FILLING IN THE MARGINS This spring, GeoPRISMS leaves behind a legacy of research by shoreline-crossing scientists and the National Science Foundation.

Supercharged Lightning

An Asteroid Double Disaster

Sooty Stalagmite Records

FROM THE EDITOR

Editor in Chief Heather Goss, [email protected] AGU Staff Crossing the Shoreline Vice President, Communications, Amy Storey Marketing,and Media Relations Editorial hey were going to meet in San Francisco last December Manager, News and Features Editor Caryl-Sue Micalizio to celebrate the end of an era. Then the community of Science Editor Timothy Oleson scientists behind GeoPRISMS­ had to make the same News and Features Writer Kimberly M. S. Cartier T News and Features Writer Jenessa Duncombe adjustments all of us did and had to move those toasts into this spring. But they nevertheless gathered for virtual sessions Production & Design at AGU’s Fall Meeting 2020 to take a look at the legacy they Manager, Production and Operations Faith A. Ishii created in a set of oral sessions titled “Advances in Under- Production and Analytics Specialist Anaise Aristide Assistant Director, Design & Branding Beth Bagley standing Continental Margin Evolution: Two Decades of Senior Graphic Designer Valerie Friedman ­GeoPRISMS and MARGINS Science.” Senior Graphic Designer J. Henry Pereira That community actually sprung up not 2 but more than Graphic Design Intern Claire DeSmit 3 decades ago, when a group met in 1988 to discuss how Earth Marketing scientists and ocean scientists could better work together. In Communications Specialist Maria Muekalia response, the Earth Sciences and Ocean Sciences divisions of Assistant Director, Marketing & Advertising Liz Zipse the National Science Foundation (NSF) teamed up to fund MARGINS, launched in 2000. Its Advertising success led to a ­10-year successor program called Geodynamic Processes at Rifting and Sub- Display Advertising Steve West ducting Margins, or ­GeoPRISMS. This issue of Eos looks at these impressive initiatives as they [email protected] come to a close this year. Recruitment Advertising [email protected] Anaïs Férot, the GeoPRISMS science coordinator at NSF, writes more about this history on Science Advisers page 20. Over these few decades, the programs have developed not only a successful model Geomagnetism, Paleomagnetism, Julie Bowles for producing good science but one that produces good scientists. The community made a ded- and Electromagnetism icated effort to support ­early-career​­ and diverse researchers and regularly participated in edu- Space Physics and Aeronomy Christina M. S. Cohen Cryosphere Ellyn Enderlin cation and outreach through initiatives like the GeoPRISMS­ Distinguished Lectureship Pro- Study of the Earth’s Deep Interior Edward J. Garnero gram, sending speakers to colleges, museums, and other public venues. Geodesy Brian C. Gunter Férot connected us with the scientists featured in this issue who have provided just a small History of Geophysics Kristine C. Harper glimpse into the volume of research ­GeoPRISMS has produced. On page 22, Noel Bartlow and Planetary Sciences Sarah M. Hörst Natural Hazards Michelle Hummel colleagues take us on a world tour of the “Slipping and Locking in Earth’s Earthquake Facto- Volcanology, Geochemistry, and Petrology Emily R. Johnson ries,” from the Nankai Trough off southwestern Japan to the Middle America Trench beneath Societal Impacts and Policy Sciences Christine Kirchhoff Costa Rica and several others. Bartlow et al. describe what the differences and commonalities Seismology Keith D. Koper Tectonophysics Jian Lin between these locations tell us about earthquake processes and how new studies can continue Near-Surface Geophysics Juan Lorenzo this work started by ­MARGINS and ­GeoPRISMS. Earth and Space Science Informatics Kirk Martinez We switch from movement of the ground to movement of water and gases with James D. Paleoceanography and Paleoclimatology Figen Mekik Mineral and Rock Physics Sébastien Merkel Muirhead and colleagues in “Earth’s Volatile Balancing Act,” page 28. Understanding how Ocean Sciences Jerry L. Miller carbon dioxide, sulfur dioxide, and water circulate between the ocean, atmosphere, and min- Global Environmental Change Hansi Singh erals in Earth gives us crucial information about the planet’s tectonic and volcanic processes Education Eric M. Riggs Hydrology Kerstin Stahl and our climate. Finally, on page 34, Lindsay L. Worthington and colleagues describe the long— Tectonophysics Carol A. Stein much longer than previously thought—process it took for Africa and North America to split. Atmospheric Sciences Mika Tosca Thanks also go to Michelle Coombs, with the Volcano Science Center at the U.S. Geological Nonlinear Geophysics Adrian Tuck Biogeosciences Merritt Turetsky Survey, who let us use her photo of lava flow on Kanaga Island in Alaska for our cover. Her Hydrology Adam S. Ward image won first place in 2017 in an annual photo contest held by the ­GeoPRISMS program. Diversity and Inclusion Lisa D. White Do you have an amazing photo from the field or lab? Send it to us at ­bit.ly/​­Eos​-postcard,­ Earth and Planetary Surface Processes Andrew C. Wilcox and we may feature it in Postcards from the Field. Usually, you’ll find these beautiful contribu- Atmospheric and Space Electricity Yoav Yair GeoHealth Ben Zaitchik tions on our final page, but in this issue we are very excited to bring you another crossword puzzle—fitting in with our theme of geoprocesses—by Russ Colson, Minnesota State Univer- ©2021. AGU. All Rights Reserved. Material in this issue may be photocopied by sity Moorhead. Enjoy! individual scientists for research or classroom use. Permission is also granted to use short quotes, figures, and tables for publication in scientific books and journals. For permission for any other uses, contact the AGU Publications Office. Eos (ISSN 0096-3941) is published monthly by AGU, 2000 Florida Ave., NW, Washington, DC 20009, USA. Periodical Class postage paid at Washington, D.C., and at additional mailing offices. POSTMASTER: Send address changes to Member Service Center, 2000 Florida Ave., NW, Washington, DC 20009, USA Member Service Center: 8:00 a.m.–6:00 p.m. Eastern time; Tel: +1-202-462-6900; Fax: +1-202-328-0566; Tel. orders in U.S.: 1-800-966-2481; [email protected]. Submit your article proposal or suggest a news story to Eos at bit.ly/Eos-proposal. Heather Goss, Editor in Chief Views expressed in this publication do not necessarily reflect official positions of AGU unless expressly stated. Randy Fiser, Executive Director/CEO

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Features

22 Slipping and Locking in 28 Earth’s Volatile Balancing Act Earth’s Earthquake Factories By James D. Muirhead et al. By Noel Bartlow et al. The cycle of gases through the ground, air, and oceans is a journey scientists are more clearly understanding. Five subduction zones and what we’ve learned there about slow-slip behavior. 34 Breaking Up Is Hard to Do, On the Cover Especially for Continents Blocky lava flow leads back to Kanaga Volcano on Kanaga By Lindsay L. Worthington et al. Island, part of the Aleutian Arc. The Alaska–Aleutian What exactly happened to Pangea to make it split? subduction zone is one of five primary sites studied under the GeoPRISMS science plan. Credit: M. L. Coombs/Alaska Volcano Observatory/USGS

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Columns

From the Editor Research Spotlight 1 Crossing the Shoreline 41 How Some Trees Survive the Summer Dry Season | A Global Look at Surface Soil Organic Carbon News 42 Determining Dissolved Organic Carbon Flows into the Gulf of Alaska | Researchers Unearth Bedrock 4 Coastal Erosion by Waves Versus Rainfall Carbon and Water Dynamics 5 Dust on the Wind 43 Juno Maps Water Ice Across Northern Ganymede | 6 Sooty Layers in Stalagmites Record Human Activity​ Untangling Drivers of Ancient Hurricane Activity in Caves 44 Can Satellites Fill Gaps in Agricultural Water 7 How Geodynamo Models Churn the Outer Core Monitoring? | A Thirstier Atmosphere Will Increase 8 Finding “Glocal” Solutions to Flooding Problems Wildfire Risk out West 9 More Acidic Water Might Supercharge Lightning 11 Drought, Not War, Felled Some Ancient Asian Editors’ Highlights Civilizations 12 An Asteroid “Double Disaster” Struck Germany​ 45 Water Stress Controls the Capacity of the Terrestrial​ in the Miocene Carbon Sink | Going Down: How Do Cities Carry That Weight? 13 Trees That Live Fast, Die Young, and Mess with Climate Models 14 Tree Rings Reveal How Ancient Forests Were Managed Positions Available 15 The Influence of Tidal Forces Extends to the Arctic’s 46 Current job openings in the Earth and space sciences Deep Sea 16 This Search for Alien Life Starts with Destroying Crossword Puzzle Bacteria on Earth 17 Terrestrial Plants Flourished after the Cretaceous- 48 Geoprocesses Paleogene Extinction Opinion 18 Student-Led Diversity Audits: A Strategy for Change 20 GeoPRISMS: A Successful Model for Interdisciplinary Research

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Coastal Erosion by Waves Versus Rainfall

oastal cliffs are vulnerable to erosion, that change regularly, like beaches and cliffs, ing for decades in our field. And one of the and multiple serious collapses have it really pays off to measure them fre- neat things about it is that it showed it’s not Coccurred in California in recent years. quently,” explained Jonathan Warrick, a an ­­either-­​­or question. It’s not a question Scientists have succeeded in quantifying and research geologist with the U.S. Geological about whether it’s waves or hydrology [erod- separating erosional effects caused by ocean Survey who was not part of the new study. ing a cliff]. These two dominant processes are waves from erosion due to rainfall. The team This problem with seasonal timescales is par- working together.” conducted more than 150 lidar surveys of the ticularly relevant in places like Southern Cal- study site in Del Mar over a ­­3-​­​­​­year period. ifornia, where, as Young noted, “both rainfall Although there have been numerous stud- and increased wave action occur in the winter. ies examining the causes of erosion in rocky Therefore, higher frequency surveys that cap- coastal bluffs, research that manages both ture individual rainfall and large wave events “With the relationships to separate wave effects from precipitation are needed to separate and quantify how quantified in this study, effects and to quantify them is rare. Adam these processes drive cliff erosion.” Young, a coastal geomorphologist at the For their new study, published in the jour- we can estimate how much Scripps Institution of Oceanography and lead nal Geomorphology, Young and his research erosion is going to occur author of the new study, chalks this up to how team mapped a 2.­­5-​­​­​­kilometer (1.­­5-​­​­​­mile) infrequently cliff data are usually gathered. stretch of cliffs and adjacent beaches an aver- for a particular storm “Typically, we only had one or two lidar sur- age of once per week for 3 years (bit­ ​.ly/­ forecast at the study site.” veys a year,” Young said. “Those are great, coastal-cliff​­​­​­­ -​​ erosion).​­­­ The researchers gath- but they only provide seasonally averaged ered the bulk of their richly detailed data set information.” by using a truck-­­ mounted​­​­​­ lidar system. They Data collected at only seasonal timescales drove slowly along the beach in multiple are a problem when you’re trying to tease passes, aiming the lidar system at different Being able to distinguish between wave out the details of cliff erosion processes. “In angles to precisely capture all the variations effects and rainfall effects is important when studies of coastal systems, especially those of the cliff face and the beach elevation. They it comes to modeling and forecasting cliff supplemented their lidar data with wave erosion, Young explained. “Currently, most pressure sensors they buried along the beach, models use either waves or rainfall to drive as well as with rainfall data provided by their cliff erosion, but usually not combined local weather station and data from the together. In many locations such as Southern nearby La Jolla tide gauge. California, both processes are important.” He clarified by email, “With the relationships New Findings from Improved​ quantified in this study, we can estimate how Data Collection much erosion is going to occur for a particular The combination of more frequent data col- storm forecast at the study site.” Young also lection and a better remote sensing system— specified that this new information enables the researchers’ truck-­­ mounted​­​­​­ lidar system scientists to forecast how high on the cliff’s was an upgrade from GPS and the ­­all-​­​­​­terrain profile the erosion from an incoming storm vehicles they had previously been using— is likely to occur. enabled the scientists to quantify the rela- The team’s work could also be influential tionships between wave-­­ driven​­ and rainfall-­­ ​ for cliff modeling that looks at longer time­ driven­​­​­ cliff erosion. Their analyses of the data scales, such as projecting how quickly and found that erosion of the lower part of the how far coastal cliffs will retreat. As Warrick cliff was more strongly correlated with wave explained, “having an understanding like impacts and that rainfall was more closely this and quantifying it is essential for [cliff correlated with erosion of the upper cliff. change] forecasts. Ultimately, we would like “In our coastal [research] community, to know how much erosion [to expect] over we’ve long asked the question about why the next century—whether it is ten meters or cliff change occurs and what are the driving a hundred meters—and these studies are forces,” Warrick said. He explained that going to help us do those forecasts in the although scientists have understood that future.” “­­ocean- and ­­land-​­​­​­based processes” are the The new study was funded by the California primary processes that contribute to cliff fail- Department of Parks and Recreation and by Erosion threatens cliffs in Southern California’s Tor- ure, “it’s been challenging to measure those the U.S. Army Corps of Engineers. rey Pines State Natural Preserve. Visitors are competing processes and compare them.” warned to stay at least 10 feet away from the cliff Speaking about Young’s findings, Warrick base to avoid injuries in the event of a collapse. stated, “[This study] really helps us answer By Jady Carmichael (@jadycarmichael), Science Credit: iStockPhoto.com/Aaron Hawkins some of those questions that we’ve been ask- Writer

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Dust on the Wind

So Abell, his professor of Earth, environmental, and plan- mentor Gisela etary sciences at Brown University. That tem- Winckler, and their perature difference would have led to differ- colleagues decided ences in air pressure as well as ultimately to go back to the making the westerlies stronger and shifting Plio­cene. “At first, them toward the equator. it might sound a But how to prove that? Abell and colleagues ­little weird, right?” knew that if the westerlies did indeed move said Winckler, an toward the tropics as Earth got colder, they isotope geochem- should find a higher percentage of dust at the ist at Lamont-­ more southerly 36th parallel than at the 44th Doherty. “You have parallel—and they did. to go back 3 mil- “I think it’s a clever way of using a climate lion years?” But, proxy—dust preserved in two marine sedi- she said, that time ment cores at different latitudinal posi- period mirrors the tions—to try and tease apart how the westerly carbon dioxide lev- wind belt shifted during these large-­­ scale​­​­​­ cli- els that exist on mate transitions,” said Sarah Aarons, an iso- Earth now, along tope geochemist at Scripps Institution of Scientists studied dust in this sediment core, cut lengthwise here, drilled from the with temperature Oceanography who was not involved in the floor of the North Pacific Ocean to assess changing patterns in the westerly winds. levels similar to study. “And ultimately, I think it’s import- Credit: Jordan Abell/Lamont-​­​­​­Doherty Earth Observatory those Earth may ant...because scientists will be able to incor- face in a few de- porate that information into climate models cades if it contin- to more accurately represent what we could ues to warm—2°C– expect in the future.” rom the 15th to the 17th century, Euro- 4°C higher than today’s levels. The team’s results were published in pean sailors rode prevailing winds Although there are no Pliocene wind Nature (­bit.ly/­­weakened​-​­­­westerlies). Fknown as the westerlies to reach lucra- records, there are records of millions of tive spice markets in Southeast Asia. This years’ worth of dust that have piled up on the New Precipitation Patterns powerful atmospheric system, which blows ocean floor.The team analyzed two ­­8-meter-​­​­​­­ ​ The upshot of the phenomenon is that if west to east around Earth’s middle latitudes, ­​­​­long sediment cores from two places in the Earth warms to the level of the Pliocene, the also brought prosperity to the ancient king- North Pacific Ocean at about the 36th and westerlies will no longer blow across the mid- dom of Loulan on China’s Silk Road by way of 45th parallels. dle latitudes, which could mean much less consistent rain to feed its crops. rain for North America, Europe, and other In addition to ships and moisture, the temperate zones in the north, as well as in westerlies transport dust, sometimes over parts of Australia and New Zealand in the astonishingly long distances. In 2003, scien- south. That shift may not happen for centu- tists traced particles carried by ­­westerlies “At first, it might sound a ries, though, and there is still much to learn from China’s Taklamakan Desert to the little weird, right? You have about how much of a shift will happen. French Alps. Much of the westerlies’ dust, Abell and his coauthors hope to get more however, drops into the northern Pacific to go back 3 million years?” precise data about the degree of shift by Ocean, which is why scientists at Columbia studying sediment cores from when Earth was University’s ­­Lamont-​­​­​­Doherty Earth Obser- transitioning from the icy Pleistocene to the vatory thought that might be the place to look contemporary Holocene. There are many for concrete evidence to confirm that the Temperature Extremes Led​ more sediment cores available for that time westerlies are shifting toward the poles as the to Wind Shifts period than for the earlier Pliocene to Pleisto- climate warms. The researchers also looked at one particular cene, and by comparing a set of cores from A number of researchers have posited that point in time, 2.73 million years ago. The north to south, the researchers believe they the westerlies may be shifting, based on com- Pliocene was waning, Earth was cooling, and might be able to say how many degrees the puter modeling and satellite data showing the Pleistocene ice age, with its woolly mam- westerlies will shift. “Our work in the Pliocene changes to ocean currents. Those data sets moths and ­­saber-​­​­​­toothed cats, was starting is really important,” Abell said, “but being however, don’t go back very far. “It’s hard to to take hold. During ice ages like the Pleisto- able to constrain some of these uncertainties differentiate natural variability from ­­longer-​ cene, both the tropics and the poles got even more is what we hope to do next.” ­​­​­term trends with just several decades’ worth colder. The temperature drop at the poles, of data,” said Jordan Abell, a doctoral student however, was much greater—around 6°C – in Earth and environmental sciences at 10°C compared with 2°C at the equator, By Nancy Averett (@nancyaverett), Science ­­Lamont-­Doherty. explained Timothy D. Herbert, a coauthor and Writer

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Sooty Layers in Stalagmites Record Human Activity​ in Caves

Back in the laboratory, the scientists split the stalagmites lengthwise to reveal their interior layers. They were astonished to find that 14 of the stalagmites were shot through with layers of black soot and charcoal up to a millimeter thick and easily visible to the naked eye. That discovery changed the direc- tion of the investigation, said Koç. The researchers had initially planned to use the stalagmites to reconstruct the ancient climate in the region. “Our main purpose was to collect clean and suitable samples for paleoclimate research,” said Koç. But now the hunt was on to better under- stand these layers. Koç and his colleagues focused on three stalagmites from Tabak Cave and Kocain Cave with particularly well defined black layers. These layers, the researchers suggested, revealed a human presence in these caves.

Evidence of Fires Researches are studying evidence of soot and charcoal from human-­­ ​­​­​­set fires in cave formations like these in The black layers in the speleothems are the Damlatas Cave in Antalya, Turkey. Credit: iStock.com/EvrenKalinbacak result of people carrying torches or setting fires in the caves, Koç and his collaborators said. Combustion releases particles of black charcoal that hitch a ride on air currents, and aves have long been used as places an adventure, said Koç, and these trips were in a cave, some of these particles are bound to of shelter, burial, and ritual. Now no exception. In one cave, the team had to end up sticking to growing stalagmites. (The Cresearchers have analyzed stalagmites shimmy through an extremely narrow pas- same effect can be seen today on the stone from two caves in southwestern Turkey and sageway barely wider than a person, and they surfaces of old buildings exposed to pollution.) found that they contain layers of soot and found human and animal remains in addition The researchers estimated the ages of the charcoal, presumably from ­­human-​­​­​­set fires. to pieces of pottery. speleothems’ normal layers using ­uranium-​­​­​ By precisely dating the stalagmite layers ­thorium dating. By tabulating the ages of lay- bracketing this black carbon, the scientists ers adjacent to each band of soot and char- estimated that people were exploring these coal, they estimated when the black carbon caves more than 6,000 years ago. These “People might have used was deposited and therefore when humans results reveal how geophysical data can com- were exploring these caves. plement archaeological records. these caves as a shelter during the summer.” A Summer Refuge? The Allure of Caves Koç and his colleagues found three layers of To many ancient cultures, the dark passage- soot and charcoal in the stalagmites from ways of caves represented a metaphorical Tabak Cave. They dated the layers to roughly connection to another world. Even today, 6,700, 7,100, and 7,400 years before the pres- with the advent of powerful flashlights that Natural Record Keepers ent, with an uncertainty of about 200 years. slice through darkness, caves are still allur- Koç and his collaborators observed many That’s surprisingly early, said Koç, but it ing—the National Speleological Society, a stalagmites and stalactites. Because speleo- makes sense that people were inhabiting the nonprofit organization devoted to cave explo- thems like these grow slowly over time, caves. Turkey is notoriously hot in June, July, ration, counts more than 7,000 members. they’re record keepers of past environmen- and August, so maybe these caves functioned “They’re special places,” said Koray Koç a tal conditions: Scientists have used them to as a refuge from the heat, he said. “People paleoclimatologist at Akdeniz University in reconstruct droughts and climate variability, might have used these caves as a shelter Antalya, Turkey. among other changes. Koç and his colleagues during the summer.” In 2015, Koç and his colleagues headed collected 16 stalagmites, the shortest about It’s unlikely that the layers of black carbon underground to explore several caves in the length of a pinkie finger and the longest are due to nonanthropogenic triggers like southwestern Turkey. Spelunking is always topping a meter. ­­far­away wildfires. That’s because the ventila-

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tion in Tabak Cave is poor—airborne particles circulating aboveground probably wouldn’t How Geodynamo Models​ have traveled far into the cave. (The stalag- mites the researchers analyzed were tens of Churn the Outer Core meters—and several narrow passageways— beyond the entrance.) Furthermore, archae- eep beneath our feet, Earth’s liquid ological artifacts like pottery shards found in iron outer core sloshes and churns, Tabak Cave confirm the presence of humans Dslowly crystallizing to form the solid deep underground who probably needed a inner core while simultaneously generating source of light. our planet’s magnetic field. In a recent study, The stalagmite from Kocain Cave exhibited Domenico Meduri, a geodynamo modeler at a wider spread in the ages of its five soot and the University of Liverpool, focused on the charcoal layers: 470, 810, 1,500, 1,700, and past 10 million years of this erratic, roiling 2,800 years before present. It’s possible that motion—more like river rapids than calm some of these layers derive from aboveground waters—using state-­­ ​­​­​­­of-​­​­​­­the-​­​­​­art computa- fires, the researchers acknowledged, because tional facilities and refined code. of Kocain Cave’s wide, open entrance and lack Meduri and his team, using their own sim- of narrow passageways. ulations, successfully reproduced salient fea- These results are an important demon- tures of the paleomagnetic field preserved in stration of the value of geophysical data, said volcanic rocks. Such features include not only Koç. The ability to precisely age date a spe- pole reversals—where north and south swap leothem has the potential to be a boon to places—but also other fundamental charac- archaeology, he said. “In archaeological teristics of the paleomagnetic field recorded These maps show a simulated magnetic field rever- studies, the trickiest part is getting robust by rock samples. sal. Purple indicates a magnetic field pointing inward, ages.” Two ingredients spurred the team’s success. toward the core, and orange indicates a magnetic They found that the most commonly modeled field pointing outward and away from Earth’s surface. driver of the outer core’s movements—differ- The darker the shading, the more intense the mag- ences in temperature—cannot explain paleo- netic field is. Credit: Domenico Meduri “In archaeological studies, magnetic field measurements. Instead, it is the composition of the swirling liquid that the trickiest part is getting plays an important role. Within the simula- robust ages.” tions, they also turned the knobs that approx- cauldron from the bottom up. This, she said, imate the physical characteristics of the mov- is compositional convection. ing molten metal, confirming that although To model the two drivers of convection, Earth’s core behaves mostly like a dipolar bar Meduri said his team modified where the magnet—with only two poles—it may hover buoyancy forces congregate. “In the chemical Breaking Down Barriers between the dipolar and multipolar regimes. model, [buoyancy forces] are located close to Ségolène Vandevelde, an archaeologist who The research was published in Geophysical the inner core boundary, whereas in thermal studies speleothems at the University of Research Letters (bit​.ly/numerical­­ ​-dynamo­­ ​ models, [buoyancy forces are distributed] Paris 1 Pantheon-​­​­​­Sorbonne, agreed. This -­simulations). throughout the whole fluid.” work breaks down barriers between geologi- None of Meduri’s solutions driven by ther- cal and archaeological approaches to science, Stirring the Cauldron mal convection matched the ­­long-​­​­​­term said Vandevelde, who was not involved in the Two phenomena drive the outer core’s turbu- paleomagnetic field data gleaned from rocks. research. “Speleothems are often used as lent movement: thermal convection and The only ones that worked for his team, said environmental and paleoclimate archives. compositional convection. Thermal convec- Korte, were “those driven by compositional Here, [scientists] use them as an archaeolog- tion occurs because the outer core is cooling convection.” ical record.” along with the rest of Earth, explained Mon- These results were published in the Jour- ika Korte, a paleomagnetist from the Helm- Bar Magnet Behavior nal of Archaeological Science (bit.ly/­­turkey​ holtz Centre in Potsdam, Germany, who was “To really have an ­­Earth-like​­​­​­ dynamo run—a -­stalagmites). not involved in the new study. As the metal- long run that simulates thousands or millions A lot more information can be mined from lic liquid loses heat, colder material sinks of years of field evolution—[the run] should these speleothems, said Vandevelde. “It’d be toward the inner core, pushing hotter liquid reflect the ­­long-​­​­​­term average that we see in really interesting to synchronize all the dif- upward, resulting in movement within the the data,” said Korte. The simulation should ferent sequences of the Tabak Cave speleo- entire outer core driven by temperature vari- include the observation that on average, the thems to reconstruct a complete chronology ations, she said. magnetic field tends to behave as though a of human occupation in the cave.” As the outer core processes form the inner bar magnet resides within Earth’s core. core, said Korte, the light elements that crys- But a successful simulation must also cap- tallize at the boundary are too buoyant to be ture reversals, which “are a fundamental fea- By Katherine Kornei (@KatherineKornei), incorporated into Earth’s metal heart and ture of Earth’s magnetic field,” said Meduri. Science Writer instead rise through the fluid, stirring the Other observations from paleomagnetic data,

SCIENCE NEWS BY AGU // Eos.org 7 NEWS

like how variable the magnetic field intensity is and how much the geomagnetic poles wan- Finding “Glocal” Solutions​ der, he said, must also be replicated. Previous studies that could not successfully to Flooding Problems simulate paleomagnetic field data from the past 10 million years were “quite concern- provided useful information to the Chinese ing,” said Meduri. If simulations of Earth’s Ministry for Emergency Management when geodynamo do not comply with paleomag- record rainfall in 2020 posed an immediate netic measurements, he said, “then what’s threat—an event that eventually affected the point of using these models to study the 40 million people, according to Wu’s team magnetic field?” (bit​.ly/­glocal​-­solution). Changing the buoyancy force distribu- tion—the major difference between compo- Forecasting Floods Throughout​ sitional and thermal convection—will not, by the World itself, create Earth-­­ ​­​­​­like simulations, said Global flood models approximate the complex Meduri. Instead, his team had to turn various relationships between precipitation and local knobs that change the physical properties of hydrology. Accurate, ­­real-​­​­​­time precipitation the modeled fluid. data buttress any such model. These physical properties, said Korte, “are Some global flood models use ­­satellite-​­​­​ not exactly known because we cannot just go ­measured precipitation estimates, but down to the Earth’s core and directly measure according to Bob Adler, an atmospheric sci- them.” Instead, she said, “they have to be entist at the University of Maryland not inferred.” involved with Wu’s latest work, “it’s a very For example, one of these knobs controls complex thing trying to estimate surface the vigor of the liquid outer core’s move- rainfall—what’s falling out of the bottom of ment. Too calm? No reversals. Too turbulent? a cloud—by looking at it from space.” One “The simulations are no longer very ­­Earth-​ Xin’an River Hydropower Station, in the province of upgrade in Wu’s calculations, Adler said, is ­like,” said Meduri, and behave not as a bar Zhejiang, China, discharges floodwaters of Qiandao the use of numerous rain gauges China has magnet but as multiple unstable poles pro- Lake in July 2020, a period of record rainfall in the installed. These gauges can feed accurate, truding in different places—a multipolar region. Credit: MasaneMiyaPA/Wikimedia, CC ­­BY-​­​­​­SA ­­real-​­​­​­time precipitation data into the model magnetic field. 4.0 (bit.ly/ccbysa4-0) to produce high-­­ ​­​­​­quality rain forecasts. Such What you need, Meduri said, is to turn the forecasting, said Wu in his paper, “always knob just enough to find the “sweet spot” plays the most important role in driving between those two magnetic regimes, where models.” the geomagnetic poles flip every so often ype “flooding today” into your search If precipitation data and forecasting pro- while maintaining that bar ­magnet-​­like engine and you will likely find at least vide the foundation, hydrology frames the behavior on average. For these successful Tone place battling rising waters some- rest of the issue with ­regional- and ­local-​ simulations, the magnetic field briefly exhib- where in the world—Mozambique today, ­scale runoff and routing models that follow its multipolar behavior during the reversal Yorkshire yesterday, Hawaii tomorrow. Floods rain when it hits land. The hydrology compo- before settling back down to look more like a occur when water encroaches on dry land, nent begins with a land surface model that stable bar magnet. “In this way,” he said, “we which can happen during ­hurricane-​­induced dictates how much water goes into the ground could get dipolar [bar magnet-­­ ​­​­​­like] models storm surges or when heavy precipitation (or versus how much is available as runoff, said with ­­high-​­​­​­enough directional and intensity snowmelt) has nowhere to go. These different Adler. Then the runoff goes into a routing variability.” flood sources have an important commonal- model that directs the water downstream, he “That’s really the fundamental contribu- ity: They all start with weather. said, allowing scientists to calculate the total tion of our work,” Meduri said. “We’ve known “Weather patterns, which cause flooding, volume of water flowing through a river at a for at least 25 years that numerical simula- are happening at the global scale,” said Guy given time. tions capture reversals, but do they also cap- Schumann, a flood hydrologist with the Uni- With this information, Wu and his col- ture the directional and intensity variability versity of Colorado Boulder’s Institute of Arc- leagues can forecast areas likely to be inun- we observe [in the rocks] on these long tic and Alpine Research, “but impacts of floods dated with water—information best visual- timescales or not?” are very localized.” Local effects include costs ized as a flood map. Providing these “timely “Our work,” he said, “is really a bridge to the economy, displacement of populations, and accurate maps showing current and ­­days-​ between purely theoretical dynamo simula- and loss of life. ­​­​­ahead flood risk [is the responsibility of] the ​­​­​­ ND ­­ BY- 2.0 (bit.ly/ccbynd2-0)

tions and what we observe of the Earth’s Schumann and a team of scientists led by international hydrometeorological commu- CC magnetic field. We were trying to match the Huan Wu, a professor at Sun ­­Yat-sen​­​­​­ Univer- nity,” said Wu and his coauthors in their two.” sity in Guangdong, China, developed an inno- paper. vative flood model linking global precipita- As an end user of flood maps, natural hazard tion patterns with localized hydrology—where mitigation strategist Kevin Zerbe, not part of By Alka Tripathy-­­ ​­​­​­Lang (@DrAlkaTrip), Science water goes once it finds land. Their work, this study, said that inundation at the spatial

Writer published in Advances in Atmospheric Science, resolution Wu provided to the Chinese gov- Credit: Warren Tyrer/Flickr,

8 Eos // APRIL 2021 NEWS

ernment—water depth every 5–10 meters—is “what’s really missing.” At least in parts of More Acidic Water​ China, Wu found a way to model the hydrol- ogy of each watershed that, Zerbe said, is so Might Supercharge Lightning unique and continually changing. According to Zerbe, “those kinds of mapping products simple laboratory experiment has with a surprising answer: Nobody knows. The would be valuable when it comes to preparing sparked new insight into the poten- prevailing assumption in the field was that for an oncoming flooding event.” A tial impact of climate change on any surface on Earth—rock, soil, ocean, or the intensity of ocean lightning. A team of lake—could be considered a perfect conduc- The Valley of Death researchers in Israel gradually changed the tor. But data show that lightning behaves dif- Wu and his team bridged what Schumann acidity of a beaker of water while shooting it ferently over land than over sea—it is far called the “valley of death,” or the gap with an electrical spark. As the water became more frequent over continents, and evidence between scientists and end users. By con- more acidic, the flash became brighter. If suggests that it is often more intense over the necting to the national authorities in China, what they observed in the lab is indicative of ocean. Schumann said, “[Wu] managed to get his how lightning acts in nature, ocean lightning model into the hands of the...people who are could become around 30% more intense by responsible for acting.” century’s end under a worst-­­ ​­​­​­case climate The metaphorical valley of death can scenario, according to the scientists. become literal when scientists cannot com- Such a rise in intensity could threaten the The researchers wondered municate with decisionmakers, especially in safety of marine life and oceangoing vessels whether the ocean itself countries that may not be able to make their alike, the authors of a paper in Scientific own flood maps. Global flood models serve a Reports argue (bit.ly/­­lightning-​ intensity).​­­­ But could have something humanitarian purpose, said Schumann, let- other experts in the field caution that this to do with the pattern. ting agencies like the United Nations rapidly makeshift lightning in a beaker could behave respond to flooding in regions with fewer very differently than ­­real-​­​­​­world lightning in resources. In particular, Wu and his col- the atmosphere. leagues called on meteorologists and hydrol- ogists to work together on “glocal” solutions, An Illuminating Line of Inquiry A 2019 paper in the Journal of Geophysical reflecting the dual nature of the problem. The idea for the experiment started with a Research: Atmospheres mapped the global dis- “We [need] a lot more local information in conversation over lunch between lead author tribution of a kind of lightning known as a these global models,” Schumann said, which, Mustafa Asfur, a lecturer at Israel’s Ruppin superbolt, which is 100–1,000 times brighter he explained, must include a global high-­­ ​­​­​ Academic Center, and Jacob Silverman, an than an ordinary lightning bolt (bit​.ly/­ ­resolution topographic data set to underlie ocean biogeochemist with the National Insti- superbolts). Researchers found that almost runoff models and maps of existing local tute of Oceanography in Haifa. “I started to all superbolt hot spots were over oceans and flood defenses—levees, walls, and dams, for ask innocent questions about what happens seas, but they had no ready explanation for example—that control where water flows. to seawater when lightning strikes it,” Silver- why that might be the case. The best freely available global digital eleva- man said. Silverman and Asfur wondered whether the tion models of topography have a resolution When Asfur and Silverman began digging ocean itself could have something to do with of 30 meters per pixel, he said, and they’re into the scientific literature, they were met the pattern. “I have a feeling that maybe we’re often outdated because topography changes in regions with active tectonics or flooding. To obtain ­­higher-​­​­​­resolution data, he said, “someone needs to pay for that.” The need for global models that can accu- rately forecast flooding several days ahead while providing information at both local and regional scales has never been higher. As the climate warms and exacerbates extreme pre- cipitation events, Zerbe said, flooding events will become more unpredictable. “Climate change is invalidating history as a good indi- cator of what’s going to happen in the future, and that’s all the more reason that we need ​­​­​­ ND ­­ BY- 2.0 (bit.ly/ccbynd2-0)

CC really great modeling and simulations and data,” said Zerbe. “History just isn’t as reli- able as it once was.”

By Alka Tripathy-­­ ​­​­​­Lang (@DrAlkaTrip), Science

Credit: Warren Tyrer/Flickr, Writer

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In a new experiment, researchers filled beakers with water and suspended one electrode about a centimeter above the water and another about 3 centimeters below, in a setup that produced a 1-million-volt spark with a current of about 20 amperes. When pure water (center) was made saltier (left) or more acidic (right), the spark became visi- bly brighter. Credit: Mustafa Asfur

missing something,” Silverman said. “Maybe used two methods of changing the pH of and other ocean infrastructure might need to the conductivity of the ground does matter.” the water in the experiment by adding a update their lightning protections. More strong acid and by bubbling carbon dioxide. intense lightning over the oceans could also A Strikingly Simple Setup Like salinity, acidification had a measurable produce louder booms that stress sea crea- To test the idea, Asfur and his team came up impact on the brightness of the sparks. The tures already harried by human noise pollu- with a simple laboratory setup that replicated spark intensity increased more than 2 times tion. lightning striking the ocean. They filled a But it’s not time to start implementing new beaker with water and suspended one elec- lightning protections just yet, according to trode about a centimeter above the water and Vernon Cooray, a lightning physicist with another about 3 centimeters below, in a setup “A simple experiment goes Uppsala University in Sweden who was not that produced a ­­1-​­​­​­­million-​­​­​­volt spark with a involved in the study. Cooray said that a spark current of about 20 amperes. They measured a long way toward of a few centimeters interacts with water very the spark’s intensity using an optical fiber provoking ideas and differently than a spark of several hundred spectrometer that measured relative irradi- meters. ance units. provoking further work.” “The methods are sound, and the conclu- The team first measured how salinity sions made about the laboratory discharges affected the brightness of the spark, zapping are correct,” he said. “Unfortunately, the water ranging from normal tap water to a results cannot be extended to lightning.” salty sample from the Dead Sea. Sure enough, Williams also advised caution about apply- the sparks in the saltier beakers produced faster using the carbon dioxide bubbling ing the lab results to ­­real-​­​­​­world lightning, brighter flashes, the team reported in a study method to lower the pH. which is not only much longer but also at least published last year (bit.ly/­­intense​-­­­lightning​ These results “caught me off guard at 100 times more intense. Even so, he considers -­­over​-​­oceans). first,” said Earle Williams, a physical meteo- the new research to be valuable. Next, the researchers turned their atten- rologist with the Massachusetts Institute of “It’s an important contribution whenever tion to another property of water that can Technology who was not involved in the you have results in the lab where you can change its conductivity: acidification. They study. “My expectation was that it wouldn’t measure things that shed important light on matter much what the material was.” ­­large-​­​­​­scale phenomena,” he said. “A simple experiment goes a long way toward provoking More Than Just a Flash in the Beaker? ideas and provoking further work.” u Read the latest news If lightning is indeed growing more intense at Eos.org over the oceans as climate change makes oceans more acidic, shipping vessels, oil rigs, By Rachel Fritts (@rachel_fritts), Science Writer

10 Eos // APRIL 2021 NEWS

Drought, Not War, Felled Some Ancient Asian Civilizations

he central Asian civilizations of the Otr-ar oasis, located at the junction of Tthe Syr Darya and Arys Rivers in what is now southern Kazakhstan, flourished during classical antiquity. Located on the Silk Road, with access to floodwater-irrigated land spanning some 50,000 square kilometers (about twice the size of Mesopotamia), the region became known as Transoxania. At its height, it was described as the “land of the thousand cit- ies.” However, the region fell into stagnation at the end of the Medieval period, with its decline coinciding with a Mongol invasion in the early 13th century. After a partial recov- ery, Otr-ar finally collapsed by the 17th cen- tury and the region remains uninhabited today. But the cause of Otr-ar’s decline was likely not the changing tides of warfare but instead the changing climate.

The Sands of Time Mongol warriors like these have long been associated with the fall of the central Asian civilizations of Transoxa- In a new study published in the Proceedings of nia, but climate change may have been as much to blame. Credit: From the Jāmi˘ al-tawārīkh the National Academy of Sciences of the United States of America, an interdisciplinary team of researchers reported that the Otr-ar oasis had been in a prolonged period of decline long The researchers collected samples from the University whose lab specializes in the OSL before the Mongols invaded (bit.ly/­​­central​ canals by hammering metal scaffolding tubes technique but who was not involved in this -­­asia-​­​­​­­river-​­​­​­civilizations). into the sediment, being careful to seal both study. When the sand is exposed to the Sun, The clues lie in irrigation canals that the ends from light exposure before they were its luminescence signal is known and effec- ancient civilizations of Transoxania relied on shipped back to the laboratory for analysis. tively “zeroed.” And when the sand is bur- for agriculture. ied—because, say, the canal that was carrying “People and communities lived and were the sand was no longer flowing—it is exposed shaped by the environment,” said Mark to the latent radioactivity of the surrounding Macklin, a professor of river systems and sediments. global change at the University of Lincoln in “We assumed with our “There’s basically a proportionality between the United Kingdom. “And in the case of cen- dating that the canals radiation exposure and luminescence,” and tral Asia, [they] may be shaped by the avail- with knowledge of the rate of radiation expo- ability of water.... If you don’t have water, you would have been sure, it is possible to calculate when the sand don’t have crops; you can’t live.” abandoned only when the was buried, said Rittenour. Transoxania’s canals were previously The researchers also reconstructed climate thought to have been destroyed by the Mon- Mongols arrived. But that records in the region over the past 2,000 gols during their invasion. Macklin and his wasn’t the case. They were years, which revealed that the canals were colleagues studied the canals with a combi- abandoned during periods of prolonged nation of radiocarbon dating and a technique already going into disuse drought that both weakened the civilizations called optically stimulated luminescence probably 100 years before.” before the Mongols arrived and stunted their (OSL), which dates the last time that sand was recovery afterward. Archaeological records exposed to sunlight. further corroborated the coincident timing of “We assumed with our dating that the the region’s cultural decline. canals would have been abandoned only when the Mongols arrived,” Macklin said. “But that “Every handful of sand is radioactive,” said Climatic and Cultural Interactions wasn’t the case. They were already going into Tammy Rittenour, a professor of paleoclima- Climate conditions likely interacted with disuse probably 100 years before.” tology and Quaternary geology at Utah State regional conflict to influence the rise of Trans­

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oxania as well as its fall. For example, an Arab invasion between 650 and 760 coincided with An Asteroid “Double Disaster”​ a wet period, and the region not only recov- ered quickly but prospered afterward, Macklin Struck Germany in the Miocene said. “By contrast, when the Mongol army arrived in 1218, there [had been] probably ­­100-​ ­​­​­150 years of prolonged drought, and already the place wasn’t in good shape.” These converging lines of climatic and cul- tural interactions paint a more nuanced pic- ture of human history in the region, one in which the climate helped shape the legacies of militaristic ambitions.

“History never, ever quite repeats itself. Our understanding of what happened in the past is informative of what we can say might happen in the future.” St. George’s church in Nördlingen, Germany, is built from rock forged by an asteroid impact. Credit: Renardo la vulpo/Wikimedia, CC ­BY-​­SA 4.0 (bit.ly/ccbysa4-02)

One ­­take-​­​­​­home message of the study is the power of applying multiple dating meth- Gothic church rises high above the on the Earth. When you see two sitting right ods “to ensure you know the age of your fea- medieval town of Nördlingen, Ger- next to one another, it’s natural to think tures or your deposits, so you can really con- A many. But unlike most churches, there’s an association.” firm the results,” said Rittenour. “And that, St. George’s is composed of a very special However, scientists have theoretically along with the link to archaeology, cultural type of rock: suevite, a ­coarse-grained​­ breccia determined that the binary asteroid scenario changes, and climate, makes this an excellent that’s formed only in powerful impacts. That is unlikely. That’s because most binary aster- paper.” discovery and other lines of evidence have oids orbit each other too closely to produce “History never, ever quite repeats itself,” helped researchers determine that Nördlin- two distinct craters were they to slam into Macklin said. “Our understanding of what gen lies within an impact crater. Now scien- a rocky body, Bottke and his colleagues happened in the past is informative of what tists have unearthed evidence that this crater showed back in the 1990s. “If you’re going to we can say might happen in the future.” and another one just 40 kilometers away were get two separate craters from the impact of a Indeed, central Asia looks very different formed by a “double disaster” of two inde- binary asteroid, they have to be pretty well today, with large-­­ ​­​­​­scale commercial farming pendent asteroid impacts. That revises a pre- separated,” said Bottke. dominating the landscape. The Aral Sea, into vious theory that these features are the relics which the ­­life-​­​­​­giving rivers of Transoxania of a one-­ ​­two cosmic punch from a pair of Two Craters near Stuttgart drain, has now virtually disappeared, Macklin gravitationally bound asteroids striking Earth Now Elmar Buchner, a geologist at the Neu-­ ​ said. simultaneously. ­Ulm University of Applied Sciences in Ger- “This research is showing that climate many, and his colleagues have investigated change does have a real impact on society,” A Handful of Double Craters the provenance of two impact craters near he said. “And we can see that very clearly. It Our planet is dotted with nearly 200 con- Stuttgart using observational data. They can happen very rapidly. You can see it within firmed impact structures, and a handful of focused on the ­24-​­kilometer-​­diameter Ries a generation.” them appear in close pairs. Some researchers crater—which encompasses the town of And, he added, “the rate of climate change have proposed that these apparent double Nördlingen—and the ­4-​­kilometer-​­diameter [in this study] is significantly less than what craters are scars created by binary asteroids Steinheim Basin, which are located roughly we’re seeing now.” slamming into Earth at the same time. That 40 kilometers from each other. makes sense, said William Bottke, a planetary The Ries crater formed about 14.8 million scientist at the Southwest Research Institute years ago during the Miocene epoch, Argon-­​ By Richard J. Sima (@richardsima), Science in Boulder, Colo., not involved in the new argon­ age dating has revealed. The age of the Writer research. “We don’t have that many craters Steinheim Basin hasn’t been conclusively

12 Eos // APRIL 2021 NEWS

measured, but some researchers have sug- gested that it formed contemporaneously. “It Trees That Live Fast, Die Young,​ was nearly dogma in Germany that this must be the result of a double impact at the same and Mess with Climate Models time,” said Buchner. nder a ­business-​­as-​­usual scenario to reach their maximum size sooner in life. Two Episodes of Ground Shaking of greenhouse gas emissions, the The entire process means that trees will store Buchner and his collaborators investigated Uaverage global temperature might carbon for a shorter time, accelerating the outcroppings of rock in the region around the increase by almost 5°C through the end of the carbon cycle and potentially increasing car- craters and found a layer of jumbled, frac- century. This climate change could cause a ­1-​ bon concentrations in the atmosphere. tured sediments. That wasn’t a surprise— ­meter increase in sea levels, possibly wreak- “This can have an important effect on for- such seismites are a sign that powerful seis- ing havoc on coastal regions and demanding est carbon sinks in the future,” said Roel mic waves passed through the region, which hundreds of billions of dollars every year in Brienen, a professor at the School of Geogra- would have certainly occurred after an aster- adaptation and mitigation measures. As grim phy at the University of Leeds in the United oid impact. However, the researchers found as this scenario may sound, it might be opti- Kingdom. that this seismite horizon was crosscut by a mistic. Brienen led a study showing that the trade-­ ​ second horizon, this one consisting of vertical According to recent research, there are ­off between tree longevity and growth rate is tubelike features known as clastic dikes. The ­carbon cycle feedbacks not accounted for by almost universal, extending from high lati- discovery of these two distinct seismite units current climate models. The reason is that tudes to the tropics. An international team of is evidence of two separate episodes of ground forests, which can absorb about a third of researchers observed tree ring data sets on shaking, Buchner and his colleagues con- greenhouse gas emissions, might be rela- 110 tree species all over the world and noticed cluded. That rules out a strike by a binary tively ­short-lived​­ carbon stocks in the future that on average, 50% of early growth increase asteroid, which would have launched just one as trees live fast and die young. meant a 23% life span reduction. “While this round of seismic waves. Scientists are concerned because carbon relation across species was already known, we uptake is a “critical ecosystem service that found this difference also occurs within spe- our forests are providing by effectively slow- cies,” Brienen said. ing the rate of climate change—and buying The finding is important, but the paper The researchers found that us time while we figure out policies to address doesn’t account for the variation in tree it,” said Andrew Reinmann, an assistant pro- reproduction and seedling production, this seismite horizon was fessor of geography at the City University of observed Oswald Schmitz, a professor of pop- crosscut by a second New York. ulation and community ecology at Yale Uni- Carbon dioxide (CO2) stimulates the growth versity’s School of the Environment not horizon, this one consisting of trees due to carbon uptake during their involved in the study. of vertical tubelike features development. This process, which scientists It’s possible that there could be a carbon call CO2 fertilization, can accelerate tree balance, with enough sprouting seedlings to known as clastic dikes. growth, with more carbon available in the replace dead trees, said Schmitz—but the car- atmosphere (especially under higher tem- bon cycle is rarely that simple. “Carbon cycle peratures) causing trees to have shorter life models don’t really account for such nuanced spans. The trees die sooner because higher dynamics, especially if there’s regeneration The impact that created the Ries crater must metabolism rates can cause them to age faster failure—by continuing deforestation, for have formed first, the scientists surmised, and invest less in defenses or a more efficient instance,” Schmitz explained. because blocks of limestone—ejecta from the hydraulic architecture, or simply cause them Temperature might play an important role Ries impact—cap the lower seismite horizon. in the relationship between tree longevity That’s consistent with previous research sug- and growth as well: According to another gesting that fossils within the Ries crater are a paper from the same group, published in the few hundred thousand years older than fossils Proceedings of the National Academy of Sciences found within the Steinheim Basin. of the United States of America, tropical trees This region “witnessed a double disaster in grow twice as fast as those in temperate and the Middle Miocene,” the researchers con- boreal regions but live half as long (bit​.ly/­ cluded in their paper, which was published in tropical​-­tree-​­longevity). The study analyzed Scientific Reports( bit.ly/­ seismite­ ​-horizons).­ tree ring data from more than 3,300 tree pop- That’s rare but not unheard of, said Bottke. ulations and 438 species across different “If you only have so much terrain and you biomes. keep adding craters, eventually, two are going Lead author Giuliano Locosselli, a to be very close to one another, just by researcher at the Biosciences Institute at the chance.” Forests in temperate and boreal regions, like this University of São Paulo in Brazil, said there one at Parc Régional du Poisson Blanc in Quebec, is only so much heat trees can withstand Canada, store much of their carbon in the soil, as without having their life spans shortened. By Katherine Kornei (@KatherineKornei), organic matter takes longer to decompose and, con- The hotter it gets, the more water evaporates

Science Writer sequently, release CO2. Credit: Ali Kazal/Unsplash from trees. “We saw that mean annual tem-

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peratures above 25.4°C affect tree longevity because [trees are] already operating in their Tree Rings Reveal How​ limit—too much evaporation might cause water stress and affect their survival,” Locos- Ancient Forests Were Managed selli said. lear-​­cutting a forest is relatively Climate Modeling Challenges easy—just pick a tree and start chop- According to Reinmann, merging these and ­Cping. But there are benefits to more other processes that happen to trees into sophisticated forest management. One tech- global carbon cycle–­ climate​­ feedback models nique—which involves repeatedly harvesting would make them a lot more accurate than smaller trees every 30 or so years but leaving they are now. Overall impacts could be an upper story of larger trees for longer peri- immense. “If, under a future climate, forest ods (60, 90, or 120 years)—ensures a steady carbon absorption plummets and we didn’t supply of both firewood and construction account for that, we would throw off the timber. effectiveness of our climate change policies,” To determine when this management prac- he said. tice first arose in Europe, researchers have Incorporating and verifying such diverse analyzed oak construction timbers from his- data, however, is a Herculean task. Pieter torical buildings and archaeological sites Tans, a senior scientist at NOAA’s Global ­dating from the 4th to the 21st century. They and his colleagues were surprised by this, Monitoring Laboratory not involved in the spotted a characteristic tree ring pattern because no mention of this forest manage- research, pointed out that in addition to data indicative of this technique in timber dating ment practice appears in historical docu- about forest carbon, assessing a forest’s back to the 6th century. That was a surprise, ments until roughly 500 years later, in the effect on climate models must also include the researchers noted, because this forest 13th century. soil moisture conditions and carbon storage, management practice shows up in historical It’s probable that forest management aboveground plant canopy structure, and documents beginning only in the 13th century. practices were not well documented prior to myriad other variables. the High Middle Ages (­1000-​­1250), the A particularly difficult assessment to make A Pattern in the Rings researchers suggested. “Forests are mainly involves the gas itself. “It’s easier for us to The coppice-​­with-​­standards management ​ mentioned in the context of royal hunting see something in methane than in CO2,” Tans practice produces a ­two-​­story forest, said interests or donations,” said Muigg. Dendro- said. “Carbon dioxide has large sources and Bernhard Muigg, a dendrochronologist at chronological studies are particularly import- large sinks, with huge fluxes of net photosyn- the University of Freiburg in Germany. “You ant because they can reveal information not thesis and seasonal uptake, for example—but have an upper story of single trees that are captured by a sparse historical record, he the respiration that returns that gas to the allowed to grow for several understory gen- added. atmosphere is equally large, and there’s also erations.” These results were published in Scien- a large interannual variability.” That arrangement imprints a characteris- tific Reports (bit.ly/sustainable­ ​-forest­ ​ The research community is rising to the tic tree ring pattern in a forest’s upper story -­management). challenge. Brienen has been working with a trees (the “standards”): thick rings indicative “It’s nice to see the longevity and the his- group in France to incorporate tree longevity of heavy growth, which show up at regular tory of ­coppice-​­with-​­standards,” said Ian ­trade-​­off data in the Organising Carbon and intervals as the surrounding smaller trees are Short, a forestry researcher at Teagasc, the Hydrology in Dynamic Ecosystems land sur- cut down. “The trees are growing faster,” said Agriculture and Food Development Authority face model. “It only started quite recently, so Muigg. “You can really see it with your naked in Ireland, not involved in the research. This we don’t have any results to show yet,” eye.” technique is valuable because it promotes Brienen said. Muigg and his collaborators characterized conservation and habitat biodiversity, Short As more accurate climate models are still that dendrochronological pattern in 161 oak said. “In the next 10 or 20 years, I think we’ll in the works, researchers were unanimous trees growing in central Germany, one of the see more ­coppice-​­with-​­standards coming about one thing: We have to do more as a few remaining sites in Europe with actively back into production.” society to curb greenhouse gas emissions to managed ­coppice-​­with-​­standards forests. In the future, Muigg and his collaborators avoid further strangling natural carbon They found up to nine cycles of heavy growth hope to analyze a larger sample of historic uptake capacities. in the trees, the oldest of which was planted timbers to trace how the practice spread “We know what to do,” Tans said. “We can in 1761. The researchers then turned to a his- throughout Europe. It will be interesting to still have a good life while consuming a lot torical data set—over 2,000 oak timbers from understand where the technique originated less energy. Renewables technology is ready buildings and archaeological sites in Germany and how it propagated, said Muigg, and there to go. Furthermore, if we think about the and France dating from between 300 and are plenty of old pieces of wood waiting to be work it’ll take to reform our entire energy 2015—to look for a similar pattern. analyzed. “There [are] tons of dendrochrono- infrastructure, it’s really a jobs program.” logical data.” A Gap of 500 Years The team found wood with the characteristic By Meghie Rodrigues (@meghier), Science coppice-­ ​­with-​­standards tree ring pattern By Katherine Kornei (@KatherineKornei),

Writer dating to as early as the 6th century. Muigg Science Writer Opposite: iStock.com/Ja’Crispy

14 Eos // APRIL 2021 NEWS

The Influence of Tidal Forces​ Extends to the Arctic’s Deep Sea

rom more than 384,000 kilometers 3 days?” wondered Andreia ­Plaza-Faverola,​­ a away, the Moon’s gravity pulls at Earth project leader at Norway’s Centre for Arctic Fand its oceans, affecting activity even Gas Hydrate, Environment and Climate, and hundreds of meters below the sea surface. a coauthor of the study. “There are not many Oceanographers know that tides can affect things that could explain those peaks in the methane emissions that seep from the sea- pressure.” floor, and now a research team has shown The team compared its data with the tidal that this influence extends into the deep Arc- cycles and found an answer. The pore pres- tic. sure hundreds of meters below the ocean sur- face seemed to change with the tides, even Unexpected Findings though tidal height varied by just 1 meter. The team, led by Nabil Sultan, a geotechnics Through modeling, the group also saw that at Aboard the R/V Kronprins Haakon, scientists researcher at the French marine sciences low tide, when water column height decreased deployed piezometers to measure sediment proper- institute Ifremer, set out to the Arctic Ocean. by about 1 meter, the pressure in the water ties. Credit: Robin Hjertenes The team intended to measure the pressure column dropped, which the authors think and temperature of fluids within the sedi- allowed gas seepage through seabed frac- ments along the Vestnesa Ridge on the Sval- tures, whereas high tides seemed to reduce bard continental margin to see how geological both the height and the volume of methane (bit.ly/­arctic​-­methane​-­emissions), is that it processes in the area might affect that pres- emitted. shows there could be much more gas activity sure. The researchers chose two sites that “It is interesting to see with this data that than scientists are picking up with hydro- they expected wouldn’t have methane gas such small changes in pressure are affecting acoustic surveys, the traditional method for plumes, trying to avoid geologically active gas accumulations that are very close to the identifying methane emission sites. “They’re structures to learn about background sedi- seafloor,” said ­Plaza-​­Faverola. able to address what’s happening between ment properties. acoustic surveys, and what’s happening is a To get their measurements, the team really cool ­high-​­frequency change in meth- deployed a piezometer, a rodlike device that ane flux,” said Joel Johnson, a geology pro- can measure pressure within sediment pores, fessor at the University of New Hampshire. equipped with temperature sensors. Embed- The pore pressure “There might be more gas going into the ded 7 meters into the sediment of the Arctic hundreds of meters below ocean than we thought because of this tidal seabed, the device collected data for 4 days flux above faulted areas where there’s lots of before the researchers brought it back to the the ocean surface seemed free gas.” surface. They collected pore pressure and tem- to change with the tides, This study also highlighted the sensitivity perature measurements at two sites, one at of gas systems hundreds of meters below the 910 meters deep and another at 1,330 meters. even though tidal height surface. The findings suggested that a sea When the researchers got their data, their varied by just 1 meter. level rise of even 1 meter would be enough to first surprise was that the pressure readings affect the release of methane hundreds of suggested the presence of methane seeps. meters below. At these depths, the methane “We were not expecting to see any gas in the dissolves in water before reaching the sur- area,” said Sultan. face. In shallower areas (less than 50 meters Previous hydroacoustic surveys, the tradi- However, the scientists had only pressure deep), however, methane can reach the tional method used to detect these seeps from and temperature measurements and weren’t atmosphere. Future sea level rise could offset the local seabed, hadn’t shown the presence able to observe gas bubbles at the sites. In some of those emissions. of free gas. Because surveys can’t continu- future studies, the group is hoping to use “We’re not saying that the increase in ously monitor the seafloor, they can miss remotely operated vehicles to observe bub- water height is a good thing,” said Sultan. But signs of emissions that a piezometer stuck bles and see whether their release aligns with the pressure changes that will come with ris- in the sand for days can pick up. “With this the cycles identified in this study. The find- ing waters merit more investigation. “We monitoring method, we were able to show ings are also limited to two sites and data need to consider how pressure will impact that the extension of the area where we have recorded over a few days, and the team hopes this gas system.... It’s urgent today to go degassing is much [larger] than what we’re to collect data at more locations at longer study in more detail the shallowest areas in observing with classical methods,” said Sul- timescales to see how generalizable the pres- the Arctic or in areas where you have high tan. ent findings might be. concentrations of gas and gas hydrates.” The team’s next surprise was that the amount of methane released from the sedi- Sensitive and Elusive Seeps ment seems to fluctuate throughout the day. One of the most notable consequences of the By Jackie Rocheleau (@JackieRocheleau),

Opposite: iStock.com/Ja’Crispy “Why can we see so much change within research, published in Nature Communications Science Writer

SCIENCE NEWS BY AGU // Eos.org 15 NEWS

This Search for Alien Life Starts with Destroying Bacteria on Earth

ometimes it takes a little destruction of larger organic molecules, said Waite, who to unlock the secrets of the universe. is also a coinvestigator on the instrument. S In a lab at Imperial College London, That way, scientists will be able to study Tara Salter used high temperatures to destroy exactly what material is coming out of the samples of bacteria and archaea, leaving plumes. behind molecular fragments. With this pyrol- ysis process, Salter attempted to simulate Flying Through Plumes…in the Lab what might happen to molecules that smash To simulate a spacecraft’s flight through into a spacecraft like bugs on a windshield. Europa’s plumes, Salter heated specimens of Specifically, Salter simulated a spacecraft extremophile bacteria in a special chamber to flying through the ­geyser-​­like plumes of the 650°C, which mimics the destructive force of outer solar system’s ocean moons. Scientists smashing into a spacecraft. The heat destroys have observed plumes spouting from the icy the molecules to some extent, and what’s left shells of both Saturn’s moon Enceladus is a smorgasbord of fragments. Salter then and Jupiter’s moon Europa—and they want analyzed fragments with her lab’s mass spec- to send spacecraft through those plumes trometer and created a catalog. to investigate what kinds of molecules are “You can simplify a bacteria into proteins, being ejected from the extraterrestrial oceans carbohydrates, and lipids,” among other below. things, Salter said. In her analysis, she found Any molecule colliding with a spacecraft fragments of amino acids; fatty acid chains flying at speeds of several kilometers per sec- that make up lipids; and molecules contain- ond would be “smashed to smithereens,” ing oxygen, hydrogen, and carbon from the Salter said. carbohydrates. Even if microbes are part of plume ejecta, After analyzing the fragments, Salter cre- sampling spacecraft likely won’t be able to NASA’s Europa Clipper, set to launch in 2024, will ated a library of molecular signatures—one observe entire organisms—just bits of them. study Jupiter’s icy moon Europa. Credit: JoAnna she hopes to expand and share with fellow “Being able to put back together the organism Wendel scientists. from detecting small parts is the big aim” of “Work like this can help us unlock hidden her research, Salter said. She hopes that her gems in previous data sets like the measure- ­smashed-​­up bacteria samples, and the ments Cassini made of the Enceladus plume molecular fragments they leave behind, will water vapor spewing from Enceladus’s south and will also help us inform future measure- help future scientists investigate the possi- pole. Cassini didn’t discover just water mol- ments by missions designed to search for life bility of life on one of these ocean worlds. ecules in the plume—there also seemed to be in these alien oceans,” said Morgan Cable, a Salter presented the research at AGU’s Fall fragments of organic molecules clinging to planetary scientist at NASA’s Jet Propulsion Meeting 2020 (bit​.ly/­life-­on​-­icy​-­moons). the speeding grains of ice. Laboratory in Pasadena, Calif., who wasn’t But Cassini’s instruments weren’t designed involved in the research. to distinguish between large organic mole- However, “we also need to keep in mind cules, said Hunter Waite, a program direc- that we might encounter only trace amounts tor of mass spectrometry at the Southwest of life, where that biosignature spectrum “Being able to put back Research Institute in San Antonio. could be hidden underneath a strong abiotic together the organism from Now that we know that a future spacecraft signature,” she said. needs to be able to detect large, complex Salter has more plans for destruction. She detecting small parts is the organics, NASA is prepared. The agency's wants to destroy bacteria cells using ultravi- big aim.” next mission to the outer solar system, olet radiation—to mimic the surface of Europa Clipper, will study another moon that Europa—and to heat up the cells in the pres- contains a liquid water ocean, Jupiter’s satel- ence of water to see how water affects what lite Europa. Numerous observations from the molecules get left behind. Galileo spacecraft and the Hubble Space Tele- From the dust of pulverized bacteria, sci- Far-Away Oceans scope indicate that like Enceladus, Europa entists hope to compile a complete library of Back in 2005, NASA’s Cassini spacecraft made sports plumes shooting from its surface. molecular fragments that can help identify a spectacular discovery: Underneath many Whether those plumes originate in the life on another world. kilometers of ice on Saturn’s moon Enceladus moon’s internal ocean or in a subsurface res- churned a vast ocean of liquid water. Cassini ervoir remains to be seen. discovered this ocean almost by accident Europa Clipper’s mass spectrometer will be By JoAnna Wendel (@JoAnnaScience), Science when it flew through ­geyser-​­like plumes of able to detect and determine the composition Writer

16 Eos // APRIL 2021 NEWS

Terrestrial Plants Flourished After the ­Cretaceous–​ ­Paleogene Extinction

t first glance, Chambery Coulee might This finding aligns with previous research look like any other valley in the vast on prehistoric pollen samples, which showed A prairies of southern Saskatchewan. an increase in angiosperm (flowering plant) But for Robert Bourque and his colleagues at pollen, especially species similar to today’s McGill University in Quebec, Chambery Cou- birch and elm trees, in the time following the lee is a window into the deep past, a place that extinction event. holds the secrets of the mass extinction that Researchers also analyzed the carbon and ended the age of the dinosaurs 66 million hydrogen isotopes in the n­ -​­alkanes, which years ago. allowed them to reconstruct changes in the Their recent study uses compounds in carbon cycle and the water cycle. In contrast plant waxes to shed new light on how plant to the long-­ term​­ changes in plant communi- communities, the water cycle, and the carbon ties they observed after the extinction event, cycle changed after the ­dinosaur-​­killing the team did not find obvious long-­ ​­term Chicxulub asteroid impact, which marked the changes in precipitation or the carbon cycle end of the Cretaceous period and the begin- subsequent to the event. ning of the Paleogene (bit.ly/­terrestrial​ So what was responsible for the long-­ ​ -ecosystems).­ Bourque, who received his ­lasting changes in plant ecology? Researchers master of science degree from McGill and is hypothesized that this burst of terrestrial now a Ph.D. student at Rensselaer Polytech- plant abundance was due to another factor: nic Institute in New York, said, “Plant waxes the sudden disappearance of the dinosaurs. provide a unique opportunity in looking With just about every large terrestrial herbi- through certain lenses at the global ecosys- vore wiped from the face of Earth, terrestrial tem at the time, since plant waxes record plants flourished. atmospheric [carbon dioxide] as well as the hydrogen derived from rainfall. So we’re able to use them as proxies for looking at these Frenchman Valley in Chambery Coulee, Saskatche- environmental signatures.” wan, above, was one of the sites at which research- Even though it is now widely accepted that Chambery Coulee is a ers traced changes in plant ecology following the the asteroid impact was the root cause of the window into the deep past, Chicxulub impact event. Credit: R. D. Bourque extinction event, the specific mechanism (or mechanisms) by which the impact wiped out a place that holds the the majority of all plant and animal species secrets of the mass on Earth is still not fully understood. Studying Bourque had similar thoughts. “Looking at environmental changes that took place extinction that ended a finer scale across the boundary would be around the time of the impact may help sci- extremely interesting, to try and better esti- entists figure out the answer. the age of the dinosaurs mate what happened over what time period,” 66 million years ago. he said. “And broadening the scope to other Changing Ecosystems sites from the same time period would be Bourque and his colleagues analyzed leaf wax incredibly interesting.” n-​­alkanes (a type of hydrocarbon) that had MacLeod said there’s a lot of interest in been preserved in ancient fluvial sediments in improving our understanding of this time Chambery Coulee and another site near Sas- Next Steps period, especially because “the ­Cretaceous-​ katchewan’s Highway 37 to learn more about Ken MacLeod, a geology professor at the Uni- ­Paleogene impact is, I think, literally the only how the world changed. These leaf wax com- versity of Missouri, said he would like to event in the Phanerozoic [the past 541 million pounds, Bourque said, “come in a variety of... see the paper’s line of inquiry expanded to years] with ­global-​­scale implications that chain lengths, and different types of plants include more samples, across both time and manifest on timescales shorter than anthro- produce different ratios of these chain lengths. geographic space. More samples from the pogenic changes.” Studying how Earth sys- Typically, aquatic plants will produce shorter time period would help provide greater reso- tems responded to perturbations in the past, chain lengths, whereas terrestrial plants pro- lution of exactly when these environmental MacLeod said, might help us understand the duce longer ones.... So we noticed that there’s changes occurred, whereas more samples response of these systems in the present, a shift from more ­shorter-​­length plant waxes from around the world would help determine which is also a period of rapid change. to longer ones going across the boundary.” how widespread this phenomenon was—did This change implies that terrestrial plants it occur only in southern Saskatchewan, were becoming more abundant compared with across all of North America, or even perhaps By Hannah Thomasy (@HannahThomasy), aquatic plants after the extinction event. around the entire planet? Science Writer

SCIENCE NEWS BY AGU // Eos.org 17 OPINION

Student-Led Diversity Audits: A Strategy for Change

he underrepresentation of ethnic minorities throughout the geosciences Tis well documented and just as true at the University of Oxford in the United King- dom as it is anywhere else. A 2019 report from the university noted that although admission of students from minoritized racial and ethnic backgrounds was disproportionally low ­university-​­wide, the Department of Earth Sciences admitted the lowest proportion of Black and non-­ Asian​­ ethnic minorities—half as many as the next lowest department. Many frameworks for addressing repre- sentation issues shift a disproportionate amount of responsibility to members of these groups by expecting them to both identify and solve the issues they raise. This “minority tax” can unintentionally exacerbate the prob- lems that these initiatives seek to address.

Shifting the Burden of Developing Solutions In response to this admissions report and the widening attention being paid to issues of diversity in higher education, a group of grad- uate students from the Department of Earth Sciences at Oxford initiated a ­student-​­led The Radcliffe Camera, originally built to house a science library, is a symbol of the University of Oxford, where diversity audit. geoscience students conducted an innovative diversity audit. Credit: Benjamin Fernando Our aim in executing this audit was to empower students in our community to raise issues that they saw or experienced at the university that burdened ethnic minority stu- might be harder to reach conclusive actions presented our report to department faculty dents, without the expectation that those strictly from the data provided by surveys; and invited them to respond. students would be required to enact the solu- instead, we organized focus groups, which tions themselves. Instead, our team would would allow for more nuanced discussion and Key Themes from the Audit assess the responses and offer suggestions to immediate feedback. In June 2020, around 200 geoscience students the faculty with some direction for how they Our main focus group, which took place and faculty from Oxford and the U.K. commu- could implement each solution. Key to this over part of an afternoon, was open to all stu- nity attended our announcement and discus- plan was engaging white students to assist dents and faculty within our department. sion of the report and its findings. The event with brainstorming and developing ideas and About 20 people attended, from undergrad- was held virtually and included the head of in making an extra effort to encourage fellow uates to professors. The first half of the ses- our department, as well as representatives allies to attend. sion was spent on identifying problems; the from the Geological Society of London and the We approached this effort from the point second half was dedicated to identifying solu- Royal Astronomical Society. of view of concerned graduate students, tions. We followed this session with some After presenting our results, an attendee rather than experts in diversity, equity, and small-group and ­one-​­on-​­one discussions asked us to identify three key messages. inclusion. As such, we offer this as an exam- to develop specific ideas and address prob- Although our key messages are well known to ple of an experimental project, which has lems related to a particular incident that a those pursuing more diversity in the geosci- sparked progress from our department so far. participant did not want to air in a bigger ences, our audit provided specific supporting group. examples that helped lead us toward solu- Organizing the Audit Through From these discussions, we identified tions at our university. Focus Groups 42 specific recommendations for addressing The first key message is that the geosci- Early on, we decided to rely on qualitative the lack of representation of minoritized stu- ences’ ethnic minority student populations rather than quantitative methods for identi- dents within the Department of Earth Sci- are not homogeneous—as a result, neither fying issues. In a community with so few ences at Oxford. Each recommendation are the challenges they face, nor the solu- BAME (U.K. terminology for Black, Asian, and included a description of the rationale for the tions. For example, the underrepresentation minority ethnic) students, anonymization of action, our suggestion on each action’s prior- of Black British students at Oxford can be responses is impossible. We also thought it ity, and a recommended timeline. Finally, we traced to a disproportionately low percentage

18 Eos // APRIL 2021 OPINION

of Black applicants compared with the U.K. that directly addresses some of these con- Faculty Responses population. British students of Indian heri- cerns—such as emphasizing the technology Although faculty were invited to our working tage, however, apply in roughly the same per- and coding skills required of many geoscience groups, our group of students sequestered to centage as exists in the national population careers. write the report. Our suggestion for students but are admitted at lower rates than white or Universities should also be cognizant of stu- looking to replicate this process at their own Black applicants with equal qualifications. dents applying from communities that have schools is to lay some more groundwork with Addressing low admissions, then, requires a politically or historically fraught relationship faculty, such as requesting a private meeting targeted solutions. For Black students, that with geological industry, such as England’s with university leadership before presenting might mean focusing on outreach and com- Black Country or Indigenous communities the report publicly. This interaction can help munity engagement strategies that acknowl- in the United States. These students may reject ensure that the report launch is seen as an edge underlying discrimination in the school- or at least be discouraged from pursuing the opportunity to develop new collaborations ing system [­Joseph-​­Salisbury, 2020]. For geosciences as a topic of study. We recom- rather than a time to criticize existing efforts. British Indian students, it likely means thor- mend that schools seek more input from these In our discussions with faculty about the oughly examining the admissions process communities and find ways to showcase geo- report, we were quickly able to find many for biases. science careers on the other end of the spec- places to work together on the 42 actions we The second message is that inclusion trum from natural resource extraction. suggested. The department wrote a ­point-by-​­ ​ efforts help everyone. Although our work ­point reply just 2 weeks after our report was focused on students from ethnic minorities, Fieldwork Shouldn’t Always Require released, publishing it on the school’s website we were able to identify the commonalities a Field alongside our original report. It highlighted a that different minoritized groups face. The challenges and risks of fieldwork are number of items that as of last July had been Finally, the idea that diversity is important many when it comes to minoritized stu- initiated or were already underway. For those to recruitment while inclusion is important dents—whether racial or ethnic minorities, that the department considered unfeasible, it to retention is partially true but overly sim- offered detailed explanations. plistic. The separation here neglects many These are just first steps, of course. We of the crossovers between these concerns. For were able to propel these discussions into a example, students who feel excluded while dedicated town hall at AGU’s Fall Meeting obtaining their undergraduate degree will In our discussions with 2020 to discuss the report and its methodol- be more challenging to recruit to postgradu- faculty about the report, ogy. Overall, we are encouraged by the ate education. responses to our diversity audit at Oxford and These broader themes led us to our 42 rec- we were quickly able to optimistic that we have begun a fruitful col- ommendations—including the following two find many places to work laboration with the faculty to continue to that are focused on adaptations of recruit- address these issues. ment and fieldwork. together on the 42 actions we suggested. Acknowledgments Recruitment Should Take Cultural The author is first and foremost grateful for Context into Account Gwen Antell’s partnership in developing this Many of us are guilty of assuming that the audit and her invaluable advice in conduct- only significant barrier to increased univer- ing the focus groups and writing the text of sity admissions of minoritized groups in geo- women, LGBTQ+ people, or those with dis- the report. The efforts of the University of science majors is a lack of awareness of the abilities. Reduced familiarity with the out- Oxford’s Chris Ballentine, Isobel Walker, and field. It’s reassuring to think that simply doors has been discussed as one—though Conall MacNiocaill in preparing the depart- more dedicated outreach and engagement certainly not the only—reason for reduced ment’s response are also deeply appreciated, will be enough to boost the diversity of participation in the geosciences by ethnic as are the inputs of all those who participated future classes. minorities, who are much more likely in the in our focus groups. I am also grateful to The reality is more complex. Some fami- United Kingdom to be urban based [Giles et al., Rebecca Colquhoun for her support in syn- lies—particularly first-­ generation​­ immigrant 2020]. This is an underlying problem that thesizing ideas for this article. families that want a more financially secure universities are not realistically in a position future for their children—may not see the to address. References geosciences as offering as much job security What universities can do, however, is put Giles, S., et al. (2020), Barriers to fieldwork in undergraduate geoscience degrees, Nat. Rev. Earth Environ., 1, 77–78,­ https://​ as more traditional careers in medicine more effort into highlighting the relevance doi­ .​ org/­ 10.1038/​­ s43017​­ -​ 020­ -​ 0022-5.­ or law. Furthermore, they may see the Earth of the geosciences to urban populations. This ­Joseph-Salisbury,​­ R. (2020), Race and racism in English second- sciences as requiring skills that are niche might be done through discussions of ary schools, Runnymede, London, bit.ly/­ runnymede​­ -​ racism-­ in­ ​ -secondary­ -​ schools.­ rather than broadly transferable. the geoscience contributions to climate In our report, we suggest that the univer- change solutions and the United Nations’ sity address these concerns in several ways, Sustainable Development Goals. But it can including holding separate ­parents-​­only also be done more practically, for example, by By Benjamin Fernando (benjamin­ ​.fernando@­ ​ and ­students-​­only sessions to encourage highlighting work in urban geology or the seh­ .​ ox­ .​ ac.uk),­ University of Oxford, Oxford U.K. questions on unfamiliar subjects with less applications of civil geophysics and urging fear of embarrassment. We also recommend the development of urban fieldwork in uni- u Read the article at ­bit.ly/​­Eos​ producing an application guide for parents versity courses. -diversity­ -​ audits­

SCIENCE NEWS BY AGU // Eos.org 19 OPINION

GeoPRISMS: A Successful Model for Interdisciplinary Research

n 1988, 65 scientists from a wide range of ­GeoPRISMS (Geodynamic Processes at Rifting duction zone for the SCD initiative. Scientists disciplines gathered in a meeting room in and Subducting Margins), to carry on the mis- engaged in ­GeoPRISMS research addressed IIrvine, Calif., to discuss ways to advance sion of ­MARGINS to foster collaborative, five science themes that encompass com- their understanding of the complex Earth ­shoreline-​­crossing science. The scope of monalities among continental margin pro- systems called continental margins. These ­GeoPRISMS, which began in 2010 and will cesses: the origin and evolution of conti­ 57 men and 8 women shared a visionary idea: last through this year, expanded beyond nental crust; fluids and melts and their What if the Earth sciences and the ocean sci- ­MARGINS to address novel scientific ques- interactions; ­tectonic–​­sediment–​­climate ences, two fields that were traditionally inde- tions with direct societal impacts—such as interactions; geochemical cycles; and plate pendent and funded separately—and divided questions related to understanding geo- boundary deformation and geodynamics. by that nebulous boundary that is the shore- logic hazards and managing coastal environ- This article provides a glance at some line—could be connected? What if terrestrial ments—and to include study of inactive and of the distinctive elements of ­GeoPRISMS and marine geoscientists had a better way to exhumed margins as well as the role of surface that have enabled fundamental advances in share knowledge, communicate ideas, and processes in the evolution of continental mar- scientific understanding while also contrib- establish new approaches to investigate the gins. The program would also expand engage- uting to building a strong, vibrant research active geological processes shaping continen- ment of early-­ ​­career scientists to increase community. tal margins? From that meeting, the concept diversity and inclusion in these fields. of an interdisciplinary, integrative, amphib- Supporting the Next Generation ious research program took shape. More than of Geoscientists 30 years later, those of us who have been A strength of ­GeoPRISMS has been its stead- involved in the process are proud to look back GeoPRISMS addressed novel fast support of early-­ ​­career researchers on the success born of this idea. and their professional development through Following that 1988 meeting, it took more scientific questions with a range of experiential and educational activ- than a decade of planning before the first direct societal impacts, such ities. ­Early-​­career scientists—defined here iteration of this effort, called ­MARGINS, got as undergraduates, graduates, postdocs, under way. MARGINS­ launched in 2000 and as questions related to assistant researchers, and pretenure faculty was jointly funded by the National Science understanding geologic members—have had a central place within Foundation (NSF) Earth Sciences and Ocean hazards and managing the program and have been heavily engaged Sciences divisions. The program started small in planning processes and research projects. but quickly gained momentum with a cohort coastal environments. They have received financial support to attend of geophysicists, geochemists, volcanolo- ­GeoPRISMS meetings and workshops and gists, and sedimentologists all eager to invitations to lead breakout groups, convene develop a common language and work toward workshops, and present keynote lectures. the same goals. The range of data collected The ­GeoPRISMS science plan included two Since 2010, 300 ­early-​­career researchers through MARGINS­ and, more important, the broad initiatives: to study Rift Initiation and have received networking support and back- integration of those data have transformed Evolution (RIE) and Subduction Cycles and ground training at premeeting symposia our knowledge of subduction zones and rifts. Deformation (SCD). The initiatives targeted in preparation for subsequent discussions In 2009, NSF acknowledged the success of active and passive margins at five primary at planning and implementation meetings ­MARGINS in its Decadal Review and indicated sites around the world: the Eastern North that might otherwise have been overwhelm- it would support a continuation of these American Margin and the East African Rift ing. Student competitions held each year efforts. The community came up with a System for the RIE initiative; and Cascadia, during the annual GeoPRISMS­ town hall event ­10-year plan for a successor program, called New Zealand, and the Alaska–­ ​­Aleutian sub- at AGU’s Fall Meeting gave exposure to the research of more than 200 students, who had chances to network, engage with peers, and meet NSF representatives. ­GeoPRISMS has also supported 14 postdoc- toral researchers in conducting up to 2 years of multidisciplinary research at U.S. institu- tions. These scholarships encouraged indi- viduals to further develop research skills, diversify their expertise, and establish peer relationships. The scholarship program has proven successful: Everyone who completed their postdoctoral appointment has since Participants in the GeoPRISMS Subduction Cycles and Deformation Initiative met to discuss research progress in moved into subsequent faculty or research Redondo Beach, Calif., in 2015. Credit: Anaïs Férot, GeoPRISMS positions.

20 Eos // APRIL 2021 OPINION

­GeoPRISMS has funded a number of large, The benefits of the DLP went beyond shar- of accomplishments (bit​.ly/GeoPRISMS­ ​ ­long-​­duration data collection efforts called ing programmatic updates. The lecture -­volume). This issue of Eos highlights several community projects, including the Cascadia series offered opportunities for students to efforts that have led to discoveries made Initiative, the Alaska Amphibious Commu- interact with experts and be exposed to via the ­GeoPRISMS subduction and rift initia- nity Seismic Experiment, and the Eastern unfamiliar areas of science and research. In tives, communicating the breadth and impor- North American Margin Community Seismic conjunction with their lectures, DLP speak- tance of the program’s science to a broad audi- Experiment. Data sets from these projects ers often set aside time to meet with stu- ence. have been made publicly available immedi- dents and answer questions regarding career Two decades of collaboration through the ately, and many projects have been funded and research opportunities, in some cases MARGINS and ­GeoPRISMS programs have subsequently to use those data. stimulating students’ interest—and infusing forged solid relationships between NSF’s a sense of possibility—in pursuing alterna- Ocean Sciences and Earth Sciences divisions. tive paths in science. In its 2020 report about the future of the NSF The DLP also helped improve representa- Division of Earth Sciences, the National Acad- tion of women in science, technology, engi- emies of Sciences, Engineering, and Medicine The Distinguished neering, and mathematics (STEM) fields: As (­NASEM) recognized the potential of research Lectureship Program offered highlighted in feedback from host institu- connecting terrestrial and ocean environ- opportunities for students to tions and attendees, exposure to success- ments to advance knowledge about many ful female scientists discussing their accom- key research topics, such as the dynamics interact with experts and be plishments inspired female ­early-​­career of Earth’s interior and mitigating risks from exposed to unfamiliar areas researchers to pursue education in the geo- earthquakes, eruptions, and tsunamis. And sciences. The program extended the reach ­NASEM encouraged efforts in the scientific of science and research. and inclusiveness of ­GeoPRISMS science community to further support interdis­ as well by bringing ­high-​­caliber speakers ciplinary research that capitalizes on connec- to institutions that were geographically iso- tions across divisions at NSF. lated, such as in Hawaii and Puerto Rico, The grassroots efforts that have stressed Expeditions associated with the commu- or that had little or no budget to bring in guest the importance of decisionmaking by nity experiments, from marine seismic data speakers. Such visits helped spur new collab- a research community, rather than by only a acquisitions to onshore field campaigns, pro- orations, strengthen professional networks, handful of scientists, have allowed ­GeoPRISMS vided unique opportunities for ­early-​­career and inspire new avenues of research and com- to lead the way among peer research pro- scientists to receive training, gain experi- munication among students, other ­early-​ grams, such as the late NSF ­EarthScope pro- ence, and develop skills in interdisciplinary ­career scientists, and more established gram, in defining and carrying out community science. Hundreds of researchers have par- researchers. experiments and expeditions. GeoPRISMS­ ticipated in all aspects of onboard and field effectively brought together and trained science activities, including instrument The Legacy of GeoPRISMS a broadly interdisciplinary group of scientists preparation, deployment, and recovery; data As ­GeoPRISMS comes to a close after its run to be the next generation of practitioners acquisition and processing; and live commu- of more than 10 years, the time is right to in a highly collaborative culture. nicating about research efforts. consider its legacy and look ahead to work As revealed by current ­GeoPRISMS demo- still to be done to advance geoscience under- graphics, the program has also fostered Raising Geoscience Awareness standing and further develop a diverse com- a research community balanced with respect ­GeoPRISMS developed and maintained an munity of researchers. to gender and career status. These same Education & Outreach program geared toward ­GeoPRISMS executed the vision of an inter- demographics also reveal, however, that engaging the wider science community and disciplinary program while demonstrating there is still much work to be done within the the public. The ­GeoPRISMS Distinguished the value of science driven by a community geosciences to address long-­ ​­standing ineq- Lectureship Program (DLP), for example, of researchers. The program has supported uities and shortcomings in represen­tation played an instrumental role in disseminating a wide range of integrated research approaches and inclusivity. Research programs built upon new findings and illustrating the depth and and leveraged strong international collab­ ­GeoPRISMS’s successful model should lead breadth of the program. orations, thereby developing fundamental the way in developing best practices to Starting in 2010, the DLP sponsored 10 lec- understanding of ­shoreline-​­crossing Earth attract, train, and retain BIPOC­ (Black, Indig- ture series articulated around GeoPRISMS­ systems and their importance in global pro- enous, and people of color) students and research topics. Through the program, cesses, as well as of resource distribution and scholars. This is an essential shift to ensure 36 scientists from a wide range of disciplines geohazards. The ­high-​­quality data sets col- that the geosciences become and remain truly and career levels—half of them women— lected by GeoPRISMS­ investigators are just, inclusive, equitable, and diverse. traveled across the United States to share appropriately cataloged, archived, and acces- with public audiences the ­cutting-​­edge sci- sible to the community to support and pro- ence they conducted through ­GeoPRISMS. All mote the principles of findable, accessible, By Anaïs Férot (­axf303@psu​­ .​ ­edu), GeoPRISMS told, 226 institutions, from ­moderate-​­sized interoperable, and reusable (FAIR) data and to Office, Pennsylvania State University, University community and liberal arts colleges to muse- establish a robust data legacy. Park ums and public venues, hosted DLP speakers, ­GeoPRISMS researchers have been synthe- and more than 10,000 people have attended sizing the resulting science products to be com- u Read the article at ­bit.ly/​Eos​ these lectures. piled in a special volume celebrating a decade -GeoPRISMS­

SCIENCE NEWS BY AGU // Eos.org 21 22 Eos // APRIL 2021 Geodetic observations collected during back-to-back decadal research campaigns have revealed crucial new insights into the start–stop and slow-motion behavior of subduction zones. SLIPPING AND LOCKING IN EARTH'S EARTHQUAKE FACTORIES

By Noel Bartlow, Laura M. Wallace, Julie Elliott, and Susan Schwartz

Downtown Anchorage, Alaska, was devastated by shaking during the ­second-​­largest earthquake ever recorded, which occurred along the ­Alaska–​­Aleutian subduction on 27 March 1964. Credit: Everett Collection Historical/Alamy Stock Photo

SCIENCE NEWS BY AGU // Eos.org 23 hat do 1952, 1960, 1964, 2004, geodesy, a field focused on measuring subtle which may in turn trigger further earth- and 2011 have in common? In displacements of Earth’s surface. Geodetic quakes. each of those years, a cata- studies enable delineation of locked por- The study of slow-­ ​­slip behavior is still strophic subduction zone tions of subducting plate interfaces in young and we do not yet fully understand earthquake and tsunami—col- unprecedented detail and have revealed all the possible interactions between ­slow-​ W lectively the five largest earth- regions in many subduction zones world- ­slip and regular earthquakes, but recent quakes ever recorded—occurred somewhere wide where future large earthquakes may observational advances have led to great around the world. Subduction zones, where nucleate. progress. Much of this progress was one tectonic plate dives below another in During interseismic periods, subduction spurred by the National Science Founda- fits and starts on its way into Earth’s man- zones are not static but, rather, host a vari- tion’s (NSF) ­GeoPRISMS (Geodynamic Pro- tle, create the largest and most destructive ety of smaller, ­slow-​­slip events (SSEs) cesses at Rifting and Subducting Margins) earthquakes and tsunamis on our planet. [Schwartz and Rokosky, 2007, and references program (­2010–​­2021) and its predecessor, Revealing the dynamics of how subduction therein], the discovery of which in the late the ­MARGINS program (­2000–​­2010). Both zones slip and the factors that influence 1990s provided a new perspective on the programs supported studies of subduction them is crucial in assessing the hazards they mechanics of subduction zones. SSEs zones off Costa Rica, Nankai (Japan), Cas- represent. involve a few to tens of centimeters of slip cadia, Alaska, and New Zealand. Together In the time between large earthquakes, along a plate interface over days to years, these locales exhibit virtually every known called the interseismic period, the interface rather than over the seconds to minutes flavor of subduction slip behavior, between downgoing and overlying plates timescales of regular earthquakes. Imaged megathrust locking characteristics, and can become locked due to friction, accumu- using high-­ precision​­ geodesy, SSEs are subduction margin physical properties lating stresses for hundreds of years or essentially ­slow-​­motion earthquakes that (e.g., rate of plate convergence, amount of more, most of which will ultimately be do not create damaging seismic waves or sediment input, age of subducting plate, released in future earthquakes (Figure 1). tsunamis. However, because SSEs add stress etc.). This variety has provided outstand- Our understanding of subduction zone slip to locked fault zones, they may trigger dam- ing opportunities to resolve the physical behavior has been transformed over the aging earthquakes, as has been suggested in processes leading to slow slip and to large past 2 decades, thanks in large part to the the cases of the 2011 ­Tohoku-​­Oki earth- megathrust earthquakes and to investigate advent of ­high-precision​­ Global Navigation quake in Japan and Chile’s 2014 Iquique relationships among SSEs, subduction Satellite Systems (GNSS; GPS is one of four earthquake [Ito et al., 2013; Socquet et al., plate interface locking, and large earth- GNSS systems) and other techniques from 2017]. Earthquakes can also trigger SSEs, quakes.

Fig. 1. Geodetic measurements that can be made at subduction zones to discern megathrust locking and slip behavior include those from Global Navigation Satellite Sys- tems (GNSS), synthetic aperture radar (SAR), absolute pressure gauges (APGs), and borehole instruments (such as the Circulation Obviation Retrofit Kit, or CORK, offshore borehole instrument). The graph at bottom right shows an example of a continuous GNSS site time series of subduction zone slip affected byslow- ­ ​­slip events (SSEs, marked with shaded blue bars). Typical megathrust behavior is shown, but specific behavior at subduction zones globally can vary from what is represented here.

24 Eos // APRIL 2021 Here we highlight examples of progress Rica was one of the first regions chosen as a GPS/GNSS data from southern Cascadia in our understanding of slip behavior at the focus site for the program. With support have revealed a newly identified phenome- five subduction zone focus sites of the NSF from ­MARGINS, GPS/GNSS and regional non of offshore earthquakes triggering programs. seismic observations covering the Nicoya changes in plate interface locking [Materna Peninsula began in 1999 and continue today. et al., 2019], raising the possibility that plate The Nankai Trough These 2 decades of instrumental coverage locking varies in time, even during inter- This subduction zone off southwestern captured the most recent large earthquake, seismic periods. This observation chal- Japan has a long history of producing great a magnitude 7.6 event on 5 September 2012, lenges the common assumption that inter- earthquakes (magnitude > 8.0). Numerous allowing the late interseismic period lead- seismic locking is temporally steady and ­Japanese-​­led geodetic studies have indi- ing up to the event, as well as the coseismic motivates a need to monitor locking in sub- cated that the subduction interface in the and postseismic phases of the earthquake duction zones for potential changes over source region of past great earthquakes cycle, to be well recorded. time. along the Nankai Trough is currently Geodetic observations during the late Geodetic data have also revealed that locked, suggesting that elastic strain interseismic phase led researchers to iden- like the Nankai subduction zone, the accruing right now will be relieved in tify a region of the plate interface that Cascadia subduction zone features deep future megathrust earthquakes. Studies at appeared frictionally locked and that subse- SSEs that are strongly Nankai have benefited from seafloor quently matched closely with the area that associated with tec- GNSS-­ Acoustic​­ sensors that enable ruptured during the 2012 Nicoya earthquake tonic tremor [Rog- centimeter-­ level​­ resolution of horizontal [e.g., Protti et al., 2014]. However, areas of ers and Dragert, movements of the seafloor. These move- the plate interface that experienced SSEs 2003]. The ments reveal the degree of shallow locking prior to the 2012 earthquake did not rupture influence of near the trench, and tracking them will during the main shock [Dixon et al., 2014]. If these inform tsunami hazard assessments in this behavior is characteristic of other sub- SSEs and future earthquakes. duction zones, it suggests that better moni- tremor The Nankai Trough is also the site of a toring of SSEs could provide valuable infor- on the diverse range of geodetically detected SSEs, mation for earthquake and tsunami timing many of which are accompanied by tectonic forecasting. of tremor that largely occurs downdip of (i.e., large deeper along the plate interface) the Cascadia Subduction Zone ­earthquake-​­producing seismogenic zone, Large earthquakes occur every few hundred which is locked between earthquakes (Fig- years in the Cascadia subduction zone, most ure 1). Tectonic tremor is a ­low-​­amplitude, recently in January 1700. Geodetic models ­long-​­duration seismic signal that is broadly agree on the presence of a strongly depleted in ­high-frequency​­ energy com- locked zone located mainly offshore in the pared with typical earthquakes. Some of region where past earthquake ruptures are these SSEs are shorter, lasting a few days to inferred to have occurred. How close to the weeks, while others last a year or more surface this locking extends, which will sig- [Hirose et al., 2010]. Recently, observations nificantly influence the size of future tsu- from instrumented seafloor boreholes namis, is poorly determined, thus limit- revealed episodic SSEs near the trench, ing scientists’ ability to forecast hazards. updip of (i.e., shallower than) the locked The GeoPRISMS program has enabled seismogenic zone [Araki et al., 2017]. Poten- installation of ­GNSS-​­Acoustic sites tial triggering relationships between these offshore Cascadia that should soon SSEs and earthquakes are not yet clear, and help answer this question, delin- continuing studies—for which Japan is well eating the updip limit of lock- equipped—will be important in establish- ing. Meanwhile, onshore ing what, if any, relationships exist.

The Middle America Trench This rapidly converging subduction zone is responsible for generating earthquakes of magnitude 7 and greater about every 50 years beneath the Nicoya Peninsula, Costa Rica [Protti et al., 2014]. Because of the regularity of large earthquakes here, the presence of land very close to the trench, and the presumption that the region was late in its earthquake cycle when the ­MARGINS program was getting under way, Costa

SCIENCE NEWS BY AGU // Eos.org 25 earthquakes is unclear and deserves further study.

The Alaska–Aleutian Subduction Zone The ­second-​­largest earthquake ever recorded, the magnitude 9.2 Prince William Sound earthquake of 1964, occurred on this subduction zone, which has since generated other events of magnitude ­7–8 and greater. Geodetic studies have revealed strong lock- ing in areas that slipped during the 1964 earthquake [e.g., Li et al., 2016; Elliott and Freymueller, 2020]. Some areas that slipped less during the 1964 event appear to be par- tially locked or continuously slipping today, suggesting that some locked patches may persist through multiple earthquake cycles. SSEs also occur along the Alaska subduc- tion zone, generally as multiyear events downdip of the locked zone, although at Spahr Webb (standing) and Pete Liljegren from Columbia University’s ­Lamont-​­Doherty Earth Observatory do final least some of these seemingly long SSEs checks on an APG/ocean bottom seismometer instrumentation package for a 2018 deployment offshore New may comprise bursts of multiple shorter Zealand’s Hikurangi subduction zone. Credit: Neville Palmer, GNS Science subevents [Li et al., 2016; Rous- set et al., 2019]. As with other subduction zones, the updip extent of three seafloor ­GNSS-​­Acoustic sites, which earthquake [Wallace et al., 2018]. Absolute locking is poorly offer improved resolution of shallow lock- pressure gauges (APGs) deployed on the resolved because ing during the period leading up to the 2020 seafloor near the northern Hikurangi mar- of a lack of sea- magnitude 7.8 Simeonof earthquake. gin recorded centimeter-­ scale​­ vertical floor data. A deformation during these SSEs, revealing recently The Hikurangi Subduction Zone that SSEs can propagate close to the sea- funded Onshore GNSS data sets have revealed that floor. ­GeoPRISMS has enabled additional ­GeoPRISMS locking at the Hikurangi subduction zone, deployments of GNSS-­ Acoustic​­ instru- project beneath New Zealand’s North Island, varies ments and APGs to investigate offshore installed significantly along the subduction interface. SSEs and locking at Hikurangi. The largest area of locking occurs beneath the capital city of Wellington and has sub- Putting It All Together stantial earthquake and tsunami hazard A wide range of subduction slip behavior is implications for residents. displayed at the ­GeoPRISMS and ­MARGINS A large variety of SSEs, occurring at a focus sites, but a few observations are com- range of depths and with widely varying mon to all or most of them. Geodetically duration, recurrence, and magnitude char- imaged fault locking has generally coincided acteristics, have also been observed on the with areas that have ruptured in the past. In Hikurangi subduction zone [Wallace, 2020]. the case of Costa Rica, it coincided with the And intriguing interplays between SSEs eventual ruptures of ­then-​­future earth- and recent New Zealand earthquakes have quakes. A variety of ­slow-​­slip types clearly been seen, including unprecedented accommodate large portions of plate motion and widespread triggering of SSEs in these subduction zones, although the following the 2016 magnitude 7.8 details vary widely among different regions. Kaikoura Slow slip also typically occurs outside regions of strong fault locking; however, we cannot rule out the possibility that seismic ruptures (and tsunamigenesis) could occur in regions currently dominated by slow slip. Despite advances in detecting SSEs, signif- icant gaps exist in our ability to detect smaller and shorter transient events and to reconcile seismological and geodetic observations of slip events. More widespread use of instru- ments like borehole tiltmeters, strainmeters,

26 Eos // APRIL 2021 and pressure sensors is required to bridge operate and the hazards they pose. Future Rogers, G., and H. Dragert (2003), Episodic tremor and slip on the Cascadia subduction zone: The chatter of silent slip, Sci- these gaps. Recent evidence also indicates programs should ensure continued progress ence, 300(5627), 1,942–1,943, https://​­doi​.­org/​­10.1126/​­science​ that locations of strongly locked regions may in this societally important area of research .­1084783. Rousset, B., et al. (2019), Weeks-­ long​­ and years-­ long​­ slow slip and vary over time; detecting these “coupling and generate new discoveries about the tectonic tremor episodes on the south central Alaska mega­ transients” (and resolving the processes that physical processes underpinning our planet’s thrust, J. Geophys. Res. Solid Earth, 122(12), 13,392–13,403, produce them) requires improvements in largest earthquake and tsunami factories. https://doi​­ .org/​ 10.1029/​­ 2019JB018724.​­ Schwartz, S. Y., and J. M. Rokosky (2007), Slow slip events and data analysis and modeling techniques. seismic tremor at circum-­ Pacific​­ subduction zones, Rev. Geo- The value of seafloor geodetic sensors to References phys., 45(3), RG3004, https://doi​­ .​ org/­ 10.1029/​­ 2006RG000208.​­ resolving ­near-​­trench subduction deforma- Araki, E., et al. (2017), Recurring and triggered slow-­ slip​­ events near Socquet, A., et al. (2017), An 8 month slow slip event triggers pro- the trench at the Nankai Trough subduction megathrust, Science, gressive nucleation of the 2014 Chile megathrust, Geophys. Res. tion processes is now well demonstrated at 356(6343), ­1157–​­1160, https://​­doi​.­org/​­10.1126/​­science​.­aan3120. Lett., 44(9), 4,046–4,053, https://doi​­ .​ org/­ 10.1002/​­ 2017GL073023.​­ ­MARGINS and ­GeoPRISMS focus sites and Dixon, T. H., et al. (2014), Earthquake and tsunami forecasts: Rela- Wallace, L. M. (2020), Slow slip events in New Zealand, Annu. Rev. tion of slow slip events to subsequent earthquake rupture, Proc. Earth Planet. Sci., 48, 175–203, https://doi​­ .​ org/­ 10.1146/​­ annurev​­ ​ should be more widely applied at other sub- Natl. Acad. Sci. U. S. A., 111(48), 17,039–­ 17,044,​­ https://doi​­ .​ org/­ ​ -earth­ -​ 071719­ -​ 055104.­ duction zones. Addressing knowledge gaps 10.1073/­ pnas​­ .​ 1412299111.­ Wallace, L. M., et al. (2018), Triggered slow slip and afterslip on about crustal deformation throughout the Elliott, J., and J. T. Freymueller (2020), A block model of present-­ ​ the southern Hikurangi subduction zone following the Kaikōura ­day kinematics of Alaska and western Canada, J. Geophys. earthquake, Geophys. Res. Lett., 45(10), 4,710–4,718, https://doi​­ ​ subduction earthquake cycle will require Res. Solid Earth, 125(7), e2019JB018378, https://doi​­ .​ org/­ 10.1029/​­ ​ .org/­ 10.1002/​­ 2018GL077385.​­ long (decades and beyond), uninterrupted 2019JB018378.­ Hirose, H., et al. (2010), Slow earthquakes linked along dip in the time series of data from numerous subduc- Nankai subduction zone, Science, 330(6010), 1,502, https://doi​­ ​ Author Information tion zones, both onshore and offshore. This .org/­ 10.1126/​­ science​­ .​ 1197102.­ Noel Bartlow (nbartlow@­ ku​­ .​ edu),­ University Ito, Y., et al. (2013), Episodic slow slip events in the Japan subduc- need underscores the importance of main- tion zone before the 2011 Tohoku-­ Oki​­ earthquake, Tectonophys- of Kansas, Lawrence; Laura M. Wallace, Insti- taining continuous geodetic and seismolog- ics, 600, 14–26,­ https://doi​­ .org/​ 10.1016/​­ j.tecto​­ .​ 2012­ .​ 08.022.­ tute for Geophysics, University of Texas at ical infrastructure. It will also require that Li, S., J. Freymueller, and R. McCaffrey (2016), Slow slip events and Austin; also at GNS Science, Lower Hutt, New ­time-dependent​­ variations in locking beneath Lower Cook Inlet geodetic observations be further integrated of the Alaska–­ Aleutian​­ subduction zone, J. Geophys. Res. Solid Zealand; Julie Elliott, Purdue University, West with a range of other geophysical, geologi- Earth, 121(2), 1,060–1,079, https://​­doi​.­org/​­10.1002/​­2015JB012491. Lafayette, Ind.; and Susan Schwartz, Univer- Materna, K., et al. (2019), Dynamically triggered changes of plate cal, laboratory, and modeling studies. interface coupling in southern Cascadia, Geophys. Res. Lett., sity of California, Santa Cruz ­MARGINS and ­GeoPRISMS have enabled 46(22), 12,890–12,899, https://doi​­ .​ org/­ 10.1029/​­ 2019GL084395.​­ Protti, M., et al. (2014), Nicoya earthquake rupture anticipated by u great advances in our ability to observe sub- geodetic measurement of the locked plate interface, Nat. Geo- Read the article at ­bit.ly/​­Eos​ duction zones and to understand how they sci., 7, 117–121, https://doi​­ .​ org/­ 10.1038/​­ ngeo2038.​­ -­earthquake​-­factories Read it first on Articles are published on Eos.org before they appear in the magazine. Visit Eos.org daily for the latest news and perspectives. Ham Radio Forms a Planet-Sized Space Weather Sensor Network bit.ly/Eos-hamradio Geological Surveys Unite to Improve Critical Mineral Security bit.ly/Eos-minerals Dangerous Heat, Unequal Consequences bit.ly/Eos-heat Coastal Flooding Enhances Methane Buildup in Forests bit.ly/Eos-flooding-methane Moon’s Largest Crater Holds Clues About Early Lunar Mantle bit.ly/Eos-lunar-mantle Cubist Geomorphology: Your Kinship with Picasso, Explained bit.ly/Eos-geo-cubism

SCIENCE NEWS BY AGU // Eos.org 27 By James D. Muirhead, Samer Naif, Tobias P. Fischer, and Donna J. Shillington

How do greenhouse gases and water circulate from minerals deep below Earth’s surface into the atmosphere and oceans—and then back again? Our understanding continues to evolve.

Steam and gas rise from a volcano on the island of Java, Indonesia. Credit: iStock­ ​.­com/Russian Labo

28 Eos // APRIL 2021 SCIENCE NEWS BY AGU // Eos.org 29 arth’s hot, pressurized interior ever, down below, they often remain chem- is composed primarily of rock ically bound to minerals or in a liquid state that, despite being solid, con- due to the massive pressures they experi- tains vast stores of fluids rich ence. Deep volatiles play critical roles in in carbon and dissolved gases. driving volcanic and plate tectonic pro- Unlike the ­free-​­flowing water- cesses on our planet. For example, the pres- ways of Earth’s surface or the groundwater ence of water in rock reduces the tempera- Ejust beneath, however, these subsurface tures required to melt rock, which promotes fluids have long been trapped within miner- the formation of magmas that feed volcanic als deep inside the planet, some since its eruptions. Deep volatiles can also weaken formation 4.5 billion years ago. Indeed, and damage rocks, allowing Earth to deform there is likely more water stored in Earth’s more readily by flowing or fracturing, and interior than is on its surface, constituting a they influence the occurrence of earth- global ocean in the rock below our feet quakes. [Hirschmann, 2006]. Volatiles escape Earth’s interior when We refer to these deep fluids as vola- they are dissolved in magmas that ascend tiles—the most common of which include toward the surface in volcanic regions. As water, carbon dioxide (CO2), and sulfur magmas cool and solidify, either as erupted dioxide (SO2)—because they readily turn to lavas or as igneous rocks emplaced in the gas in Earth’s ­near-​­surface region. How- crust, they release their dissolved gases, which can then be expelled through fuma- roles near volcano summits or through sea- floor vents (often called black smokers for UNDERSTANDING HOW VOLATILES the dark billowing plumes of precipitating minerals that pour from them). If, as CYCLE THROUGH OUR PLANET magma rises to the near surface, the dis- solved volatiles transform into gas bubbles IS CRITICAL FOR IMPROVING that rapidly expand, they can catastrophi- cally fragment magma to drive explosive OUR KNOWLEDGE OF EARTH’S volcanic eruptions. Gases expelled in volcanic regions— TECTONIC AND VOLCANIC water vapor, CO2, SO2, methane, and oth- ers—can become incorporated into surface PROCESSES AND OF THE water and into minerals within crustal rocks. They can also, however, collect and EVOLUTION OF ITS CLIMATE. reside in our atmosphere for up to thou- sands of years (although human activities today release much greater amounts of these gases into the atmosphere). The con- centrations of these gases in our atmo- sphere play critical roles in controlling global temperatures. Understanding how volatiles cycle through our planet’s atmosphere, oceans, and rocky interior is thus critical for improving our knowledge of Earth’s tec- tonic and volcanic processes, as well as of the evolution of its climate both today and through geologic time. Scientific advances in the 20th century provided a foundation for investigations into deep volatile trans- port during the National Science Foundation–­ funded​­ MARGINS­ program (2000–­ 2010)​­ and its successor GeoPRISMS­ (Geodynamic Processes at Rifting and Sub- ducting Margins) program (2010–2021). Studies occurring within or alongside these programs have since revolutionized our Vigorous fumarole activity releases gases that produce sulfur deposits at Kiska volcano in the western Aleutian understanding of where volatiles are Islands. Credit: Tobias Fischer located, how they are transported from the

30 Eos // APRIL 2021 Fig. 1. This simplified illustration shows a selection of volatile inputs to and outputs from Earth’s interior at various tectonic settings. Common volatile species like water (H2O), carbon dioxide (CO2 ), and sulfur dioxide (SO2 ) are incorporated into the lithosphere below the seafloor as water circulates through faults or is trapped in ocean sediments. Magmatic, volcanic, and tectonic processes at volcanic arcs, continental rifts, and mid-­ ​­ocean ridges help to liberate volatiles trapped in rocks and release these gases into the atmosphere. This figure does not show all volatile species or all of the natural processes controlling their migration. The influences of human activities on the release of greenhouse gases like CO2 into Earth’s atmosphere are also not shown.

ocean and the atmosphere into the litho- sphere (comprising the crust and the INTERACTIONS BETWEEN uppermost mantle), and how they are incorporated into magmas on their jour- SEAWATER AND ROCKS AT MID- ney back to Earth’s surface. OCEAN RIDGES LEAD TO THE Origins of Volcanic Arc Volatiles The origins of magmatic volatiles FORMATION OF HYDROUS remained a controversial topic until rela- tively recently. Early studies in the 1960s MINERALS THAT ULTIMATELY STORE suggested that water dissolved in magma was primarily meteoric, originating as COMPONENTS OF SEAWATER rainfall that circulated within the crust before being incorporated into magma. WITHIN OCEANIC LITHOSPHERE. Beginning in the late 1980s, scientists recognized another, potentially deeper source for volatiles at subduction zones ducting plates [Marty and Jambon, 1987]. (Figure 1). At these convergent tectonic Later studies showed the same for mag- plate boundaries, where one lithospheric matic water at volcanic arcs [Giggenbach, plate sinks beneath another, ­volatile-​­laden 1992]. material is recycled from the shallow and It is now known that the volatiles surficial Earth into its deep interior. Most of released at arc volcanoes were originally Earth’s subaerial volcanoes (i.e., those that incorporated into the lithosphere largely are exposed to the atmosphere) are found through processes occurring within the sea- along volcanic arc systems above subduc- floor millions of years earlier. The global tion zones. By examining the abundances of ­mid-​­ocean ridge system, a 65,000-​ carbon, nitrogen, and noble gases like argon ­kilometer-​­long divergent plate boundary and helium, researchers demonstrated that that accounts for most of Earth’s volcanism, most of the CO2 and nitrogen released at is key in volatile assimilation. These ridges these volcanoes originated from the sub- are localities of intense hydrothermal circu-

SCIENCE NEWS BY AGU // Eos.org 31 lation of seawater through the crust, where volatile storage resulting from subduction fluids migrate through developing faults than previously thought, with these vola- and fractures and fluid convection is driven tiles incorporated into minerals in the crust by heating from submarine volcanism and and the mantle. magmatism. The resulting interactions ­Bending-​­related hydration prior to sub- between seawater and rocks at ­mid-​­ocean duction could contribute the largest amount ridges lead to mineral alteration and the of water entering subduction zones. Some formation of hydrous minerals that ulti- theoretical and observational studies suggest mately store components of seawater that volatiles may penetrate tens of kilome- within oceanic lithosphere [ Alt, 1995]. ters into the oceanic mantle because of this Sediments deposited and rock formed bending [Cai et al., 2018], with the oceanic atop seafloor crust as a result of sedimen- mantle storing 4 times more water than sub- tary processes in ocean basins also store ducting oceanic crust. However, contrasting studies suggest that volatile penetration is limited to the top few kilometers of oceanic mantle [Korenaga, 2017], leaving the sub- THE APPARENT DEFICIT IN CARBON ducting mantle with ­4–8 times less water than the overlying oceanic crust. As such, OUTPUTS BASED ON CURRENT ­bending-​­related hydration of the oceanic crust and mantle remains poorly con- OBSERVATIONS AND CALCULATIONS strained. Refining the large uncertainties in water fluxes at subduction zones is critical SUGGESTS THE LIKELIHOOD for balancing the global water budget. OF A SOURCE OF DEEP CARBON. Missing Sources of Deep Carbon Because CO2 is a greenhouse gas that plays a key role in controlling Earth’s climate, the such elements as hydrogen, sulfur, and car- scientific community is particularly inter- bon [ Jarrard, 2003]. And immediately prior ested in balancing the outputs and inputs of to subduction, a final and critical hydration deep carbon in addition to studying water stage results from the bending and faulting fluxes. The amount of CO2 in Earth’s atmo- of the lithosphere at subduction margins, sphere has remained within a narrow range which enables deeper and more pervasive (typically 150–400 parts per million) hydration [Ranero et al., 2003]. Following throughout the past 10 million or so years, subduction, some of these volatiles are later conditions that have maintained an “ice- released back into the atmosphere as water, house climate” (as distinct from “green- CO2, SO2, and other gases because of mag- house climate” periods in the more distant matic and volcanic processes. past). Stable atmospheric CO2 levels require a Tracking Volatiles Through balance between deep carbon outputs and Subduction Zones inputs. But compilations of carbon fluxes The potential role that faults play in allow- reveal that the amount of carbon trans- ing seawater to infiltrate and hydrate oce- ported into Earth’s interior by subducting anic mantle was of wide interest to the plates significantly exceeds the amount ­MARGINS research community, and inves- released at volcanic arcs [Kelemen and Man- tigations of the topic continued during the ning, 2015]. These observations suggest that ­GeoPRISMS program. Recent work has since the crust and the mantle at subduction confirmed that faults do indeed penetrate zones sequester substantial quantities of the lithosphere, drive fluids into the crust, carbon, and likely also other critical volatile and likely hydrate the crust and the upper- components. most mantle [e.g., Grevemeyer et al., 2018]. The apparent deficit in carbon outputs This work has provided more accurate con- based on current observations and calcula- straints on the volumetric inputs and out- tions further suggests the likelihood of a puts of volatiles at subduction zones. currently unrecognized source of deep car- These studies also revealed that although bon. Earth’s global ­mid-​­ocean ridge system some volatiles delivered into the deep Earth is one possible explanation. At ­mid-​­ocean at subduction zones are released back into ridges, carbon is extracted from mantle rock the atmosphere and the ocean at arc volca- when this rock melts and is then released noes, large volumes also remain trapped in into the ocean during submarine volcanism. the subsurface. Studies now point to higher Quantifying CO2 fluxes from these settings

32 Eos // APRIL 2021 has been the focus of numerous studies over Technological advances using ­satellite- the past few decades [Wong et al., 2019]. and unoccupied aerial ­vehicle–​­based remote Recently, however, these studies have sensing, combined with ­high-​­resolution started to converge on a common value for geophysical studies and geodynamic mod- the total carbon flux from ­mid-​­ocean ridges els, may help track emissions from these that is too low to make up the apparent car- environments and are needed to obtain a bon deficit, hinting that there are still other more complete picture of volatile fluxes on critical sources responsible for the remain- Earth. Quantifying these fluxes is relevant ing carbon. for many current and future community sci- The GeoPRISMS­ program targeted studies entific efforts and is essential in developing at other potential sources of deep carb­on. In a comprehensive understanding of past and particular, the role of continental rifts (e.g., current environmental change on our planet the East African Rift System) has been of as well as of Earth’s volcanic and seismic significant interest. Not only are large hazards. magma volumes produced at these settings, but they also represent locations where References Earth’s continents split apart through the Alt, J. C. (1995), Subseafloor processes inmid- ­ ocean​­ ridge hydro- thermal systems, in Seafloor Hydrothermal Systems: Physical, formation of deep cracks and faults (Fig- Chemical, Biological, and Geological Interactions, Geophys. ure 1). Monogr. Ser., vol. 91, edited by S. E. Humphris et al., pp. 85–114,­ AGU, Washington, D.C. Recent studies show that in addition to Cai, C., et al. (2018), Water input into the Mariana subduction volcanoes, widespread faulting at continen- zone estimated from ocean-­ bottom​­ seismic data, Nature, 563, tal rift systems provides pathways for deep 389–392, https://doi​­ .​ org/­ 10.1038/​­ s41586​­ -​ 018­ -​ 0655-4.­ Giggenbach, W. F. (1992), Isotopic shifts in waters from geother- CO2 to reach the surface. Furthermore, mal and volcanic systems along convergent plate boundaries compared with ­mid-​­ocean ridges, conti- and their origin, Earth Planet. Sci. Lett., 113, 495–510, https://doi​­ ​ .org/10.1016/​­ 0012​­ -​ 821X​­ (92)​­ 90127-H.​­ nental rifts occur in comparatively ancient Grevemeyer, I., C. R. Ranero, and M. Ivandic (2018), Structure of continental lithosphere, thereby tapping oceanic crust and serpentinization at subduction trenches, Geo- volumetrically large carbon stores accumu- sphere, 14, 395–­ 418,​­ https://doi​­ .​ org/­ 10.1130/​­ GES01537.1.​­ lated over billions of years [Muirhead et al., Hirschmann, M. M. (2006), Water, melting, and the deep Earth H2O cycle, Annu. Rev. Earth Planet. Sci., 34, 629–653, https://​ 2020]. doi­ .​ org/­ 10.1146/​­ annurev​­ .​ earth­ .​ 34­ .​ 031405­ .​ 125211.­ Jarrard, R. D. (2003), Subduction fluxes of water, carbon dioxide, chlorine, and potassium, Geochem. Geophys. Geosyst., 4(5), Improving the Picture 8905, https://doi​­ .​ org/­ 10.1029/​­ 2002GC000392.​­ of Earth’s Volatiles Kelemen, P. B., and C. E. Manning (2015), Reevaluating carbon Over the past few decades, much progress fluxes in subduction zones, what goes down, mostly comes up, Proc. Natl. Acad. Sci. U. S. A., 112, E3997–E4006, https://doi​­ .​ org/­ ​ has been made toward constraining global 10.1073/­ pnas​­ .​ 1507889112.­ water and carbon fluxes in and out of Korenaga, J. (2017), On the extent of mantle hydration caused by plate bending, Earth Planet. Sci. Lett., 457, 1–­ 9, https://​­ doi​­ .​ org/­ ​ Earth’s interior. But significant gaps remain 10.1016/­ j.epsl​­ .​ 2016­ .​ 10.011.­ in our understanding, particularly of carbon Marty, B., and A. Jambon (1987), C3He in volatile fluxes from the emissions from volcanically and tectonically solid Earth: Implications for carbon geodynamics, Earth Planet. Sci. Lett., 83, 16–­ 26,​­ https://doi.org/10.1016/0012-­ 821X(87)​­ ​ active regions as well as of fluxes of other 90047-1.­ important volatiles such as nitrogen, meth- Muirhead, J. D., et al. (2020), Displaced cratonic mantle con- ane, and halogens. centrates deep carbon during continental rifting, Nature, 582, 67–­ 72,​­ https://doi.org/10.1038/s41586-­ 020-​­ 2328-​­ 3.​­ Continental rifts arguably represent the Plank, T., and C. E. Manning (2019), Subducting carbon, Nature, biggest source of uncertainty in global car- 574, 343–­ 352,​­ https://doi.org/10.1038/s41586-­ 019-​­ 1643-​­ z.​­ bon flux estimates [Plank and Manning, Ranero, C. R., et al. (2003), Bending-­ related​­ faulting and mantle serpentinization at the Middle America Trench, Nature, 425, 2019]. Quantifying total CO2 fluxes from 367–­ 373,​­ https://doi.org/10.1038/nature01961. continental rifts is thus a critical endeavor Wong, K., et al. (2019), Deep carbon cycling over the past 200 million years: A review of fluxes in different tectonic settings, for future deep carbon studies. Other Frontiers Earth Sci., 7, 1–22, https://doi​­ .​ org/­ 10.3389/​­ feart​­ .​ 2019­ ​ uncertain sources of global CO2 outputs, all .00263.­ of which also require further study, include regions of diffuse volatile degassing via Author Information soils, volcanic lakes, and volcanic aquifers. James D. Muirhead (james­ .​ muirhead@­ ​ However, our ability to measure volatile ­fulbrightmail​.­org), University of Auckland, Auck- fluxes at these settings is limited because land, New Zealand; Samer Naif, Georgia Insti- of their size and complexity. The 3,000-​ tute of Technology, Atlanta; Tobias P. Fischer, ­kilometer-​­long East African Rift System, University of New Mexico, Albuquerque; and for example, features thousands of faults. Donna J. Shillington, Northern Arizona Uni- Each fault releases a relatively small versity, Flagstaff amount of gas, but cumulatively they may represent a significant volume of carbon u Read the article at ­bit.ly/​­Eos​ release. -­balancing​-­act

SCIENCE NEWS BY AGU // Eos.org 33 BREAK ING UP IS HARD TO DO, ESPECIALLY FOR CONTI NENTS

By Lindsay L. Worthington, Brandon D. Shuck, Anne Bécel, Zachary C. Eilon, and Colton Lynner

A ­decade-​­long research collaboration has revealed that the split between Africa and North America roughly 200 million years ago was more drawn out than

previously thought. veleri_kz – stock.adobe.com

34 Eos // APRIL 2021 BREAK ING UP IS HARD TO DO, ESPECIALLY FOR CONTI NENTS

he cyclic amalgamation and rupture of supercontinents is one of Earth’s fundamental tectonic processes, ultimately affecting nearly every aspect of the planetary surface on which we live, from global climate to species evolution, through its control of land distribution, ocean circulation, atmospheric compo- T sition, and other factors. Continental and oceanic crust today preserves signatures of these ­make-​­and-​­break cycles, which have occurred several times through geologic time. But the evidence is rarely easy to interpret, leaving many questions outstanding. For example, continents are really hard to break, and scientists are still trying to explain how they do. Models imply that plate tectonic forces alone are not strong enough to pull continents apart, so additional mechanisms must contribute. In many places where continents have broken apart, geoscientists have inferred a role for extensive magmatism. Magmas may have enabled continental breakups by heating and weakening continental tectonic plates [Buck, 2006], but it is often not clear where, when, and how much magma was involved. Roughly 200 million years ago, the world’s most recent super- continent, Pangea, began to rup- ture. The eastern North Ameri- can continental margin (ENAM), stretching from Florida to Nova Scotia, offers glimpses into the conditions leading to Pangea’s demise, with records of exten-

veleri_kz – stock.adobe.com sion (i.e., the stretching or

SCIENCE NEWS BY AGU // Eos.org 35 Magmatism Splits a Supercontinent Passive margins exist at transitions between continents and oceans where no active tec- tonic plate boundary occurs. Previous work has suggested that continental rifts, where landmasses split apart, and the margins they leave behind can be classified as either magma rich or magma poor. The model for ­magma-​­rich margins imagines voluminous bursts of magmatism injected into the crust, quickly weakening and eroding the existing continent and triggering breakup over a very short time frame. The ENAM has long been a type example of a ­magma-​­rich margin [Holbrook and Kele- men, 1993]. It is characterized by the pres- ence of voluminous lava flows such as the Central Atlantic Magmatic Province (CAMP) and volcanic deposits that line the edge of the continental shelf, forming the East Coast Magnetic Anomaly (ECMA; Figure 2), which spans the length of the margin off- shore [Greene et al., 2020]. However, new seismic and magnetic data collected during the ­ENAM-​­CSE suggest that the ENAM doesn’t entirely fit the mold of a typical ­magma-​­rich margin. Detailed computer models of the crustal structure created from these data show that magmatic intrusions into the lower continental crust during the breakup of Pangea were limited to distinct Fig. 1. The data acquisition footprint of the Eastern North American Margin Community Seismic Experiment patches beneath the continental margin, (­ENAM-​­CSE) off the coast of North Carolina is shown here (modified fromLynner et al. [2020]). The experiment rather than being widespread [Shuck et al., included a ­1-year broadband seismometer array deployment, collection of ­wide-​­aperture active source seismic 2019]. And modeling of magnetic data profiles to constrain crustal structure across and along the margin, and multichannel seismic reflection imaging shows that volcanism associated with the expanded upon the EarthScope Transportable Array footprint. The extents of the East Coast Magnetic Anomaly initial formation of the ECMA was emplaced (ECMA) on the continental slope and of the Blake Spur Magnetic Anomaly (BSMA) on the abyssal plain are indi- over millions of years, rather than during a cated. The inset map shows a representation of Pangea roughly 200 million years ago created by the PLATES short pulse, and that extension rates during Project at the University of Texas at Austin. the earliest stages of breakup were far slower than previously estimated [Davis et al., 2018]. A short but intense magmatic event that pulling apart of rock) and magmatism extending farther seaward from the North occurred about 200 million years ago, the frozen into the geologic structure of the Carolina coastal plain than previous studies CAMP is the most areally extensive large current passive margin. Through exten- and offering a complete picture of the Pan- igneous province recorded in Earth’s his- sive input from the research community, gean breakup. The experiment involved tory, spreading 10 million square kilometers the ­GeoPRISMS (Geodynamic Processes at multiple ­shoreline-​­crossing, ­controlled-​ across the heart of Pangea, with records Rifting and Subducting Margins) program, a ­source seismic profiles and an array of found in Africa, North America, and South decadal initiative sponsored by the National broadband ocean bottom seismometers, America. This feature has long been thought Science Foundation, chose the ENAM as a allowing for ­high-​­resolution, ­along-​­margin of as a driving factor in continental breakup, focus site at which to investigate the role of comparisons of crust and upper mantle although recent results suggest a more magmatism during the initial rifting of Pan- structure (Figure 1). nuanced role. Early extension [e.g., Withjack gea and in subsequent rift evolution. The amphibious multiscale experimental et al., 2012] may have created the conditions In 2014–2015, the ENAM Community focus and ­open-​­access data arrangement for widespread decompression melting of Seismic Experiment (­ENAM-​­CSE; Figure 1) have since led to a wealth of new findings the mantle that resulted in the CAMP [Lynner et al., 2020] provided the first related to the formation and evolution of [Marzen et al., 2020]. The subsequent immediately open data sets focused on mul- the ENAM, forcing scientists to reconsider emplacement of CAMP volcanics, in turn, tiscale seismic imaging over a passive mar- much of what we thought we knew about then facilitated further extension and mag- gin. The CSE encompassed a roughly ­500-​ continental breakup and the formation of matism that eventually gave way to suc- ­kilometer-​­wide section of the margin, this passive margin. cessful rifting.

36 Eos // APRIL 2021 A Prolonged Breakup It is surprisingly difficult to put a finger on the timing and geographic location of the continental breakup that created the ENAM. Traditional viewpoints suggest that the ECMA marks the boundary between stretched continental crust and the earliest oceanic crust that formed after breakup and that it therefore represents the location of the continental rupture and initial seafloor spreading. Given the volcanic nature of the rift, scientists expected the CSE data to show a gradual decrease in crustal thickness seaward of the ECMA to about 7 kilometers, the average value for normal oceanic crust. Instead, the data reveal a roughly ­200-​ ­kilometer-​­wide anomalous zone of thin and heavily faulted “­proto-​­oceanic” crust [Bécel et al., 2020] (Figure 2). Although the crust in this region appears to be similar to normal oceanic crust, it is thinner and rougher and has faster seismic velocities [Shuck et al., 2019]. Studies using the mineral content of crystallized magmas to infer ancient mantle temperatures were synthesized with seis- mic results to help explain this mysterious zone of igneous crust. Together these data Graduate student Kate Volk watches the response from the subbottom profiler aboard the R/VEndeavor during indicate that a 15- to ­20-​­kilometer-​­thick the ­ENAM-​­CSE (top left). Students Kara Epple, Matthew Karl, and Sasha Montelli help deploy an 8-kilometer-­ ​­long layer of lithosphere (dark green in Figure 2) seismic streamer on the R/V Marcus Langseth (top right). Engineers and technicians from Woods Hole Oceano- acted like a lid, preventing melting of the graphic Institution recover a broadband ocean bottom seismometer aboard the R/V Endeavor (bottom left). shallow mantle. As a result, rather than Beatrice Magnani and Dan Lizarralde recover one of the 80 seismometers deployed for 1 month in North Caro- quick establishment of a ­mid-​­ocean ridge lina and Virginia in 2014 (bottom right). Credit (clockwise from top left): Gary Linkevich, Donna Shillington, Anne that channels deep melt toward a spreading Bécel, Yanjun Hao axis, diffuse melt instead percolated upward slowly throughout the stretching plate [Shuck et al., 2019]. The rough texture of the ­proto-​­oceanic upper crust and the slow of the ECMA. Findings from the CSE suggest fate of Pangea was set, the Atlantic Ocean rates of extension here indicated by seismic that complete rupture of the continental was born, and Africa and North America reflection imaging support this interpreta- lithosphere finally occurred at the BSMA, began their slow drift apart, which continues tion [Bécel et al., 2020]. accompanied by a magmatic pulse and the to this day. Relatively warm mantle temperatures initiation of normal sea- beneath Pangea during its breakup, floor spreading in the cen- inferred from petrological models and tral Atlantic. chemical signatures of CAMP basalts, show The rifting process was that this lithospheric lid consisted of con- likely delayed because of tinental rock, likely a stubborn remnant of the strong, thick litho- the supercontinent. Evidently, the conti- sphere of the superconti- The rifting process was nental plate had not yet fully ruptured at nent Pangea, which long the ECMA during formation of the anoma- resisted the intense but likely delayed because lous region of early oceanic crust, and the slow stretching forces of the strong, thick battered lithosphere was hanging on by a despite the presence of thread. abundant magmatism. But lithosphere of Pangea, If the current African and North Ameri- the hot mantle astheno- can plates did not fully separate at the sphere gradually eroded the which long resisted ECMA, when and where did they finally lithosphere until persistent intense but slow break apart? Another prominent magnetic deformation and magma- anomaly, the Blake Spur Magnetic Anomaly tism eventually delivered stretching forces. (BSMA), marks the rapid onset of normal the final blow. And about oceanic crust about 200 kilometers seaward 168 million years ago, the

SCIENCE NEWS BY AGU // Eos.org 37 A Modern Analogue in East Africa Our updated views of the ancient rifting of Pangea influence our understanding of the second GeoPRISMS rifting focus site, the cur- rently active East African Rift (EAR). Often thought of as the archetypal “narrow rift,” the EAR is cited as a region where magma- tism is splitting a modern continent in two. However, lessons from the ENAM demand that we rethink simplistic para- digms for the ongoing breakup of the Afri- can continent. Current plate motions show broad extension that encompasses much of the Ethiopian plateau, well beyond the ­fault-​­bounded main rift. And new seismic data [Petruska and Eilon, 2020] from the rift flanks reveal high temperatures and, likely, mantle melt at roughly ­100-​­kilometer depth, extending well beyond the main locus of recent (younger than 10 million years) extension. Furthermore, ongoing EAR rifting and changes in extension rates from north (i.e., the Afar region) to south (i.e., in Kenya) allow us to see how rifting progresses episodically Fig. 2. This schematic shows tectonic domains present along the ENAM. Offshore magnetic anomaly data lie through time [e.g., Ebinger et al., 2013], over seafloor bathymetry data. Results from the ­ENAM-​­CSE suggest that the full lithospheric rupture of Pangea grounding the evidence of similar waxing occurred along the BSMA, not the ECMA as previously thought. Magnetic anomaly data are from version 3 of the and waning in the rate of Pangean rifting 200 Earth Magnetic Anomaly Grid (2–arc­ minute resolution); bathymetry data are from the ETOPO1­ Global Relief million years ago. If these dynamics persist, Model. Both data sets are publicly available from the National Centers for Environmental Information. the EAR may provide a modern analogue to ENAM rifting, whereby continental thinning becomes widely distributed, delaying or forestalling eventual breakup. Active Processes on a Passive Margin cesses. In particular, the ENAM region The multiscale observational focus in stud- hosts several active geohazards, and it A Formative Legacy ies of the ENAM supported and promoted appears to encapsulate more complex The impact of GeoPRISMS’s focus on rifting by ­GeoPRISMS has not only recast our mantle dynamics (see Figure 2) than sug- extends beyond the scientific accomplish- views on the Mesozoic rifting of Pangea but gested by the research community’s previ- ments it has fostered. The program’s rifting also shed light on far more recent pro- ous understanding. initiative, including the ­ENAM-​­CSE, has New seismic imaging of the shallow sedi- revitalized a community of researchers by ments across much of the ­ENAM-​­CSE study involving them in fieldwork, seminars, area indicates a high potential for subma- miniworkshops, and conferences; more than rine landslides and associated geohazards, 700 attendees have attended ­ENAM-​­focused Lessons from including tsunami generation [Hill et al., meetings, for example. Since the conclusion 2018]. Passive margins have long been rec- of the ­ENAM-​­CSE, more than 200 presenta- the ENAM ognized as hosting significant earthquakes. tions have showcased undergraduate and demand that we ­Present-​­day crustal stresses along the graduate research conducted under the ENAM are sufficient to create earthquakes umbrella of GeoPRISMS at major national rethink simplistic with widespread shaking and damage, as conferences, and numerous papers on the demonstrated by the 2011 magnitude 5.8 topic have been published in that time. paradigms for the earthquake in Mineral, Va. [Wolin et al., The GeoPRISMS program has thus not ongoing breakup 2012]. Ongoing and active asthenospheric only been instrumental in driving improved flow beneath the margin (both onshore and understanding of a fundamental Earth pro- of the African offshore) [e.g., Lynner and Bodmer, 2017], cess; it has also been formative for a new continent. putatively driven by gradients in mantle generation of scientists, whose professional temperature and viscosity, may exacerbate networks and approach to collaborative both sets of hazards by creating localized research and ­community-​­driven science mantle upwellings and downwellings that will carry forward into the next several affect surface topography and intraplate decades of investigations into continental stresses. rifting.

38 Eos // APRIL 2021 Acknowledgments References Marzen, R. E., et al. (2020), Limited and localized magmatism in the Central Atlantic Magmatic Province, Nat. Commun., 11(1), The ENAM-­ ​­CSE study area includes tradi- Bécel, A., et al. (2020), Evidence for a prolonged continental breakup resulting from slow extension rates at the eastern 3397, https://doi​­ .​ org/­ 10.1038/​­ s41467​­ -​ 020­ -​ 17193-6.­ tional lands and waters of many Indige- North American volcanic rifted margin, J. Geophys. Res. Petruska, J., and Z. Eilon (2020), Investigation into the localization nous Peoples, including the Lumbee, Solid Earth, 125, e2020JB020093, https://doi​­ .​ org/­ 10.1029/​­ ​ of rifting within the northern Main Ethiopian Rift using Rayleigh 2020JB020093.­ waves and receiver functions, paper 682297 presented at Fall Skaruhreh/Tuscarora, Hatteras, Roanoke, Buck, W. R. (2006), The role of magma in the development of the Meeting 2020, AGU, agu.​ confex­ .​ com/­ agu/​­ fm20/​­ meetingapp​­ .​ cgi/­ ​ and Chesapeake territories. We thank the Afro-­ Arabian​­ Rift System, in The Afar Volcanic Province Within Paper/­ 682297.​­ the East African Rift System, edited by G. Yirgu, C. J. Ebinger, Shuck, B. D., H. J. A. Van Avendonk, and A. Bécel (2019), The role captains and crews of the R/Vs Marcus G. and P. K. H. Maguire, Spec. Publ. Geol. Soc. London, 259, of mantle melts in the transition from rifting to seafloor spread- Langseth and Endeavor, the Seismic Source 43–54,­ https://doi​­ .​ org/­ 10.1144/​­ GSL​­ .​ SP­ .​ 2006­ .​ 259.01.05.­ ing offshore eastern North America, Earth Planet. Sci. Lett., 525, https://doi​­ .​ org/­ 10.1016/​­ j.epsl​­ .​ 2019­ .​ 115756.­ Facility, the Ocean Bottom Seismograph Davis, J. K., A. Bécel, and W. R. Buck (2018), Estimating emplace- ment rates for seaward-­ dipping​­ reflectors associated with Withjack, M. O., R. W. Schlische, and P. E. Olsen (2012), Devel- Instrument Pool (OBSIP; now OBSIC), and the US East Coast Magnetic Anomaly, Geophys. J. Int., 215(3), opment of the passive margin of eastern North America, in all technical personnel and student volun- 1,594–1,603, https://doi​­ .​ org/­ 10.1093/​­ gji/​­ ggy360.​­ Regional Geology and Tectonics: Phanerozoic Rift Systems and Ebinger, C. J., J. van Wijk, and D. Keir (2013), The time scales of Sedimentary Basins, pp. 300–335, Elsevier, New York, https://​ teers for their efforts during data acquisi- continental rifting: Implications for global processes, in The Web doi­ .​ org/­ 10.1016/​­ B978​­ -​ 0­ -​ 444­ -​ 56356­ -​ 9­ .​ 00012-2.­ tion. We gratefully acknowledge the of Geological Sciences: Advances, Impacts, and Interactions, Wolin, E., et al. (2012), Mineral, Virginia, earthquake illustrates edited by M. E. Bickford, Spec. Pap. Geol. Soc. Am., 500, 1–26,­ seismicity of a passive-­ aggressive​­ margin, Geophys. Res. ­ENAM-​­CSE principal investigators: Harm https://doi​­ .​ org/­ 10.1130/​­ 2013​­ .​ 2500(11).­ Lett., 39, L02305, https://doi​­ .​ org/­ 10.1029/​­ 2011GL050310.​­ van Avendonk, Donna Shillington, Beatrice Greene, J. A., M. Tominaga, and N. C. Miller (2020), ­Along-margin​­ Magnani, Dan Lizar­ralde, Brandon Dugan, variations in breakup volcanism at the eastern North American margin, J. Geophys. Res. Solid Earth, 125, e2020JB020040, Author Information Matt Hornback, Steven Harder, Anne https://doi​­ .​ org/­ 10.1029/​­ 2020JB020040.​­ Lindsay L. Worthington (lworthington@­ unm​­ ​ Bécel, Jim Gaherty, Maureen Long, Gail Hill, J. C., et al. (2018), Subsurface controls on the development of .edu), University of New Mexico, Albuquerque; the Cape Fear Slide Complex, central US Atlantic Margin, Geol. Christeson, Lara Wagner, and Maggie Ben- Soc. Spec. Publ., 477, SP477-17,­ https://doi​­ .​ org/­ 10.1144/​­ SP477.17.​­ Brandon D. Shuck, Institute for Geophysics, oit. Data from the ­ENAM-​­CSE are available Holbrook, W. S., and P. B. Kelemen (1993), Large igneous province University of Texas at Austin; Anne Bécel, on the US Atlantic margin and implications for magmatism Lamont-­ Doherty​­ Earth Observatory, Columbia at the Marine Geoscience Data System. See during continental breakup, Nature, 364(6436), 433–436, Lynner et al. [2020] for full data set cita- https://doi​­ .​ org/­ 10.1038/​­ 364433a0.​­ University, Palisades, N.Y.; Zachary C. Eilon, tions. EarthScope Transportable Array data Lynner, C., and M. Bodmer (2017), Mantle flow along the eastern University of California, Santa Barbara; and North American margin inferred from shear wave splitting, Geol- are available at the IRIS (Incorporated ogy, 5(10), 867–870, https://doi​ .​ org/­ 10.1130/​­ G38980.1.​­ Colton Lynner, University of Delaware, Newark Research Institutions for Seismology) Data Lynner, C., et al. (2020), The Eastern North American Margin Com- munity Seismic Experiment: An amphibious active-­ and passive-­ ​ u Management Center (virtual network code source­ dataset, Seismol. Res. Lett., 91(1), 533–540, https://doi​­ ​ Read the article at ­bit.ly/​ ­US-TA). .org/­ 10.1785/​­ 0220190142.​­ ­Eos-­continental​-­breakup

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Dylan de Jonge/Unsplash RESEARCH SPOTLIGHT

How Some Trees Survive the Summer Dry Season

n important component of Earth’s which groundwater recedes at the beginning hydrologic cycle is transpiration—the of the dry season. These results indicate that A movement of water through plants. the trees’ use of rock moisture may be due to Because transpiration affects near-­ ​­surface the groundwater’s low oxygen content and temperatures, streamflows, and the produc- location within bedrock of low permeability. tivity of ecosystems, understanding potential The findings highlight that not all ground- sources of subsurface moisture and how water is accessible to plants, even when it is plants use them is crucial for developing within reach of their roots, and suggest that accurate dynamic vegetation and land surface patterns of water uptake by oaks in Mediter- models. Our knowledge of these processes, ranean climates may be site specific. Because however, is far from complete, in part because forests are commonly located on hillsides they are hidden below the ground. with thin soils that overlie weathered bed- To better understand where trees get their rock, the results further suggest that water from, Hahm et al. studied Oregon white extraction of rock moisture may be a globally oaks (Quercus garryana), deciduous hardwoods Researchers studied Oregon white oaks like those important process. that thrive in Pacific Northwest locales with pictured here to test the hypothesis that they As one of a growing number of studies thin soils underlain by highly weathered bed- required groundwater during the dry summer months. demonstrating that trees can tap into water rock. Because these gnarled oaks have deep Credit: Colin Durfee, CC BY 2.0 (bit.ly/​­ccby2-0) stored within weathered bedrock, this paper taproots, scientists have long assumed they has important implications for forest man- draw upon groundwater to survive the long agement, according to the authors. The dry seasons typical of the Mediterranean cli- results emphasize the need to better under- mate in their range. Zone Observatory. The data showed that stand the distribution of water in weathered To test this hypothesis, the researchers despite the presence of groundwater just a bedrock on a landscape scale to improve pre- used a combination of isotopic analyses and few meters below the surface, these trees dictions of how forests will respond to hydrologic measurements to characterize the during summer depend primarily on water extended drought. (Water Resources Research, sources of water used by the oaks at a study drawn from the soil and the deep unsaturated https://​­doi​.­org/​­10.1029/​­2020WR027419, site in Northern California’s Eel River Critical zone, the region of weathered bedrock from 2020) —Terri Cook, ­Science ­Writer

A Global Look at Surface Soil Organic Carbon

ealthy soil is paramount to life on Earth. In addition to its impor- tance in agriculture, soil is the foundation for almost every Hterrestrial ecosystem on the planet. Soil organic carbon (SOC) is frequently used as a gauge of soil health, it plays an important role in terrestrial carbon cycling, and it carries huge implications for climate change adaptation. Understanding these dynamics on a planetary scale will be vital as humanity attempts to feed a growing population under increasing stress from a warming planet. In a new study, Endsley et al. used remote sensing to study surface SOC dynamics globally, drawing data from NASA’s Soil Moisture Active Pas- sive (SMAP) satellite, which combines radiometer measurements of Earth’s surface ­low-​­frequency microwave emissions with modeling to SOC and found that their model generally agreed well with them. The calculate soil moisture and the ­freeze-thaw​­ state. In particular, SMAP’s researchers say that the new model will allow them to monitor seasonal microwave radiometer data can be combined with a physical model of and annual changes in SOC and will also offer a view of how ecosystems plant carbon uptake and soil decomposition to estimate the global ter- and the planet at large respond to floods, droughts, and other ­short-term​­ restrial carbon budget in the SMAP Level 4 Carbon (L4C) product. The events. ( Journal of Geophysical Research: Biogeosciences, https://​­doi​.­org/​ team used SMAP L4C in combination with other satellite data, such as ­10.1029/​­2020JG006100, 2020) —­David Shultz, ­Science Writer­ vegetation observations from Moderate Resolution Imaging Spectro- radiometer instruments, to create a model that would specifically char- acterize SOC. The result is a global estimation of SOC to a depth of 5 centimeters with u Read the latest news at Eos.org a horizontal resolution of 9 square kilometers. The scientists compared

Dylan de Jonge/Unsplash their estimates with prior measurements and soil inventory records of

SCIENCE NEWS BY AGU // Eos.org 41 RESEARCH SPOTLIGHT

Determining Dissolved Organic Carbon Flows into the Gulf of Alaska

Territory, represents an incredibly complex confluence of glaciers, forests, mountains, and plateaus with river systems that drain into bays, fjords, and channels before reach- ing the Pacific Ocean. To build the model of carbon flux, the researchers combined a digital elevation model with estimated shapes of watershed boundaries and glacier extents as well as gridded data representing mean monthly runoff. To calculate the total amount of freshwater runoff, they used a distributed climate water balance model calibrated with measurements taken from watersheds in the The variety of land cover and soil types draining into the Gulf of Alaska and coastal estuaries is illustrated in this study area. watershed within the Héen Latinee Experimental Forest bordering Lynn Canal to the north of Juneau, Alaska. The scientists calculated that overall, the Credit: Richard Edwards, U.S. Forest Service region exports 430 cubic kilometers of fresh water and 1.17 teragrams of dissolved organic carbon annually to the Pacific Ocean. Their model shows that watershed type, location, mid ongoing climate change, understanding how and where and flow rate are important variables that control the spatial and tem- carbon is moving across ecosystems has become a top research poral patterns of carbon flux. The team says that despite the region’s A priority. This type of “carbon accounting” helps scientists immense size and importance for both commercial fishing and climate, determine where the planet is sequestering and releasing ­atmosphere-​ the Gulf of Alaska has been chronically understudied compared with ­warming carbon compounds and is especially important at the bound- other sections of the North American coastline. The new results high- aries between different ecosystems. light the significance of the region and provide a starting point for In a new study, Edwards et al. investigate how rivers in western Can- unraveling the complexity of the dynamic ecosystems and their effects ada and southeastern Alaska transport dissolved organic carbon and on climate and humanity. ( Journal of Geophysical Research: Biogeosciences, fresh water into the Gulf of Alaska. The study region, which spans from https://​­doi​.org/­ ​­10.1029/​­2020JG005725, 2021) —­David Shultz, ­Science northern British Columbia to the southwestern corner of the Yukon ­Writer

Researchers Unearth Bedrock Carbon and Water Dynamics

n Earth’s surface, countless plants forest in Northern California. They note pat- thus carries the effects of bedrock weather- and animals grow and move, taking terns in carbon dynamics that followed sea- ing on the slope beyond the immediate eco- Oin and releasing carbon. Beneath all sonal cycles. In the wet season, up to about system. that, the soil teems with insects, microbes, 80% of the carbon produced in the bedrock This research contributes to the study of an and fungi, all bustling and respiring. The bed- dissolved into water and accelerated further underresearched carbon source that has yet rock farther below the surface, in contrast, weathering in the rock and soil. In the dry to be adequately factored into scientists’ may seem sterile, although it, too, often hosts season, bedrock respiration continued as understanding of the global carbon cycle. life. Trees and other plants commonly work trees drew water from deeper bedrock zones Future research, they suggest, should expand their roots all the way down into bedrock fis- when the soil above dried out. on these findings to look at conditions in sures, bringing along accompanying The researchers also note that dissolved other seasons, ecosystems, and scales to illu- microbes. This deep rooting markedly inorganic carbon (DIC) flowed downslope at minate the role of weathered bedrock and changes the chemistry of that fractured bed- their hillside study site and accumulated in deep rooting in carbon cycling and climate rock and the water that flows through it. the groundwater at the hill’s base and that dynamics. ( Journal of Geophysical Research: In a new study, Tune et al. investigated car- DIC originating from the weathered bedrock Biogeosciences, https://​­doi​.­org/​­10.1029/​ bon cycling and fluxes within weathered bed- accounted for 63%-80% of the total amount 2020JG005795,­ 2020) —Elizabeth Thompson, rock several meters beneath an ­old-​­growth exported from the hillslope. This process ­Science Writer

42 Eos // APRIL 2021 RESEARCH SPOTLIGHT

Juno Maps Water Ice Across Northern Ganymede

upiter’s moon Ganymede is the largest tial resolution of up to 23 kilometers per tions, the researchers found largely good planetary satellite in the solar system. pixel. agreement. This congruence enabled them to JIt’s also one of the most intriguing: As Juno flies past Ganymede, the spacecraft extend the global water ice map for Ganymede Ganymede is the only moon with its own can observe physical locations on the moon’s to much more northerly latitudes. magnetic field, it is the most differentiated of surface from a variety of angles. By compar- Observations in other spectral bands also all moons, and it likely possesses a subsurface ing the brightness of these regions across a revealed the presence of nonwater chemical ocean of liquid water. It was studied by the range of observation and illumination geom- species on the surface of Ganymede, includ- early Jupiter flybys made by the Pioneer and etries, the authors developed a photometric ing possible detections of hydrated magne- Voyager spacecraft, but our understanding model for Ganymede’s surface reflectance. sium salts, ammonia, carbon dioxide, and a today rests largely on observations made by They observed that ­wavelength-​­dependent range of organic molecules. The authors note NASA’s Galileo orbiter from 1995 to 2003. reflectance relationships sometimes break that 2020 offered additional opportunities for Mura et al. now report some of the first in down in the vicinity of relatively fresh craters, Juno to make polar observations of Gany- situ observations of Ganymede since the end perhaps because of a larger average size of ice mede, as does 2021, and suggest that continu- of the Galileo mission. They used the Jovian grains in these regions. ing observations from JIRAM will help set Infrared Auroral Mapper ( JIRAM) on board Combining their model with spectral obser- observation strategies in future observing NASA’s Juno spacecraft to take images and vations of the ­2-micrometer water ice absorp- campaigns like the Europa Clipper and Jupiter spectra of the moon’s north polar region. On tion band allowed the authors to map the dis- Icy Moons Explorer ( JUICE) missions. ( Journal 26 December 2019, Juno passed Ganymede at tribution of water ice in the north polar region. of Geophysical Research: Planets, https://​­doi​ a distance of about 100,000 kilometers, Where these estimates overlapped with maps .­org/​­10.1029/​­2020JE006508, 2020) —Morgan­ enabling JIRAM to map this region at a spa- derived from Earth-­ based​­ telescopic observa- Rehnberg,­ ­Science ­Writer

Untangling Drivers of Ancient Hurricane Activity

orecasts of hurricane frequency in a warming world remain unclear. Although scientists believe climate change will increase Fstorm intensity, the data are murkier about whether climate will drive more hurricanes in the future. For coastal communities, under- standing ­long-​­term hurricane trends is consequential: The Congres- sional Budget Office estimates that tropical cyclones cost the U.S. economy $54 billion annually. To inform understanding of climate’s role in past and future hurri- cane activity, Wallace et al. investigated whether climate explains pat- terns of long-­ ​­term hurricane occurrence recorded in sediment cores. Using sandy layers in cores from South Andros Island in the Bahamas as a reference, the authors developed a model to mimic hurricane pat- terns captured in the sediments over thousands of years. They then generated 1,000 different “pseudorecords” from the same climate sim- ulation, each of which represented a theoretical hurricane history at a single location. Each individual record contained intervals of active and quiet hurri- cane activity that resembled the real patterns in the Bahamas sediment cores. If climate were responsible for these intervals, then the periods of activity and quiet should have occurred at approximately the same times in all the pseudorecords.­ However, the researchers found that the This image, captured by the European Space Agency’s ­Sentinel-3 satellite, shows intervals occurred at very different times in each record, leading them the massive extent of Hurricane Dorian, one of the most powerful Atlantic hurri- to conclude that the hurricane patterns over the past millennium canes on record, as it passed over the Bahamas in September 2019. Credit: Euro- observed in the sediment cores more likely resulted from randomness pean Space Agency, CC ­BY-​­SA 2.0 (­bit.ly/​­ccbysa2-0) than from climate variations. That is not to say that hurricanes occur randomly, the researchers note, but rather that climate does not clearly explain the pattern seen in any single sedimentary record. The authors inferred that if randomness shapes individual paleohu- broader data compilations to tease out climate’s role in long-­ term​­ hur- rricane records, then no single location history can implicate climate ricane activity. (Geophysical Research Letters, https://​­doi​.org/­ ​­10.1029/​ as the driver of storm patterns. The results thus highlight the need for ­2020GL091145, 2021) —Aaron­ Sidder,­ ­Science ­Writer

SCIENCE NEWS BY AGU // Eos.org 43 RESEARCH SPOTLIGHT

Can Satellites Fill Gaps in Agricultural Water Monitoring?

s Earth’s population continues to ers are using. Installing metering devices on sensing methodologies for this purpose increase and anthropogenic climate irrigation wells is one potential solution, but remain large and may lead to substantial wel- A change threatens the habitability farmers may not cooperate with these efforts fare losses for farmers. of parts of our planet, freshwater manage- for fear of being charged for drawing too A major goal of the new study was to exam- ment is becoming a ­life-​­or-​­death issue for much water. As a result, metering remains ine how past research validated satellite esti- millions. Agriculture uses more of Earth’s rare in rich countries and is almost nonexis- mates of water use, particularly how they fresh water than any other sector, primarily tent in ­low-​­income areas. compared with in situ measurements. Of for crop irrigation. In places where water is An alternative solution that many scien- 26 studies that sought to use satellite data to scarce, policymakers are eager to regulate tists have proposed is using satellite remote estimate irrigation water use, only 7 com- water usage and incentivize more conscien- sensing to try to monitor irrigation water pared findings with measurements collected tious practices. usage. But in a new ­meta-analysis​­ of numer- on the ground at spatial scales relevant to a Key to advancing these goals, however, is ous past studies spanning 1980–2020, Foster single field or farm. Furthermore, the results accurately measuring how much water farm- et al. suggest that uncertainties in remote from this small group of validated studies showed that there were large differences— between 20% and 60%—between the satellite estimates and farmers’ actual water use. The authors also calculated the impact that these errors would have on both farmers’ incomes and water systems. They show that water use measurement errors could have severe impacts on agricultural profitability and could reduce the ability to effectively manage scarcity and competition over water resources. The authors conclude that remote sensing should not be seen as a quick fix to ­long-​­standing challenges of in situ water monitoring and that greater transparency is needed about uncertainties in these methods and their implications for water policy. (Water Resources Research, https://​­doi​.­org/​­10.1029/​ 2020WR028378,­ 2020) —David­ Shultz, ­Science A field in southern Alberta, Canada, is irrigated. Credit: Marcia O’Connor, CC BY 2.0 (bit.ly/ccbyy2-0)​­ ­Writer

A Thirstier Atmosphere Will Increase Wildfire Risk out West

ecent years have seen the largest, most drying out vegetation and making it more region will become 6–10 times more common destructive wildfires on record in Cal- flammable. Previous research has explored during summer and 4–6 times more common Rifornia. Accompanying these extreme how climate change will affect fire risk in the during autumn. This increase—driven pri- events have been extreme levels of evapora- ­California-​­Nevada region, but the specific marily by rising air temperatures spurred by tive demand—the degree to which the atmo- influences of future changes in evaporative climate change—will significantly boost the sphere “wants” to evaporate water from demand have been unclear. risk of extreme wildfires. The researchers plants and the ground, regardless of how The researchers used a tool called the Evap- also show that the likelihood of extreme much water is available. orative Demand Drought Index to explore multiyear droughts will increase, poten- A new analysis of global climate model ­short-​­term (­2-​­week) changes in evaporative tially posing threats to water supplies in the simulations by McEvoy et al. suggests that demand that could affect fire risk. They also region. evaporative demand will increase in Califor- used the tool to examine ­longer-term​­ changes These new findings could help inform nia and Nevada through the end of the cen- in evaporative conditions that could help development of ­long-​­term strategies for tury, driving increased risk of more extreme drive multiyear droughts. wildfire and water resource management in wildfires and drought. The analysis predicts that by the end of California and Nevada. (Earth’s Future, https://​ High evaporative demand—a thirstier this century, short-­ term​­ extremes in evapo- ­doi.​ ­org/10.1029/​­ 2020EF001736,​­ 2020) —Sarah­ atmosphere—can boost wildfire danger by rative demand in the ­California-​­Nevada Stanley, ­Science ­Writer

44 Eos // APRIL 2021 AGU ADVANCES EDITORS PRESENT THE LATEST RESEARCH // EDITORS’ HIGHLIGHTS

Water Stress Controls the Capacity of the Terrestrial Carbon Sink

Satellite observations over the past nearly higher GPP in the middle and high latitudes, during episodic drought, a positive climate 4 decades have captured changes in plant counterbalanced by accelerated decreases at feedback. The emergence of water stress at photosynthetic activity tied to increased lower latitudes (10°N–10°S), including the higher latitudes could switch regions of neg- greenness, concurrent with increasing Amazon, Congo, and Southeast Asian rain ative climate feedback to positive feedback, atmospheric carbon dioxide. Using an forests. accelerating the global downward trend in improved light use efficiency model and The increases in GPP at higher latitudes carbon uptake by plants in the future. This hydrometeorological data (e.g., air tempera- result from warmer temperatures and longer study demonstrates the strong coupling ture, vapor pressure deficit, and root zone growing seasons, a negative climate feedback. between the water and carbon cycles and soil moisture), Madani et al. estimated the The decreases in the tropics’ GPP result from highlights water stress controls on the ter- evolution of spatially varying gross primary increased atmospheric water stress, further restrial carbon sink. (https://doi​­ .​ ­org/10.1029/​­ ​ productivity (GPP) globally. The results show enhanced by reductions in soil moisture ­2020AV000180, 2020) —Ana­ Barros­

Going Down: How Do Cities Carry That Weight?

A B

The weight of cities might matter either in bending of the lithosphere or in more local isostatic (“floating”) adjustment between fault blocks. (a) Modeling of flexure shows that a city-sized load produces only a trivial effect, but (b) isostatic subsidence of a local fault block could reach appreciable maximum values depending on local lithospheric thickness. Credit: Parsons, 2020

Most everyone knows that humans affect their environment, but our in relative sea level matter a great deal. (https://​­doi​.­org/​­10.1029/​ thinking usually focuses on domains like the atmosphere or oceans. ­2020AV000277, 2020) —Peter­ Zeitler­ Parsons provides an intriguing look at an Earth-­ system​­ linkage that gets little attention: the direct impacts of humans on the solid Earth. Focus- ing on the Bay Area in California, he shows that the mass added by building cities can cause modest but appreciable subsidence, something u Sign up for the AGU Advances digest: that should be folded into assessment and planning for sea level rise. agu.org/advances-digest It will be interesting to see this sort of analysis done for other tectonic settings, particularly low-lying conurbations where even small changes

SCIENCE NEWS BY AGU // Eos.org 45 POSITIONS AVAILABLE

• Experience and working knowl- marine science emphasis areas in The Career Center (findajob.agu.org) is AGU’s main resource edge of using observations for model biological, physical, chemical, and calibration and statistical downscal- geological oceanography, as well as for recruitment advertising. ing techniques hydrographic science and undergrad- • Experience in computer science, uate ocean engineering. Marine Sci- AGU offers online and printed recruitment advertising in Eos ­high-​­performance computing, cloud ence faculty and graduate programs to reinforce your online job visibility and your brand. computing (Amazon AWS) are based out of Stennis Space Center. Visit employers.agu.org for more information. • Experience with GIS tools (Arc- The Marine Science and Ocean Engi- GIS, QGIS, GDAL) neering undergraduate programs are • FM Global is an Equal Opportu- delivered at the USM Gulf Coast Cam- Eos is published monthly. nity Employer and is committed to pus in Long Beach, MS as well as at attracting, developing and retaining USM’s main campus in Hattiesburg, Deadlines for ads in each issue are published at eos.org/advertise. a diverse workforce. MS. The Long Beach campus is near Eos accepts employment and open position advertisements from governments, Contact: the Port of Gulfport, which is the individuals, organizations, and academic institutions. We reserve the right to Applicants are encouraged to send home port for USM’s R/V Point Sur accept or reject ads at our discretion. a recent CV to Tiara Adducie (­tiara​ and the new UNOLS Regional Class .­adducie@​­fmglobal​.­com) OR directly Research Vessel R/V Gilbert R. Mason. Eos is not responsible for typographical errors. apply online to job # ­2020-​­10186 The Port of Gulfport also features the Marine Research Center, which has a state-­ ​­of-​­the-​­art fabrication lab, Employer: University of Southern testing tank, and laboratory space. Atmospheric Sciences and innovative leadership in the fol- Mississippi Applicants must hold a Ph.D. in lowing research areas: Position: Asst. or Assoc. Professor of engineering or a related field and have Employer: FM Global Severe Weather (severe convec- Ocean Engineering • research experience related to the Position: ­Post-​­doctoral Fellow- tion, hail, winter storms, nor’easters) Location: Stennis Space Center, Mis- ocean. The successful candidate will be ships – Weather and Climate Risks Tropical Cyclones sissippi; Gulfport, Mississippi • required to pass a NASA background Location: Norwood, Massachusetts Wildfire The Division of Marine Science in • security check to work at Stennis, Exciting and interesting technical Climate Change the School of Ocean Science and Engi- • and a USM employment background challenges await when you join a Required: neering (SOSE) at The University of check. Preference will be given to can- ­world-class​­ research team dedicated PhD degree in atmospheric or Southern Mississippi invites qualified • didates with experience in developing to reducing the impact of natural environmental science (or related applicants for a ­full-​­time, ­9-month, academic programs and curriculums. hazards and climate risks! FM Global quantitative field) ­tenure-​­track faculty position in The candidate has participated in an is a market leader in commercial and Broad physical and process-­ ​ Ocean Engineering at the assistant or • ABET accreditation process. The can- industrial property insurance and ­level understanding of at least one of associate professor level to begin in didate should have ­post-​­doctoral loss prevention, providing more the following core research areas: Fall 2021. Rank and salary will be research experience, a demonstrated than ­one-​­third of FORTUNE 1000 severe weather, tropical cyclones, commensurate with experience. record of scholarship, service, grant companies with ­engineering-​­based wildfire, climate change The successful candidate will have development, communication, and risk management and property Solid knowledge of the funda- the opportunity to contribute to the • commitment to diversity, and has insurance solutions. FM Global helps mentals of climate change including continued development of the under- experience in managing a research clients maintain continuity in their uncertainties and impacts for at least graduate Ocean Engineering pro- group. The candidate should have a business operations by drawing upon two (preferably more) key perils: gram, which started in 2017, and lead national or international reputation state-­ ​­of-​­the-​­art engineering and major precipitation, drought, wild- its ABET accreditation. Moreover, the for excellence in their discipline. research. fire, riverine/coastal flooding, sea candidate is expected to develop a Applications must be submitted The Structures and Natural Haz- level rise, tropical cyclones, and strong, externally funded research through the jobs.usm.edu candidate ards research group at FM Global is severe weather program, publish ­peer-​­reviewed lit- portal (req1742). Review of applica- looking for creative, ­self-​­motivated Demonstrated experience using erature, mentor students, participate • tions begins 3/15/2021 and continues individuals. Selected candidates will or developing global and/or regional in undergraduate instruction and until the position is filled, with an work alongside a unique group of sci- climate models, analyzing output develop courses in their area of study. anticipated start date of 8/2021. For entists across engineering, earth, and from global climate model ensem- The candidate should demonstrate questions, please contact the chair atmospheric sciences to protect the bles, and combining large atmo- the potential to contribute across dis- of the search committee, maarten­ ​ value of our clients’ businesses. This spheric datasets in formats including ciplines and promote the continued .­buijsman@​­usm​.­edu. is done by developing methods to NetCDF, HDF, and GRIB. interdisciplinary growth of the aca- identify hazards, assess risk, and pro- • Strong analytical skills and solid demic and research programs within duce loss prevention solutions that knowledge of probability and statis- the SOSE. Employer: Washington University are efficient and ­cost-​­effective. The tics The SOSE includes two academic Position: Postdoctoral Position in positions provide an opportunity to • ­Hands-​­on experience using, divisions, Marine Science and Coastal Data Visualization for Planetary engage in solving real-­ ​­world sci- developing, and evaluating statistical Sciences, and several R&D centers. and Space Sciences ence and engineering problems with and numerical models The Division of Marine Science is Location: Saint Louis, Missouri immediate impact. This position is • Experienced writing shell scripts based at the NASA’s John C. Stennis The Department of Earth and Plan- for a term of up to three years, renew- and using APIs for process automa- Space Center. Stennis Space Center is etary Sciences at Washington Univer- able each year. The role is typically tion. Excellent programming skills in a “federal city” that boasts the world’s sity in Saint Louis seeks a motivated focused on performing publishable at least two programming languages largest concentration of oceanogra- postdoctoral research associate to work as part of a strategic research including Python, R, Matlab, Fortran phers and hydrographers. Marine manage a unique data visualization program under the mentorship of a • Excellent oral and written com- ­Science faculty benefit from close program within the Fossett Labora- program manager or senior research munication and presentation skills. working relationships with ­on-​­site tory for Virtual Planetary Exploration. staff member(s). Demonstrated efficiency communi- federal agencies, including the Naval The Fossett Lab is a leader in the Requirements: cating highly technical and scientific Research Laboratory-­ ​­Stennis Space development of applications and out- Candidates will evaluate, develop, insights to ­non-​­technical audiences Center, the Naval Oceanographic reach experiences that leverage Aug- and implement techniques and Desired: Office, the Naval Meteorology and mented Reality (AR) technology for ­models that will lead to impactful • Solid research record (including Oceanography Command, the USGS, education and research in Earth, improvements in risk analytics and publications) and demonstrated and NOAA including its National Data planetary, and space science. The suc- loss prevention for atmospheric and expertise on natural hazards for the Buoy Center and the National Centers cessful candidate will collaborate with ­climate-​­related perils. Strong desire following key perils: severe weather, for Environmental Information. the Fossett Lab Director to build and to expand their research experience tropical cyclones, wildfire, climate Marine Science (under)graduate maintain AR experiences that serve beyond academia and bring expertise change programs extend across traditional the needs of Washington University

46 Eos // APRIL 2021 POSITIONS AVAILABLE

instructors and scholars, and coordi- ­Professor-​­Research (­non-​­tenure) basin, and global scale ­circulations–​ both a forced ocean and a fully nate educational and outreach activ- and will collaborate with existing ­impacts the cycling of carbon, nutri- ­coupled-to-​­ atmosphere​­ context. The ities with students, faculty, adminis- geoscience-­ ​­focused research pro- ents, and oxygen, with an emphasis candidate would focus on the devel- trators, and alumni. grams at LSU. on the Southern Ocean. opment of numerical methods and The candidate selected for this The successful candidate will hold Individuals will join a vigorous algorithms in the regional version of position will also conduct research as a PhD in Earth Science or a related interdisciplinary research group MOM6, and would participate in the an associate of the McDonnell Center field and a minimum of 12 years of under the direction of Professor Cur- development of new regional appli- for the Space Sciences (MCSS), and experience ­post-​­PhD in a research tis Deutsch at Princeton University cations to be used to address ques- will contribute to this vibrant research setting and three (3) years supervisory and in close collaboration with col- tions in predictability, climate and community studying planetary mate- experience. Questions regarding the laborators at the member institutions Earth system model ­down-​­scaling, rials, surfaces, and processes. In their job position can be sent to Dr. Kevin of the Southern Ocean Carbon and ecosystem science and fisheries. application materials, the candidate Xu (­kxu@lsu​­ .​ ­edu), Search Committee Climate Observations and Modeling The ideal candidate has a strong should describe their research inter- Chair. Review of applications will (­SOCCOM) project sponsored by NSF background in one or more areas ests and list potential collaborators begin on March 1, 2021, and will con- Polar Programs. Available resources among dynamical oceanography, from among the faculty fellows of the tinue until the position is filled. Apply include ­state-​­of-​­the-​­science ocean dynamical meteorology, applied MCSS. or learn more about the position on physics and biogeochemistry models mathematics, or numerical methods. Candidates must have a PhD in the LSU Career Site ­bit​.­ly/​­3aInmpC. and observational data sets of South- Experience with scientific software Earth, planetary, or space science, a ern Ocean biogeochemistry with development will be advantageous in record of excellent scholarship, and Employer: Portland State University unprecedented temporal and spatial this research. demonstrated interest in science Position: Postdoctoral Scholar coverage. Candidates must have a Ph.D. in communication, data visualization, Location: Portland, Oregon Candidates must have received a either oceanography, meteorology, and programming for AR/VR envi- The Department of Civil and Envi- Ph.D. in the earth sciences, applied applied mathematics, physics, or a ronments. ronmental Engineering at Portland math, or the physical, biological, or related field. Initial appointment is The initial appointment will be for State University has a Postdoctoral chemical sciences. Rigorous training for one year with the possibility of one year and is renewable for a sec- scholar position open. The successful in oceanic sciences is preferred along renewal subject to satisfactory per- ond year. Salary is highly competi- candidate will participate in a ­team-​ with very strong dynamical, model- formance and available funding. tive, and research and travel funding ­oriented project focused on develop- ing, and quantitative skills. Postdoc- Complete applications, including will be available. Washington Univer- ing watershed and riverine water toral appointments are initially for a CV with a list of publications, a sity is an equal opportunity and affir- quality transport and fate models. one year with the renewal for sub­ statement of research interests (no mative action employer. Duties for this position include, but sequent years based on satisfactory more than 2 pages including refer- To apply, please contact Professor are not limited to: performance and continued funding. ences), and contact information of Phil Skemer (pskemer@­ ​­wustl​.edu),­ 1) modifying and evaluating water- A competitive salary is offered com- 3 references should be submitted by Fossett Lab Director, with a state- shed and riverine water quality mod- mensurate with experience and qual- March 31, 2021, 11:59 p.m. EST for full ment of interest, CV, and contact els; ifications. consideration. Princeton is inter- information for three references. 2) developing and testing trans- Applicants are asked to submit a ested in candidates who, through port and biogeochemical processes of cover letter, vitae, a publication list, their research, will contribute to the nutrients and toxic chemicals; a statement of research experience diversity and excellence of the aca- and interests, and names of at least demic community. Applicants Biogeosciences 3) performing data analysis; and 4) developing and/or contributing 3 references. Applicants should apply should apply online https://­ ​­www​ online to https://­ www​­ .​ princeton­ .​ edu/­ ​ .­princeton​.­edu/​­acad​-­positions/​ Employer: Louisiana State University to project products including reports, ­acad​-­positions/​­position/​­19561. position/­ 19521.​­ Position: Director of the Louisiana journal articles, and presentations. Review of applications will begin For more information about the Geological Survey (LGS) and State Successful candidates will have a as soon as they are received and con- research project and application pro- Geologist (R00053299) Ph.D. in hydrology, hydraulics, envi- tinue until the position is filled. This cess, please contact Robert Hallberg Location: Baton Rouge, Louisiana ronmental engineering, chemical position is subject to the University’s (robert­ ​.hallberg@­ ​­noaa​.gov),­ Charlie The Office of Research and Eco- oceanography, biogeochemistry, or a background check policy. Stock (­charles​.­stock@​­noaa​.gov), or nomic Development at Louisiana related field. The candidate must Princeton University is an equal Alistair Adcroft (­aadcroft@princeton​­ ​ State University invites applications have experience in numerical model opportunity/affirmative action .­edu). for the position of Director of the and programming such as Fortran, employer and all qualified appli- This position is subject to the ­Louisiana Geological Survey (LGS) Python, etc. cants will receive consideration for ­University’s background check pol- and State Geologist. The individual For further details or to apply to employment without regard to age, icy. Princeton University is an equal selected for this appointment will this position, please visit: race, color, religion, sex, sexual ori- opportunity/affirmative action guide existing programs in applied https://jobs​­ .​ ­hrc.​ ­pdx.​ ­edu/postings/​­ ​ entation, gender identity or expres- employer, and all qualified appli- geosciences; build new programs that ­33507 sion, national origin, disability status, cants will receive consideration for support stewardship and develop- protected veteran status, or any other employment without regard to age, ment of the State’s natural resources; Employer: Princeton University characteristic protected by law. race, color, religion, sex, sexual ori- and provide the State and its citizens Position: Research at the intersection entation, gender identity or expres- with geological information relevant of ocean physics and biogeochem- sion, national origin, disability status, to economic resources, environ­ istry protected veteran status, or any other mental protection, and natural haz- Location: Princeton, New Jersey Ocean Sciences characteristic protected by law. ards. The Director will position LGS The AOS Program’s ocean biogeo- in a leadership role in such areas as chemistry group seeks energetic and Employer: Princeton University coastal processes critical to the enthusiastic postdoctoral or more Position: Postdoc in regional ocean State’s economy and environment; senior researchers to participate in model development W T C M E M E O P T S innovative approaches to natural ­process-​­oriented studies using the- Location: Princeton, New Jersey W O R S T E P I C B R A T W E A T H E R I N G R O O M resources: geothermal energy, oil, ory, modeling, and observations to The Atmospheric and Oceanic Sci- T I D A L S P I T coal, & natural gas, raw materials, develop understanding at the inter- ences Program, in association with O P E N T O R I R E E F S water, coastal systems; and new section of ocean physics and biogeo- NOAA’s Geophysical Fluid Dynamics F O R T H T E C T O N I S M chemistry. This effort is part of a T I S S U E L O A F N H S opportunities such as carbon capture, Laboratory (GFDL), seeks a postdoc- B A L A N C E storage and utilization. The Director broad study of ocean circulation, the toral or more senior researcher to T O P C R O P O S I R I S will expand upon LGS’s current global carbon cycle, and climate work in the area of regional ocean V O L C A N I S M S N I P S strengths in geological mapping, change. Of particular interest is how model development. S H A R P N E A T C F O S T E S T L I M I T water resources, GIS and cartography, ocean dynamics at a range of spatial This work involves further devel- A G E S S U B D U C T I O N and shallow crust geophysics. The ­scales—from submesoscale/meso- oping the regional capabilities of the G O A T A F R O G E N R E Director will hold the rank of scale fronts and eddies to regional, MOM6 numerical ocean model, in O P U S R O A N G E T

SCIENCE NEWS BY AGU // Eos.org 47 CROSSWORD

Geoprocesses By Russ Colson, Minnesota State University Moorhead

ACROSS 1 2 3 4 5 6 7 8 9 10 11 Calls for Proposals 1 Cmplx attacked 11 Sept. 2001 4 Child’s response to the question, “Who 12 13 14 15 16 wants some candy?” 8 Chooses 17 18 19 AGU Fall Meeting 2021 12 The baddest of the bad 15 Type of long poem 20 21 22 16 Unruly child 17 Geoprocess in which Earth’s atmosphere 23 24 25 26 27 28 29 30 13–17 December interacts with crustal rock 19 Separate space in a building 31 32 33 34 20 Related to a process observed daily along coastlines 35 36 37 38 21 Feature formed by crustal processes that New Orleans, LA carry sediment across the entrance of an 39 40 estuary 23 Not closed 41 42 43 44 45 46 47 48 49 25 Shapes of donuts—or actress Spelling 28 High-diversity continental shelf 50 51 52 53 environments at risk due to climate Submission Deadline 14 April change 54 55 56 57 31 Forward, as in “from this day _____”

33 Geoprocess in which crustal rocks are 58 59 60 61 deformed by internal forces Group of specialized cells in animals 35 62 63 64 65 66 67 68 37 Opposite of work hard, or baked quantity of bread 69 70 71 38 Healthcare provider in Great Britain (abbr.) 39 Central concept in understanding 72 73 74 equilibrium in Earth systems, such as glacier mass _____ or atmospheric energy _____ 41 Physics toy 44 Food from the Earth DOWN 30 Service for sending brief texts, 45 Egyptian god of food from the Earth 1 An information system in which briefly 50 Geoprocess common at active plate documents are identified by URLs 32 Toppers for tires? margins in which gases and molten rock 2 Part of a glacier where the terminal 34 Beef or chicken in a shell? emerge from the crust moraine accumulates 36 Deserve through labor 53 They make little pieces 3 Features formed when meteorites strike 40 Cut of meat 54 Like obsidian flakes a planet 41 Home entertainment radio slayers 55 Not slovenly 4 Bordeaux wine grape of the 1950s? 57 Head financial executives (abbr.) 5 Start for -dermal, -genetic, or -center 42 Companion to aah 58 Shell of a one-celled creature—or a 6 Time for 70 heart beats (abbr.) 43 High, flat landscape challenge in class 7 Heart tests (abbr.) 46 Stir up (violence) 60 No more fish allowed 8 Potatoes with onions and peppers 47 Geoprocess in which crustal plates 62 Geological subdivisions of periods and 9 Amino acid chain pull apart epochs 10 The Way, in Chinese philosophy 48 First sale of company stock (abbr.) 64 Geoprocess common near active 11 Imaging instrument that won the 1986 49 Snake sound continental margins in which crustal rock Nobel Prize in physics, or scanning 51 Tops of mountains or waves AGU Fall Meeting brings together a diverse, collaborative community is returned to the mantle tunneling microscope (abbr.) 52 Sea salt from Essex HELP SHAPE THE 69 Bearded, with kids? 13 Periods of work, as in “I had a couple of 56 Germanic god of war of Earth and space scientists and partners dedicated to discovery 70 High-volume hairstyle _____ as a geologist” 59 Russian emperor and solutions to societal challenges. Proposals are invited for topics 71 Type, as of a movie or book 14 A doctorate in religious studies (abbr.) 61 Unit for small mass in medicine (abbr.) across a broad range of scientific disciplines and sessions that focus 72 Work, as of music or art 18 Many do it three times per day 62 Time word in Star Wars opening DISCUSSION DURING #AGU21 73 Horse of a different color? 22 Start for -or and -ion, referring to jobs crawl on areas such as diversity, inclusion and ethics; open and fair data; new 74 Procure—or understand 23 Frequently 63 U.S. political party technologies; engineering and design and science communication. 24 Hawaiian food made from taro root Flying saucer, e.g. 65 Science is interwoven into and a component of everything around the 26 Illness return 66 Undergarment agu.org/fall-meeting 27 Venerated or representative symbol 67 Source material for metals world. Submit your session proposal and tell us “what science is” for you! See page 47 for the answer key. 29 Earth’s first vertebrates (without the 68 What’s cut down after a basketball Now accepting proposals for vowel) tournament • General scientific sessions • Union and special sessions 48 Eos // APRIL 2021 • Town halls • Scientific workshops Calls for Proposals AGU Fall Meeting 2021 13–17 December New Orleans, LA

Submission Deadline 14 April

AGU Fall Meeting brings together a diverse, collaborative community HELP SHAPE THE of Earth and space scientists and partners dedicated to discovery and solutions to societal challenges. Proposals are invited for topics across a broad range of scientific disciplines and sessions that focus on areas such as diversity, inclusion and ethics; open and fair data; new DISCUSSION DURING #AGU21 technologies; engineering and design and science communication. Science is interwoven into and a component of everything around the agu.org/fall-meeting world. Submit your session proposal and tell us “what science is” for you! Now accepting proposals for • General scientific sessions • Union and special sessions • Town halls • Scientific workshops