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Hydrologists show environmental damage from fog reduction is observable from outer space

Thu, 06/04/2020 - 18:11

It’s now possible to use satellite data to measure the threat of climate change to ecological systems that depend on water from fog, according to a newly-published study.

The paper, in the AGU journal Geophysical Research Letters, presents the first clear evidence that the relationship between fog levels and vegetation status is measurable using remote sensing. The discovery opens up the potential to easily and rapidly assess fog’s impact on ecological health across large land masses — as compared to painstaking ground-level observation.

“It’s never been shown before that you can observe the effect of fog on vegetation from outer space,” said Lixin Wang, an associate professor in the School of Science at Indiana University-Purdue University Indianapolis (IUPUI), who is the senior author on the study. “The ability to use the satellite data for this purpose is a major technological advance.”

Two satellite images show vegetation change from fog in two areas of the Namib desert. The left image shows the areas during periods of lower fog; the right image shows the areas during periods of higher fog. Greener areas inside the squares indicate vegetation greening. Image courtesy of Lixin Wang, Indiana University.

The need to understand the relationship between fog and vegetation is urgent since environmental change is reducing fog levels across the globe. The shift most strongly affects regions that depend upon fog as a major source of water, including the redwood forests in California, the Atacama desert in Chile and the Namib desert in Namibia, with the latter two currently recognized as World Heritage sites under the United Nations due to their ecological rarity.

“The loss of fog endangers plant and insect species in these regions, many of which don’t exist elsewhere in the world,” said Na Qiao, a visiting student at IUPUI, who is the study’s first author. “The impact of fog loss on vegetation is already very clear. If we can couple this data with large-scale impact assessments based on satellite data, it could potentially influence environmental protection policies related to these regions.”

Fog readings were taken at two weather stations near the Gobabeb Namib Research Institute in the Namib desert of Namibia. Photo courtesy of Lixin Wang, Indiana University.

The study is based on optical and microwave satellite data, along with information on fog levels from weather stations at two locations operated by the Gobabeb Namib Research Institute in the Namib desert. The satellite data was obtained from NASA and the U.S. Geological Survey. The fog readings were taken between 2015 and 2017.

At least once a year, Wang and student researchers, including both graduate and undergraduate students from IUPUI, travel to the remote facility — a two-hour drive on a dirt road from the nearest city — to conduct field research.

The study found a significant correlation between fog levels and vegetation status near both weather stations during the entire time of the study. Among other findings, the optical data from the site near the research facility revealed obvious signs of plant greening following fog, and up to 15 percent higher measures during periods of fog versus periods without fog.

Similar patterns were seen at the second site, located near a local rock formation. The microwave data also found significant correlation between fog and plant growth near the research facility, and up to 60 percent higher measures during periods of fog versus periods without fog.

Lixin Wang, left, and a colleague conduct water research in the Namib desert. Photo courtesy of Lixin Wang, Indiana University

The study’s conclusions are based on three methods of remotely measuring vegetation: two based on optical data, which is sensitive to the vibrance of greens in plants, and a third based on microwave data, which is sensitive to overall plant mass, including the amount of water in stems and leaves. Although observable by machines, the changes in vegetation color are faint enough to go undetected by the human eye.

Next, the team will build upon their current work to measure the effect of fog on vegetation over longer periods of time, which will assist with future predictions. Wang also aims to study the relationship in other regions, including the redwood forests in California.

“We didn’t even know you could use satellite data to measure the impact of fog on vegetation until this study,” he said. “If we can extend the period under investigation, that will show an even more robust relationship. If we have 10 years of data, for example, we can make future predictions about the strength of this relationship and how this relationship has been changing over time due to climate change.”

Additional authors were Wenzhe Jiao, a Ph.D. student at IUPUI, who made significant contributions to the satellite data processing, as well as Changping Huang and Lifu Zhang of the Chinese Academy of Science and Maggs-Kölling and Eugene Marais of the Gobabeb Namib Research Institute. Qiao is also a student at the Chinese Academy of Science.

This post was originally published on the Indiana University website.

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How climate killed corals

Mon, 05/18/2020 - 15:11

A squad of climate-related factors is responsible for the massive Australian coral bleaching event of 2016. If we’re counting culprits: it’s two by sea, one by land.

First, El Niño brought warmer water to the Coral Sea in 2016, threatening Australia’s Great Barrier Reef’s corals. Long-term global warming meant even more heat in the region, according to a new study. And in a final blow that year, a terrestrial heatwave swept over the coast, blanketing the reef system well into the winter, according to Kris Karnauskas, a researcher at the University of Colorado Boulder, a Fellow with the Cooperative Institute for Research in Environmental Sciences (CIRES) and author of the new study in AGU’s journal Geophysical Research Letters.

The final toll: more than half the coral in some parts of the Great Barrier Reef died.

This animation shows the terrestrial heatwave moving through Queensland, Australia during April and May 2016. The heatwave crossed the coastline and spilled over the Great Barrier Reef in early May. The Great Barrier Reef stretches along the Queensland coast for 2,300 kilometers (1,400 miles) and is mostly within just 50 kilometers (31 miles) of the coast.
Credit: Kris Karnauskas.

“When the Great Barrier Reef bleached severely back in 2016, it earned global attention,” said Karnauskas. “Some speculated it was global warming, others thought it was El Niño, but the actual role of those two forces have not really been disentangled. As a physical climate scientist with a bias for the ocean, I thought I should dig in.”

Karnauskas dissected the reasons behind the excessively warm water in Northern Australia’s Coral Sea—water warm enough to “bleach” and kill coral, especially in the northern Great Barrier Reef. Karnauskas used satellite observations and a mathematical technique to fingerprint what phenomena led to what amount of warming, and when. It was the interaction of two key things, he found, that caused the coral-killing heat: A marine heatwave followed by a terrestrial one, both exacerbated by global warming.

First came a marine heatwave. It was El Niño that initially caused a spike in sea surface temperature by shifting the usual clouds away from the region, but global warming trends increased its intensity and extended it by several months by raising the background temperature. Then, a land-borne heatwave moved across eastern Australia and spilled out over the ocean just as the first phase of the marine heatwave was ending.

“It turns out that El Niño did play a role, and the eventual warmth was certainly higher because of the long-term trend, but the reason it lasted so long was actually this terrestrial heatwave lurking over eastern Australia until the marine warming event was just finally waning, and then: bang, the heatwave leaked out over the coastline,” Karnauskas said. “That warm air over the ocean changed the way heat is exchanged between the ocean and atmosphere, keeping the warmth and bleaching going for an extra month or so.”

Increased water temperatures off the northeastern Australian coast triggered mass death of corals on an unprecedented scale. The hot water persisted for months and caused extensive damage to the ecosystem—drastically changing the species composition of the region.

“This new finding reveals that climate variability and change can lead to marine impacts in surprising, compounding ways, including heatwaves both on land and in the ocean,” said Karnauskas. “From heatwaves to hurricanes, we need to double down on efforts to understand the complexities of how anthropogenic climate change will influence extreme events in the future.”

This post was originally published on the CIRES website.

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New evidence of watery plumes on Jupiter’s moon Europa

Tue, 05/12/2020 - 15:17

Jupiter’s moon Europa is a fascinating world. On its surface, the moon appears to be scratched and scored with reddish-brown scars, which rake across the surface in a crisscrossing pattern. These scars are etched into a layer of water ice, which is thought to be at least several kilometers thick and covering a vast – and potentially habitable – subsurface ocean.

The ‘scars’ seen in this view of the moon from NASA’s Galileo spacecraft are a series of long cracks in its icy surface, thought to arise as Jupiter tugs at Europa and breaks the ice apart. The colors visible across the moon’s surface are representative of the surface composition and size of the ice grains: reddish-brown areas, for instance, contain high proportions of non-ice substances, while blue-white areas are relatively pure.

Scientists are keen to explore beneath Europa’s thick blanket of ice, and they can do so indirectly by hunting for evidence of activity emanating from below. A new study, led by European Space Agency (ESA) research fellow Hans Huybrighs and published in the AGU journal Geophysical Research Letters, did exactly this. Building on previous magnetic field studies by Galileo, the simulation-based study aimed to understand why fewer than expected fast-moving protons – which are subatomic particles with a positive charge – were recorded in the vicinity of the moon during one of the flybys of the moon by the Galileo probe.

The new study is based on data collected by Galileo during a flyby of Europa in 2000. The image comprises data acquired by the Galileo Solid-State Imaging (SSI) experiment on the spacecraft’s first and fourteenth orbits through the Jupiter system, in 1995 and 1998, respectively, and was recently re-processed in 2014. The image scale is 1.6 km/pixel, and the north pole of the moon is to the right. Credit: NASA/JPL-Caltech/SETI Institute

Researchers initially put this down to Europa obscuring the detector and preventing these usually abundant charged particles from being measured. However, Hans and colleagues found that some of this proton depletion was due to a plume of water vapor shooting out into space. This plume disrupted Europa’s thin, tenuous atmosphere and perturbed the magnetic fields in the region, altering the behavior and prevalence of nearby energetic protons.

Scientists have suspected the existence of plumes at Europa already since the times of the Galileo mission, however indirect evidence for their existence has only been found in the last decade. Excitingly, if such plumes are indeed present, breaking through the moon’s icy shell, they would offer a possible way to access and characterize the contents of its subsurface ocean, which would otherwise be hugely challenging to explore.

These prospects are of great interests to ESA’s upcoming Juice mission, planned for launch in 2022 to investigate Jupiter and its icy moons. Juice will carry the equipment needed to directly sample particles within the moon’s water vapor plumes and also to detect them remotely, aiming to reveal the secrets of its vast, mysterious ocean.

Scheduled to arrive in the Jupiter system in 2029, the mission will study the potential habitability and the underground oceans of three of the giant planet’s moons – Ganymede, Callisto and Europa. As this new study demonstrates, tracing the energetic charged and neutral particles in Europa’s vicinity offers huge promise in efforts to probe the moon’s atmosphere and wider cosmic environment – and this is precisely what Juice plans to do.

The new study is based on data collected by Galileo during a flyby of Europa in 2000. The image comprises data acquired by the Galileo Solid-State Imaging (SSI) experiment on the spacecraft’s first and fourteenth orbits through the Jupiter system, in 1995 and 1998, respectively, and was recently re-processed in 2014. The image scale is 1.6 km/pixel, and the north pole of the moon is to the right.

This post was originally published on the ESA website.

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Sounding Saturn’s depths with its seismic icy rings

Tue, 05/12/2020 - 14:43

By Larry O’Hanlon

The secrets of Saturn’s veiled interior are leaking out by way of the planet’s spectacular rings, according to a line of research that has taken four decades to come to fruition. In the last few years, what was first considered a sort of wacky hypothesis – that scientists can use Saturn’s rings to learn about  its structure — has turned into a singular window into Saturn’s surprisingly fluid and leviathan depths.

“People thought it was crazy back in the 1980s,” said Christopher Mankovich, a planetary scientist at Caltech and author of a new commentary in AGU Advances explaining the story behind the remarkable science. “Today we’re using the rings to listen to Saturn’s structure.”

A simplified and exaggerated model of how the bell-like seismic ringing of Saturn is transmitted gravitationally to the planet’s icy rings. Credit: Christopher Mankovich.

It all started with a hypothesis in a 1982 Eos article entitled, ‘Are Saturn’s Rings a Seismograph for Planetary Inertial Oscillations?,’ by Dave Stevenson. He proposed the billions of small ice crystals which form Saturn’s rings ought to be measurably affected by seismic vibrations within the giant planet. Theoretically, effects on the rings could be used as a sort of seismograph to learn about structures inside of Saturn, using the same science that allows seismologists to use the ringing of seismic waves on Earth to explore the structure of our own planet. 

The seismic waves bouncing around inside of Saturn are not moving through space to reach the rings – because seismic waves don’t move through outer space. But Saturn’s gravity has a tight grip on the icy particles in the rings, and the bell-like ringing mass of the planet could stir the rings by way of oscillations in Saturn’s gravitational field, according to the hypothesis.

If this hypothesis was correct, it would be a boon to planetary scientists who had been unable to penetrate the nebulous depths of Saturn well enough to even confirm the planet’s daily rotation rate, much less any details about its internal structure. The trouble is, it’s a hard hypothesis to test without watching the rings very closely, which isn’t possible from Earth. 

“Voyager hinted at it,” said Mankovich referring to the flybys of Voyager 1 and Voyager 2 in 1980 and 1981. They imaged unexpected and enticing complexity in the rings that were later traced to the periodic gravitational tugs from Saturn’s moons.

In the years that followed, planetary scientists fleshed out Stevenson’s original idea in a series of papers in 1990, 1991 and 1993. But it wasn’t until the Cassini spacecraft reached Saturn in 2004 and started gathering detailed observations that the seismic rings hypothesis could be tested.

Cassini was able to detect and measure the oscillations in the rings by peering through Saturn’s rings from various angles to see bright stars in the background. By measuring how the starlight varied over time, the oscillations caused by Saturn’s gravitational field could be observed  spiraling outward in the rings.

Even more amazing, the scientists found that ice particles in different locations in the rings resonate with different Saturnian seismic frequencies, similar to how plucking an E string on a harp can cause other E strings at different octaves to vibrate. When the ice particles at a certain distance from Saturn  resonate, they can launch waves that propagate outwards through the rings. This breakthrough was published in 2013 by researchers Matthew Hedman and Phillip Nicholson.

“Saturn’s rings thus, incredibly, form a natural frequency-domain seismograph for the planet’s normal mode oscillations,” Mankovich writes in the new commentary.

What the ring seismology has recently suggested, as described in a 2014 paper by Jim Fuller, is that planetary scientists had it wrong about Saturn’s interior. Instead of being all angry, turbulent depths with  huge convection currents, Saturn appears to have some areas with a very calm, stably-layered hydrogen-rich envelope that smoothly transitions down to an ice and rock core.

It’s not a detailed picture yet, but it’s a start and an entirely new and unexpected way to use Cassini data to study one of the most inaccessible places in the solar system.

“So it’s going to be a major way to study the interior of the planet,” Mankovich said.

Larry O’Hanlon is a freelance geoscience writer and editor in New Mexico. He manages the AGU Blogosphere.

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Going against the trend

Wed, 05/06/2020 - 16:03

Climate and marine scientists are observing pervasive warming of the ocean and the land surfaces across the globe. Since the middle of the 19th century, the average global temperature recorded on the land surface has risen by around one degree centigrade, and by 0.6 degrees across the ocean surface. Global warming has been most pronounced in the alpine regions and the Arctic.

Over the period 1982 to 2011, however, a cooling trend was recorded in surface waters in some parts of the Southern Ocean around the Antarctic continent, specifically in the area south of 55 degrees latitude. This cooling was strongest in the Pacific sector of the Southern Ocean, where the ocean surface cooled by around 0.1°C per decade, and the weakest in the Indian and parts of the Atlantic sectors.

Climate and marine scientists have so far been unable to provide satisfactory explanations as to why parts of the Southern Ocean have bucked the trend of global warming. Now a group of scientists led by Nicolas Gruber of the Swiss Federal Institute of Technology in Zürich has solved the puzzle with the help of simulations with a high-resolution ocean model.

Observation‐derived Southern Ocean (south of 40° S) temperature and salinity changes between 1982 and 2011. Left: Sea‐surface temperature changes derived from satellite observations (Reynolds et al., 2007). Left: Surface ocean salinity changes (Levitus et al., 2012). Black lines demark the Pacific, Atlantic, and Indian Ocean sectors, each subdivided into four regions (see section 2.5), by the Subantarctic Front, sea‐ice edge, and the continental shelf. Lower right: Zonal mean temperature and salinity (lower right) changes (Levitus et al., 2012). Credit: Haumann, et al., 2020/AGU.

Simulations highlight the influence of sea ice
In a paper just published in the AGU journal AGU Advances, the scientists use a series of simulations to show that sea-ice changes are the most probable cause for the cooling of the surface waters in the Southern Ocean. Only when Alex Haumann, lead author and Gruber’s former doctoral student, and the team incorporated the observed changes in sea ice into the model were they able to correctly replicate the observed pattern of the temperature changes. When they omitted this effect and only took into account the other potential factors – such as a more vigorous ocean circulation or increased freshwater fluxes from the melting of the Antarctic glaciers – the pattern was not accurately simulated.

Their considering of the role of sea ice in causing the surface cooling was based on the observation that over the same period as the cooling took place, i.e., from 1982 to 2011, the sea-ice extent steadily increased in the Southern Ocean around Antarctica, while in the Arctic it shrunk significantly over the same period.

A few years ago, Haumann and Gruber and various colleagues already discovered the reason for this expansion of sea ice in the Southern Ocean. They noticed that stronger southerly winds over this period propelled more of the sea ice that is being formed along the coast out into the open sea, enhancing the melting there. The resulting stronger conveyor-belt enhanced the transport of freshwater from near the continent out into the open ocean. This is because when sea ice is being formed from seawater, the salt is left behind, whereas when the sea ice melts in the summer well away from the coast, the freshwater is released into the surface, reducing the salinity of the seawater there.

This reduction in surface salinity strengthened the vertical stratification of the seawater: the fresher, and in this part of the ocean lighter water stays in the upper 100 m, while the denser saltier water remains below. In general, the saltier and colder the water, the greater its density and the greater its depth in the ocean.

Smaller heat exchange between the water layers
The stronger stratification reduced the exchange of heat between the deeper layers and the surface water, causing the heat to remain trapped at depth. In addition, the air above the Southern Ocean during winter is generally colder than the temperature of the seawater. Combined with the reduction of the vertical exchange of heat in the ocean, this ultimately created the observed situation where the surface water cooled and the subsurface warmed.

The strong role of salinity in controlling the vertical stratification is a peculiarity of the Southern Ocean, since there is actually very little difference in temperature between the ocean’s surface water and the subsurface: only a few tenths of a degree. The strong salinity driven stratification also explains why the surface cooling did not induce deep mixing.

No material to feed global-warming skeptics
“The cooling of the Southern Ocean over three decades is really unusual, bearing in mind that otherwise all other parts of the planet, especially the land surface, have warmed up,” Gruber said.

Cooling in just one area of the ocean should not be interpreted as a reduction of the long-term warming of the global climate system as a whole. It is merely a redistribution of heat in the Southern Ocean from the surface to the deeper layers of the ocean. “We assume the strong winds pushing the sea ice in the Southern Ocean northward are potentially a side-effect of climate change,” Gruber stresses. “Climate change is clearly man-made and cannot be disputed simply because one area of the ocean shows signs of cooling.”

In addition, the current study went only up to 2011. “We have observed a trend reversal since 2015. The sea ice around the Antarctic is now starting to recede at a rapid rate,” Gruber said. “And this is very much in line with the overall trend of continuing global warming.”

This post was originally published on the Swiss Federal Institute of Technology in Zürich website.

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New Mexico badlands help researchers understand past Martian lava flows (video)

Mon, 04/27/2020 - 14:37

An aerial view of the McCartys flow field in western New Mexico, which is twice the size of Washington, D.C. Cracks in the rock show how the lava shrank as it cooled. Inflation pits can also be seen: pits that formed when the lava flowed and inflated around an obstacle.
Credit: Christopher Hamilton.

By Lauren Lipuma

Planetary scientists are using a volcanic flow field in New Mexico to puzzle out how long past volcanic eruptions on Mars might have lasted, a finding that could help researchers determine if Mars was ever hospitable to life. 

People don’t usually think of New Mexico as a volcanically active place, but it has some of the youngest (geologically speaking) large lava flows in the continental United States.

Christopher Hamilton, a planetary scientist at the University of Arizona, has been studying one particular flow, the McCartys, for nearly 10 years. Hidden in plain sight along Route 66, the McCartys is part of a large volcanic flow field in New Mexico’s El Malpais National Monument that was erupted several thousand years ago. El Malpais, or the badlands, is so named for the desolate, rocky landscape it encompasses.

Hamilton and his colleagues are trying to understand how long it took for the McCartys flow field to be laid down, which will help them understand how past eruptions on Earth and Mars affected their planet’s ability to host life.

How long a lava flow lasts helps determine an eruption’s effect on a planet’s habitability. Lavas erupted quickly over days or weeks can release a lot of gas into the atmosphere and potentially alter a planet’s climate. But lavas erupted slowly over years or decades can release heat into the ground, which can warm groundwater and generate hydrothermal systems that support exotic forms of microbial life.

“I like to think about it like the tortoise and the hare,” Hamilton said. “You’re erupting the same amount of material, but is it done in this gradual process, or is done in a very fast process?”

Christopher Hamilton and colleagues use kites to study the McCartys lava flow field from the air.
Credit: Christopher Hamilton.

As lava advances, it inflates, just like rising bread. As the outermost lava cools, it forms a crust scientists can measure. In a new study in AGU’s Journal of Geophysical Research: Planets, Hamilton and his colleagues measured how thick the McCartys crust is to estimate how long it took for the lava to grow. The thicker the crust, the longer the eruption lasted.

The McCartys flow is huge, covering about 310 square kilometers (120 square miles). The 2018 eruption of Hawaii’s Kilauea volcano was tiny by comparison: at its end, the eruption had covered about 35 square kilometers (14 square miles) of land with lava.

To study such a large area, the researchers mounted cameras on kites and collected extremely detailed images from the air.

“The kites became our personal satellites, acquiring high-resolution images to transform the observations we’re making on the ground into an aerial perspective so we can study other terrains on Mars,” Hamilton said.

Combining the kite images with measurements from the ground, Hamilton and his team estimate that the southern branch of the McCartys was laid down over the course of about two years, but as a whole, the eruption could have lasted for over a decade.

Because the McCartys flow was erupted over a long period of time, the researchers suspect similar lava fields on Mars were also erupted slowly. They argue that the thick lava flows of Mars’s Hrad Vallis—in some places as tall as a 20-story office building—were laid down over several decades. These flows likely contained enough heat to have sustained hydrothermal systems hospitable to microbial life for hundreds to thousands of years, according to Hamilton.

“Hrad Vallis has the potential to have interacted with water and generated hydrothermal systems,” he said.

The McCartys has attracted the interest of volcanologists for over a century, but it has many more secrets to tell about the geologic history of the Southwest and the search for life throughout the solar system.

Lauren Lipuma is a science writer and video producer at AGU.

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Promising signs for Perseverance rover in its quest for past Martian life

Thu, 04/23/2020 - 15:12

By Danielle Torrent Tucker

Undulating streaks of land visible from space reveal rivers once coursed across the Martian surface – but for how long did the water flow? Enough time to record evidence of ancient life, according to a new study.

Scientists have speculated that the Jezero crater on Mars – the site of the next NASA rover mission to the Red Planet – could be a good place to look for markers of life. A new analysis of satellite imagery supports that hypothesis. By modeling the length of time it took to form the layers of sediment in a delta deposited by an ancient river as it poured into the crater, researchers have concluded that if life once existed near the Martian surface, traces of it could have been captured within the delta layers.

NASA’s Mars Perseverance Rover, expected to launch in July 2020, will land in Jezero crater, pictured here. The image was taken by instruments on NASA’s Mars Reconnaissance Orbiter, which regularly captures potential landing sites for future missions. (Image Credit: NASA/JPL-Caltech/ASU)

“There probably was water for a significant duration on Mars and that environment was most certainly habitable, even if it may have been arid,” according to lead author Mathieu Lapôtre, an assistant professor of geological sciences at Stanford’s School of Earth, Energy & Environmental Sciences (Stanford Earth). “We showed that sediments were deposited rapidly and that if there were organics, they would have been buried rapidly, which means that they would likely have been preserved and protected.”

Jezero crater was selected for NASA’s next rover mission partly because the site contains a river delta, which on Earth are known to effectively preserve organic molecules associated with life. But without an understanding of the rates and durations of delta-building events, the analogy remained speculative. The new research, published online on April 23 in AGU Advances, offers guidance for sample recovery in order to better understand the ancient Martian climate and duration of the delta formation for NASA’s Perseverance Rover to Mars, which is expected to launch in July 2020 as part of the first Mars sample return mission.

An unvegetated meandering river at the McLeod Springs Wash in the Toiyabe basin of Nevada is an example of what researchers think is analogous to the ancient streams of Jezero crater on Mars. (Image credit: Alessandro Ielpi)

Extrapolating from Earth

The study incorporates a recent discovery the researchers made about Earth: Single-threaded sinuous rivers that don’t have plants growing over their banks move sideways about ten times faster than those with vegetation. Based on the strength of Mars’ gravity, and assuming the Red Planet did not have plants, the scientists estimate that the delta in Jezero crater took at least 20 to 40 years to form, but that formation was likely discontinuous and spread out across about 400,000 years.

“This is useful because one of the big unknowns on Mars is time,” Lapôtre said. “By finding a way to calculate rate for the process, we can start gaining that dimension of time.”

Because single-threaded, meandering rivers are most often found with vegetation on Earth, their occurrence without plants remained largely undetected until recently. It was thought that before the appearance of plants, only braided rivers, made up of multiple interlaced channels, existed. Now that researchers know to look for them, they have found meandering rivers on Earth today where there are no plants, such as in the McLeod Springs Wash in the Toiyabe basin of Nevada.

“This specifically hadn’t been done before because single-threaded rivers without plants were not really on anyone’s radar,” Lapôtre said. “It also has cool implications for how rivers might have worked on Earth before there were plants.”

This illustration depicts NASA’s Perseverance rover operating on the surface of Mars. (Image credit: NASA/JPL-Caltech)

The researchers also estimated that wet spells conducive to significant delta buildup were about 20 times less frequent on ancient Mars than they are on Earth today.

“People have been thinking more and more about the fact that flows on Mars probably were not continuous and that there have been times when you had flows and other times when you had dry spells,” Lapôtre said. “This is a novel way of putting quantitative constraints on how frequently flows probably happened on Mars.”

Findings from Jezero crater could aid our understanding of how life evolved on Earth. If life once existed there, it likely didn’t evolve beyond the single-cell stage, scientists say. That’s because Jezero crater formed over 3.5 billion years ago, long before organisms on Earth became multicellular. If life once existed at the surface, its evolution was stalled by some unknown event that sterilized the planet. That means the Martian crater could serve as a kind of time capsule preserving signs of life as it might once have existed on Earth.

“Being able to use another planet as a lab experiment for how life could have started somewhere else or where there’s a better record of how life started in the first place – that could actually teach us a lot about what life is,” Lapôtre said. “These will be the first samples that we’ve seen as a rock on Mars and then brought back to Earth, so it’s pretty exciting.”

This post was originally published in the Stanford Science Digest.

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South Asia faces increased double-threat of extreme heat, extreme pollution

Tue, 04/21/2020 - 19:29

By Leslie Lee

Scientists know that extreme heat has a negative impact on the human body — causing distress in the respiratory and cardiovascular systems. They also know that extreme air pollution can also have serious impacts on the human body. But as climate change impacts continue globally, how often will humans be threatened by both of those extremes when they occur simultaneously?

A new study in the AGU journal AGU Advances, answers that question for South Asia.

High‐particulate matter conditions at India Gate. Credit: Adnan Abidi/REUTERS.

“South Asia is a hot-spot for future climate change impacts,” said Yangyang Xu, an atmospheric scientist at Texas A&M University and lead author of the new study. Extreme heat occurrences worldwide have increased in recent decades, and at the same time, many cities are facing severe air pollution problems, featuring episodes of high particulate matter (PM) pollution, he said. This study provides an integrated assessment of human exposure to rare days of both extreme heat and high PM levels.

“Our assessment projects that occurrences of heat extremes will increase in frequency by 75% by 2050, that is an increase from 45 days a year to 78 days in a year,” Xu said. More concerning is the rare joint events of both extreme heat and extreme PM will increase in frequency by 175% by 2050. Climate change is not just a global average number, it is something you can feel in your neighborhood. 

The study’s regional focus was South Asia: Afghanistan, Bangladesh, Bhutan, India, Myanmar, Nepal, and Pakistan. The scientists used a high-resolution, decadal-long model simulation, using a state-of-the-science regional chemistry-climate model. Xu led the first of its kind research project, and scientists from the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, led the development of the fully coupled chemistry-climate model and performed model simulations for the present-day and future conditions.

“These models allow chemistry and climate to affect each other at every time step,” said Rajesh Kumar, a project scientist at NCAR and co-author of the new study. The study was also co-authored by Mary Barth and Gerald A. Meehl, both senior scientists at NCAR, with most of the analysis done by Texas A&M atmospheric sciences graduate student Xiaokang Wu.

As climate change impacts continue to become reality, it is important for scientists to consider human impacts of multiple extreme conditions happening simultaneously, Xu said. Projected increases in humidity and temperature are expected to cause extreme heat stress for the people of South Asia, where the population is projected to increase from 1.5 billion people to 2 billion by 2050.

“It is important to extend this analysis on the co-variability of heat and haze extremes in other regions of the world, such as the industrial regions of the U.S., Europe, and East Asia,” Barth said.

The analysis also showed that the fraction of land exposed to prolonged dual-extreme days increases by more than tenfold in 2050, much larger than the increase when assessed individually.

“I think this study raises a lot of important concerns, and much more research is needed over other parts of the world on these compounded extremes, the risks they pose, and their potential human health effects,” Xu said.

Leslie Lee is the communications coordinator for the College of Geosciences at Texas A&M  University. This post was originally published on the Texas A&M website.

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Continued carbon dioxide emissions will impair human cognition

Tue, 04/21/2020 - 14:33

As the 21st century progresses, rising atmospheric carbon dioxide (CO2) concentrations will cause urban and indoor levels of the gas to increase, and that may significantly reduce our basic decision-making ability and complex strategic thinking, according to a new study. By the end of the century, people could be exposed to indoor CO2 levels up to 1,400 parts per million (ppm)—more than three times today’s outdoor levels, and well beyond what humans have ever experienced.

“It’s amazing how high CO2 levels get in enclosed spaces,” said climate researcher Kris Karnauskas, lead author of the new study published in the AGU journal GeoHealth. “It affects everybody—from little kids packed into classrooms to scientists, business people and decision-makers to regular folks in their houses and apartments.” Karnauskas is an associate professor at the University of Colorado Boulder (CU Boulder) and a fellow at the Cooperative Institute for Research in Environmental Sciences (CIRES).

“Building ventilation typically modulates CO2 levels in buildings, but there are situations when there are too many people and not enough fresh air to dilute the CO2,” said Shelly Miller, professor in CU Boulder’s school of engineering and coauthor of the new study. Carbon dioxide can also build up in poorly ventilated spaces over longer periods of time, such as overnight while sleeping in bedrooms, she said.

Put simply, when we breathe air with high CO2 levels, the CO2 levels in our blood rise, reducing the amount of oxygen that reaches our brains. Studies show that this can increase sleepiness and anxiety, and impair cognitive function.

Rising CO2 levels in outdoor air can cause indoor air in crowded spaces to reach levels that impair cognitive ability. Credit: AGU.

We all know the feeling: Sit too long in a stuffy, crowded lecture hall or conference room and many of us begin to feel drowsy or dull. In general, CO2 concentrations are higher indoors than outdoors, the authors wrote. And outdoor CO2 in urban areas is higher than in pristine locations. The CO2 concentrations in buildings are a result of both the gas that is otherwise in equilibrium with the outdoors, but also the CO2 generated by building occupants as they exhale.

Atmospheric CO2 levels have been rising since the Industrial Revolution, reaching a 414 ppm peak at NOAA’s Mauna Loa Observatory in Hawaii in 2019. In the ongoing scenario in which people on Earth do not reduce greenhouse gas emissions, the Intergovernmental Panel on Climate Change predicts outdoor CO2 levels could climb to 930 ppm by 2100. And urban areas typically have around 100 ppm CO2 higher than this background.

Karnauskas and his colleagues developed a comprehensive approach that considers predicted future outdoor CO2 concentrations and the impact of localized urban emissions, a model of the relationship between indoor and outdoor CO2 levels and the impact on human cognition. They found that if the outdoor CO2 concentrations do rise to 930 ppm, that would nudge the indoor concentrations to a harmful level of 1,400 ppm.

“At this level, some studies have demonstrated compelling evidence for significant cognitive impairment,” said Anna Schapiro, assistant professor of psychology at the University of Pennsylvania and a coauthor of the new study. “Though the literature contains some conflicting findings and much more research is needed, it appears that high-level cognitive domains like decision-making and planning are especially susceptible to increasing CO2 concentrations.”

In fact, at 1,400 ppm, CO2 concentrations may cut our basic decision-making ability by 25 percent, and complex strategic thinking by around 50 percent, the authors found.

The cognitive impacts of rising CO2 levels represent what scientists call a “direct” effect of the gas’ concentration, much like ocean acidification. In both cases, elevated CO2 itself—not the subsequent warming it also causes—is what triggers harm.

The team says there may be ways to adapt to higher indoor CO2 levels, but the best way to prevent levels from reaching harmful levels is to reduce fossil fuel emissions. This would require globally adopted mitigation strategies such as those set forth by the Paris Agreement of the United Nations Framework Convention on Climate Change.

Karnauskas and his coauthors hope these findings will spark further research on the ‘hidden’ impacts of climate change such as those on cognition. “This is a complex problem, and our study is at the beginning. It’s not just a matter of predicting global (outdoor) CO2 levels,” he said. “It’s going from the global background emissions to concentrations in the urban environment, to the indoor concentrations, and finally the resulting human impact. We need even broader, interdisciplinary teams of researchers to explore this: investigating each step in our own silos will not be enough.”

This post was originally published on the CIRES website.

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Dust devils may roam hydrocarbon dunes on Saturn’s moon Titan

Thu, 04/16/2020 - 15:01
Smoggy, with a chance of dust devils: conditions at the surface of Saturn’s moon Titan may spawn convective whirlwinds

By Liza Lester

Hazy, orange Titan, Saturn’s largest moon, passes in front of the planet and its rings in this true-color image from Casssini.
Credit: NASA

Meteorological conditions on Saturn’s large moon Titan, the strange, distant world that may be the most Earth-like in the solar system, appear conducive to the formation of dust devils, according to new research in AGU’s journal Geophysical Research Letters.

If true, these dry whirlwinds may be primary movers of dust on the surface of Titan, as they are on Mars.

The Cassini spacecraft, which toured Saturn’s system from 2004 to 2017, observed dunes in the moon’s equatorial region covering as much as 30% of the surface and a large dust storm.

The dust on Titan’s dunes is believed to originate as hydrocarbon aerosols raining out of the moon’s atmosphere, according to Brian Jackson, a planetary scientist at Boise State University in Idaho and the lead author of the new study. It likely has a plasticky texture unlike the more familiar grit found on Earth or Mars.

Rare, big dust storms look impressive, but dust devils loft more total dust into the atmosphere, even on Earth, where winds are more influential than on Mars or Titan.

“Winds at the surface of Titan are usually very weak. Unless there is a big storm rolling through, there’s probably not that much wind, and so dust devils may be one of the main dust transport mechanisms on Titan—if they exist,” Jackson said.

Lines of dunes contour the Shangri-La Sand Sea on Titan, Saturn’s largest moon. Credit: NASA/JPL-Caltech/ASI/Université Paris-Diderot

Dust devils have not been observed on Titan. The authors of the new study predicted the possible presence of dust devils by applying meteorological models to data acquired from the moon’s surface during the brief visit of Cassini’s Huygens probe in 2005.

Dusty mystery

Dust devils form in dry, calm conditions when sunlight warms the ground and near-surface air. Rising warm air creates vortices made visible by sand and dust caught up in the whirl. Dust devils share some physical properties with tornadoes but are always dry and do not grow as large and destructive. But scientists don’t entirely understand how dust devils work.

“When we plug the numbers in for how much dust the dust devil ought to lift based on the wind speeds we see, they seem to be able to lift more dust than we would expect. There may be some other mechanism which is helping them pull this dust—or the equations are just wrong,” Jackson said.

Jackson and his students have chased dust devils across southeastern Oregon’s Alvord Desert with small airborne drones carrying meteorological instruments, in an ongoing effort to get a look inside.

Exceptionally dry conditions on the Red Planet beget many dust devils during Martian summers, when they can grow immense, reaching 8 kilometers (5 miles) high. Mars’ atmosphere is so thin even 200-mile-an-hour winds only cause a gently buffeting. This makes the dust-lifting power of dust devils important to the global movement of dust on Mars.

“We can watch dust devils skitter across the surface of Mars and see what their internal structure is like, but that doesn’t tell us how much dust they are lifting. Mars’ atmosphere is really, really dusty and dust plays an important role in the climate. Dust devils are probably, if not the dominant mechanism, one of the most important mechanisms for lofting the dust,” Jackson said.

Dust devils whirl across the surface of Mars in images captured by Spirit rover in 2005. Credit: NASA

If they exist on Titan, dust devils may be similarly important, although winds at the surface of Titan are typically gentle for the opposite reason: Titan’s atmosphere is one and a half times the density of Earth’s, but the moon has only one seventh of Earth’s gravity. This makes Titan’s atmosphere hard to get moving, according to Jackson.

“It’s just this enormous, puffy atmosphere. When you’ve got that much air it’s hard to get it churning. So you just don’t usually get big winds on the surface of Titan so far as we know,” said Jackson.

Like Earth’s, Titan’s atmosphere is mostly nitrogen, but it also includes influential amounts of ethane and methane, the major components of natural gas. Titan is the only world in the solar system other than Earth where scientists have observed evidence of flowing rivers and liquid surface lakes, but scientists believe these Earth-like features on the cold, distant moon are not water but liquid hydrocarbons.

Confirmation of the new study’s dust devil prediction may have to wait on the arrival of NASA’s Dragonfly mission in 2034. Jackson says buffeting from dust devil encounters would be unlikely to trouble the large octocopter as it explores the moon’s surface.

—Liza Lester is a senior media relations specialist at AGU.

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Greenland Ice Sheet meltwater can flow in winter, too

Thu, 04/09/2020 - 15:59

By Kathy Bogan, CIRES

Liquid meltwater can sometimes flow deep below the Greenland Ice Sheet in winter, not just in the summer, according to work published in the AGU journal Geophysical Research Letters today. That finding means that scientists seeking to understand sea-level rise and the future of the Greenland Ice Sheet need to collect data during the dark Arctic winter with scant hours of daylight and temperatures that dip below -30 degrees Celsius (-22 degrees Fahrenheit).

“This observation raises questions for the Greenland research community, and motivates the need for future work on wintertime hydrology in Greenland,” said lead author Lincoln Pitcher, a Visiting Fellow at CIRES, part of the University of Colorado Boulder. Pitcher began this work while he was a graduate student at the University of California Los Angeles, and his co-authors are from seven different states and Denmark.

The Isortoq River draining from the terminus of Isunguata Sermia outlet glacier in southwest Greenland in July 2014. Flowing water was discovered in this river the following winter while the river was frozen over and temperatures were below freezing. Credit: CIRES

When evidence suggested that some of Greenland’s glaciers were storing meltwater through the winter, Pitcher set out for southwest Greenland to see if any of this meltwater was also leaving the ice sheet during winter. In February 2015, he and his colleague Colin Gleason of the University of Massachusetts Amherst dragged a ground-penetrating radar across frozen rivers downstream of the edge of the ice sheet and drilled boreholes to see if any water was leaving the ice sheet and flowing beneath river ice. They surveyed rivers draining five Greenland Ice Sheet outlet glaciers, and discovered meltwater flowing at just one site, the Isortoq River. In summertime, the Isotoq drains meltwater from the terminus of the Isunguata Sermia outlet glacier. In winter, the river appears frozen, but Pitcher and Gleason found slowly flowing liquid water there.

It was “a trickle, not a torrent,” Pitcher said, and the water was flowing below half a meter of ice while temperatures were well below zero. Pitcher and Gleason collected water samples and geochemical analysis indicated that it had come from under the ice sheet itself.

The team concluded that it is possible the bed of the Greenland Ice Sheet can stay wet and drain small amounts of water year-round. This finding is important for understanding how meltwater from the ice surface moves through the ice sheet, is retained, refreezes and/or ultimately drains into rivers and/or the global ocean.

It is often assumed that Greenland’s drainage system lies dormant during winter. Pitcher’s team’s findings highlight a growing need for year-round Arctic hydrologic investigations, not just in summer.

Kathy Bogan is a graphic designer at CIRES. This post was originally published on the CIRES website.

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Shelf sediments, freshwater runoff from rivers brings more carbon, nutrients to North Pole

Wed, 04/08/2020 - 14:27

Freshwater runoff from rivers and continental shelf sediments are bringing significant quantities of carbon and trace elements into parts of the Arctic Ocean via the Transpolar Drift—a major surface current that moves water from Siberia across the North Pole to the North Atlantic Ocean, according to a new study by researchers at Woods Hole Oceanographic Institution (WHOI) and their international colleagues.

In 2015, oceanographers conducting research in the Arctic Ocean as part of the International GEOTRACES program found much higher concentrations of trace elements in surface waters near the North Pole than in regions on either side of the current. Their results published this week in AGU’s Journal of Geophysical Research-Oceans.

“Many important trace elements that enter the ocean from rivers and shelf sediments are quickly removed from the water column,” explains WHOI marine chemist Matthew Charette, lead author of the study. “But in the Arctic, they are bound with abundant organic matter from rivers, which allows the mixture to be transported into the central Arctic, over 1,000 kilometers from their source.”

An international team of scientists aboard the U.S. Coast Guard Cutter Healy and the German research icebreaker Polarstern met at the North Pole in 2015 to survey elements in the Arctic Ocean. (Photo by Stefan Hendricks, Alfred Wegener Institute)

Trace elements, like iron, form essential building blocks for ocean life. As the Arctic warms and larger swaths of the ocean become ice-free for longer periods of time, marine algae are becoming more productive. A greater abundance of trace elements coming from rivers and shelf sediments can lead to increases in nutrients reaching the central Arctic Ocean, further fueling algal production.

Map of the USCGC Healy route during 2015 expedition in the Arctic Ocean as part of the International GEOTRACES program. (Illustration by Natalie Renier, © Woods Hole Oceanographic Institution)

“It’s difficult to say exactly what changes this might bring,” says Charette. “but we do know that the structure of marine ecosystems is set by nutrient availability.”

Nutrients fuel the growth of phytoplankton, a microscopic algae that forms the base of the marine food web. Generally speaking, more phytoplankton brings more zooplankton—small fish and crustaceans, which can then be eaten by top ocean predators like seals and whales.

Higher concentrations of trace elements and nutrients previously locked up in frozen soils (permafrost) are expected to increase as more river runoff reaches the Arctic, which is warming at a much faster rate than most anywhere else on Earth. While an increase in nutrients may boost Arctic marine productivity, Charette cautions that the continued loss of sea ice will further exacerbate climate warming, which will impact ecosystems more broadly.

“The Arctic plays an important role in regulating Earth’s climate, with the ice cover reflecting sunlight back to space, helping to mitigate rising global temperatures due to greenhouse gas emissions,” he adds. “Once the ice is gone, the Arctic Ocean will absorb more heat from the atmosphere, which will only make our climate predicament worse.”


This post was originally published on the WHOI website.

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NASA study adds a pinch of salt to El Niño models

Wed, 04/08/2020 - 00:36

NASA/CONAE’s Aquarius satellite (2011-2015) collected sea surface salinity (saltiness) data over the entire globe.
Credit: NASA/Greg Shirah.

By Jessica Merzdorf

When modeling the El Niño-Southern Oscillation (ENSO) ocean-climate cycle, adding satellite sea surface salinity — or saltiness — data significantly improves model accuracy, according to a new study.

ENSO is an irregular cycle of warm and cold climate events called El Niño and La Niña. In normal years, strong easterly trade winds blow from the Americas toward southeast Asia, but in an El Niño year, those winds are reduced and sometimes even reversed. Warm water that was “piled up” in the western Pacific flows back toward the Americas, changing atmospheric pressure and moisture to produce droughts in Asia and more frequent storms and floods in the Americas. The reverse pattern is called a La Niña, in which the ocean in the eastern Pacific is cooler than normal.

The team used NASA’s Global Modelling and Assimilation Office (GMAO) Sub-seasonal-To-Seasonal (S2S) coupled ocean/atmosphere forecasting system (GEOS-S2S-2) to model three past ENSO events: The strong 2015 El Niño, the 2017 La Niña and the weak 2018 El Niño.

Pulling from NASA’s Soil Moisture Active Passive (SMAP) mission, the past NASA-CONAE (Argentinian Space Agency) Aquarius mission and the European Space Agency’s Soil Moisture Ocean Salinity (SMOS) mission, they compared the forecast model’s accuracy for each of the three events with and without assimilating SSS data into the models’ initialization. In other words: One model run’s initial conditions included SSS data, and the other did not.

Adding assimilation of SSS data to the GEOS model helped it to depict the depth and density of the ocean’s top layer more accurately, which led to better representations of large-scale circulation in response to ENSO. As a result, the models’ predictions for the three case studies more closely reflected actual observations, compared to what forecasting models predicted at the time.

“In our three case studies, we examined different phases of ENSO,” said Eric Hackert, a research scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland and lead author of the new study in AGU’s Journal of Geophysical Research: Oceans. “For the big El Niño in 2015, assimilating the salinity data damped the signal — our original model was overestimating the amplitude of the event. For the other two ENSO events, the forecasts originally predicted the wrong sign: For example, in 2017, the model without salinity data forecasted an El Niño, while the real ocean produced a La Niña. However, for each case we examined, adding satellite salinity to the initialization improved the forecasts.”

The study is one of the first to incorporate SSS data into forecast initialization for a global coupled model of interactions between the ocean, atmosphere, land, aerosols and sea ice. GEOS and other models used to help predict ENSO events do not typically include SSS. However, ocean surface salinity plays an important role in ocean currents, evaporation and interaction with the atmosphere, and heat transfer from the tropics to the poles. Colder, saltier water is denser and heavier than warmer, fresher water, and the large-scale temperature and precipitation shifts of ENSO events change ocean circulation and interactions between the water and atmosphere.

Both phases of the ENSO cycle affect ecosystems, economies, human health, and wildfire risk — making ENSO forecasts vital for many people around the world, Hackert said.

“For example, forecasts and observations gave a strong indication that there would be a big El Niño in 1997, which would lead to drought in northeast Brazil,” he said. “This allowed the government of Brazil to issue a statement to subsistence farmers, encouraging them to plant drought-resistant corn instead of high-yield varieties. In this case, good ENSO forecasts along with government action may have saved many lives. This is just one example of many socio-economic benefits for extending useful El Niño predictions.”

Including satellite SSS data also makes models useful for longer periods — accurate ENSO forecasts without salinity data only extend out 4 months, while those with SSS data cover 7 months, Hackert said.

“Rather than having one season of confidence in your forecast, you have two seasons,” Hackert said. “If your growing season is six months down the line, a longer quality forecast gives you an improved understanding of whether you need to plant high-yield or drought-resistant varieties. Another example would be that you have plenty of time to fix your roof if you live in Southern California (since El Niño typically brings rainy conditions to the southern US).”

Having access to an ongoing record of satellite SSS data is essential for making forecasts accurate and reliable, Hackert said.

“In current forecast systems, satellite and ocean observations are optimally combined using models and data assimilation techniques to help define the state of the ocean,” he said. “This study shows that adding satellite SSS to the suite of current observations helps to characterize the near-surface ocean state, leading to improved seasonal forecasts. We recommend that other forecast model systems around the world adopt SSS into their systems.”

Jessica Merzdorf is a science writer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. This post originally appeared as a feature article on the NASA website.

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Scientists propose explanation for night sky glow of STEVE

Tue, 04/07/2020 - 13:54

Alberta Aurora Chasers capture STEVE on the evening of April 10, 2018 in Prince George, British Columbia, Canada. Robert Downie kneels in the foreground while photographer Ryan Sault captures the narrow ribbon of white-purple hues overhead. The vibrant green aurora is seen in the distant north, located to the right in the photo.
Credit: Ryan Sault.

By Lauren Lipuma

Researchers have just published a theory of what powers the celestial phenomenon known as STEVE, the aurora-like glow amateur sky-watchers brought to scientists’ attention in 2016.

The northern and southern lights, or aurora, typically show up as swirling green ribbons of light spreading across the night sky near the poles. But STEVE is a thin ribbon of mauve or white light that stretches from east to west, closer to the equator than where auroras usually appear and at much higher altitudes.

Scientists first thought STEVE was a new kind of aurora, but previous research shows its light is not produced the same way. Researchers are still unsure of what generates STEVE’s light, but a group of space physicists now suspect STEVE lights up when fast-flowing rivers of plasma jumpstart certain chemical reactions high in the atmosphere.

The theory is untested, but if it proves correct, it would mean there is a new mechanism for generating glowing lights in Earth’s upper atmosphere, according to the researchers.

“It’s just exciting for me to find something where, you could ask a very simple question about it, like, ‘What is this?’ And it turns out the answer to that question is very nuanced and exciting and may indicate some new physics,” said Brian Harding, a space physicist at the University of California Berkeley and lead author of a new study describing the theory in AGU’s journal Geophysical Research Letters.

A different kind of light

Earth’s magnetic field creates a cocoon around the planet called the magnetosphere. When charged particles streaming from the sun disturb Earth’s magnetosphere, some particles in the magnetosphere – mostly bare protons and electrons – rain down into the upper atmosphere. These charged particles excite oxygen and nitrogen gas in the atmosphere, which produces light of varying colors.

When scientists first began studying STEVE, they thought it was a kind of aurora. But a 2018 study found its glow is not due to charged particles raining down into Earth’s upper atmosphere, and researchers have been puzzling over what causes STEVE ever since.

The first scientific study published on STEVE found a stream of fast-moving plasma – a hot gas of charged particles and electrons – passing through the atmosphere right where STEVE events occurred. The researchers suspected these particles were connected to STEVE but were unsure whether they were the cause of it. These super-fast plasma flows stream through the upper atmosphere when the magnetosphere is disturbed, at about the speed it takes to orbit Earth, and STEVE occurs only during the fastest flows.

Harding and his colleagues suspect the fastest plasma rivers break chemical bonds in the upper atmosphere, triggering reactions that produce light. In the new study, Harding and his colleagues devised a theory to explain how this process could produce STEVE’s characteristic band of light and tested their idea with a simple simulation to see if the chemistry worked out.  

Earth’s atmosphere is mostly made of nitrogen and oxygen gas: pairs of nitrogen and oxygen atoms bound together (N2 and O2). But in the upper atmosphere where STEVE occurs, oxygen molecules more easily break apart, and single atoms of oxygen are often found (O).

Harding and his team propose that when the streams of plasma are hot and fast enough, they can split apart nitrogen molecules (N2), which then combine with single oxygen atoms to form nitric oxide (NO). The nitric oxide then grabs another free oxygen atom to create nitrogen dioxide (NO2), a reaction that also produces light. The researchers suspect STEVE’s glow is the light from this chemical reaction, which makes sense because STEVE is found right where these plasma streams occur.

The researchers tested their theory with a simple simulation and found the idea is viable – in theory, the chemistry can explain the behavior of STEVE. The idea hasn’t been tested yet in the atmosphere, but Harding finds it an intriguing prospect.  

“It would be more exciting if this were wrong, then we’re back at square one, and nature had confounded us again,” he said.

Lauren Lipuma is a science writer and multimedia producer at AGU.

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Flooding Stunted 2019 Cropland Growing Season, Resulting in More Atmospheric CO2

Tue, 03/31/2020 - 19:11

By Robert Perkins

Severe flooding throughout the Midwest—which triggered a delayed growing season for crops in the region—led to a reduction of 100 million metric tons of net carbon uptake during June and July of 2019, according to a new study.

For reference, the massive California wildfires of 2018 released an estimated 12.4 million metric tons of carbon into the atmosphere. And although part of this deficit due to floods was compensated for later in the growing season, the combined effects are likely to have resulted in a 15 percent reduction in crop productivity relative to 2018, the study authors say.

The study, published March 31, 2020, in the journal AGU Advances, describes how the carbon uptake was measured using satellite data. Researchers used a novel marker of photosynthesis known as solar-induced fluorescence to quantify the reduced carbon uptake due to the delay in the crops’ growth. Independent observations of atmospheric CO2 levels were then employed to confirm the reduction in carbon uptake.

“We were able to show that it’s possible to monitor the impacts of floods on crop growth on a daily basis in near real time from space, which is critical to future ecological forecasting and mitigation,” says Yi Yin, research scientist at Caltech and lead author of the study.

Record rainfalls soaked the Midwest during the spring and early summer of 2019. For three consecutive months (April, May, and June), the National Oceanic and Atmospheric Administration reported that 12-month precipitation measurements had hit all-time highs. The resulting floods not only damaged homes and infrastructure but also impacted agricultural productivity, delaying the planting of crops in large parts of the Corn Belt, which stretches from Kansas and Nebraska in the west to Ohio in the east.

To assess the environmental impact of the delayed growing season, scientists at Caltech and JPL, which Caltech manages for NASA, turned to satellite data. As plants convert carbon dioxide (CO2) and sunlight into oxygen and energy through photosynthesis, a small amount of the sunlight they absorb is emitted back in the form of a very faint glow. The glow, known as solar-induced fluorescence, or SIF, is far too dim for us to see with bare eyes, but it can be measured through a process called satellite spectrophotometry.

The Caltech-JPL team quantified SIF using measurements from a European Space Agency (ESA) satellite-borne instrument to track the growth of crops with unprecedented detail. They found that the seasonal cycle of the 2019 crop growth was delayed by around two weeks and the maximum seasonal photosynthesis was reduced by about 15 percent. The stunted growing season was estimated to have led to a reduction in carbon uptake by plants of around 100 million metric tons from June to July 2019.

“SIF is the most accurate signal of photosynthesis by far that can be observed from space,” says Christian Frankenberg, professor of environmental science and engineering at Caltech. “And since plants absorb carbon dioxide during photosynthesis, we wanted to see if SIF could track the reductions in crop carbon uptake during the 2019 floods.”

To find out, the team analyzed atmospheric CO2 measurements from NASA’s Orbiting Carbon Observatory-2 (OCO-2) satellite as well as from aircraft from NASA’s Atmospheric Carbon and Transport America (ACT-America) project. “We found that the SIF-based estimates of reduced uptake are consistent with elevated atmospheric CO2 when the two quantities are connected by atmospheric transport models,” says Brendan Bryne, co-corresponding author of the study and a NASA postdoc fellow at JPL.

“This study illuminates our ability to monitor the ecosystem and its impact on atmospheric CO2 in near real time from space. These new tools allow for global sensing of biospheric uptake of carbon dioxide,” says Paul Wennberg, the R. Stanton Avery Professor of Atmospheric Chemistry and Environmental Science and Engineering, director of the Ronald and Maxine Linde Center for Global Environmental Science, and founding member of the Orbiting Carbon Observatory project.

The paper is titled “Cropland carbon uptake delayed and reduced by 2019 Midwest floods.” Co-authors at Caltech include Junjie Liu, visiting associate in environmental science and engineering; Philipp Köhler, research scientist; Liyin He (MS ’18), graduate student; Rupesh Jeyaram, undergraduate student; and Vincent Humphrey, postdoctoral scholar. Other co-authors include Troy Magney of UC Davis; Kenneth J. Davis, Tobias Gerken, and Sha Feng of Pennsylvania State University; and Joshua P. Digangi of NASA. This research was funded by NASA.

This post was originally published on the Caltech website.

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Darkness, not cold, likely responsible for dinosaur-killing extinction

Thu, 03/19/2020 - 13:17

Roughly 66 million years ago an asteroid slammed into the Yucatan peninsula. New research shows darkness, not cold, likely drove a mass extinction after the impact.
Credit: NASA.

By Lauren Lipuma

New research finds soot from global fires ignited by an asteroid impact could have blocked sunlight long enough to drive the mass extinction that killed most life on Earth, including the dinosaurs, 66 million years ago.

The Cretaceous–Paleogene extinction event wiped out about 75 percent of all species on Earth. An asteroid impact at the tip of Mexico’s Yucatán Peninsula caused a period of prolonged cold and darkness, called an impact winter, that likely fueled a large part of the mass extinction. But scientists have had a hard time teasing out the details of the impact winter and what the exact mechanism was that killed life on Earth.

A new study in AGU’s journal Geophysical Research Letters simulates the contributions of the impact’s sulfur, dust, and soot emissions to the extreme darkness and cold of the impact winter. The results show the cold would have been severe but likely not devastating enough to drive a mass extinction. However, soot emissions from global forest fires darkened the sky enough to kill off photosynthesizers at the base of the food web for well over a year, according to the study.

“This low light seems to be a really big signal that would potentially be devastating to life,” said Clay Tabor, a geoscientist at the University of Connecticut and lead author of the new study. “It seems like these low light conditions are a probable explanation for a large part of the extinction.”

The results help scientists better understand this intriguing mass extinction that ultimately paved the way for humans and other mammals to evolve. But the study also provides insight into what might happen in a nuclear winter scenario, according to Tabor.

“The main driver of a nuclear winter is actually from soot in a similar type situation,” Tabor said. “What it really highlights is just how potentially impactful soot can be on the climate system.”

The impact and extinction

The Chicxulub asteroid impact spewed clouds of ejecta into the upper atmosphere that then rained back down to Earth. The returning particles would have had enough energy to broil Earth’s surface and ignite global forest fires. Soot from the fires, along with sulfur compounds and dust, blocked out sunlight, causing an impact winter lasting several years. Previous research estimates average global temperatures plummeted by at least 26 degrees Celsius (47 degrees Fahrenheit).

Scientists know the extreme darkness and cold were devastating to life on Earth but are still teasing apart which component was more harmful to life and whether the soot, sulfate, or dust particles were most disruptive to the climate.

In the new study, Tabor and his colleagues used a sophisticated climate model to simulate the climatic effects of soot, sulfates, and dust from the impact.

Their results suggest soot emissions from global fires absorbed the most sunlight for the longest amount of time. The model showed soot particles were so good at absorbing sunlight that photosynthesis levels dropped to below one percent of normal for well over a year.

“Based on the properties of soot and its ability to effectively absorb incoming sunlight, it did a very good job at blocking sunlight from reaching the surface,” Tabor said. “In comparison to the dust, which didn’t stay in the atmosphere for nearly as long, and the sulfur, which didn’t block as much light, the soot could actually block almost all light from reaching the surface for at least a year.”

A refuge for life

The darkness would have been devastating to photosynthesizers and could explain the mass extinction through a collapse of the food web, according to the researchers. All life on Earth depends on photosynthesizers like plants and algae that harvest energy from sunlight.

Interestingly, the temperature drop likely wasn’t as disturbing to life as the darkness, according to the study.

“It’s interesting that in their model, soot doesn’t necessarily cause a much larger cooling when compared other types of aerosol particles produced by the impact-but soot does cause surface sunlight to decline a lot more,” said Manoj Joshi, a climate dynamics professor at the University of East Anglia in the United Kingdom who was not connected to the new study.

In regions like the high latitudes, the results suggest oceans didn’t cool significantly more than they do during a normal cycle of the seasons.

“Even though the ocean cools by a decent amount, it doesn’t cool by that much everywhere, particularly in the higher latitude regions,” Tabor said. “In comparison to the almost two years without photosynthetic activity from soot, it seems to be a secondary importance.”

As a result, high latitude coastal regions may have been refuges for life in the months after the impact. Plants and animals living in the Arctic or Antarctic are already used to large temperature swings, extreme cold, and low light, so they may have had a better chance of surviving the impact winter, according to the researchers. 

Lauren Lipuma is a science writer at AGU. 

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Small climate change effects can be the most obvious

Wed, 03/11/2020 - 17:51

Relatively small changes to the climate in some parts of the world can be more obvious than larger changes elsewhere, according to a new study in the AGU journal Geophysical Research Letters.

A team led by the University of Reading looked at how climate change has already changed temperatures and rainfall patterns worldwide to the point that they would be unfamiliar to people living at the end of the 19th century. Crucially, they then examined how these changes compared with climate fluctuations already experienced in different regions of the globe.

They found mid-latitude countries like the UK and US were experiencing relatively large changes in temperature compared to tropical regions, but the experience of these changes were being masked by the fact the weather in these countries is more erratic.

Emergence of global and local temperature change from 1850-2018. Top: Global Mean Surface Temperatures (GMST, grey), smoothed with a 41-year lowess filter (black). Bottom: Oxford annual temperature (grey) and scaled smoothed GMST (black). Credit: AGU, Hawkins, et al. GRL 2020.

Conversely, the smaller changes in countries in the tropics were found to be the most obvious and may be having a greater impact on society because people are used to a generally more settled climate.

Professor Ed Hawkins, climate scientist and lead author at the University of Reading and NCAS, said: “These findings are important as it shows there is no one-size-fits-all approach to adapting to climate change.

“Climate change impacts in some countries are being hidden by their own changeable weather. People in these countries are already used to coping with swings between hot and cold or wet and dry conditions, meaning even sizable changes to their climate may be less obvious. Alternatively, countries with steady climates are more likely to notice their warming climate, despite the changes being less dramatic.

“Where climate change is smaller, we run the risk of thinking it is insignificant. We need to realise where climate change might be hiding in plain sight because this tends to be regions which are more vulnerable and less able to adapt.”

Professor Manoj Joshi, a co-author at the University of East Anglia, said: “An example of such noticeable changes might be temperatures in the warmest months of the year exceeding the limits that societies have become familiar with over the last century.”

The study was by scientists from the University of Reading, University of East Anglia, Victoria University of Wellington, University of Oxford, University of Melbourne and University of Chile.

This post originally appeared on the University of Reading website.

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Major Greenland glacier collapse 90 years ago linked to climate change

Tue, 03/10/2020 - 20:19

By Larry O’Hanlon

Ninety years ago there were no satellites to detect changes in Greenland’s coastal glaciers, but a new study combining historical photos with evidence from ocean sediments suggests climate change was already at work in the 1930s and led to a major collapse of the one of Greenland’s largest coastal glaciers.

The only reason scientists today know about the Kangerlussuaq Glacier’s dramatic retreat in the 1930s is the existence of both aerial and ground-level photos taken by explorers before and after the glacier’s tongue had dislodged itself from a submarine ridge. The ridge had pinned the glacier in place, perhaps making the glacier relatively more stable than many other coastal Greenland glaciers.

“We found out about the collapse by looking at old pictures,” said geologist Flor Vermassen of the Geological Survey of Denmark and Greenland. “And this matched our findings from the sediments.” Vermassen is the lead author of a new paper describing the Kangerlussuaq collapse in the AGU journal Geophysical Research Letters.

Photographic evidence of a major change in Kangerlussuaq presented in a 1937 paper by Wager et al. a) The yellow dot is the position where the land‐based photographs were taken in 1930 and 1936. The direction and fields of view for the images are indicated by the gray triangles. Note that the photo from 1936 was aimed in a slightly more northern direction. b) Photograph of the floating ice tongue in August 1930. c) Photograph of the ice mélange in May 1936.

The historical aerial and ground-level photos were from Danish and British expeditions that set out to Greenland’s east coast from 1930 through 1935. The photos show a dramatic retreat of the glacier following a well-documented period of air and water warming in the 1920s, Vermassen explained.

The images above, cropped to the areas they overlap and animated.

To confirm the timing of the Kangerlussuaq collapse and the changing water temperatures, Vermassen and his colleagues analyzed sediment cores collected from the seafloor in front of the glacier. They found chemical and physical evidence that confirmed the warming, including a layer of debris that marked the melting of ice and the fall of ice-rafted debris onto the sea floor.

Surprisingly, the collapse of Kangerlussuaq stands out among Greenland glaciers not because it is early, but because it is late. The year 1900 has been used by researchers as a Greenland‐wide point in time when glaciers started to retreat, Vermassen and his colleagues write. It was the pinning of this glacier against a large submarine ridge that might have kept Kangerlussuaq stable for years longer.

“It’s a rare thing to be able to show such a big event before the satellite era.” Vermassen said. “It fits in the general decrease in ice in the 20th century.”

Larry O’Hanlon is a freelance science writer and manager of AGU’s blogosphere

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Researchers develop new explanation for destructive earthquake vibrations

Tue, 03/03/2020 - 18:07

Earthquakes produce seismic waves with a range of frequencies, from the long, rolling motions that make skyscrapers sway, to the jerky, high-frequency vibrations that cause tremendous damage to houses and other smaller structures. A pair of geophysicists has a new explanation for how those high-frequency vibrations may be produced.

In a new paper published in the AGU journal Geophysical Research Letters, Brown University researchers Victor Tsai and Greg Hirth propose that rocks colliding inside a fault zone as an earthquake happens are the main generators of high-frequency vibrations. That’s a very different explanation than the traditional one, they say, and it could help explain puzzling seismic patterns made by some earthquakes. It could also help scientists predict which faults are likely to produce the more damaging quakes.

“The way we normally think of earthquakes is that stress builds up on a fault until it eventually fails, the two sides slip against each other, and that slip alone is what causes all the ground motions we observe,” said Tsai. “The idea of this paper is to evaluate whether there’s something other than just slip. The basic question is: If you have objects colliding inside the fault zone as it slips, what physics could result from that?”

Drawing from mathematical models that describe the collisions of rocks during landslides and other debris flows, Tsai and Hirth developed a model that predicts the potential effects of rock collisions in fault zones. The model suggested the collisions could indeed be the principal driver of high-frequency vibrations. And combining the collision model with more traditional frictional slip models offers reasonable explanations for earthquake observations that don’t quite fit the traditional model alone, the researchers say. 

For example, the combined model helps explain repeating earthquakes — quakes that happen at the same place in a fault and have nearly identical seismic wave forms. The odd thing about these quakes is that they often have very different magnitudes, yet still produce ground motions that are nearly identical. That’s difficult to explain by slip alone, but makes more sense with the collision model added, the researchers say. 

“If you have two earthquakes in the same fault zone, it’s the same rocks that are banging together — or at least rocks of basically the same size,” Tsai said. “So if collisions are producing these high-frequency vibrations, it’s not surprising that you’d get the same ground motions at those frequencies regardless of the amount of slip that occurs.”

The collision model also may help explain why quakes at more mature fault zones — ones that have had lots of quakes over a long period of time — tend to produce less damage compared to quakes of the same magnitude at more immature faults. Over time, repeated quakes tend to grind down the rocks in a fault, making the faults smoother. The collision model predicts that smoother faults with less jagged rocks colliding would produce weaker high-frequency vibrations.

Tsai says that more work needs to be done to fully validate the model, but this initial work suggests the idea is promising. If the model does indeed prove valid, it could be helpful in classifying which faults are likely to produce more or less damaging quakes.

“People have made some observations that particular types of faults seem to generate more or less high-frequency motion than others, but it has not been clear why faults fall into one category or the other,” he said. “What we’re providing is a potential framework for understanding that, and we could potentially generalize this to all faults around the world. Smoother faults with rounded internal structures may generally produce less high-frequency motions, while rougher faults would tend to produce more.”

The research also suggests that some long-held ideas about how earthquakes work might need revising. 

“In some sense it might mean that we know less about certain aspects of earthquakes than we thought,” Tsai said. “If fault slip isn’t the whole story, then we need a better understanding of fault zone structure.”

This post was originally published on the Brown University website.

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Shark may avoid cold blood by holding its breath on deep dives

Wed, 02/19/2020 - 15:00

By Liza Lester

Scalloped hammerhead sharks stay warm as they descend into cold, deep water off the coast of Hawaii, suggesting the cold-blooded species may maintain its body temperature on dives by holding its breath, according to new research presented at the Ocean Sciences Meeting 2020 in San Diego, California.

The new results are surprising because typically, hammerhead sharks quickly assimilate the temperature of the surrounding water. The sharks are not known to have physiological means to retain or generate heat internally, according to Mark Royer, a marine biologist at the University of Hawaii Manoa, who will present the new research on Thursday, February 20.

A scalloped hammerhead shark (Sphryna lewini) eyeballs the photographer outside the Shark Lab at the Hawaii Institute of Marine Biology in Kāneʻohe, Hawaii.
Credit: Mark Royer.

Royer tracked scalloped hammerhead sharks making frequent, short trips 800 meters below the surface.

Water off the coast of Hawaii drops from a comfortable 25 degrees Celsius (75 degrees Fahrenheit) at the surface to temperatures closer to the inside of a refrigerator, about 4 degrees Celsius (40 degrees Fahrenheit), at 800 meters (2,600 feet) below the surface.

Royer suspects the hammerheads are modulating their behavior to keep their muscles warm enough for active hunting at depth.

“Hammerheads are a tropical and warm temperate species. When their body temperature gets too low, they lose muscle function, visual acuity, and their metabolism slows down. If a shark gets too cold, it can’t keep itself moving and breathe,” Royer said.

Sharks breathe by pulling oxygen into their blood from ocean water as it rushes into their mouths and out through their gill slits. They have to keep moving forward to avoid drowning. Water contact over the large surface of their gills also quickly cools or warms their blood to the temperature of the water.

Royer thinks the scalloped hammerhead sharks may be simply shutting their mouths, or clamping their gills shut, on dives to keep out the water and avoid getting chilled.

“The laws of thermodynamics hold,” Royer said. “We know the water is super cold and the sharks are staying warm. So the sharks can’t be dumping body heat out through their gills.”

Some warm-blooded fish species, like bluefin tuna and great white sharks, have specialized muscle in core of their bodies that rewarms their blood and allows them to hunt in colder water. The hammerheads do not have analogous anatomy, although Royer said it is possible they have a previously unknown ability to divert blood away from their gills.

“We don’t know what the mechanism is, whether it’s simply closing their mouths and closing their gills, or if they’re shunting the blood away from their gills. Either one of those mechanisms means there is no longer gas exchange at the gills, so the shark is basically holding its breath in a way that a shark can while it’s conducting these deep dives,” Royer said.

Royer tagged hammerheads with a package of sensors that recorded the sharks’ depth, tailbeats, and the pitch and roll of their bodies, as well as the temperature of their muscle and that of the surrounding water, following them from Kāneʻohe Bay, in the island of Oahu, as they made repeated dives of off the coast to depths over 800 meters (2,600 feet). He followed nine sharks for 7 to 23 days, gathering over 1,750 hours of data.

During dives, the sharks cruised leisurely down to about 100 meters (330 feet). Then their noses pitched down 80 degrees and they sprinted to the depths.

“They’re almost like a dive-bombers,” Royer said.

Body temperatures held constant past 150 meters (500 feet) depth, where researchers would expect to observe the sharks beginning to cool down, and as the sharks swam vigorously at depth. After about five minutes, the sharks dashed back up to about 300 meters (1,000 feet), where they slowed down, and their body temperatures abruptly dropped.

The sharks spent roughly 45 minutes at the surface, as their bodies slowly warmed, before repeating the dive cycle.

Researchers aren’t certain what the sharks are doing on their dives, but occasional discoveries of deep sea squid beaks in hammerhead stomachs suggests the sharks are hunting prey that live in deep water. Royer plans to include cameras in future work, to learn more about what the sharks are doing on their dives and observe their mouths and gills.

—Liza Lester is a science writer in AGU’s Public Information Office



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