Alpine Fault study shows new evidence for regular magnitude 8 earthquakes

University of Nevada - Reno seismologist Glenn Biasi spent eight days in the dense forests on the western side of the Southern Alps on the South Island of New Zealand to study the Alpine Fault, among the world's longest, straightest and fastest moving plate boundary faults. Photo courtesy University of Nevada, Reno. -  Photo courtesy University of Nevada, Reno.
University of Nevada – Reno seismologist Glenn Biasi spent eight days in the dense forests on the western side of the Southern Alps on the South Island of New Zealand to study the Alpine Fault, among the world’s longest, straightest and fastest moving plate boundary faults. Photo courtesy University of Nevada, Reno. – Photo courtesy University of Nevada, Reno.

A new study published in the prestigious journal Science, co-authored by University of Nevada, Reno’s Glenn Biasi and colleagues at GNS Science in New Zealand, finds that very large earthquakes have been occurring relatively regularly on the Alpine Fault along the southwest coastline of New Zealand for at least 8,000 years.

The Alpine Fault is the most hazardous fault on the South Island of New Zealand, and about 80 miles northwest of the South Island’s main city of Christchurch.

The team developed evidence for 22 earthquakes at the Hokuri Creek site, which, with two additional from nearby, led to the longest continuous earthquake record in the world for a major plate boundary fault. The team established that the Alpine Fault causes, on average, earthquakes of around a magnitude 8 every 330 years. Previous data put the intervals at about 485 years.

Relative motion of Australian and Pacific plates across the Alpine Fault averages almost an inch per year. This motion builds up, and then is released suddenly in large earthquakes. The 530-mile-long fault is among the longest, straightest and fastest moving plate boundary faults in the world. More than 23 feet of potential slip has accumulated in the 295 years since the most recent event in A.D. 1717.

Biasi, working with the GNS Science team led by Kelvin Berryman, used paleoseismology to extend the known seismic record from 1000 years ago to 8,000 years ago. They estimated earthquake dates by combining radiocarbon dating leaves, small twigs and marsh plants with geologic and other field techniques.

“Our study sheds new light on the frequency and size of earthquakes on the Alpine Fault. Earthquakes have been relatively periodic, suggesting that this may be a more general property of simple plate boundary faults worldwide,” Biasi, of the Nevada Seismological Laboratory said. “By comparison, large earthquakes on California’s San Andreas Fault have been less regular in size and timing.”

“Knowing the average rate of earthquakes is useful, but is only part of the seismic hazard equation,” he said. “If they are random in time, then the hazard does not depend on how long it has been since the most recent event. Alpine Fault earthquakes are more regular in their timing, allowing us to use the time since the last earthquake to adjust the hazard estimate. We estimate the 50-year probability of a large Alpine fault earthquake to be about 27 percent.”

A magnitude 7.1 earthquake centered near Christchurch, the largest city in the South Island of New Zealand, caused extensive damage to buildings on Sept. 2, 2010, and no deaths. On Feb. 22, 2011, a triggered aftershock measuring magnitude 6.3, with one of the strongest ground motions ever recorded worldwide in an urban area, struck the city killing 185 people.

Hidden rift valley discovered beneath West Antarctica reveals new insight into ice loss

Scientists have discovered a one mile deep rift valley hidden beneath the ice in West Antarctica, which they believe is contributing to ice loss from this part of the continent.

Experts from the University of Aberdeen and British Antarctic Survey (BAS) made the discovery below Ferrigno Ice Stream, a region visited only once previously, over fifty years ago, in 1961, and one that is remote even by Antarctic standards.

Their findings, reported in Nature this week reveal that the ice-filled ancient rift basin is connected to the warming ocean which impacts upon contemporary ice flow and loss.

The West Antarctic Ice Sheet is of great scientific interest and societal importance as it is losing ice faster than any other part of Antarctica with some glaciers shrinking by more than one metre per year.

Understanding the processes that influence ice loss from West Antarctica is important to improve predictions of its future behaviour in a warming world.

Dr Robert Bingham, a glaciologist working in the University of Aberdeen’s School of Geosciences and lead author of the study, discovered the rift valley whilst undertaking three months of fieldwork with British Antarctic Survey in 2010.

Dr Bingham, whose fieldwork was funded by the UK’s Natural Environment Research Council (NERC) said: “Over the last 20 years we have used satellites to monitor ice losses from Antarctica, and we have witnessed consistent and substantial ice losses from around much of its coastline.

“For some of the glaciers, including Ferrigno Ice Stream, the losses are especially pronounced, and, to understand why, we needed to acquire data about conditions beneath the ice surface.”

The team gathered the data using an ice-penetrating radar system towed behind a skidoo driven across the relatively flat ice surface, over a distance of 1500 miles – greater than that between London and Athens.

Dr Bingham continued: “What we found is that lying beneath the ice there is a large valley, parts of which are approximately a mile deeper than the surrounding landscape.

“If you stripped away all of the ice here today, you’d see a feature every bit as dramatic as the huge rift valleys you see in Africa and in size as significant as the Grand Canyon.

“This is at odds with the flat ice surface that we were driving across – without these measurements we would never have known that it was there.

“What’s particularly important is that this spectacular valley aligns perfectly with the recordings of ice-surface lowering and ice loss that we have witnessed with satellite observations over this area for the last twenty years.”

Co-author and geophysicist Dr Fausto Ferraccioli from British Antarctic Survey added: “The newly discovered Ferrigno Rift is part of a huge and yet poorly understood rift system that lies beneath the West Antarctic Ice Sheet.

“What this study shows is that this ancient rift basin, and the others discovered under the ice that connect to the warming ocean can influence contemporary ice flow and may exacerbate ice losses by steering coastal changes further inland.”

Professor David Vaughan, from British Antarctic Survey leads Ice2sea, a major EU-funded FP7 research programme to improve projections of global and regional sea-level. He said, “Thinning ice in West Antarctica is currently contributing nearly 10 per cent of global sea level rise. It’s important to understand this hot spot of change so we can make more accurate predictions for future sea level rise.”

The research in Nature is part of the British Antarctic Survey Icesheets Programme, which examines the role of ice sheets in the Earth System, and the processes that control ice-sheet change. It monitors current change and sets this in context with the past allowing more accurate projections for increases in global sea level to be made.

An earthquake in a maze

The colored circles on the large map indicate the complex spatial rupture pattern as a function of time during the Sumatra earthquake in April 2012. The white star indicates the epicenter of the magnitude-8.6 mainshock. The area shaded in darker red in the inset indicates the location of the area of study. -  Caltech/Meng et al.
The colored circles on the large map indicate the complex spatial rupture pattern as a function of time during the Sumatra earthquake in April 2012. The white star indicates the epicenter of the magnitude-8.6 mainshock. The area shaded in darker red in the inset indicates the location of the area of study. – Caltech/Meng et al.

The powerful magnitude-8.6 earthquake that shook Sumatra on April 11, 2012, was a seismic standout for many reasons, not the least of which is that it was larger than scientists thought an earthquake of its type could ever be. Now, researchers from the California Institute of Technology (Caltech) report on their findings from the first high-resolution observations of the underwater temblor, they point out that the earthquake was also unusually complex-rupturing along multiple faults that lie at nearly right angles to one another, as though racing through a maze.

The new details provide fresh insights into the possibility of ruptures involving multiple faults occurring elsewhere-something that could be important for earthquake-hazard assessment along California’s San Andreas fault, which itself is made up of many different segments and is intersected by a number of other faults at right angles.

“Our results indicate that the earthquake rupture followed an exceptionally tortuous path, breaking multiple segments of a previously unrecognized network of perpendicular faults,” says Jean-Paul Ampuero, an assistant professor of seismology at Caltech and one of the authors of the report, which appears online today in Science Express. “This earthquake provided a rare opportunity to investigate the physics of such extreme events and to probe the mechanical properties of Earth’s materials deep beneath the oceans.”

Most mega-earthquakes occur at the boundaries between tectonic plates, as one plate sinks beneath another. The 2012 Sumatra earthquake is the largest earthquake ever documented that occurred away from such a boundary-a so-called intraplate quake. It is also the largest that has taken place on a strike-slip fault-the type of fault where the land on either side is pushing horizontally past the other.

The earthquake happened far offshore, beneath the Indian Ocean, where there are no geophysical monitoring sensors in place. Therefore, the researchers used ground-motion recordings gathered by networks of sensors in Europe and Japan, and an advanced source-imaging technique developed in Caltech’s Seismological Laboratory as well as the Tectonics Observatory to piece together a picture of the earthquake’s rupture process.

Lingsen Meng, the paper’s lead author and a graduate student in Ampuero’s group, explains that technique by comparing it with how, when standing in a room with your eyes closed, you can often still sense when someone speaking is walking across the room. “That’s because your ears measure the delays between arriving sounds,” Meng says. “Our technique uses a similar idea. We measure the delays between different seismic sensors that are recording the seismic movements at set locations.” Researchers can then use that information to determine the location of a rupture at different times during an earthquake. Recent developments of the method are akin to tracking multiple moving speakers in a cocktail party.

Using this technique, the researchers determined that the three-minute-long Sumatra earthquake involved at least three different fault planes, with a rupture propagating in both directions, jumping to a perpendicular fault plane, and then branching to another.

“Based on our previous understanding, you wouldn’t predict that the rupture would take these bends, which were almost right angles,” says Victor Tsai, an assistant professor of geophysics at Caltech and a coauthor on the new paper.

The team also determined that the rupture reached unusual depths for this type of earthquake-diving as deep as 60 kilometers in places and delving beneath the Earth’s crust into the upper mantle. This is surprising given that, at such depths, pressure and temperature increase, making the rock more ductile and less apt to fail. It has therefore been thought that if a stress were applied to such rocks, they would not react as abruptly as more brittle materials in the crust would. However, given the maze-like rupture pattern of the earthquake, the researchers believe another mechanism might be in play.

“One possible explanation for the complicated rupture is there might have been reduced friction as a result of interactions between water and the deep oceanic rocks,” says Tsai. “And,” he says, “if there wasn’t much friction on these faults, then it’s possible that they would slip this way under certain stress conditions.”

Adding to the list of the quake’s surprising qualities, the researchers pinpointed the rupture to a region of the seafloor where seismologists had previously considered such large earthquakes unlikely based on the geometry of identified faults. When they compared the location they had determined using source-imaging with high-resolution sonar data of the topography of the seafloor, the team found that the earthquake did not involve what they call “the usual suspect faults.”

“This part of the oceanic plate has fracture zones and other structures inherited from when the seafloor formed here, over 50 million years ago,” says Joann Stock, professor of geology at Caltech and another coauthor on the paper. “However, surprisingly, this earthquake just ruptured across these features, as if the older structure didn’t matter at all.”

Meng emphasizes that it is important to learn such details from previous earthquakes in order to improve earthquake-hazard assessment. After all, he says, “If other earthquake ruptures are able to go this deep or to connect as many fault segments as this earthquake did, they might also be very large and cause significant damage.”

Croscat Volcano may have been the last volcanic eruption in Spain 13,000 years ago

The volcanic region of La Garrotxa, with some forty volcanic cones and some twenty lava flows, is considered to be the best conserved region in the Iberian Peninsula. It is also the youngest volcanic area. Although the approximate age of some of these volcanic constructions is known, one of the main problems when studying volcanoes is to pinpoint the chronology of each of their eruptions. Several geochronological studies have been conducted, but existing data is scarce and imprecise. With regard to the chronology of the Croscat Volcano, considered one of the most recent volcanic constructions, the latest dating was obtained with the technique of thermoluminescence conducted in the 1980s.

A group of scientists from the Universitat Autònoma de Barcelona, the University of Girona and the Catalan Institute of Human Palaeoecology and Social Evolution (IPHES), together with researchers from the Garrotxa Volcanoes Natural Park and the environmental sector firms Axial Geologia i Medi Ambient and Tosca, developed a programme to locate chronologically the final moment of volcanic eruptions in the region.

Researchers recently published the first results in an article in the journal Geologica Acta. The first volcano they worked on was the Croscat Volcano. Soil dating was carried out using the C-14 dating method – very precise and easy to conduct in many laboratories – with the organic material found on the surface of the earth right before the moment of eruption.

“The general idea is based on the hypothesis that if scientists could date the palaeosoil found right below the lava clay ejected by the volcano, they would have the dating of the moment before the eruption” explains Maria Saña, researcher at the UAB Department of Prehistory.

Scientists perforated the clay found in the region of Pla del Torn, a few metres to the northeast of the volcanic cone. Two tests were carried out, at 12 and 15 metres deep, which reached the base of the clay layer and the surface of the palaeosoil.

Pollinic analysis was conducted with the samples obtained from the surface of this pre-volcano level. This aided scientists in learning about the vegetation of the area in the moment before the Croscat Volcano erupted. Several 14C analyses were later made to determine the organic material contained in the samples.

The palynological analysis of the soil at the time of eruption, conducted by IPHES, revealed that the landscape of La Garrotxa was quite open, with Mediterranean meadows and steppes cotaining gramineae, asteraceae and artemisia. Oaks and holm oaks were also discovered, which indicates that temperatures were mild, a symptom of the beginning of the thawing period following the last Ice Age. The presence of riverside trees (elms, alders and willows), as well as aquatic herbs and plants (cyperaceae, bulrush, alisma, etc.) are proof that during that period there was also an increase in rainfalls.

Dating has shown that the age of the upper part of the soil dates back approximately between 13,270 and 13,040 years and that immediately after that moment the eruption of the Croscat Volcano took place.

Fools’ gold found to regulate oxygen

As sulfur cycles through Earth’s atmosphere, oceans and land, it undergoes chemical changes that are often coupled to changes in other such elements as carbon and oxygen. Although this affects the concentration of free oxygen, sulfur has traditionally been portrayed as a secondary factor in regulating atmospheric oxygen, with most of the heavy lifting done by carbon. However, new findings that appeared this week in Science suggest that sulfur’s role may have been underestimated.

Drs. Itay Halevy of the Weizmann Institute’s Environmental Science and Energy Research Department (Faculty of Chemistry), Shanan Peters of the University of Wisconsin and Woodward Fischer of the California Institute of Technology, were interested in better understanding the global sulfur cycle over the last 550 million years – roughly the period in which oxygen has been at its present atmospheric level of around 20%. They used a database developed and maintained by Peters at the University of Wisconsin, called Macrostrat, which contains detailed information on thousands of rock units in North America and beyond.

The researchers used the database to trace one of the ways in which sulfur exits ocean water into the underlying sediments – the formation of so-called sulfate evaporite minerals. These sulfur-bearing minerals, such as gypsum, settle to the bottom of shallow seas as seawater evaporates. The team found that the formation and burial of sulfate evaporites were highly variable over the last 550 million years, due to changes in shallow sea area, the latitude of ancient continents and sea level. More surprising to Halevy and colleagues was the discovery that only a relatively small fraction of the sulfur cycling through the oceans has exited seawater in this way. Their research showed that the formation and burial of a second sulfur-bearing mineral – pyrite – has apparently been much more important.

Pyrite is an iron-sulfur mineral (also known as fools’ gold), which forms when microbes in seafloor sediments use the sulfur dissolved in seawater to digest organic matter. The microbes take up sulfur in the form of sulfate (bound to four oxygen atoms) and release it as sulfide (with no oxygen). Oxygen is released during this process, thus making it a source of oxygen in the air. But because this part of the sulfur cycle was thought be minor in comparison to sulfate evaporite burial, (which does not release oxygen) its effect on oxygen levels was also thought to be unimportant.

In testing various theoretical models of the sulfur cycle against the Macrostrat data, the team realized that the production and burial of pyrite has been much more significant than previously thought, accounting for more than 80% of all sulfur removed from the ocean (rather than the 30-40% in prior estimates). As opposed to the variability they saw for sulfate evaporite burial, pyrite burial has been relatively stable throughout the period. The analysis also revealed that most of the sulfur entering the ocean washed in from the weathering of pyrite exposed on land. In other words, there is a balance between pyrite formation and burial, which releases oxygen, and the weathering of pyrite on land, which consumes it. The implication of these findings is that the sulfur cycle regulates the atmospheric concentration of oxygen more strongly than previously appreciated.

Return to the Japan Trench

This shows the researchers running the sensor array into tubing. -  JAMSTEC/IODP, photo taken by Jim Mori
This shows the researchers running the sensor array into tubing. – JAMSTEC/IODP, photo taken by Jim Mori

On July 16, 2012, Chikyu, operations in the second part of the Integrated Ocean Drilling Program (IODP) Japan Trench Fast Drilling Project (JFAST), achieved another objective by installing temperature sensors across the plate boundary where the science team infers the fault slipped during the 2011 Tohoku Earthquake.

The scientists got on board the state-of-the-art scientific drilling vessel Chikyu to meet the challenge of measuring temperature directly from the fault zone. The recorded data should help to understand why such large earthquake slip occurred that generated the devastating Tsunami.

This is the first time to measure the frictional heat produced by the fault slip of a great subduction zone earthquake, remarked the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) in their press release about completion of the project issued on July 19, 2012. JAMSTEC is the IODP Implementing Organization for Japan that operates the Chikyu.

“During the original expedition last April and May, it seemed at almost every step of the way there was some problem or delay,” said Prof. James Mori of Kyoto University, Co-Chief Scientist who led this expedition.

There were many steps in the deployment of the observatory; preparation of the underwater camera system, running the long pipe to the ocean floor, setting the wellhead, borehole re-entries, underwater instrument releases, borehole drilling, casing installation and temperature instrument programming.

“There were difficult technical aspects for the borehole which reached 855 meters below the seafloor in nearly 7000 meters of water. Chikyu, or any other research ship, has never drilled in such deep water, so there were many engineering challenges,” Mori continued.

JFAST had two main objectives: to collect geological samples to analyze the physical properties of the fault zone and to measure the temperature near the fault to understand the frictional heat produced by fault slip.

During the original expedition of over 50 days, Chikyu drilled two boreholes and achieved the first goal to collect geological samples and other geophysical data to analyze the physical properties of the fault zone. The deepest hole set a new record depth for ocean scientific drilling with a total of 7768.5 m measured from the rig floor (7740 m below sea level).

However, during that expedition the temperature sensors were not deployed because of many delays caused by technical problems and bad weather.

Prof. Frederick Chester of Texas A&M University, geologist and the other Co-Chief Scientist of the project continues that “fault temperature rises rapidly from frictional heat when earthquakes occur but the heat is absorbed by the surrounding strata over a period of several years, and the temperature returns to the original level, so it is vital to measure the temperature as soon as possible after the earthquake.”

“We were very fortunate on this project that additional expedition days were provided so that we had the opportunity to try again for the observatory deployment,” Mori expressed. In fact, this really was the last chance to place the observatory before the temperature signal would become too small to measure.

“Detailed knowledge of the actual drilling conditions and instrument performance, which were gained by drilling engineers from experience during the first expedition, contributed immensely to the success the second time,” he continued in presenting an overview of the projects.

JFAST II took place onboard the scientific drilling vessel Chikyu, and the expedition was completed on July 19.

“The deployment of the temperature sensors has been an exciting technical accomplishment, but the real scientific results come when we see the recorded data,” Mori added.

“We already have a plan to return to the site this autumn or later to extract the instrument string from the borehole, using a remotely operated vehicle (ROV) in the very deep water.” Recovery of the instrument string will be the final major challenge in an attempt to better understand the dynamics of seismic slip.

The IODP scientists represent wide-ranging disciplines of the Earth and life science, including geology, geochemistry, paleomagnetism, sedimentology, geophysics and microbiology, and are contributing their expertise so that this research may yield new understanding of the mechanisms of the huge earthquake and tsunami that devastated eastern Japan in 2011.

X-rays illuminate the origin of volcanic hotspots

This is an illustration showing how the mantle plumes can be emitted from the core-mantle boundary region to reach the Earth's crust. Due to the lateral displacement of the tectonic plates at the surface, the mantle plumes can create a series of aligned hot spot volcanoes. A mid ocean ridge and a subducted plate are also shown. -  ESRF/Denis Andrault/Henri Samuel
This is an illustration showing how the mantle plumes can be emitted from the core-mantle boundary region to reach the Earth’s crust. Due to the lateral displacement of the tectonic plates at the surface, the mantle plumes can create a series of aligned hot spot volcanoes. A mid ocean ridge and a subducted plate are also shown. – ESRF/Denis Andrault/Henri Samuel

Scientists have recreated the extreme conditions at the boundary between Earth’s core and its mantle, 2,900 km beneath the surface. Using the world’s most brilliant beam of X-rays, they probed speck-sized samples of rock at very high temperature and pressure to show for the first time that partially molten rock under these conditions is buoyant and should segregate towards the Earth’s surface. This observation is a strong evidence for the theory that volcanic hotspots like the Hawaiian Islands originate from mantle plumes generated at the Earth’s core-mantle boundary. The results are published in Nature dated 19 July 2012.

The group of scientists was led by Denis Andrault from the Laboratoire Magmas et Volcans of University Blaise Pascal in Clermont, and included scientists from the CNRS in Clermont and the European Synchrotron Radiation Facility (ESRF) in Grenoble, France.

Most volcanoes are situated where continental plates are pushed or pulled against each other. Here, the continental crust is weakened, and the magma can break through to the surface. The Pacific “Ring of Fire”, for example, exhibits such plate movements, resulting in powerful Earthquakes and numerous active volcanoes.

Volcanic hotspots are of a completely different nature because most of them are far away from plate boundaries. The Hawaiian Islands, for example, are a chain of volcanoes thought to have their origin in a mysterious hot spot beneath the Pacific ocean floor. Every island in the chain starts as an active volcano fed by the hot spot that eventually rises above the ocean surface. As plate tectonics move the volcano away from the hotspot, it becomes extinct. The hot spot will in the meantime create another volcano: the next island in the chain. The Hawaiian Islands are one of many examples of this process, like the Canary Islands, La Réunion or the Azores.

The nature of the hot-spot source and its location in the mantle have remained elusive to the present day. One explanation is narrow streams of magma conveyed to the Earth’s surface from the boundary between the Earth’s core of liquid iron and the solid mantle of silicate rock. Whether the lowermost mantle expels such streams of magma called mantle plumes is one of today’s major controversies among geologists.

What material can be stored at the core-mantle boundary and become sufficiently light to rise through 2900 km of thick solid mantle? This was the question Denis Andrault and his colleagues addressed when they set out to recreate in a laboratory the conditions found at the core-mantle boundary. They compressed tiny pieces of rock, the size of a speck of dust and ten times thinner than a human hair, between the tips of two conical diamonds to a pressure of more than one million bar. A laser beam then heated these samples to temperatures between 3000 and 4000 degrees Celsius, which scientists believe is representative of the 200km-thick core-mantle boundary. The samples are extremely small compared to the natural processes occurring in the Earth. However, the melting processes are very well reproduced experimentally. Therefore, the observations can be confidently transferred from micron scale in the experiments to kilometer scale in the deep mantle.

Beams of X-rays at the ESRF, focused to a diameter of one 1000th of a millimetre, were used to map these samples and identify where the solid rock had melted. “Obviously, these tiny samples produce weak interaction signals, and this is why it is important to have the most brilliant X-ray beams for this type of experiments, says Mohammed Mezouar, the scientist responsible for the high-pressure beamline ID27 at the ESRF.

Once regions with molten rock had been identified, another X-ray technique was used at the ESRF to compare the chemical compositions of previously molten and solid parts. “It is the iron content which is decisive for the density of molten rock at the core-mantle boundary. Its accurate knowledge allowed us to determine that molten rock under these conditions is actually lighter than solid,” says Denis Andrault.

Gravity makes the light liquid rock from a hotspot move slowly upwards like a bubble in water until it reaches the surface where the magma plume will form a volcano. The hotspots of liquid occur in the relatively thin boundary region between the solid lower mantle and the liquid outer core of the Earth where the temperature rises over a distance of just 200 kilometres from 3000 to 4000 degrees. This steep rise is caused by the vicinity of the much hotter core and induces a partial melting of the rocks.

The results of the experiment are also of great significance for the understanding of the early history of the Earth, as they provide an explanation why many chemical elements playing a key role in our daily life gradually accumulated from the Earth’s inside to its thin crust, close to the surface.

“We know less about the Earth’s mantle than about the surface of Mars. It is impossible to drill a hole of even 100 kilometres into the Earth, so we have to recreate it in the laboratory. This is important knowledge, because active hot spot volcanoes like those in Iceland can be dangerous and disruptive for the daily lives of people far away”, concludes Denis Andrault.

Glacier break creates ice island 2 times the size of Manhattan

Petermann Glacier connects the Greenland ice sheet to the Arctic Ocean. The vast flat expanse stretching into the background is Petermann Glacier, well over one-third of which has now broken off. -  Photo courtesy of professor Andreas Muenchow, University of Delaware
Petermann Glacier connects the Greenland ice sheet to the Arctic Ocean. The vast flat expanse stretching into the background is Petermann Glacier, well over one-third of which has now broken off. – Photo courtesy of professor Andreas Muenchow, University of Delaware

An ice island twice the size of Manhattan has broken off from Greenland’s Petermann Glacier, according to researchers at the University of Delaware and the Canadian Ice Service. The Petermann Glacier is one of the two largest glaciers left in Greenland connecting the great Greenland ice sheet with the ocean via a floating ice shelf.

Andreas Muenchow, associate professor of physical ocean science and engineering in UD’s College of Earth, Ocean, and Environment, reports the calving on July 16, 2012, in his “Icy Seas” blog. Muenchow credits Trudy Wohleben of the Canadian Ice Service for first noticing the fracture.

The discovery was confirmed by reprocessing data taken by MODIS, the Moderate Resolution Imaging Spectroradiometer aboard NASA’s Terra and Aqua satellites.

At 46 square miles (120 square km), this latest ice island is about half the size of the mega-calving that occurred from the same glacier two years ago. The 2010 chunk, also reported by Muenchow, was four times the size of Manhattan.

“While the size is not as spectacular as it was in 2010, the fact that it follows so closely to the 2010 event brings the glacier’s terminus to a location where it has not been for at least 150 years,” Muenchow says.

“The Greenland ice sheet as a whole is shrinking, melting and reducing in size as the result of globally changing air and ocean temperatures and associated changes in circulation patterns in both the ocean and atmosphere,” he notes.

Muenchow points out that the air around northern Greenland and Ellesmere Island has warmed by about 0.11 +/- 0.025 degrees Celsius per year since 1987.

“Northwest Greenland and northeast Canada are warming more than five times faster than the rest of the world,” Muenchow says, “but the observed warming is not proof that the diminishing ice shelf is caused by this, because air temperatures have little effect on this glacier; ocean temperatures do, and our ocean temperature time series are only five to eight years long – too short to establish a robust warming signal.”

The ocean and sea ice observing array that Muenchow and his research team installed in 2003 with U.S. National Science Foundation support in Nares Strait, the deep channel between Greenland and Canada, has recorded data from 2003 to 2009.

The Canadian Coast Guard Ship Henry Larsen is scheduled to travel to Nares Strait and Petermann Fjord later this summer to recover moorings placed by UD in 2009. These mooring data, if recovered, will provide scientists with ocean current, temperature, salinity and ice thickness data at better than hourly intervals from 2009 through 2012. The period includes the passage of the 2010 ice island directly over the instruments.

According to Muenchow, this newest ice island will follow the path of the 2010 ice island, providing a slow-moving floating taxi for polar bears, seals and other marine life until it enters Nares Strait, the deep channel between northern Greenland and Canada, where it likely will get broken up.

“This is definitely déjà vu,” Muenchow says. “The first large pieces of the 2010 calving arrived last summer on the shores of Newfoundland, but there are still many large pieces scattered all along eastern Canada from Lancaster Sound in the high Arctic to Labrador to the south.”

Prior to 2010, the last time such a sizable ice island was born in the region was 50 years ago. In 1962, the Ward Hunt Ice Shelf, on the northern coast of Ellesmere Island in Nunavut, Canada, calved a 230-square-mile island.

To clean up the mine, let fungus reproduce

<IMG SRC="/Images/469108700.jpg" WIDTH="350" HEIGHT="350" BORDER="0" ALT="This colony of the fungus S. aciculosa shows manganese oxide deposits at the base of the reproductive bodies. Researchers have shown that superoxide transforms manganese into its environmentally useful mineral state. – Photo courtesy of Colleen Hansel”>
This colony of the fungus S. aciculosa shows manganese oxide deposits at the base of the reproductive bodies. Researchers have shown that superoxide transforms manganese into its environmentally useful mineral state. – Photo courtesy of Colleen Hansel

Harvard-led researchers have discovered that an Ascomycete fungus that is common in polluted water produces environmentally important minerals during asexual reproduction.

The key chemical in the process, superoxide, is a byproduct of fungal growth when the organism produces spores. Once released into the environment, superoxide reacts with the element manganese (Mn), producing a highly reactive mineral that aids in the cleanup of toxic metals, degrades carbon substrates, and controls the bioavailability of nutrients.

The results, which will inform a wide range of future studies in microbiology, environmental chemistry, developmental biology, and geobiology, were published online this week in the Proceedings of the National Academy of Sciences (PNAS).

Manganese is a versatile element, existing in multiple oxidation states and phases. Naturally occurring in the Earth’s crust, it plays essential roles in carbon sequestration, photosynthesis, and the transport and fate of nutrients and contaminants.

It can be an especially important reactant in polluted water, such as the runoff from coal mines. When the ion Mn(II) is converted to higher oxidized states, Mn(III) and Mn(IV), it forms a reactive mineral that is extremely useful in getting other pollutants-like arsenic, cadmium, and cobalt-under control and out of the water.

“If you can get manganese to oxidize, then it forms these really active minerals, manganese oxides, which are environmental sponges that will clean up the water,” explains principal investigator Colleen Hansel, a faculty associate and former associate professor of environmental microbiology at the Harvard School of Engineering and Applied Sciences (SEAS). She is currently an associate scientist at Woods Hole Oceanographic Institution. “A lot of coal mine drainage remediation relies on getting bacteria and fungi to oxidize manganese to make these minerals.”

“One problem with in situ remediation is that if you don’t know how and why processes are occurring, you can’t stimulate the organisms to do it. That’s been a big problem with the remediation of coal mine drainage sites. To stimulate microbial activity, the approach has been to provide complex carbon sources like corn cobs and straw and let the ‘bugs’ go to town, but it frequently doesn’t work.”

It turns out that the common fungus Stilbella aciculosa only produces the necessary ingredient, superoxide, during cell differentiation (an aspect of growth and development)-specifically, during the formation of asexual reproductive structures. The finding implies that adding excessive nutrients to polluted water may not necessarily contribute to remediation, unless it is designed to induce fungal reproduction.

For the fungus, superoxide appears to serve as cellular signal that moderates cell differentiation. The chemical’s subsequent role in oxidizing environmental manganese so rapidly and efficiently may just be a useful coincidence, beneficial to humans but of little consequence to the fungus.

All of the manganese-oxidizing bacteria and Ascomycete fungi known to date are heterotrophs; like humans, they eat carbon and breathe oxygen.

“They’re not eating manganese the way some organisms eat other metals like iron,” says Hansel. “This has been an enigma, in the field of metal biogeochemistry. According to evolutionary theory, organisms usually perform a process for a reason. But for decades no one has understood why or how bacteria and some groups of fungi (the Ascomycota) were oxidizing manganese, because they weren’t doing it to gain energy.”

Still, Hansel suggests that there may be more to the process than meets the eye.

“It looks like an accidental side reaction, but we don’t really know, because manganese oxides are very reactive and could therefore provide some indirect benefits to the organism,” she says. “The manganese oxides could, for instance, degrade recalcitrant carbon and thus feed the fungi new carbon sources that they can metabolize better. Maybe they are ‘purposely’ doing it. We want to address these biochemical questions and the evolutionary implications, as well as determine the larger relevance of superoxide-based metal cycling. How important is this process in terms of the biogeochemistry of other metals like iron and mercury? How significant is its impact on the ecology of microbial ecosystems?”

With co-authors Carolyn A. Zeiner (a graduate student at SEAS), Cara M. Santelli (a former postdoc, now at the Smithsonian National Museum of Natural History), and Samuel M. Webb (Stanford Synchrotron Radiation Lightsource), Hansel identified the biochemical mechanism that leads to the oxidation of manganese, including the class of enzymes (NADPH oxidases) that spur the process.

The team’s discovery that superoxide is the key player in fungal oxidation of manganese is especially exciting because some bacteria actually do it the same way, even using the same enzymes. The idea that prokaryotes and eukaryotes developed this homology raises intriguing questions in the history of evolution.

“We’re traveling down a whole new avenue in biogeochemistry,” says Hansel. “It’s exciting right now to be one of the people sitting in the front seat.”

Trigger for past rapid sea level rise discovered

The cause of rapid sea level rise in the past has been found by scientists at the University of Bristol using climate and ice sheet models.

The process, named ‘saddle-collapse’, was found to be the cause of two rapid sea level rise events: the Meltwater pulse 1a (MWP1a) around 14,600 years ago and the ‘8,200 year’ event. The research is published today in Nature.

Using a climate model, Dr Lauren Gregoire of Bristol’s School of Geographical Sciences and colleagues unearthed the series of events that led to saddle-collapse in which domes of ice over North America became separated, leading to rapid melting and the opening of an ice free corridor. Evidence of these events has been recorded in ocean cores and fossil coral reefs; however, to date the reason behind the events was unclear and widely debated.

Ice domes up to 3 km thick (three times the height of Snowdon), formed in regions of high snowfall and higher topography, such as the Rocky Mountains. Together with the saddles – lower valleys of ice between the domes – these made up the ice sheet.

Towards the end of the last ice age, at the time of mammoths and primitive humans, the climate naturally warmed. This started to melt ice at increasingly high elevations, eventually reaching and melting the saddle area between the ice domes. This triggered a vicious circle in which the melting saddle would lower, reach warmer altitudes and melt even more rapidly until the saddle had completely melted. In just 500 years, the saddles disappeared and only the ice domes remained.

The melted ice flowed into the oceans leading to rapid sea level rises of 9 m in 500 years during the Meltwater pulse 1a event 14,600 years ago and 2.5 m in the second event, 8,200 years ago.

Dr Gregoire, lead author of the study, said: “We didn’t expect our model to produce such a rapid sea level rise. We got really excited when we realised that the events we simulated corresponded to real events!”

In the model, Dr Gregoire found that saddle-collapse could explain a significant amount of the sea level rise observed: “The meltwater pulse produced by the saddle-collapse can explain more than half of the sea level jump observed around 14,600 years ago. The rest probably came from the progressive melting of ice sheets in Europe and Antarctica.”

This research not only identifies the process which caused the melting of the North American ice sheet and the trigger for rapid sea level rises in the past, but also increases our understanding of the nature of ice sheets and climate change, allowing further questions to be posed and, with more research, answered.

Research like this allows climate and ice sheet models to be tested against evidence from the real world. If climate models are able to reflect patterns observed in natural records our confidence in them increases. This is particularly relevant where the models are also used to investigate the effect of climate change on ice sheets in the future.