Another concern arises over groundwater contamination from fracking accidents

The oil and gas extraction method known as hydraulic fracturing, or fracking, could potentially contribute more pollutants to groundwater than past research has suggested, according to a new study in ACS’ journal Environmental Science & Technology. Scientists are reporting that when spilled or deliberately applied to land, waste fluids from fracking are likely picking up tiny particles in the soil that attract heavy metals and other chemicals with possible health implications for people and animals.

Tammo S. Steenhuis and colleagues note that fracking, which involves injecting huge volumes of fluids underground to release gas and oil, has led to an energy boom in the U.S. But it has also ignited controversy for many reasons. One in particular involves flowback, which refers to fluids that surge back out of the fracked wells during the process. It contains water, lubricants, solvents and other substances from the original fracking fluid or extracted from the shale formation. High-profile spills and in some places, legal application of these liquids to land, have raised alarms. Research has linked fracking to groundwater contamination that could have major health effects. But another factor that no one has really addressed could play a role: colloids. These tiny pieces of minerals, clay and other particles are a concern because they attract heavy metals and other environmental toxins, and have been linked to groundwater contamination. Steenhuis’ team set out to take a closer look.

To simulate what would happen to colloids in soil after a fracking spill, the researchers flushed flowback fluids through sand with a known amount of colloids. They found that the fluids dislodged about a third of the colloids, far more than deionized water alone. When they increased the flow rate, the fluids picked up an additional 36 percent. “This indicates that infiltration of flowback fluid could turn soils into an additional source of groundwater contaminants such as heavy metals, radionuclides and microbial pathogens,” the scientists conclude. More research with real soils is planned.

Victoria’s volcano count rises

Geologists have discovered three previously unrecorded volcanoes in volcanically active southeast Australia.

The new Monash University research, published in the Australian Journal of Earth Sciences, gives a detailed picture of an area of volcanic centres already known to geologists in the region.

Covering an area of 19,000 square kilometres in Victoria and South Australia, with over 400 volcanoes, the Newer Volcanics Province (NVP) features the youngest volcanoes in Australia including Mount Schank and Mount Gambier.

Focusing on the Hamilton region, lead researcher Miss Julie Boyce from the School of Geosciences said the surprising discovery means additional volcanic centres may yet be discovered in the NVP.

“Victoria’s latest episode of volcanism began about eight million years ago, and has helped to shape the landscape. The volcanic deposits, including basalt, are among the youngest rocks in Victoria but most people know little about them,”Miss Boyce said.

“Though it’s been more than 5000 years since the last volcanic eruption in Australia, it’s important that we understand where, when and how these volcanoes erupted. The province is still active, so there may be future eruptions.”

The largest unrecorded volcano is a substantial maar-cone volcanic complex – a broad, low relief volcanic crater caused by an explosion when groundwater comes into contact with hot magma – identified 37 kilometres east of Hamilton.

Miss Boyce said the discoveries were made possible only by analysing a combination of satellite photographs, detailed NASA models of the topography of the area and the distribution of magnetic minerals in the rocks, alongside site visits to build a detailed picture of the Hamilton region of the NVP.

“Traditionally, volcanic sites are analysed by one or two of these techniques. This is the first time that this multifaceted approach has been applied to the NVP and potentially it could be used to study other volcanic provinces worldwide.”

The NVP is considered active, as carbon dioxide is released from the Earth’s mantle in several areas, where there is a large heat anomaly at depth. With an eruption frequency of one volcano every 10,800 years or less, future eruptions may yet occur.

It’s hoped that this multifaceted approach will lead to a better understanding of the distribution and nature of volcanism, allowing for more accurate hazard analysis and risk estimates for future eruptions.

Breakthrough provides picture of underground water

Superman isn’t the only one who can see through solid surfaces. In a development that could revolutionize the management of precious groundwater around the world, Stanford researchers have pioneered the use of satellites to accurately measure levels of water stored hundreds of feet below ground. Their findings were published recently in Water Resources Research.

Groundwater provides 25 to 40 percent of all drinking water worldwide, and is the primary source of freshwater in many arid countries, according to the National Groundwater Association. About 60 percent of all withdrawn groundwater goes to crop irrigation. In the United States, the number is closer to 70 percent. In much of the world, however, underground reservoirs or aquifers are poorly managed and rapidly depleted due to a lack of water-level data. Developing useful groundwater models, availability predictions and water budgets is very challenging.

Study co-author Rosemary Knight, a professor of geophysics and senior fellow, by courtesy, at the Stanford Woods Institute for the Environment, compared groundwater use to a mismanaged bank account: “It’s like me saying I’m going to retire and live off my savings without knowing how much is in the account.”

Lead author Jessica Reeves, a postdoctoral scholar in geophysics, extended Knight’s analogy to the connection among farmers who depend on the same groundwater source. “Imagine your account was connected to someone else’s account, and they were withdrawing from it without your knowing.”

Until now, the only way a water manager could gather data about the state of water tables in a watershed was to drill monitoring wells. The process is time and resource intensive, especially for confined aquifers, which are deep reservoirs separated from the ground surface by multiple layers of impermeable clay. Even with monitoring wells, good data is not guaranteed. Much of the data available from monitoring wells across the American West is old and of varying quality and scientific usefulness. Compounding the problem, not all well data is openly shared.

To solve these challenges, Reeves, Knight, Stanford Woods Institute-affiliated geophysics and electrical engineering Professor Howard Zebker, Stanford civil and environmental engineering Professor Peter Kitanidis and Willem Schreüder of Principia Mathematica Inc. looked to the sky.

The basic concept: Satellites that use electromagnetic waves to monitor changes in the elevation of Earth’s surface to within a millimeter could be mined for clues about groundwater. The technology, Interferometric Synthetic Aperture Radar (InSAR), had previously been used primarily to collect data on volcanoes, earthquakes and landslides.

With funding from NASA, the researchers used InSAR to make measurements at 15 locations in Colorado’s San Luis Valley, an important agricultural region and flyway for migrating birds. Based on observed changes in Earth’s surface, the scientists compiled water-level measurements for confined aquifers at three of the sampling locations that matched the data from nearby monitoring wells.

“If we can get this working in between wells, we can measure groundwater levels across vast areas without using lots of on-the-ground monitors,” Reeves said.

The breakthrough holds the potential for giving resource managers in Colorado and elsewhere valuable data as they build models to assess scenarios such as the effect on groundwater from population increases and droughts.

Just as computers and smartphones inevitably get faster, satellite data will only improve. That means more and better data for monitoring and managing groundwater. Eventually, InSAR data could play a vital role in measuring seasonal changes in groundwater supply and help determine levels for sustainable water use.

In the meantime, Knight envisions a Stanford-based, user-friendly online database that consolidates InSAR findings and a range of other current remote sensing data for soil moisture, precipitation and other components of a water budget. “Very few, if any, groundwater managers are tapping into any of the data,” Knight said. With Zebker, postdoctoral fellow Jingyi Chen and colleagues at the University of South Carolina, Knight recently submitted a grant proposal for this concept to NASA.

Studies show movements of continents speeding up after slow ‘middle age’

Two studies show that the movement rate of plates carrying the Earth’s crust may not be constant over time. This could provide a new explanation for the patterns observed in the speed of evolution and has implications for the interpretation of climate models. The work is presented today at Goldschmidt 2014, the premier geochemistry conference taking place in Sacramento, California, USA.

The Earth’s continental crust can be thought of as an archive of Earth’s history, containing information on rock formation, the atmosphere and the fossil record. However, it is not clear when and how regularly crust formed since the beginning of Earth history, 4.5 billion years ago.

Researchers led by Professor Peter Cawood, from the University of St. Andrews, UK, examined several measures of continental movement and geologic processes from a number of previous studies. They found that, from 1.7 to 0.75 billion years ago (termed Earth’s middle age), Earth appears to have been very stable in terms of its environment, with little in the way of crust building activity, no major fluctuations in atmospheric composition and few major developments seen in the fossil record. This contrasts markedly with the time periods either side of this, which contained major ice ages and changes in oxygen levels. Earth’s middle age also coincides with the formation of a supercontinent called Rodinia, which appears to have been stable throughout this time.

Professor Cawood suggests this stability may have been due to the gradual cooling of the earth’s crust over time. “Before 1.7 billion years ago, the Earth’s crust would have been substantially hotter, meaning that continental plate movement may have been governed by different rules to those that operate today,” said Professor Cawood. “0.75 billion years ago, the crust reached a point where it had cooled sufficiently to allow modern day plate tectonics to start working, in particular allowing subduction zones to form (where one plate of the crust moves under another). This increase in activity could have kick-started a myriad of changes including the break-up of Rodinia and changes to levels of key elements in the atmosphere and seas, which in turn may have induced evolutionary changes in the life forms present.”

This view is backed up by work from Professor Kent Condie from New Mexico Tech, USA, which suggests the movement rate of the Earth’s crust is not constant but may be speeding up over time. Professor Condie examined how supercontinents assemble and break up. “Our results challenge the view that the rate of plate movement is stable over time,” said Professor Condie. “The interpretation of data from many other disciplines such as stable isotope geochemistry, palaeontology and paleoclimatology in part rely on the assumption that the movement rate of the Earth’s crust is constant.”

Results from these fields may now need to be re-examined in light of Condie’s findings. “We now urgently need to collect further data on critical time periods to understand more about the constraints on plate speeds and the frequency of collision between continental blocks,” concluded Professor Condie.

New hi-tech approach to studying sedimentary basins

A radical new approach to analysing sedimentary basins also harnesses technology in a completely novel way. An international research group, led by the University of Sydney, will use big data sets and exponentially increased computing power to model the interaction between processes on the earth’s surface and deep below it in ‘five dimensions’.

As announced by the Federal Minister for Education today, the University’s School of Geosciences will lead the Basin GENESIS Hub that has received $5.4 million over five years from the Australian Research Council (ARC) and industry partners.

The multitude of resources found in sedimentary basins includes groundwater and energy resources. The space between grains of sand in these basins can also be used to store carbon dioxide.

“This research will be of fundamental importance to both the geo-software industry, used by exploration and mining companies, and to other areas of the energy industry,” said Professor Dietmar Müller, Director of the Hub, from the School of Geosciences.

“The outcomes will be especially important for identifying exploration targets in deep basins in remote regions of Australia. It will create a new ‘exploration geodynamics’ toolbox for industry to improve estimates of what resources might be found in individual basins.”

Sedimentary basins form when sediments eroded from highly elevated regions are transported through river systems and deposited into lowland regions and continental margins. The Sydney Basin is a massive basin filled mostly with river sediments that form Hawkesbury sandstone. It is invisible to the Sydney population living above it but has provided building material for many decades.

“Previously the approach to analysing these basins has been based on interpreting geological data and two-dimensional models. We apply infinitely more computing power to enhance our understanding of sedimentary basins as the product of the complex interplay between surface and deep Earth processes,” said Professor Müller.

Associate Professor Rey, a researcher at the School of Geosciences and member of the Hub said, “Our new approach is to understand the formation of sedimentary basins and the changes they undergo, both recently and over millions to hundreds of millions of years, using computer simulations to incorporate information such as the evolution of erosion, sedimentary processes and the deformation of the earth’s crust.”

The researchers will incorporate data from multiple sources to create ‘five-dimensional’ models, combining three-dimensional space with the extra dimensions of time and estimates of uncertainty.

The modelling will span scales from entire basins hundreds of kilometres wide to individual sediment grains.

Key geographical areas the research will focus on are the North-West shelf of Australia, Papua New Guinea and the Atlantic Ocean continental margins.

The Hub’s technology builds upon the exponential increase in computational power and the increasing amount of available big data (massive data sets of information). The Hub will harness the capacity of Australia’s most powerful computer, launched in 2013.

New evidence for oceans of water deep in the Earth

Researchers from Northwestern University and the University of New Mexico report evidence for potentially oceans worth of water deep beneath the United States. Though not in the familiar liquid form — the ingredients for water are bound up in rock deep in the Earth’s mantle — the discovery may represent the planet’s largest water reservoir.

The presence of liquid water on the surface is what makes our “blue planet” habitable, and scientists have long been trying to figure out just how much water may be cycling between Earth’s surface and interior reservoirs through plate tectonics.

Northwestern geophysicist Steve Jacobsen and University of New Mexico seismologist Brandon Schmandt have found deep pockets of magma located about 400 miles beneath North America, a likely signature of the presence of water at these depths. The discovery suggests water from the Earth’s surface can be driven to such great depths by plate tectonics, eventually causing partial melting of the rocks found deep in the mantle.

The findings, to be published June 13 in the journal Science, will aid scientists in understanding how the Earth formed, what its current composition and inner workings are and how much water is trapped in mantle rock.

“Geological processes on the Earth’s surface, such as earthquakes or erupting volcanoes, are an expression of what is going on inside the Earth, out of our sight,” said Jacobsen, a co-author of the paper. “I think we are finally seeing evidence for a whole-Earth water cycle, which may help explain the vast amount of liquid water on the surface of our habitable planet. Scientists have been looking for this missing deep water for decades.”

Scientists have long speculated that water is trapped in a rocky layer of the Earth’s mantle located between the lower mantle and upper mantle, at depths between 250 miles and 410 miles. Jacobsen and Schmandt are the first to provide direct evidence that there may be water in this area of the mantle, known as the “transition zone,” on a regional scale. The region extends across most of the interior of the United States.

Schmandt, an assistant professor of geophysics at the University of New Mexico, uses seismic waves from earthquakes to investigate the structure of the deep crust and mantle. Jacobsen, an associate professor of Earth and planetary sciences at Northwestern’s Weinberg College of Arts and Sciences, uses observations in the laboratory to make predictions about geophysical processes occurring far beyond our direct observation.

The study combined Jacobsen’s lab experiments in which he studies mantle rock under the simulated high pressures of 400 miles below the Earth’s surface with Schmandt’s observations using vast amounts of seismic data from the USArray, a dense network of more than 2,000 seismometers across the United States.

Jacobsen’s and Schmandt’s findings converged to produce evidence that melting may occur about 400 miles deep in the Earth. H2O stored in mantle rocks, such as those containing the mineral ringwoodite, likely is the key to the process, the researchers said.

“Melting of rock at this depth is remarkable because most melting in the mantle occurs much shallower, in the upper 50 miles,” said Schmandt, a co-author of the paper. “If there is a substantial amount of H2O in the transition zone, then some melting should take place in areas where there is flow into the lower mantle, and that is consistent with what we found.”

If just one percent of the weight of mantle rock located in the transition zone is H2O, that would be equivalent to nearly three times the amount of water in our oceans, the researchers said.

This water is not in a form familiar to us — it is not liquid, ice or vapor. This fourth form is water trapped inside the molecular structure of the minerals in the mantle rock. The weight of 250 miles of solid rock creates such high pressure, along with temperatures above 2,000 degrees Fahrenheit, that a water molecule splits to form a hydroxyl radical (OH), which can be bound into a mineral’s crystal structure.

Schmandt and Jacobsen’s findings build on a discovery reported in March in the journal Nature in which scientists discovered a piece of the mineral ringwoodite inside a diamond brought up from a depth of 400 miles by a volcano in Brazil. That tiny piece of ringwoodite — the only sample in existence from within the Earth — contained a surprising amount of water bound in solid form in the mineral.

“Whether or not this unique sample is representative of the Earth’s interior composition is not known, however,” Jacobsen said. “Now we have found evidence for extensive melting beneath North America at the same depths corresponding to the dehydration of ringwoodite, which is exactly what has been happening in my experiments.”

For years, Jacobsen has been synthesizing ringwoodite, colored sapphire-like blue, in his Northwestern lab by reacting the green mineral olivine with water at high-pressure conditions. (The Earth’s upper mantle is rich in olivine.) He found that more than one percent of the weight of the ringwoodite’s crystal structure can consist of water — roughly the same amount of water as was found in the sample reported in the Nature paper.

“The ringwoodite is like a sponge, soaking up water,” Jacobsen said. “There is something very special about the crystal structure of ringwoodite that allows it to attract hydrogen and trap water. This mineral can contain a lot of water under conditions of the deep mantle.”

For the study reported in Science, Jacobsen subjected his synthesized ringwoodite to conditions around 400 miles below the Earth’s surface and found it forms small amounts of partial melt when pushed to these conditions. He detected the melt in experiments conducted at the Advanced Photon Source of Argonne National Laboratory and at the National Synchrotron Light Source of Brookhaven National Laboratory.

Jacobsen uses small gem diamonds as hard anvils to compress minerals to deep-Earth conditions. “Because the diamond windows are transparent, we can look into the high-pressure device and watch reactions occurring at conditions of the deep mantle,” he said. “We used intense beams of X-rays, electrons and infrared light to study the chemical reactions taking place in the diamond cell.”

Jacobsen’s findings produced the same evidence of partial melt, or magma, that Schmandt detected beneath North America using seismic waves. Because the deep mantle is beyond the direct observation of scientists, they use seismic waves — sound waves at different speeds — to image the interior of the Earth.

“Seismic data from the USArray are giving us a clearer picture than ever before of the Earth’s internal structure beneath North America,” Schmandt said. “The melting we see appears to be driven by subduction — the downwelling of mantle material from the surface.”

The melting the researchers have detected is called dehydration melting. Rocks in the transition zone can hold a lot of H2O, but rocks in the top of the lower mantle can hold almost none. The water contained within ringwoodite in the transition zone is forced out when it goes deeper (into the lower mantle) and forms a higher-pressure mineral called silicate perovskite, which cannot absorb the water. This causes the rock at the boundary between the transition zone and lower mantle to partially melt.

“When a rock with a lot of H2O moves from the transition zone to the lower mantle it needs to get rid of the H2O somehow, so it melts a little bit,” Schmandt said. “This is called dehydration melting.”

“Once the water is released, much of it may become trapped there in the transition zone,” Jacobsen added.

Just a little bit of melt, about one percent, is detectible with the new array of seismometers aimed at this region of the mantle because the melt slows the speed of seismic waves, Schmandt said.

How Earth avoided global warming, last time around

Geochemists have calculated a huge rise in atmospheric CO2 was only avoided by the formation of a vast mountain range in the middle of the ancient supercontinent, Pangea. This work is being presented to the Goldschmidt geochemistry conference in Sacramento, California.

Around 300 million years ago, plate tectonics caused the continents to aggregate into a giant supercontinent, known as “Pangea”. The sheer size of the continent meant that much of the land surface was far from the sea, and so the continent became increasingly arid due to lack of humidity. This aridity meant that rock weathering was reduced; normally, a reduction in rock weathering means that CO2 levels rise, yet in spite of this CO2 levels – which had been falling prior to the mountain formation- continued to drop, eventually undergoing the most significant drop in atmospheric CO2 of the last 500 million years. This phenomenon has remained unexplained, until now.

Now a group of French scientists from the CNRS in Toulouse have produced a model which seems to explain this contradiction. The period coincides with the rise of a vast series of mountains in the interior of Pangea, the “Hercynian” mountains”. These mountains arose in a wide belt, running from what is now the Appalachians, through to Ireland, South-Western England, through Paris and the Alps into Germany, and on further East.

According to team leader, Dr Yves Godderis (CNRS, Toulouse, France):

“The formation of these mountains meant that the rock weathering, which was threatening to slow to a walk through much of the supercontinent, was able to continue. The steep slopes of these Hercynian mountains produced physical erosion. Occurring in a humid equatorial environment, this physical erosion promoted rock weathering and removing CO2 from the atmosphere”.

He continued, “We believe that it is this which led to the dramatic drop in atmospheric levels of CO2. We estimate that if it hadn’t been for the formation of the Hercynian mountains, the atmospheric CO2 levels would have reached around 25 times the pre-industrial level, meaning that CO2 levels would have reached around 7000 ppm (parts per million). Let me put that into a present-day context; the current atmospheric CO2 levels are around 400 ppm, so this means that we would have seen CO2 rise to a level around 17 times current levels. This would obviously have had severe effects on the environment of that time. But the formation of the mountains in fact contributed to the greatest fall in atmospheric CO2 in the last 500 million years”.

The team believes that even if the mountains had not formed and CO2 levels rose sharply, this would not have led to a runaway greenhouse effect as happened on Venus, because the increasing temperatures would have led to rocks being ultimately weathered, heat compensating for the scarcity of water. Rock weathering would have removed CO2 from the atmosphere, thus stopping the rising temperatures.

“So it would eventually have been self-correcting” said Dr Godderis, “but there’s no doubt that this would have stalled Earth’s temperature at a high level for a long, long time. The world would look very different today if these mountains had not developed when they did.

This is a new model which explains some of the events in the 80 million years following the start of the Carboniferous period, and of course the ideas need to be confirmed before we can be sure that the model is completely accurate. The take-home message is that the factors affecting atmospheric CO2 over geological periods of time are complex, and our understanding is still evolving”.

From today, the Earth is around 60 million years older — and so is the moon

Work presented today at the Goldschmidt Geochemistry Conference in Sacramento, California shows that the timing of the giant impact between Earth’s ancestor and a planet-sized body occurred around 40 million years after the start of solar system formation. This means that the final stage of Earth’s formation is around 60 million years older than previously thought.

Geochemists from the University of Lorraine in Nancy, France have discovered an isotopic signal which indicates that previous age estimates for both the Earth and the Moon are underestimates. Looking back into “deep time” it becomes more difficult to put a date on early Earth events. In part this is because there is little “classical geology” dating from the time of the formation of the Earth – no rock layers, etc. So geochemists have had to rely on other methods to estimate early Earth events. One of the standard methods is measuring the changes in the proportions of different gases (isotopes) which survive from the early Earth.

Guillaume Avice and Bernard Marty analysed xenon gas found in South African and Australian quartz, which had been dated to 3.4 and 2.7 billion years respectively. The gas sealed in this quartz is preserved as in a “time capsule”, allowing Avice and Marty to compare the current isotopic ratios of xenon, with those which existed billions of years ago. Recalibrating dating techniques using the ancient gas allowed them to refine the estimate of when the earth began to form. This allows them to calculate that the Moon-forming impact is around 60 million years (+/- 20 m. y.) older than had been thought.

Previously, the time of formation of the Earth’ s atmosphere had been estimated at around 100 million years after the solar system formation. As the atmosphere would not have survived the Moon-forming impact, this revision puts the age up to 40 million years after the solar sytem formation (so around 60 million years older than previously thought).

According to Guillaume Avice:

“It is not possible to give an exact date for the formation of the Earth*. What this work does is to show that the Earth is older than we thought, by around 60 m.

“The composition of the gases we are looking at changes according the conditions they are found in, which of course depend on the major events in Earth’s history. The gas sealed in these quartz samples has been handed down to us in a sort of “time capsule”. We are using standard methods to compute the age of the Earth, but having access to these ancient samples gives us new data, and allows us to refine the measurement”.

The xenon gas signals allow us to calculate when the atmosphere was being formed, which was probably at the time the Earth collided with a planet-sized body, leading to the formation of the Moon. Our results mean that both the Earth and the Moon are older than we had thought”.

Bernard Marty added

“This might seem a small difference, but it is important. These differences set time boundaries on how the planets evolved, especially through the major collisions in deep time which shaped the solar system”

Geologists confirm oxygen levels of ancient oceans

Assistant Professor Zunli Lu co-authored the study. -  Syracuse University News Services
Assistant Professor Zunli Lu co-authored the study. – Syracuse University News Services

Geologists in the College of Arts and Sciences have discovered a new way to study oxygen levels in the Earth’s oldest oceans.

Zunli Lu and Xiaoli Zhou, an assistant professor and Ph.D. student, respectively, in the Department of Earth Sciences, are part of an international team of researchers whose findings have been published by the journal Geology (Geological Society of America, 2014). Their research approach may have important implications for the study of marine ecology and global warming.

“More than 2.5 billion years ago, there was little to no oxygen in the oceans, as methane shrouded the Earth in a haze,” says Lu, a member of Syracuse University’s Low-Temperature Geochemistry Research Group. “Organisms practicing photosynthesis eventually started to overpower reducing chemical compounds [i.e., electron donors], and oxygen began building up in the atmosphere. This period has been called the Great Oxidation Event.”

Using a novel approach called iodine geochemistry, Lu, Zhou and their colleagues have confirmed the earliest appearance of dissolved oxygen in the ocean’s surface waters.

Central to their approach is iodate, a form of iodine that exists only in oxygenated waters. When iodate is detected in carbonate rocks in a marine setting, Lu and company are able to measure the elemental ratio of iodine to calcium. This measurement, known as a proxy for ocean chemistry, helps them figure out how much oxygen has dissolved in the water.

“Iodine geochemistry enables us to constrain oxygen levels in oceans that have produced calcium carbonate minerals and fossils,” says Lu, who developed the proxy. “What we’ve found in ancient rock reinforces the proxy’s reliability. Already, we’re using the proxy to better understand the consequences of ocean deoxygenation, due to rapid global warming.”

Researchers find major West Antarctic glacier melting from geothermal sources

Thwaites Glacier, the large, rapidly changing outlet of the West Antarctic Ice Sheet, is not only being eroded by the ocean, it’s being melted from below by geothermal heat, researchers at the Institute for Geophysics at The University of Texas at Austin (UTIG) report in the current edition of the Proceedings of the National Academy of Sciences.

The findings significantly change the understanding of conditions beneath the West Antarctic Ice Sheet where accurate information has previously been unobtainable.

The Thwaites Glacier has been the focus of considerable attention in recent weeks as other groups of researchers found the glacier is on the way to collapse, but more data and computer modeling are needed to determine when the collapse will begin in earnest and at what rate the sea level will increase as it proceeds. The new observations by UTIG will greatly inform these ice sheet modeling efforts.

Using radar techniques to map how water flows under ice sheets, UTIG researchers were able to estimate ice melting rates and thus identify significant sources of geothermal heat under Thwaites Glacier. They found these sources are distributed over a wider area and are much hotter than previously assumed.

The geothermal heat contributed significantly to melting of the underside of the glacier, and it might be a key factor in allowing the ice sheet to slide, affecting the ice sheet’s stability and its contribution to future sea level rise.

The cause of the variable distribution of heat beneath the glacier is thought to be the movement of magma and associated volcanic activity arising from the rifting of the Earth’s crust beneath the West Antarctic Ice Sheet.

Knowledge of the heat distribution beneath Thwaites Glacier is crucial information that enables ice sheet modelers to more accurately predict the response of the glacier to the presence of a warming ocean.

Until now, scientists had been unable to measure the strength or location of heat flow under the glacier. Current ice sheet models have assumed that heat flow under the glacier is uniform like a pancake griddle with even heat distribution across the bottom of the ice.

The findings of lead author Dusty Schroeder and his colleagues show that the glacier sits on something more like a multi-burner stovetop with burners putting out heat at different levels at different locations.

“It’s the most complex thermal environment you might imagine,” said co-author Don Blankenship, a senior research scientist at UTIG and Schroeder’s Ph.D. adviser. “And then you plop the most critical dynamically unstable ice sheet on planet Earth in the middle of this thing, and then you try to model it. It’s virtually impossible.”

That’s why, he said, getting a handle on the distribution of geothermal heat flow under the ice sheet has been considered essential for understanding it.

Gathering knowledge about Thwaites Glacier is crucial to understanding what might happen to the West Antarctic Ice Sheet. An outlet glacier the size of Florida in the Amundsen Sea Embayment, it is up to 4,000 meters thick and is considered a key question mark in making projections of global sea level rise.

The glacier is retreating in the face of the warming ocean and is thought to be unstable because its interior lies more than two kilometers below sea level while, at the coast, the bottom of the glacier is quite shallow.

Because its interior connects to the vast portion of the West Antarctic Ice Sheet that lies deeply below sea level, the glacier is considered a gateway to the majority of West Antarctica’s potential sea level contribution.

The collapse of the Thwaites Glacier would cause an increase of global sea level of between 1 and 2 meters, with the potential for more than twice that from the entire West Antarctic Ice Sheet.

The UTIG researchers had previously used ice-penetrating airborne radar sounding data to image two vast interacting subglacial water systems under Thwaites Glacier. The results from this earlier work on water systems (also published in the Proceedings of the National Academy of Sciences) formed the foundation for the new work, which used the distribution of water beneath the glacier to determine the levels and locations of heat flow.

In each case, Schroeder, who received his Ph.D. in May, used techniques he had developed to pull information out of data collected by the radar developed at UTIG.

According to his findings, the minimum average geothermal heat flow beneath Thwaites Glacier is about 100 milliwatts per square meter, with hotspots over 200 milliwatts per square meter. For comparison, the average heat flow of the Earth’s continents is less than 65 milliwatts per square meter.

The presence of water and heat present researchers with significant challenges.

“The combination of variable subglacial geothermal heat flow and the interacting subglacial water system could threaten the stability of Thwaites Glacier in ways that we never before imagined,” Schroeder said.