Speed matters for ice-shelf breaking

It won’t help the Titanic, but a newly derived, simple law may help scientists improve their climate models and glaciologists predict where icebergs will calve off from their parent ice sheets, according to a team of Penn State researchers.

“To predict the future of the ice sheet and to understand the past, we have to put the information into a computer,” says Richard B. Alley, the Evan Pugh professor of geosciences. “The models we have do not currently have any way to figure out where the big ice sheets end and where the ice calves off to form icebergs.”

Ice sheets, such as those in Antarctica and Greenland, spread under their own weight and flow off land over the oceans. The Ross Ice Shelf in Antarctica floats for as much as 500 miles over the ocean before the edges begin to break and create icebergs. Other ice shelves only edge over the water for a mile or two.

“The problem of when things break is a really hard problem because there is so much variability,” says Alley. “Anyone who has dropped a coffee cup knows this. Sometimes the coffee cup breaks and sometimes it bounces.”

The coffee cup’s breaking depends on what it hits and where it hits, but the most important variable is the distance the cup falls or is thrown. Below a certain distance, the cup will always remain intact, while above a certain distance, it will always break; for in-between distances, the results are variable.

For iceberg calving, the important variable – the one that accounts for the largest portion of when the iceberg breaks — is the rate at which ice shelves spread, the team reports in today’s (Nov. 28) issue of Science. When ice shelves spread, they crack because of the stresses of spreading. If they spread slowly, those cracks do not propagate through the entire shelf and the shelf remains intact. If the shelf spreads rapidly, the cracks propagate through the shelf and pieces break off.

“Spreading explains most of what is observed on the ice sheet,” says Alley. “However, the equations come out a little better if we include a few other things.”

These factors are the width of the ice shelf and the thickness. With a narrow shelf between two ridges, for example, the sides hold back the ice movement, slowing the overall movement and making it harder to break the ice. Thicker ice shelves spread more quickly so this affects the location of ice calving as well.

The basic equation for ice calving is the rate of spreading times the width of the shelf times the thickness times a constant. The researchers realize that this does not capture the totality of variation in the ice calving process but does account for a large percentage of the variability.

Plate tectonics started over 4 billion years ago, geochemists report

A new picture of the early Earth is emerging, including the surprising finding that plate tectonics may have started more than 4 billion years ago – much earlier than scientists had believed, according to new research by UCLA geochemists reported Nov. 27 in the journal Nature.

“We are proposing that there was plate-tectonic activity in the first 500 million years of Earth’s history,” said geochemistry professor Mark Harrison, director of UCLA’s Institute of Geophysics and Planetary Physics and co-author of the Nature paper. “We are reporting the first evidence of this phenomenon.”

“Unlike the longstanding myth of a hellish, dry, desolate early Earth with no continents, it looks like as soon as the Earth formed, it fell into the same dynamic regime that continues today,” Harrison said. “Plate tectonics was inevitable, life was inevitable. In the early Earth, there appear to have been oceans; there could have been life – completely contradictory to the cartoonish story we had been telling ourselves.”

“We’re revealing a new picture of what the early Earth might have looked like,” said lead author Michelle Hopkins, a UCLA graduate student in Earth and space sciences. “In high school, we are taught to see the Earth as a red, hellish, molten-lava Earth. Now we’re seeing a new picture, more like today, with continents, water, blue sky, blue ocean, much earlier than we thought.”

The Earth is 4.5 billion years old. Some scientists think plate tectonics – the geological phenomenon involving the movement of huge crustal plates that make up the Earth’s surface over the planet’s molten interior – started 3.5 billion years ago, others that it began even more recently than that.

The research by Harrison, Hopkins and Craig Manning, a UCLA professor of geology and geochemistry, is based on their analysis of ancient mineral grains known as zircons found inside molten rocks, or magmas, from Western Australia that are about 3 billion years old. Zircons are heavy, durable minerals related to the synthetic cubic zirconium used for imitation diamonds and costume jewelry. The zircons studied in the Australian rocks are about twice the thickness of a human hair.

Hopkins analyzed the zircons with UCLA’s high-resolution ion microprobe, an instrument that enables scientists to date and learn the exact composition of samples with enormous precision. The microprobe shoots a beam of ions, or charged atoms, at a sample, releasing from the sample its own ions, which are then analyzed in a mass spectrometer. Scientists can aim the beam of ions at specific microscopic areas of a sample and conduct a high-resolution isotope analysis of them without destroying the object.

“The microprobe is the perfect tool for determining the age of the zircons,” Harrison said.

The analysis determined that some of the zircons found in the magmas were more than 4 billion years old. They were also found to have been formed in a region with heat flow far lower than the global average at that time.

“The global average heat flow in the Earth’s first 500 million years was thought to be about 200 to 300 milliwatts per meter squared,” Hopkins said. “Our zircons are indicating a heat flow of just 75 milliwatts per meter squared – the figure one would expect to find in subduction zones, where two plates converge, with one moving underneath the other.”

“The data we are reporting are from zircons from between 4 billion and 4.2 billion years ago,” Harrison said. “The evidence is indirect, but strong. We have assessed dozens of scenarios trying to imagine how to create magmas in a heat flow as low as we have found without plate tectonics, and nothing works; none of them explain the chemistry of the inclusions or the low melting temperature of the granites.”

Evidence for water on Earth during the planet’s first 500 million years is now overwhelming, according to Harrison.

“You don’t have plate tectonics on a dry planet,” he said.

Strong evidence for liquid water at or near the Earth’s surface 4.3 billion years ago was presented by Harrison and colleagues in a Jan. 11, 2001, cover story in Nature.

“Five different lines of evidence now support that once radical hypothesis,” Harrison said. “The inclusions we found tell us the zircons grew in water-saturated magmas. We now observe a surprisingly low geothermal gradient, a low rate at which temperature increases in the Earth. The only mechanism that we recognize that is consistent with everything we see is that the formation of these zircons was at a plate-tectonic boundary. In addition, the chemistry of the inclusions in the zircons is characteristic of the two kinds of magmas today that we see at place-tectonic boundaries.”

“We developed the view that plate tectonics was impossible in the early Earth,” Harrison added. “We have now made observations from the Hadean (the Earth’s earliest geological eon) – these little grains contain a record about the conditions under which they formed – and the zircons are telling us that they formed in a region with anomalously low heat flow. Where in the modern Earth do you have heat flow that is one-third of the global average, which is what we found in the zircons? There is only one place where you have heat flow that low in which magmas are forming: convergent plate-tectonic boundaries.”

Three years ago, Harrison and his colleagues applied a technique to determine the temperature of ancient zircons.

“We discovered the temperature at which these zircons formed was constant and very low,” Harrison said. “You can’t make a magma at any lower temperature than what we’re seeing in these zircons. You look at artists’ conceptions of the early Earth, with flying objects from outer space making large craters; that should make zircons hundreds of degrees centigrade hotter than the ones we see. The only way you can make zircons at the low temperature we see is if the melt is water-saturated. There had to be abundant water. That’s a big surprise because our longstanding conception of the early Earth is that it was dry.”

Getting warmer? Prehistoric climate can help forecast future changes

The first comprehensive reconstruction of an extreme warm period shows the sensitivity of the climate system to changes in carbon dioxide (CO2) levels as well as the strong influence of ocean temperatures, heat transport from equatorial regions, and greenhouse gases on Earth’s temperature.

New data allow for more accurate predictions of future climate and improved understanding of today’s warming. Past warm periods provide real data on climate change and are natural laboratories for understanding the global climate system.

Scientists examined fossils from 3.3 to 3.0 million years ago, known as the mid-Pliocene warm period. Research was conducted by the Pliocene Research, Interpretation and Synoptic Mapping (PRISM) group, led by the U.S. Geological Survey.

“PRISM’s research provides objective, unbiased data for climate modelers to better understand the environment in which we live and for decision makers to make informed adaptation and mitigation strategies that yield the greatest benefits to society and the environment,” said Senior Advisor to USGS Global Change Programs Thomas Armstrong. “This is the most comprehensive global reconstruction for any warm period and emphasizes the importance of examining the past state of Earth’s climate system to understand the future.”

The mid-Pliocene experienced the most extreme warming over the past 3.3 million years. Global average temperatures were 2.5ฐC (4.5ฐF) greater than today and within the range projected for the 21st century by the Intergovernmental Panel on Climate Change.

“Exploring the mid-Pliocene will further understanding on the role of ocean circulation in a warming world, the impacts of altered storm tracks, polar versus tropical sensitivity, and the impacts of altered atmospheric CO2 and oceanic energy transport systems,” said USGS scientist Harry Dowsett, also lead scientist for PRISM. “We used fossils dated to the mid-Pliocene to reconstruct sea surface and deepwater ocean temperatures, and will continue research by studying specific geographic areas, vegetation, sea ice extent and other environmental characteristics during the Pliocene.”

Since CO2 levels during the mid-Pliocene were only slightly higher than today’s levels, PRISM research suggests that a slight increase in our current CO2 level could have a large impact on temperature change. Research also shows warming of as much as 18ฐC, bringing temperatures from -2ฐC to 16ฐC, in the high latitudes of the North Atlantic and Arctic Oceans during the mid-Pliocene. Warming in the Pacific, similar to a present day El Ni๑o, was a characteristic of the mid-Pliocene. Global sea surface and deep water temperatures were found to be warmer than those of today, impacting the ocean’s circulation system and climate. Data suggest the likely cause of mid-Pliocene warmth was a combination of several factors, including increased heat transport from equatorial regions to the poles and increased greenhouse gases.

PRISM has been chosen by the Pliocene Model Intercomparison Project of Paleoclimate Modelling Intercomparison Project Phase II as the dataset against which to run and test the performance of climate models for the Pliocene.

Sea level rise alters bay’s salinity

 This is a map of the Chesapeake Bay estuary. – NOAA

While global-warming-induced coastal flooding moves populations inland, the changes in sea level will affect the salinity of estuaries, which influences aquatic life, fishing and recreation.

Researchers from Penn State and the University of Maryland Center for Environmental Science are studying the Chesapeake Bay to see how changes in sea level may have affected the salinity of various parts of the estuary.

“Many have hypothesized that sea-level rise will lead to an increase in estuarine salinity, but the hypothesis has never been evaluated using observations or 3-D models of estuarine flow and salinity,” says Timothy W. Hilton, graduate student in meteorology at Penn State.

“The Chesapeake is very large, the largest estuary in the U.S. and it is very productive,” says Raymond Najjar, associate professor of meteorology. “It has been the site of many large fisheries and supported many fishermen. A lot of money has gone into cleaning up the bay and reducing nutrient and sediment inputs. Climate change might make this work easier, or it could make it harder

The Chesapeake is naturally saltier near its mouth and fresher near the inflow of rivers. The researchers, who also included Ming Li and Liejun. Zhong of the University of Maryland Center for Environmental Science, studied the Chesapeake Bay, using two complementary approaches, one based on a statistical analysis of historical data and one based on a computer model of the bay’s flow and salinity.

They looked at historical data for the Susquehanna River as it flows into the Chesapeake Bay from 1949 to 2006. The flow of this fresh water into the bay naturally changes salinity. After accounting for the change in salinity due to rivers, the researchers found an increasing trend in salinity. The researchers reported their results in a recent edition of Journal of Geophysical Research.

The team then ran a hydrodynamic model of the Bay using present-day and reduced sea level conditions. The salinity change they found was consistent with the trend determined from the statistical analysis, supporting the hypothesis that sea-level rise has significantly increased salinity in the Bay. However, the Penn State researchers note that historical salinity data is limited and sedimentation reshapes the bed of the Bay. There are also cyclical effects partially due to Potomac River flow, Atlantic Shelf salinity and winds.

“Salt content affects jelly fish, oysters, sea grasses and many other forms of aquatic life,” says Hilton. “The Chesapeake Bay is a beautiful place, used for recreation and for people’s livelihoods. It is a real jewel on the East Coast and changes in salinity can alter its uses. Our research improves our understanding of the influence of climate change on the Bay and can therefore be used to improve costly restoration strategies.

Can China’s future earthquakes be predicted?

Ji ShaoCheng of the Universit้ de Montr้al’s affiliated engineering school ษcole Polytechnique is part of a team studying last May’s devastating earthquake in China.

On May 12, 2008, at 2:28 p.m., China’s Szechwan province changed forever. In the space of 90 seconds, an earthquake equivalent to 1,200 H-bombs pulverized the earth’s crust for more than 280 kilometers. Entire cities disappeared and eight million homes were swallowed up. This resulted in 70,000 deaths and 20,000 missing.

Two months later, ShaoCheng arrived in Szechwan province to study the damage first hand. The extent of the damage was unimaginable: roads and bridges collapsed, schools turned into rubble, and bodies of men and women everywhere.

According to ShaoCheng this tragedy could have been avoided. “There hasn’t been on earthquake in Szechwan province for 300 years. Chinese authorities thought the fault was dead,” he says.

The problem is that China relied on GPS data, which showed movements of 2 mm per year in certain areas when in reality the shifts were much bigger. “GPS is high-tech, but do we really know how to interpret its data?,” he questions.

ShaoCheng was recruited by one of his ex-colleagues with whom he completed his PhD in Montpellier and who now works for the Chinese Academy of Geological Sciences. His mission is to dig three narrow wells, 3-kilometers deep, into the earth’s crust for a whopping \$75 million.

“The drilling will allow us to see the characteristics of the rocks before and after the earthquake. We will also measure their thermal properties and fluid pressure,” says ShaoCheng. “One of these wells will have a seismometer and another will be equipped with a device similar to a stethoscope designed to listen to the earth’s heartbeat.”

It is expected to take five years of hard labour to rebuild the devastated region.

Missing radioactivity in ice cores bodes ill for part of Asia

 Naimona’nyi’s frozen ice cap lacks critical radioactive signal, based on the latest study by Ohio State University researchers. This could foretell drastic water shortages for people living in the Indian sub-continent. – Photo courtesy ©Thomas Nash 2007

When Ohio State glaciologists failed to find the expected radioactive signals in the latest core they drilled from a Himalayan ice field, they knew it meant trouble for their research.

But those missing markers of radiation, remnants from atomic bomb tests a half-century ago, foretell much greater threat to the half-billion or more people living downstream of that vast mountain range.

It may mean that future water supplies could fall far short of what’s needed to keep that population alive.

In a paper just published in Geophysical Research Letters, researchers from the Byrd Polar Research Center explain that levels of tritium, beta radioactivity emitters like strontium and cesium, and an isotope of chlorine are absent in all three cores taken from the Naimona’nyi glacier 19,849 feet (6,050 meters) high on the southern margin of the Tibetan Plateau.

“We’ve drilled 13 cores over the years from these high-mountain regions and found these signals in all but one – this one,” explained Lonnie Thompson, University Distinguished Professor of Earth Sciences at Ohio State.

The absence of radioactive signals in the top portion of these cores is a critical problem for determining the age of the ice in the cores. The signals, remnants of the 1962-63 Soviet Arctic nuclear blasts and the 1952-58 nuclear tests in the South Pacific, provide well-dated benchmarks to calibrate the core time scales.

“We rely on these time markers to date the upper part of the ice cores and without them, extracting the climate history they preserve becomes more challenging,” Thompson said.

“We drilled three cores through the ice to bedrock at Naimona’nyi in 2006,” said Natalie Kehrwald, a doctoral student at Ohio State and lead author on the paper. “When we analyzed the top 50 feet (15 meters) of each core, we found that the beta radioactivity signal was barely above normal background levels.”

Tritium, an isotope of hydrogen, and chlorine-36 were also both absent from the Naimona’nyi cores, she said. They were able, however, to find a small amount of a lead isotope, lead-210, which allowed them to date the top of the core.

“We were able to get a date of approximately 1944 A.D.,” Kehrwald said, “and that, coupled with the other missing signals, means that no new ice has accumulated on the surface of the glacier since 1944,” nearly a decade before the atomic tests.

While the loss of the radioactive horizons to calibrate the cores poses a challenge for Thompson’s research, he worries more about the possibility that other high-altitude glaciers in the region, like Naimona’nyi, are no longer accumulating ice and the impact that could have on water resources for the people living in these regions.

“When you think about the millions of people over there who depend on the water locked in that ice, if they don’t have it available in the future, that will be a serious problem,” he said.

Seasonal runoff from glaciers like Naimona’nyi feeds the Indus, the Ganges and the Brahmaputra rivers in that part of the Asian subcontinent. In some places, for some months each year, those rivers are severely depleted now, the researchers said. The absence of new ice accumulating on the glaciers will only worsen that problem.

“The current models that predict river flow in the region have taken recent glacial ‘retreat’ into account,” said Kehrwald, “but they haven’t considered that some of these glaciers are actually thinning until now.

“If the thinning isn’t included, then whatever strategies people adopt in their efforts to adapt to reductions in river flow simply won’t work.”

Thompson fears that what’s happening to the Naimona’nyi glacier may be happening to many other high-altitude glaciers around the world. “I think that this has tremendous implications for future water supplies in the Andes, as well as the Himalayas, and for people living in those regions.”

The absence of the radioactive signals in the 2006 Naimona’nyi core also suggests that Thompson and his colleagues have been lucky with their previous expeditions to other ice fields.

“We have to wonder — if we were to go back to previous drill sites, some drilled in the 1980s, and retrieved new cores — would these radioactive signals be present today?” he asked.

“My guess is that they would be missing.” The researchers’ recent work has shown similar thinning on glaciers in Africa, South America and in Asia in the past few years.

Forests may play overlooked role in regulating climate

In a study to be published next week in the Proceedings of the National Academy of Sciences, scientists led by a team at the University of New Hampshire show that forests may influence the Earth’s climate in important ways that have not previously been recognized.

When sunlight reaches the Earth’s surface it can either be absorbed and converted to heat or reflected back to outer space, where it doesn’t influence the Earth’s temperature. Scott Ollinger, a professor at the UNH Institute for the Study of Earth, Oceans, and Space and the department of Natural Resources and the Environment, and colleagues have discovered that, of the total amount of sunlight that falls on forests, the fraction that gets reflected back to space is directly related to levels of nitrogen in their foliage.

While scientists have long known that nitrogen-rich foliage is more efficient at pulling carbon dioxide out of the atmosphere, this new discovery suggests that nitrogen plays an important additional role in the Earth’s climate system that has never before been considered. Specifically, trees with high levels of foliar nitrogen have a two-fold effect on climate by simultaneously absorbing more CO2 and reflecting more solar radiation than their low-nitrogen counterparts.

Ollinger and UNH colleagues Andrew Richardson, Mary Martin, Dave Hollinger, Steve Frolking, and others, stumbled upon the discovery while poring over six years worth of data they collected from research sites across North America. The study involved a novel combination of NASA satellite- and aircraft-based instruments, along with meteorological towers from the AmeriFlux network and leaf-level measurements to analyze various aspects of forest canopies. When Ollinger noticed that the overall reflectivity of forest canopies (also known as albedo) rose and fell in conjunction with leaf nitrogen, he had a eureka moment.

“Bits and pieces of evidence for this have been around for years but nobody put them together before because it’s a question we hadn’t even thought to ask,” Ollinger says. “Scientists have long been aware of the importance of albedo, but no one suspected that the albedo of forests might be influenced by nitrogen. And because most of the effect is in the infra-red region of the sun’s spectrum, beyond that which human eyes can detect, the pattern isn’t immediately obvious.”

The newly discovered link between foliar nitrogen and canopy albedo adds an interesting new twist to the understanding of the climate system and raises intriguing questions about the underlying nature of ecosystem-climate interactions.

Changes in climate, air pollution, land use, and species composition can all influence nitrogen levels in foliage, and all of these may be part of a climate feedback mechanism that climate models have not yet examined. Future research planned by the team will involve examining the underlying causes for why the relationship exists and working with climate modelers to determine how the nitrogen-albedo mechanism will influence predictions of climate change.

Glacial erosion changes internal mountain structure, responses to plate tectonics

 A network of these devises was deployed as part of the STEEP program in order to record, characterize, and locate the numerous earthquakes related to the St. Elias orogen each year. – Photograph taken by Aaron L. Berger in 2006

Intense glacial erosion has not only carved the surface of the highest coastal mountain range on earth, the spectacular St. Elias range in Alaska, but has elicited a structural response from deep within the mountain.

This interpretation of structural response is based on real-world data now being reported, which supports decades of model simulations of mountain formation and evolution regarding the impact of climate on the distribution of deformation associated with plate tectonics.

A team of researchers from seven universities report the results of their field studies, on the structural response of the St. Elias range to glacial erosion, in Nature Geosciences*. The paper was a partnership of Aaron L. Berger, whose Ph.D. research it encompassed, his major professor, James A. Spotila, both with the Virginia Tech geosciences department; Sean P.S. Gulick of the Institute for Geophysics, Jackson School of Geosciences, at the University of Texas at Austin; and other colleagues. Berger and Spotila headed the land-based erosion research team. Gulick headed the ocean-based seismic reflection and sedimentation research team. The project is part of the National Science Foundation-funded St. Elias Erosion-Tectonics Project (STEEP), lead by Terry L. Pavlis of the University of Texas, El Paso.

The St. Elias range is a result of 10 million years of the North American plate pushing material up as it overrides the Pacific plate, then the material being worn down by glaciers. A dramatic cooling across the earth about three million years ago resulted in the onset of widespread glaciation. A million years ago, glacial conditions became more intense and glaciers grew larger over longer periods, and transitioned into more erosive ice streams that changed the shape and evolution of the mountains. The process continues today, resulting in the particularly active and dramatic St. Elias “orogen” – geologists’ word for mountains that grow from collision of tectonic plates.

“The collisions of tectonic plates over millions of years leave a record in the sediments, but it is a history that is difficult to extract. The signals of the impact of climate are even more difficult to track. Which is why scientists have used mathematical models,” said Spotila.

Models create a simplified numeric version of an orogen. Then scientists can change variables in the mathematical formula to determine what happens as a result of climate – whether rain or glaciers. “Models are important in that they showed us that climate change can effect mountain growth,” Spotila said. “And the St. Elias orogen behaves very differently than ones that are at lower latitudes and receive most of their precipitation as rain,” he said.

Armed with the insight of the models, Spotila, his Virginia Tech students, and colleagues at other universities have braved the mountain over many years to collect physical evidence. They have been dropped in remote and dangerous locations by helicopter to place instruments and collect samples to determine bedrock cooling rates and sedimentation.

“But our data set wouldn’t have shown the complete picture,” said Spotila. “We looked at the erosion history onshore and Gulick’s team looked at the record off shore – the shelf where the eroded sediment rest.”

Offshore seismic and borehole data indicate that the increase in offshore sedimentation corresponds to a one-million-year ago change in glaciation and deformation.

How does a change of the mountain surface result in a change of its internal structure? Spotila explained, “If you push snow with a plow, it will always pile up in front of the plow with the same shape,” called the Coulomb wedge when applied to the making of mountains. As the North America plate slips over the Pacific plate, it piles up material for the St Elias orogen with a short side toward the plow inland and a long slope down to the ocean, with the toe dipping into the sea.

Enter the glacier. As glacial conditions took hold across the St. Elias orogen, the landscape began to be defined by glacial landforms left on its surface. However, the more extreme glacial cycles, and associated increased erosion, of the last million years pushed the orogen to a tipping point, beyond which the orogen was forced to totally restructure itself, Berger said. There are deformation zones where as much as half of the wedge was removed, the researchers report in the journal article.

Due the onset of accelerated glacial erosion, the St. Elias orogen struggled to maintain its wedge shape. “Rock faulting and folding has become more intense as the orogen internally deforms to adjust to the intensified erosion,” said Spotila. “The flux of rock from the mountains to the sea is increasing dramatically.”

Berger uses an analogy of a bulldozer pushing sand across the ground. “As the glaciers erode the top of the mountains (the top of the pile of sand), the orogen – or entire body of sand, begins readjusting itself internally to maintain its wedge-shape. If you could remove the glaciers and watch the process, the flank of the mountain range where the largest glaciers are located would begin to get planed away by erosion, reducing mean elevation. The removal of this rock would change the local tectonic stress fields, resulting in focused deformation, which would begin to push the mountains back up to replace the eroded material.”.

The research showed how a change in climate led to a change in the way the motion of tectonic plates is accommodated by structural deformation within the orogen, Spotila said. “The wedge is still present but has narrowed with the eroded material deposited across the toe. Some faults, which previously responded to the push of the plow or tectonic plate, are relocated to respond to the erosion.”

Spotila concludes, “It is remarkable that climate and weather and the atmosphere can have such a profound impact on tectonics and the behavior of the solid earth.”

Acid soils in Slovakia tell somber tale

Increasing levels of nitrogen deposition associated with industry and agriculture can drive soils toward a toxic level of acidification, reducing plant growth and polluting surface waters, according to a new study published online in Nature Geoscience.

The study, conducted in the Tatra Mountains of Slovakia by the University of Colorado, University of Montana, Slovak Academy of Sciences, and the U.S. Geological Survey, shows what can happen when nitrogen deposition in any part of the world increases to certain levels – levels similar to those projected to occur in parts of Europe by 2050, according to some global change models.

On the basis of these results, the authors warn that the high levels of nitrogen deposited in Europe and North America over the past half century already may have left many soils susceptible to this new stage of acidification. The results of this further acidification, wrote the authors, are highly reduced soil fertility and leaching of acids and toxic metals into surface waters.

A long history of human-influenced nitrogen deposition has left soils in the Western Tatra Mountains of Slovakia highly acidic. The study reveals that the increased nitrogen load in the region triggers the release of soluble iron into alpine grassland soils. This iron release is indicative of extreme soil acidification, comparable to conditions seen in soils exposed to acid mine drainage.

“Recovery from such extreme chemical change could only occur in geologic time, which is why soil is considered a non-renewable resource,” said USGS scientist Jill Baron, who helped analyze and interpret the study results.

In addition to this research, Dr. Baron has investigated the impacts of nitrogen deposition in Rocky Mountain National Park for 26 years. “The Rocky Mountains and the Tatra Mountains represent the two ends of the atmospheric deposition effects trajectory,” Dr. Baron said. “The effects of nitrogen deposition in Rocky Mountain National Park are just beginning to be observed, allowing resource managers the opportunity to help the region recover if deposition is reduced. In the Tatra Mountains National Park, however, soils are far beyond natural recovery in human time frames.”

Much of the eastern U.S. and Northern Europe fall in the middle of the effects spectrum, she added.

Rocky Mountain and Tatra National Parks are sister parks, with scientists and managers beginning to cooperate in studies to understand both. Dr. Baron’s work in Rocky Mountain National Park led to the establishment of a nitrogen threshold for the park in 2006, the first time the nation has established a critical load of a pollutant for any park environment. An agreement in 2007 between the Environmental Protection Agency, National Park Service, and Colorado Department of Health and Environment enabled the agencies to set target loads for reducing nitrogen emissions by 2012 to improve ecological conditions.

Measuring water from space

Observations from satellites now allow scientists to monitor changes to water levels in the sea, in rivers and lakes, in ice sheets and even under the ground. As the climate changes, this information will be crucial for monitoring its effects and predicting future impacts in different regions.

Sea level rise in one of the major consequences of global warming, but it is much more difficult to model and predict than temperature. It involves the oceans and their interaction with the atmosphere, the ice sheets, the land waters and even the solid Earth, which modifies the shapes of ocean basins. Measurements from tidal gauges show that for most of the twentieth century, sea levels rose by 1.8 mm per year on average.

Since the 1990s, a number of altimeter satellites have been measuring the height of the ocean surface and this has dramatically improved our understanding of sea level rise. Currently, three altimeter satellites cover the entire globe every 10 to 35 days, and can measure the height of the sea surface to a precision of 1 to 2 cm.

These measurements show that since the start of 1993, sea level has been rising by 3.3 mm a year, almost double the rate of the previous 50 years. “It could be that we are seeing a decadal fluctuation, and in the near future the rate will fall again,” says Anny Cazenave, from the Laboratoire d’Etudes en Géophysique et Océanographie Spatiale (LEGOS) in Toulouse, “but I do not think so. For several years now, the rate of rise has not changed significantly.”

Melting ice fills the sea

Cazenave’s team, and other groups, calculate that for 1993-2003, about half of the sea level rise was due to the oceans expanding as they became warmer, and the other half was due to shrinking land ice. Since 2003, ocean warming has had a temporary break but sea level has continued to rise. Now, about 80% of the annual sea level rise can be attributed to accelerated land ice loss from glaciers, Greenland and Antarctica. This has been revealed by a brand new satellite technique, called space gravimetry.

The GRACE mission comprises two satellites, launched in 2002, which measure how the Earth’s gravity field varies with time. The gravity field depends on how mass is distributed on Earth, and affects the speed of satellites in orbit. By closely monitoring the speed of both satellites, as they orbit the planet, it is possible to measure the change in mass of water or ice in different regions.

The method has shown that the Greenland ice sheet is losing about 150 gigatonnes of ice each year, two thirds of which is large chunks of ice flowing rapidly into the sea. The combined effect of ice loss from Greenland and West Antarctica has contributed about 1 mm per year to the rising seas over the past five years

Rivers run low

Using GRACE, Cazenave and others have also looked at changes in water storage in river basins. In the period from 2002-2006, they found that some basins, including the Congo and the Mississippi, have been losing water, but river systems in the boreal regions are gaining water.

Meanwhile, scientists at the European Space Agency, collaborating with DeMontfort University in the UK, have begun to use data from the satellites that measure sea level, to assess lake and river levels on land.

Fresh inland water is much in demand, but those managing it suffer from a grave lack of information about how much of it there is. “The number of river gauges is diminishing every day, and many catchments are now entirely unmeasured,” says Jérôme Benveniste of the European Space Agency’s data processing centre ESRIN, in Frascati, Italy. “But we have 16 years’ worth of data on river and lake levels. It’s just a question of processing it all.”

The work Benveniste is leading can recreate water levels in reservoirs, or lakes, and reconstruct the annual ebb and flow in large river basins like the Amazon.

Other teams are combining these surface water level measurements with gravimetry measurements from the GRACE satellites, to derive the amount of ground water stored in each catchment. “International cooperation is essential in achieving this goal, with global coverage and local validation of the data,” says Benveniste. “At the moment, Europe is leading the field.”