EOS

The near-Earth space is filled with charged particles that come from two sources, the solar wind and the Earth’s upper atmosphere. A new article published in Reviews of Geophysics investigates the relative importance of the two sources of charged particles and their effects on plasma dynamics, especially the process of magnetic reconnection, which is responsible of coupling the Sun magnetic field to the Earth’s magnetic field. Here the authors explain what ionospheric ions are, what we understand about them, and what there is still to discover.

What are ionospheric ions and where do they come from?

Up in the higher altitudes of the atmosphere is the ionosphere where there are increasing number of charged particles ionized by the Sun’s radiation. These “ionospheric ions” reflect the make-up of Earth’s atmosphere: ionized hydrogen, oxygen, nitrogen, and helium can all be found in this region of space.

Electromagnetic processes can give some of these ions enough energy to escape the Earth’s gravity potential, and magnetic field lines guide these particles in their journey to outer space, where they are further energized.

If that escaping rate remained constant, it would take around 1,000 billion years to deplete the atmosphere.Most of these particles do not go back to the atmosphere, and the net average escaping rate is roughly 5,250 tons per year.

This sounds like a large number, but it is actually a very small fraction of the Earth’s atmosphere. If that escaping rate remained constant, it would take around 1,000 billion years to deplete the atmosphere.

Although the loss of ionospheric ions is small, what impact do they have on near-Earth space?

The near-Earth space environment is known as the magnetosphere, i.e., the region where the Earth’s magnetic field dominates over the Sun’s magnetic field. The magnetosphere is like a magnetic bubble immersed in the heliosphere, the region where the Sun’s magnetic field dominates within the solar system. When certain conditions are met, the coupling between these two regions becomes very efficient, allowing large amounts of energy and particles from the Sun to enter the magnetosphere, generating geomagnetic storms and a variety of space weather phenomena.

The magnetosphere is constantly filled by particles from the solar wind and the Earth’s ionosphere.The magnetosphere is constantly filled by particles from two sources: the solar wind and the Earth’s ionosphere.

The relative contribution of the two sources is variable and roughly of the same order of magnitude, but their properties are quite different.

Solar wind ions entering the magnetosphere are composed mainly of H+ ions and a few percent of He++ ions. Ionospheric ions are initially cold, i.e., have lower thermal energy than the solar wind, and often contain large amounts of O+ ions in addition to the much lighter H+ ions.

Ionospheric ions circulate in the magnetosphere following magnetic field convection and are the origin of various magnetospheric populations, including for instance plasmaspheric plumes or the warm plasma cloak. These populations eventually reach the interface between the magnetosphere and the solar wind, i.e., the magnetopause, and change its properties. Therefore, depending on the time-history (hours to days) of the solar wind and the magnetosphere, the magnetopause changes its location and properties, potentially affecting the efficiency of the coupling between the two regions.

Artist rendition of the MMS mission orbiting in formation the Earth’s magnetosphere, to study its interaction with the solar wind. Credit: NASA/Goddard Space Flight Center (Public domain)

How have recent observations and models advanced our understanding of the behavior of ionospheric ions?

The NASA Magnetospheric Multiscale (MMS) mission has revolutionized our understanding of magnetic reconnection, the main process at work for coupling the Earth’s magnetosphere to the solar wind. Its spatial and time resolution has enabled us to understand how different charged particle populations are energized by the reconnecting magnetic fields.

Thanks to that mission, combined with high-performance numerical modeling, we now understand much better how ionospheric ions modify the reconnection process at a microphysical level. Ionospheric ions circulating in the magnetosphere are accelerated at reconnection sites and constitute a significant sink of energy for the reconnection process. In addition, depending on the ion mass, initial energy, and where the ions are entrained in a reconnection site, different energization mechanisms, some of them more efficient than others, come into play.

Main regions of the Earth’s magnetosphere. Ionospheric ions (light blue) escape and fill the outer magnetosphere until they exit the Earth space environment. Credit: Toledo-Redondo et al. [2021], Figure 1What are some of the unresolved questions where further research, data gathering, or modeling is needed?

We still understand relatively little about how magnetic reconnection microphysics shapes the magnetosphere system as a whole.We still understand relatively little about how these recent discoveries about magnetic reconnection microphysics shape the magnetosphere system as a whole.

The impact of cold ions is still an open field of research, as cold ions introduce a new length-scale and many plasma processes depend on the coupling between different scales.

The MMS dataset is continuously growing and only a portion has been extensively analyzed. Combining it with other mission datasets, such as for instance Cluster or THEMIS, to perform large statistical studies in the solar wind parameter space, will shed light about how the system reacts to ionospheric ions on a global scale.

Moreover, global 3D magnetospheric numerical models coupled to the ionosphere are very advanced nowadays and will also deepen our understanding of the global picture of ion circulation and energization in the magnetosphere in response to different kinds of solar activity.

There is yet another ionospheric population, which is even less understood: cold electrons. They also outflow from the ionosphere, and these are even harder to characterize than cold ions. Electrons play crucial roles on magnetic reconnection and wave generation in the magnetosphere. So far, because of the immense difficulty of observing these low-energy electrons, the effects of cold electrons remain largely unexplored.

Particle-in-cell simulation of magnetic reconnection, the main coupling process between the solar wind and the Earth’s magnetosphere. The color coding represents plasma number density. The magnetic field lines (solid black lines) break and reconnect at the Electron Diffusion Region, generating reconnection outflow jets. Credit: Toledo-Redondo et al. [2021], Figure 13—Sergio Toledo (Sergio.Toledo@um.es; 0000-0002-4459-8783), University of Murcia, Spain and University of Toulouse, France; Mats André (0000-0003-3725-4920), Swedish Institute of Space Physics, Sweden; Nicolas Aunai (0000-0002-9862-4318), Laboratoire de Physique des Plasmas, France; Charles R. Chappell (0000-0002-1703-6769) Vanderbilt University, USA; Jérémy Dargent (0000-0002-7131-3587), University of Pisa, Italy; Stephen A. Fuselier (0000-0003-4101-7901), Southwest Research Institute and University of Texas at San Antonio, USA; Alex Glocer (0000-0001-9843-9094), NASA Goddard Space Flight Center, USA; Daniel B. Graham (0000-0002-1046-746X), Swedish Institute of Space Physics, Sweden; Stein Haaland (0000-0002-1241-7570), Max-Planck Institute for Solar Systems Research, Germany, University of Bergen and The University Centre in Svalbard, Norway; Michal Hesse (0000-0003-0377-9673), NASA Ames Research Center, USA; Lynn, M. Kistler (0000-0002-8240-5559), University of New Hampshire, USA; Benoit Lavraud (0000-0001-6807-8494), University of Bordeaux, France; Wenya Li (0000-0003-1920-2406), National Space Science Center, China; Thomas E. Moore (0000-0002-3150-1137), NASA Goddard Space Flight Center, USA; Paul Tenfjord (0000-0001-7512-6407), University of Bergen, Norway; and Sarah K. Vines (0000-0002-7515-3285), Johns Hopkins University Applied Physics Laboratory, USA

Autonomous vehicles are jauntily steering through the streets of more and more cities, but the navigation systems in these vehicles remain an evolving technological concept. As companies vie for the rights to urban terrains, they typically use sensors based on optical properties (like light waves and video) or radio waves to map and navigate the environment. These options may not provide the best coverage, especially in bad weather. A team of researchers at the University of Michigan is turning to nature to develop something better.

“Animals have the amazing ability to find their way using sound,” said Bogdan Popa, an assistant professor of mechanical engineering at the university and principal investigator on the project. “We want to develop a sensor that uses sound like animals.”

Previous efforts with sound have failed because sound waves do not travel as far in air as light and radio waves. In fact, current ultrasound sensors have a range of only 1 meter and produce low-resolution maps.

Popa plans to leverage knowledge from nature to advance this technology.

Dolphins, bats, and whales use echolocation, a technique where a sound pulse is emitted into the environment. When the pulse encounters an object, it bounces off and sends reflections back to the animal to decipher. Using this approach, animals can navigate their terrain, find food, and avoid predators—all of which happens very quickly.

Popa believes echolocation offers a tantalizing new opportunity that will allow autonomous vehicles to operate in an uncertain world under inclement weather conditions while retaining their autonomy.

The Sensor of the Future

Sound has a limited range as it travels through the air. To propel sound waves more efficiently, Popa and his team constructed an acoustic lens using passive and active metamaterials.

Similar to an optical lens, the acoustic lens consists of two engineered pieces of patterned plastic that are capable of focusing ultrasonic sound waves (35–45 kilohertz) in any desired direction with only the slightest deformation. This capability means that the lens can be fixed to the vehicle and does not need to be cleaned or realigned. With only minor adjustments, the lens can project a focused wave in almost any direction. Popa likens this new sensor to a laser beam compared to traditional sound applications that are more like an incandescent light bulb.

The team also developed a process to analyze the vast amount of information contained in the returning echoes. To do this, they made the project even more multidisciplinary, turning to computer science to interpret biological sensory signals. The Michigan team developed a convolutional neural network, consisting of individual deep learning algorithms that can differentiate, weigh, and assign importance to self-labeled images.

“Using some experiments with dolphins to understand their behavior, we developed a series of neural networks,” said Popa. “Each neural network is specialized to recognize one object, like a type of fish, a threat, rocks, etc.”

For the first stage of the study, the team plans to develop a series of neural networks. Each network will be trained to interpret the returning echoes for a specific object and determine whether the object is present in the environment and its likeliest position.

“This is a modular approach that is more decentralized,” said Popa. “It is easier to do as opposed to one algorithm that has to provide all the data.”

Once identified, the object will be placed on the map in front of the vehicle. Popa plans to simultaneously map the environment with multiple neural networks to identify many different objects to recreate the world before the vehicle.

Next Steps

Once a network is trained, Popa believes it will be able to provide an answer to questions about location almost instantaneously. The team plans to layer neural network after neural network to provide the power of interpretation for an array of incoming echoes.

“For me, the most exciting part is understanding how the natural world does what it does in such an efficient way. We hope to replicate or equal the performance of these biological systems.”Although the team is still acquiring the data to train the various algorithms in the neural networks, they plan to test the system using virtual simulations. If all goes well, they will release the new acoustic sensor-based navigation system into the real world to see how it helps autonomous vehicles navigate the streets.

“Since this technology is still in the beginning stages, it’s hard to say how it will compare with current sensors,” said Teddy Ort, a Ph.D. candidate in the Computer Science and Artificial Intelligence Laboratory at the Massachusetts Institute of Technology. “If it could provide detailed 3D data at range, it could prove very valuable not only to replace, but perhaps to augment the current sensor suites.” Ort did not contribute to this study.

As the demand for autonomous vehicle technology increases, Popa’s contribution could improve the safety of vehicles navigating every community, large and small.

“For me, the most exciting part is understanding how the natural world does what it does in such an efficient way,” said Popa. “We hope to replicate or equal the performance of these biological systems.”

—Stacy Kish (@StacyWKish), Science Writer

Atmospheric levels of carbon dioxide (CO2) are the highest they’ve been in 800,000 years, and they are rising. Since the beginning of the Industrial Age, CO2 levels have increased nearly 50%. The consequences of increased levels of atmospheric CO2 are numerous and have far-reaching negative impacts, including on agriculture, climate, and human health, among others. To make matters worse, once CO2 is added to the atmosphere, it sticks around for hundreds to thousands of years.

Although increasing CO2 levels affect Earth and much of its life, plants are particularly sensitive to variations in these levels. They rely on the gas for survival, and changing carbon concentrations can affect everything from their growth rate to their nutritional value to their toxicity. Some hardy species are benefiting from current conditions, including an invasive plant known as famine weed (Parthenium hysterophorus). New research published in Nature Plants shows that one type of this toxic weed became more lethal under current CO2 levels, possibly making it more competitive and invasive.

Plants in a Carbon-Rich Atmosphere

“The question was, Why is one [famine weed biotype] spreading all over the place and the other is just kind of hanging out?”Famine weed is a flowering plant native to Central and South America but has become an invasive species in parts of Africa, Australia, and the Indian subcontinent. Interestingly, two biotypes of famine weed were introduced into Australia in the 1950s, but only one flourished in its new home.

“The question was, Why is one spreading all over the place and the other is just kind of hanging out?” asked Julie Wolf, a plant physiologist at the U.S. Department of Agriculture and the corresponding author of the study.

According to the international research team that examined how the increase in atmospheric CO2 over the past 170 years has likely changed the biochemistry of the two types of native famine weed plants, the answer lies in one of the organism’s less appealing traits. Famine weed produces a particularly nasty, carbon-based toxin called parthenin that prevents other plants from growing around it. It can also cause severe skin irritation and asthma in humans. This toxin is thought to contribute to the prolific spread of the plant by killing competing plants and possibly deterring predation.

“The current invasiveness and nastiness of [the invasive biotype] is probably being exacerbated to some degree by current CO2 levels.”At current CO2 levels, the invasive biotype produced more toxin by mass than the noninvasive biotype and more toxins than at preindustrial carbon levels, Wolf said. “The current invasiveness and nastiness of [the invasive biotype] is probably being exacerbated to some degree by current CO2 levels,” she said. With the increasing availability of carbon, it is easier for the invasive biotype to grow larger and produce more carbon-based toxin, possibly leading to its increased competitiveness, Wolf explained. The chemistry of the invasive biotype has probably adapted to use high levels of CO2 to its advantage, the authors say.

Focusing on the Future, Overlooking the Past

Further tests will be needed to see how famine weed fares as CO2 levels continue their upward climb, but the implications of its current adaptation are much broader. Danielle Way, a plant physiologist and associate professor at Western University who was not a part of the study, said this research illustrates that the selective pressure of the current level of atmospheric carbon may have already begun to favor carbon-adapted plants. These adaptations may have gone unnoticed because plant-response research has focused on future CO2 changes over the change we have already created.

“What have we already done to our system that is maybe passing under the radar because we’re really focusing on those even larger changes in CO2 and climate that we expect over the next 50 to 100 years?” Wolf asked. Unfortunately, the plants best equipped to thrive in these new conditions may not be the most beneficial to humans. “A plant that is successful in terms of persisting persists in the best way it can, and that might not match what we want from the plants,” said Wolf.

“A lot of times, people uniformly think that CO2 will be a benefit for plants, but it’s very much more diverse and varied.”That doesn’t mean only increased toxicity. Other research studying plant responses in even higher CO2 environments has found that for many food crops, although the size of the plant increased, its nutritional value decreased. When grown under high levels of CO2, species like wheat and rice end up with less protein and lower concentrations of micronutrients even though the individual grains can be larger in size.

Predicting exactly which plants will flourish in an increasingly CO2-rich world is difficult. “A lot of times, people uniformly think that CO2 will be a benefit for plants, but it’s very much more diverse and varied,” Wolf said. She hopes that this work will act as an alarm bell, pushing the community to investigate how plants have already changed in our current, carbon-rich atmosphere to learn what the future holds. Otherwise, we risk a planet rendered increasingly inhospitable not only by temperature and climate but also by the species we share it with.

—Fionna M. D. Samuels (@Fairy__Hedgehog), Science Writer

This piece was produced with support from the National Association of Science Writers’ David Perlman Virtual Mentoring Program.

On rotating planets, differential heating between the poles and the equator gives rise to instabilities. These are manifested as transient disturbances (e.g., Earth’s mid-latitude storms) that transport enthalpy poleward, thereby lessening the temperature gradients and quenching the instabilities. Scientists have long sought to understand how the resultant temperature gradients depend on the degree of destabilization, along with other properties of the system. Gallet & Ferrari [2021] develop a scaling law that quantifies these dependencies and shows how meridional temperature gradients respond – weakly – to changes in the forcing. Their scaling theory bounds the utility of the longstanding but ultimately incorrect hypothesis that eddies relax temperature gradients to a state of marginal stability. These new results provide a fully non-linear benchmark for numerical methods used to simulate geophysical flows, for guiding thinking as to the behavior of less idealized flows, and for inspiring aspiring theoreticians.  As Vallis [2021] points out in a companion Viewpoint, extracting order from turbulence is often seen as academic hardscrabble, which makes the fertility of Gallet and Ferrari’s accomplishment all the more remarkable.

Citation: Gallet, B. & Ferrari, R. [2021]. A quantitative scaling theory for meridional heat transport in planetary atmospheres and oceans. AGU Advances, 2, e2020AV000362. https://doi.org/10.1029/2020AV000362

—Bjorn Stevens, Editor, AGU Advances

Since 1997, NASA has successfully landed five rovers on Mars. The rovers have beamed back data that indicate life cannot survive on the Martian surface; we do not know whether life persists below the ground, however. For subterranean life to endure on Mars or elsewhere, microbes would have to convert—or fix—elements from their inorganic form to a usable, organic form. This skill, known as lithoautotrophy, comes in handy for Earth-bound bacteria, too—specifically for microbes living in caves. These cave environments often lack nutrients because of the absence of sunshine and organic material enjoyed by life on the surface.

In a new paper, Selensky et al. try to move us closer to understanding whether underground extraterrestrial life could exist by exploring carbon cycling in the lava caves at Lava Beds National Monument in California. As lava flows from a volcanic eruption, a stiff outer shell eventually solidifies as magma continues to flow inside, creating hollow tubes. Because lava tubes form through volcanism, they are presumed to exist elsewhere in the solar system, making them valuable models for planetary speleology.

In California, the authors examined the carbon sources used by cave bacteria living in biofilms (colorful microbial communities on the cave walls), speleothems, and soil. They compared carbon isotope signatures in bacterial fatty acids to carbon sources outside the cave.

The researchers found that the fatty acids produced by Actinobacteria in biofilms bear isotope signatures that could not derive from outside sources. In other words, the bacteria are fixing carbon in situ. In contrast, bacteria from other cave features, such as the speleothems, assimilate organic carbon derived from the surface.

The results suggest that some bacteria in basaltic cave ecosystems are fixing their carbon, which indicates that the microbes survive independently of the surface environment. The findings challenge the paradigm that all cave microbiota subsist on surface inputs. Furthermore, the authors say the conclusions have significant and positive implications for the search for extraterrestrial life. (Journal of Geophysical Research: Biogeosciences, https://doi.org/10.1029/2021JG006430, 2021)

—Aaron Sidder, Science Writer

Like Earth, Jupiter’s magnetic field channels electrically charged particles into its atmosphere, resulting in the formation of brilliant aurorae near its poles. However, the brightness and variety of Jupiter’s auroral emissions exceed those generated on our planet. Of particular interest are patches of emission that originate from even closer to the poles than the main aurorae, a feature that appears far stronger at Jupiter than at Earth or Saturn.

Emission in the polar region can be fleeting, lasting minutes or sometimes only seconds. The polar auroral area can be further divided into three morphologies: “dark” regions of minimal emission, “active” regions of vigorous emission, and, at the highest latitudes, “swirl” regions of turbulent emission.

NASA’s Juno spacecraft has detected downward particle fluxes that can account for the main emission. However, no such flux has been found that could account for the bulk of the polar emissions, especially those from the swirl regions. Masters et al. propose a mechanism that would not yet have been observed by Juno: magnetic reconnection occurring not far above the Jovian cloud tops.

The authors perform one-dimensional magnetohydrodynamic modeling to track the evolution of individual magnetic field lines in the vicinity of Jupiter’s pole. They model the region starting at the top of the planet’s atmosphere and extending 2 Jovian radii from that point. This region lies entirely below any extant spacecraft observations.

Waves moving through the plasma enter the model domain from above, generated by interactions farther out in the planet’s magnetosphere. The propagation of these waves has the effect of deflecting the idealized magnetic field lines from a perfectly vertical position. This is a small effect, on the order of 0.01°, but it may be sufficient to kick-start magnetic reconnection events between neighboring field lines.

During reconnection, adjacent field lines break and reform in a more energetically favorable configuration. This process releases energy stored within the field, which is carried away by the acceleration of nearby charged particles. The authors suggest downward traveling energetic electrons may be the source of the swirl regions in Jupiter’s polar aurorae.

Finally, the authors suggest that this effect isn’t important at Earth or Saturn because of their weaker magnetic fields. Jupiter’s field is more than an order of magnitude stronger, and the reconnection rate increases by roughly the square of that value. Thus, Jupiter has strong polar aurorae, whereas Earth and Saturn do not. (Journal of Geophysical Research: Space Physics, https://doi.org/10.1029/2021JA029544, 2021)

—Morgan Rehnberg, Science Writer

June to September is known as “the monsoon” in the Southwest. For these few months, rains quench Earth’s thirst, bringing cactus blooms, insect hatches, and the sweet smell of creosote bushes. But sometimes the monsoon doesn’t come.

Over the past 20 years, the average temperature has risen across the Southwest, from California to Colorado, and drought is shifting from a transient condition to a way of life. Torrential rains that hit Flagstaff, Ariz., earlier this month were a blip amid a 26-year long-term drought that’s left the Lake Mead reservoir on the Nevada-Arizona border at its lowest level since the 1930s. In efforts to conserve water, Las Vegas recently banned “nonfunctional” grass, and the Hopi Nation ordered livestock reductions.

Earth is entering a period that some scientists have called the “no-analog future” because climate change has left them unable to use past experience to predict future weather trends, like rain and water availability. But this month, a new monitoring project called the Surface Atmosphere Integrated Field Laboratory, or SAIL, started collecting data that scientists hope will fill holes in hydrology models and guide water policy in this uncertain future.

This platform holds instruments, including a rain gauge to measure the amount of liquid precipitation that falls during the SAIL field campaign in Gothic, Colo. Credit: U.S. Department of Energy Atmospheric Radiation Measurement (ARM) user facility. Photo by John Bilberry, Los Alamos National Laboratory, CC BY-NC-SA 2.0

Over the next 2 years, SAIL will use dozens of instruments—including radar, lidar, cameras, balloons, and other equipment—nestled near the Rocky Mountain town of Crested Butte, Colo., to measure clouds, aerosols, wind, temperature, precipitation, and a wide array of other weather features with greater consistency and frequency than any previous project. Putting all this information together, SAIL scientists hope to learn how much water enters upper Colorado River watersheds through rain and snow as well as what happens to that water as it makes its way downstream to communities like Window Rock, Phoenix, and Las Vegas. This information can improve models of how water moves through mountainous regions worldwide—information that will help communities that depend on mountain runoff.

Opening the Black Box

“They’re taking what was this big black box between the atmosphere and the streamflow, and they’re opening that up.”Scientists have known for years that the amount of water flowing down from mountains is declining as temperatures rise, but Indiana University hydrologist Adam Ward likens the reasons for this decline to a black box. A self-described “SAIL enthusiast” who’s not directly involved in the project, Ward said he’s excited about SAIL because “they’re taking what was this big black box between the atmosphere and the streamflow, and they’re opening that up.”

Opening this black box will require what Lawrence Berkeley National Laboratory geologist and SAIL senior scientist Ken Williams calls “extreme collaboration.” Several government labs and nonprofit organizations are working with nearly a dozen academic institutions to make this multimillion dollar per year venture possible.

“Our work has really embraced what we call a community watershed concept,” Williams said, referring to the wide variety of expertise represented in SAIL. “It’s allowed our collective research team to gather data that ranges from the tops of trees, to soils, to underlying bedrock.” All this information is necessary to build complex hydrological models to predict water availability more accurately in the coming decades.

Aerosols in the Colorado Rockies

Jessie Creamean is an atmospheric scientist at Colorado State University who joined SAIL to research how dustlike particles called aerosols contribute to snow in the Colorado Rockies. Snow is particularly important to water availability in mountainous watersheds because snowpack that builds up during the winter melts slowly throughout the summer and provides downstream regions with a continuous supply of water.

Just as plants germinate from seeds, storms stem from aerosols.Just as plants germinate from seeds, storms stem from aerosols. These tiny particles bring water molecules together to turn clouds into precipitation. As a graduate student working in the Sierra Nevada Mountains in California, Creamean found that aerosols from as far away as North Africa could affect snowfall. Now, she’s excited to characterize the role that aerosols play in the Rockies, not only because of their scientific merit but also because of the role snow plays in her life. “I’m an avid backcountry skier,” she said. “And so a healthy snowpack really affects my happiness in the winter, quite frankly.”

Alejandro Flores is a Boise State University hydrologist and SAIL researcher who’s taking research like Creamean’s and turning it into models to predict precipitation. Although processes that occur in the atmosphere are important for snow, the interface between the land and the atmosphere matters just as much, Flores said. He’s excited about SAIL’s radar system, which, when combined with other instruments, will give scientists a minute-by-minute view of how snow accumulates on the ground and how water enters the soil. Although previous projects have collected similar data, none have collected such frequent readings over as long a period of time as SAIL.

“It’s a new way of doing science, to get the modelers and the observational teams coordinating from day one.”“This topic is one that is very important to me, not only professionally but also personally,” said Flores, who grew up in Colorado. “I know and understand the pressures that are being put on water in the West by things like climate change.”

Ward said the consistency of the project’s data will make it useful for his own research on mountain streamflow. Earth scientists are often stuck tying together observations made by many different groups in many different ways, and the lack of internal consistency makes it difficult to draw conclusions. But with SAIL, scientists will have a complete set of consistent data describing the inner workings of a watershed.

“It’s a new way of doing science, to get the modelers and the observational teams coordinating from day one,” Ward said.

—Saima Sidik (@saimamaysidik), Science Writer

Biogeochemical cycles describe the flow of elements in the Earth systems. They are strongly influenced by biological and anthropogenic activity and, in turn, influence other aspects of the Earth systems and human environment. Biogeochemical Cycles: Ecological Drivers and Environmental Impact, a book published by AGU, demonstrates how biogeochemical cycles developed over time and how they manifest in different environments, and presents new methodologies available to quantify and predict flow of the elements. Here the book’s editors give an overview of our understanding of biogeochemical cycles and summarize current challenges and opportunities for research.

What makes biogeochemical cycles such an interesting field of study?

The biogeochemical cycles of the elements influence most of the abiotic factors that govern life.The biogeochemical cycles of the elements influence most of the abiotic factors that govern life. Studying biogeochemical cycles is important for understanding how natural ecosystems resist Anthropocene stresses, and also for anticipating and modeling the sustainable functioning of human-impacted ecosystems such as agricultural soils.

Example of isotope analysis application to elemental cycles. Credit: Nägler et al. [2020], Figure 8.7 What is the interest of the Critical Zone concept in the study of biogeochemical cycles?

The Critical Zone is a porous skin of the Earth’s land surface extending from the top of the vegetation canopy to the lower limits of freely circulating groundwater (NRC, 2001). It is a useful concept in biogeochemistry because it brings together soils, vegetation, rocks, and water. Geologically speaking, it is a very thin layer, but it is the layer that shelters life, including humans.

Link between structure and function in critical zone. Credit: Moravec and Chorover [2020], Figure 6.1What are some of the challenges in determining cause and effect relationships within biogeochemical cycles?

Earth systems are incredibly complex and interconnected meaning that one change can trigger multiple abiotic and biological responses and feedbacks. This, for example, can make studying effects of climate change on organic carbon preservation and cycling in soils challenging.

Structure of microbial decomposition models. Credit: Abs and Ferrière [2020], Figure 5.1, adapted from Georgiou et al. [2017]How do human activities affect, and how are they affected by, biogeochemical cycles?

It is hard to name something in the environment that is not influenced by humans, including  biogeochemical cycles. Climate change is a big concern now and effects of climate change and feedbacks are particularly dramatic in the regions of the permafrost. Herndon et al. [2020] demonstrated influence of warming on the cycles of redox‐sensitive elements in permafrost‐affected ecosystems. One of the biggest concerns is positive feedback on the global warming due to the release of CO2 and methane, but many other elements, such as P, N, S, and Fe, are affected.

Why is there urgency in studying the interconnectedness of different ecosystems?

Earth is one system with numerous subsystems that are continuously interacting. Different ecosystems cannot be fully understood if they are studied in isolation because they are not closed systems.Earth is one system with numerous subsystems such as the biosphere, hydrosphere, atmosphere, and the tectonic system that are continuously interacting. Different ecosystems cannot be fully understood if they are studied in isolation because they are not closed systems. There is a continuous exchange of materials, energy, and living matter among them and they are all connected through the biogeochemical cycles.

To understand complex relationships, processes and feedback loops within landscape evolutions we need to understand how different ecosystems are connected in space and time.

The urgency of studying the interconnectedness of different ecosystems is coming from seizing the current opportunities that are offered by the Critical Zone Exploration Network via providing locations for the studies and collaborations among various experts.

What are some of the major gaps in our understanding of biogeochemical cycles where additional research is needed?

Our book lists nine major gaps, of which the two most important are: quantification of the effects of biological weathering across scales, and application of biogeochemical knowledge to solve societal problems.

Spanning orders of magnitude in spatial and temporal scales of processes is challenging in geosciences and adding the connected biological processes makes understanding even more complex. The establishment of the Critical Zone Observatories and their Exploration Network provides opportunities to investigate processes are various scales at numerous locations.

Application and transformation of knowledge to solve societal problems are becoming more pressing and relevant as humans exert a significant influence on the environment, including biogeochemical cycles.

The interdisciplinarity of biogeochemistry and the existing uncertainties in the research findings make it challenging to directly influence decision making. Increased collaborations between fields of biogeochemistry, humanities, and social sciences can offer results and apply solutions for societal problems, such as sustainable food production, food security, carbon management, and sequestration.

Biogeochemical Cycles: Ecological Drivers and Environmental Impact, 2021, ISBN: 978-1-119-41331-8, list price $199.95 (print), $160.00 (ebook). AGU members receive 35 percent off all books at Wiley.com. Log in to your AGU member profile to access the discount code.

—Katerina Dontsova (dontsova@arizona.edu,  0000-0003-2177-8965),  University of Arizona, USA; Zsuzsanna Balogh‐Brunstad ( 0000-0002-5749-1213), Hartwick College, USA; and Gaël Le Roux ( 0000-0002-1579-0178), National Center for Scientific Research, France

Editor’s Note: It is the policy of AGU Publications to invite the authors or editors of newly published books to write a summary for Eos Editors’ Vox.

Earth’s critical zone, which spans from the treetops to the base of groundwater, is where soils and minerals, water and air, and plants and animals all interact and influence one another [Brantley et al., 2007]. These interactions shape the physical landscapes we live on, sustain the waterways and soils that nourish us, and influence climate and the atmosphere we breathe.

The linkages between the critical zone and human well-being have motivated studies of this layer of Earth’s surface that since the mid-2000s, have often been coordinated through numerous place-based Critical Zone Observatories (CZOs) and, more recently, in theme-based Critical Zone Networks (CZNs). These coordinated CZO/CZN efforts have achieved major advances in understanding critical zone characteristics such as soil development, porosity and permeability evolution, and water distribution by addressing common problems using shared infrastructure and data [Sullivan et al., 2017].

The overwhelming focus on silicate landscapes in critical zone science has left large gaps in our knowledge of Earth’s surface and how it affects humans.However, established CZOs cover only a fraction of Earth’s surface and disproportionately represent silicate mineral–dominated landscapes as opposed to those composed of mainly carbonate minerals. The efforts largely neglect the nearly 15% of Earth’s ice-free surface that is underlain almost entirely by carbonate bedrock [Goldscheider et al., 2020] and the larger fraction of the planet with mixed silicate and carbonate bedrock.

Bedrock mineralogy exerts fundamental controls on many aspects of the critical zone, from water availability to soil composition to the many interactions that occur between life and rocks. The overwhelming focus on silicate landscapes in critical zone science has thus left large gaps in our knowledge of Earth’s surface and how it affects humans. Now scientists are looking to address these gaps by refocusing attention on neglected carbonate landscapes through the lens of critical zone science.

Carbonates Versus Silicates

Carbonate minerals such as calcite and aragonite differ in many ways from silicate minerals such as quartz and clays. Whereas silicate minerals are created predominantly through inorganic, or abiotic, means, carbonate minerals form mostly through biotic processes in organisms such as corals and algae. Especially in marine environments, these minerals can form thick deposits of nearly pure carbonate sediments. Carbonate sediments can lithify into dense rock and dissolve to form caves, shaping the critical zone where carbonate minerals dominate.

A karst weathering surface is exposed on Mount Kanin in the Julian Alps of Slovenia, near the Classical Karst region from which karst gets its name. Credit: Matthew Covington

The physical and chemical breakdown, or weathering, of bedrock minerals, whether silicate or carbonate, influences many characteristics of Earth’s critical zone, such as soil types and distribution; land surface morphology; and water quality, retention, and drainage [National Research Council, 2001]. These characteristics combine to provide services, including reducing pollution and providing plants with nutrients, that sustain ecosystems and societies. Human activities, especially modifications to drainages and application of excess nutrients, also affect how life and rock interact in the critical zone.

Earth’s critical zone should be considered a gradient between two compositional end-members: the silicate critical zone and carbonate critical zone.With their distinctive properties, carbonate and silicate minerals weather differently. Silicate minerals weather incongruently to produce new solid materials (e.g., alteration minerals) as well as dissolved species. In contrast, carbonate minerals weather congruently—they dissolve completely, leaving behind large voids in the landscape (e.g., caves and sinkholes). Thus, critical zone characteristics, for example, the architecture of physical properties, water and gas flow, and distribution of substrates where biology and geology intersect, will vary depending on the primary mineral content of bedrock. In recognition of the importance of mineralogy, we propose that Earth’s critical zone should be considered a gradient between two compositional end-members: the silicate critical zone and carbonate critical zone.

Neglected No More

The Carbonate Critical Zone Research Coordination Network (CCZ-RCN) was established in 2019, in part to further transdisciplinary and collaborative research into the critical zone amid landscapes composed of carbonate or mixed carbonate-silicate mineralogies (see sidebar).

The CCZ-RCN convened its first workshop in fall 2020, and the 70 participants reached consensus on 22 important research questions that define unknowns about the carbonate critical zone [Martin and CCZ-RCN Participants, 2021]. The questions align with five key research areas that focus on specific carbonate critical zone characteristics, differences between the carbonate and silicate critical zone, and the effects of varying carbonate and silicate mineral contents and that provide directions for future critical zone studies. These areas involve research into the following: (1) the boundaries and scales of critical zone environments; (2) the biological, chemical, and physical processes at work; (3) the rates and time frames of these processes; (4) carbon dynamics in the critical zone; and (5) the critical zone and society.

Below, we describe the processes and background relevant to each of the five research areas and highlight important questions to be addressed in future work.

Boundaries and Scales

An important difference between the effects of congruent and incongruent weathering is varying permeability, which can be orders of magnitude greater in the carbonate critical zone than in the silicate critical zone. Unlike in silicate terrains, permeability in carbonate terrains tends to scale with the distance over which it is measured, from wellbore to basin scales. The configuration of permeable and impermeable materials influences the movement of water, solutes, and gases into, through, and out of the critical zone, leading to questions of how permeability distribution alters carbonate critical zone architecture. Large voids also allow human access below the surface, which can enrich critical zone studies.

A key question about the critical zone is how the lower boundary should be defined.A key question about the critical zone is how the lower boundary should be defined [Sullivan et al., 2017]. This question is complicated by differences between the carbonate and silicate critical zone lower boundaries. The lower boundary of the carbonate critical zone varies with the location and morphology of voids, which can form a nonplanar surface hundreds to thousands of meters below the land surface. In contrast, the silicate critical zone lower boundary is typically a few meters to tens of meters below the land surface and roughly follows the surface topography.

Biological, Chemical, and Physical Processes

Feedbacks occur among many biological, chemical, and physical processes within the critical zone and with external drivers that force internal processes. For example, physical weathering and fracturing of rock caused by tectonic forces increase surface area and hydrologic connectivity, thus enhancing mineral dissolution. This feedback can produce heterogeneous porosity and permeability distributions that are hallmarks of the carbonate critical zone, in contrast to the regular decrease in porosity and permeability with depth in the silicate critical zone.

Additional feedbacks exist between flow rates and magnitudes, chemical compositions of water and gases, and biological activity in the critical zone. Recharge locations shift with external forcing, such as when floods raise stream elevations above the groundwater table and recharge aquifers through spring vents [Brown et al., 2014]. These shifts alter the structure and activity of biological communities and disrupt gradients in pH and reduction-oxidation conditions that develop from metabolic processes.

Cave divers explore a sinkhole in the carbonate critical zone of the Yucatán Peninsula, Mexico, where a layer of sulfide-oxidizing microbes marks a reduction-oxidation boundary between fresh water and underlying salt water. Credit: Jason Gulley

These and other changes in reduction-oxidation conditions are linked to production and consumption of the three primary greenhouse gases: carbon dioxide, methane, and nitrous oxide. However, the impacts of these shifts on atmospheric compositions of the gases are unknown and represent an example of more general questions about how linked hydrological and biological processes within the carbonate critical zone change magnitudes and fluxes of reaction products.

Rates and Time

Timescales for many processes are shortened in the carbonate critical zone compared with the silicate critical zone because of faster reaction rates of carbonate compared to silicate minerals and elevated flow rates through high-permeability zones. These characteristics create sensitivities to rare and short-lived extreme events that may alter equilibrium states within the carbonate critical zone. For example, flooding of caves with organic carbon–rich surface waters is known to cause mass mortality of troglobitic species that live entirely in underground habitats.

The rapid responses in the carbonate critical zone may provide a bellwether for wider climate change impacts on critical zone processes.The rapid responses in the carbonate critical zone may provide a bellwether for wider climate change impacts on critical zone processes. Improving our understanding of the rates and timescales of processes, such as the effects of changing flood, drought, and fire frequencies, in the carbonate critical zone will provide vital information for comparison with the slower response of the silicate critical zone, where change may occur at timescales longer than common observational periods. Observations of rapid change in the carbonate critical zone should thus aid in the development of models that predict overall responses of Earth’s critical zone to climate change.

Carbon Dynamics

Carbonate minerals represent the largest global store of carbon, making research into carbon dynamics in the carbonate critical zone particularly important. Through numerous reactions and interactions, the inorganic carbon store is linked to organic carbon production, remineralization, and production of various natural acids. Carbonate mineral dissolution by carbonic acid consumes carbon dioxide, contributing to short-term drawing down of atmospheric carbon dioxide levels. However, carbonate mineral dissolution by other acids has the opposite effect of producing carbon dioxide, coupling the carbonate critical zone and climate [Martin, 2017].

Although equilibrium is often assumed between soil carbon dioxide and groundwater, disequilibrium may result from heterogeneous distributions of recharge, flow paths, and respiration often seen in the carbonate critical zone. Understanding the controls of this disequilibrium, which drives carbon dioxide dissolution or evasion and alters pH, weathering reactions, and carbonate mineral dissolution or precipitation, is critical in linking the carbonate critical zone to the global climate system.

Organic carbon cycling is coupled to ecosystem metabolism (the ways that plants, animals, and microorganisms process carbon) through fixation of inorganic carbon to organic matter and remineralization of organic matter to carbon dioxide and nutrients like nitrogen and phosphorous. This nutrient generation supports ecosystems above and below the land surface, although excess anthropogenic nutrients can alter aquatic ecosystems common in clear-water streams of carbonate terrains. Links between dissolved and gaseous carbon dioxide distributions, organic carbon fixation, and mineral weathering make finding answers to questions about carbon dynamics key to understanding many carbonate critical zone processes.

The Critical Zone and Society

The carbonate critical zone, especially where karst landscapes form, has important ecological, social, cultural, economic, and aesthetic values. From the water resources it harbors for up to 25% of the world’s population to common geohazards (e.g., sinkholes), the carbonate critical zone is key to the sustenance and resilience of local communities that rely on its services.

Distinct characteristics of the carbonate critical zone increase its vulnerability to human activities, from dispersed infiltration of pollutants to soil erosion and rocky desertification.However, distinct carbonate critical zone characteristics also increase its vulnerability to human activities, from dispersed infiltration of pollutants to soil erosion and rocky desertification. Local communities’ reliance on and impacts on carbonate critical zone services suggest that those communities should play an important role in the management and maintenance of carbonate critical zone services. In exchange, local communities should receive equitable distribution of the critical zone services, such as access to reliable water supplies, waste handling, and fertile soils. This equity is especially important where these services are limited.

Inputs from local stakeholder groups, through coproduction of scientific research based on experiential and local knowledge, would not only enrich our understanding but also ensure research outcomes reach and benefit the local communities. This approach requires an equitable exchange of rewards and values stemming from research participation by local stakeholders and mainstream scientists [e.g., Harris et al., 2021].

A More Holistic View of the Critical Zone

Carbonate and silicate minerals are end-members of a spectrum of critical zone bedrock compositions, and fundamental differences in their physical and chemical properties create distinct characteristics in Earth’s critical zone. Studies of these two end-members, as well as of regions of mixed mineralogical compositions, can provide a better understanding of the critical zone in its entirety.

To date, however, critical zone research has predominantly emphasized silicate landscapes, leaving us well short of such a holistic understanding. With increased focus on the neglected carbonate critical zone—particularly on the research directions and questions outlined here—we can fill important knowledge gaps about a part of Earth upon which we humans depend so closely.

Acknowledgments

This material is based upon work supported by the National Science Foundation (NSF) under grant EAR-1905259. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of NSF. We gratefully acknowledge valuable contributions of all participants in the workshop as listed in the workshop report.

Diverse Research Needs Diverse Researchers

A subset of participants at the fall 2020 CCZ-RCN workshop developed an action plan with the goal of increasing diversity in the RCN by implementing inclusive RCN activities and creating a space to nurture equitable and accessible participation by scientists with differing backgrounds and identities. Although the plan is just a small step within a small group, it may provide a template of ways to enhance and improve diversity, equity, and inclusion (DEI) throughout the geosciences. Increased diversity will enrich talents and skills, experiences and interests, worldviews, frameworks, and approaches in the study and understanding of the carbonate critical zone.

The first RCN workshop was planned to enhance collaboration among people with different identities, backgrounds, and experiences. Meeting organizers created small working groups based on demographic information from a preworkshop survey. They promoted equitable and inclusive participation of all attendees using the Technology of Participation facilitation method that fosters authentic participation and meaningful collaboration.

In the working group and plenary sessions, participants reflected on the causes and consequences of limited diversity in the geosciences. They discussed ways to enhance DEI within the RCN. Invited speakers described successful DEI programs in the geosciences, including Sparks for Change and the Louis Stokes Alliances for Minority Participation. A DEI interest group was formed to support the development and implementation of the DEI action.

Future RCN activities will include webinars, training sessions, and networking opportunities at conferences and workshops. Travel grants have been established to support students from underrepresented demographics. The RCN will recruit students from minority-serving colleges and universities, particularly at the graduate level, to attend the next workshop (April 2022), training activities, and field trips. The RCN aims to demonstrate how changing the designs of workshops and other activities can enhance inclusion, diversity, equity, and accessibility and further transdisciplinary, collaborative science to improve understanding of the carbonate critical zone.

As rising temperatures across the Arctic thaw increasingly larger areas of permafrost, more and more organic carbon stored within these frozen soils is being released. Because microbes can convert this liberated material into greenhouse gases that further accelerate the warming, its fate is of grave concern.

Despite general agreement that the warming climate is amplifying the carbon cycle in northern high-latitude watersheds, the amount of permafrost thawing into Arctic rivers is poorly constrained because of the lack of a reliable tracer. To help address this gap, Rogers et al. use a novel approach to search for old permafrost-derived carbon in Russia’s Kolyma River, whose 650,000-square-kilometer watershed is completely underlain by frozen soils.

The authors employed two independent techniques to chemically fingerprint thawed permafrost carbon and track it within the Kolyma watershed during late summer, when the most permafrost thaws. The results from both techniques point to the same conclusion: Relatively little old organic carbon is derived from thawing permafrost in the Kolyma River, which is dominated by modern inputs. Importantly, the team’s analyses indicate this conclusion is true for both microbially unaltered and microbially degraded permafrost carbon.

Using a mixing model to further constrain their results, Rogers and colleagues estimated that a maximum of just 0.8% to 7.7% of the river’s late summer dissolved organic carbon comes from undegraded permafrost. This amount translates to about 6% of the 0.82 teragram of the load the Kolyma delivers to the ocean each year.

This conclusion suggests that despite increased thawing, large northern high-latitude rivers are currently transporting only minor amounts of permafrost-derived dissolved organic carbon to the Arctic Ocean. These findings have important implications for understanding the evolution of dissolved organic carbon during permafrost thaw and river transport. More knowledge of where this thawed carbon resides and how it’s affecting the Arctic’s changing carbon cycle is necessary to improve assessments of the region’s potential to accelerate global warming. (Journal of Geophysical Research: Biogeosciences, https://doi.org/10.1029/2020JG005977, 2021)

—Terri Cook, Science Writer

Volcanic eruptions can have a massive effect on Earth’s climate. Volcanic ash and gases from the 1815 eruption of Mount Tambora, Indonesia, for example, contributed to 1816 being the “year without a summer,” with crop failures and famines across the Northern Hemisphere. In 1991, the eruption of Mount Pinatubo in the Philippines cooled the climate for around 3 years.

Large volcanic eruptions like Tambora and Pinatubo send plumes of ash and gas high into the atmosphere. Sulfate aerosols from these plumes scatter sunlight, reflecting some of it back into space. This scattering warms the stratosphere but cools the troposphere (the lowest layer of Earth’s atmosphere) and Earth’s surface.

“What really matters is whether these [volcanic aerosols] are injected into the stratosphere.”Now new research published in Nature Communications has found that climate change could increase the cooling effect of large eruptions like these, which typically occur a couple of times every century. The study also found, however, that the cooling effects of smaller, more frequent eruptions could be reduced dramatically.

“What really matters is whether these [volcanic aerosols] are injected into the stratosphere—that is, above 16 kilometers in the tropics under current climate conditions and closer to 10 kilometers at high latitudes,” explained Thomas Aubry, a geophysicist at the University of Cambridge in the United Kingdom and lead author of the new study. “If [aerosols] are injected at these altitudes, they can stay in the atmosphere for a couple of years. If they are injected at lower altitudes, they are essentially going to be washed out by precipitation in the troposphere. The climatic effect will only last for a few weeks.”

The power of a volcanic eruption influences the elevation at which gases enter the atmosphere, with stronger eruptions injecting more aerosols into the stratosphere. The buoyancy of the gases also contributes to the elevation at which they settle in the atmosphere. Climate change could affect this buoyancy: As the atmosphere warms, it becomes less dense, increasing the elevation at which aerosols reach neutral buoyancy.

Modeling Mount Pinatubo

Aubry and his colleagues used models of both climate and volcanic plumes to simulate what happens to aerosols emitted by a volcanic eruption in the present climate and how that could change by the end of the century with continued global warming. In their models, all the eruptions occurred at Mount Pinatubo.

They found that for moderate-magnitude eruptions, the height at which sulfate aerosols settle in the atmosphere remained the same in a warmer climate. But the cooling effect of such eruptions was reduced by around 75%. This discrepancy has less to do with volcanic emissions and more to do with the atmosphere: The height of the stratosphere is predicted to increase with climate change. Aerosols from moderate volcanic eruptions will therefore be more likely to remain in the troposphere and be removed by rain, reducing their potency.

Volcanic plumes will rise around 1.5 kilometers higher in the stratosphere in a warmer climate.For large eruptions, models indicated that volcanic plumes will rise around 1.5 kilometers higher in the stratosphere in a warmer climate. This change in elevation will result in the aerosols spreading faster around the world. This increase in aerosol spread is mainly due to a predicted acceleration of the Brewer-Dobson circulation, which moves air in the troposphere upward into the stratosphere and then toward the poles. The change in Brewer-Dobson circulation is associated with climate change.

In addition to enhancing the global cooling effect of the aerosols, the increase in aerosol spread reduces the rate at which the sulfate particles bump into each other and grow. This further increases their cooling effect by allowing them to better reflect sunlight.

“There is a sweet spot in terms of the size of these tiny and shiny particles where they are very efficient at scattering back the sunlight,” explained Anja Schmidt, an atmospheric scientist at the University of Cambridge and coauthor of the paper. “It happens to be that in this global warming scenario that [we] simulated, these particles grow close to the size where they are very efficient in terms of scattering.”

“We find that the radiative forcing (the amount of energy removed from the planet system by the volcanic aerosol) would be 30% larger in the warm climate, compared to the present-day climate,” Aubry said. “Then we suggest that would amplify the surface cooling by 15%.”

Stefan Brönnimann, a climate scientist at the University of Bern who was not involved in the new research, said that the study is interesting because “it makes us think about the processes involved [between volcanic emissions and climate] in a new way.”

Brönnimann noted, however, that the simulations limited their models to eruptions of Mount Pinatubo in the summer. It would be interesting to see whether the conclusions still hold for eruptions at different latitudes and in different seasons, he said.

A Changing Stratosphere

It is difficult to say whether the amplified cooling from large volcanic eruptions or the decrease in cooling from smaller eruptions will have a net effect on climate, Aubry said.

Schmidt said that current increases in the frequency and intensity of forest fires could also alter the climatic effects of volcanic eruptions because they are affecting the composition of the stratosphere. “There is really a lot of aerosol pollution in the stratosphere, probably on a scale that we’ve never seen before.”

—Michael Allen (michael_h_allen@hotmail.com), Science Writer

Ground-based early warning systems for flooding are frequently washed away or damaged by floods, as in the case of the Babai River during the August 2014 event. Therefore, proper use of satellite-based rainfall estimates (SREs) is critical at the time of failure of gauge data. However, relying on these SRE products requires a prior performance evaluation with respect to the gauge data. Also, gauge data frequently suffer from data gaps.

Talchabhadel et al. (2021) demonstrate the applicability of well-performing SRE products to fill gauge data gaps and correct the poor performing SRE products with the information of the gauge data on an hourly scale. Their study took a representative case in the West Rapti River basin, Nepal, for an extreme weather event of August 2014.

Application of SREs is a good head start in data-scarce regions. Furthermore, the methodology and findings are scalable in the areas of flood management in Nepal and beyond.

Citation: Talchabhadel, R., Nakagawa, H., Kawaike, K., Yamanoi, K., Musumari, H., Adhikari, T. R., & Prajapati, R. [2021]. Appraising the potential of using satellite-based rainfall estimates for evaluating extreme precipitation: A case study of August 2014 event across the West Rapti River Basin, Nepal. Earth and Space Science, 8, e2020EA001518. https://doi.org/10.1029/2020EA001518

—Jonathan H. Jiang, Editor, Earth and Space Science

World hunger has been increasing since 2014 after falling for decades, and Africa in particular has suffered from this trend. More than 20% of people in Africa are currently affected by hunger, and more than one third are undernourished, the United Nations estimates.

“To date, there is very little work done to try to quantify the relationship between conflict, climate, and food insecurity. This paper does exactly that.”New research suggests that in Africa at least, this increase in food insecurity is being driven by an uptick in violent conflict. An analysis of food insecurity in sub-Saharan Africa between 2009 and 2019 found that the impacts of drought, although significant, remained relatively steady over the period, whereas violent conflict had an increasingly significant impact. Warfare exacerbates and prolongs the impacts of drought by displacing people, affecting local supply chains, and preventing outside aid, the team reported in a new study published in Nature Food.

“This is an excellent paper that comes at the right time,” said Krishna Krishnamurthy, a climate and food security analyst at the environmental consulting and engineering firm Tetra Tech who was not involved in the new research. “To date, there is very little work done to try to quantify the relationship between conflict, climate, and food insecurity. This paper does exactly that.”

Conflict Worsens the Impacts of Drought over Time

To understand the role of potential drivers of food insecurity in Africa, the researchers used a tool called the Famine Early Warning Systems Network to look at the effects of different hazards in 14 of the continent’s most food-insecure countries. Taken together, these countries represent about 70% of the continent’s population that is affected by hunger. The team also analyzed the hazards’ impacts on different occupations, like farming and livestock herding, to figure out whether some livelihoods made people more vulnerable than others. They also looked at how crises unfolded over time and how long communities suffered from hunger as a result.

Because the study data set is continuous, “we can look at not just isolated events but also how food crises have evolved over time.”Because the study data set is continuous, “we can look at not just isolated events but also how food crises have evolved over time,” said Weston Anderson, an agroclimatologist at the University of Maryland and lead author of the new study. Although previous research focused on specific events, this team analyzed an entire region over time to try to spot wider trends.

The team found that although droughts could have devastating impacts on crops and livestock, they tended to last for a discrete period of time. The destabilizing effects of violent conflicts, on the other hand, could cause food insecurity that lasted years. When drought occurs in a conflict zone, Anderson explained, it’s harder for food aid to reach people, and it’s harder for society to function.

Food Insecurity Is Context Specific

The drivers of food security aren’t the same everywhere, and conflict isn’t driving food security in every country, Anderson said. Violence in three countries—Nigeria, Somalia, and South Sudan—made up the lion’s share of conflict-driven food insecurity found in the study, he said, emphasizing that conflict is very context specific. In Nigeria, for example, violent conflict largely associated with the Boko Haram terrorist group began to trigger food insecurity in 2014 and continues to affect food security today. “That [conflict is] certainly protracted and prolonged in a way drought isn’t,” Anderson said.

But as climate change affects the frequency and intensity of drought events, it’s crucial to better understand how these stressors interact. It’s also crucial to understand that these hazards can have different impacts on different groups. One of the most important takeaways from the study, Anderson said, was that food insecurity crises hit livestock herders harder than any other group.

Food insecurity crises analyzed in the study tended to affect 40% to 50% of herders in a given population, compared to fewer than 15% of individuals in other livelihood groups. Herders also suffered for twice as long after droughts—2 years instead of 1—because they would sell their livestock to pay for food.

Climate Change Could Play a Bigger Role in the Future

The team cautions that the research has its limitations. Although they found that locusts have little impact on food insecurity, for instance, the study didn’t cover the most recent devastating locust outbreak in East Africa. In 2019 and 2020, swarms of locusts numbering in the tens of millions took out more than 10,000 square kilometers of pastureland in East Africa, putting an estimated 5 million people at risk of hunger. The researchers also didn’t include Madagascar in their data set, and the country is currently suffering from a brutal drought linked to climate change that is driving famine in the region.

“Our findings don’t diminish the possibility that climate change could lead to droughts that cause food crises, even though that’s not what we found during this time period,” Anderson said.

Erin Coughlan De Perez, a disaster risk management and climate change adaptation researcher at Tufts University, called the study “a good contribution to our understanding of food security.” While cautioning that it’s not a predictive model, she said that the research still provides helpful context that could improve early-warning systems for hunger crises in Africa. It shows that herders, for instance, “experience drought completely differently,” she said. “I think it’s critical that we highlight differences in people’s experiences.”

“We live in an unprecedented time with violence, climate-induced crises, and other shocks,” Krishnamurthy said. “There is an urgency to start addressing the root causes of these issues.”

—Rachel Fritts (@rachel_fritts), Science Writer

Floating along Venus’s thick atmosphere are shadowy patches, morphing in shape and size, like huge algal blooms. Scientists first photographed these atmospheric features in 1927, and some researchers have suggested that these so-called unknown absorbers could be signs of life.

“Could there be life in the clouds?”“For all we know [they] could be bacteria,” said Sanjay Limaye, a planetary scientist at the University of Wisconsin–Madison. “Could there be life in the clouds?”

Although scientists have their hypotheses, no one has confirmed what is causing the dark areas in the atmosphere. NASA’s new mission to Venus, DAVINCI+ (Deep Atmosphere Venus Investigation of Noble Gases, Chemistry, and Imaging), may bring scientists closer to an answer.

DAVINCI+ Answers the Call

The mission, announced in June, will drop a probe into Venus’s clouds—a beach ball–sized titanium sphere that will dive through the atmosphere and, for more than an hour, collect data while falling about 70 kilometers (43.5 miles). This mission, scheduled to launch between 2028 and 2030, will be the first time a spacecraft will probe the planet’s atmosphere in situ since 1985 when the Soviet Union’s Vega 2 investigated the planet’s atmosphere.

“We’re still trying to get the right measurements to simply ask the right questions.”Set to launch around 2029, DAVINCI+ isn’t designed to detect life. “We’re still trying to get the right measurements to simply ask the right questions,” said Jim Garvin, DAVINCI+’s principal investigator. But among the mission’s other scientific goals, researchers hope it will help solve the mystery of these atmospheric patches and, more broadly, provide a deeper understanding of the atmosphere, which is crucial for determining Venus’s habitability.

An Old, Unanswered Question

Is there life on Venus? Because Venus has many similarities to Earth—such as its size and interior composition—many scientists once thought Venus could be an oasis for life. But when spacecraft began exploring Venus in the 1960s, they uncovered an inhospitable surface environment. The planet showcases a thick carbon dioxide atmosphere with crushing average pressures 92 times those at Earth’s sea level and surface temperatures hot enough to melt lead.

Then in 1967, Harold Morowitz and Carl Sagan proposed that although life can’t survive on the surface, some microbes may possibly survive in the clouds. Early Venus missions found evidence of water vapor in the atmosphere. In the cloud layers roughly 50 kilometers (30 miles) above the planet’s surface, atmospheric pressures are comparable to those at Earth’s sea level, and temperatures range between 100°C (212°F) and 60°C (140°F)—much cooler and more hospitable than the surface. On Earth, for instance, some organisms—such as microbes in hydrothermal vents—can survive in temperatures as high as 121°C (249.8°F).

In addition, the patches are created when something, perhaps microbes or some biological process, absorbs primarily ultraviolet light from the Sun amounting to about half the Sun’s energy that reaches Venus, according to Limaye. In 2018, Limaye and his colleagues found that the patches absorbed light at many of the same wavelengths as some terrestrial bacteria and biological molecules, such as proteins.

Using DAVINCI+ to Get One Step Closer

The unknown absorbers, of course, could be nonbiological. Scientists have already detected some sulfur-bearing compounds in Venus’s atmosphere that absorb at least some of the ultraviolet light, and other similar chemical species might be the main cause of the dark patches, Garvin said. DAVINCI+ will try to help determine the chemistry that’s producing the bulk of these dark patches and perhaps point scientists toward a biological or nonbiological origin.

During two flybys before it releases the probe, the DAVINCI+ carrier spacecraft will try to identify the absorbers using a high-resolution ultraviolet spectrometer. An ultraviolet camera will also take videos of the clouds at high resolution and study how the dark patches move.

If life does exist in the clouds, it likely would have originated the same way it did on Earth: in an ocean. Some computer models of Venus’s ancient climate suggest it did once have a shallow ocean, chemical traces of which might still exist in the planet’s atmosphere. An onboard mass spectrometer will measure hydrogen and its chemical sibling deuterium to reveal how much water the surface has lost throughout Venus’s history. The probe’s laser spectrometer will not only help identify what’s absorbing ultraviolet light but also measure chemicals important for determining habitability, such as sulfuric acid, water, and chemical nutrients.

“It is a great time to be interested in Venus….We’re going to learn spectacular stuff.”Vastly superior to the instruments that last visited Venus decades ago, the spectrometers “are an order of magnitude higher in resolution [and] precision,” Garvin said.

DAVINCI+ won’t be alone at Venus. In the next decade, NASA, the European Space Agency, and the Indian Space Research Organisation will send three more spacecraft—VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy), EnVision, and a to-be-named orbiter—to the planet, beginning a new era of Venus exploration. “It is a great time to be interested in Venus,” Garvin said. “We’re going to learn spectacular stuff.”

—Jaime Cordova (@jaimecor_94), Science Writer

Although referred to as DAVINCI+ in this article, the mission is in the process of changing its name, from DAVINCI+ to DAVINCI.

This piece was produced with support from the National Association of Science Writers’ David Perlman Virtual Mentoring Program.

Rock glaciers are enigmatic landforms composed of mixtures of rock and ice that behave in a manner distinct from debris-free glaciers. The insulating properties of the rock debris contained within a rock glacier make these features resistant to climatic warming, but their evolution is poorly understood.

Cusicanqui et al. [2021] present, in unprecedented detail, an elegant investigation of the geometry and dynamics of Laurichard rock glacier in France. It spans nearly seven decades and provides a benchmark for future studies of these features.

The results demonstrate that while the net annual mass turnover of Laurichard rock glacier is close to zero, it is experiencing significant change—losing mass from the upper and middle sections while the lower section has advanced by over ten meters. The flow of the rock glacier is so slow, at less than one meter per year, that these recent changes may represent a response to cooling during the Little Ice Age about 200 years ago. However, an acceleration in rock glacier flow after the 1990s observed here and elsewhere in the European Alps is likely driven by increasing basal temperatures arising from recent climatic heating.

Citation: Cusicanqui, D., Rabatel, A., Vincent, C., Bodin, X., Thibert, E., & Francou, B. [2021]. Interpretation of volume and flux changes of the Laurichard rock glacier between 1952 and 2019, French Alps. Journal of Geophysical Research: Earth Surface, 126, e2021JF006161. https://doi.org/10.1029/2021JF006161

—Ann Rowan, Associate Editor, JGR: Earth Surface

A little bit of global warming may go a long way. A recent mathematical analysis of the climate of the Cenozoic­—our current geologic era, starting at the demise of the dinosaurs 66 million years ago—says that natural processes may amplify small amounts of warming, turning them into “hyperthermal” events that can last for thousands of years or longer. This finding suggests that human-induced climate change could make our planet susceptible to more extreme warming events in the future.

“We considered all of the fluctuations involved rather than picking out the big ones.”Scientists have studied several major Cenozoic warming events in detail, including the Paleocene-Eocene Thermal Maximum, in which global temperatures jumped by more than 5°C and remained elevated for tens of thousands of years. Such events can help scientists understand how the planet responds to climate changes and predict how it might react to current human-caused changes.

Constantin Arnscheidt and Daniel Rothman of the Lorenz Center at the Massachusetts Institute of Technology, however, decided to examine the climate–carbon cycle history of the entire period. Their study was published in Science Advances.

“We wanted to understand the more general behavior of sub-million-year climate–carbon cycle fluctuations throughout the Cenozoic,” said Arnscheidt, a graduate student and the study’s lead author. “And so, for the first time, we considered all of the fluctuations involved rather than picking out the big ones.”

Warming Bias

The researchers used a database of benthic foraminifera found in deep-ocean sediments. The single-celled organisms are protected by shells of calcium carbonate. Changes in surface temperature, surface inorganic carbon, ocean chemistry, and other climate factors alter the carbon and oxygen isotope ratios in the shells, making it possible for scientists to use them as climate proxies.

Arnscheidt and Rothman used statistical methods to analyze the database. “Climate fluctuations on a wide range of timescales are the result of many complex processes that are impossible to model exactly,” said Arnscheidt. “Stochastic models, which have long been employed to understand shorter-term climate variability, capture essential aspects of this behavior by including random-noise terms.”

Their results showed an imbalance between global warming and global cooling, with a strong bias toward extreme warming events. There were more warming than cooling events, they produced a greater swing in temperatures, and they lasted longer. This trend continued until the start of the Pliocene, about 5.3 million years ago, when the global climate cooled considerably and ice sheets began covering North America.

Unidentified natural processes pump additional carbon and other warming compounds into the atmosphere and increase the temperature, leading to extreme and long-lasting warming events.The bias in the statistics was consistent with the principle of “multiplicative noise,” in which the extent of changes in a system depends on its state. In this case, if temperature variations over periods of thousands or tens of thousands of years increase as the climate gets warmer, “this would result in a warming bias precisely like the one observed,” Arnscheidt said.

A warming bias would suggest that a little bit of global warming may trigger natural biological or geochemical processes (which the researchers say still need to be identified) that operate more efficiently under warmer conditions. These processes pump additional carbon and other warming compounds into the atmosphere and increase the temperature even more, leading to extreme and long-lasting warming events.

The initial impulse for warming events could come from changes in the eccentricity of Earth’s orbit, which varies over a period of about 100,000 years. Scientists have observed that some warming events appear to align with this cycle but haven’t been able to explain how the changing eccentricity could cause large climate swings. The new model suggests that although the initial change in climate caused by the cycle might be small, the multiplier effects could turn it into a major event.

Exploring Climate’s Operational Boundaries

The new study suggests that if current warming continues, the climate could become more susceptible to extreme warming events like those seen in the geologic record.“The paper does push us to explore much more Earth’s response to orbital forcing in the different climate states,” said Thomas Westerhold, director of the Center for Marine Environmental Sciences at the University of Bremen, Germany, who led the development of the foraminifera database but was not involved in this project. “The climate system seems to have operational boundaries that once they are passed, the system moves into a different state….We need to know where those boundaries are that once crossed, we cannot simply make undone.”

The study doesn’t say that multiplicative effects will boost the effects of anthropogenic climate change anytime soon, Arnscheidt noted. It does, however, suggest that if current warming continues, the climate could become more susceptible to extreme warming events like those seen in the geologic record.

“Fundamentally, this study highlights that there is much yet to be learned about the mechanisms governing Earth’s long-term climate evolution and that human climate forcing today may have far-reaching effects on the long-term future,” Arnscheidt said.

—Damond Benningfield (damond5916@att.net), Science Writer

Robbie Mallett often thinks about the first time he stood on old sea ice in the Arctic.

“It’s like a landscape,” he said. “It’s got ridges and landforms almost. It’s just an amazing place. And I think it’s a really sad thing that we’re basically losing a whole place.”

Mallett is a Ph.D. student and sea ice researcher at University College London. His most recent research accentuates how the loss of this sea ice landscape could accelerate because of one unique characteristic: It can float away.

In a new paper published in Communications Earth and Environment, Mallett and other researchers describe how powerful winds during the winter of 2020–2021 blew a vast amount of sea ice south into warmer waters, putting it at risk of melting over the summer.

A Sprawling High-Pressure System

“It almost wasn’t appropriate to call it the ‘Beaufort Sea high’ at all. It was just this huge, sprawling, high-pressure system that dominated the whole Arctic Ocean.”The investigation started after Mallett received an interesting email from his graduate adviser, Julienne Stroeve. She told him that an area of high pressure over the Beaufort Sea near the north coast of Alaska (the Beaufort Sea high) was unusually strong.

“It almost wasn’t appropriate to call it the ‘Beaufort Sea high’ at all,” Mallett said. “It was just this huge, sprawling, high-pressure system that dominated the whole Arctic Ocean.”

The location and strength of the Beaufort Sea high, associated with a sudden warming in the stratosphere on 5 January 2020, generated record-breaking surface winds that persistently swirled around the center of the Arctic Ocean. Mallett wanted to investigate how much older sea ice was at the whim of these winds.

Robbie Mallett experienced the perennial sea ice in the Arctic during a 2019 research expedition. Credit: Robbie Mallett Old Sea Ice Blew into the Beaufort Sea

Scientists are particularly interested in older sea ice, called perennial sea ice, that has lasted through at least one melt season. Perennial ice is thicker, so it has a better chance of surviving the summer months when its cooling properties are most crucial. “It shows up when you need it,” Mallett said.

The researchers used a series of satellite images in the microwave spectrum to track the ice flow over months. They also used data from the European Space Agency’s satellite CryoSat radar altimeter, which bounces pulses off the ice’s surface to determine its age based on how thick it is. “When you combine that with how the ice is moving, you can see what the old ice is getting up to,” said Mallett.

The winds associated with the strong Beaufort Sea high blew ice westward from the north of Greenland toward Alaska. The winds flushed first-year ice out of the Beaufort Sea, replacing it with old ice from the Arctic. By the end of the winter, nearly a quarter of all the perennial sea ice in the Arctic Ocean was in the Beaufort Sea, which is not a hospitable place for sea ice to spend the summer.

“It’s in a dangerous place,” Mallett said. “It’s in a place that is just much warmer, both in the air and water temperature.”

“Thinner Ice Is More Mobile”

Thinner ice in the Arctic is associated with the warming climate, and although the researchers did not attribute the events of last winter to climate change, Kent Moore, a University of Toronto atmospheric physicist, expects that thinner ice is generally a factor in ice transport. “Thinner ice is more mobile,” said Moore, who was not involved in the new research.

Moore is curious whether the ice tracked in 2020 was as mobile in other years when the Beaufort Sea high was extreme or the outcome was the consequence of thinner ice. If thinner ice were to blame, we might expect more ice to be blown around in the future.

“The last ice area may not be as resilient to climate change as we think.”Thinning ice appears to be affecting a stretch of the Arctic Ocean known as the last ice area, which scientists predicted will retain ice even after other regions become ice free in the summer. Last summer, ice blew out of the last ice area, and Mallett and colleagues also found that ice left the region last winter, although Mallett said it’s hard to know exactly how much.

“The last ice area may not be as resilient to climate change as we think,” Moore said.

For now, though, it’s not all bad news in the Beaufort Sea. New satellite data came out in early August, and Mallett said a lot of the ice is still intact.

“It’s surprised me how tough that ice has been in the Beaufort Sea,” Mallett said. “All we can do is wait for the next data release.”

—Andrew Chapman (@andrew7chapman), Science Writer

Basaltic melts erupting on the Earth’s surface preserve information on the temperature and pressure of the Earth’s upper mantle in the region where they form at several tens of kilometers mantle depth. The retrieval of the mantle temperatures – a key parameter to understanding mantle flow – is complicated, however, because the basaltic melts cool en route to surface and modify through crystallization of several mineral phases, such as olivine ± plagioclase ± clinopyroxene in variable extent and proportions. The accuracy of upper mantle temperatures thus critically depends on how well the individual crystallization paths can be reversed.

Krein et al. [2021] present a sophisticated automated algorithm named ‘ReversePetrogen’ (RevPET) that return erupted basaltic melts to ‘primary’ melts (that is melts in equilibrium with mantle prior to crystallization) by back-adding the most plausible mineral assemblage lost. Application of RevPET to existing large data sets of basaltic melts (n=13,589) from the global mid-ocean ridge system retrieves viable primary melts and associated mantle temperatures and pressures, for 72 percent of the data. The robustness of RevPET is validated through general consistency with earlier studies that predict comparable ranges of apparent mantle melting temperatures (Tp* = 1322°C ± 56°C) beneath the mid-ocean ridges.

While this result is remarkable, the true asset of the RevPET algorithm is that it allows to explore the interplay between basalt composition and the inherent mantle heterogeneity, melting mode and temperature. Thus, the RevPET tool is valuable for designing future experimental and observational studies that explore the thermal state of an inaccessible region of Earth.

Citation: Krein, S. B., Molitor, Z. J., & Grove, T. L. [2021]. ReversePetrogen: A Multiphase dry reverse fractional crystallization-mantle melting thermobarometer applied to 13,589 mid-ocean ridge basalt glasses. Journal of Geophysical Research: Solid Earth, 126, e2020JB021292. https://doi.org/10.1029/2020JB021292

—Susanne Straub, Associate Editor, JGR: Solid Earth

It is now widely accepted that both climate and tectonics interact to play a role in shaping mountain landscapes, but beyond that, uncertainty remains as to the degree to which each plays a role, and how. Mandal et al. [2021] report erosion rates based on cosmogenic 10Be measurements made on Siwalik Group sediments shed from Himalaya. As pointed out in an accompanying Viewpoint by Codilean and Sadler [2021], determining accurate erosion rates in this way is difficult, but the dataset raises interesting questions about the roles of tectonics and climate in active settings. Mandal et al. go on to propose that the ~1-Myr cyclicity evident in their dataset results not from a climate driver, but from an emergent phenomenon related to tectonic accretion of material to the Himalaya. This proposal will generate debate and stimulate more study of how specific sets of processes impact the coupled tectonic/climate system.

Citation: Kumar, S., Scherier, D. & Wittmann, H. [2021]. Tectonic accretion controls erosional cyclicity in the Himalaya. AGU Advances, 2, e2021AV000487. https://doi.org/10.1029/2021AV000487

—Peter Zeitler, Editor, AGU Advances

Global methane emissions are increasing, but we are not sure why. Positive feedbacks of CH4 emissions from wetlands to climate change may be contributing to the increase. Ma et al. [2021] combine biogeochemical models and satellite-derived CH4 concentration observations to examine climatic feedbacks to emissions from wetlands, from the equator to the poles. Tropical wetlands emit the 72% of global wetland emissions of CH4, and those emissions are shown to be most sensitive to changes in precipitation. In contrast, higher latitude wetlands emit much less overall, but their emissions are highly sensitive to temperature. In a companion Viewpoint, Thompson [2021] describes the novel way that Ma et al. [2021]  compare bottom-up estimates based on land surface models to those derived from a top-down atmospheric inversion model. She also notes that positive feedbacks of wetland CH4 emissions to climate change will require still stronger mitigation efforts in other sectors to avoid exceeding 1.5°C or even 2.0°C global warming.

Citation: Ma, S., Worden, J., Zhang, Y., Poulter, B., Cusworth, D. et al. [2021]. Satellite constraints on the latitudinal distribution and temperature sensitivity of wetland methane emissions. AGU Advances, 2, e2021AV000408.  https://doi.org/10.1029/2021AV000408

—Eric Davidson, Editor, AGU Advances