Fountain of youth underlies Antarctic Mountains

Images of the ice-covered Gamburtsev Mountains revealed water-filled valleys, as seen by the cluster of vertical lines in this image. -  Tim Creyts
Images of the ice-covered Gamburtsev Mountains revealed water-filled valleys, as seen by the cluster of vertical lines in this image. – Tim Creyts

Time ravages mountains, as it does people. Sharp features soften, and bodies grow shorter and rounder. But under the right conditions, some mountains refuse to age. In a new study, scientists explain why the ice-covered Gamburtsev Mountains in the middle of Antarctica looks as young as they do.

The Gamburtsevs were discovered in the 1950s, but remained unexplored until scientists flew ice-penetrating instruments over the mountains 60 years later. As this ancient hidden landscape came into focus, scientists were stunned to see the saw-toothed and towering crags of much younger mountains. Though the Gamburtsevs are contemporaries of the largely worn-down Appalachians, they looked more like the Rockies, which are nearly 200 million years younger.

More surprising still, the scientists discovered a vast network of lakes and rivers at the mountains’ base. Though water usually speeds erosion, here it seems to have kept erosion at bay. The reason, researchers now say, has to do with the thick ice that has entombed the Gamburtsevs since Antarctica went into a deep freeze 35 million years ago.

“The ice sheet acts like an anti-aging cream,” said the study’s lead author, Timothy Creyts, a geophysicist at Columbia University’s Lamont-Doherty Earth Observatory. “It triggers a series of thermodynamic processes that have almost perfectly preserved the Gamburtsevs since ice began spreading across the continent.”

The study, which appears in the latest issue of the journal Geophysical Research Letters, explains how the blanket of ice covering the Gamburtsevs has preserved its rugged ridgelines.

Snow falling at the surface of the ice sheet draws colder temperatures down, closer to protruding peaks in a process called divergent cooling. At the same time, heat radiating from bedrock beneath the ice sheet melts ice in the deep valleys to form rivers and lakes. As rivers course along the base of the ice sheet, high pressures from the overlying ice sheet push water up valleys in reverse. This uphill flow refreezes as it meets colder temperature from above. Thus, ridgelines are cryogenically preserved.

The oldest rocks in the Gamburtsevs formed more than a billion years ago, in the collision of several continents. Though these prototype mountains eroded away, a lingering crustal root became reactivated when the supercontinent Gondwana ripped apart, starting about 200 million years ago. Tectonic forces pushed the land up again to form the modern Gamburtsevs, which range across an area the size of the Alps. Erosion again chewed away at the mountains until earth entered a cooling phase 35 million years ago. Expanding outward from the Gamburtsevs, a growing layer of ice joined several other nucleation points to cover the entire continent in ice.

The researchers say that the mechanism that stalled aging of the Gamburtsevs at higher elevations may explain why some ridgelines in the Torngat Mountains on Canada’s Labrador Peninsula and the Scandinavian Mountains running through Norway, Sweden and Finland appear strikingly untouched. Massive ice sheets covered both landscapes during the last ice age, which peaked about 20,000 years ago, but many high-altitude features bear little trace of this event.

“The authors identify a mechanism whereby larger parts of mountains ranges in glaciated regions–not just Antarctica–could be spared from erosion,” said Stewart Jamieson, a glaciologist at Durham University who was not involved in the study. “This is important because these uplands are nucleation centers for ice sheets. If they were to gradually erode during glacial cycles, they would become less effective as nucleation points during later ice ages.”

Ice sheet behavior, then, may influence climate change in ways that scientists and computer models have yet to appreciate. As study coauthor Fausto Ferraccioli, head of the British Antarctic Survey’s airborne geophysics group, put it: “If these mountains in interior East Antarctica had been more significantly eroded then the ice sheet itself
may have had a different history.”

Other Authors


Hugh Carr and Tom Jordan of the British Antarctic Survey; Robin Bell, Michael Wolovick and Nicholas Frearson of Lamont-Doherty; Kathryn Rose of University of Bristol; Detlef Damaske of Germany’s Federal Institute for Geosciences and Natural Resources; David Braaten of Kansas University; and Carol Finn of the U.S. Geological Survey.

Copies of the paper, “Freezing of ridges and water networks preserves the Gamburtsev Subglacial Mountains for millions of years,” are available from the authors.

Scientist Contact


Tim Creyts

845-365-8368

tcreyts@ldeo.columbia.edu

Climate capers of the past 600,000 years

The researchers remove samples from a core segment taken from Lake Van at the center for Marine environmental sciences MARUM in Bremen, where all of the cores from the PALEOVAN project are stored. -  Photo: Nadine Pickarski/Uni Bonn
The researchers remove samples from a core segment taken from Lake Van at the center for Marine environmental sciences MARUM in Bremen, where all of the cores from the PALEOVAN project are stored. – Photo: Nadine Pickarski/Uni Bonn

If you want to see into the future, you have to understand the past. An international consortium of researchers under the auspices of the University of Bonn has drilled deposits on the bed of Lake Van (Eastern Turkey) which provide unique insights into the last 600,000 years. The samples reveal that the climate has done its fair share of mischief-making in the past. Furthermore, there have been numerous earthquakes and volcanic eruptions. The results of the drilling project also provide a basis for assessing the risk of how dangerous natural hazards are for today’s population. In a special edition of the highly regarded publication Quaternary Science Reviews, the scientists have now published their findings in a number of journal articles.

In the sediments of Lake Van, the lighter-colored, lime-containing summer layers are clearly distinguishable from the darker, clay-rich winter layers — also called varves. In 2010, from a floating platform an international consortium of researchers drilled a 220 m deep sediment profile from the lake floor at a water depth of 360 m and analyzed the varves. The samples they recovered are a unique scientific treasure because the climate conditions, earthquakes and volcanic eruptions of the past 600,000 years can be read in outstanding quality from the cores.

The team of scientists under the auspices of the University of Bonn has analyzed some 5,000 samples in total. “The results show that the climate over the past hundred thousand years has been a roller coaster. Within just a few decades, the climate could tip from an ice age into a warm period,” says Doctor Thomas Litt of the University of Bonn’s Steinmann Institute and spokesman for the PALEOVAN international consortium of researchers. Unbroken continental climate archives from the ice age which encompass several hundred thousand years are extremely rare on a global scale. “There has never before in all of the Middle East and Central Asia been a continental drilling operation going so far back into the past,” says Doctor Litt. In the northern hemisphere, climate data from ice-cores drilled in Greenland encompass the last 120,000 years. The Lake Van project closes a gap in the scientific climate record.

The sediments reveal six cycles of cold and warm periods


Scientists found evidence for a total of six cycles of warm and cold periods in the sediments of Lake Van. The University of Bonn paleoecologist and his colleagues analyzed the pollen preserved in the sediments. Under a microscope they were able to determine which plants around the eastern Anatolian Lake the pollen came from. “Pollen is amazingly durable and is preserved over very long periods when protected in the sediments,” Doctor Litt explained. Insight into the age of the individual layers was gleaned through radiometric age measurements that use the decay of radioactive elements as a geologic clock. Based on the type of pollen and the age, the scientists were able to determine when oak forests typical of warm periods grew around Lake Van and when ice-age steppe made up of grasses, mugwort and goosefoot surrounded the lake.

Once they determine the composition of the vegetation present and the requirements of the plants, the scientists can reconstruct with a high degree of accuracy the temperature and amount of rainfall during different epochs. These analyses enable the team of researchers to read the varves of Lake Van like thousands of pages of an archive. With these data, the team was able to demonstrate that fluctuations in climate were due in large part to periodic changes in the Earth’s orbit parameters and the commensurate changes in solar insolation levels. However, the influence of North Atlantic currents was also evident. “The analysis of the Lake Van sediments has presented us with an image of how an ecosystem reacts to abrupt changes in climate. This fundamental data will help us to develop potential scenarios of future climate effects,” says Doctor Litt.

Risks of earthquakes and volcanic eruptions in the region of Van

Such risk assessments can also be made for other natural forces. “Deposits of volcanic ash with thicknesses of up to 10 m in the Lake Van sediments show us that approximately 270,000 years ago there was a massive eruption,” the University of Bonn paleoecologist said. The team struck some 300 different volcanic events in its drillings. Statistically, that corresponds to one explosive volcanic eruption in the region every 2000 years. Deformations in the sediment layers show that the area is subject to frequent, strong earthquakes. “The area around Lake Van is very densely populated. The data from the core samples show that volcanic activity and earthquakes present a relatively high risk for the region,” Doctor Litt says. According to media reports, in 2011 a 7.2 magnitude earthquake in the Van province claimed the lives of more than 500 people and injured more than 2,500.

Publication: “Results from the PALEOVAN drilling project: A 600,000 year long continental archive in the Near East”, Quaternary Science Reviews, Volume 104, online publication: (http://dx.doi.org/10.1016/j.quascirev.2014.09.026)

Volcano hazards and the role of westerly wind bursts in El Niño

On June 27, lava from Kīlauea, an active volcano on the island of Hawai'i, began flowing to the northeast, threatening the residents in a community in the District of Puna. -  USGS
On June 27, lava from Kīlauea, an active volcano on the island of Hawai’i, began flowing to the northeast, threatening the residents in a community in the District of Puna. – USGS

On 27 June, lava from Kīlauea, an active volcano on the island of Hawai’i, began flowing to the northeast, threatening the residents in Pāhoa, a community in the District of Puna, as well as the only highway accessible to this area. Scientists from the U.S. Geological Survey’s Hawaiian Volcano Observatory (HVO) and the Hawai’i County Civil Defense have been monitoring the volcano’s lava flow and communicating with affected residents through public meetings since 24 August. Eos recently spoke with Michael Poland, a geophysicist at HVO and a member of the Eos Editorial Advisory Board, to discuss how he and his colleagues communicated this threat to the public.

Drilling a Small Basaltic Volcano to Reveal Potential Hazards


Drilling into the Rangitoto Island Volcano in the Auckland Volcanic Field in New Zealand offers insight into a small monogenetic volcano, and may improve understanding of future hazards.

From AGU’s journals: El Niño fades without westerly wind bursts

The warm and wet winter of 1997 brought California floods, Florida tornadoes, and an ice storm in the American northeast, prompting climatologists to dub it the El Niño of the century. Earlier this year, climate scientists thought the coming winter might bring similar extremes, as equatorial Pacific Ocean conditions resembled those seen in early 1997. But the signals weakened by summer, and the El Niño predictions were downgraded. Menkes et al. used simulations to examine the differences between the two years.

The El Niño-Southern Oscillation is defined by abnormally warm sea surface temperatures in the eastern Pacific Ocean and weaker than usual trade winds. In a typical year, southeast trade winds push surface water toward the western Pacific “warm pool”–a region essential to Earth’s climate. The trade winds dramatically weaken or even reverse in El Niño years, and the warm pool extends its reach east.

Scientists have struggled to predict El Niño due to irregularities in the shape, amplitude, and timing of the surges of warm water. Previous studies suggested that short-lived westerly wind pulses (i.e. one to two weeks long) could contribute to this irregularity by triggering and sustaining El Niño events.

To understand the vanishing 2014 El Niño, the authors used computer simulations and examined the wind’s role. The researchers find pronounced differences between 1997 and 2014. Both years saw strong westerly wind events between January and March, but those disappeared this year as spring approached. In contrast, the westerly winds persisted through summer in 1997.

In the past, it was thought that westerly wind pulses were three times as likely to form if the warm pool extended east of the dateline. That did not occur this year. The team says their analysis shows that El Niño’s strength might depend on these short-lived and possibly unpredictable pulses.

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Worldwide retreat of glaciers confirmed in unprecedented detail

The worldwide retreat of glaciers is confirmed in unprecedented detail. This new book presents an overview and detailed assessment of changes in the world's glaciers by using satellite imagery -  Springer
The worldwide retreat of glaciers is confirmed in unprecedented detail. This new book presents an overview and detailed assessment of changes in the world’s glaciers by using satellite imagery – Springer

Taking their name from the old Scottish term glim, meaning a passing look or glance, in 1994 a team of scientists began developing a world-wide initiative to study glaciers using satellite data. Now 20 years later, the international GLIMS (Global Land Ice Measurements from Space) initiative observes the world’s glaciers primarily using data from optical satellite instruments such as ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) and Landsat.

More than 150 scientists from all over the world have contributed to the new book Global Land Ice Measurements from Space, the most comprehensive report to date on global glacier changes. While the shrinking of glaciers on all continents is already known from ground observations of individual glaciers, by using repeated satellite observations GLIMS has firmly established that glaciers are shrinking globally. Although some glaciers are maintaining their size, most glaciers are dwindling. The foremost cause of the worldwide reductions in glaciers is global warming, the team writes.

Full color throughout, the book has 25 regional chapters that illustrate glacier changes from the Arctic to the Antarctic. Other chapters provide a thorough theoretical background on glacier monitoring and mapping, remote sensing techniques, uncertainties, and interpretation of the observations in a climatic context. The book highlights many other glacier research applications of satellite data, including measurement of glacier thinning from repeated satellite-based digital elevation models (DEMs) and calculation of surface flow velocities from repeated satellite images.

These tools are key to understanding local and regional variations in glacier behavior, the team writes. The high sensitivity of glaciers to climate change has substantially decreased their volume and changed the landscape over the past decades, affecting both regional water availability and the hazard potential of glaciers. The growing GLIMS database about glaciers also contributed to the Intergovernmental Panel on Climate Change (IPCC)’s Fifth Assessment Report issued in 2013. The IPCC report concluded that most of the world’s glaciers have been losing ice at an increasing rate in recent decades.

More than 60 institutions across the globe are involved in GLIMS. Jeffrey S. Kargel of the Department of Hydrology and Water Resources at the University of Arizona coordinates the project. The GLIMS glacier database and GLIMS web site are developed and maintained by the National Snow and Ice Data Center (NSIDC) at the University of Colorado in Boulder.

Global Land Ice Measurements from Space</em?

Hardcover $279.00; £180.00; € 199,99

Springer and Praxis Publishing (2014) ISBN 978-3-540-79817-0

Also available as an eBook

Fracture-controlled erodibility, great rock climbing

Tuolumne Meadows in Yosemite National Park is an iconic American landscape: It is a sub-alpine meadow surrounded by glacially sculpted granitic outcrops in the Sierra Nevada Mountains. Because of its accessibility and aesthetic appeal, it is a focal point for both vacationers (up to 4,200 people per day) and geoscientists. It also has historical significance: The idea for a Yosemite National Park came to John Muir and Robert Underwood Johnson over a campfire there.

As the largest sub-alpine meadow in the Sierra Nevada, Tuolumne Meadows is also a geomorphic anomaly: The presence of broad and open topography is commonly associated with bedrock erodibility. In contrast, the nearby vertical rock walls — including Cathedral Peak, Matthes Crest, and Lembert Dome — suggest bedrock durability. Despite these geomorphic differences, the entire region is underlain by the same lithology, the Cathedral Peak Granodiorite.

In this new study published in the November 2014 issue of GSA Today, authors Richard A. Becker, Basil Tikoff, Paul R. Riley, and Neal R. Iverson present evidence that this anomalous landscape is the result of preferential glacial erosion of highly fractured bedrock. In particular, tabular fracture clusters (TFCs) are common in the Cathedral Peak Granodiorite in the Tuolumne Meadows area. TFCs are dense networks of sub-parallel opening-mode fractures that are clustered into discrete, tabular (book-like) zones.

The authors conclude that Tuolumne Meadows resulted from ice flowing perpendicularly to high TFC concentrations. In contrast, ice flowing parallel to variable TFC concentrations formed the vertical rock walls. Thus, the exceptional rock climbing around Tuolumne Meadows is a direct result of fracture-controlled variations in erodibility — on the 10 meter to 100 meter scale — within a single lithology. This finding supports the contention that landscape evolution is strongly controlled by bedrock fracturing and that tectonic processes that result in fracturing may generally exert a fundamental and underappreciated role in geomorphology.

ARTICLE

Preexisting fractures and the formation of an iconic American landscape: Tuolumne Meadows, Yosemite National Park, USA

Richard A. Becker et al., Dept. of Geoscience, University of Wisconsin, 1215 W. Dayton Street, Madison, Wisconsin 53706, USA, USA, Pages 4–10; doi: 10.1130/GSATG203A.1.

New study finds oceans arrived early to Earth

In this illustration of the early solar system, the dashed white line represents the snow line -- the transition from the hotter inner solar system, where water ice is not stable (brown) to the outer Solar system, where water ice is stable (blue). Two possible ways that the inner solar system received water are: water molecules sticking to dust grains inside the 'snow line' (as shown in the inset) and carbonaceous chondrite material flung into the inner solar system by the effect of gravity from protoJupiter. With either scenario, water must accrete to the inner planets within the first ca. 10 million years of solar system formation. -  Illustration by Jack Cook, Woods Hole Oceanographic Institution
In this illustration of the early solar system, the dashed white line represents the snow line — the transition from the hotter inner solar system, where water ice is not stable (brown) to the outer Solar system, where water ice is stable (blue). Two possible ways that the inner solar system received water are: water molecules sticking to dust grains inside the ‘snow line’ (as shown in the inset) and carbonaceous chondrite material flung into the inner solar system by the effect of gravity from protoJupiter. With either scenario, water must accrete to the inner planets within the first ca. 10 million years of solar system formation. – Illustration by Jack Cook, Woods Hole Oceanographic Institution

Earth is known as the Blue Planet because of its oceans, which cover more than 70 percent of the planet’s surface and are home to the world’s greatest diversity of life. While water is essential for life on the planet, the answers to two key questions have eluded us: where did Earth’s water come from and when?

While some hypothesize that water came late to Earth, well after the planet had formed, findings from a new study led by scientists at the Woods Hole Oceanographic Institution (WHOI) significantly move back the clock for the first evidence of water on Earth and in the inner solar system.

“The answer to one of the basic questions is that our oceans were always here. We didn’t get them from a late process, as was previously thought,” said Adam Sarafian, the lead author of the paper published Oct. 31, 2014, in the journal Science and a MIT/WHOI Joint Program student in the Geology and Geophysics Department.

One school of thought was that planets originally formed dry, due to the high-energy, high-impact process of planet formation, and that the water came later from sources such as comets or “wet” asteroids, which are largely composed of ices and gases.

“With giant asteroids and meteors colliding, there’s a lot of destruction,” said Horst Marschall, a geologist at WHOI and coauthor of the paper. “Some people have argued that any water molecules that were present as the planets were forming would have evaporated or been blown off into space, and that surface water as it exists on our planet today, must have come much, much later—hundreds of millions of years later.”

The study’s authors turned to another potential source of Earth’s water— carbonaceous chondrites. The most primitive known meteorites, carbonaceous chondrites, were formed in the same swirl of dust, grit, ice and gasses that gave rise to the sun some 4.6 billion years ago, well before the planets were formed.

“These primitive meteorites resemble the bulk solar system composition,” said WHOI geologist and coauthor Sune Nielsen. “They have quite a lot of water in them, and have been thought of before as candidates for the origin of Earth’s water.

In order to determine the source of water in planetary bodies, scientists measure the ratio between the two stable isotopes of hydrogen: deuterium and hydrogen. Different regions of the solar system are characterized by highly variable ratios of these isotopes. The study’s authors knew the ratio for carbonaceous chondrites and reasoned that if they could compare that to an object that was known to crystallize while Earth was actively accreting then they could gauge when water appeared on Earth.

To test this hypothesis, the research team, which also includes Francis McCubbin from the Institute of Meteoritics at the University of New Mexico and Brian Monteleone of WHOI, utilized meteorite samples provided by NASA from the asteroid 4-Vesta. The asteroid 4-Vesta, which formed in the same region of the solar system as Earth, has a surface of basaltic rock—frozen lava. These basaltic meteorites from 4-Vesta are known as eucrites and carry a unique signature of one of the oldest hydrogen reservoirs in the solar system. Their age—approximately 14 million years after the solar system formed—makes them ideal for determining the source of water in the inner solar system at a time when Earth was in its main building phase. The researchers analyzed five different samples at the Northeast National Ion Microprobe Facility—a state-of-the-art national facility housed at WHOI that utilizes secondary ion mass spectrometers. This is the first time hydrogen isotopes have been measured in eucrite meteorites.

The measurements show that 4-Vesta contains the same hydrogen isotopic composition as carbonaceous chondrites, which is also that of Earth. That, combined with nitrogen isotope data, points to carbonaceous chondrites as the most likely common source of water.

“The study shows that Earth’s water most likely accreted at the same time as the rock. The planet formed as a wet planet with water on the surface,” Marschall said.

While the findings don’t preclude a late addition of water on Earth, it shows that it wasn’t necessary since the right amount and composition of water was present at a very early stage.

“An implication of that is that life on our planet could have started to begin very early,” added Nielsen. “Knowing that water came early to the inner solar system also means that the other inner planets could have been wet early and evolved life before they became the harsh environments they are today.

New study shows 3 abrupt pulse of CO2 during last deglaciation

A new study shows that the rise of atmospheric carbon dioxide that contributed to the end of the last ice age more than 10,000 years ago did not occur gradually, but was characterized by three “pulses” in which C02 rose abruptly.

Scientists are not sure what caused these abrupt increases, during which C02 levels rose about 10-15 parts per million – or about 5 percent per episode – over a period of 1-2 centuries. It likely was a combination of factors, they say, including ocean circulation, changing wind patterns, and terrestrial processes.

The finding is important, however, because it casts new light on the mechanisms that take the Earth in and out of ice age regimes. Results of the study, which was funded by the National Science Foundation, appear this week in the journal Nature.

“We used to think that naturally occurring changes in carbon dioxide took place relatively slowly over the 10,000 years it took to move out of the last ice age,” said Shaun Marcott, lead author on the article who conducted his study as a post-doctoral researcher at Oregon State University. “This abrupt, centennial-scale variability of CO2 appears to be a fundamental part of the global carbon cycle.”

Some previous research has hinted at the possibility that spikes in atmospheric carbon dioxide may have accelerated the last deglaciation, but that hypothesis had not been resolved, the researchers say. The key to the new finding is the analysis of an ice core from the West Antarctic that provided the scientists with an unprecedented glimpse into the past.

Scientists studying past climate have been hampered by the limitations of previous ice cores. Cores from Greenland, for example, provide unique records of rapid climate events going back 120,000 years – but high concentrations of impurities don’t allow researchers to accurately determine atmospheric carbon dioxide records. Antarctic ice cores have fewer impurities, but generally have had lower “temporal resolution,” providing less detailed information about atmospheric CO2.

However, a new core from West Antarctica, drilled to a depth of 3,405 meters in 2011 and spanning the last 68,000 years, has “extraordinary detail,” said Oregon State paleoclimatologist Edward Brook, a co-author on the Nature study and an internationally recognized ice core expert. Because the area where the core was taken gets high annual snowfall, he said, the new ice core provides one of the most detailed records of atmospheric CO2.

“It is a remarkable ice core and it clearly shows distinct pulses of carbon dioxide increase that can be very reliably dated,” Brook said. “These are some of the fastest natural changes in CO2 we have observed, and were probably big enough on their own to impact the Earth’s climate.

“The abrupt events did not end the ice age by themselves,” Brook added. “That might be jumping the gun a bit. But it is fair to say that the natural carbon cycle can change a lot faster than was previously thought – and we don’t know all of the mechanisms that caused that rapid change.”

The researchers say that the increase in atmospheric CO2 from the peak of the last ice age to complete deglaciation was about 80 parts per million, taking place over 10,000 years. Thus, the finding that 30-45 ppm of the increase happened in just a few centuries was significant.

The overall rise of atmospheric carbon dioxide during the last deglaciation was thought to have been triggered by the release of CO2 from the deep ocean – especially the Southern Ocean. However, the researchers say that no obvious ocean mechanism is known that would trigger rises of 10-15 ppm over a time span as short as one to two centuries.

“The oceans are simply not thought to respond that fast,” Brook said. “Either the cause of these pulses is at least part terrestrial, or there is some mechanism in the ocean system we don’t yet know about.”

One reason the researchers are reluctant to pin the end of the last ice age solely on CO2 increases is that other processes were taking place, according to Marcott, who recently joined the faculty of the University of Wisconsin-Madison.

“At the same time CO2 was increasing, the rate of methane in the atmosphere was also increasing at the same or a slightly higher rate,” Marcott said. “We also know that during at least two of these pulses, the Atlantic Meridional Overturning Circulation changed as well. Changes in the ocean circulation would have affected CO2 – and indirectly methane, by impacting global rainfall patterns.”

“The Earth is a big coupled system,” he added, “and there are many pieces to the puzzle. The discovery of these strong, rapid pulses of CO2 is an important piece.”

Researchers resolve the Karakoram glacier anomaly, a cold case of climate science

The researchers found that low-resolution models and a lack of reliable observational data obscured the Karakoram's dramatic shifts in elevation over a small area and heavy winter snowfall. They created a higher-resolution model that showed the elevation and snow water equivalent for (inlaid boxes, from left to right) the Karakoram range and northwest Himalayas, the central Himalayas that include Mount Everest, and the southeast Himalayas and the Tibetan Plateau. For elevation (left), the high-resolution model showed the sharp variations between roughly 2,500 and 5,000 meters above sea level (yellow to brown) for the Karakoram, while other areas of the map have comparatively more consistent elevations. The model also showed that the Karakoram receive much more annual snowfall (right) than other Himalayan ranges (right), an average of 100 centimeters (brown). The researchers found that the main precipitation season in the Karakoram occurs during the winter and is influenced by cold winds coming from Central Asian countries, as opposed to the heavy summer monsoons that provide the majority of precipitation to the other Himalayan ranges. -  Image by Sarah Kapnick, Program in Atmospheric and Oceanic Sciences
The researchers found that low-resolution models and a lack of reliable observational data obscured the Karakoram’s dramatic shifts in elevation over a small area and heavy winter snowfall. They created a higher-resolution model that showed the elevation and snow water equivalent for (inlaid boxes, from left to right) the Karakoram range and northwest Himalayas, the central Himalayas that include Mount Everest, and the southeast Himalayas and the Tibetan Plateau. For elevation (left), the high-resolution model showed the sharp variations between roughly 2,500 and 5,000 meters above sea level (yellow to brown) for the Karakoram, while other areas of the map have comparatively more consistent elevations. The model also showed that the Karakoram receive much more annual snowfall (right) than other Himalayan ranges (right), an average of 100 centimeters (brown). The researchers found that the main precipitation season in the Karakoram occurs during the winter and is influenced by cold winds coming from Central Asian countries, as opposed to the heavy summer monsoons that provide the majority of precipitation to the other Himalayan ranges. – Image by Sarah Kapnick, Program in Atmospheric and Oceanic Sciences

Researchers from Princeton University and other institutions may have hit upon an answer to a climate-change puzzle that has eluded scientists for years, and that could help understand the future availability of water for hundreds of millions of people.

In a phenomenon known as the “Karakoram anomaly,” glaciers in the Karakoram mountains, a range within the Himalayas, have remained stable and even increased in mass while many glaciers nearby — and worldwide — have receded during the past 150 years, particularly in recent decades. Himalayan glaciers provide freshwater to a densely populated area that includes China, Pakistan and India, and are the source of the Ganges and Indus rivers, two of the world’s major waterways.

While there have been many attempts to explain the stability of the Karakoram glaciers, the researchers report in the journal Nature Geoscience that the ice is sustained by a unique and localized seasonal pattern that keeps the mountain range relatively cold and dry during the summer. Other Himalayan ranges and the Tibetan Plateau — where glaciers have increasingly receded as Earth’s climate has warmed — receive most of their precipitation from heavy summer monsoons out of hot South and Southeast Asian nations such as India. The main precipitation season in the Karakoram, however, occurs during the winter and is influenced by cold winds coming from Central Asian countries such as Afghanistan to the west, while the main Himalayan range blocks the warmer air from the southeast throughout the year.

The researchers determined that snowfall, which is critical to maintaining glacier mass, will remain stable and even increase in magnitude at elevations above 4,500 meters (14,764 feet) in the Karakoram through at least 2100. On the other hand, snowfall over much of the Himalayas and Tibet is projected to decline even as the Indian and Southeast Asian monsoons increase in intensity under climate change.

First author Sarah Kapnick, a postdoctoral research fellow in Princeton’s Program in Atmospheric and Oceanic Sciences, said that a shortage of reliable observational data and the use of low-resolution computer models had obscured the subtleties of the Karakoram seasonal cycle and prevented scientists from unraveling the causes of the anomaly.

For models, the complication is that the Karakoram features dramatic shifts in elevation over a small area, Kapnick said. The range boasts four mountains that are more than 8,000 meters (26,246 feet) high — including K2, the world’s second highest peak — and numerous summits that exceed 7,000 meters, all of which are packed into a length of about 500 kilometers (300 miles).

Kapnick and her co-authors overcame this obstacle with a high-resolution computer model that broke the Karakoram into 50-kilometer pieces, meaning that those sharp fluctuations in altitude were better represented.

In their study, the researchers compared their model with climate models from the United Nations’ Intergovernmental Panel on Climate Change (IPCC), which averages a resolution of 210-kilometer squares, Kapnick said. At that scale, the Karakoram is reduced to an average height that is too low and results in temperatures that are too warm to sustain sufficient levels of snowfall throughout the year, and too sensitive to future temperature increases.

Thus, by the IPCC’s models, it would appear that the Karakoram’s glaciers are imperiled by climate change due to reduced snowfall, Kapnick said. This region has been a great source of controversy ever since the IPCC’s last major report, in 2007, when the panel misreported that Himalayan glaciers would likely succumb to climate change by 2035. More recent papers using current IPCC models have similarly reported snowfall losses in this region because the models do not accurately portray the topography of the Karakoram, Kapnick said.

“The higher resolution allowed us to explore what happens at these higher elevations in a way that hasn’t been able to be done,” Kapnick said. “Something that climate scientists always have to keep in mind is that models are useful for certain types of questions and not necessarily for other types of questions. While the IPCC models can be particularly useful for other parts of the world, you need a higher resolution for this area.”

Jeff Dozier, a professor of snow hydrology, earth system science and remote sensing at the University of California-Santa Barbara, said that the research addresses existing shortcomings in how mountain climates are modeled and predicted, particularly in especially steep and compact ranges. Dozier, who was not involved in the research, conducts some of his research in the Hindu Kush mountains west of the Karakoram.

Crucial information regarding water availability is often lost in computer models, observational data and other tools that typically do not represent ranges such as Karakoram accurately enough, Dozier said. For instance, a severe 2011 drought in Northern Afghanistan was a surprise partly due to erroneous runoff forecasts based on insufficient models and surface data, he said. The high-resolution model Kapnick and her co-authors developed for Karakoram potentially resolves many of the modeling issues related to mountain ranges with similar terrain, he said.

“The Karakoram Anomaly has been a puzzle, and this paper gives a credible explanation,” Dozier said. “Climate in the mountains is obviously affected strongly by the elevation, but most global climate models don’t resolve the topography well enough. So, the higher-resolution model is appropriate. About a billion people worldwide get their water resources from melting snow and many of these billion get their water from High Mountain Asia.”

The researchers used the high-resolution global-climate model GFDL-CM2.5 at the Geophysical Fluid Dynamics Laboratory (GFDL), which is on Princeton’s Forrestal Campus and administered by the National Oceanic and Atmospheric Administration (NOAA). The researchers simulated the global climate — with a focus on the Karakoram — based on observational data from 1861 to 2005, and on the IPCC’s greenhouse-gas projections for 2006-2100, which will be included in its Fifth Assessment Report scheduled for release in November.

The 50-kilometer resolution revealed conditions in Karakoram on a monthly basis, Kapnick said. It was then that she and her colleagues could observe that the monsoon months in Karakoram are not only not characterized by heavy rainfall, but also include frigid westerly winds that keep conditions in the mountain range cold enough for nearly year-round snowfall.

“There is precipitation during the summer, it just doesn’t dominate the seasonal cycle. This region, even at the same elevation as the rest of the Himalayas, is just colder,” Kapnick said.

“The high-resolution model shows us that things don’t happen perfectly across seasons. You can have statistical variations in one month but not another,” she continued. “This allows us to piece out those significant changes from one month to the next.”

Kapnick, who received her bachelor’s degree in mathematics from Princeton in 2004, worked with Thomas Delworth, a NOAA scientist and Princeton lecturer of geosciences and atmospheric and oceanic sciences; Moestasim Ashfaq, a scientist at the Oak Ridge National Laboratory Climate Change Science Institute; Sergey Malyshev, a climate modeler in Princeton’s Department of Ecology and Evolutionary Biology based at GFDL; and P.C.D. “Chris” Milly, a research hydrologist for the U.S. Geological Survey based at GFDL who received his bachelor’s degree in civil engineering from Princeton in 1978.

While the researchers show that the Karakoram will receive consistent — and perhaps increased — snowfall through 2100, more modeling work is needed to understand how the existing glaciers may change over time as a result of melt, avalanches and other factors, Kapnick said.

“Our work is an important piece to understanding the Karakoram anomaly,” Kapnick said. “But that balance of what’s coming off the glacier versus what’s coming in also matters for understanding how the glacier will change in the future.”

The paper, “Snowfall less sensitive to warming in Karakoram than in Himalayas due to a unique seasonal cycle,” was published online in-advance-of-print Oct. 12 by Nature Geoscience.

Past climate change and continental ice melt linked to varying CO2 levels

Scientists at the Universities of Southampton and Cardiff have discovered that a globally warm period in Earth’s geological past featured highly variable levels of CO2.

Previous studies have found that the Miocene climatic optimum, a period that extends from about 15 to 17 million years ago, was associated with big changes in both temperature and the amount of continental ice on the planet.

Now a new study, published in Paleoceanography, has found that these changes in temperature and ice volume were matched by equally dramatic shifts in atmospheric CO2.

Using more detailed records than has previously been available, scientists have shown that CO2 levels in this period reached around 500 ppm (parts per million), the same level that the Intergovernmental Panel on Climate Change (IPPC) projects for the end of the century.

Lead author Rosanna Greenop, from Ocean and Earth Science at the University of Southampton, says: “The drivers of short term, orbital-scale temperature and ice volume change during warm periods of the Earth’s history have never been analysed before. Here we are able to show that in the same way as the more recent ice ages are linked with cycles of CO2, it also plays an important role in cyclical climate changes during warm periods.

Researchers also showed that at low levels of CO2, ice volume varied strongly, but at higher levels, there was little or no additional change in volume. The authors of the study hypothesis that there must be a portion of the East Antarctic ice sheet that varies in volume at the lower end of the CO2 range. However, the absence of additional ice melt at higher CO2 levels suggests that there is also a portion of the ice sheet that remains stable at the maximum CO2 levels.

Evidence suggests that the northern Hemisphere and West Antarctic ice sheets did not exist during the warm Miocene climatic optimum.

“While we recognise that the Miocene climatic optimum is not a perfect analogue for our own warm future, the geological past does represent an actual reality that the Earth system experienced,” says the University of Southampton’s Dr Gavin Foster, co-author of the study. “As such the findings of this study have large implications for the stability of the continental ice sheets in the future. They indicate that portions of the East Antarctic ice sheet can act in a dynamic fashion, growing and shrinking in response to climate forcing.”

Co-author Caroline Lear, of Cardiff University, adds: “We tend to think of the Antarctic ice sheet as a sluggish ice sheet, but these records show that in past warm climates it has been surprisingly sensitive to natural variations in carbon dioxide levels.

Icebergs once drifted to Florida, new climate model suggests

This is a map showing the pathway taken by icebergs from Hudson Bay, Canada, to Florida. The blue colors (behind the arrows) are an actual snapshot from the authors' high resolution model showing how much less salty the water is than normal. The more blue the color the less salty it is than normal. In this case, blue all the way along the coast shows that very fresh, cold waters are flowing along the entire east coast from Hudson Bay to Florida. -  UMass Amherst
This is a map showing the pathway taken by icebergs from Hudson Bay, Canada, to Florida. The blue colors (behind the arrows) are an actual snapshot from the authors’ high resolution model showing how much less salty the water is than normal. The more blue the color the less salty it is than normal. In this case, blue all the way along the coast shows that very fresh, cold waters are flowing along the entire east coast from Hudson Bay to Florida. – UMass Amherst

Using a first-of-its-kind, high-resolution numerical model to describe ocean circulation during the last ice age about 21,000 year ago, oceanographer Alan Condron of the University of Massachusetts Amherst has shown that icebergs and meltwater from the North American ice sheet would have regularly reached South Carolina and even southern Florida. The models are supported by the discovery of iceberg scour marks on the sea floor along the entire continental shelf.

Such a view of past meltwater and iceberg movement implies that the mechanisms of abrupt climate change are more complex than previously thought, Condron says. “Our study is the first to show that when the large ice sheet over North America known as the Laurentide ice sheet began to melt, icebergs calved into the sea around Hudson Bay and would have periodically drifted along the east coast of the United States as far south as Miami and the Bahamas in the Caribbean, a distance of more than 3,100 miles, about 5,000 kilometers.”

His work, conducted with Jenna Hill of Coastal Carolina University, is described in the current advance online issue of Nature Geosciences. “Determining how far south of the subpolar gyre icebergs and meltwater penetrated is vital for understanding the sensitivity of North Atlantic Deep Water formation and climate to past changes in high-latitude freshwater runoff,” the authors say.

Hill analyzed high-resolution images of the sea floor from Cape Hatteras to Florida and identified about 400 scour marks on the seabed that were formed by enormous icebergs plowing through mud on the sea floor. These characteristic grooves and pits were formed as icebergs moved into shallower water and their keels bumped and scraped along the ocean floor.

“The depth of the scours tells us that icebergs drifting to southern Florida were at least 1,000 feet, or 300 meters thick,” says Condron. “This is enormous. Such icebergs are only found off the coast of Greenland today.”

To investigate how icebergs might have drifted as far south as Florida, Condron simulated the release of a series of glacial meltwater floods in his high-resolution ocean circulation model at four different levels for two locations, Hudson Bay and the Gulf of St. Lawrence.

Condron reports, “In order for icebergs to drift to Florida, our glacial ocean circulation model tells us that enormous volumes of meltwater, similar to a catastrophic glacial lake outburst flood, must have been discharging into the ocean from the Laurentide ice sheet, from either Hudson Bay or the Gulf of St. Lawrence.”

Further, during these large meltwater flood events, the surface ocean current off the coast of Florida would have undergone a complete, 180-degree flip in direction, so that the warm, northward flowing Gulf Stream would have been replaced by a cold, southward flowing current, he adds.

As a result, waters off the coast of Florida would have been only a few degrees above freezing. Such events would have led to the sudden appearance of massive icebergs along the east coast of the United States all the way to Florida Keys, Condron points out. These events would have been abrupt and short-lived, probably less than a year, he notes.

“This new research shows that much of the meltwater from the Greenland ice sheet may be redistributed by narrow coastal currents and circulate through subtropical regions prior to reaching the subpolar ocean. It’s a more complicated picture than we believed before,” Condron says. He and Hill say that future research on mechanisms of abrupt climate change should take into account coastal boundary currents in redistributing ice sheet runoff and subpolar fresh water.