FILLING IN THE MARGINS - This spring, GeoPRISMS leaves behind a legacy of research by shoreline-crossing scientists and the National Science ...
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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, Eos_EIC@agu.org
Crossing the Shoreline AGU Staff
Vice President, Communications, Amy Storey
Marketing,and Media Relations
T
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 G eoPRISMS had to make the same News and Features Writer Kimberly M. S. Cartier
adjustments all of us did and had to move those toasts into News and Features Writer Jenessa Duncombe
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 steve@mediawestinc.com
come to a close this year. Recruitment Advertising recruitmentsales@wiley.com
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 G eoPRISMS 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
Planetary Sciences Sarah M. Hörst
glimpse into the volume of research GeoPRISMS has produced. On page 22, Noel Bartlow and
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
Atmospheric and Space Electricity Yoav Yair
and we may feature it in Postcards from the Field. Usually, you’ll find these beautiful contribu-
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;
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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
SCIENCE NEWS BY AGU // Eos.org 1
CONTENT
28
22 34
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
2 Eos // APRIL 2021
CONTENT
6 44
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
Bacteria on Earth
Crossword Puzzle
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
AmericanGeophysicalUnion @AGU_Eos company/american-geophysical-union AGUvideos americangeophysicalunion americangeophysicalunion
SCIENCE NEWS BY AGU // Eos.org 3
NEWS
Coastal Erosion by Waves Versus Rainfall
C
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
occurred 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 (b it. ly/ forecast at the study site.”
veys a year,” Young said. “Those are great, coastal-cliff-e
rosion). 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
4 Eos // APRIL 2021
NEWS
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.”
F
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).
known 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-m eter- 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
SCIENCE NEWS BY AGU // Eos.org 5
NEWS
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
C
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
researchers 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
results reveal how geophysical data can com-
“People might have used was deposited and therefore when humans
were exploring these caves.
plement archaeological records. these caves as a shelter
A Summer Refuge?
The Allure of Caves
during the summer.” 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-
6 Eos // APRIL 2021
NEWS
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—
D
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 slowly 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-
imate the physical characteristics of the mov-
cauldron from the bottom up. This, she said,
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 l ong- t erm
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/t urkey 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 m easured 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.”
T
the geomagnetic poles flip every so often ype “flooding today” into your search If precipitation data and forecasting pro-
while maintaining that bar m agnet-like engine and you will likely find at least vide the foundation, hydrology frames the
behavior on average. For these successful one 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
tions and what we observe of the Earth’s Schumann and a team of scientists led by international hydrometeorological commu-
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-
8 Eos // APRIL 2021NEWS
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
A
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.” 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-i ntensity). 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
Credit: Warren Tyrer/Flickr, CC BY-ND 2.0 (bit.ly/ccbynd2-0)
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
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
Writer
SCIENCE NEWS BY AGU // Eos.org 9NEWS
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
spectrometer that measured relative irradi-
provoking ideas and differently than a spark of several hundred
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 2021NEWS
Drought, Not War, Felled Some Ancient Asian
Civilizations
T
he central Asian civilizations of the
- oasis, located at the junction of
Otrar
the 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-
- finally collapsed by the 17th cen-
ery, Otrar
tury and the region remains uninhabited
today.
- ’s decline was likely
But the cause of Otrar
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 Otrar - 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
SCIENCE NEWS BY AGU // Eos.org 11NEWS
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
A
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- 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 o ne-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 N eu-
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 2021NEWS
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.
U
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 average 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 t rade-
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 CO 2 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-
SCIENCE NEWS BY AGU // Eos.org 13You can also read
