TERMITES vs. DESERTS

FROM:  THE NATIONAL SCIENCE FOUNDATION
Dirt mounds made by termites in Africa, South America, Asia could prevent spread of deserts
Termites create oases of moisture, plant life
February 5, 2015

Termites might not top the list of humanity's favorite insects, but new research suggests that their large dirt mounds are crucial to stopping deserts from spreading into semi-arid ecosystems.

The results indicate that termite mounds could make these areas more resilient to climate change.

The findings could also inspire a change in how scientists determine the possible effects of climate change on ecosystems.

In the parched grasslands and savannas, or drylands, of Africa, South America and Asia, termite mounds store nutrients and moisture and via internal tunnels, allow water to better penetrate the soil.

As a result, vegetation flourishes on and near termite mounds in ecosystems that are otherwise vulnerable to desertification.

Researchers report in this week's issue of the journal Science that termites slow the spread of deserts into drylands by providing a moist refuge for vegetation on and around their mounds.

Drylands with termite mounds can survive on significantly less rain than those without termite mounds.

Not all termites are pests

"This study demonstrates that termite mounds create important refugia for plants and help to protect vast landscapes in Africa from the effects of drought," said Doug Levey, program director in the National Science Foundation's Division of Environmental Biology, which funded the research.

"Clearly," said Levey, "not all termites are pests."

The research was inspired by the fungus-growing termite species, Odontotermes, but the results apply to all types of termites that increase resource availability on or around their mounds.

Corresponding author Corina Tarnita, a Princeton University ecologist and evolutionary biologist, said that termite mounds also preserve seeds and plant life, which helps surrounding areas rebound faster once rainfall resumes.

"Because termites allow water to penetrate the soil better, plants grow on or near the mounds as if there were more rain," said Tarnita. "The vegetation on and around termite mounds persists longer and declines slower.

"Even when you get to harsh conditions where vegetation disappears from the mounds, re-vegetation is still easier. As long as the mounds are there the ecosystem has a better chance to recover."

The stages of desertification: Where termites fit in

In grasslands and savannas, five stages mark the transition to desert, each having a distinct pattern of plant growth.

The researchers found that these plant growth patterns exist on a much smaller scale than previously thought. Overlaying them is the pattern of termite mounds covered by dense vegetation.

The termite-mound pattern, however, looks deceptively similar to the last and most critical of the five stages that mark the transition of drylands to desert.

Vegetation patterns that might be interpreted as the onset of desertification could mean the opposite: that plants are persevering thanks to termite mounds.

Termite mounds help grassland plants persevere

Robert Pringle, an ecologist and evolutionary biologist at Princeton and co-author of the paper, said that the unexpected function of termites in savannas and grasslands suggests that ants, prairie dogs, gophers and other mound-building creatures could also have important roles in ecosystem health.

"This phenomenon and these patterned landscape features are common," Pringle said.

"Exactly what each type of animal does for vegetation is hard to know in advance. You'd have to get into a system and determine what is building the mounds and what the properties of the mounds are.

"I like to think of termites as linchpins of the ecosystem in more than one way. They increase the productivity of the system, but they also make it more stable and more resilient."

Termites: Linchpins of the ecosystem

A mathematical model developed for the work determines how these linchpins affect plant growth.

The scientists applied tools from physics and mathematical and numerical analysis to understand a biological phenomenon, said paper first author Juan Bonachela of Strathclyde University in Scotland.

The model allowed the researchers to apply small-scale data to understand how rainfall influences vegetation growth and persistence in the presence and absence of termites across an entire ecosystem.

"Similar studies would be extremely challenging to perform in the field and would require very long-term experiments," Bonachela said.

"Models such as this allow us to study the system with almost no constraint of time or space and explore a wide range of environmental conditions with a level of detail that can't be attained in the field."

Additional support for the research was provided by a Princeton Environmental Institute Grand Challenges grant, the National Geographic Society, the Andrew W. Mellon Foundation and a John Templeton Foundation Foundational Questions in Evolutionary Biology grant.

-NSF-
Media Contacts
Cheryl Dybas, NSF

EARTH'S PAST CHANGING POLARITY

FROM:  NATIONAL SCIENCE FOUNDATION 

Geomagnetic reversal: Understanding ancient flips and flops in Earth's polarity
Researcher boards R/V Sikuliaq to gather data about Earth's geomagnetic history
Imagine one day you woke up, and the North Pole was suddenly the South Pole.

This geomagnetic reversal would cause your hiking compass to seem impossibly backwards. However, within our planet's history, scientists know that this kind of thing actually has happened...not suddenly and not within human time scales, but the polarity of the planet has in fact reversed, which has caused scientists to wonder not only how it's happened, but why.

This week, as the National Science Foundation (NSF) research vessel R/V Sikuliaq continues its journey towards its home port in University of Alaska Fairbanks' Marine Center in Seward, Alaska, she detours for approximately 35 days as researchers take advantage of her close proximity to the western Pacific Ocean's volcanic sea floors. With the help of three types of magnetometers, they will unlock more of our planet's geomagnetic history that has been captured in our Earth's crust there.

"The geomagnetic field is one of the major physical properties of planet Earth, and it is a very dynamic property that can change from milliseconds to millions of years. It is always, always changing," said the expedition's chief scientist, Masako Tominaga, an NSF-funded marine geophysicist from Michigan State University. "Earth's geomagnetic field is a shield, for example. It protects us from magnetic storms--bursts from the sun--so very pervasive cosmic rays don't harm us. Our research will provide data to understand how changes in the geomagnetic field have occurred over time and give us very important clues to understand the planet Earth as a whole."

Flipping and flopping

Reportedly, the last time, a geomagnetic reversal occurred was 780,000 years ago, known as the Brunhes-Matuyama reversal. Bernard Brunhes and Motonori Matuyama were the geophysicists who identified that reversal in 1906.

Researchers Tominaga, Maurice Tivey (from Woods Hole Oceanographic Institution) and William Sager (from University of Houston) have an interest that goes further back in history to the Jurassic period, 145-200 million years ago when a curious anomaly occurred. Scientists originally thought that during this time period, no geomagnetic reversals had happened at all. However, data--like the kind that Tominaga's team will be collecting--revealed that in fact, the time period was full of reversals that occurred much more quickly.

"We came to the conclusion that it was actually 'flipping flopping,' but so fast that it did not regain the full strength of the geomagnetic field of Earth like today's strength. That's why it was very low," Tominaga explained. "The Jurassic period is distinctive. We think that understanding this part of the geomagnetic field's behavior can provide important clues for computer simulation where researchers have been trying to characterize this flipping and flopping. Our data could help predict future times when we might see these reversals again."

Better tools equal better data

For approximately three decades, researchers like Tominaga have been probing this area of the western Pacific seafloor. With her cruise on R/V Sikuliaq, Tominaga and Tivey come with even more technology in hand.

Thirty years ago, researchers didn't have access to autonomous underwater vehicles (AUV) that could go to deeper, harder-to-reach ocean areas. However, that is just one of three ways Tominaga's team will deploy three magnetometers during its time at sea. One magnetometer will be towed at the seasurface from R/V Sikuliaq. Another will trail behind the ship at mid-water depth, and the third will be part of the AUV at near the seafloor.

"The seafloor spreading at mid-ocean ridge occurred because of volcanic eruption over time. And when this molten lava formed the seafloor, it actually recorded ambient geomagnetic data. So when you go from the very young ocean seafloor right next to the mid-ocean ridge to very, very old seafloor away from the mid-ocean ridge, a magnetometer basically unveils changes in the geomagnetic field for us," Tominaga said. "The closer we can get to the seafloor, the better the signal. That's the rule of thumb for geophysics."

With the help of R/V Sikuliaq's ship's crew, Tominaga and Tivey, a cruise archivist who is also a computer engineer/scientist, and seven students (three of whom are undergraduates), the team will run 24 hours a day/seven days a week operations, deploying underway geophysics, the magnetometers, collecting data and then moving on to the next site.

Naturally, the weather can waylay even the best plans. "Our goal is always about the science, but the road likely will be winding," Tominaga said. "The most enjoyable part of this work is to be able to work together with this extremely diverse group of people. The Sikuliaq crew, the folks at UAF and those connected to the ship from NSF have all been committed to seeing this research happen, which is incredibly gratifying.... When we make things happen together as a team, it is really rewarding."

Focus on fundamentals

Not surprisingly, this kind of oceanographic research is among some of the most fundamental, serving as a foundation for other research where it might correlate or illuminate. Additionally, because the causes and impacts of these geomagnetic changes are unknown, connections to currents, weather patterns, and other geologic phenomenon can still be explored also.

"NSF, along with the entire science community, has waited years for this unique state-of-the-art Arctic vessel, and the timing couldn't be more critical," said Rose DuFour, NSF program director. "Our hope is to use R/V Sikuliaq to help carry out the abundant arctic-based seagoing science missions that go beyond NSF-funded science and extend to those from other federal agencies, like Office of Naval Research as well."

Tominaga notes that another key part to the cruise's mission is record keeping; it's why an archivist is part of her team. He even will blog daily (with pictures). As foundational research, it's important to "keep every single record intact," and she believes this broadcasting daily narrative will assist in this effort.

"Without going there, getting real data--providing ground truth--how do we know what is going on?" Tominaga said, explaining fieldwork's importance.

Tominaga is quite clear on what prompts her to keep one of the busiest fieldwork schedules, even during a season usually reserved for family and friends, sipping eggnog or champagne. "I was 'raised' as a scientist/marine geophysicist, and I don't just mean academically," she said. "I really looked up to my mentors and friends and how they handed down what they know-so unselfishly. And when I was finishing my Ph.D., I realized that there will be a time I will hand down these things to the next generation. Now, as a professor at Michigan State University, I'm the one who has to pass the torch, if you will--knowledge, experience, and skills at sea. That's what drives me."

-- Ivy F. Kupec
Investigators
Masako Tominaga
Maurice Tivey
William Sager
Related Institutions/Organizations
Woods Hole Oceanographic Institution
Locations
Western Pacific Seafloor , Hawaii
Related Programs
Marine Geology and Geophysics

COMPUTER SIMULATIONS, STATISTICAL TECHNIQUES INDICATE CALIFORNIA DROUGHT LIKELY LINKED TO CLIMATE CHANGE

FROM:  NATIONAL SCIENCE FOUNDATION 

Cause of California drought linked to climate change

Extreme atmospheric conditions responsible for drought more likely to occur in current global warming.

The atmospheric conditions associated with the unprecedented drought in California are very likely linked to human-caused climate change, researchers report

Climate scientist Noah Diffenbaugh of Stanford University and colleagues used a novel combination of computer simulations and statistical techniques to show that a persistent region of high atmospheric pressure over the Pacific Ocean--one that diverted storms away from California--was much more likely to form in the presence of modern greenhouse gas concentrations.

The result, published today in the Bulletin of the American Meteorological Society, is one of the most comprehensive studies to investigate the link between climate change and California's ongoing drought.

"Our research finds that extreme atmospheric high pressure in this region--which is strongly linked to unusually low precipitation in California--is much more likely to occur today than prior to the emission of greenhouse gases that began during the Industrial Revolution in the 1800s," says Diffenbaugh.

The exceptional drought crippling California is by some measures the worst in state history.

Combined with unusually warm temperatures and stagnant air conditions, the lack of precipitation has triggered a dangerous increase in wildfires and incidents of air pollution across the state.

The water shortage could result in direct and indirect agricultural losses of at least $2.2 billion and lead to the loss of more than 17,000 seasonal and part-time jobs in 2014 alone.

Such effects have prompted a drought emergency in the state; the federal government has designated all 58 California counties as natural disaster areas.

"In the face of severe drought, decision-makers are facing tough choices about the allocation of water resources for urban, agricultural and other crucial needs," says Anjuli Bamzai, program director in the National Science Foundation's (NSF) Division of Atmospheric and Geospace Sciences, which funded the research.

"This study places the current drought in historical perspective and provides valuable scientific information for dealing with this grave situation. "

Scientists agree that the immediate cause of the drought is a particularly tenacious "blocking ridge" over the northeastern Pacific--popularly known as the Ridiculously Resilient Ridge, or "Triple R"--that prevented winter storms from reaching California during the 2013 and 2014 rainy seasons.

Blocking ridges are regions of high atmospheric pressure that disrupt typical wind patterns in the atmosphere.

"Winds respond to the spatial distribution of atmospheric pressure," says Daniel Swain of Stanford, lead author of the paper.

"We have seen this amazingly persistent region of high pressure over the northeastern Pacific for many months, which has substantially altered atmospheric flow and kept California largely dry."

The Triple R was exceptional for both its size and longevity.

While it dissipated briefly during the summer months of 2013, it returned by fall 2013 and persisted through much of the winter, California's wet season.

"At its peak in January 2014, the Triple R extended from the subtropical Pacific between California and Hawaii to the coast of the Arctic Ocean north of Alaska," says Swain, who coined the term "ridiculously resilient ridge" to highlight the persistent nature of the blocking ridge.

Like a large boulder that has tumbled into a narrow stream, the Triple R diverted the flow of high-speed air currents known as the jet stream far to the north, causing Pacific storms to bypass not only California, but also Oregon and Washington.

As a result, rain and snow that would normally fall on the West Coast were instead re-routed to Alaska and as far north as the Arctic Circle.

An important question for scientists and decision-makers has been whether human-caused climate change has influenced the conditions responsible for California's drought.

Given the important role of the Triple R, Diffenbaugh and colleagues set out to measure the probability of such extreme ridging events.

The team first assessed the rarity of the Triple R in the context of the 20th century historical record.

Analyzing the period since 1948, for which comprehensive atmospheric data are available, the researchers found that the persistence and intensity of the Triple R in 2013 were unrivaled by any previous event.

To more directly address the question of whether climate change played a role in the probability of the 2013 event, the team collaborated with scientist Bala Rajaratnam, also of Stanford.

Rajaratnam applied advanced statistical techniques to a large suite of climate model simulations.

Using the Triple R as a benchmark, Rajaratnam compared geopotential heights--an atmospheric property related to pressure--between two sets of climate model experiments.

One set mirrored the present climate, in which the atmosphere is growing increasingly warmer due to human emissions of carbon dioxide and other greenhouse gases.

In the other set of experiments, greenhouse gases were kept at a level similar to those that existed just prior to the Industrial Revolution.

The researchers found that the extreme heights of the Triple R in 2013 were at least three times as likely to occur in the present climate as in the preindustrial climate.

They also found that such extreme values are consistently tied to unusually low precipitation in California, and to the formation of atmospheric ridges over the northeastern Pacific.

"We've demonstrated with high statistical confidence that large-scale atmospheric conditions similar to those of the Triple R are far more likely to occur now than in the climate before we emitted large amounts of greenhouse gases," Rajaratnam says.

"In using these advanced statistical techniques to combine climate observations with model simulations, we've been able to better understand the ongoing drought in California," Diffenbaugh adds.

"This isn't a projection of 100 years in the future. This is an event that is more extreme than any in the observed record, and our research suggests that global warming is playing a role right now."

The research was also supported by the National Institutes of Health. Rajaratnam was also supported in part by DARPA, the Air Force Office of Scientific Research and the UPS fund.

-NSF-
Media Contacts
Cheryl Dybas, NSF,

SCIENTISTS REPORT CALIFORNIA GROUNDWATER DEPLETION MAY INCREASE EARTHQUAKE RISK

FROM:  NATIONAL SCIENCE FOUNDATION 

California Central Valley groundwater depletion slowly raises Sierra Nevada mountains

Changes may trigger small earthquakes, scientists find

Winter rains and summer groundwater pumping in California's Central Valley make the Sierra Nevada and Coast Mountain Ranges sink and rise by a few millimeters each year, creating stress on the state's faults that could increase the risk of an earthquake.

Gradual depletion of the Central Valley aquifer, because of groundwater pumping, also raises these mountain ranges by a similar amount each year--about the thickness of a dime--with a cumulative rise over the past 150 years of up to 15 centimeters (6 inches), according to calculations by a team of geophysicists.

The scientists report their results in this week's issue of the journal Nature.

While the seasonal changes in the Central Valley aquifer have not yet been firmly associated with any earthquakes, studies have shown that similar levels of periodic stress, such as that caused by the motions of the moon and sun, increase the number of microquakes on the San Andreas Fault.

If these subtle seasonal load changes are capable of influencing the occurrence of microquakes, it's possible that they can sometimes also trigger a larger event, said Roland Bürgmann, a geoscientist at the University of California, Berkeley and co-author of the Nature paper.

"The stress is very small, much less than you need to build up stress on a fault leading to an earthquake, but in some circumstances such small stress changes can be the straw that breaks the camel's back," Bürgmann said. "It could just give that extra push to get a fault to fail."

The study, based on GPS measurements from California and Nevada between 2007 and 2010, was led by scientists Colin Amos at Western Washington University and Pascal Audet of the University of Ottawa.

The detailed GPS analyses were performed by William Hammond and Geoffrey Blewitt of the University of Nevada, Reno, as part of a National Science Foundation (NSF) grant. Hammond and Blewitt, along with Amos and Audet, are also co-authors of this week's paper.

"Other studies have shown that the San Andreas Fault is sensitive to small-scale changes in stress," said Amos.

"These appear to control the timing of small earthquakes on portions of the fault, leading to more small earthquakes during drier periods of the year. Previously, such changes were thought to be driven by rainfall and other hydrologic causes."

This work ties overuse of groundwater by humans in the San Joaquin Valley to increases in the height of nearby mountain ranges and possible increases in the number of earthquakes on the San Andreas Fault, said Maggie Benoit, program director in NSF's Division of Earth Sciences, which funded the research.

"When humans deplete groundwater," said Benoit, "the amount of mass or material in Earth's crust is reduced. That disrupts Earth's force balances, causing uplift of nearby mountains and reducing a force that helps keep the San Andreas fault from slipping."

Draining of the Central Valley

Water has been pumped from California's Central Valley for more than 150 years, changing what used to be a marsh and extensive lake, Tulare Lake, into fertile agricultural fields.

In that time, about 160 cubic kilometers (40 cubic miles) of water was removed--the capacity of Lake Tahoe--dropping the water table in some areas more than 120 meters (400 feet) and the ground surface 5 meters (16 feet) or more.

The weight of water removed allowed the underlying crust or lithosphere to rise by so-called isostatic rebound, which may have raised the Sierra as much as half a foot since about 1860.

The same rebound happens as a result of the state's seasonal rains.

Torrential winter storms drop water and snow across the state, which eventually flow into Central Valley streams, reservoirs and underground aquifers, pushing down the crust and lowering the Sierra 1-3 millimeters.

In the summer, water flow into the Pacific Ocean, evaporation and ground water pumping for irrigation, which has accelerated because of drought, allows the crust and surrounding mountains to rise again.

Bürgmann said that the flexing of Earth's crust downward in winter would clamp the San Andreas fault tighter, lowering the risk of quakes, while in summer the upward flexure would relieve this clamping and perhaps increase the risk.

"The hazard is ever so slightly higher in the summer than in the wintertime," he said. "This suggests that climate and tectonics interact, and that water changes ultimately affect the deeper Earth."

High-resolution mapping with continuous GPS

Millimeter-precision measurements of elevation have been possible only in the last few years. Improved continuous GPS networks--part of the NSF EarthScope Plate Boundary Observatory, which operates 1,100 stations around the western United States--and satellite-based interferometric synthetic aperture radar have provided the data.

The measurements revealed a steady yearly rise of the Sierra of 1-2 millimeters per year, which was initially ascribed to tectonic activity deep underground, even though the rate was unusually high.

The new study provides an alternative and more reasonable explanation for the rise of the Sierra in historic times.

"The Coast Range is doing the same thing as the Sierra Nevada, which is part of the evidence that this can't be explained by tectonics," Bürgmann said.

"Both ranges have uplifted over the last few years and both exhibit the same seasonal up and down movement in phase. This tells us that something has to be driving the system at a seasonal and long-term sense, and that has to be groundwater recharging and depletion."

In response to the current drought, about 30 cubic kilometers (7.5 cubic miles) of water has been removed from Central Valley aquifers between 2003 and 2010, causing a rise of about 10 millimeters (2/5 inch) in the Sierra over that time.

-NSF-



Media Contacts
Cheryl Dybas, NSF