicality of speech, Bellier said, "You bet I was excited when I got the proposal."

In 2012, Knight, postdoctoral fellow Brian Pasley and their colleagues were the first to reconstruct the words a person was hearing from recordings of brain activity alone.

More recently, other researchers have taken Knight's work much further. Eddie Chang, a UC San Francisco neurosurgeon and senior co-author of the 2012 paper, has recorded signals from the motor area of the brain associated with jaw, lip and tongue movements to reconstruct the speech intended by a paralyzed patient, with the words displayed on a computer screen.

That work, reported in 2021, employed artificial intelligence to interpret the brain recordings from a patient trying to vocalize a sentence based on a set of 50 words.

While Chang's technique is proving successful, the new study suggests that recording from the auditory regions of the brain, where all aspects of sound are processed, can capture other aspects of speech that are important in human communication.

"Decoding from the auditory cortices, which are closer to the acoustics of the sounds, as opposed to the motor cortex, which is closer to the movements that are done to generate the acoustics of speech, is super promising," Bellier added. "It will give a little color to what's decoded."

For the new study, Bellier reanalyzed brain recordings obtained in 2012 and 2013 as patients were played an approximately 3-minute segment of the Pink Floyd song, which is from the 1979 album The Wall. He hoped to go beyond previous studies, which had tested whether decoding models could identify different musical pieces and genres, to actually reconstruct music phrases through regression-based decoding models.

Bellier emphasized that the study, which used artificial intelligence to decode brain activity and then encode a reproduction, did not merely create a black box to synthesize speech. He and his colleagues were also able to pinpoint new areas of the brain involved in detecting rhythm, such as a thrumming guitar, and discovered that some portions of the auditory cortex -- in the superior temporal gyrus, located just behind and above the ear -- respond at the onset of a voice or a synthesizer, while other areas respond to sustained vocals.

The researchers also confirmed that the right side of the brain is more attuned to music than the left side.

"Language is more left brain. Music is more distributed, with a bias toward right," Knight said.

"It wasn't clear it would be the same with musical stimuli," Bellier said. "So here we confirm that that's not just a speech-specific thing, but that's it's more fundamental to the auditory system and the way it processes both speech and music."

Knight is embarking on new research to understand the brain circuits that allow some people with aphasia due to stroke or brain damage to communicate by singing when they cannot otherwise find the words to express themselves.

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