Mark Torres wins Sloan Research Fellowship

By Kendall Schoemann (staff writer in Rice University’s Office of Public Affairs)

Two Rice University faculty members have been selected as 2019 Alfred P. Sloan Research Fellows.

Rice University geochemist Mark Torres

Mark Torres (Photo courtesy of Rice University)

Mark Torres, assistant professor of Earth, environmental and planetary sciences, was honored for his work in the field of ocean sciences, and Ming Yi, assistant professor of physics and astronomy, was awarded for physics. The two-year, $70,000 fellowships seek to stimulate fundamental research by early-career scientists and scholars while recognizing their distinguished performance and unique potential to make substantial contributions to their fields.

Torres and Yi are among 126 U.S. and Canadian researchers to receive a 2019 fellowship.

“This fellowship gives me freedom to pursue interesting ideas and, in a sense, validates the work I’ve started to do at Rice,” Torres said. “At this point in my career, these are my first steps on my own, and it’s nice to know those steps are headed in the right direction.”

Torres’ high school was attached to a museum of paleontology, which sparked his passion for studying Earth. Encouraged to turn this passion into a career, he took geology classes and found work at the interface between geology and chemistry to be the most captivating. His research concerns how concentrations of carbon dioxide and oxygen in the atmosphere are regulated over geologic time and what makes planets habitable.

“The chemistry of the ocean is really important,” Torres said. “The amount of carbon dioxide in the atmosphere is very dependent on the chemistry of the ocean. Most of my research so far has focused on how rivers, by delivering different chemical elements to the ocean, influence ocean chemistry and atmospheric carbon dioxide. On the other hand, the way in which chemical elements get removed from ocean water should be just as important and will be the focus of my work supported by this fellowship.”

Yi’s research lab, an experimental condensed matter physics group, aims to advance the fundamental understanding of exotic properties in materials using spectroscopy tools such as angle-resolved photoemission spectroscopy and X-ray scattering.

Rice University Physicist Ming Yi

Ming Yi (Photo courtesy of Dawn Harmer/SLAC National Accelerator Laboratory)

“Materials that have exotic properties, such as superconductivity, can revolutionize our future,” Yi said. “My job is to figure out, from a fundamental physics point of view, why these materials have these amazing properties.”

New to Rice, Yi has been on campus since January. “I’m very excited to be at Rice, and I’m honored to receive this award,” she said. “In certain ways, I think it shows that the Rice community is very supportive of young professors, and it’s an encouragement for me to start my own group.”

With her fellowship support, Yi will focus on ways to control and tune exotic material properties. “As physicists, we like to figure out patterns, or overarching frameworks that describe a phenomenon,” she said. “Our goal is to figure out rules to describe and unify the things we see in nature.”

Torres earned a bachelor’s degree in geology from Pitzer College in 2010 and a Ph.D. in geochemistry from the University of Southern California in 2015. He joined Rice in 2017 from the California Institute of Technology.

Yi earned a bachelor’s degree in physics from the Massachusetts Institute of Technology in 2007 and a Ph.D. in physics from Stanford University in 2014. She joined Rice in 2018 from the University of California, Berkeley.

The Alfred P. Sloan Foundation is a philanthropic, not-for-profit, grant-making institution based in New York. Established in 1934 by Alfred Pritchard Sloan Jr., then-president and chief executive officer of General Motors Co., the foundation makes grants in support of original research and education in science, technology, engineering, mathematics and economics.

Dr. Richard Gordon, Lin Zheng, Daniel Woodworth under EoS Research Spotlight

A Research Spotlight highlighting their paper, “Pacific Plate Apparent Polar Wander, Hot Spot Fixity, and True Polar Wander During the Formation of the Hawaiian Island and Seamount Chain From an Analysis of the Skewness of Magnetic Anomaly 20r (44 Ma)” has been published on Eos.org.

First Things First

text and images by Linda Welzenbach

After 24 hours of travel from Houston, Texas to Punta Arenas, Chile, I arrived exhausted yet excited (and perhaps just a wee bit anxious of the unknown) to be part of something very unique.  My name is Linda Welzenbach and my role on this expedition is to share the scientific discoveries that will come from our journey to Antarctica on board the RVIB (research vessel/ice breaker) Nathaniel B. Palmer (NBP).  Akin to a spacecraft exploring new frontiers beyond Earth, the Nathaniel B. Palmer and her marine operations specialists will navigate safe passage through Antarctica’s icy waters for the 26 ITGC scientists and the wide array of science activities they have planned over the next two months.

This first post will bring you aboard to see what she has to offer, and how scientists become seafaring explorers.  NBP’s origins and history will be highlighted in a later post.

Welcome to the Nathaniel B. Palmer! She is a beautiful ship, with commodious berths…if you can find the one green door among many that is assigned to you.

The NBP’s vitals can be found on the USAP website HERE

Upon arriving Sunday evening, we discover that the ship would be leaving a day early. The NBP was thirsty and if we wanted to stay on schedule, we would need to leave for the “gas station” Monday evening.

Prior to departure, we head to the U.S. Antarctic Program warehouse for orientation and distribution of the necessary Extreme Cold Weather (ECW) gear.

Radio journalist Carolyn Beeler models the steel toed boots needed to work on deck and onshore.

We are on board for just a couple hours, yet the first task will be to participate in a simulated exit.  As part of that exercise, we must be able to put on flotation suits, which are required for situations that call for abandoning ship (below).  During the cruise we will practice several more drills of this nature, to build muscle memory in the event of a real emergency.

Interpretive dance is the best approach for getting into the flotation suit.

Dr. Rebecca Totten Minzoni (left) and her Ph.D. student Victoria Fitzgerald successfully complete the flotation suit challenge.

There are two covered life boats for passengers- each one can hold the full complement of scientists.

THOR scientist Dr. Alastair Graham in the surprisingly comfortable life boat.

In anticipation of an evening departure, we met in the laboratory to unpack and sort through all the core processing supplies, stowing them securely in anticipation of the rough seas that characterize Drake’s passage. To see live weather, and forecasts, click HERE.

THOR team members (l to r)- Rebecca Totten Minzoni, Alastair Graham, Rachel Clark, Rob Larter- sort through and distribute core processing supplies in the core processing lab. All drawers and cabinets have dog-locks to ensure they do not open during passage through rough seas.

A bit after 7pm, #NBP1902 left Punta Arenas to refuel.  As of this posting, we are back in Punta Arenas, and remain here until maintenance activities have been completed.

 

Linda is the science communications specialist in the Department of Earth, Environmental and Planetary Sciences at Rice University. She is a geologist and veteran of two expeditions to collect meteorites from Antarctica. Her role for THOR is public outreach, and so she will communicate science activities during the first scientific cruise in 2019-NBP19-02 and serves as the project webmaster.

Planetary collision that formed the moon made life possible on Earth

– JANUARY 23, 2019

Study: Planetary delivery explains enigmatic features of Earth’s carbon and nitrogen

Most of Earth’s essential elements for life — including most of the carbon and nitrogen in you — probably came from another planet.

Earth most likely received the bulk of its carbon, nitrogen and other life-essential volatile elements from the planetary collision that created the moon more than 4.4 billion years ago, according to a new study by Rice University petrologists in the journal Science Advances.

 

A study by Rice University scientists (from left) Gelu Costin, Chenguang Sun, Damanveer Grewal, Rajdeep Dasgupta and Kyusei Tsuno found Earth most likely received the bulk of its carbon, nitrogen and other life-essential elements from the planetary collision that created the moon more than 4.4 billion years ago. The findings appear in the journal Science Advances. (Photo by Jeff Fitlow/Rice University)

The evidence was compiled from a combination of high-temperature, high-pressure experiments in Dasgupta’s lab, which specializes in studying geochemical reactions that take place deep within a planet under intense heat and pressure.“From the study of primitive meteorites, scientists have long known that Earth and other rocky planets in the inner solar system are volatile-depleted,” said study co-author Rajdeep Dasgupta. “But the timing and mechanism of volatile delivery has been hotly debated. Ours is the first scenario that can explain the timing and delivery in a way that is consistent with all of the geochemical evidence.”

In a series of experiments, study lead author and graduate student Damanveer Grewal gathered evidence to test a long-standing theory that Earth’s volatiles arrived from a collision with an embryonic planet that had a sulfur-rich core.

The sulfur content of the donor planet’s core matters because of the puzzling array of experimental evidence about the carbon, nitrogen and sulfur that exist in all parts of the Earth other than the core.

“The core doesn’t interact with the rest of Earth, but everything above it, the mantle, the crust, the hydrosphere and the atmosphere, are all connected,” Grewal said. “Material cycles between them.”

One long-standing idea about how Earth received its volatiles was the “late veneer” theory that volatile-rich meteorites, leftover chunks of primordial matter from the outer solar system, arrived after Earth’s core formed. And while the isotopic signatures of Earth’s volatiles match these primordial objects, known as carbonaceous chondrites, the elemental ratio of carbon to nitrogen is off. Earth’s non-core material, which geologists call the bulk silicate Earth, has about 40 parts carbon to each part nitrogen, approximately twice the 20-1 ratio seen in carbonaceous chondrites.

 

Rice University petrologists have found Earth most likely received the bulk of its carbon, nitrogen and other life-essential volatile elements from the planetary collision that created the moon more than 4.4 billion years ago. (Image courtesy of Rice University)

“Nitrogen was largely unaffected,” he said. “It remained soluble in the alloys relative to silicates, and only began to be excluded from the core under the highest sulfur concentration.”Grewal’s experiments, which simulated the high pressures and temperatures during core formation, tested the idea that a sulfur-rich planetary core might exclude carbon or nitrogen, or both, leaving much larger fractions of those elements in the bulk silicate as compared to Earth. In a series of tests at a range of temperatures and pressure, Grewal examined how much carbon and nitrogen made it into the core in three scenarios: no sulfur, 10 percent sulfur and 25 percent sulfur.

Carbon, by contrast, was considerably less soluble in alloys with intermediate sulfur concentrations, and sulfur-rich alloys took up about 10 times less carbon by weight than sulfur-free alloys.

Using this information, along with the known ratios and concentrations of elements both on Earth and in non-terrestrial bodies, Dasgupta, Grewal and Rice postdoctoral researcher Chenguang Sun designed a computer simulation to find the most likely scenario that produced Earth’s volatiles. Finding the answer involved varying the starting conditions, running approximately 1 billion scenarios and comparing them against the known conditions in the solar system today.

“What we found is that all the evidence — isotopic signatures, the carbon-nitrogen ratio and the overall amounts of carbon, nitrogen and sulfur in the bulk silicate Earth — are consistent with a moon-forming impact involving a volatile-bearing, Mars-sized planet with a sulfur-rich core,” Grewal said.

Dasgupta, the principal investigator on a NASA-funded effort called CLEVER Planets that is exploring how life-essential elements might come together on distant rocky planets, said better understanding the origin of Earth’s life-essential elements has implications beyond our solar system.

“This study suggests that a rocky, Earth-like planet gets more chances to acquire life-essential elements if it forms and grows from giant impacts with planets that have sampled different building blocks, perhaps from different parts of a protoplanetary disk,” Dasgupta said.

“This removes some boundary conditions,” he said. “It shows that life-essential volatiles can arrive at the surface layers of a planet, even if they were produced on planetary bodies that underwent core formation under very different conditions.”

Dasgupta said it does not appear that Earth’s bulk silicate, on its own, could have attained the life-essential volatile budgets that produced our biosphere, atmosphere and hydrosphere.

“That means we can broaden our search for pathways that lead to volatile elements coming together on a planet to support life as we know it.”

Additional co-authors on the Science Advances study are Kyusei Tsuno and Gelu Costin, both of Rice. The research was supported by NASA, the Deep Carbon Observatory and the David and Lucile Packard Foundation.

CLEVER Planets is part of the Nexus for Exoplanet System Science, or NExSS, a NASA astrobiology research coordination network that is dedicated to the study of planetary habitability. CLEVER Planets involves more than a dozen research groups from Rice, NASA’s Johnson Space Center, UCLA, the University of Colorado Boulder and the University of California, Davis. More information is available at cleverplanets.org.

A schematic depicting the formation of a Mars-sized planet (left) and its differentiation into a body with a metallic core and an overlying silicate reservoir. The sulfur-rich core expels carbon, producing silicate with a high carbon to nitrogen ratio. The moon-forming collision of such a planet with the growing Earth (right) can explain Earth’s abundance of both water and major life-essential elements like carbon, nitrogen and sulfur, as well as the geochemical similarity between Earth and the moon. (Image courtesy of Rajdeep Dasgupta)

Feds, states can help biochar live up to its soil-saving potential

MIKE WILLIAMS – JANUARY 11, 2019

Study shows how government promotes agricultural, environmental benefits – and could do more

Even though every dollar spent on soil improvement can save much more in environmental costs down the road, startup costs can sometimes make it hard for farmers to implement best environmental practices. A team of researchers from Rice and North Dakota State universities argues that this is especially true for using biochar, but that the problem can be addressed through well-designed policy.

Biochar is a porous, charcoal-like material produced via pyrolysis, the high-temperature decomposition of biomass. Studies show biochar improves soil water properties and enhances agricultural production by an average of 15 percent. It also reduces nutrient leaching, increases nitrogen available to plants and reduces the release of nitrogenous gases, which can improve local air quality.

Charcoal-like biochar improves soil hydration and enhances agricultural production while it curtails nutrient leaching, increases nitrogen available to plants and reduces the release of gas pollutants. A new study by researchers at Rice University and North Dakota State University gathers current and potential sources of government support to promote the production and use of biochar.

Charcoal-like biochar improves soil hydration and enhances agricultural production while it curtails nutrient leaching, increases nitrogen available to plants and reduces the release of gas pollutants. Courtesy of Ghasideh Pourhashem

A policy study led by Ghasideh Pourhashem, a former postdoctoral fellow at Rice’s Baker Institute for Public Policy and now an assistant professor at North Dakota State, surveys existing government programs and details how they support the use of biochar to enhance agricultural productivity, sequester carbon and preserve valuable soil. The federal government already has 35 programs that do – or could – promote the deployment of biochar to improve agricultural preservation and head off future environmental woes, according to Pourhashem and her team.

For the open-access study in Global Change Biology Bioenergy, Pourhashem worked with Rice mentors Caroline Masiello, a professor of Earth, Environmental and Planetary Sciences, and Kenneth Medlock, the James A. Baker, III, and Susan G. Baker Fellow in Energy and Resource Economics.

“Our previous research has shown that wide-scale application of biochar across the United States’ agricultural soils can save millions of dollars in health costs by improving regional air quality,” said Pourhashem, who joined North Dakota’s Department of Coatings and Polymeric Materials and Center for Sustainable Materials Science in 2017 and is a member of the US Biochar Initiative advisory board.

But despite the accumulating evidence, she said biochar adoption has been slow.

“Our new study shows how policy frameworks can support biochar as a resource-saving, crop-boosting and health care-improving material,” Pourhashem said.

The researchers note the United States has long invested in biofuels like ethanol, and they argue that biochar deserves similar long-term support to improve the nation’s soil and food security strategy.

Masiello, a biogeochemist and expert on biochar, noted the financial disconnect between those who bear the cost of land-management changes and those who benefit.

“There are plenty of farmers who want to do the right thing, but the benefits of biochar don’t accrue entirely on-farm,” she said, citing examples like cleaner water and air. “This paper is about how policy can connect the costs borne by farmers with the benefits to us all.”

Rice University alumna Ghasideh Pourhashem led an effort to gather and categorize a list of government resources available to promote the development of biochar to preserve valuable soil, enhance agricultural production and improve air quality.

The only active loan guarantee program the researchers identified for biochar production is the Department of Agriculture’s Biorefinery, Renewable Chemical and Bio-based Product Manufacturing Assistance Program, which provides up to $250 million per project. But other programs run by the Department of Energy, the Department of Agriculture and initiatives in Iowa, Oregon, Colorado and Minnesota provide nearly $250 million more in grants, matching or production payments and tax credits. The researchers also identified eight programs that offer a total of nearly $30 million in research and development funding that implicitly support biochar.

The researchers determined that government’s emphasis on biochar production is inadequate and tilts heavily toward biofuels. They also noted the need for more upfront investment in large biochar-focused production rather than small-scale facilities. They suggested investment could be encouraged by the development of a broadly accepted set of product standards for biochar.

“The potential long-term impacts of biochar are enormous,” Medlock said. “Much of the recent support for biochar has focused on its use for carbon dioxide sequestration, but the benefits are much broader. The potential effects on local air quality and water quality have implications that extend far beyond the application site, which makes policy supportive of investment in biochar production and market development something that should be seriously considered.”

Shih Yu “Elsie” Hung, an energy forum research analyst at the Baker Institute, is co-author of the paper. Rice’s Shell Center for Sustainability supported the research.

Dr. Gelu Costin’s research on Hematane nominated for “The Most Significant Material Science News of 2018”

‘True polar wander’ may have caused ice age

JADE BOYD – NOVEMBER 19, 2018

Rice U. scientists use Hawaiian hot spot to study movement of Earth’s poles

Earth’s latest ice age may have been caused by changes deep inside the planet. Based on evidence from the Pacific Ocean, including the position of the Hawaiian Islands, Rice University geophysicists have determined Earth shifted relative to its spin axis within the past 12 million years, which caused Greenland to move far enough toward the north pole to kick off the ice age that began about 3.2 million years ago.

Daniel Woodworth and Richard Gordon. (Photo by Jeff Fitlow/Rice University)

Their study in the journal Geophysical Research Letters is based on an analysis of fossil signatures from deep ocean sediments, the magnetic signature of oceanic crust and the position of the mantle “hot spot” that created the Hawaiian Islands. Co-authors Richard Gordon and Daniel Woodworth said the evidence suggests Earth spun steadily for millions of years before shifting relative to its spin axis, an effect geophysicists refer to as “true polar wander.

“The Hawaiian hot spot was fixed, relative to the spin axis, from about 48 million years ago to about 12 million years ago, but it was fixed at a latitude farther north than we find it today,” said Woodworth, a graduate student in Rice’s Department of Earth, Environmental and Planetary Sciences. “By comparing the Hawaiian hot spot to the rest of the Earth, we can see that that shift in location was reflected in the rest of the Earth and is superimposed on the motion of tectonic plates. That tells us that the entire Earth moved, relative to the spin axis, which we interpret to be true polar wander.”

The movement of the Pacific plate across a mantle hotspot created the Hawaiian islands over millions of years. (Image courtesy of National Geophysical Data Center/USGS/Wikimedia Commons)

By volume, Earth is mostly mantle, a thick layer of solid rock that flows under intense pressure and heat. The mantle is covered by an interlocking puzzle of rocky tectonic plates that ride atop it, bumping and slipping against one another at seismically active boundaries. Hot spots, like the one beneath Hawaii, are plumes of hot solid rock that rise from deep within the mantle.

Gordon, the W.M. Keck Professor of Earth, Environmental and Planetary Science, said the new findings build on two 2017 studies: one from his lab that showed how to use hot spots as a global frame of reference for tracking the movement of tectonic plates and another from Harvard University that first tied true polar wander to the onset of the ice age.

“We’re taking these hot spots as marked trackers of plumes that come from the deep mantle, and we’re using that as our reference frame,” he said. “We think the whole global network of hotspots was fixed, relative to the Earth’s spin axis, for at least 36 million years before this shift.”

Island chains like the Hawaiians are formed when tectonic plates move across a mantle plume “hot spot.” (Illustration courtesy of Los688/Wikimedia Commons)

Like any spinning object, Earth is subject to centrifugal force, which tugs on the planet’s fluid interior. At the equator, where this force is strongest, Earth is more than 26 miles larger in diameter than at the poles. Gordon said true polar wander may occur when dense, highly viscous bumps of mantle build up at latitudes away from the equator.

“Imagine you have really, really cold syrup, and you’re putting it on hot pancakes,” Gordon said. “As you pour it, you temporarily have a little pile in the center, where it doesn’t instantly flatten out because of the viscosity of the cold syrup. We think the dense anomalies in the mantle are like that little temporary pile, only the viscosities are much higher in the lower mantle. Like the syrup, it will eventually deform, but it takes a really, really long time to do so.”

If the mantle anomalies are massive enough, they can unbalance the planet, and the equator will gradually shift to bring the excess mass closer to the equator. The planet still spins once every 24 hours and true polar wander does not affect the tilt of Earth’s spin axis relative to the sun. The redistribution of mass to a new equator does change Earth’s poles, the points on the planet’s surface where the spin axis emerges.

Woodworth said the hot spot data from Hawaii provides some of the best evidence that true polar wander was what caused Earth’s poles to start moving 12 million years ago. Islands chains like the Hawaiians are formed when a tectonic plate moves across a hot spot.

True polar wander occurs when the entire Earth shifts relative to its spin axis. (Illustration courtesy of Victor C. Tsai/Wikimedia Commons)

“True polar wander shouldn’t change hot spot tracks because the hot spot track is the record of the motion of the plate relative to the hot spot,” Woodworth said.

Gordon said, “It was only about a 3 degree shift, but it had the effect of taking the mantle under the tropical Pacific and moving it to the south, and at the same time, it was shifting Greenland and parts of Europe and North America to the north. That may have triggered what we call the ice age.”

Earth is still in an ice age that began about 3.2 million years ago. Earth’s poles have been covered with ice throughout the age, and thick ice sheets periodically grow and recede from poles in cycles that have occurred more than 100 times. During these glacial cycles, ice has extended as far south as New York and Yellowstone National Park. Earth today is in an interglacial period in which ice has receded toward the poles.

Gordon said true polar wander is not merely a change in the location of Earth’s magnetic poles. As the planet spins, it’s iron core produces a magnetic field with “north” and “south” poles near the spin axis. The polarity of this field flips several times every million years, and these changes in polarity are recorded in the magnetic signatures of rocks the world over. The paleomagnetic record, which is often used to study the movement of tectonic plates across Earth’s surface, contains many instances of “apparent polar wander,” which tracks the motion of the spin axis and which includes the effects of both plate motion and true polar wander, Gordon said.

An illustration depicting the minimum (interglacial, black) and maximum (glacial, grey) glaciation of the northern hemisphere during the ice age that began about 3.2 million years ago. (Image courtesy of Hannes Grobe/AWI/Wikimedia Commons)

He said Earth’s mantle is ever-changing as new material constantly cycles in and out from tectonic plates. The drawing down and recycling of plates via subduction provides a possible explanation for the highly viscous mantle anomalies that probably cause true polar wander.

“In class, I often demonstrate this with lead fishing weights and pliers,” Gordon said. “It’s easy to deform the lead with the pliers, and it’s not brittle. It doesn’t crack or fly apart when it fails. That’s a pretty good analogy for mantle flow because that’s the way silicate rock deforms under intense heat and pressure.”

He and Woodworth are working with colleagues to extend their analysis, both from 12 million years ago to the present as well as further into the past than the 48-million-year start date in the newly published study.

The National Science Foundation supported the research.

Blue Hole Belize- Dr. André Droxler leads geological science activities for historic submersible expedition

Ice-age climate clues unearthed

Rice scientist’s method helps interpret climate data from lake sediments

– OCTOBER 24, 2018

How cold did Earth get during the last ice age? The truth may lie deep beneath lakes and could help predict how the planet will warm again.

Sediments in lake beds hold chemical records of ages past, among them the concurrent state of the atmosphere above. Scientists led by a Rice University professor and her colleagues have devised a new computational model to interpret what they reveal.

Sylvia Dee, an assistant professor of Earth, environmental and planetary sciences, and her colleagues have created a computational Lake Proxy System Model to translate data from deep beneath lake surface waters in a way that relates more directly to measurable climate model variables.

Rice University climate scientist Sylvia Dee created PRYSM, a computational modeling system, to improve climate models that use paleoclimate proxies from lake beds or other sources.

Their work is part of a public software platform created by Dee called PRYSM, and is described in the American Geophysical Union journal Paleoceanography and Paleoclimatology.

Scientists who study past climate analyze geochemical signals from archives like corals and ice cores, or encoded in the rings of old trees, but not everyone interprets the data in the same way. Dee’s quest has been to design simple models that help interpret observations of past climate more uniformly with climate models, and in the process make these invaluable archives more relevant to studies of future climate change.

“We have climate model simulations going back thousands of years,” said Dee, who joined Rice this year. “They help us understand the drivers of past temperature and precipitation changes, but we have to use climate data from the past to ground truth the models.

“For example, if a climate model shows strong agreement with the temperature reconstructions we have from lakes, we might conclude this model’s physics are robust and that it can do a better job simulating what will happen under future anthropogenic warming.”

Lake beds store evidence of climate history in layered sediment that can be analyzed and dated by extracting cores. Dee’s study used climate model data to explore and understand the lake archives scientists use to reconstruct atmospheric conditions for a given time.

“Some of the richest temperature and precipitation histories that we have on Earth come from lakes,” Dee said. “People have been measuring indicators in sediments for years, but it isn’t straightforward to compare that data to climate models.

“That’s where I come in,” she said. “I’m part of a group of scientists focused on translating between what climate models tell us about past changes in the climate system and what the data are telling us.”

Dee and her team simulated lake temperatures and climate archives in two lakes in Africa, Malawi and Tanganyika, stretching back to the last glacial maximum about 21,000 years ago, when global temperatures were estimated to be between 3 to 5 degrees Celsius colder than today.

Sediments under Lake Tanganyika in Africa store chemicals that give paleoclimatologists information about atmospheric conditions in ancient times. A Rice University professor has created a computational model that helps translate what they find. Courtesy of Sylvia Dee

“That’s a clear target for climatologists,” she said. “We have clues from the past that tell us how cold the African continent was. It’s the last time in Earth’s climate history that there was a dramatic shift in mean climate due to carbon dioxide forcing, and we use it as a test bed for climate model performance.”

In the test case, PRYSM’s simulation revealed that lake temperature proxies underestimated air temperature changes. “People generally assume that lake temperature reconstructions from sediments reflect air temperature changes,” Dee said. “We assume they change in tandem. Our model simulations show that the lake is actually damping the temperature signal.

“For example, if modeled air temperatures show a 4 degree Celsius warming since the last glacial maximum in Africa and the lake damps that signal to 3 degrees, we might wrongly conclude that air temperatures were a full degree warmer than they really were. We’re essentially able to quantify how much error one might expect in our interpretation of past temperature change. Those errors are incurred by the lake alone,” she said.

“That’s important to know,” Dee said. “These lake reconstructions are some of the only data available to help us understand how temperatures will evolve on the African continent in a warming world. Our hope is that PRYSM helps pin down these climate changes with higher confidence.”

The open-source PRYSM is version 2.0, designed explicitly to model climate archives in lakes. Dee built the first version to model ice cores, corals, cave deposits and tree-ring cellulose.

She and her colleagues plan to add more known paleoclimate proxies over time. Because PRYSM is open source, anyone can access the code (through GitHub) and enhance it.

“I’m trying to get everyone in the modeling and paleoclimate communities to talk to each other,” Dee said. “PRYSM is an effort to get both communities to understand we cannot compare apples to oranges. We need to compare paleoclimate data and model simulations in a more formal way, and in doing so, we hope to dramatically improve our interpretations of past climate changes.

“The great thing about being able to get snapshots of temperatures in the past is that we can hopefully build a broader understanding of how the planet is going to react to continued anthropogenic climate change,” she said. “We have direct measurements of what’s happened in the last 150 years. But if we look further back in time, we have bigger changes in carbon dioxide, bigger changes in volcanism and larger ice sheets on Earth. Those are heavy hammers. They help us understand how the climate reacts to stronger forcing.”

Co-authors of the paper are James Russell, an associate professor of Earth, environmental and planetary sciences, graduate student Ashling Neary and undergraduate Zihan Chen, all at Brown University, and Carrie Morrill, a research scientist at the Cooperative Institute for Research in Environmental Sciences, a partnership of the National Oceanic and Atmospheric Administration and the University of Colorado Boulder.

The research was supported by the Peter Voss Postdoctoral Fellowship, the Institute at Brown for Environment and Society, the Brown University Department of Earth, Environmental and Planetary Sciences, and the University of Texas at Austin Institute for Geophysics.

Tiny northwest quakes tied to deep-crust structure

– OCTOBER 25, 2018

Rice University scientists uncover relationship between tremors, water at the Cascadia margin

HOUSTON – (Oct. 25, 2018) – The earthquakes are so small and deep that someone standing in Seattle would never feel them. In fact, until the early 2000s, nobody knew they happened at all. Now, scientists at Rice University have unearthed details about the structure of Earth where these tiny tremors occur.

Rice postdoctoral researcher and seismologist Jonathan Delph and Earth scientists Fenglin Niu and Alan Levander make a case for the incursion of fluid related to slippage deep inside the Cascadia margin off the Pacific Northwest’s coast.

Rice University scientists studied how the density of microseismicity, or small tremors, related to the seismic structure of the Pacific Northwest in the United States. Red lines in the graphic at left correspond to cross-sections from northern Washington (top), central Oregon (middle), and northern California (bottom). The researchers determined a strong correlation exists between tremor density and underthrusting sediments (brown material in the graphics on right). Fluids that are released from the downgoing slab are concentrated in these sediments and lead to very slow seismic velocities in the region. Illustration by Jonathan Delph.

Their paper, which appears in the American Geophysical Union journal Geophysical Research Letters, links fluids escaping from deep subduction to the frequent shakes that Delph said happen in relative slow motion when compared to the sudden, violent jolts occasionally felt by Southern Californians at the southern end of the west coast.

“These aren’t large, instantaneous events like a typical earthquake,” Delph said. “They’re seismically small, but there’s a lot of them and they are part of the slow-slip type of earthquake that can last for weeks instead of seconds.”

Delph’s paper is the first to show variations in the scale and extent of fluids that come from dehydrating minerals and how they relate to these low-velocity quakes. “We are finally at the point where we can address the incredible amount of research that’s been done in the Pacific Northwest and try to bring it all together,” he said. “The result is a better understanding of how the seismic velocity structure of the margin relates to other geologic and tectonic observations.”

Rice University postdoctoral researcher Jonathan Delph led a study that found evidence of water escaping during subduction and infiltrating sedimentary material related to small tremors that occur beneath the Pacific Northwest of the United States.

The North American plate and Juan de Fuca plate, a small remnant of a much larger tectonic plate that used to subduct beneath North America, meet at the Cascadia subduction zone, which extends from the coast of northern California well into Canada. As the Juan de Fuca plate moves to the northeast, it sinks below the North American plate.

Delph said fluids released from minerals as they heat up at depths of 30 to 80 kilometers propagate upward along the boundary of the plates in the northern and southern portions of the margin, and get trapped in sediments that are subducting beneath the Cascadia margin.

“This underthrust sedimentary material is being stuck onto the bottom of the North American plate,” he said. “This can allow fluids to infiltrate. We don’t know why, exactly, but it correlates well with the spatial variations in tremor density we observe. We’re starting to understand the structure of the margin where these tremors are more prevalent.”

Delph’s research is based on extensive seismic records gathered over decades and housed at the National Science Foundation-backed IRIS seismic data repository, an institutional collaboration to make seismic data available to the public.

“We didn’t know these tremors existed until the early 2000s, when they were correlated with small changes in the direction of GPS stations at the surface,” he said. “They’re extremely difficult to spot. Basically, they don’t look like earthquakes. They look like periods of higher noise on seismometers.

“We needed high-accuracy GPS and seismometer measurements to see that these tremors accompany changes in GPS motion,” Delph said. “We know from GPS records that some parts of the Pacific Northwest coast change direction over a period of weeks. That correlates with high-noise ‘tremor’ signals we see in the seismometers. We call these slow-slip events because they slip for much longer than traditional earthquakes, at much slower speeds.”

He said the phenomenon isn’t present in all subduction zones. “This process is pretty constrained to what we call ‘hot subduction zones,’ where the subducting plate is relatively young and therefore warm,” Delph said. “This allows for minerals that carry water to dehydrate at shallower depths.

“In ‘colder’ subduction zones, like central Chile or the Tohoku region of Japan, we don’t see these tremors as much, and we think this is because minerals don’t release their water until they’re at greater depths,” he said. “The Cascadia subduction zone seems to behave quite differently than these colder subduction zones, which generate large earthquakes more frequently than Cascadia. This could be related in some way to these slow-slip earthquakes, which can release as much energy as a magnitude 7 earthquake over their duration. This is an ongoing area of research.”

Levander is the Carey Croneis Professor of Earth, Environmental and Planetary Sciences and Niu is a professor of Earth, environmental and planetary sciences at Rice. The Wiess Postdoctoral Fellowship at Rice supported the research.

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Read the abstract at https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL079518.

Follow Rice News and Media Relations via Twitter @RiceUNews.

Related materials:

Jonathan Delph website: https://jrdelph.wordpress.com

Incorporated Research Institutions for Seismology (IRIS): https://www.iris.edu/hq/

Global Seismology Group at Rice: http://www.gseis.rice.edu/index.html