This is a ‘living’ megalopa larva. Credit: Photo by Hsiu-Lin Chin
NHM curator co-authors paper on 150-million-year-old fossilized crab larva, found in southern Germany
A paper in the journal Nature Communications (March 9, 2015) co-written by NHM Crustacea curator Dr. Jody Martin describes a 150-million-year-old crab larva fossil specimen from southern Germany. The new fossil provides critical evidence for understanding the early rise of crabs.
Arthropods (they of a hard outer-skeleton, like crustaceans, spiders, and insects) very often have larval phases that are completely different from the adults — such as caterpillars and butterflies. Allegedly, one of the reasons crabs have been so successful is that their larval life habits (diet, locomotion, etc.) are decoupled from their adult life habits.
Most ancient fossils display a suite of “primitive” features, consistent with their early evolution and allowing them to be distinguished from their modern descendants. But the fossil described in this paper, despite its age, possesses a very modern morphology, indistinguishable from many crab larvae living today. “It’s amazing, but if we did not know this was a 150-million-year-old fossil, we might think that it came from today’s ocean,” Dr. Martin said. “This came as quite a surprise to all of us.”
True crabs are the most successful group of decapod crustaceans, with about 7,000 living species known. This success is most likely coupled to their life history which includes two specialized larval forms, zoea and megalopa. The new fossil is of the latter larval type (the megalopa), and it is the first such fossil ever reported.
True crabs as a group are comparably young, starting to diversify only about 100 million years ago (mya), with a dramatic increase in species richness beginning approximately 50 mya — though the early evolution of crabs is still very incompletely known.
Reference:
Joachim T. Haug, Joel W. Martin, Carolin Haug. A 150-million-year-old crab larva and its implications for the early rise of brachyuran crabs. Nature Communications, 2015; 6: 6417 DOI: 10.1038/ncomms7417
Three-dimensional perspective view of the likelihood that each region of California will experience a magnitude 6.7 or larger earthquake in the next 30 years (6.7 matches the magnitude of the 1994 Northridge earthquake, and 30 years is the typical duration of a homeowner mortgage). Credit: USGS
A new California earthquake forecast by the U.S. Geological Survey and partners revises scientific estimates for the chances of having large earthquakes over the next several decades.
The Third Uniform California Earthquake Rupture Forecast, or UCERF3, improves upon previous models by incorporating the latest data on the state’s complex system of active geological faults, as well as new methods for translating these data into earthquake likelihoods.
The study confirms many previous findings, sheds new light on how the future earthquakes will likely be distributed across the state and estimates how big those earthquakes might be.
Compared to the previous assessment issued in 2008, UCERF2, the estimated rate of earthquakes around magnitude 6.7, the size of the destructive 1994 Northridge earthquake, has gone down by about 30 percent. The expected frequency of such events statewide has dropped from an average of one per 4.8 years to about one per 6.3 years.
However, in the new study, the estimate for the likelihood that California will experience a magnitude 8 or larger earthquake in the next 30 years has increased from about 4.7% for UCERF2 to about 7.0% for UCERF3.
“The new likelihoods are due to the inclusion of possible multi-fault ruptures, where earthquakes are no longer confined to separate, individual faults, but can occasionally rupture multiple faults simultaneously,” said lead author and USGS scientist Ned Field. “This is a significant advancement in terms of representing a broader range of earthquakes throughout California’s complex fault system.”
Two kinds of scientific models are used to inform decisions of how to safeguard against earthquake losses: an Earthquake Rupture Forecast, which indicates where and when the Earth might slip along the state’s many faults, and a Ground Motion Prediction model, which estimates the ground shaking given one of the fault ruptures. The UCERF3 model is of the first kind, and is the latest earthquake-rupture forecast for California. It was developed and reviewed by dozens of leading scientific experts from the fields of seismology, geology, geodesy, paleoseismology, earthquake physics and earthquake engineering.
The USGS partner organizations that contributed to this product include the Southern California Earthquake Center, the California Geological Survey and the California Earthquake Authority.
“We are fortunate that seismic activity in California has been relatively low over the past century. But we know that tectonic forces are continually tightening the springs of the San Andreas fault system, making big quakes inevitable,” said Tom Jordan, Director of the Southern California Earthquake Center and a co-author of the study. “The UCERF3 model provides our leaders and the public with improved information about what to expect, so that we can better prepare.”
Ice ages come and go on Earth. Credit: University of Southern Denmark
Natural forces have always caused the climate on Earth to fluctuate. Now researchers have found geological evidence that some of the same forces as today were at play 1.4 billion years ago.
Fluctuating climate is a hallmark of Earth, and the present greenhouse effect is by far the only force affecting today’s climate. On a larger scale the Earth’s climate is also strongly affected by how the Earth orbits around the sun; this is called orbital forcing of climate change. These changes happen over thousands of years and they bring ice ages and warming periods.
Now researchers from University of Southern Denmark, China National Petroleum Corporation and others have looked deep into Earth’s history and can reveal that orbital forcing of climate change contributed to shaping the Earth’s climate 1.4 billion years ago.
“This study helps us understand how past climate changes have affected Earth geologically and biologically,” says Donald Canfield, principal investigator and professor at Nordic Center for Earth Evolution, University of Southern Denmark.
The evidence comes from analyses of sedimentary records from the approximately 1.4 billion-year-old and exceptionally well preserved Xiamaling Formation in China.
Changes in wind patterns and ocean circulations
The sediments in the Xiamaling Formation have preserved evidence of repeated climate fluctuations, reflecting apparent changes in wind patterns and ocean circulation that indicates orbital forcing of climate change.
Today Earth is affected by fluctuations called the Milankovich cycles. There are three different Milankovich cycles, and they occur each 20,000, 40,000 and 100,000 years. Over the last one million years these cycles have caused ice ages every 100,000 years, and right now we are in the middle of a warming period that has so far lasted 11,000 years.
“Earth’s climate history is complex. With this research we can show that cycles like the Milankovich cycles were at play 1.4 billion years ago — a period, we know only very little about,” says Donald Canfield, adding:
“This research will also help us understand how Milankovitch cyclicity ultimately controls climate change on Earth.”
In the new scientific paper in the journal PNAS, the researchers report both geochemical and sedimentological evidence for repeated, short-term climate fluctuations 1.4 billion years ago. For example the fossilized sediments show how layers of organic material differed over time, indicating cycle changes in wind patterns, rain fall and ocean circulations.
“These cycles were a little different than today’s Milankovich cycles. They occurred every 12-16,000 years, 20-30,000 years and every 100,000 years. They were a little shorter — probably because the Moon was closer to Earth 1.4 billion years ago,” explains Donald Canfield.
Reference:
Shuichang Zhang, Xiaomei Wang, Emma U. Hammarlund, Huajian Wang, M. Mafalda Costa, Christian J. Bjerrum, James N. Connelly, Baomin Zhang, Lizeng Bian, Donald E. Canfield. Orbital forcing of climate 1.4 billion years ago. Proceedings of the National Academy of Sciences, 2015; 201502239 DOI: 10.1073/pnas.1502239112
This map shows the location of the aquifer in Oregon’s southern Willamette Valley where the research was conducted. The area is south of Eugene. Credit: Courtesy of Scott C. Maguffin
University of Oregon geologist Qusheng Jin initially labeled his theory “A Wild Hypothesis.” Now his study of arsenic cycling in a southern Willamette Valley aquifer is splashing with potential significance for arsenic-compromised aquifers around the world.
In a paper online ahead of regular publication in the journal Nature Geoscience, Jin’s five-member team reports on a bacterial process that turns toxic inorganic arsenic into organic forms that usually are considered to be less dangerous. Jin’s conclusion now is that organic arsenic should be monitored.
“No one has touched on the link between arsenic on the surface and in groundwater,” said Jin, a professor in the UO Department of Geological Sciences. “Traditionally the presence of the organic form in groundwater has been ignored. The focus has always been on inorganic forms, arsenate and arsenite.”
That approach, Jin said, over-simplifies the view on arsenic levels and overlooks how human activities, including pumping and irrigation, or environmental factors such as heavy rain or drought may influence organic forms.
Water is considered safe to drink when total arsenic levels are below 10 micrograms per liter. Levels above that are considered cancer risks.
Arsenic is a natural element found in abundance in the Earth’s crust. Organic arsenic, Jin said, is made up of a series of carbon-containing forms. Total arsenic is commonly assumed to be a pure metalloid form. Arsenic often changes forms as it moves through the environment. It also is used in some pesticides, herbicides and wood preservatives and in chicken feed.
The organic arsenic that caught the team’s attention is dimethylarsinate (DMA). This intermediate stage is a floating mishmash of dissolved organic forms along with inorganic arsenite and arsenate already floating freely in the water.
DMA’s concentration — sometimes exceeding 10 percent of inorganic arsenic — always correlates with the overall arsenite level, Jin said. Eventually, he added, the conversion process can turn arsenic into arsine, a volatile gas similar to fluorescent phosphine that rises as the result of decomposition in graveyards.
The fieldwork, led by Jin, involved gathering water samples at depths ranging from 20 to 40 meters (66 to 131 feet) from 23 wells located on rural properties near Creswell, Oregon. In 10 of the wells tested, DMA was found with concentrations as high as 16.5 micrograms per liter.
The aquifer consists of volcanic sandstone, tuff and silicic ash, overlaid by lava flows and river sediments. The basin floor dates to 33 million years ago. Organic arsenic in the aquifer, the researchers noted, is similar to that in aquifers in Florida and New Jersey in the United States and in Argentina, China (Inner Mongolia and Datong), Cypress, Taiwan and West Bengal. Arsenic in groundwater is a challenge worldwide, including all 48 contiguous U.S. states.
To test the hypothesis that arsenic cycling was occurring by way of native bacteria, UO doctoral student Scott C. Maguffin conducted a series of three laboratory experiments involving dissolved arsenite and arsenate taken from wells in the study area. The addition of ethanol in the final experiment stimulated bacterial activity, resulting in DMA concentrations much higher than those found in the field.
“I am concerned about the impact of this cycling process in aquifers,” Jin said. “If this process is as important as we believe it is, it will impact the transport and fate of arsenic in groundwater. Many organic arsenic forms are volatile and prone to diffusion. Where will these organic arsenic forms go? Will they ever make to the surface?”
The findings, Jin added, open a window on naturally occurring arsenic cycling and how, eventually, it might be manipulated to treat arsenic-contaminated water. “The cycling is important,” he said. “This basic science provides a conceptual framework to understand arsenic behavior in the environment.”
This is the team from the University of Kansas unearthing fossils in Libya, despite dangers. Credit: Yaowalak Chaimanee, University of Poitiers, France
Libya hasn’t been terribly hospitable for scientific research lately.
Since the 2011 toppling of Muammar Gaddafi, fighters tied to various tribes, regions and religious factions have sewn chaos across that nation. Most recently, ISIS militants in Libya committed mass beheadings that triggered retaliatory bombings by neighboring Egypt.
“Currently, it is obviously very dangerous to be a Western scientist in Libya,” said Christopher Beard, Distinguished Foundation Professor of Ecology and Evolutionary Biology at the University of Kansas. “Even Libyan citizens are not immune to random violence.”
In spite of this turmoil, Beard and a team including fellow scientists from KU’s Biodiversity Institute have just published a discovery of mammal fossils uncovered in the Zallah Oasis in the Sirt Basin of central Libya. The fossils date back to the early Oligocene, between about 30 and 31 million years ago.
According to Beard, their paper in the Journal of African Earth Sciences sheds light on a poorly documented interval of our own evolutionary history, and shows climate and environmental change can utterly alter a local ecosystem — from a wet, subtropical forest in the Eocene to a dry desert today.
This valuable knowledge makes taking calculated risks in a war-torn land worth the risk.
“The most important factor is to have local collaborators who are experienced and who have a good feeling for what is impossible or dangerous,” Beard said. “Our Libyan collaborator is an experienced and highly accomplished professor of geology at Tripoli University. He has excellent ties to the Libyan petroleum industry, and he knows the Sahara Desert of Libya as well as anyone. We consulted closely with him prior to our 2013 expedition, and when he gave us the green light that it was safe to return to the country — thanks largely to his logistical arrangements with a local oil company — we felt safe about going back, despite State Department warnings against travel to Libya.”
Beard, who participated in both the Libyan fieldwork and subsequent analysis of the fossil finds, said taking care of logistics was the hardest part of the work.
“The arrangements were hard to put in place, because we had to coordinate among a team of four different nationalities, and we required the consent and active participation of our colleagues working at Zuetina Oil Company in Zallah,” he said.
Working in the Zallah Oasis in Libya’s Sirt Basin — an area that has “sporadically” produced fossil vertebrates since the 1960s — the team discovered a highly diverse and unique group of fossil mammals dating to the Oligocene, the final epoch of the Paleogene period, a time marked by a broad diversity of animals that would seem strange to us today, but also development of species critical to human evolution.
Beard said that the fossil species his team discovered in Libya were surprisingly different from previous fossils tied to the Oligocene discovered in next-door Egypt.
“The fact that we are finding different species in Libya suggests that ancient environments in northern Africa were becoming very patchy at this time, probably because of global cooling and drying which began a short time earlier,” he said. “That environmental patchiness seems to have promoted what we call ‘allopatric speciation.’ That is, when populations of the same species become isolated because of habitat fragmentation or some other barrier to free gene flow, given enough time, different species will emerge. We are still exploring how this new evolutionary dynamic may have impacted the evolution of primates and other mammals in Africa at this time.”
Because Beard’s work focuses on the origin and evolution of primates and anthropoids — the precursors to humans — he found the Libyan discovery of a new species of the primate Apidium to be the most exciting of the fossils uncovered by the team.
“These are the first anthropoid primate fossils known from the Oligocene of Libya and the only anthropoid fossils of this age known from Africa outside of Egypt,” said the researcher. “Earlier hypotheses suggested that anthropoids as a group may have evolved in response to the global cooling and drying that occurred at the Eocene-Oligocene boundary. Our new research indicates this was certainly not the case, because anthropoids had already been around for several million years in Africa prior to that boundary. But the climate change still had a deep impact on anthropoid evolution, because habitat fragmentation and an increased level of allopatric speciation took place as a result. Anthropoids, being forest dwellers, would have been particularly impacted by forest fragmentation during the Oligocene.”
Unfortunately, ongoing strife in Libya makes a return visit to the Sirt Basin site impossible at the moment. Indeed, armed conflict in that nation prohibits outside scientist from visiting to safely conduct any kind of field research.
“The window has now passed,” Beard said. “Field research like that which our team conducts cannot begin again until the country is stabilized and the personal security of scientific researchers in the field can be assured.”
Reference:
Pauline M.C. Coster, K. Christopher Beard, Mustafa J. Salem, Yaowalak Chaimanee, Michel Brunet, Jean-Jacques Jaeger. A new early Oligocene mammal fauna from the Sirt Basin, central Libya: Biostratigraphic and paleobiogeographic implications. Journal of African Earth Sciences, 2015; 104: 43 DOI: 10.1016/j.jafrearsci.2015.01.006
An abandoned house in the centre of Chaitén township partially buried by ash from the 2008 eruption of Chaitén Volcano.
A study by a Victoria University earth scientist has revealed the frightening potential risk posed by a recently active volcano in southern Chile, and provides insight into what could happen in New Zealand.
Associate Professor Brent Alloway, from Victoria University of Wellington’s School of Geography, Environment and Earth Sciences (SGEES) is senior co-author in collaborative research (Chile-New Zealand-Argentina-United Kingdom) which was the cover story in January’s issue of the leading journal Geology.
The article reveals the past history of the Chaitén volcano in southern Chile, which erupted in 2008, resulting in the partial destruction of nearby Chaitén township and serious disruption to population centres, infrastructure and economy downwind in Argentina.
“The 2008 Chaitén eruption made international headlines at the time since, in the eyes of the media, it was an out-of-the-blue event occurring without warning,” says Dr Alloway.
“From a scientific point of view it was a unique and exciting opportunity to view an explosive rhyolitic (high silica) eruption—the first of its type to be experienced world-wide since the Novarupta (Alaska) eruption of 1912.
“The eruption provided an unprecedented scientific opportunity to examine all facets of such an eruption ranging from magma ascendency rates to ash-fall effects on infrastructure and organisms. This eruption was also recognised as being similar in magnitude, as well as physical and chemical characteristics, to what could be reasonably be expected in future eruptions from volcanic centres situated in the Taupo Volcanic Zone here in New Zealand.”
Sediments from a small lake located close to Chaitén Volcano revealed 26 volcanic ash layers that were deposited over the last 10,000 years, 10 of which came from Chaitén Volcano. So, in addition to the 2008 eruption, there had been three previously unknown eruptions between 600 and 850 A.D. as well as another at around 420 A.D. That means eruptions have been occurring at Chaitén about every 200 years over the last 1000 years.
“It’s pretty clear that our results will need to be carefully considered by both the Chilean authorities and the local community as they continue with restoration and rebuilding in the aftermath of the 2008 eruption. There’s always a likelihood that there will be another eruption at Chaitén, the timing of which, along with its magnitude, cannot be predicted with any certainty.
“Real-time seismic monitoring of Chaitén Volcano should assist in providing timely advance warning of an impending eruption and help to prevent any loss of life in the future.”
Chaitén volcano is visited and studied by third and fourth year earth science students at Victoria University as part of a field-trip based course held in southern Chile and Argentina, run by Dr Alloway every two years.
Fully experimental image of a nanoscaled and ultrafast optical rogue wave retrieved by Near-field Scanning Optical Microscope (NSOM). The flow lines visible in the image represent the direction of light energy. Credit: Image courtesy of KAUST – King Abdullah University of Science and Technology
A new study published in Nature Physics features a nano-optical chip that makes possible generating and controlling nanoscale rogue waves. The innovative chip was developed by an international team of physicists, led by Andrea Fratalocchi from KAUST (Saudi Arabia), and is expected to have significant applications for energy research and environmental safety.
Can you imagine how much energy is in a tsunami wave, or in a tornado? Energy is all around us, but mainly contained in a quiet state. But there are moments in time when large amounts of energy build up spontaneously and create rare phenomena on a potentially disastrous scale. How these events occur, in many cases, is still a mystery.
To reveal the natural mechanisms behind such high-energy phenomena, Andrea Fratalocchi, assistant professor in the Computer, Electrical and Mathematical Science and Engineering Division of King Abdullah University of Science and Technology (KAUST), led a team of researchers from Saudi Arabia and three European universities and research centers to understand the dynamics of such destructive events and control their formation in new optical chips, which can open various technological applications. The results and implications of this study are published in the journal Nature Physics.
“I have always been fascinated by the unpredictability of nature,” Fratalocchi said. “And I believe that understanding this complexity is the next frontier that will open cutting edge pathways in science and offer novel applications in a variety of areas.”
Fratalocchi’s team began their research by developing new theoretical ideas to explain the formation of rare energetic natural events such as rogue waves — large surface waves that develop spontaneously in deep water and represent a potential risk for vessels and open-ocean oil platforms.”
“Our idea was something never tested before,” Fratalocchi continued. “We wanted to demonstrate that small perturbations of a chaotic sea of interacting waves could, contrary to intuition, control the formation of rare events of exceptional amplitude.”
A planar photonic crystal chip, fabricated at the University of St. Andrews and tested at the FOM institute AMOLF in the Amsterdam Science Park, was used to generate ultrafast (163 fs long) and subwavelength (203 nm wide) nanoscale rogue waves, proving that Fratalocchi’s theory was correct. The newly developed photonic chip offered an exceptional level of controllability over these rare events.
Thomas F. Krauss, head of the Photonics Group and Nanocentre Cleanroom at the University of York, UK, was involved in the development of the experiment and the analysis of the data. He shared, “By realizing a sea of interacting waves on a photonic chip, we were able study the formation of rare high energy events in a controlled environment. We noted that these events only happened when some sets of waves were missing, which is one of the key insights our study.”
Kobus Kuipers, head of nanophotonics at FOM institute AMOLF, NL, who was involved in the experimental visualization of the rogue waves, was fascinated by their dynamics: “We have developed a microscope that allows us to visualize optical behavior at the nanoscale. Unlike conventional wave behavior, it was remarkable to see the rogue waves suddenly appear, seemingly out of nowhere, and then disappear again…as if they had never been there.”
Andrea Di Falco, leader of the Synthetic Optics group at the University of St. Andrews said, “The advantage of using light confined in an optical chip is that we can control very carefully how the energy in a chaotic system is dissipated, giving rise to these rare and extreme events. It is as if we were able to produce a determined amount of waves of unusual height in a small lake, just by accurately landscaping its coasts and controlling the size and number of its emissaries.”
The outcomes of this project offer leading edge technological applications in energy research, high speed communication and in disaster preparedness.
Fratalocchi and the team believe their research represents a major milestone for KAUST and for the field. “This discovery can change once and for all the way we look at catastrophic events,” concludes Fratalocchi, “opening new perspectives in preventing their destructive appearance on large scales, or using their unique power for ideating new applications at the nanoscale.”
Reference:
C. Liu, R. E. C. van der Wel, N. Rotenberg, L. Kuipers, T. F. Krauss, A. Di Falco, A. Fratalocchi. Triggering extreme events at the nanoscale in photonic seas. Nature Physics, 2015; DOI: 10.1038/nphys3263
Researchers from the University of Pennsylvania spent two years constructing an ‘idealized river,’ a doughnut-shaped apparatus the size of a large fish tank. Within the ‘river’ a rotating lid drives the flow of liquid over a bed of spherical acrylic particles. By adding a fluorescent dye to the fluid and shining a laser through the apparatus, the team was able to produce images of the internal ‘river bed’ structure and precisely track the motion of individual particles over the course of days. Credit: University of Pennsylvania
Rivers drive the evolution of Earth’s surface by eroding and depositing sediment. But for nearly a century, geologists have puzzled over why theoretical models, which use principles of physics to predict patterns of sediment transport in rivers, have rarely matched observations from nature.
“Anybody that needs to predict when particles on a landscape will move, such as when and how erosion will occur, needs better equations,” said Douglas Jerolmack, an associate professor in the University of Pennsylvania’s Department of Earth and Environmental Science in the School of Arts and Sciences.
Most models predict that rivers only transport sediment during conditions of high flow and, moreover, that only particles on the surface of the river bed move due to the force of the flowing water above. But using a custom laboratory apparatus, a new study led by Jerolmack shows that, even when a river is calm, sediment on and beneath the river bed slowly creeps forward. The study’s new model of sediment transport — involving both the motion of surface grains pushed by flowing water and the creep beneath the surface resulting from interactions among particles — may substantially improve geologists’ abilities to predict erosion rates and landscape evolution over time and could also help inform future civil engineering projects.
Jerolmack brought together a diverse team for the study, including Douglas Durian, a professor in Penn’s Department of Physics and Astronomy, and Morgane Houssais and Carlos Ortiz, both Earth and Environmental Science postdoctoral researchers.
Their study will be published in the journal Nature Communications.
During flood events, rivers mobilize and erode large quantities of sediment. But for decades, geologists have faced a peculiar problem: predicting, even roughly, how much sediment a flood of a given size will erode. Even within a single river, this quantity can fluctuate dramatically.
“Many people for a long time have assumed that the reason predicting particle erosion is hard is because there’s turbulence and the flow force is fluctuating wildly,” Jerolmack said.
He began to suspect that something else — besides more accurate fluid dynamics — was missing from sediment transport models when he noticed that the “threshold of motion,” or the flow rate needed to begin mobilizing any sediment, was also highly inconsistent from flood to flood.
“The way in which the threshold of motion appeared to change from one flood to another made me suspicious that something else was going on, something not related to the fluid,” he said.
Jerolmack, whose interests straddle the boundary between earth science and physics, is part of an interdisciplinary research group at Penn’s Materials Research Science and Engineering Center that meets weekly. Through these meetings, he discovered that a lot of the strange behavior his research group observed in rivers was similar to behavior physicists and materials scientists observe in disordered materials, such as sand piles, foams and glass.
Jerolmack began discussing the problem with Durian, a soft-condensed-matter physicist whose work focuses on the structure and flow of disordered solids which lack a predictable molecular structure. The two researchers came to suspect that some problems facing sediment transport models might, indeed, have nothing to do with fluid dynamics but, rather, with the structure of the granular river bed itself.
“Granular-materials scientists understand that there’s a changing resistance to motion all the time,” Jerolmack said. “This led us to wonder if our system is just a subset of a broad class of systems other physicists have been studying.”
When force is applied to a disordered solid like sand, the material undergoes structural reorganization, which can affect its resistance to motion. Jerolmack and Durian reasoned that rivers are granular systems where the force comes from the flowing current. Therefore the riverbed’s granular structure would be altered by the flow, influencing its resistance to future motion.
“If the granular structure of the bed itself is changing over time, that could cause the threshold of motion to change from flood to flood,” said Jerolmack.
To examine changes in a river bed’s structure over time required a sophisticated experiment. Jerolmack recruited Houssais and Ortiz, who brought complementary expertise in river transport and small-scale particle dynamics, to tackle the problem. The team spent two years constructing an “idealized laboratory river,” a doughnut-shaped apparatus the size of a large fish tank. Within the “river” a rotating lid drives the flow of liquid over a bed of spherical acrylic particles. By adding a fluorescent dye to the fluid and shining a laser through the apparatus, the team was able to produce images of the internal “river bed” structure and precisely track the motion of individual particles over the course of days.
From a series of experiments at different flow rates, the team observed three distinct types of sediment transport occurring simultaneously. Within the river itself, particles either flowed quickly and at lower concentrations near the surface of the water, or more slowly, at higher concentrations, near the river bed. But within the river bed itself, the researchers observed a third type of motion: exceedingly slow particle creep associated with structural rearrangements of the granular bed. All previous research had assumed these grains were immobile. This confirmed their suspicion that granular flow — flow resulting from grain-grain interactions — in addition to fluid dynamics, can contribute to the erosion of sediment in a river.
A significant implication of this discovery is that the elusive “threshold to motion” in a river might not actually exist; in other words, particle motion slows down, but does not stop, as the river current diminishes. Rather, even in calm rivers with slow currents, granular creep may still erode sediment, albeit imperceptibly slowly.
Putting these insights together, the researchers confirmed their hunch that emerging theories describing the flow of disordered, granular systems can also describe all of the types of sediment transport observed in rivers; only a slight modification is needed to account for the fluid force. While sediment creep probably makes an insignificant contribution to erosion under high flow conditions, creep may represent the dominant erosional force during calm periods. But that idea remains to be tested in a natural system.
“We can’t say anything about the level of creep in rivers because no one has ever measured it,” Jerolmack said. “However, the slow creep of soil down a hillside due to gravity is well known, and a next step is to examine whether the underlying physics are the same.”
The idea that creep may represent a missing mechanism in river erosion holds important implications. For instance, it’s possible that by taking longer-duration measurements in the field, geologists will be able to capture more of the sediment transport due to creep, improving their overall erosion estimates within a system. This, in turn, may improve predictions of how a landscape will evolve over time.
“People often wonder how long they have to measure sediment transport in rivers to get a reliable result,” Houssais said. “We were able to infer the time you need to overcome the variability of the system and show that this time increases the slower your system moves.”
If the new theory proves robust in nature, it may also help inform future civil engineering projects.
“If you put a building on the soil, the ground will very slowly deform,” said Ortiz. “People have thought hard about how to prevent that. The phenomena we document brings new perspective to why this deformation occurs.”
“If we can understand when and how erosion occurs,” Jerolmack said, “and show that our model is robust, some other smart person is going to take our result and develop a useful tool from that. We’re producing a basic science result right now, but the applications are probably only as limited as our imaginations.”
Reference:
Morgane Houssais, Carlos P. Ortiz, Douglas J. Durian, Douglas J. Jerolmack. Onset of sediment transport is a continuous transition driven by fluid shear and granular creep. Nature Communications, 2015; 6: 6527 DOI: 10.1038/ncomms7527
Scaphites is a genus of extinct cephalopod belonging to the family of heteromorph ammonites (suborder Ancyloceratina). They were a widespread genus that thrived during the Cretaceous period.
Scaphites generally have a chambered, boat-shaped shell. The initial part (juvenile stage) of the shell is generally more or less involute (tightly-coiled) and compressed, giving no hint of the heteromorphic shell form yet to come. The terminal part (adult stage) is much shorter, erect, and bends over the older shell like a hook. They have transverse, branching ribs with tubercles (small bumps) along the venter.
Reconstructions of the body within the shell can be made to portray Scaphites as either a benthic (bottom-dwelling) or planktonic animal, depending on where the center of gravity is located. Since useful fossils of the soft-body parts of cephalopods are highly rare, little is known about how this animal actually fit into its shell and lived its life.
Because Scaphites and its relatives in Superfamily Scaphitaceae are restricted to certain divisions of the Cretaceous (ca. 144 to 66.4 million years ago), they are useful in some areas as an index fossil. A notable example is the Late Cretaceous Western Interior Seaway in North America, in which several endemic lineages of scaphite species evolved and now serve as the basis for a highly resolved regional biostratigraphy.
The Panj river forms much of the border |between Tajikistan and Afghanistan
The Panj River , also known as Pyandzh River or Pyanj River (derived from its Russian name “Пяндж”), is a tributary of the Amu Darya. The river is 1,125 km long and forms a considerable part of the Afghanistan – Tajikistan border.
The river is formed by the confluence of the Pamir River and the Wakhan River near the village of Qila-e Panja. From there, it flows westwards, forming the border of Afghanistan and Tajikistan. After passing the city of Khorog, capital of the Gorno-Badakhshan Autonomous Region of Tajikistan it receives water from one of its main tributaries, the Bartang River. It then turns towards the southwest, before joining the river Vakhsh and forming the greatest river of Central Asia, the Amudarya. Panj played a very important role during Soviet times, and was a strategic river during the Soviet military operations in Afghanistan in the 1980s.
Note : The above story is based on materials provided by Wikipedia.
This is a microscopic photo of the foraminifer Globigerinoides ruber, which is used in this study. Credit: Frank J.C. Peeters, VU University Amsterdam
New research in Nature Communications showing how tiny creatures drifted across the ocean before falling to the seafloor and being fossilised has the potential to improve our understanding of past climates.
The research published in Nature Communications has identified which planktic foraminifera gathered up in core samples from the ocean floor, drifted thousands of kilometres and which species barely moved at all.
The research will help scientists to more accurate distinguish which fossils most accurately reflect ocean and temperature states in the locaiton where they were found.
“This research will help scientists improve the study of past climates because they will be able to look at a species of foraminifera and the core location to very quickly get a sense of how site-specific that particular proxy measure is,” said Dr Van Sebille, lead-author of the study and a climate scientist at the ARC Centre of Excellence for Climate System Science at UNSW Australia.
“In a way it will give us a good indication of whether the creature we are looking at to get our past-temperature estimates was a bit of a globetrotter or a stay at home type.”
For many decades, deriving past temperatures from the shells of creatures living tens of thousands of years ago has been key to understanding climates of the past.
However, interpreting the records has never been easy. This is the reason that many studies have very large margins of error when they use ocean sediments as a way of establishing past temperatures. It also explains why there is a greater focus on the trend of these results over the actual temperature.
“The older the proxy, the wider the margin of error. This is because ocean currents can change, tectonic plates move and there is even variation in which level of the ocean various plankton can be found,” said Dr Scussolini, a contributing author and climate scientist at VU University, Amsterdam.
“This research allows us for the first time to grasp the margins of error caused by drift and also opens an entirely new dimension for the interpretation of the deep-sea climate data.”
The international team used state-of-the-art computer models and analysis on fossil shells to investigate the impact of oceanic drift. In extreme cases the variation in temperature between where the fossilised shell was found and where it came from could be up to 3°C.
In other cases for specific plankton and in areas of the ocean where currents were particularly slow, the variation in temperature was negligible.
As a result, the team is now working on creating a tool, so fellow researchers can easily estimate how large the impact of drift for the location is likely to be. This tool will also be extended to other species of plankton.
“Our results highlight the importance of the ocean currents in transporting anything that floats,” said Dr Van Sebille.
“By picking apart this variation we can add another level of certainty to estimates of past temperatures, opening a door that may help us discover what future climate change may bring to our planet.”
Reference:
Erik van Sebille, Paolo Scussolini, Jonathan V. Durgadoo, Frank J. C. Peeters, Arne Biastoch, Wilbert Weijer, Chris Turney, Claire B. Paris, Rainer Zahn. Ocean currents generate large footprints in marine palaeoclimate proxies. Nature Communications, 2015; 6: 6521 DOI: 10.1038/ncomms7521
Manuel Martínez Escandell, Francisco Rodríguez Reinoso and Joaquín Silvestre Albero. Credit: Image courtesy of Asociación RUVID
The Laboratory of Advanced Materials, belonging to the University of Alicante’s department of Inorganic Chemistry, has developed a technology that allows the preparation of artificial methane hydrates. The research has been published by the scientific journal Nature Communications.
Research has been led by Joaquín Silvestre Albero, Francisco Rodríguez Reinoso and Manuel Martínez Escandell, and carried out by Mirian E. Casco, who is currently completing an internship at the University of Alicante. These researchers have demonstrated that it is possible to prepare methane hydrates in a laboratory by imitating, and even enhancing, natural processes through the use of activated carbon materials as nano-reactors. One of the keys of this research was that scientists were able to reduce the process to form methane hydrates, which takes a long time in nature, to just a few minutes, thus making its technological applicability much easier.
The University of Alicante has been working on the design and synthesis of highly-performing activated carbon for over 30 years. In the words of Joaquín Silvestre, head researcher, “these materials show a great potential to not only eliminate polluting molecules in the air and in industrial waterways, but also to be used as gas storage systems.”
These results are a step forward to understanding the artificial synthesis process of these natural structures, and a new pathway into the use of fuels such as natural gas for transport (instead of petrol and diesel), or for long-distance transport of natural gas (e.g. as opposed to current transport conditions, where gas is liquefied at -162ºC, since this new technique allows for gas to be transported at a temperature that is much closer to room temperature). “Our results show that some of our coals can supply amounts as high as 300 methane volumes stored at 100 atmospheres for each volume unit of wet coal,” researchers say.
Silvestre explains that this research has taken advantage of the so-called “confinement” effect to artificially synthesize methane hydrates inside the coal’s cavities or pores. “Methane hydrates have been prepared on activated carbon materials that were previously wetted under gentler pressure and temperature conditions (30 atmospheres and 2ºC) than in a natural environment.”
Once the synthesis and analysis had been carried out at the University of Alicante’s laboratories, the study went on to its final stage in Rutherford Appleton Laboratory in Oxford (United Kingdom), where neutron scattering was performed, and in ALBA synchrotron in Barcelona (Spain). “These studies are the first experimental evidence that it is possible to form methane hydrates in a confined space, with a nature-like stoichiometry and significantly higher kinetics.”
Other members of LMA international group are Japanese lecturer Katsumi Kaneko, who is collaborating in the development of CONCERT project on the subject matter of this study, and Fernando Rey, from the Instituto de Tecnología Química of Valencia (ITQ-CSIC), who collaborated in the measurements taken in ALBA and Oxford accelerators. Researcher Timmy Ramirez, now a member of US Oak Ridge National Laboratory and former researcher in chief of Oxford’s neutron accelerator, has also participated in this research.
Scientific grounds
Gas hydrates (also known as clathrates) are crystalline structures similar to a cage, where a group of molecules surrounds a central molecule of a certain nature. When said cage is made up of water molecules and there is a methane molecule inside the cavity, what we call methane hydrates are formed. Methane hydrates are formed in nature under very specific physical, chemical and geological conditions that can only be found in the bottom of the oceans, or, less frequently, in the subsoil of cold regions such as Siberia, which is known as permafrost. The origin of methane causing these marine hydrates is in the thermal, microbial and bacterial decomposition of organic matter that is dragged by river currents for millions of years. As a consequence, methane hydrates reserves are located in continental slopes, near the shore, approximately 300-500 m underground, where enough organic matter is accumulated and there is the right combination of pressure and temperature. Methane hydrates are Earth’s largest natural gas reserve. They are located near the continental area, and according to the calculations their reserves are double those of all fossil fuels (oil, natural gas and coal) that currently exist on Planet Earth. According to experts, there are 5,000 gigatons of methane, which is approximately 500 times the amount of carbon that is emitted every year from burning coal, oil and natural gas. In 2013, the first exploration to extract methane by de pressurising marine deposits was carried out in Japan. This technology is expected to be available in 2018.
The hydrate’s formula is (CH4)4(H2O)23, or one mol of methane per 5.75 mols of water, corresponding to 13.4% of methane weight (one cubic metre of hydrate releases 180 cubic metres of methane, the main component of natural gas). The hydrates’ high energy density and their stability when temperatures are higher than liquid natural gas (-2ºC vs -162ºC) mean that methane hydrates can be a future solution for long-distance transport of methane in large quantities, as long as they can be synthetically prepared by imitating nature within a reasonably short period of time (in just a few minutes)
Reference:
Mirian E. Casco, Joaquín Silvestre-Albero, Anibal J. Ramírez-Cuesta, Fernando Rey, Jose L. Jordá, Atul Bansode, Atsushi Urakawa, Inma Peral, Manuel Martínez-Escandell, Katsumi Kaneko, Francisco Rodríguez-Reinoso. Methane hydrate formation in confined nanospace can surpass nature. Nature Communications, 2015; 6: 6432 DOI: 10.1038/ncomms7432
No one really knows how the High Plains got so high. About 70 million years ago, eastern Colorado, southeastern Wyoming, western Kansas and western Nebraska were near sea level. Since then, the region has risen about 2 kilometers, leading to some head scratching at geology conferences.
Now researchers at the Cooperative Institute for Research in Environmental Sciences (CIRES) and the Department of Geological Sciences at the University of Colorado Boulder have proposed a new way to explain the uplift: Water trapped deep below Earth’s crust may have flooded the lower crust, creating buoyancy and lift. The research appears online this week in the journal Geology and could represent a new mechanism for elevating broad regions of continental crust.
“The High Plains are perplexing because there is no deformation — such as major faults or volcanic activity — in the area to explain how this big, vast area got elevated,” said lead author Craig Jones, a CIRES fellow and associate professor of geology at CU-Boulder. “What we suggest is that by hydrating the lower crust, it became more buoyant, and the whole thing came up.”
“It’s like flooding Colorado from below,” Jones said.
Jones and his colleagues propose the water came from the subducting Farallon oceanic plate under the Pacific Ocean 75 to 45 million years ago. This slab slid underneath the North American continental plate, bringing with it a tremendous amount of water bound in minerals. Trapped and under great pressure and heat, the water was released from the oceanic plate and moved up through the mantle and toward the lower crust. There, it hydrated lower crust minerals, converting dense ones, like garnet, into lighter ones, such as mica and amphibole.
Shaded topographic map of the High Plains and Southern Rocky Mountains showing the locations of active source seismic profiles. Xenolith localities are shown in triangles. Images to the right of the topographic map show results from various experiments designed to understand seismic structure. Images are from several previously published studies, as indicated. Credit: CIRES
“If you get rid of the dense garnet in the lower crust, you get more elevation because the crust becomes more buoyant,” Jones said. “It’s like blowing the water out of a ballast tank in a submarine.”
Jones had the lightbulb moment for this idea when colleagues, including co-author Kevin Mahan, were describing xenoliths (pieces of crust ejected by volcanic eruptions) from across Wyoming and Montana. The researchers were reviewing the xenoliths’ composition and noticed something striking. Xenoliths near the Canadian border were very rich in garnet. But farther south, the xenoliths were progressively more hydrated, the garnet replaced by mica and other less-dense minerals. In southern Wyoming, all the garnet was gone.
Upon hearing these findings, Jones blurted out, “You’ve solved why Wyoming is higher than Montana,” a puzzle that other theories haven’t been able to explain.
At the time, Mahan, a CU-Boulder assistant professor of geological sciences, noted that the alteration of garnet was thought to be far too ancient, from more than a billion years ago, to fit the theory. But since then, he and another co-author, former CU-Boulder graduate student Lesley Butcher, dated the metamorphism of one xenolith sample from the Colorado Plateau and discovered it had been hydrated “only” 40-70 million years ago.
Past seismic studies also support the new mechanism. These studies show that from the High Plains of Colorado to eastern Kansas, the crustal thickness or density correlates with a decline in elevation, from about 2 kilometers in the west to near sea level in the east. A similar change is seen from northern Colorado north to the Canadian border. In other words, as the crust gets less hydrated, the elevation of the Great Plains also gets lower.
“You could say it’s just by happenstance that we seem to have thicker more buoyant crust in higher-elevation Colorado than in lower-elevation central Kansas,” Jones said, “but why would crust buoyancy magically correlate today with topography if that wasn’t what created the topography?”
Still, Jones is quick to point out that this mechanism “is not the answer, but a possible answer. It’s a starting point that gives other researchers a sense of what to look for to test it,” he said.
Video:
Reference:
C. H. Jones, K. H. Mahan, L. A. Butcher, W. B. Levandowski, G. L. Farmer. Continental uplift through crustal hydration. Geology, 2015; DOI: 10.1130/G36509.1
This artist’s impression shows how Mars may have looked about four billion years ago. The young planet Mars would have had enough water to cover its entire surface in a liquid layer about 140 metres deep, but it is more likely that the liquid would have pooled to form an ocean occupying almost half of Mars’s northern hemisphere, and in some regions reaching depths greater than 1.6 kilometres. Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org)
A primitive ocean on Mars held more water than Earth’s Arctic Ocean, and covered a greater portion of the planet’s surface than the Atlantic Ocean does on Earth, according to new results published today. An international team of scientists used ESO’s Very Large Telescope, along with instruments at the W. M. Keck Observatory and the NASA Infrared Telescope Facility, to monitor the atmosphere of the planet and map out the properties of the water in different parts of Mars’s atmosphere over a six-year period. These new maps are the first of their kind.
The results appear online in the journal Science today.
About four billion years ago, the young planet would have had enough water to cover its entire surface in a liquid layer about 140 metres deep, but it is more likely that the liquid would have pooled to form an ocean occupying almost half of Mars’s northern hemisphere, and in some regions reaching depths greater than 1.6 kilometres.
“Our study provides a solid estimate of how much water Mars once had, by determining how much water was lost to space,” said Geronimo Villanueva, a scientist working at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, USA, and lead author of the new paper. “With this work, we can better understand the history of water on Mars.”
The new estimate is based on detailed observations of two slightly different forms of water in Mars’s atmosphere. One is the familiar form of water, made with two hydrogen atoms and one oxygen, H2O. The other is HDO, or semi-heavy water, a naturally occurring variation in which one hydrogen atom is replaced by a heavier form, called deuterium.
As the deuterated form is heavier than normal water, it is less easily lost into space through evaporation. So, the greater the water loss from the planet, the greater the ratio of HDO to H2O in the water that remains.
The researchers distinguished the chemical signatures of the two types of water using ESO’s Very Large Telescope in Chile, along with instruments at the W. M. Keck Observatory and the NASA Infrared Telescope Facility in Hawaii. By comparing the ratio of HDO to H2O, scientists can measure by how much the fraction of HDO has increased and thus determine how much water has escaped into space. This in turn allows the amount of water on Mars at earlier times to be estimated.
In the study, the team mapped the distribution of H2O and HDO repeatedly over nearly six Earth years — equal to about three Mars years — producing global snapshots of each, as well as their ratio. The maps reveal seasonal changes and microclimates, even though modern Mars is essentially a desert.
Ulli Kaeufl of ESO, who was responsible for building one of the instruments used in this study and is a co-author of the new paper, adds: “I am again overwhelmed by how much power there is in remote sensing on other planets using astronomical telescopes: we found an ancient ocean more than 100 million kilometres away!”
The team was especially interested in regions near the north and south poles, because the polar ice caps are the planet’s largest known reservoir of water. The water stored there is thought to document the evolution of Mars’s water from the wet Noachian period, which ended about 3.7 billion years ago, to the present.
The new results show that atmospheric water in the near-polar region was enriched in HDO by a factor of seven relative to Earth’s ocean water, implying that water in Mars’s permanent ice caps is enriched eight-fold. Mars must have lost a volume of water 6.5 times larger than the present polar caps to provide such a high level of enrichment. The volume of Mars’s early ocean must have been at least 20 million cubic kilometres.
Based on the surface of Mars today, a likely location for this water would be the Northern Plains, which have long been considered a good candidate because of their low-lying ground. An ancient ocean there would have covered 19% of the planet’s surface — by comparison, the Atlantic Ocean occupies 17% of the Earth’s surface.
“With Mars losing that much water, the planet was very likely wet for a longer period of time than previously thought, suggesting the planet might have been habitable for longer,” said Michael Mumma, a senior scientist at Goddard and the second author on the paper.
It is possible that Mars once had even more water, some of which may have been deposited below the surface. Because the new maps reveal microclimates and changes in the atmospheric water content over time, they may also prove to be useful in the continuing search for underground water.
Reference:
G. L. Villanueva, M. J. Mumma, R. E. Novak, H. U. Käufl, P. Hartogh, T. Encrenaz, A. Tokunaga, A. Khayat, M. D. Smith. Strong water isotopic anomalies in the martian atmosphere: Probing current and ancient reservoirs. Science, 2015 DOI: 10.1126/science.aaa3630
Individual cows can produce up to 500 liters of methane a day; the species accounts for about one-third of total methane emissions. The structures shown represent the structure of methane. Credit: Danielle Gruen (edited by Jose-Luis Olivares/MIT)
Methane is a potent greenhouse gas, second only to carbon dioxide in its capacity to trap heat in Earth’s atmosphere for a long time. The gas can originate from lakes and swamps, natural-gas pipelines, deep-sea vents, and livestock. Understanding the sources of methane, and how the gas is formed, could give scientists a better understanding of its role in warming the planet.
Now a research team led by scientists at MIT and including colleagues from the Woods Hole Oceanographic Institution, the University of Toronto, and elsewhere has developed an instrument that can rapidly and precisely analyze samples of environmental methane to determine how the gas was formed.
The approach, called tunable infrared laser direct absorption spectroscopy, detects the ratio of methane isotopes, which can provide a “fingerprint” to differentiate between two common origins: microbial, in which microorganisms, typically living in wetlands or the guts of animals, produce methane as a metabolic byproduct; or thermogenic, in which organic matter, buried deep within the Earth, decays to methane at high temperatures.
The researchers used the technique to analyze methane samples from settings including lakes, swamps, groundwater, deep-sea vents, and the guts of cows, as well as methane generated by microbes in the lab.
“We are interested in the question, ‘Where does methane come from?'” says Shuhei Ono, an assistant professor of geochemistry in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “If we can partition how much is from cows, natural gas, and other sources, we can more reliably strategize what to do about global warming.”
Ono and his colleagues, including first author and graduate student David Wang, publish their results this week in the journal Science.
Locking in on methane’s frequency
Methane is a molecule composed of one carbon atom linked to four hydrogen atoms. Carbon can come as one of two isotopes (carbon-12 or carbon-13); hydrogen can also take two forms, including as deuterium — an isotope of hydrogen with one extra neutron.
The authors looked for a very rare molecule of doubly isotope-substituted methane, known as 13CH3D — a molecule with both an atom of carbon-13 and a deuterium atom. Detecting 13CH3D was crucial, the researchers reasoned, as it may be a signal of the temperature at which methane formed — essential for determining whether methane is microbial or thermogenic in origin.
Last year, Ono and colleagues, working with scientists from Aerodyne Research, built an instrument to detect 13CH3D. The technique uses infrared spectroscopy to detect specific frequencies corresponding to minute motions within molecules of methane; different frequencies correspond to different isotopes. This spectroscopic approach, which is fundamentally different from the classical mass spectrometric methods being developed by others, has the advantage of portability, allowing its potential deployment in field locations.
Methane’s pulse
The team collected samples of methane from settings such as lakes, swamps, natural gas reservoirs, the digestive tracts of cows, and deep ancient groundwater, as well as methane made by microbes in the lab.
The group noticed something surprising and unexpected in some samples. For example, based on the isotope ratios they detected in cow rumen, they calculated that this methane formed at 400 degrees Celsius — impossible, as cow stomachs are typically about 40 C. They observed similar incongruences in samples from lakes and swamps. The isotope ratios, they reasoned, must not be a perfect indicator of temperature.
Instead, Wang and his colleagues identified a relationship between a feature of the bonds linking carbon and hydrogen in methane molecules — a quality they deemed “clumpiness” — and the rate at which methane was produced: The clumpier the bond, the slower the rate of methanogenesis.
“Cow guts produce methane at very high rates — up to 500 liters a day per cow. They’re giant methane fermenters, and they prefer to make less-clumped methane, compared to geologic processes, which happen very slowly,” Wang says. “We’re measuring a degree of clumpiness of the carbon and hydrogen isotopes that helps us get an idea of how fast the methane formed.”
The researchers applied this new interpretation to methane formed by microbes in the lab, and found good agreement between the isotopes detected and the rates at which the gas formed. They then used the technique to analyze methane from Kidd Creek Mine, in Canada — one of the deepest accessible points on Earth — and two sites in California where the Earth’s mantle rock reacts with groundwater. These are sites in which the origins of methane were unclear.
“It’s been a longstanding question how those fluids were developed,” Wang says. “Now we have a baseline that we can use to explore how methane forms in environments on Earth and beyond.”
Reference:
David T. Wang, Danielle S. Gruen, Barbara Sherwood Lollar, Kai-Uwe Hinrichs, Lucy C. Stewart, James F. Holden, Alexander N. Hristov, John W. Pohlman, Penny L. Morrill, Martin Könneke, Kyle B. Delwiche, Eoghan P. Reeves, Chelsea N. Sutcliffe, Daniel J. Ritter, Jeffrey S. Seewald, Jennifer C. McIntosh, Harold F. Hemond, Michael D. Kubo, Dawn Cardace, Tori M. Hoehler, and Shuhei Ono. Nonequilibrium clumped isotope signals in microbial methane. Science, 5 March 2015 DOI: 10.1126/science.aaa4326
“The force required to rip this reef material from the seafloor and deposit it that far above the shoreline had to have been tremendous,” said CU-Boulder scientist Larry Benson. “We think the tsunami wave height was at least 15 feet and potentially much higher than that.” Credit: Illustration by Samantha Davies, University of Colorado
The eastern coastline of Mexico’s Yucatan Peninsula, a mecca for tourists, may have been walloped by a tsunami between 1,500 and 900 years ago, says a new study involving Mexico’s Centro Ecological Akumal (CEA) and the University of Colorado Boulder.
There are several lines of evidence for an ancient tsunami, foremost a large, wedge-shaped berm about 15 feet above sea level paved with washing machine-sized stones, said the researchers. Set back in places more than a quarter of a mile from shore, the berm stretches for at least 30 miles, alternating between rocky headlands and crescent beaches as it tracks the outline of the Caribbean coast near the plush resorts of Playa del Carmen and Cancun.
Radiocarbon dates of peat beneath the extensive berm indicate a tsunami, which may have consisted of two or even three giant waves, likely slammed the coastline sometime after A.D. 450. In addition, ruins of Post-Classic Mayan structures built between A.D. 900 and 1200 were found atop parts of the berm, indicating the tsunami occurred prior to that time.
“I was quite shocked when I first walked these headlands and saw this large berm paved with boulders running long distances in both directions,” said CEA scientist Charles Shaw. “My initial thought was that a huge wave came through here in the past, and it must have packed quite a punch.”
A paper on the subject by Shaw and Larry Benson, an adjunct curator of anthropology at the University of Colorado Museum of Natural History, was published online this week in the Journal of Coastal Research.
The boulders that cover the face and top of the berm are composed of coral and fine-grained limestone, said Benson. “The force required to rip this reef material from the seafloor and deposit it that far above the shoreline had to have been tremendous,” he said. “We think the tsunami wave height was at least 15 feet and potentially much higher than that.”
In addition, the researchers have found “outlier berms,” spanning some 125 miles along the Yucatan coastline that suggest the tsunami impacted a very large region. “I think there is a chance this tsunami affected the entire Yucatan coast,” said Benson.
The berm is composed of two layers of coarse sand as well as both small and large boulders. The beaches between the headland areas contain mostly sandy carbonate material with small boulders that likely were eroded from nearby bays during the event, said Shaw.
It is not clear what might have caused the tsunami, which can be triggered by a variety of events ranging from earthquakes and underwater landslides to volcanic eruptions and oceanic meteor strikes. While scientists have found evidence a “super-typhoon” deposited rocky berms on the Australian coastline, the sediments in those berms occur in well-sorted bands, while the Yucatan berm is composed of coarse, unlayered sands suggesting different processes were involved in sediment deposition.
“If hurricanes can build these types of berms, why is there only a single berm off the Yucatan coast given the numerous hurricanes that have made landfall there over the past century?” said Shaw. “That is a big part of our argument for a tsunami wave. We think we have the pieces of evidence we need for this event to have occurred.”
Benson and Shaw suggest the tsunami could be more accurately dated by coring mangrove swamp sediments found along the coast in order to locate the carbonate sand deposited by the massive wave, then radiocarbon dating the peaty material above and below the sand.
One implication of the Yucatan tsunami is the potential destruction another one could cause. While the geologic evidence indicates tsunamis in the region are rare — only 37 recorded in the Caribbean basin since 1492 — the Yucatan coastline, which was only lightly populated by Mayans 1,500 years ago, is now home to a number of lavish resort communities and villages inhabited by some 1.4 million people.
“If such an event occurs in the future, it would wreak havoc along the built-up coastline, probably with a great loss of life,” said Benson. But it’s far more likely that powerful hurricanes like the Class 5 Hurricane Gilbert that made landfall on the Yucatan Peninsula in 1988, killing 433 people in the Caribbean and the Gulf of Mexico and causing more than $7 billion in damage, will slam the coastline, said the researchers.
Reference:
Charles E. Shaw and Larry Benson. Possible Tsunami Deposits on the Caribbean Coast of the Yucatán Peninsula. Journal of Coastal Research, 2014; DOI: 10.2112/JCOASTRES-D-14-00084.1
A group of emperor penguins is resting and preening next to a tide crack in the ice near the Gould Bay colony. Credit: Dr Tom Hart
A study of how climate change has affected emperor penguins over the last 30,000 years found that only three populations may have survived during the last ice age, and that the Ross Sea in Antarctica was likely the refuge for one of these populations
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The Ross Sea is likely to have been a shelter for emperor penguins for thousands of years during the last ice age, when much of the rest of Antarctica was uninhabitable due to the amount of ice.
The findings, published today in the journal Global Change Biology, suggest that while current climate conditions may be optimal for emperor penguins, conditions in the past were too extreme for large populations to survive.
A team of researchers, led by scientists from the universities of Southampton, Oxford, Tasmania and the Australian Antarctic Division, and supported in Antarctica by Adventure Network International, examined the genetic diversity of modern and ancient emperor penguin populations in Antarctica to estimate how they had been changing over time.
The iconic species is famed for its adaptations to its icy world, breeding on sea ice during the Antarctic winter when temperatures regularly drop below -30 °C. However, the team discovered that conditions were probably too harsh for emperor penguins during the last ice age and that the population was roughly seven times smaller than today and split up into three refugial populations.
Gemma Clucas, a PhD student from Ocean and Earth Science at the University of Southampton and one of the lead authors of the paper, explained: “Due to there being about twice as much sea ice during the last ice age, the penguins were unable to breed in more than a few locations around Antarctica. The distances from the open ocean, where the penguins feed, to the stable sea ice, where they breed, was probably too far. The three populations that did manage to survive may have done so by breeding near to polynyas — areas of ocean that are kept free of sea ice by wind and currents.”
One of these polynyas that supported a population of emperor penguins throughout the last ice age was probably in the Ross Sea. The researchers found that emperor penguins that breed in the Ross Sea are genetically distinct from other emperor penguins around Antarctica.
Jane Younger, a PhD student from the Australian Institute for Marine and Antarctic Sciences and the other lead author of the paper, said: “Our research suggests that the populations became isolated during the last ice age, pointing to the fact that the Ross Sea could have been an important refuge for emperor penguins and possibly other species too.”
Climate change may affect the Ross Sea last out of all regions of Antarctica. Due to changes in wind patterns associated with climate change, the Ross Sea has in fact experienced increases rather than decreases in the extent of winter sea ice over the last few decades, although this pattern is predicted to reverse by the end of the century.
Dr Tom Hart from the University of Oxford and one of the organisers of this study added: “It is interesting that the Ross Sea emerges as a distinct population and a refuge for the species. It adds to the argument that the Ross Sea might need special protection.”
Reference:
Jane L. Younger, Gemma V. Clucas, Gerald Kooyman, Barbara Wienecke, Alex D. Rogers, Philip N. Trathan, Tom Hart, Karen J. Miller. Too much of a good thing: sea ice extent may have forced emperor penguins into refugia during the last glacial maximum. Global Change Biology, 2015; DOI: 10.1111/gcb.12882
This is a close up view of the mandible just steps from where it was sighted by Chalachew Seyoum, ASU graduate student, who is from Ethiopia. Credit: Brian Villmoare
A fossil lower jaw found in the Ledi-Geraru research area, Afar Regional State, Ethiopia, pushes back evidence for the human genus — Homo — to 2.8 million years ago, according to a pair of reports published March 4 in the online version of the journal Science. The jaw predates the previously known fossils of the Homo lineage by approximately 400,000 years. It was discovered in 2013 by an international team led by Arizona State University scientists Kaye E. Reed, Christopher J. Campisano and J Ramón Arrowsmith, and Brian A. Villmoare of the University of Nevada, Las Vegas.
For decades, scientists have been searching for African fossils documenting the earliest phases of the Homo lineage, but specimens recovered from the critical time interval between 3 and 2.5 million years ago have been frustratingly few and often poorly preserved. As a result, there has been little agreement on the time of origin of the lineage that ultimately gave rise to modern humans. At 2.8 million years, the new Ledi-Geraru fossil provides clues to changes in the jaw and teeth in Homo only 200,000 years after the last known occurrence of Australopithecus afarensis (“Lucy”) from the nearby Ethiopian site of Hadar.
Found by team member and ASU graduate student Chalachew Seyoum, the Ledi-Geraru fossil preserves the left side of the lower jaw, or mandible, along with five teeth. The fossil analysis, led by Villmoare and William H. Kimbel, director of ASU’s Institute of Human Origins, revealed advanced features, for example, slim molars, symmetrical premolars and an evenly proportioned jaw, that distinguish early species on the Homo lineage, such as Homo habilis at 2 million years ago, from the more apelike early Australopithecus. But the primitive, sloping chin links the Ledi-Geraru jaw to a Lucy-like ancestor.
“In spite of a lot of searching, fossils on the Homo lineage older than 2 million years ago are very rare,” says Villmoare. “To have a glimpse of the very earliest phase of our lineage’s evolution is particularly exciting.”
In a report in the journal Nature, Fred Spoor and colleagues present a new reconstruction of the deformed mandible belonging to the 1.8 million-year-old iconic type-specimen of Homo habilis (“Handy Man”) from Olduvai Gorge, Tanzania. The reconstruction presents an unexpectedly primitive portrait of the H. habilis jaw and makes a good link back to the Ledi fossil.
“The Ledi jaw helps narrow the evolutionary gap between Australopithecus and early Homo,” says Kimbel. “It’s an excellent case of a transitional fossil in a critical time period in human evolution.”
Global climate change that led to increased African aridity after about 2.8 million years ago is often hypothesized to have stimulated species appearances and extinctions, including the origin of Homo. In the companion paper on the geological and environmental contexts of the Ledi-Geraru jaw, Erin N. DiMaggio, of Pennsylvania State University, and colleagues found the fossil mammal assemblage contemporary with this jaw to be dominated by species that lived in more open habitats–grasslands and low shrubs–than those common at older Australopithecus-bearing sites, such as Hadar, where Lucy’s species is found.
“We can see the 2.8 million year aridity signal in the Ledi-Geraru faunal community,” says research team co-leader Kaye Reed, “but it’s still too soon to say that this means climate change is responsible for the origin of Homo. We need a larger sample of hominin fossils, and that’s why we continue to come to the Ledi-Geraru area to search.”
The research team, which began conducting field work at Ledi-Geraru in 2002, includes:
Erin N. DiMaggio (Pennsylvania State University), Christopher J. Campisano (ASU Institute of Human Origins and School of Human Evolution and Social Change), J. Ramón Arrowsmith (ASU School of Earth and Space Exploration), Guillaume Dupont-Nivet (CNRS Géosciences Rennes), and Alan L. Deino (Berkeley Geochronology Center), who conducted the geological research
Faysal Bibi (Museum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science), Margaret E. Lewis (Stockton University), John Rowan (ASU Institute of Human Origins and School of Human Evolution and Social Change), Antoine Souron (Human Evolution Research Center, University of California, Berkeley), and Lars Werdelin (Swedish Museum of Natural History), who identified the fossil mammals
Kaye E. Reed (ASU Institute of Human Origins and School of Human Evolution and Social Change), who reconstructed the past habitats based on the faunal communities
David R. Braun (George Washington University), who conducted archaeological research
Brian A. Villmoare (University of Nevada Las Vegas), William H. Kimbel (ASU Institute of Human Origins and School of Human Evolution and Social Change), and Chalachew Seyoum (ASU Institute of Human Origins and School of Human Evolution and Social Change, and Authority for Research and Conservation of Cultural Heritage, Addis Ababa), who analyzed the hominin fossil
Reference:
Brian Villmoare, William H. Kimbel, Chalachew Seyoum, Christopher J. Campisano, Erin Dimaggio, John Rowan, David R. Braun, J. Ramon Arrowsmith, Kaye E. Reed. Early Homo at 2.8 Ma from Ledi-Geraru, Afar, Ethiopia. Science, 2015 DOI: 10.1126/science.aaa1343
Schematic map of the Mediterranean, showing its different basins and its main wind and fluvial patterns. Credit: Image courtesy of University of Granada
An international team of scientists which included three University of Granada and the Andalusian Institute of Earth Sciences researchers (a joint UGR-CISC centre) have found new data on the weather in the Mediterranean basin over the course of the past 20,000 years thanks to the chemical composition of sediments deposited in its seabed.
This work has been published in the journal Quaternary Science Reviews. Its authors include Francisca Martínez Ruiz y David Gallego Torres (Andalusia Institute of Earth Sciences, CSIC-UGR), both of them members of the RNM179 research group, as well as Miguel Ortega Huertas (from the Mineralogy and Petrology Department). The other co-authors are Miriam Kastner (Scripps Institution of Oceanography, UCSD, La Jolla, USA), Marta Rodrigo Gámiz (NIOZ Royal Netherlands Institute for Sea Research, Texel, The Netherlands) and Vanesa Nieto Moreno (Biodiversität und Klima Forschungszentrum, Frankfurt am Main, Germany).
Francisca Martínez Ruiz is the principal author. This researcher at the Andalusian Institute of Earth Sciences explains that “the study of the chemical composition of seabed sediments is particularly interesting because, beyond mere instrumental data, only indirect markers can provide information about what the climate was like in the past”
This high-resolution study of seabed sediments allows for a description of the climate in the past which will contribute to our knowledge of current climate change, and also to speculate with different climate change scenarios for the future. For purposes such as these “The Mediterranean is” according to Francisca Martínez, “an exceptional natural lab for paleoenvironmental research, since its nature as a semi-enclosed basin makes it particularly sensitive to, and turns it into an amplifier of, the effects of global change.”
Last Glacial Maximum
The interval of time surveyed by this scientific publication is of particular interest due to the significant climate changes that have taken place since the Last Glacial Maximum (LGM), such as the last Heinrich event (periods during which waves of icebergs dropped from glaciers and crossed the North Atlantic), the Bolling-Allerod transition, the Younger Dryas (a phase of climate cooling towards the end of the Pleistocene) and Holocene climate oscillations.
Scientists have evaluated the usefulness of the different geochemical and mineralogical markers for climatic variability, and have concluded that those which provide the most reliable and accurate sort of information are the following: Ti/Al relations (i.e. titanium and aluminium) and Zr/Al (zirconium and aluminium) for the interpretation of variations in wind patterns, and therefore for the reconstruction of arid and wet cycles; relations MG/Al (magnesium and aluminium), K(Al (potassium and aluminium) and Rb/Al (rubidium and aluminium) as markers for the variation in fluvial patterns, and the conditions for oxygenation reconstructed thanks to the relations between trace metals (U, Mo, V, Co, Ni, Cr, i.e. uranium, molybdenum, vanadium, cobalt, nickel and chromium)
The study of biological productivity has turned out to be of particular interest. It was reconstructed from the barium (Ba) content in sediments derived from biogenic baryte.
“Given that much climate change is cyclical,” prof. Martínez points out, “predicting the evolution of future climate and its control mechanisms, both natural and anthropogenic, requires a proper understanding of past climate systems, and of the response of its different components (atmosphere, biosphere, lithosphere, hydrosphere, cryosphere) at a scale larger than that of instrumental record.”
Reference:
F. Martinez-Ruiz, M. Kastner, D. Gallego-Torres, M. Rodrigo-Gámiz, V. Nieto-Moreno, M. Ortega-Huertas. Paleoclimate and paleoceanography over the past 20,000 yr in the Mediterranean Sea Basins as indicated by sediment elemental proxies. Quaternary Science Reviews, 2015; 107: 25 DOI: 10.1016/j.quascirev.2014.09.018
Physicists are using this computerized 3-D rendering of beads in a box to serve as a model for soil, sand or snow. Colored lines show the network of forces as the virtual particles are pushed together. Thick red lines connect the particles that are experiencing the brunt of the force. By studying the forces inside granular materials as they’re pressed, pushed or squeezed, the researchers hope to better understand phenomena like the jamming of grain hoppers or the early warning signs of earthquakes and avalanches. Credit: Nicolas Brodu.
Pick up a handful of sand, and it flows through your fingers like a liquid. But when you walk on the beach, the sand supports your weight like a solid. What happens to the forces between the jumbled sand grains when you step on them to keep you from sinking?
An international team of researchers collaborating at Duke University have developed a new way to measure the forces inside materials such as sand, soil or snow under pressure.
Described in the March 5 issue of Nature Communications, the technique uses lasers coupled with force sensors, digital cameras and advanced computer algorithms to peer inside and measure the forces between neighboring particles in 3-D.
The new approach will allow researchers to better understand phenomena like the jamming of grain hoppers or the early warning signs of earthquakes and avalanches, said study co-author Nicolas Brodu, now at the French institute Inria.
Whether footprints in sand, or the force of gravity on a mountain slope, physicists have long sought to understand what happens inside granular materials as they’re pressed, pushed or squeezed.
For centuries this simple question has been surprisingly difficult to answer. But more recently, thanks to advances in 3-D imaging techniques and the number-crunching power of computers, researchers are starting to get a better picture of what happens when granular materials like soil or snow are pushed together.
Brodu, along with physicists Robert Behringer of Duke University and Joshua Dijksman of Wageningen University in the Netherlands, describe how they use simple tools to measure the network of forces at it spreads from one particle to the next.
The researchers use a solution of hundreds of translucent hydrogel beads in a Plexiglass box to simulate materials like soil, sand or snow.
A piston repeatedly pushes down on the beads in the box while a sheet of laser light scans the box, and a camera takes a series of cross-sectional images of the illuminated sections.
Like MRI scans used in medicine, the technique works by converting these cross-sectional “slices” into a 3-D image.
Custom-built imaging software stacks the hundreds of thousands of 2-D images together to reconstruct the surface of each individual particle in three dimensions, over time. By measuring the tiny deformations in the particles as they are squeezed together, the researchers are able to calculate the forces between them.
The new approach will help researchers better understand a range of natural and manmade hazards, such as why farmworkers stepping into grain bins sometimes experience a quicksand effect and are suddenly sucked under.
“This gives us hope of understanding what happens in disasters like a landslide, when packed soil and rocks on a mountain become loose and slide down,” Brodu said. “First it acts like a solid, and then for reasons physicists don’t completely understand, all of a sudden it destabilizes and starts to flow like a liquid. This transition from solid to liquid can only be understood if you know what’s going on inside the soil.”
The team has already used results from their technique to create a new model for the way particulate matter behaves, which is concurrently published in the journal Physical Review E.
Video:
Physicists are using this computerized 3-D rendering of beads in a box to serve as a model for soil, sand or snow. Colored lines show the network of forces as the virtual particles are pushed together. Thick red lines connect the particles that are experiencing the brunt of the force. By studying the forces inside granular materials as they’re pressed, pushed or squeezed, the researchers hope to better understand phenomena like the jamming of grain hoppers or the early warning signs of earthquakes and avalanches.
Credit: Video courtesy of Nicolas Brodu.
Reference:
“Spanning the Scales of Granular Materials through Microscopic Force Imaging,” Brodu, N., J. A. Dijksman and R. P. Behringer. Nature Communications, March 2015. DOI: 10.1038/ncomms7361
Note : The above story is based on materials provided by Duke University.
