Greenland ice may exaggerate magnitude of 13,000-year-old deep freeze

Ice samples pulled from nearly a mile below the surface of Greenland glaciers have long served as a historical thermometer, adding temperature data to studies of the local conditions up to the Northern Hemisphere’s climate.

But the method — comparing the ratio of oxygen isotopes buried as snow fell over millennia — may not be such a straightforward indicator of air temperature.

“We don’t believe the ice cores can be interpreted purely as a signal of temperature,” says Anders Carlson, a University of Wisconsin-Madison geosciences professor. “You have to consider where the precipitation that formed the ice came from.”

According to a study published today by the Proceedings of the National Academy of Sciences, the Greenland ice core drifts notably from other records of Northern Hemisphere temperatures during the Younger Dryas, a period beginning nearly 13,000 years ago of cooling so abrupt it’s believed to be unmatched since.

Such periods of speedy cooling and warming are of special interest to climate scientists, who are teasing out the mechanisms of high-speed change to better understand and predict the changes occurring in our own time.

In the case of the Younger Dryas, average temperatures — based on the Greenland ice — plummeted as much as 15 degrees Celsius in a few centuries, and then shot back up nearly as much (over just decades) about 1,000 years later.

“In terms of temperature during the Younger Dryas, the only thing that looks like Greenland ice cores are Greenland ice cores,” Carlson says. “They are supposed to be iconic for the Northern Hemisphere, but we have four other records that do not agree with the Greenland ice cores for that time. That abrupt cooling is there, just not to the same degree.”

Working with UW-Madison climatologist Zhengyu Liu, collaborators at the National Center for Atmospheric Research and others, Carlson found their computer climate model breaking down on the Younger Dryas.

While it could reliably recreate temperatures in the Oldest Dryas — a similar cooling period about 18,000 years ago — they just couldn’t find a lever in the model that would simulate a Younger Dryas that matched the Greenland ice cores.

“You can totally turn off ocean circulation, have Arctic sea ice advance all the way across the North Atlantic, and you still will have a warmer climate during the Younger Dryas than the Oldest Dryas because of the carbon dioxide,” Carlson say.

By the time the Younger Dryas rolled around, there was more carbon dioxide in the air — about 50 parts per million more. The warming effects of that much CO2 overwhelmed the rest of the conditions that make the Oldest and Younger Dryas so alike, and demonstrates a heightened sensitivity for Arctic temperatures to rising greenhouse gases in the atmosphere.

The researchers zeroed in on the Northern Hemisphere’s temperature outlier, Greenland ice cores, and found that the conversion of oxygen isotope ratio to temperature typically used on the ice cores did not account for the sort of crash climate change occurring during the Younger Dryas. It assumes prevailing winds and jet streams and storm tracks are providing the moisture for Greenland precipitation from the Atlantic Ocean.

“The Laurentide ice sheet, which covered much of North America down into the northern United States, is getting smaller as the Younger Dryas approaches,” Carlson says. “That’s like taking out a mountain of ice three kilometers high. As that melts, it allows more Pacific Ocean moisture to cross the continent and hit the Greenland ice sheet.”

The two oceans have distinctly different ratios of oxygen isotopes, allowing for a different isotope ratio where the water falls as snow.

“We ran an oxygen isotope-enabled atmosphere model, so we could simulate what these ice cores are actually recording, and it can match the actual oxygen isotopes in the ice core even though the temperature doesn’t cool as much,” Carlson says. “That, to us, means the source of precipitation has changed in Greenland across the last deglatiation. And therefore that the strict interpretation of this iconic record as purely temperature of snowfall above this ice sheet is wrong.”

By the study’s findings, Greenland temperatures may not have cooled as significantly as climate headed into the Younger Dryas relative to the Oldest Dryas, because of the rise in atmospheric carbon dioxide that had occurred since the Oldest Dryas.

“You can say at the end of the Younger Dryas it warmed 10, plus or minus five, degrees Celsius. But what happened on this pathway into the event, you can’t see,” Carlson says.

It’s a fresh reminder from an ancient ice core that climate science is full of nuance, according to Carlson.

“Abrupt climate changes have happened, but they come with complex shifts in the way climate inputs like moisture moved around,” he says. “You can’t take one difference and interpret it solely as changes in temperature, and that’s what we’re seeing here in the Greenland ice cores.”

Mercury mineral evolution

Mineral evolution posits that Earth’s near-surface mineral diversity gradually increased through an array of chemical and biological processes. A dozen different species in interstellar dust particles that formed the solar system have evolved to more than 4500 species today. Previous work from Carnegie’s Bob Hazen demonstrated that up to two thirds of the known types of minerals on Earth can be directly or indirectly linked to biological activity. Now Hazen has turned his focus specifically on minerals containing the element mercury and their evolution on our planet as a result of geological and biological activity. His work, published in American Mineralogist, demonstrates that the creation of most minerals containing mercury is fundamentally linked to several episodes of supercontinent assembly over the last 3 billion years.

Mineral evolution is an approach to understanding Earth’s changing near-surface geochemistry. All chemical elements were present from the start of our Solar System, but at first they formed comparatively few minerals–perhaps no more than 500 different species in the first billion years. As time passed on the planet, novel combinations of elements led to new minerals. Although as much as 50% of the mercury that contributed to Earth’s accretion was lost to volatile chemical processing, 4.5 billion years of mineral evolution has led to at least 90 different mercury-containing minerals now found on Earth.

Hazen and his team examined the first-documented appearances of these 90 different mercury-containing minerals on Earth. They were able to correlate much of this new mineral creation with episodes of supercontinent formation–periods when most of Earth’s dry land converged into single landmasses. They found that of the 60 mercury-containing minerals that first appeared on Earth between 2.8 billion and 65 million years ago, 50 were created during three periods of supercontinent assembly. Their analysis suggests that the evolution of new mercury-containing minerals followed periods of continental collision and mineralization associated with mountain formation.

By contrast, far fewer types of mercury-containing minerals formed during periods when these supercontinents were stable, or when they were breaking apart. And in one striking exception to this trend, the billion-year-long interval that included the assembly of the Rodinian supercontinent (approximately 1.8 to 0.8 billion years ago) saw no mercury mineralization anywhere on Earth. Hazen and his colleagues speculate that this hiatus could have been due to a sulfide-rich ocean, which quickly reacted with any available mercury and thus prevented mercury from interacting chemically with other elements.

The role of biology is also critical in understanding the mineral evolution of mercury. Although mercury is rarely directly involved in biological processes–except in some rare bacteria–its interactions with oxygen came about entirely due to the appearance of the photosynthetic process, which plants and certain bacteria use to convert sunlight into chemical energy. Mercury also has a strong affinity for carbon-based compounds that come from biological material, such as coal, shale, petroleum, and natural gas products.

“Our work shows that in the case of mercury, evolution seems to have been driven by hydrothermal activity associated with continents colliding and forming mountain ranges, as well as by the drastic increase in oxygen caused by the rise of life on Earth,” Hazen said. “Future work will have to correlate specific mineral occurrences to specific tectonic events.”

Future work will also focus on the minerals of other elements to see how they differ and correlate with mercury’s mineral evolution, and to new strategies for locating as yet undiscovered deposits of critical resources.

“It’s important to keep honing in on the ways that minerals have evolved on our planet from their simple elemental origins to the vast array in existence today,” Hazen said.

Elephant seals help uncover slower-than-expected Antarctic melting

Don’t let the hobbling, wobbling, and blubber fool you into thinking elephant
seals are merely sluggish sun bathers. In fact, scientists are benefiting from these seals’
surprisingly lengthy migrations to determine critical information about Antarctic melting and
future sea level rise.

A team of scientists have drilled holes through an Antarctic ice shelf, the Fimbul Ice Shelf, to
gather the first direct measurements regarding melting of the shelf’s underside. A group of
elephant seals, outfitted with sensors that measure salinity, temperature, and depth sensors added
fundamental information to the scientists’ data set, which led the researchers to conclude that
parts of eastern Antarctica are melting at significantly lower rates than current models predict.

“It has been unclear, until now, how much warm deep water rises below the Fimbul Ice shelf,
and previous ocean models, focusing on the circulation below the Fimbul Ice Shelf, have
predicted temperatures and melt rates that are too high, suggesting a significant mass loss in this
region that is actually not taking place as fast as previously thought,” said lead author of the
study and PhD student at the Norwegian Polar Institute (NPI), Tore Hattermann.

The Fimbul Ice Shelf – located along eastern Antarctica in the Weddell Sea – is the sixth largest
of the forty-three ice shelves that dapple Antarctica’s perimeter. Both its size and proximity to
the Eastern Antarctic Ice Sheet – the largest ice sheet on Earth, which if it melted, could lead to
extreme changes in sea level – have made the Fimbul Ice Shelf an attractive object of study.

The team is the first to provide direct, observational evidence that the Fimbul Ice Shelf is melting
from underneath by three, equally important processes. Their results confirm a 20-year-old
theory about how ice shelves melt that, until now, was too complex to be further investigated
with models that had no direct observations for comparison. These processes likely apply to
other areas of Antarctica, primarily the eastern half because of its similar water and wind
circulation patterns, Hattermann said.

The scientists report their findings on June 22 in the journal Geophysical Research Letters, a
publication of the American Geophysical Union.

Using nearly 12 tons of equipment, the scientists drilled three holes of an average depth of 230
meters (820 feet) that were dispersed approximately 50-100 kilometers (31-62 miles) apart along
the shelf, which spans an area roughly twice the size of New Jersey. The location of each hole
was strategically chosen so that the various pathways by which water moves beneath the ice
shelf could be observed.

What the team observed was that during the summer, relatively warm surface waters are pushed
beneath the ice shelves by strong wind-driven currents. While this happens, another process
transports warm water deeper in the ocean towards the coast and below the ice.

Combining with those effects is a process inherent to the cold ocean waters: The freezing point
of water depends on its depth. The deeper the water, the lower its freezing point. Water of a
constant temperature will freeze on the surface but remain liquid (or melt, if it was already
frozen) at a given depth, like at the bottom of an ice shelf. Therefore, there is a slight but
continuous melting of the Fimbul Ice Shelf’s undersides due to this physical phenomenon.

To understand the extent to which these three processes interact and melt the ice shelf, scientists
needed a detailed record of annual water cycles and circulation around eastern Antarctica. Enter
nine male elephant seals that swam 1,600 kilometers (about 1,000 miles) from Bouvet Island
(written as Bouvetoya in Norwegian), in the middle of the Southern Ocean, to the outskirts of the
Fimbul Ice Shelf.

Hattermann and his team borrowed the “seal data” from biologists of the Norwegian Polar
Institute, who originally gathered the data during their Marine Mammal Exploration of the
Oceans Pole to Pole (MEOP) research project, part of the International Polar Year program.

“Nobody was expecting that the MEOP seals from Bouvetoya would swim straight to the
Antarctic and stay along the Fimbul Ice Shelf for the entire winter,” Hattermann said. “But, this
behavior certainly provided an impressive and unique data set.”

For nine consecutive months, the sensors atop the seals’ heads read the temperature and salinity
of the waters along the outskirts of the Fimbul Ice Shelf and recorded their changes over time. To
collect the same amount of continuous data from a ship would not only incur far greater cost but
would be almost impossible during the winter months due to dangerous ice buildup.

From the “seal data”, the scientists accumulated enough knowledge concerning the area’s water
circulation and how it changes over the seasons to construct the most complete picture of what
and how the Fimbul Ice Shelf is melting from the bottom up.

It turns out that past studies, which were based on computer models without any direct data for
comparison or guidance, overestimate the water temperatures and extent of melting beneath the
Fimbul Ice Shelf. This has led to the misconception, Hattermann said, that the ice shelf is losing
mass at a faster rate than it is gaining mass, leading to an overall loss of mass. The model results
were in contrast to the available data from satellite observations, which are supported by the new
measurements.

The team’s results show that water temperatures are far lower than computer models predicted,
which means that the Fimbul Ice Shelf is melting at a slower rate. Perhaps indicating that the
shelf is neither losing nor gaining mass at the moment because ice buildup from snowfall has
kept up with the rate of mass loss, Hattermann said.

“Our data shows what needs to be included in the next generation models, in order to be able to
do a good job in predicting future melt rates,” Hattermann said.

Because wind patterns and water cycles are similar for large parts of eastern Antarctica,
Hattermann said, his team’s results could help predict the next time when a section of the Fimbul
Ice Shelf, or other ice shelves along the eastern coast of Antarctica, may break off. Because ice
shelves are already submerged, their melting does not directly influence sea level rise. However,
the rate that ice shelves are melting is still crucial to this issue, he said.

“Ice shelves act as a mechanical barrier for the grounded inland ice that continuously moves
from higher elevation towards the coast,” Hattermann said. “Once an ice shelf is removed, this
ice flow may speed up, which then increases the loss of grounded ice, causing the sea level rise.”

New deglaciation data opens door for earlier First Americans migration

A new study of lake sediment cores from Sanak Island in the western Gulf of Alaska suggests that deglaciation there from the last Ice Age took place as much as 1,500 to 2,000 years earlier than previously thought, opening the door for earlier coastal migration models for the Americas.

The Sanak Island Biocomplexity Project, funded by the National Science Foundation, also concluded that the maximum thickness of the ice sheet in the Sanak Island region during the last glacial maximum was 70 meters – or about half that previously projected – suggesting that deglaciation could have happened more rapidly than earlier models predicted.

Results of the study were just published in the professional journal, Quaternary Science Reviews.


The study, led by Nicole Misarti of Oregon State University, is important because it suggests that the possible coastal migration of people from Asia into North America and South America – popularly known as “First Americans” studies – could have begun as much as two millennia earlier than the generally accepted date of ice retreat in this area, which was 15,000 years before present.

Well-established archaeology sites at Monte Verde, Chile, and Huaca Prieta, Peru, date back 14,000 to 14,200 years ago, giving little time for expansion if humans had not come to the Americas until 15,000 years before present – as many models suggest.

The massive ice sheets that covered this part of the Earth during the last Ice Age would have prevented widespread migration into the Americas, most archaeologists believe.

“It is important to note that we did not find any archaeological evidence documenting earlier entrance into the continent,” said Misarti, a post-doctoral researcher in Oregon State’s College of Earth, Ocean, and Atmospheric Sciences. “But we did collect cores from widespread places on the island and determined the lake’s age of origin based on 22 radiocarbon dates that clearly document that the retreat of the Alaska Peninsula Glacier Complex was earlier than previously thought.”

“Glaciers would have retreated sufficiently so as to not hinder the movement of humans along the southern edge of the Bering land bridge as early as almost 17,000 years ago,” added Misarti, who recently accepted a faculty position at the University of Alaska at Fairbanks.

Interestingly, the study began as a way to examine the abundance of ancient salmon runs in the region. As the researchers began examining core samples from Sanak Island lakes looking for evidence of salmon remains, however, they began getting radiocarbon dates much earlier than they had expected. These dates were based on the organic material in the sediments, which was from terrestrial plant macrofossils indicating the region was ice-free earlier than believed.

The researchers were surprised to find the lakes ranged in age from 16,500 to 17,000 years ago.

A third factor influencing the find came from pollen, Misarti said.

“We found a full contingent of pollen that indicated dry tundra vegetation by 16,300 years ago,” she said. “That would have been a viable landscape for people to survive on, or move through. It wasn’t just bare ice and rock.”

The Sanak Island site is remote, about 700 miles from Anchorage, Alaska, and about 40 miles from the coast of the western Alaska Peninsula, where the ice sheets may have been thicker and longer lasting, Misarti pointed out. “The region wasn’t one big glacial complex,” she said. “The ice was thinner and the glaciers retreated earlier.”

Other studies have shown that warmer sea surface temperatures may have preceded the early retreat of the Alaska Peninsula Glacier Complex (APGC), which may have supported productive coastal ecosystems.

Wrote the researchers in their article: “While not proving that first Americans migrated along this corridor, these latest data from Sanak Island show that human migration across this portion of the coastal landscape was unimpeded by the APGC after 17 (thousand years before present), with a viable terrestrial landscape in place by 16.3 (thousand years before present), well before the earliest accepted sites in the Americas were inhabited.”

Silicon strip detectors look for the heaviest element

Silicon alpha-particle detectors developed and built at the Institute of Electron Technology (ITE) in Warsaw, Poland, in cooperation with the Institut für Radiochemie – Technische Universität München (IR TUM) in Munich are currently being used in an international experiment aimed at producing and detecting atomic nuclei of the as yet undiscovered element 120. The experiment, conducted at the Centre for Heavy Ion Research (GSI Helmholtzzentrum für Schwerionenforschung GmbH) in Darmstadt, began a few weeks ago and will continue until the end of the year.

The semiconductor devices designed to detect alpha particles (as well as beta particles and protons) were developed from the ground up in Warsaw by a team of engineers from ITE, and are protected by patents. The devices earned international acclaim and are used in leading nuclear research centres, including the GSI centre in Darmstadt and the Joint Institute for Nuclear Research in Dubna. They contributed, among others, to the discovery of heavy atomic nuclei, including isotope 283 of element 112 (copernicium, Cn) in Dubna, and isotopes 270, 271 and 277 of element 108 (hassium, Hs) in Darmstadt. In 2009 they made it possible to observe a record number of thirteen nuclei of isotopes 288 and 289 of element 114 (flerovium) during a single experiment in Darmstadt. The devices played a crucial role in the experimental confirmation of the island of stability theory. The results of the experiments conducted using the ITE detectors are the subject of highly cited publications in prestigious scientific journals, including “Nature”. The research described in these publications led the International Union of Pure and Applied Chemistry and the International Union of Pure and Applied Physics to officially recognize and add to the periodic table elements 112 and 114.

“In contrast to the majority of semiconductor devices, our detectors have a very large p-n junction area, a thick electrically active area and a high radiation resistance. Many complex technical problems had to be solved in order to build devices with optimum operating parameters,” says Maciej Węgrzecki, MSc, Eng, head of the team developing silicon detectors at ITE.

Detectors from ITE are currently being used in an experiment employing the TASCA (TransActinide Separator and Chemistry Apparatus) ion separator at the Centre for Heavy Ion Research in Darmstadt. The aim of the experiment is to gain an understanding of the physical and chemical properties of elements with atomic number greater than 104, and to produce, for the first time, nuclei of the element with atomic number 120.

Alpha-particle detectors built at ITE are manufactured on silicon plates with specially crafted diffusion regions. When a particle passes through a detector, it creates electron-hole pairs in the semiconductor material, which induces electrical current. State-of-the-art detectors from ITE are double-sided: they have two parallel detecting surfaces, each covered with 16 semiconductor strips. The strips on a one surface are perpendicular to the strips on the other surface. By measuring signals from the strips on both surfaces, it is possible to accurately determine where the particle passed through the detector.

The Institute of Electron Technology supplied the 16-strip silicon detectors to the GSI centre in Darmstadt in January. At the centre they were installed in the Focal Plane Detector Box (FPDB), which forms part of the TASCA ion separator. Eight double-sided strip detectors and two single-sided 8-strip detectors were mounted on FPDB sides.

Understanding faults and volcanics, plus life inside a rock

Orange-like rocks in Utah with iron-oxide rinds and fossilized bacteria inside that are believed to have eaten the interior rock material, plus noted similarities to “bacterial meal” ingredients and rock types on Mars; fine-tuning the prediction of volcanic hazards and warning systems for both high population zones and at Tristan da Cunha, home to the most remote population on Earth; news from SAFOD; and discovery in Germany of the world’s oldest known mosses.


Biosignatures link microorganisms to iron mineralization in a paleoaquifer

Karrie A. Weber et al., School of Biological Sciences, University of Nebraska, Lincoln, Nebraska 68588, USA. Posted online 15 June 2012; doi: 10.1130/G33062.1.

Iron oxide rocks in an ancient aquifer give scientists clues about where to look for past life on Mars and other planets, including Earth. Scientists at the University of Nebraska-Lincoln and University of Western Australia have been studying rocks in Utah that resemble an orange with an iron cemented rind and an interior that consists of glued sand. These rocks formed millions of years ago in an ancient aquifer. Using microscopic methods, Karrie Weber and colleagues found tiny fossilized bacteria inside of these rocks, along with evidence corroborating that the bacteria were once alive inside the rock. Weber and colleagues think that these bacteria “ate” the iron in the rock to form the iron oxide mineral-rich rind. All of the ingredients for a bacterial meal exist on Mars and other areas on Earth. This has led the Weber and colleagues to theorize that similar iron-rich rocks could have been formed by bacteria and could still be forming today. The scientists are continuing to study how bacteria form rocks below Earth’s surface so to better understand the conditions that support life and the signatures that life leaves behind. This research is supported by the University of Nebraska Research Office and Nebraska Tobacco Settlement Fund.


Relationship between dike and volcanic conduit distribution in a highly eroded monogenetic volcanic field: San Rafael, Utah, USA

Koji Kiyosugi et al., Dept. of Geology, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida 33620, USA. Posted online 15 June 2012; doi: 10.1130/G33074.1.

Cities like Auckland (NZ) and Mexico City are located within active volcanic fields, where new volcanoes will likely form in the future, creating a wide range of hazards. Where will these volcanoes form and what warning will residents have of impending eruptions? The geologic record preserved in old volcanic fields helps address this question. Koji Kiyosugi and colleagues studied magmatic system below an extinct volcanic field: the San Rafael subvolcanic field in Utah, USA. Below volcanoes, intrusive magma bodies formed before and during volcanic eruptions create vertical pipes (conduits) and vertical and horizontal sheets (dikes and sills, respectively). It is possible to observe these features of the magmatic system in great detail in this eroded volcanic field. Kiyosugi and colleagues mapped 63 conduits, ~2000 dike segments, and 12 sill complexes in the San Rafael. They find that the distribution of volcano conduits matches the major features of dike distribution, including development of clusters and distribution of outliers. These statistical models are then applied to the distributions of volcanoes in several recently active volcanic fields, where the distribution of intrusive magma bodies must be inferred from very sparse data. This comparison supports the use of statistical models in probabilistic hazard assessment for distributed volcanism.


Tristan da Cunha: Constraining eruptive behavior using the 40Ar/39Ar dating technique

Anna Hicks et al., Dept. of Environmental Sciences, University of East Anglia, Norwich Research Park, Norwich, Norfolk NR4 7TJ, UK. Posted online 15 June 2012; doi: 10.1130/G33059.1.

Tristan da Cunha (South Atlantic) is an active volcano and home to the most remote population in the world. The volcano last erupted in 1961, forcing the temporary evacuation of all 261 islanders. In an attempt to constrain eruptive behavior and better anticipate likely future activity, new 40Ar/39Ar ages were measured on 15 rock samples, carefully selected to reflect possible temporal correlations between eruptive style, composition, or vent location. All sample sites were precisely dated, including a very young deposit (3,000 plus or minus 1,000 years old). Results revealed no spatio-temporal pattern to activity at parasitic cones and recent volcanism from these eruptive centers varies in style, volume, and composition with time. Timing of a large-scale sector collapse was constrained to a 14,000-year window, and ages showed that the northern sector of the edifice was built very rapidly. It seems likely that the entire edifice was constructed piecemeal and has a far more complex evolution that previously assumed. Of particular significance to hazard assessment is the discovery that the summit was contemporaneously active with recent activity on the flanks and inhabited low lying coastal strips. The results present significant uncertainty in terms of anticipating future eruptive scenarios, and reflect the necessity for effective risk reduction measures on Tristan.


Bubble geobarometry: A record of pressure changes, degassing, and regassing at Mono Craters, California

James M. Watkins et al., Dept. of Earth and Planetary Science, University of California, Berkeley, California 94720-4767, USA. Posted online 15 June 2012; doi: 10.1130/G33027.1.

Obsidian, natural volcanic glass, is one of the most recognizable rocks on Earth’s surface. Obsidian exhibits a wide range in textures that record volcanic processes. For example, flow bands in obsidian and healed fractures provide field evidence that lava can break and then heal (like silly putty) in volcanic feeder systems. The orientation of bubbles and microscopic crystals can be used to infer obsidian flow dynamics and the timing and rates of crystallization. In this study, James M. Watkins and colleagues use new measurements on bubbles in obsidian to infer the pressure history of rising magma. Unlike bubbles that grow in an open can of soda, bubbles in magma can both grow and shrink as they rise toward Earth’s surface. The study shows, for the first time, that the glass around bubbles preserves a record of physical changes in the magma feeder system prior to eruption. The measurements thus offer a new probe for inferring volcanic processes that are inaccessible to direct observation


Frictional properties and sliding stability of the San Andreas fault from deep drill core

B.M. Carpenter et al., Dept. of Geosciences and Energy Institute Center for Geomechanics, Geofluids, and Geohazards, Pennsylvania State University, University Park, Pennsylvania 16802, USA. Posted online 15 June 2012; doi: 10.1130/G33007.1.

Experimental studies on samples collected from the actively slipping San Andreas Fault, as part of San Andreas Fault Observatory at Depth (SAFOD) drilling in central California, USA, have provided important new insights into the mechanics and slip behavior of the fault at depth. B.M. Carpenter and colleagues report, for the first time, on the frictional properties of intact fault rock samples recovered from seismogenic depths. Their results explain several fundamental and longstanding observations along the San Andreas fault, including (1) the inferred extreme mechanical weakness and creeping behavior of the active fault in central California; (2) the occurrence and observed stress drop of repeating micro-earthquakes on faults to the northeast of the actively creeping fault strand; and (3) highly localized fault weakness, as documented by an extraordinarily sharp transition from frictionally weak fault rock within the main creeping strand of the San Andreas fault to stronger wall rock more than a mile away.


Subsidence of the West Siberian Basin: Effects of a mantle plume impact

Peter J. Holt et al., Geospatial Research Ltd., Durham University, Durham DH1 3LE, UK. Posted online 15 June 2012; doi: 10.1130/G32885.1.

Comparison of computer modeling results with the observed subsidence patterns from the West Siberian Basin provides new insight into the origin of the Siberian Traps flood basalts and constrains the temperature, size, and depth of an impacting mantle plume head during and after the eruption of the Siberian Traps at the Permian-Triassic boundary (250 million years ago). Peter J. Holt and colleagues compare subsidence patterns from a one-dimensional model of conductive heat flow to observed subsidence calculated from studies of the sediments in the basin. This results in a best-fit scenario with a 50-km-thick initial plume head with a temperature of 1500 degrees Celsius situated 50 km below the surface, and an initial regional crustal thickness of 34 km, which is in agreement with published values. The observed subsidence and modeling results agree very well, including a 60-90-million-year delay between the eruption of the flood basalts and the first regional sedimentation. These results reemphasize the viability of a mantle plume origin for the Siberian Traps, provide important constraints on the dynamics of mantle plume heads, and suggest a thermal control for the subsidence of the West Siberian Basin.


The relationship between surface kinematics and deformation of the whole lithosphere

L. Flesch and R. Bendick, Dept. of Earth and Atmospheric Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, Indiana 47907-2051, USA. Posted online 15 June 2012; doi: 10.1130/G33269.1.

There has been a proliferation of geoscience research efforts over the past decade because of the new understanding of how the surface of the continents are moving using GPS surface observations. This data has been used either to asses forward numerical models of lithospheric or constrain inversions for the dynamics of continents to identify the forces driving the observed deformation. Such efforts inherently assume that information about dynamics is efficiently transferred from lithospheric depths to the surface. This is indisputably the case for oceanic lithosphere, but L. Flesch and R. Bendick show that it applies only in a limited subset of the plausible mechanical strength configurations for continents. Making such an assumption in other cases results in unreasonable conclusions about either the mechanical properties of the lithosphere or incorrectly complicated heterogeneous balance of forces.



Variability in the length of the sea ice season in the Middle Eocene Arctic

Catherine E. Stickley et al., Dept. of Geology, University of Tromsø, N-9037 Tromsø, Norway. Posted online 15 June 2012; doi: 10.1130/G32976.1.

Finely laminated marine sediments of middle Eocene age (about 45 million years old) are preserved along the Lomonosov Ridge in the central Arctic. These sediments comprise two main components: (1) those indicative of sea ice (fossil species of the delicate, sea ice-dwelling diatom Synedropsis spp.[siliceous microfossils]) and sea ice-rafted debris (sea ice-IRD); and (2) those indicative of open marine conditions (e.g., other diatom taxa and siliceous microfossil types). Their coexistence strongly implies seasonality, but to know with certainty, the annual flux cycle must be reconstructed. For the first time, Catherine E. Stickley and colleagues use a non-destructive technique to resolve and reconstruct seasonal-scale flux events from these sediments. They reveal discrete productivity-flux events at ultra-high (e.g., about 30 microns) resolution and show that seasonality is expressed at the submillimeter scale by successions of discrete mono-specific laminae and micro-lenses of Synedropsis species, of sea ice-IRD, and of open-water taxa. These findings indicate that first-year winter sea ice existed in the Arctic during the middle Eocene. A preliminary assessment of annual cycles shows that suborbital variability existed on the order of multi-decadal to centennial duration. Stickley and colleagues argue that this reflects variations in the sea ice season length. Past records at such time scales are especially important because they may reveal patterns of Earth system behavior of direct relevance to modern observations of Arctic change.


Oldest known mosses discovered in Mississippian (late Visean) strata of Germany

Maren Hübers and Hans Kerp, Forschungsstelle für Paläobotanik, Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität Münster, Schlossplatz 9,48143 Münster, Germany. Posted online 15 June 2012; doi: 10.1130/G33122.1.

Today bryophytes, with about 20,000 species of hornworts, liverworts, and mosses, are the most diverse group of non-vascular land plants. Mosses are important constituents of terrestrial ecosystems, from the tropics to the high latitudes. In many modern wetland ecosystems, mosses play a major role in nutrient cycling and water storage. Molecular clock data indicate that mosses appeared before the first vascular land plants, but their fossil record is extremely poor. Carboniferous wetland environments, with their unequaled accumulation of plant biomass, likely provided ideal habitats for mosses. Coal floras have been studied in great detail, but the fossil record of Carboniferous mosses is remarkably meager, though it should be noted that mosses are often difficult to recognize. Three types of mosses showing cellular preservation have now been identified from approx. 330 million-year-old rocks from eastern Germany. These are the oldest unequivocal mosses known to date, and even though the remains are small, they demonstrate that mosses formed part of Carboniferous ecosystems. The moss fossils were obtained from organic residues after whole-rock samples had been dissolved. This method, which is now rarely used for studying Carboniferous flora, may reveal that mosses were more widespread than commonly thought.


A detailed record of shallow hydrothermal fluid flow in the Sierra Nevada magmatic arc from low-delta-18O skarn garnets

Megan E. D’Errico et al., Dept. of Geology, Trinity University, San Antonio, Texas 78212, USA. Posted online 15 June 2012; doi: 10.1130/G33008.1.

Garnet from skarns exposed at Empire Mountain, Sierra Nevada (California, USA) batholith have variable delta-18O values, including the lowest known delta-18O values of skarn garnet in North America. Such values indicate that surface-derived meteoric water was a significant component of the fluid budget of the skarn-forming hydrothermal system, which developed in response to shallow emplacement (~3.3 km) of the 109 million year old quartz diorite of Empire Mountain. Brecciation in the skarns and alteration of the Empire Mountain pluton suggests that fracture-enhanced permeability was a critical control on the depth to which surface waters penetrated to form skarns and later alter the pluton. Compared to other Sierran systems, much greater volumes of skarn rock suggest an exceptionally vigorous hydrothermal system that saw unusually high levels of decarbonation reaction progress, likely a consequence of the magma intruding relatively cold wall rocks inboard of the main locus of magmatism in the Sierran arc at that time.


The influence of a mantle plume head on the dynamics of a retreating subduction zone

Peter G. Betts et al., School of Geosciences, Monash University, Clayton, VIC 3800, Australia. Posted online 15 June 2012; doi: 10.1130/G32909.1.

Earth subduction zones are where two geological plates of the outer Earth converge and the dense ocean crust sinks into the mantle. Subduction zones form an important component of mantle convection. Mantle plumes are hot buoyant material that rises from deep in the interior of the Earth and interact with the Earth’s crust. When plumes interact with ocean crust they can form large areas of buoyant ocean floor topography. Subduction zones can migrate backward and interact with mantle plumes, causing the subduction zone to change behavior. Peter G. Betts and colleagues modeled this geological situation and have discovered that subduction zone/plume interactions can cause massive geological damage at the edges of plates. The buoyant plume head hinders subduction and causes the subduction zone to migrate forward causing intense deformation in the adjacent geological plate. The subducting oceanic plate is also damaged and large tears can form allowing the plume to migrate across plate boundaries. The Yellowstone hotspot may be an ancient example of this process.

Soil moisture climate data record observed from space

This shows dry areas and moist areas - a map created from satellite data. -  ESA / Vienna University of Technology / Free University Amsterdam
This shows dry areas and moist areas – a map created from satellite data. – ESA / Vienna University of Technology / Free University Amsterdam

The future of the world’s climate is determined by various parameters, such as the density of clouds or the mass of the Antarctic ice sheet. One of these crucial climate parameters is soil moisture, which is hard to measure on a global scale. Now, the European Space Agency (ESA), in cooperation with the Vienna University of Technology (Institute of Photogrammetry and Remote Sensing) and the Free University of Amsterdam, is presenting a data set, containing global soil moisture data from 1978 to 2010. This was possible by extensive mathematical analysis of satellite data.

Watch a video of the data here:

Warmer Climate Changes Soil Moisture

Even though soil moisture makes up only about 0.001 % of the total water found on earth, it plays a crucial rule in the climate system. “The link between climate and soil moisture is still not well understood, because so far reliable long-term data has not been available”, says professor Wolfgang Wagner (Vienna University of Technology). One of the predicted consequences of global warming is that warming will lead to higher evaporation rates and hence soil drying in some regions. But drier soils themselves will heat up the air near the land surface. This positive feedback mechanism may thus act to increase the number of extreme heat waves similar to those experienced in Western Europe in 2003 and Russia in 2010. On the other hand, hot air can hold more water and lead to increased precipitation in some regions. “The effects of climate change vary from region to region”, says Wolfgang Werner, “this makes it all the more important to have reliable long-term data for the whole globe.”

Microwaves from Space

Soil moisture can be measured with satellites using microwave radiation. Unlike visible light, microwaves can penetrate clouds. Satellites can either measure the earths natural microwave radiation to calculate the local soil moisture (passive measurement) or the satellite sends out microwave pulses and measures how strongly the pulse is reflected by the surface (active measurement). Over the years, various satellites with different measurement methods have been used. “It is a great challenge to extract reliable soil moisture data from these very different datasets, spanning several decades”, says Wolfgang Wagner.

To address the current lack of long-term soil moisture data the European Space Agency (ESA) has been supporting the development of a global soil moisture data record derived by merging measurements acquired by a series of European and American satellites. ESA is now happy to announce that the release of the first soil moisture data record spanning the period 1978 to 2010. The soil moisture data record was generated by merging two soil moisture data sets, one derived from active microwave observations and the other from passive microwave observations. The active data set was generated by the Vienna University of Vienna (TU Wien) based on observations from the C-band scatterometers on board of ERS-1, ERS-2 and METOP-A; the passive data set was generated by the VU University Amsterdam in collaboration with NASA based on passive microwave observations.

Technological Challenges

The harmonization of these datasets aimed to take advantage of both microwave techniques, but still the challenges were significant. Amongst other issues, the potential influences of mission specifications, sensor degradation, drifts in calibration, and algorithmic changes had to be accounted for as accurately as possible. Also, it had to be guaranteed that the soil moisture data retrieved from the different active and passive microwave instruments are physically consistent. As this is the first release of such a product, not all caveats and limitations of the data are yet fully understood. It will therefore require the active cooperation of the remote sensing and climate modeling communities to jointly validate the satellite and model data, and advance the science in both fields along the way.

Studying soil to predict the future of earth’s atmosphere

BYU soil scientist Richard Gill studies the effects rising levels of CO2 have on soils. -  Jaren Wilkey/BYU
BYU soil scientist Richard Gill studies the effects rising levels of CO2 have on soils. – Jaren Wilkey/BYU

When it comes to understanding climate change, it’s all about the dirt.

A new study by researchers at BYU, Duke and the USDA finds that soil plays an important role in controlling the planet’s atmospheric future.

The researchers set out to find how intact ecosystems are responding to increased levels of carbon dioxide in the atmosphere. The earth’s current atmospheric carbon dioxide is 390 parts per million, up from 260 parts per million at the start of the industrial revolution, and will likely rise to more than 500 parts per million in the coming decades.

What they found, published in the current issue of Nature Climate Change, is that the interaction between plants and soils controls how ecosystems respond to rising levels of CO2 in the atmosphere.

“As we forecast what the future is going to look like, with the way we’ve changed the global atmosphere, often times we overlook soil,” said BYU biology professor Richard Gill, a coauthor on the study. “The soils matter enormously and the feedbacks that occur in the soil are ultimately going to control the atmosphere.”

The research shows that even in the absence of climate change, humans are impacting vital ecosystems as the composition of the earth’s atmosphere changes. They observed that changes in atmospheric CO2 caused changes in plant species composition and the availability of water and nitrogen.

Researchers worry that if the ability of plants and soils to absorb carbon becomes saturated over time then CO2 in the atmosphere will increase much more quickly than it has in the past.

“We don’t just have to be concerned about climate change, we have to be concerned about the other changes in atmospheric chemistry,” Gill said. “Globally we’re changing the earth’s atmosphere and we know that is going to influence the systems we depend on. To forecast those changes, you have to understand deeply what is happening in soils.”

The BYU-Duke team has been studying the effects of increased carbon dioxide in soils for the last 12 years.

Gill’s particular role in the ongoing research is to monitor and measure the changes in the nitrogen cycle and carbon dynamics due to atmospheric CO2. To do this, Gill brings soil samples from a Texas research site back to his BYU lab and does laboratory chemistry on the soil.

Naturally, when a plant dies the nitrogen in that plant is reabsorbed back into the soil. Gill is finding that increased CO2 may help plants grow well at first, but it causes the nitrogen to be tied up in “plant litter” and microbes that usually chew it up and release it back into the soil are struggling to do so.

“The big takeaway is that humanity is changing the earth’s atmosphere; we’ve increased atmospheric CO2 by almost 50 percent since the industrial revolution and these changes have cascading effects in both natural and managed systems,” Gill said. “Whether those are changes in how plants use water or changes in soil fertility, these are byproducts of the choices we make.”

Volcanic gases could deplete ozone layer

Giant volcanic eruptions in Nicaragua over the past 70,000 years could have injected enough gases into the atmosphere to temporarily thin the ozone layer, according to new research. And, if it happened today, a similar explosive eruption could do the same, releasing more than twice the amount of ozone-depleting halogen gases currently in stratosphere due to manmade emissions.

Bromine and chlorine are gases that “love to react – especially with ozone,” said Kirstin Krüger, a meteorologist with GEOMAR in Kiel, Germany. “If they reach the upper levels of the atmosphere, they have a high potential of depleting the ozone layer.”

New research by Krüger and her colleagues, which she presented today at a scientific conference in Selfoss, Iceland, combined a mixture of field work, geochemistry and existing atmospheric models to look at the previous Nicaraguan eruptions. And the scientists found that the eruptions were explosive enough to reach the stratosphere, and spewed out enough bromine and chlorine in those eruptions, to have an effect on the protective ozone layer. Krüger’s talk was at the American Geophysical Union’s Chapman Conference on Volcanism and the Atmosphere.

Steffen Kutterolf, a chemical volcanologist with GEOMAR and one of Krüger’s colleagues, tackled the question of how much gas was released during the eruptions. He analyzed gases that were trapped by minerals crystallizing in the magma chambers, and applied a novel method that involves using the high-energy radiation from the German Electron Synchrotron in Hamburg to detect trace elements, including bromine. From that, Kutterolf estimated the amount of gas within magma before the eruptions, as well as the gas content in the lava rocks post-eruption. The difference, combined with existing field data about the size of the eruption, allowed the scientists to calculate how much bromine and chlorine are released.

Previous studies have estimated that in large, explosive eruptions – the type that sends mushroom clouds of ash kilometers high – up to 25 percent of the halogens ejected can make it to the stratosphere. For this study, the research team used a more conservative estimate of 10 percent reaching the stratosphere, to calculate the potential ozone layer depletion.

Taking an average from 14 Nicaraguan eruptions, the scientists found bromine and chlorine concentrations in the stratosphere jumped to levels that are equivalent to 200 percent to 300 percent of the 2011 concentrations of those gases. The Upper Apoyo eruption 24,500 years ago, for example, released 120 megatons of chlorine and 600 kilotons of bromine into the stratosphere.

Volcanic sulfate aerosols alone can lead to an ozone increase – if chlorine levels are at low, pre-industrial levels, Krüger said. But bromine and chlorine are halogens, gases whose atoms have seven electrons in the outer ring. To reach a stable, eight-electron configuration, these atoms will rip electrons off of passing molecules, like ozone. So when an eruption also pumps bromine and chlorine levels into the stratosphere, the ozone-depleting properties of the gases together with aerosols is expected to thin the protective layer.

“As we have bromine and chlorine together, we believe that this can lead to substantial depletion,” she said. “And this is from one single eruption.”

Because the effects are in the stratosphere, where the volcanic gases can be carried across the globe, eruptions of tropical volcanoes could lead to ozone depletion over a large area, Krüger said, potentially even impacting the ozone over polar regions. However, that’s a question for future research to address. Some volcanic gases can last in the stratosphere up to six years, she added, although the most significant impacts from eruptions like Mount Pinatubo were within the first two years.

The next step in the research, Krüger said, is to investigate how much damage to the ozone layer the volcanic gases caused in the past – and what the damage could be from future volcanic eruptions in the active Central American region.

Undersea volcano gave off signals before eruption in 2011

A team of scientists that last year created waves by correctly forecasting the 2011 eruption of Axial Seamount years in advance now says that the undersea volcano located some 250 miles off the Oregon coast gave off clear signals hours before its impending eruption.

The researchers’ documentation of inflation of the undersea volcano from gradual magma intrusion over a period of years led to the long-term eruption forecast. But new analyses using data from underwater hydrophones also show an abrupt spike in seismic energy about 2.6 hours before the eruption started, which the scientists say could lead to short-term forecasting of undersea volcanoes in the future.

They also say that Axial could erupt again – as soon as 2018 – based on the cyclic pattern of ground deformation measurements from bottom pressure recorders.

Results of the research, which was funded by the National Science Foundation, the National Oceanic and Atmospheric Administration, and the Monterey Bay Aquarium Research Institute (MBARI), are being published this week in three separate articles in the journal Nature Geoscience.

Bill Chadwick, an Oregon State University geologist and lead author on one of the papers, said the link between seismicity, seafloor deformation and the intrusion of magma has never been demonstrated at a submarine volcano, and the multiple methods of observation provide fascinating new insights.

“Axial Seamount is unique in that it is one of the few places in the world where a long-term monitoring record exists at an undersea volcano – and we can now make sense of its patterns,” said Chadwick, who works out of Oregon State’s Hatfield Marine Science Center in Newport, Ore. “We’ve been studying the site for years and the uplift of the seafloor has been gradual and steady beginning in about 2000, two years after it last erupted.

“But the rate of inflation from magma went from gradual to rapid about 4-5 months before the eruption,” added Chadwick. “It expanded at roughly triple the rate, giving a clue that the next eruption was coming.”

Bob Dziak, an Oregon State University marine geologist, had previously deployed hydrophones on Axial that monitor sound waves for seismic activity. During a four-year period prior to the 2011 eruption, there was a gradual buildup in the number of small earthquakes (roughly magnitude 2.0), but little increase in the overall “seismic energy” resulting from those earthquakes.

That began to change a few hours before the April 6, 2011, eruption, said Dziak, who also is lead author on one of the Nature Geoscience articles.

“The hydrophones picked up the signal of literally thousands of small earthquakes within a few minutes, which we traced to magma rising from within the volcano and breaking through the crust,” Dziak said. “As the magma ascends, it forces its way through cracks and creates a burst of earthquake activity that intensifies as it gets closer to the surface.

“Using seismic analysis, we were able to clearly see how the magma ascends within the volcano about two hours before the eruption,” Dziak said. “Whether the seismic energy signal preceding the eruption is unique to Axial or may be replicated at other volcanoes isn’t yet clear – but it gives scientists an excellent base from which to begin.”

The researchers also used a one-of-a-kind robotic submersible to bounce sound waves off the seafloor from an altitude of 50 meters, mapping the topography of Axial Seamount both before and after the 2011 eruption at a one-meter horizontal resolution. These before-and-after surveys allowed geologists to clearly distinguish the 2011 lava flows from the many previous flows in the area.

MBARI researchers used three kinds of sonar to map the seafloor around Axial, and the detailed images show lava flows as thin as eight inches, and as thick as 450 feet.

“These autonomous underwater vehicle-generated maps allowed us, for the first time, to comprehensively map the thickness and extent of lava flows from a deep-ocean submarine in high resolution,” said David Caress, an MBARI engineer and lead author on one of the Nature Geoscience articles. “These new observations allow us to unambiguously differentiate between old and new lava flows, locate fissures from which these flows emerged, and identify fine-scale features formed as the lava flowed and cooled.”

The researchers also used shipboard sonar data to map a second, thicker lava flow about 30 kilometers south of the main flow – also a likely result of the 2011 eruption.

Knowing the events leading up to the eruption – and the extent of the lava flows – is important because over the next few years researchers will be installing many new instruments and underwater cables around Axial Seamount as part of the Ocean Observatories Initiative. These new instruments will greatly increase scientists’ ability to monitor the ocean and seafloor off of the Pacific Northwest.

“Now that we know some of the long-term and short-term signals that precede eruptions at Axial, we can monitor the seamount for accelerated seismicity and inflation,” said OSU’s Dziak. “The entire suite of instruments will be deployed as part of the Ocean Observatories Initiative in the next few years – including new sensors, samplers and cameras – and next time they will be able to catch the volcano in the act.”

The scientists also observed and documented newly formed hydrothermal vents with associated biological activity, Chadwick said.

“We saw snowblower vents that were spewing out nutrients so fast that the microbes were going crazy,” he pointed out. “Combining these biological observations with our knowledge of the ground deformation, seismicity and lava distribution from the 2011 eruption will further help us connect underwater volcanic activity with the life it supports.”

Scientists from Columbia University, the University of Washington, North Carolina State University, and the University of California at Santa Cruz also participated in the project and were co-authors on the Nature Geoscience articles.