Liquefaction of seabed no longer a mystery

<IMG SRC="/Images/483586609.jpg" WIDTH="350" HEIGHT="222" BORDER="0" ALT="This is a pipeline floatation accident. Taken from the paper by J.S. Damgaard, B.M. Sumer, T.C. Teh, A.C. Palmer, P. Foray and D. Osorio: 'Guidelines for pipeline on-bottom stability on liquefied noncohesive seabeds' Journal of Waterway, Port, Coastal and Ocean Engineering, ASCE, vol. 132, No. 4, pp. 300-309, 2006. With permission from ASCE. – Journal of Waterway, Port, Coastal and Ocean Engineering, ASCE, vol. 132, No. 4, pp. 300-309, 2006. With permission from ASCE.”>
This is a pipeline floatation accident. Taken from the paper by J.S. Damgaard, B.M. Sumer, T.C. Teh, A.C. Palmer, P. Foray and D. Osorio: ‘Guidelines for pipeline on-bottom stability on liquefied noncohesive seabeds’ Journal of Waterway, Port, Coastal and Ocean Engineering, ASCE, vol. 132, No. 4, pp. 300-309, 2006. With permission from ASCE. – Journal of Waterway, Port, Coastal and Ocean Engineering, ASCE, vol. 132, No. 4, pp. 300-309, 2006. With permission from ASCE.

Seabed under large waves during storms may undergo liquefaction, a process in which the seabed sediment becomes liquid. Under this condition, sections of buried pipelines float to the surface of the seabed, heavy marine objects on the seabed such as breakwaters, caissons, sea mines, and pipelines sink and disappear into the seabed. How can this be explained?

Authored by renowned researcher and engineer Dr Mutlu Sumer and published by World Scientific, “Liquefaction Around Marine Structures”, features physics of liquefaction induced by large waves, mathematical modelling, floatation and sinking of marine objects in liquefied sediments. Although the main focus is the wave-induced liquefaction, it also discusses the seabed liquefaction caused by earthquakes. The book also addresses the issue of design of structures (against liquefaction) wherever it deems necessary, and provides guidelines via illustrated examples. Counter measures against seabed liquefaction is also discussed.

Many incidents with catastrophic consequences have occurred in the past due to wave-induced liquefaction of the seabed. There are also failures for which information never entered the public domain. Cost of such incidents is enormous, up to tens or even hundreds of million dollars.

The main cause of such incidents has been the fact that the structures (be it, for example, marine pipelines, or breakwaters, or caisson structures, or sea mines) have not been properly designed against liquefaction, and that has been due to the lack of knowledge, and the non-existence of guidelines for the design.

The present book essentially bridges this gap, for the first time, by collecting the state-of-the-art knowledge and building content, essentially based on the recent research conducted in the past two decades including two European research programs Liquefaction Around Marine Structures (LIMAS) and Scour Around Coastal Structures (SCARCOST) where the author was the Program Leader. The present book and the existing body of literature on earthquake-induced liquefaction (with special reference to marine structures) form a complementary source of information on liquefaction around marine structures, and will be used by consulting firms in the design of structures to ensure that incidents that occurred in the past with catastrophic dimensions can be avoided.

Dr. Mutlu Sumer is a Professor at the Technical University of Denmark, DTU Mekanik, Section for Fluid Mechanics, Coastal and Maritime Engineering. He has published two previous books with World Scientific, “Hydrodynamics Around Cylindrical Structures” and “The Mechanics of Scour in the Marine Environment”.

How productive are the ore factories in the deep sea?

About ten years after the first moon landing, scientists on earth made a discovery that proved that our home planet still holds a lot of surprises in store for us. Looking through the portholes of the submersible ALVIN near the bottom of the Pacific Ocean in 1979, American scientists saw for the first time chimneys, several meters tall, from which black water at about 300 degrees and saturated with minerals shot out. What we have found out since then: These “black smokers”, also called hydrothermal vents, exist in all oceans. They occur along the boundaries of tectonic plates along the submarine volcanic chains. However, to date many details of these systems remain unexplained.

One question that has long and intensively been discussed in research is: Where and how deep does seawater penetrate into the seafloor to take up heat and minerals before it leaves the ocean floor at hydrothermal vents? This is of enormous importance for both, the cooling of the underwater volcanoes as well as for the amount of materials dissolved. Using a complex 3-D computer model, scientists at GEOMAR Helmholtz Centre for Ocean Research Kiel were now able to understand the paths of the water toward the black smokers. The study appears in the current issue of the world-renowned scientific journal “Nature“.

In general, it is well known that seawater penetrates into the Earth’s interior through cracks and crevices along the plate boundaries. The seawater is heated by the magma; the hot water rises again, leaches metals and other elements from the ground and is released as a black colored solution. “However, in detail it is somewhat unclear whether the water enters the ocean floor in the immediate vicinity of the vents and flows upward immediately, or whether it travels long distances underground before venting,” explains Dr. Jörg Hasenclever from GEOMAR.

This question is not only important for the fundamental understanding of processes on our planet. It also has very practical implications. Some of the materials leached from the underground are deposited on the seabed and form ore deposits that may be of economically interest. There is a major debate, however, how large the resource potential of these deposits might be. “When we know which paths the water travels underground, we can better estimate the quantities of materials released by black smokers over thousands of years,” says Hasenclever.

Hasenclever and his colleagues have used for the first time a high-resolution computer model of the seafloor to simulate a six kilometer long and deep, and 16 kilometer wide section of a mid-ocean ridge in the Pacific. Among the data used by the model was the heat distribution in the oceanic crust, which is known from seismic studies. In addition, the model also considered the permeability of the rock and the special physical properties of water.

The simulation required several weeks of computing time. The result: “There are actually two different flow paths – about half the water seeps in near the vents, where the ground is very warm. The other half seeps in at greater distances and migrates for kilometers through the seafloor before exiting years later.” Thus, the current study partially confirmed results from a computer model, which were published in 2008 in the scientific journal “Science”. “However, the colleagues back then were able to simulate only a much smaller region of the ocean floor and therefore identified only the short paths near the black smokers,” says Hasenclever.

The current study is based on fundamental work on the modeling of the seafloor, which was conducted in the group of Professor Lars Rüpke within the framework of the Kiel Cluster of Excellence “The Future Ocean”. It provides scientists worldwide with the basis for further investigations to see how much ore is actually on and in the seabed, and whether or not deep-sea mining on a large scale could ever become worthwhile. “So far, we only know the surface of the ore deposits at hydrothermal vents. Nobody knows exactly how much metal is really deposited there. All the discussions about the pros and cons of deep-sea ore mining are based on a very thin database,” says co-author Prof. Dr. Colin Devey from GEOMAR. “We need to collect a lot more data on hydrothermal systems before we can make reliable statements”.

Today’s Antarctic region once as hot as California, Florida

Parts of ancient Antarctica were as warm as today’s California coast, and polar regions of the southern Pacific Ocean registered 21st-century Florida heat, according to scientists using a new way to measure past temperatures.

The findings, published the week of April 21 in the Proceedings of the National Academy of Sciences, underscore the potential for increased warmth at Earth’s poles and the associated risk of melting polar ice and rising sea levels, the researchers said.

Led by scientists at Yale, the study focused on Antarctica during the Eocene epoch, 40-50 million years ago, a period with high concentrations of atmospheric CO2 and consequently a greenhouse climate. Today, Antarctica is year-round one of the coldest places on Earth, and the continent’s interior is the coldest place, with annual average land temperatures far below zero degrees Fahrenheit.

But it wasn’t always that way, and the new measurements can help improve climate models used for predicting future climate, according to co-author Hagit Affek of Yale, associate professor of geology & geophysics.

“Quantifying past temperatures helps us understand the sensitivity of the climate system to greenhouse gases, and especially the amplification of global warming in polar regions,” Affek said.

The paper’s lead author, Peter M.J. Douglas, performed the research as a graduate student in Affek’s Yale laboratory. He is now a postdoctoral scholar at the California Institute of Technology. The research team included paleontologists, geochemists, and a climate physicist.

By measuring concentrations of rare isotopes in ancient fossil shells, the scientists found that temperatures in parts of Antarctica reached as high as 17 degrees Celsius (63F) during the Eocene, with an average of 14 degrees Celsius (57F) – similar to the average annual temperature off the coast of California today.

Eocene temperatures in parts of the southern Pacific Ocean measured 22 degrees Centigrade (or about 72F), researchers said – similar to seawater temperatures near Florida today.

Today the average annual South Pacific sea temperature near Antarctica is about 0 degrees Celsius.

These ancient ocean temperatures were not uniformly distributed throughout the Antarctic ocean regions – they were higher on the South Pacific side of Antarctica – and researchers say this finding suggests that ocean currents led to a temperature difference.

“By measuring past temperatures in different parts of Antarctica, this study gives us a clearer perspective of just how warm Antarctica was when the Earth’s atmosphere contained much more CO2 than it does today,” said Douglas. “We now know that it was warm across the continent, but also that some parts were considerably warmer than others. This provides strong evidence that global warming is especially pronounced close to the Earth’s poles. Warming in these regions has significant consequences for climate well beyond the high latitudes due to ocean circulation and melting of polar ice that leads to sea level rise.”

To determine the ancient temperatures, the scientists measured the abundance of two rare isotopes bound to each other in fossil bivalve shells collected by co-author Linda Ivany of Syracuse University at Seymour Island, a small island off the northeast side of the Antarctic Peninsula. The concentration of bonds between carbon-13 and oxygen-18 reflect the temperature in which the shells grew, the researchers said. They combined these results with other geo-thermometers and model simulations.

The new measurement technique is called carbonate clumped isotope thermometry.

“We managed to combine data from a variety of geochemical techniques on past environmental conditions with climate model simulations to learn something new about how the Earth’s climate system works under conditions different from its current state,” Affek said. “This combined result provides a fuller picture than either approach could on its own.”

Taking the pulse of mountain formation in the Andes

Sedimentary deposits near Cerdas in the Altiplano plateau of Bolivia are shown. These rocks contain ancient soils used to decipher the surface temperature and surface uplift history of the southern Altiplano. -  Photo by Carmala Garzione/University of Rochester.
Sedimentary deposits near Cerdas in the Altiplano plateau of Bolivia are shown. These rocks contain ancient soils used to decipher the surface temperature and surface uplift history of the southern Altiplano. – Photo by Carmala Garzione/University of Rochester.

Scientists have long been trying to understand how the Andes and other broad, high-elevation mountain ranges were formed. New research by Carmala Garzione, a professor of earth and environmental sciences at the University of Rochester, and colleagues sheds light on the mystery.

In a paper published in the latest Earth and Planetary Science Letters, Garzione explains that the Altiplano plateau in the central Andes-and most likely the entire mountain range-was formed through a series of rapid growth spurts.

“This study provides increasing evidence that the plateau formed through periodic rapid pulses, not through a continuous, gradual uplift of the surface, as was traditionally thought,” said Garzione. “In geologic terms, rapid means rising one kilometer or more over several millions of years, which is very impressive.”

It’s been understood that the Andes mountain range has been growing as the Nazca oceanic plate slips underneath the South American continental plate, causing the Earth’s crust to shorten (by folding and faulting) and thicken. But that left two questions: How quickly have the Andes risen to their current height, and what was the actual process that enabled their rise?

Several years ago (2006-2008), Garzione and several colleagues provided the first estimates of the timing and rates of the surface uplift of the central Andes (“Mountain Ranges Rise Much More Rapidly than Geologists Expected”) by measuring the ancient surface temperatures and rainfall compositions preserved in the soils of the central Altiplano, a plateau in Bolivia and Peru that sits about 12,000 feet above sea level. Garzione concluded that portions of the dense lower crust and upper mantle that act like an anchor on the base of the crust are periodically detached and sink through the mantle as the thickened continental plate heats up. Detachment of this dense anchor allows the Earth’s low density upper crust to rebound and rise rapidly.

More recently, Garzione and Andrew Leier, an assistant professor of Earth and Ocean Sciences at the University of South Carolina, used a relatively new temperature-recording technique in two separate studies in different regions of the Andes to determine whether pulses of rapid surface uplift are the norm, or the exception, for the formation of mountain ranges like the Andes.

Garzione and Leier (“Stable isotope evidence for multiple pulses of rapid surface uplift in the Central Andes, Bolivia”) both focused on the bonding behavior of carbon and oxygen isotopes in the mineral calcite that precipitated from rainwater; their results were similar.

Garzione worked in the southern Altiplano, collecting climate records preserved in ancient soils at both low elevations (close to sea level), where temperatures remained warm over the history of the Andes, and at high elevations where temperatures should have cooled as the mountains rose. The calcite found in the soil contains both the lighter isotopes of carbon and oxygen-12C and 16O-as well as the rare heavier isotopes-13C and 18O. Paleo-temperature estimates from calcite rely on the fact that heavy isotopes form stronger bonds. At lower temperatures, where atoms vibrate more slowly, the heavy isotope 13C-18O bonds would be more difficult to break, resulting in a higher concentration of 13C-18O bonds in calcite, compared to what is found at warmer temperatures. By measuring the abundance of heavy isotope bonds in both low elevation (warm) sites and high elevation (cooler) sites over time, Garzione used the temperature difference between the sites to estimate the elevation of various layers of ancient soils at specific points in time.

She found that the southern Altiplano region rose by about 2.5 kilometers between 16 million and 9 million years ago, which is considered a rapid rate in geologic terms. Garzione speculates that the pulsing action relates to a dense root that grows at the boundary of the lower crust and upper mantle. As the oceanic plate slips under the continental plate, the continental plate shortens and thickens, increasing the pressure on the lower crust. The basaltic composition of the lower crust converts to a very high-density rock called eclogite, which serves as an anchor to the low-density upper crust. As this root is forced deeper into the hotter part of the mantle, it heats to a temperature where it can be rapidly removed (over several million years), resulting in the rapid rise of the mountain range.

“What we are learning is that the Altiplano plateau formed by pulses of rapid surface uplift over several million years, separated by long periods (several tens of million years) of stable elevations,” said Garzione. “We suspect this process is typical of other high-elevation ranges, but more research is needed before we know for certain.”

Scientists successfully use krypton to accurately date ancient Antarctic ice

This is the sampling trench for dust studies on Taylor Glacier. Windblown dust from local sources contaminates the upper ice layers and uncontaminated samples are obtained from a meter below the glacier's surface. -  (Photo courtesy of Hinrich Schaefer)
This is the sampling trench for dust studies on Taylor Glacier. Windblown dust from local sources contaminates the upper ice layers and uncontaminated samples are obtained from a meter below the glacier’s surface. – (Photo courtesy of Hinrich Schaefer)

A team of scientists has successfully identified the age of 120,000-year-old Antarctic ice using radiometric krypton dating – a new technique that may allow them to locate and date ice that is more than a million years old.

The ability to discover ancient ice is critical, the researchers say, because it will allow them to reconstruct the climate much farther back into Earth’s history and potentially understand the mechanisms that have triggered the planet to shift into and out of ice ages.

Results of the discovery are being published this week in the Proceedings of the National Academy of Sciences. The work was funded by the National Science Foundation and the U.S. Department of Energy.

“The oldest ice found in drilled cores is around 800,000 years old and with this new technique we think we can look in other regions and successfully date polar ice back as far as 1.5 million years,” said Christo Buizert, a postdoctoral researcher at Oregon State University and lead author on the PNAS article. “That is very exciting because a lot of interesting things happened with the Earth’s climate prior to 800,000 years ago that we currently cannot study in the ice core record.”

Krypton dating is much like the more-heralded carbon-14 dating technique that measures the decay of a radioactive isotope – which has constant and well-known decay rates – and compares it to a stable isotope. Unlike carbon-14, however, krypton is a noble gas that does not interact chemically and is much more stable with a half-life of around 230,000 years. Carbon dating doesn’t work well on ice because carbon-14 is produced in the ice itself by cosmic rays and only goes back some 50,000 years.

Krypton is produced by cosmic rays bombarding the Earth and then stored in air bubbles trapped within Antarctic ice. It has a radioactive isotope (krypton-81) that decays very slowly, and a stable isotope (krypton-83) that does not decay. Comparing the proportion of stable-to-radioactive isotopes provides the age of the ice.

Though scientists have been interested in radiokrypton dating for more than four decades, krypton-81 atoms are so limited and difficult to count that it wasn’t until a 2011 breakthrough in detector technology that krypton-81 dating became feasible for this kind of research. The new atom counter, named Atom Trap Trace Analysis, or ATTA, was developed by a team of nuclear physicists led by Zheng-Tian Lu at Argonne National Laboratory near Chicago.

In their experiment at Taylor Glacier in Antarctica, the researchers put several 300-kilogram (about 660 pounds) chunks of ice into a container and melted it to release the air from the bubbles, which was then stored in flasks. The krypton was isolated from the air at the University of Bern, Switzerland, and sent to Argonne for krypton-81 counting.

“The atom trap is so sensitive that it can capture and count individual atoms,” said Buizert, who is in OSU’s College of Earth, Ocean, and Atmospheric Sciences. “The only problem is that there isn’t a lot of krypton in the air, and thus there isn’t much in the ice, either. That’s why we need such large samples to melt down.”

The group at Argonne is continually improving the ATTA detector, researchers there say, and they aim to perform analysis on an ice sample as small as 20 kilograms in the near future.

The researchers determined from the isotope ratio that the Taylor Glacier samples were 120,000 years old, and validated the estimate by comparing the results to well-dated ice core measurements of atmospheric methane and oxygen from that same period.

Now the challenge is to locate some of the oldest ice in Antarctica, which may not be as easy as it sounds.

“Most people assume that it’s a question of just drilling deeper for ice cores, but it’s not that simple,” said Edward Brook, an Oregon State University geologist and co-author on the study. “Very old ice probably exists in small isolated patches at the base of the ice sheet that have not yet been identified, but in many places it has probably melted and flowed out into the ocean.”

There also are special regions where old ice is exposed at the edges of an ice field, Brook pointed out.

“The international scientific community is really interested in exploring for old ice in both types of places and this new dating will really help,” Brook said. “There are places where meteorites originating from Mars have been pushed out by glaciers and collect at the margins. Some have been on Earth for a million years or more, so the ice in these spots may be that old as well.”

Buizert said reconstructing the Earth’s climate back to 1.5 million years is important because a shift in the frequency of ice ages took place in what is known as the Middle Pleistocene transition. The Earth is thought to have shifted in and out of ice ages every 100,000 years or so during the past 800,000 years, but there is evidence that such a shift took place every 40,000 years prior to that time.

“Why was there a transition from a 40,000-year cycle to a 100,000-year cycle?” Buizert said. “Some people believe a change in the level of atmospheric carbon dioxide may have played a role. That is one reason we are so anxious to find ice that will take us back further in time so we can further extend data on past carbon dioxide levels and test this hypothesis.”

Impact glass stores biodata for millions of years

The scorching heat produced by asteroid or comet impacts can melt tons of soil and rock, some of which forms glass as it cools. Some of that glass preserves bits of ancient plant material. -  Brown University
The scorching heat produced by asteroid or comet impacts can melt tons of soil and rock, some of which forms glass as it cools. Some of that glass preserves bits of ancient plant material. – Brown University

Asteroid and comet impacts can cause widespread ecological havoc, killing off plants and animals on regional or even global scales. But new research from Brown University shows that impacts can also preserve the signatures of ancient life at the time of an impact.

A research team led by Brown geologist Pete Schultz has found fragments of leaves and preserved organic compounds lodged inside glass created by a several ancient impacts in Argentina. The material could provide a snapshot of environmental conditions at the time of those impacts. The find also suggests that impact glasses could be a good place to look for signs of ancient life on Mars.

The work is published in the latest issue of Geology Magazine.

The scorching heat produced by asteroid or comet impacts can melt tons of soil and rock, some of which forms glass as it cools. The soil of eastern Argentina, south of Buenos Aires, is rife with impact glass created by at least seven different impacts that occurred between 6,000 and 9 million years ago, according to Schultz. One of those impacts, dated to around 3 million years ago, coincides with the disappearance of 35 animal genera, as reported in the journal Science a few years back.

“We know these were major impacts because of how far the glass is distributed and how big the chunks are,” Schultz said. “These glasses are present in different layers of sediment throughout an area about the size of Texas.”

Within glass associated with two of those impacts – one from 3 million years ago and one from 9 million years ago – Schultz and his colleagues found exquisitely preserved plant matter. “These glasses preserve plant morphology from macro features all the way down to the micron scale,” Schultz said. “It’s really remarkable.”

The glass samples contain centimeter-size leaf fragments, including intact structures like papillae, tiny bumps that line leaf surfaces. Bundles of vein-like structures found in several samples are very similar to modern pampas grass, a species common to that region of Argentina.

Chemical analysis of the samples also revealed the presence of organic hydrocarbons, the chemical signatures of living matter.

To understand how these structures and compounds could have been preserved, Schultz and his colleagues tried to replicate that preservation in the lab. They mixed pulverized impact glass with fragments of pampas grass leaves and heated the mixture at various temperatures for various amounts of time. The experiments showed that plant material was preserved when the samples were quickly heated to above 1,500 degrees Celsius.

It appears, Schultz says, that water in the exterior layers of the leaves insulates the inside layers, allowing them to stay intact. “The outside of the leaves takes it for the interior,” he said. “It’s a little like deep frying. The outside fries up quickly but the inside takes much longer to cook.”

Implications for Mars

If impact glass can preserve the signatures of life on Earth, it stands to reason that it could do the same on Mars, Schultz says. And the soil conditions in Argentina that contributed to the preservation of samples in this study are not unlike soils found on Mars.

The Pampas region of Argentina is covered with thick layers of windblown sediment called loess. Schultz believes that when an object impacts this sediment, globs of melted material roll out from the edge of the impact area like molten snowballs. As they roll, they collect material from the ground and cool quickly – the dynamics that the lab experiments showed were important for preservation. After the impact, those glasses are slowly covered over as dust continues to accumulate. That helps to preserve both the glasses and the stowaways within them for long periods – in the Argentine case, for millions of years.

Much of the surface of Mars is covered in a loess-like dust, and the same mechanism that preserved the Argentine samples could also work on Mars.

“Impact glass may be where the 4 billion-year-old signs of life are hiding,” Schultz said. “On Mars they’re probably not going to come out screaming in the form of a plant, but we may find traces of organic compounds, which would be really exciting.”

Frozen in time: 3-million-year-old landscape still exists beneath the Greenland ice sheet

This is a camp at the edge of the Greenland ice sheet. -  Paul Bierman, University of Vermont
This is a camp at the edge of the Greenland ice sheet. – Paul Bierman, University of Vermont

Some of the landscape underlying the massive Greenland ice sheet may have been undisturbed for almost 3 million years, ever since the island became completely ice-covered, according to researchers funded by the National Science Foundation (NSF).

Basing their discovery on an analysis of the chemical composition of silts recovered from the bottom of an ice core more than 3,000 meters long, the researchers argue that the find suggests “pre-glacial landscapes can remain preserved for long periods under continental ice sheets.”

In the time since the ice sheet formed “the soil has been preserved and only slowly eroded, implying that an ancient landscape underlies 3,000 meters of ice at Summit, Greenland,” they conclude.

They add that “these new data are most consistent with [the concept of] a continuous cover of Summit? by ice ? with at most brief exposure and minimal surface erosion during the warmest or longest interglacial [periods].”

They also note that fossils found in northern Greenland indicated there was a green and forested landscape prior to the time that the ice sheet began to form. The new discovery indicates that even during the warmest periods since the ice sheet formed, the center of Greenland remained stable, allowing the landscape to be locked away, unmodified, under ice through millions of years of cyclical warming and cooling.

“Rather than scraping and sculpting the landscape, the ice sheet has been frozen to the ground, like a giant freezer that’s preserved an antique landscape”, said Paul R. Bierman, of the Department of Geology and Rubenstein School of the Environment and Natural Resources at the University of Vermont and lead author of the paper.

Bierman’s work was supported by two NSF grants made by its Division of Polar Programs, 1023191 and 0713956. Thomas A. Neumann, also of the University of Vermont, but now at NASA’s Goddard Space Flight Center, a co-author on the paper, also was a co-principal investigator on the latter grant.

Researchers from Idaho State University, the University of California, Santa Barbara, and the Scottish Universities Environmental Research Centre at the University of Glasgow also contributed to the paper.

The research also included contributions from two graduate students, both supported by NSF, one of whom was supported by the NSF Graduate Research Fellowships Program.

The team’s analysis was published on line on April 17 and will appear in Science magazine the following week.

Understanding how Greenland’s ice sheet behaved in the past, and in particular, how much of the ice sheet melted during previous warm periods as well as how it re-grew is important to developing a scientific understanding of how the ice sheet might behave in the future.

As global average temperatures rise, scientists are concerned about how the ice sheets in Greenland and Antarctica will respond. Vast amounts of freshwater are stored in the ice and may be released by melting, which would raise sea levels, perhaps by many meters.

The magnitude and rate of sea level rise are unknown factors in climate models.

The team based its analysis on material taken from the bottom of an ice core retrieved by the NSF-funded Greenland Ice Sheet Project Two (GISP2), which drilled down into the ice sheet near NSF’s Summit Station. An ice core is a cylinder of ice in which individual layers of ice, compacted from snowfall, going back over millennia can be observed and sampled.

Summit is situated at an elevation of 3,216 meters (10,551 feet) above sea level.

In the case of GISP2, the core itself, taken from the center of the present-day Greenland ice sheet, was 3,054 meters (10,000 feet) deep. It provides a history of the balance of gases that made up the atmosphere at time the snow fell as well as movements in the ice sheet stretching back more than 100,000 years. It also contains a mix of silts and sediments at its base where ice and rock come together.

The scientists looked at the proportions of the elements carbon, nitrogen and Beryllium-10, the source of which is cosmic rays, in sediments taken from the bottom 13 meters (42 feet) of the GISP2 ice core.

They also compared levels of the various elements with soil samples taken in Alaska, leading them to the conclusion that the landscape under the ice sheet was indeed an ancient one that predates the advent of the ice sheet. The soil comparisons were supported by two NSF grants: 0806394 and 0806399.

Study shows air temperature influenced African glacial movements

Changes in air temperature, not precipitation, drove the expansion and contraction of glaciers in Africa’s Rwenzori Mountains at the height of the last ice age, according to a Dartmouth-led study funded by the National Geographic Society and the National Science Foundation.

The results – along with a recent Dartmouth-led study that found air temperature also likely influenced the fluctuating size of South America’s Quelccaya Ice Cap over the past millennium — support many scientists’ suspicions that today’s tropical glaciers are rapidly shrinking primarily because of a warming climate rather than declining snowfall or other factors. The two studies will help scientists to understand the natural variability of past climate and to predict tropical glaciers’ response to future global warming.

The most recent study, which marks the first time that scientists have used the beryllium-10 surface exposure dating method to chronicle the advance and retreat of Africa’s glaciers, appears in the journal Geology. A PDF is available on request.

Africa’s glaciers, which occur atop the world’s highest tropical mountains, are among the most sensitive components of the world’s frozen regions, but the climatic controls that influence their fluctuations are not fully understood. Dartmouth glacial geomorphologist Meredith Kelly and her team used the beryllium-10 method to determine the ages of quartz-rich boulders atop moraines in the Rwenzori Mountains on the border of Uganda and the Democratic Republic of Congo. These mountains have the most extensive glacial and moraine systems in Africa. Moraines are ridges of sediments that mark the past positions of glaciers.

The results indicate that glaciers in equatorial East Africa advanced between 24,000 and 20,000 years ago at the coldest time of the world’s last ice age. A comparison of the moraine ages with nearby climate records indicates that Rwenzori glaciers expanded contemporaneously with regionally dry, cold conditions and retreated when air temperature increased. The results suggest that, on millennial time scales, past fluctuations of Rwenzori glaciers were strongly influenced by air temperature.

Ancient sea-levels give new clues on ice ages

International researchers, led by the Australian National University (ANU), have developed a new way to determine sea-level changes and deep-sea temperature variability over the past 5.3 million years.

The findings will help scientists better understand the climate surrounding ice ages over the past two million years, and could help determine the relationship between carbon dioxide levels, global temperatures and sea levels.

The team from ANU, the University of Southampton (UoS) and the National Oceanography Centre (NOC) in the United Kingdom, examined oxygen isotope levels in fossils of microscopic plankton recovered from the Mediterranean Sea, dating back as far as 5.3 million years.

“This is the first step for reconstructions from the Mediterranean records,” says lead researcher Eelco Rohling from the ANU Research School of Earth Sciences.

Professor Rohling said the team focused on the flow of water through Strait of Gibraltar, which was particularly sensitive to sea-level changes.

“As continental ice sheets grew during the ice ages, flow through the Strait of Gibraltar was reduced, causing measurable changes in oxygen isotope ratios in Mediterranean waters, which became preserved in the shells of the ancient plankton,” he said.

Co-author Gavin Foster from UoS said the research for the first time found long-term trends in cooling and continental ice-volume build-up cycles over the past 5.3 Million years were not the same.

“In fact, for temperature the major step toward the ice ages of the past two million years was a cooling event at 2.7 million years ago,” he said.

“But for ice-volume, the crucial step was the development of the first intense ice age at around 2.15 million years ago. Before our results, these were thought to have occurred together at about 2.5 million years ago.”
Professor Rohling said the findings will help scientists better understand the nature of ice ages and development of coastal sediment.

“The observed decoupling of temperature and ice-volume changes provides crucial new information for our understanding of how the ice ages came about,” he said.

“However, there are wider implications. For example, a more refined sea-level record over millions of years is commercially interesting because it allows a better understanding of coastal sediment sequences that are relevant to the petroleum industry.

“Our record is also of interest to climate policy developments, because it opens the door to detailed comparisons between past atmospheric carbon dioxide concentrations, global temperatures, and sea levels, which has enormous value to long-term future climate projections.”

The findings have been published in the latest on-line edition of Nature.

Vitamin B3 might have been made in space, delivered to Earth by meteorites

Karen Smith crushes meteorites with a mortar and pestle in Goddard's Astrobiology Analytical Laboratory to prepare them for analysis. Vitamin B3 was found in all eight meteorites analyzed in the study. -  Karen Smith
Karen Smith crushes meteorites with a mortar and pestle in Goddard’s Astrobiology Analytical Laboratory to prepare them for analysis. Vitamin B3 was found in all eight meteorites analyzed in the study. – Karen Smith

Ancient Earth might have had an extraterrestrial supply of vitamin B3 delivered by carbon-rich meteorites, according to a new analysis by NASA-funded researchers. The result supports a theory that the origin of life may have been assisted by a supply of key molecules created in space and brought to Earth by comet and meteor impacts.

“It is always difficult to put a value on the connection between meteorites and the origin of life; for example, earlier work has shown that vitamin B3 could have been produced non-biologically on ancient Earth, but it’s possible that an added source of vitamin B3 could have been helpful,” said Karen Smith of Pennsylvania State University in University Park, Pa. “Vitamin B3, also called nicotinic acid or niacin, is a precursor to NAD (nicotinamide adenine dinucleotide), which is essential to metabolism and likely very ancient in origin.” Smith is lead author of a paper on this research, along with co-authors from NASA’s Goddard Space Flight Center in Greenbelt, Md., now available online in the journal Geochimica et Cosmochimica Acta.

This is not the first time vitamin B3 has been found in meteorites. In 2001 a team led by Sandra Pizzarello of Arizona State University, in Tempe discovered it along with related molecules called pyridine carboxylic acids in the Tagish Lake meteorite.

In the new work at Goddard’s Astrobiology Analytical Laboratory, Smith and her team analyzed samples from eight different carbon-rich meteorites, called “CM-2 type carbonaceous chondrites” and found vitamin B3 at levels ranging from about 30 to 600 parts-per-billion. They also found other pyridine carboxylic acids at similar concentrations and, for the first time, found pyridine dicarboxylic acids.

“We discovered a pattern – less vitamin B3 (and other pyridine carboxylic acids) was found in meteorites that came from asteroids that were more altered by liquid water. One possibility may be that these molecules were destroyed during the prolonged contact with liquid water,” said Smith. “We also performed preliminary laboratory experiments simulating conditions in interstellar space and showed that the synthesis of vitamin B3 and other pyridine carboxylic acids might be possible on ice grains.”

Scientists think the solar system formed when a dense cloud of gas, dust, and ice grains collapsed under its own gravity. Clumps of dust and ice aggregated into comets and asteroids, some of which collided together to form moon-sized objects or planetesimals, and some of those eventually merged to become planets.

Space is filled with radiation from nearby stars as well as from violent events in deep space like exploding stars and black holes devouring matter. This radiation could have powered chemical reactions in the cloud (nebula) that formed the solar system, and some of those reactions may have produced biologically important molecules like vitamin B3.

Asteroids and comets are considered more or less pristine remnants from our solar system’s formation, and many meteorites are prized samples from asteroids that happen to be conveniently delivered to Earth. However, some asteroids are less pristine than others. Asteroids can be altered shortly after they form by chemical reactions in liquid water. As they grow, asteroids incorporate radioactive material present in the solar system nebula. If enough radioactive material accumulates in an asteroid, the heat produced as it decays will be sufficient to melt ice inside the asteroid. Researchers can determine how much an asteroid was altered by water by examining chemical and mineralogical signatures of water alteration in meteorites from those asteroids.

When asteroids collide with meteoroids or other asteroids, pieces break off and some of them eventually make their way to Earth as meteorites. Although meteorites are valued samples from asteroids, they are rarely recovered immediately after they fall to Earth. This leaves them vulnerable to contamination from terrestrial chemistry and life.

The team doubts the vitamin B3 and other molecules found in their meteorites came from terrestrial life for two reasons. First, the vitamin B3 was found along with its structural isomers – related molecules that have the same chemical formula but whose atoms are attached in a different order. These other molecules aren’t used by life. Non-biological chemistry tends to produce a wide variety of molecules — basically everything permitted by the materials and conditions present — but life makes only the molecules it needs. If contamination from terrestrial life was the source of the vitamin B3 in the meteorites, then only the vitamin should have been found, not the other, related molecules.

Second, the amount of vitamin B3 found was related to how much the parent asteroids had been altered by water. This correlation with conditions on the asteroids would be unlikely if the vitamin came from contamination on Earth.

The team plans to conduct additional interstellar chemistry experiments under more realistic conditions to better understand how vitamin B3 can form on ice grains in space. “We used pyridine-carbon dioxide ice in the initial experiment,” said Smith. “We want to add water ice (the dominant component of interstellar ices) and start from simpler organic precursors (building-block molecules) of vitamin B3 to help verify our result.”