feb 20 mag

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VOL. 101 | NO. 2 Our Magnetic Brains
FEBRUARY 2020
Los Angeles’s
Shaky Underbelly
Beavers: Nature’s Firefighters
Up in
Smoke
As wildfires scorch the land,
scientists are using novel methods
to study the damage to our air.

FROM THE EDITOR
Editor in Chief
Heather Goss, AGU, Washington, D.C., USA; [email protected]
Editorial
Finding Wildfire’s Fingerprint
Manager, News and Features Editor Caryl-Sue Micalizio
Science Editor Timothy Oleson
in the Atmosphere Senior News Writer Randy Showstack
News Writer and Production Associate Kimberly M. S. Cartier
News and Production Fellow Jenessa Duncombe
Production & Design
Wildfires seem to be everywhere in the news lately. Manager, Production and Operations Faith A. Ishii
Senior Production Specialist Melissa A. Tribur
For those of us in the United States, and particularly
Editorial and Production Coordinator Liz Castenson
in California, “wildfire season” evokes a clear sense Assistant Director, Design & Branding Beth Bagley
of dread, having personally touched so many us. (I have several Senior Graphic Designer Valerie Friedman
Graphic Designer J. Henry Pereira
friends who lost homes—thankfully, though, nothing more—
during the 2017 Thomas Fire in my hometown.) As the calen- Marketing
dar turned over to 2020, wildfires in Australia had burned more
Director, Marketing, Branding & Advertising Jessica Latterman
than 10 million acres in a month—at what was only the start Assistant Director, Marketing & Advertising Liz Zipse
a blazingly hot and dry summer. In Indonesia, ultrafine par- Marketing Program Manager Angelo Bouselli
Senior Specialist, Digital Marketing Nathaniel Janick
ticles from agricultural practices that ignite peatlands have
Digital Marketing Coordinator Ashwini Yelamanchili
serious effects on the health of tens of thousands of people in
the region each year. Advertising
The air is filling with smoke. Scientists, gratefully, are busy Display Advertising Dan Nicholas
[email protected]
figuring out the answers to all our questions: What is the smoke made of, where is it all going,
Recruitment Advertising Heather Cain
and just how bad is it? We’ve compiled this special issue of Eos to take a close look at the grow- [email protected]
ing field of wildfire emissions research, pulling in experts from across a dozen disciplines of
Science Advisers
the geosciences.
Geomagnetism, Paleomagnetism, Julie Bowles
Ralph Kahn of NASA Goddard Space Flight Center offers us “A Global Perspective on Wild- and Electromagnetism
fires” on page 18. An expert on aerosols and remote sensing technology, Kahn describes the Space Physics and Aeronomy Christina M. S. Cohen
Cryosphere Ellyn Enderlin
many satellite instruments being used to study wildfire emissions today. Scientists are over-
Study of the Earth’s Deep Interior Edward J. Garnero
coming the disadvantages of observations from space from any one satellite (e.g., relatively Geodesy Brian C. Gunter
low resolution, narrow observation bands, orbital paths that limit revisits) by combining data History of Geophysics Kristine C. Harper
from what are now a wealth of instruments overhead. The gaps in these low- Earth- orbit obser- Planetary Sciences Sarah M. Hörst
Natural Hazards Michelle Hummel
vations of smoke plumes, in both spatial and temporal coverage, can also be filled in by chem- Volcanology, Geochemistry, and Petrology Emily R. Johnson
ical transport models; the models themselves can be constrained and validated by the obser- Seismology Keith D. Koper
vational data. With each pass overhead, our Earth observers are giving us a clearer picture of Tectonophysics Jian Lin
Near-Surface Geophysics Juan Lorenzo
smoke emissions and how they travel through the atmosphere.
Earth and Space Science Informatics Kirk Martinez
A major challenge right now is figuring out the effects of wildfires on global climate, and Paleoceanography and Paleoclimatology Figen Mekik
the reverse: the changing climate’s effect on wildfires. On page 30 (“Firing Up Climate Mod- Mineral and Rock Physics Sébastien Merkel
Ocean Sciences Jerry L. Miller
els”), you’ll meet the FIREX-AQ team flying over the western United States in a DC-8, trying
Global Environmental Change Philip J. Rasch
to collect enough information to more accurately incorporate fires into global climate models. Education Eric M. Riggs
It’s a herculean job when one considers the wild variations of fires in size, biomass fuel, and, Hydrology Kerstin Stahl
Tectonophysics Carol A. Stein
of course, whether they’re ignited by human or natural sources. Most models today don’t even
Atmospheric Sciences Mika Tosca
attempt to incorporate them, but FIREX-AQ and several other teams in our feature story believe Nonlinear Geophysics Adrian Tuck
that understanding wildfires is crucial to truly understanding—and forecasting—our climate. Hydrology Adam S. Ward
Earth and Planetary Surface Processes Andrew C. Wilcox
For a bit of respite from these disasters, turn to page 12 (“Beavers: Nature’s ‘Little Firefight-
Atmospheric and Space Electricity Yoav Yair
ers’”) to learn about some habitat protection provided by our favorite dam builders. Ecohy- GeoHealth Ben Zaitchik
drologist Emily Fairfax searched through records of forest fires in North America that occurred Societal Impacts and Policy Sciences Mary Lou Zoback
near beaver habitats and discovered that their dams acted as irrigation channels, keeping
nearby vegetation insulated from the flames. Be sure to visit this news story online to view ©2020. AGU. All Rights Reserved. Material in this issue may be photocopied by
the stop-motion animation Fairfax created to illustrate the beavers’ influence on their wooded individual scientists for research or classroom use. Permission is also granted
to use short quotes, figures, and tables for publication in scientific books and
surroundings (bit.ly/natures-firefighters). journals. For permission for any other uses, contact the AGU Publications Office.
Visit us at Eos.org for all these articles and many more as part of our wildfire emissions spe- 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.,
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Submit your article proposal or suggest a news story to Eos at bit.ly/Eos-proposal.
Views expressed in this publication do not necessarily reflect official positions
of AGU unless expressly stated.
Heather Goss, Editor in Chief Christine W. McEntee, Executive Director/CEO
EARTH & SPACE SCIENCE NEWS // Eos.org 1
CONTENT
24
18 30
Features
18 A Global Perspective 24 Exposing Los Angeles’s
on Wildfires Shaky Geologic Underbelly
By Ralph Kahn By Robert W. Clayton et al.
Satellites provide global-scale data that are invaluable Current calculations might underestimate the
in efforts to understand, monitor, and respond to susceptibility of Los Angeles to earthquake shaking,
wildfires and emissions, which are increasingly so researchers and volunteers are deploying seismic
affecting climate and putting humans at risk. networks around the city to remedy a data shortage.
30 Firing Up Climate Models
On the Cover
Wildfires in Russia, seen here, burned so large and so close to By Adityarup Chakravorty
population centers in 2019 that several Siberian cities were
Scientists are working to incorporate wildfire data into
choked under clouds of smoke for days. Credit: Anton Petrus/
climate models, resolving hindrances related to scale,
Moment/Getty Images
speed, and the complex feedbacks between the climate
and wildfire emissions.
2 Eos // FEBRUARY 2020
CONTENT
13 42
16 44
Columns
From the Editor AGU News
1 Finding Wildfire’s Fingerprint in the Atmosphere 35 Celebrating the 2019 Class of Fellows
News Research Spotlight
4 Using Satellites and Supercomputers to Track 41 An Intergrated History of the Australian-
Arctic Volcanoes Antarctic Basin
5 Will Melting Sea Ice Expose Marine Animals 42 Forecasting Volcanic Eruptions
to New Diseases? with Artificial Intelligence
7 Human Brains Have Tiny Bits of Magnetic Material 42 Sunlight Stimulates Brown Algae to Release
8 A Dirty Truth: Humans Began Accelerating Organic Carbon
Soil Erosion 4,000 Years Ago 43 Curiosity Rover Reveals Oxygen Mystery
9 Geophysics Recruits Radio Telescopes in Martian Atmosphere
10 What Do You Get When You Cross a Thunderstorm 44 Theoretical Models Advance Knowledge
with a Wildfire? of Ocean Circulation
11 Using Garnets to Explore Arc Magma Oxidation 44 A “Super” Solution for Modeling Clouds
12 Beavers: Nature’s “Little Firefighters”
Positions Available
Opinion
45 Current job openings in the Earth and space sciences
13 Creating Spaces for Geoscientists with Disabilities
Postcards from the Field
to Thrive
16 Improving Reproducibility in Earth Science Research
48 Bedrock flow processes are the focus of these
researchers, who say hello to us from the Laramie
Range in Wyoming.
AmericanGeophysicalUnion @AGU_Eos company/american-geophysical-union AGUvideos americangeophysicalunion americangeophysicalunion
EARTH & SPACE SCIENCE NEWS // Eos.org 3
NEWS
Using Satellites and Supercomputers
to Track Arctic Volcanoes
Conical clues of volcanic activity speckle Geophysical Research Letters in 2017 (bit . ly/ often missing. Now ArcticDEM measure-
the Aleutian Islands, a chain that measure- l ava). The success of that research ments spanning over a decade can be used to
spans the meeting place of the Pacif ic guided her current applications of ArcticDEM better understand and monitor changes to
Ring of Fire and the edge of the Arctic. (The for terrain mapping. the Arctic surface shortly following such
chain also spans the U.S. state of Alaska Monitoring long-t erm changes in a volca- events, as well as years later.
and the Far Eastern Federal District of Rus- nic landscape is important, said Dai. “Ashes For example, the volcanic eruption at
sia.) Scientists are now turning to advanced easily can flow away by water and by rain and Okmok resulted in a sudden 2 00-m eter ele-
satellite imagery and supercomputing to then cause dramatic changes after the erup- vation gain from the new cone’s formation
measure the scale of natural hazards like vol- tion,” she said. “Using this data, we can see
canic eruptions and landslides in the Aleu- these changes…so that’s pretty new.”
tians and across the Arctic surface over time. Creating time series algorithms with the
When Mount Okmok in Alaska unexpect- ArcticDEM data set, Dai tracks elevation
edly erupted in July 2008, satellite images changes from natural events and demon-
informed scientists that a new 200- meter strates the algorithms’ potential for moni-
cone had grown beneath the ashy plume. But toring the Arctic region. Her work has already
scientists suspected that topographic changes shown that erosion continues years after a
didn’t stop with the eruption and its imme- volcanic event, providing first- of- their- kind
diate aftermath. measurements of posteruption changes to
For l ong-t erm monitoring of the eruption, the landscape. Dai presented this research at
Chunli Dai, a geoscientist and senior research AGU’s Fall Meeting 2019 in San Francisco,
associate at the Ohio State University, Calif. (bit . ly/ DEMs - land - surface).
accessed an extensive collection of digital
elevation models (DEMs) recently released by Elevating Measurement Methods
ArcticDEM, a joint initiative of the National “This is absolutely the best resolution DEM
Geospatial- Intelligence Agency and the data we have,” said Hannah Dietterich, a
National Science Foundation. With Arctic- research geophysicist at the U.S. Geological
DEM, satellite images from multiple angles Survey’s Alaska Volcano Observatory not
are processed by the Blue Waters petascale involved in the study. “Certainly, for volca-
supercomputer to provide elevation mea- noes in Alaska, we are excited about this.” In this map of ArcticDEM coverage, warmer colors
sures, producing h igh-r esolution models of Volcanic events have traditionally been indicate more overlapping data sets available for
the Arctic surface. measured by aerial surveys or drones, which time series construction. Blue and red rectangles
Dai first used these models to measure are expensive and t ime-c onsuming methods mark mass wasting events, triangles identify volca-
variations in lava thickness and estimate the for l ong-t erm study. Once a hazardous event noes, and red stars show locations of active layer
volume that erupted from Tolbachik volcano occurs, Dietterich explained, the “before” detachments and retrogressive thaw slumps, both
in Kamchatka, Russia, in work published in shots in before- and- after image sets are used for studying landslides. Credit: Chunli Dai
The 2008 Okmok eruption in Alaska resulted in a new volcanic cone, as well as consistent erosion of that cone’s flanks over subsequent years. The volcano’s ring-shaped
plume is visible in the center of this satellite image. Credit: NASA image courtesy of Jeff Schmaltz, MODIS Rapid Response Team, N ASA Goddard Space Flight Center
4 Eos // FEBRUARY 2020
NEWS
Will Melting Sea Ice Expose
but also showed continuing erosion rates
along the cone flanks of up to 15 meters each
year. Marine Animals to New Diseases?
Landslides and Climate
For Dai, landslides provide an even more
exciting application of ArcticDEM technology.
Landslides are generally unmapped, she
explained, whereas “we know the locations of
volcanoes, so a lot of studies have been done.”
Mass redistribution maps for both the Kar-
rat Fjord landslide in Greenland in 2017 (bit
. ly/K arrat- F jord) and the Taan Fiord landslide
in Alaska in 2015 (bit. ly/T aan- landslide) show
significant mass wasting captured by DEMs
before and after the events.
“We’re hoping that our project with this
new data program [will] provide a mass wast-
ing inventory that’s really new to the com-
munity,” said Dai, “and people can use it,
especially for seeing the connection to global
warming.” Northern sea otters are just one of many marine mammal species that can contract the phocine distemper virus
Climate change is associated with many (PDV), which is related to the canine distemper virus. Credit: U.S. Environmental Protection Agency
landslides studied by Dai and her team, who
focus on mass wasting caused by thawing
permafrost. ArcticDEM is not currently
intended for predictive modeling, but as In 2004, Tracey Goldstein was trying to Northern sea otters “don’t move widely,”
crack a marine mammal mystery. Gold- said Goldstein, so the emergence of PDV in
stein, associate director of the One Health the Alaskan population “really surprised” her
Institute at the University of California, Davis and her colleagues. Researchers realized the
School of Veterinary Medicine, was part of a virus was likely transmitted to the otters by
“If we can measure [the
team digging for answers about why Alaska’s some species of marine mammal that had
changing Arctic northern sea otter populations were plum- contact with European harbor seals exposed
meting. to the virus. “Nomadic Arctic seals with cir-
environment], then we can
The falling number of otters was curious. cumpolar distributions (e.g., ringed and
get the linkage between Before the decline began, decreases in the bearded, Erignathus barbatus, seals) and geo-
killing of otters for the fur trade had actually graphic ranges that intersect with those of
global warming and its
sparked a population rebound, Goldstein said. harp seals, may be carriers of PDV to the
impact on the Arctic land.” Researchers still don’t know exactly what North Pacific,” researchers write in Scientific
made the otter populations dwindle. How- Reports (bit . ly/ PDV - mammals).
ever, Goldstein was shocked by something This explanation presented one big prob-
she and her colleagues discovered while lem: Contact between Arctic and s ub- A rctic
screening the animals for a variety of dis- seal species was assumed to be impossible
more data are collected over time, patterns eases. Some of the animals had been exposed due to Arctic sea ice separating the species.
may emerge that could help inform future to the phocine distemper virus (PDV), which This left the team wondering whether there
permafrost loss or coastal retreat in the Arc- is pathogenic for pinnipeds and is closely could be a connection between the rapid
tic, according to Dietterich. “It is the best related to the measles virus and the canine melting of Arctic sea ice, driven by climate
available archive of data for when crises distemper virus. change, and the emergence of PDV in the
happen.” otters.
Global climate trends indicate that Arctic Same Virus, Different Location
environments will continue to change in the This wasn’t the first time researchers identi- Boundaries Melting Away
coming years. “If we can measure that, then fied a PDV outbreak in marine mammals. An In an international study conducted between
we can get the linkage between global warm- estimated 23,000 European harbor seals were 2001 and 2016, Goldstein and her colleagues
ing and its impact on the Arctic land,” said killed after they were sickened by the virus in probed connections between virus transmis-
Dai. 1988. In 2002, a second epidemic hit the sion patterns and environmental factors to
northern Atlantic Ocean, killing approxi- understand when and how PDV was intro-
mately 30,000 harbor seals. duced into the North Pacific.
By Lara Streiff (@laragstreiff), Science Commu- However, this was the first time a PDV out- “The study is ambitious in its interdisci-
nication Program Graduate Student, University break was confirmed in the northern Pacific plinary effort to summarize immunologi-
of California, Santa Cruz Ocean. cal data on prevalence of antibodies to PDV,
EARTH & SPACE SCIENCE NEWS // Eos.org 5
NEWS
molecular data on the P DV strain, and data on sea lions. They also collected blood and tissue ice along the Russian coast was closed was
animal behavior and migration patterns” samples from 165 dead animals found on significantly associated with PDV exposure or
with ice extent data, said Karin Hårding, an beaches or that people had hunted for food. infection,” they add.
associate professor of biology and environ- The researchers then screened the samples Goldstein thinks that the PDV case pro-
mental studies at the University of Gothen- for active infection and the presence of anti- vides the first documented connection
burg in Sweden. Hårding wasn’t involved with bodies, which signify past exposure. between reduced sea ice coverage and the
the study. In addition, researchers “incorporated sat- emergence of a virus in a marine mammal
ellite telemetry data from ongoing ecological species.
studies of seals and Steller sea lions, which Hårding was more cautious. The relation-
provided a unique opportunity to combine ships between phenomena like ice coverage
animal movement and epidemiologic data of the Arctic basin and the prevalence of
In 2004, scientists
to understand the potential spread of PDV,” antibodies “will always be correlations but
confirmed the first instance they write. do not prove causal relationships,” she
The scientists noticed two spikes in Pacific wrote. “However, the authors do not claim
of a phocine distemper
PDV exposure and infection: one from 2003 [causation]. They just highlight interesting
virus outbreak in the to 2004 and another in 2009. August or Sep- patterns that coincide,” she added.
tember of 2002 and 2008 were months with As sea ice continues to melt in this warm-
northern Pacific Ocean.
reduced amounts of Arctic sea ice, resulting ing world, will marine species be exposed to
in the opening of water routes between Rus- other diseases from which they were previ-
sia’s Arctic coast and the Pacific Ocean. ously isolated? Only time will tell, but “it has
Furthermore, in both 2001 and 2007, “sea happened once, and there’s likely going to be
ice blocked passage through at least part of the opportunity for it to happen again,” Gold-
Researchers collected nasal swab and blood the Arctic Ocean bordering Russia’s coast,” stein remarked.
samples from 2,530 live animals, including the researchers note. “When controlling for
northern sea otters, ice- associated seals animal group and age class, presence of an
(including bearded, ribbon, spotted, and open water route along the northern Russian By Rachel Crowell (@writesRCrowell), Science
ringed seals), northern fur seals, and Steller coast following a year in which the Arctic sea Writer
6 Eos // FEBRUARY 2020
NEWS
Human Brains Have Tiny Bits of Magnetic Material
Scientists have mapped magnetic mate-
rials in human brains for the first time,
revealing that our brains may selec-
tively contain more magnetic material in
their lower and more ancient regions.
Researchers used seven specimens donated
in Germany to measure brain tissue for signs
of magnetite, Earth’s most magnetic mineral.
Scientists have known that other types of life,
such as special kinds of bacteria, contain
magnetite. But the distribution of magnetite
in human brains has been unclear because no
systematic study had mapped the mineral in
human tissue before.
The results could shine a light on why Humans have areas of the brain that are more magnetic than other areas. Warm colors show higher levels
humans have magnetite in their brains to of magnetic resonance, measured here in nanoampere-square meter (or its magnetic moment) per kilogram
begin with, which remains an open question. of brain tissue. The upper region of the brain, the cerebrum, has low levels. The lower in the brain you go, the
Stuart Gilder, lead author of the study and a stronger the magnetic signal grows and are particularly high in the brain stem. Credit: Gilder et al., 2018, https://
scientist at Munich University, said that the doi . org/10 . 1038/ s41598- 018- 29766- z
team’s results show that magnetic particles
exist in the “more ancient” part of the brain.
“We thought from an evolutionary stand-
point, that was important,” Gilder said. study was not so different, he said. “I could movement and autonomic functions like
essentially apply everything that I do to rock heart rate and breathing.
Magnetic Minds to brains,” Gilder said. The scientists cut the Gilder said that the pattern emerged in each
Scientists discovered the first hints of mag- preserved brains into 822 pieces and ran each of the seven brains, and it showed no differ-
nets in human brains in 1992, when a paper sample through a magnetometer, a machine ence depending on the person’s age or sex.
reported that tiny crystal grains, some barely in their lab used to measure records of Earth’s The brain stem had consistently higher mag-
wider than a DNA strand, were found in magnetic field in rocks. netization than any other region, although
human brain tissue from seven patients in Whether Gilder is studying rocks or brains, only five of the seven brains had intact brain
California (bit. l y/M agnetic- M inds). The crys- he measures their magnetism in two steps: stems.
tals looked just like the tiny magnets in mag- First, he tests a material’s natural magnetic Joseph Kirschvink, a professor at the Cali-
netotactic bacteria that help them navigate strength, which will typically be low. (Even if fornia Institute of Technology in Pasadena
along geomagnetic field lines in lakes and a material contains magnetic particles, their not involved in the study, said that the work
saltwater environments. dipoles point in random directions, poten- “confirms the biological origin of the brain
No one knows why or how magnetite gets tially canceling each other out.) magnetite.” Kirschvink said that the results
into human brains. Magnetite could serve Second, Gilder uses an electromagnet to in the study closely matched research he had
some physiological function, such as signal apply a strong magnetic field to the sample, performed in his lab, but the latest research
transmission in the brain, but scientists are which aligns the tiny magnetic particles so has “100 times more data.”
able only to speculate. One study of the fron- that they all face the same direction. “If I The scientists took pains to limit contam-
tal cortex of 37 human brains suggests that measure something that is more magnetic ination, cutting the samples with a ceramic
we breathe in magnetite from the environ- after I’ve applied a very big magnetic field, knife and staging the experiment inside a
ment through our noses. But other research- that’s proof that this material contains mag- magnetically shielded room in a forest far
ers, like Gilder, think magnetite comes from netic recording particles,” Gilder said. from urban pollution. They removed samples
internal sources. For the brain samples, the comparison with high levels of natural magnetic strength
revealed that magnetite was in “almost every that could have been polluted with fragments
From Rocks to Brains piece” of the specimens, said Gilder. of the saw cutting into the donors’ skulls
To find out some answers, Gilder and his team many years ago. Even with the potentially
dissected seven brains and measured their “The Exact Same Pattern” contaminated samples removed, the data still
magnetic strength and orientation. The The latest study reveals that the lower regions showed an anatomical pattern.
brains had been preserved in formaldehyde of the human brain, including the cerebellum Gilder presented the research at AGU’s Fall
since the 1990s, when relatives and guardians and the brain stem, had 2 or more times the Meeting 2019 in San Francisco, Calif. (bit. ly/
of the deceased donated them to science. The magnetic remanence of the upper regions of human - brain).
brains came from four men and three women the brain. The upper regions of the brain
between the ages of 54 and 87. compose the cerebrum, which is responsible
Gilder typically studies rocks in his lab to for reasoning, speech, and other tasks, By Jenessa Duncombe (@jrdscience), Staff
ascertain their geologic history, but his latest whereas the lower regions handle muscle Writer
EARTH & SPACE SCIENCE NEWS // Eos.org 7
NEWS
A Dirty Truth: Humans Began Accelerating
Soil Erosion 4,000 Years Ago
In a way, human history is etched in the soil. data that would either destroy or support the
An international team of researchers different hypotheses that were behind the
recently found evidence that we humans trends,” Carvalhais explained.
have been leaving our mark on this planet In the end, humans were the most likely
since long before the Industrial Revolution. culprit.
Around 4,000 years ago, human activities had Changes in erosion were less related to
already significantly accelerated soil erosion fluctuations in precipitation and tempera-
around lake beds on a global scale. ture, researchers found, whereas trends in
“We have been imprinting our presence deforestation coincided with the rise in ero-
[on] the landscape and in the natural world sion. Jenny and his collaborators analyzed
further back than we thought,” said Nuno pollen samples at each lake bed site to pro-
Carvalhais, a research group leader at the Max duce a proxy for tree coverage of the sur-
Planck Institute for Biogeochemistry and the rounding land; they found that decreases in
senior researcher on the study published in tree cover were tightly coupled with acceler-
Proceedings of the National Academy of Sciences ated erosion. “Deforestation at the time was
of the United States of America (bit . ly/ human caused by the human beings, because at that
- imprint). time they were starting to develop agricul-
The findings required an interdisciplinary ture,” said Jenny.
approach, with different types of analyses
allowing a more comprehensive picture of Humanity’s Past and Future
how human activities could be behind the Written in the Dirt
accelerating erosion, Carvalhais said. Although soil erosion accelerated 4,000 years
Jean-P hilippe Jenny, a French geoscientist ago in Europe, similar trends occurred only
“What you come away with
affiliated with the Max Planck Institute for recently in North America, probably following
Biogeochemistry and the Alpine Center for European immigration and importation of is the lesson that societies
Research on Trophic Networks and Lake Eco- agricultural practices.
that don’t take care of their
systems and lead author of the study, ana- The research team also found that 23% of
lyzed core samples of sediments collected lake sites had a decrease in erosion rates, soil don’t last.”
from 632 lake beds around the world. Because which may be the result of human- driven
sediments accumulate in lakes at continuous river management, such as the construction
rates, lake sediment cores can be used as a of dams.
natural archive of fluctuations in soil erosion “It means that we as human beings are
over time. now living in a time period where we have a The erosion rates produced by conven-
Combining sediment rates with radioactive huge effect on everything on the Earth, and tional agricultural practices are not sustain-
carbon dating data from each site, Jenny and all our activities will be recorded in the natu- able, and they sap crucial nutrients from the
his collaborators inferred the changes in lake ral archives,” said Jenny. soil. “What you come away with is the lesson
sedimentation accumulation rates and found “These guys have done a really remarkably that societies that don’t take care of their soil
that 35% of the sampled lakes had accelerated ambitious job putting the story together,” don’t last,” Montgomery said.
erosion over the past 10,000 years. said David Montgomery, a professor of Earth And there are broader environmental
The acceleration in erosion began around and space sciences at the University of Wash- implications too. As with many types of
4,000 years ago, and the researchers sought ington and author of Dirt: The Erosion of Civi- large- s cale human activities, increased soil
out the mechanisms that could explain this lizations. The results of the paper “put into erosion “can impact the climate in the long
trend. “We built up our hypotheses, and perspective just how powerful a force people term,” said Jenny.
based on these hypotheses, we [collected] the are on the planet today,” he said. The results of this study provide more data
e
Montgomery, who was not involved in the about “the sensitivities of the Earth system ervic
study, suggests that it was not merely defor- to climate and environmental factors, includ- e S
estation that accelerated soil erosion, but ing humans,” said Carvalhais. “And this can Wildlif
subsequent agricultural activities as well. help us improve our ability to understand and d
“oWure p hreasveen bceee [no nim] tphrein ting Tfohro wugidhe dsepfroeraeds tfaatrimoni nisg a, inneccreesassaerdy fsiorsilt esrtoep- als“oT too pgore idnictto o trh feo rfeuctausrte f,u wtuer ea slscoen naerieods .t”o S. Fish an
U.
landscape and in the sion is mainly driven by “the plow that fol- understand our history,” he added. ohn/
natural world further back ldoowwend t,h”e h tere seasi tdh.a “t Icta wusaesdn t’ht es iemropsliyo nc;u ittt winags e: Rick B
keeping them off the landscape through By Richard J. Sima (@richardsima), Science osit
than we thought.” farming practices.” Writer Opp
8 Eos // FEBRUARY 2020