Diamond impurities bonanza for geologists studying Earth’s history

This is an optical photomicrograph of a sulfide-inclusion-bearing rough diamond from Botswana. -  Steven Shirey
This is an optical photomicrograph of a sulfide-inclusion-bearing rough diamond from Botswana. – Steven Shirey

Jewelers abhor diamond impurities, but they are a bonanza for scientists.

Safely encased in super-hard diamond, impurities are unaltered, ancient minerals that tell the story of Earth’s distant past.

Researchers analyzed data from more than 4,000 of these mineral inclusions to find that continents started the cycle of breaking apart, drifting, and colliding about three billion years ago.

The research results, published in this week’s issue of the journal Science, pinpoint when this so-called Wilson cycle began.

Lead author Steven Shirey of the Carnegie Institution’s Department of Terrestrial Magnetism says that the Wilson cycle is responsible for the growth of the Earth’s continental crust, the continental structures we see today, the opening and closing of ocean basins through time, mountain building, and the distribution of ores and other materials in the crust.

“But when it all began has remained elusive until now,” Shirey says.

“We used the impurities, or inclusions, contained in diamonds, because they are perfect time capsules from great depth beneath the continents.

“They provide age and chemical information for a span of more than 3.5 billion years that includes the evolution of the atmosphere, the growth of the continental crust, and the beginning of plate tectonics.”

Co-author Stephen Richardson of the University of Cape Town says that it’s “astonishing that we can use the smallest mineral grains that can be analyzed to reveal the origin of some of Earth’s largest geological features.”

“The tiny inclusions found inside diamonds studied by this team have recorded the chemistry and evolution of the Earth over 3.5 billion years,” says Jennifer Wade, program director in the National Science Foundation (NSF)’s Division of Earth Sciences, which funded the research. “They help pinpoint when the cycle of plate tectonics first began on Earth.”

The largest diamonds come from cratons, the most ancient formations within continental interiors that have deep mantle roots or keels around which younger continental material gathered.

Cratons contain the oldest rocks on the planet, and their keels extend into the mantle more than 125 miles where pressures are sufficiently high, but temperatures sufficiently low, for diamonds to form and be stored for billions of years.

Over time, diamonds have arrived at the surface as accidental passengers during volcanic eruptions of deep magma that solidified into rocks called kimberlites.

The inclusions in diamonds come in two major varieties: peridotitic and eclogitic.

Peridotite is the most abundant rock type in the upper mantle, whereas eclogite is generally thought to be the remnant of oceanic crust recycled into the mantle by the subduction or sinking of tectonic plates.

Shirey and Richardson reviewed the data from more than 4,000 inclusions of silicate–the Earth’s most abundant material–and more than 100 inclusions of sulfide from five ancient continents.

The most crucial aspects, they say, looked at when the inclusions were encapsulated and the associated compositional trends.

Compositions vary and depend on the geochemical processing that precursor components underwent before they were encapsulated.

Two systems used to date inclusions were compared. Both rely on natural isotopes that decay at exceedingly slow but predictable rates–about one disintegration every ten years on the scale of an inclusion–making them excellent atomic clocks for determining absolute ages.

The researchers found that before 3.2 billion years ago, only diamonds with peridotitic compositions formed, whereas after three billion years ago, eclogitic diamonds dominated.

“The simplest explanation,” says Shirey, “is that this change came from the initial subduction of one tectonic plate under the deep mantle keel of another as continents began to collide on a scale similar to that of the supercontinent cycle today.

“The sequence of underthrusting and collision led to the capture of eclogite in the subcontinental mantle keel along with the fluids that are needed to make diamond.”

Concludes Richardson, “This transition marks the onset of the Wilson cycle of plate tectonics.”

Diamonds pinpoint start of colliding continents

Jewelers abhor diamond impurities, but they are a bonanza for scientists. Safely encased in the super-hard diamond, impurities are unaltered, ancient minerals that can tell the story of Earth’s distant past. Researchers analyzed data from the literature of over 4,000 of these mineral inclusions to find that continents started the cycle of breaking apart, drifting, and colliding about 3 billion years ago. The research, published in the July 22, 2011, issue of Science, pinpoints when this so-called Wilson cycle began.

Lead author Steven Shirey at the Carnegie Institution’s Department of Terrestrial Magnetism explained: “The Wilson cycle is responsible for the growth of the Earth’s continental crust, the continental structures we see today, the opening and closing of ocean basins through time, mountain building, and the distribution of ores and other materials in the crust. But when it all began has remained elusive until now. We used the impurities, or inclusions, contained in diamonds, because they are perfect time capsules from great depth beneath the continents. They provide age and chemical information for a span of more than 3.5 billion years that includes the evolution of the atmosphere, the growth of the continental crust, and the beginning of plate tectonics.”

Coauthor and longtime colleague Stephen Richardson of the University of Cape Town added: “It is astonishing that we can use the smallest mineral grains that can be analyzed to reveal the origin of some of Earth’s largest geological features.”

The largest diamonds come from cratons, the most ancient formations within continental interiors that have deep mantle roots or keels around which younger continental material gathered. Cratons contain the oldest rocks on the planet, and their keels extend into the mantle more than 125 miles (200 km) where pressures are sufficiently high, but temperatures sufficiently low, for diamonds to form and be stored for billions of years. The diamonds arrived at the surface as accidental passengers during volcanic eruptions of deep magma that solidified into rocks called kimberlites. The inclusions in diamonds come in two major varieties: peridotitic and eclogitic. Peridotite is the most abundant rock type in the upper mantle, whereas eclogite is generally thought to be the remnant of oceanic crust recycled into the mantle by the subduction or sinking of tectonic plates.

Shirey and Richardson, using their own work with other coinvestigators published in more than 20 papers over a 25-year period, reviewed the data from more than 4,000 inclusions of silicate-the Earth’s most abundant material-and more than 100 inclusions of sulfide from five ancient continents. The most crucial aspects were to look at when the inclusions were encapsulated and the associated compositional trends. Compositions vary and depend on the geochemical processing that precursor components underwent before they were encapsulated.

Two systems used to date inclusions-the rhenium-osmium and samarium-neodymium techniques-were compared. Both rely on natural isotopes that decay at exceedingly slow but predictable rates- around one disintegration every ten years on the scale of an inclusion-making them excellent atomic clocks for determining absolute ages.

The researchers found that before 3.2 billion years ago, only diamonds with peridotitic compositions formed-whereas subsequent to 3 billion years ago, eclogitic diamonds dominated. “The simplest explanation is that this change came from the initial subduction of one tectonic plate under the deep mantle keel of another as continents began to collide on a scale similar to that of the supercontinent cycle today. The sequence of underthrusting and collision led to the capture of eclogite in the subcontinental mantle keel along with the fluids that are needed to make diamonds.” remarked Shirey. “This transition marks the onset of the Wilson cycle of plate tectonics,” concluded Richardson.

Fool’s gold gives scientists priceless insight into Earth’s evolution

Fool’s gold is providing scientists with valuable insights into a turning point in the Earth’s evolution, which took place billions of years ago.

Scientists are recreating ancient forms of the mineral pyrite – dubbed fool’s gold for its metallic lustre – that reveal details of past geological events.

Detailed analysis of the mineral is giving fresh insight into the Earth before the Great Oxygenation Event, which took place 2.4 billion years ago. This was a time when oxygen released by early forms of bacteria gave rise to new forms of plant and animal life, transforming the Earth’s oceans and atmosphere.

Studying the composition of pyrite enables a geological snapshot of events at the time when it was formed. Studying the composition of different forms of iron in fool’s gold gives scientists clues as to how conditions such as atmospheric oxygen influenced the processes forming the compound.

The latest research shows that bacteria – which would have been an abundant life form at the time – did not influence the early composition of pyrite. This result, which contrasts with previous thinking, gives scientists a much clearer picture of the process.

More extensively, their discovery enables better understanding of geological conditions at the time, which informs how the oceans and atmosphere evolved.

The research, funded by the Natural Environment Research Council and the Edinburgh Collaborative of Subsurface Science and Engineering, was published in Science.

Dr Ian Butler, who led the research, said: “Technology allows us to trace scientific processes that we can’t see from examining the mineral composition alone, to understand how compounds were formed. This new information about pyrite gives us a much sharper tool with which to analyze the early evolution of the Earth, telling us more about how our planet was formed.”

Dr Romain Guilbaud, investigator on the study, said: “Our discovery enables a better understanding of how information on the Earth’s evolution, recorded in ancient minerals, can be interpreted.”

EARTH: Great Lakes geologic sunken treasure

Shipwreck enthusiasts find a bounty of nautical relics preserved in the chilly depths of the Great Lakes. But only within the last decade have explorers and scientists begun to reveal the secrets of a much different – and much more ancient – sunken treasure in Lake Huron: sinkholes.

As EARTH explores in its August feature “Great Lakes Geologic Sunken Treasure,” researchers have recently begun exploring several mysterious sinkholes in Lake Huron. These pockets of water teem with microbial life similar to that found around deep ocean hydrothermal vents or beneath ice-covered Antarctic lakes, not the kinds of microorganisms normally found in our own backyards.

Read what these scientists are finding in the exotic environments and what they might tell us about life on early Earth. Plus, read other stories on topics such as how Europe and other parts of the world are trying to surmount the sociological and political issues surrounding mining, how natural gas fracking is affecting well water and how airlines are preparing for volcanic eruptions, all in the August issue. And don’t miss the cover stories about traveling to Australia and New Zealand.

What keeps the Earth cooking?

A main source of the 44 trillion watts of heat that flows from the interior of the Earth is the decay of radioactive isotopes in the mantle and crust. Scientists using the KamLAND neutrino detector in Japan have measured how much heat is generated this way by capturing geoneutrinos released during radioactive decay. -  Lawrence Berkeley National Laboratory
A main source of the 44 trillion watts of heat that flows from the interior of the Earth is the decay of radioactive isotopes in the mantle and crust. Scientists using the KamLAND neutrino detector in Japan have measured how much heat is generated this way by capturing geoneutrinos released during radioactive decay. – Lawrence Berkeley National Laboratory

What spreads the sea floors and moves the continents? What melts iron in the outer core and enables the Earth’s magnetic field? Heat. Geologists have used temperature measurements from more than 20,000 boreholes around the world to estimate that some 44 terawatts (44 trillion watts) of heat continually flow from Earth’s interior into space. Where does it come from?

Radioactive decay of uranium, thorium, and potassium in Earth’s crust and mantle is a principal source, and in 2005 scientists in the KamLAND collaboration, based in Japan, first showed that there was a way to measure the contribution directly. The trick was to catch what KamLAND dubbed geoneutrinos – more precisely, geo-antineutrinos – emitted when radioactive isotopes decay. (KamLAND stands for Kamioka Liquid-scintillator Antineutrino Detector.)

“As a detector of geoneutrinos, KamLAND has distinct advantages,” says Stuart Freedman of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), which is a major contributor to KamLAND. Freedman, a member of Berkeley Lab’s Nuclear Science Division and a professor in the Department of Physics at the University of California at Berkeley, leads U.S. participation. “KamLAND was specifically designed to study antineutrinos. We are able to discriminate them from background noise and detect them with very high sensitivity.”

KamLAND scientists have now published new figures for heat energy from radioactive decay in the journal Nature Geoscience. Based on the improved sensitivity of the KamLAND detector, plus several years’ worth of additional data, the new estimate is not merely “consistent” with the predictions of accepted geophysical models but is precise enough to aid in refining those models.

One thing that’s at least 97-percent certain is that radioactive decay supplies only about half the Earth’s heat. Other sources – primordial heat left over from the planet’s formation, and possibly others as well – must account for the rest.

Hunting for neutrinos from deep in the Earth

Antineutrinos are produced not only in the decay of uranium, thorium, and potassium isotopes but in a variety of others, including fission products in nuclear power reactors. In fact, reactor-produced antineutrinos were the first neutrinos to be directly detected (neutrinos and antineutrinos are distinguished from each other by the interactions in which they appear).

Because neutrinos interact only by way of the weak force – and gravity, insignificant except on the scale of the cosmos – they stream through the Earth as if it were transparent. This makes them hard to spot, but on the very rare occasions when an antineutrino collides with a proton inside the KamLAND detector – a sphere filled with a thousand metric tons of scintillating mineral oil – it produces an unmistakable double signal.

The first signal comes when the antineutrino converts the proton to a neutron plus a positron (an anti-electron), which quickly annihilates when it hits an ordinary electron – a process called inverse beta decay. The faint flash of light from the ionizing positron and the annihilation process is picked up by the more than 1,800 photomultiplier tubes within the KamLAND vessel. A couple of hundred millionths of a second later the neutron from the decay is captured by a proton in the hydrogen-rich fluid and emits a gamma ray, the second signal. This “delayed coincidence” allows antineutrino interactions to be distinguished from background events such as hits from cosmic rays penetrating the kilometer of rock that overlies the detector.

Says Freedman, “It’s like looking for a spy in a crowd of people on the street. You can’t pick out one spy, but if there’s a second spy following the first one around, the signal is still small but it’s easy to spot.”

KamLAND was originally designed to detect antineutrinos from more than 50 reactors in Japan, some close and some far away, in order to study the phenomenon of neutrino oscillation. Reactors produce electron neutrinos, but as they travel they oscillate into muon neutrinos and tau neutrinos; the three “flavors” are associated with the electron and its heavier cousins.

Being surrounded by nuclear reactors means KamLAND’s background events from reactor antineutrinos must also be accounted for in identifying geoneutrino events. This is done by identifying the nuclear-plant antineutrinos by their characteristic energies and other factors, such as their varying rates of production versus the steady arrival of geoneutrinos. Reactor antineutrinos are calculated and subtracted from the total. What’s left are the geoneutrinos.

Tracking the heat

All models of the inner Earth depend on indirect evidence. Leading models of the kind known as bulk silicate Earth (BSE) assume that the mantle and crust contain only lithophiles (“rock-loving” elements) and the core contains only siderophiles (elements that “like to be with iron”). Thus all the heat from radioactive decay comes from the crust and mantle – about eight terawatts from uranium 238 (238U), another eight terawatts from thorium 232 (232Th), and four terawatts from potassium 40 (40K).

KamLAND’s double-coincidence detection method is insensitive to the low-energy part of the geoneutrino signal from 238U and 232Th and completely insensitive to 40K antineutrinos. Other kinds of radioactive decay are also missed by the detector, but compared to uranium, thorium, and potassium are negligible contributors to Earth’s heat.

Additional factors that have to be taken into account include how the radioactive elements are distributed (whether uniformly or concentrated in a “sunken layer” at the core-mantle boundary), variations due to radioactive elements in the local geology (in KamLAND’s case, less than 10 percent of the expected flux), antineutrinos from fission products, and how neutrinos oscillate as they travel through the crust and mantle. Alternate theories were also considered, including the speculative idea that there may be a natural nuclear reactor somewhere deep inside the Earth, where fissile elements have accumulated and initiated a sustained fission reaction.

KamLAND detected 841 candidate antineutrino events between March of 2002 and November of 2009, of which about 730 were reactor events or other background. The rest, about 111, were from radioactive decays of uranium and thorium in the Earth. These results were combined with data from the Borexino experiment at Gran Sasso in Italy to calculate the contribution of uranium and thorium to Earth’s heat production. The answer was about 20 terawatts; based on models, another three terawatts were estimated to come from other isotope decays.

This is more heat energy than the most popular BSE model suggests, but still far less than Earth’s total. Says Freedman, “One thing we can say with near certainty is that radioactive decay alone is not enough to account for Earth’s heat energy. Whether the rest is primordial heat or comes from some other source is an unanswered question.”

Better models are likely to result when many more geoneutrino detectors are located in different places around the globe, including midocean islands where the crust is thin and local concentrations of radioactivity (not to mention nuclear reactors) are at a minimum.

Says Freedman, “This is what’s called an inverse problem, where you have a lot of information but also a lot of complicated inputs and variables. Sorting those out to arrive at the best explanation among many requires multiple sources of data.”

Deep below the Deepwater Horizon oil spill

This is a graphic explanation of escaped petroleum dispersion 1,000 meters below the sea. -  EPFL
This is a graphic explanation of escaped petroleum dispersion 1,000 meters below the sea. – EPFL

For the first time, scientists gathered oil and gas directly as it escaped from a deep ocean wellhead – that of the damaged Deepwater Horizon oil rig. What they found allows a better understanding of how pollution is partitioned and transported in the depths of the Gulf of Mexico and permits superior estimation of the environmental impact of escaping oil, allowing for a more precise evaluation of previously estimated repercussions on seafloor life in the future.

The explosion of the Deepwater Horizon rig in April 2010 was both a human and an environmental catastrophe. Getting the spill under control was an enormous challenge. The main problem was the depth of the well, nearly 1,500 meters below the sea surface. It was a configuration that had never been tried before, and the pollution it unleashed after methane gas shot to the surface and ignited in a fiery explosion is also unequalled. Much research has been done since the spill on the effects on marine life at the ocean’s surface and in coastal regions. Now, École Polytechnique Fédérale de Lausanne (EPFL) professor Samuel Arey and the Woods Hole Oceanographic Institute reveal in the advance online edition of Proceedings of the National Academy of Sciences how escaped crude oil and gas behave in the deep water environment.

Into the deep


In June 2010, with the help of a remotely operated vehicle (ROV), Woods Hole scientists reached the base of the rig and gathered samples directly from the wellhead using a robotic arm. The oceanographers also made more than 200 other measurements at various water depths over a 30-kilometer area. These samples were then analyzed with the help of the US National Oceanic and Atmospheric Administration and the dissolution of hydrocarbons was modeled at EPFL. This model showed how the properties of hydrocarbons are important in understanding the wellhead structure and pollution diffusion-how pollution spreads out-in the depths.

From the ROV to the lab


Lab analysis led the scientists to describe for the first time the physical basis for the deep sea trajectories of light-weight, water-soluble hydrocarbons such as methane, benzene, and naphthalene released from the base of the rig. The researchers observed, for example, that at a little more than 1,000 meters below the surface, a large plume spread out from the original gusher, moving horizontally in a southwest direction with prevailing currents. Unlike a surface spill, from which these volatile compounds evaporate into the atmosphere, in the deep water under pressure, light hydrocarbon components predominantly dissolve or form hydrates, compounds containing water molecules. And depending on its properties, the resulting complex mixture can rise, sink, or even remain suspended in the water, and possibly go on to cause damage to seafloor life far from the original spill.

By comparing the oil and gas escaping from the well with the mixture at the surface, EPFL’s Samuel Arey, head of Environmental Chemistry Modeling Laboratory, and colleagues were able to show that the composition of the deep sea plumes could be explained by significant dissolution of light hydrocarbons at 1 kilometer depth. In other words, an important part of the oil spreads out in underwater plumes, so we need a more precise evaluation of previously estimated repercussions on seafloor life in the future. Arey’s methodology offers a better estimation of how pollution travels and the potential deep sea consequences of spills.

“Modeling the environmental fate of hydrocarbons in deep water ecosystems required a new approach, with a global view, in order to correctly understand the impact of the pollution,” explains Arey. This research will have a significant impact on assessments of the environmental impact of deep water oil spills.

Rising oceans — too late to turn the tide?

If sea levels rose to where they were during the Last Interglacial Period, large parts of the Gulf of Mexico would be under water (red areas), including half of Florida and several Caribbean islands. -  Jeremy Weiss, Department of Geosciences, The University of Arizona
If sea levels rose to where they were during the Last Interglacial Period, large parts of the Gulf of Mexico would be under water (red areas), including half of Florida and several Caribbean islands. – Jeremy Weiss, Department of Geosciences, The University of Arizona

Thermal expansion of seawater contributed only slightly to rising sea levels compared to melting ice sheets during the Last Interglacial Period, a University of Arizona-led team of researchers has found.

The study combined paleoclimate records with computer simulations of atmosphere-ocean interactions and the team’s co-authored paper is accepted for publication in Geophysical Research Letters.

As the world’s climate becomes warmer due to increased greenhouse gases in the atmosphere, sea levels are expected to rise by up to three feet by the end of this century.

But the question remains: How much of that will be due to ice sheets melting as opposed to the oceans’ 332 million cubic miles of water increasing in volume as they warm up?

For the study, UA team members analyzed paleoceanic records of global distribution of sea surface temperatures of the warmest 5,000-year period during the Last Interglacial, a warm period that lasted from 130,000 to 120,000 years ago.

The researchers then compared the data to results of computer-based climate models simulating ocean temperatures during a 200-year snapshot as if taken 125,000 years ago and calculating the contributions from thermal expansion of sea water.

The team found that thermal expansion could have contributed no more than 40 centimeters – less than 1.5 feet – to the rising sea levels during that time, which exceeded today’s level up to eight meters or 26 feet.

At the same time, the paleoclimate data revealed average ocean temperatures that were only about 0.7 degrees Celsius, or 1.3 degrees Fahrenheit, above those of today.

“This means that even small amounts of warming may have committed us to more ice sheet melting than we previously thought. The temperature during that time of high sea levels wasn’t that much warmer than it is today,” said Nicholas McKay, a doctoral student at the UA’s department of geosciences and the paper’s lead author.

McKay pointed out that even if ocean levels rose to similar heights as during the Last Interglacial, they would do so at a rate of up to three feet per century.

“Even though the oceans are absorbing a good deal of the total global warming, the atmosphere is warming faster than the oceans,” McKay added. “Moreover, ocean warming is lagging behind the warming of the atmosphere. The melting of large polar ice sheets lags even farther behind.”

“As a result, even if we stopped greenhouse gas emissions right now, the Earth would keep warming, the oceans would keep warming, the ice sheets would keep shrinking, and sea levels would keep rising for a long time,” he explained.

They are absorbing most of that heat, but they lag behind. Especially the large ice sheets are not in equilibrium with global climate,” McKay added. “

Jonathan Overpeck, co-director of the UA’s Institute of the Environment and a professor with joint appointments in the department of geosciences and atmospheric sciences, said: “This study marks the strongest case yet made that humans – by warming the atmosphere and oceans – are pushing the Earth’s climate toward the threshold where we will likely be committed to four to six or even more meters of sea level rise in coming centuries.”

Overpeck, who is McKay’s doctoral advisor and a co-author of the study, added: “Unless we dramatically curb global warming, we are in for centuries of sea level rise at a rate of up to three feet per century, with the bulk of the water coming from the melting of the great polar ice sheets – both the Greenland and Antarctic Ice Sheets.”

According to the authors, the new results imply that 4.1 to 5.8 meters, or 13.5 to 19 feet, of sea level rise during the Last Interglacial period was derived from the Antarctic Ice Sheet, “reemphasizing the concern that both the Antarctic and Greenland Ice Sheets may be more sensitive to warming temperatures than widely thought.”

“The central question we asked was, ‘What are the warmest 5,000 years we can find for all these records, and what was the corresponding sea level rise during that time?'” McKay said.

Evidence for elevated sea levels is scattered all around the globe, he added. On Barbados and the Bahamas, for example, notches cut by waves into the rock six or more meters above the present shoreline have been dated to being 125,000 years old.

“Based on previous studies, we know that the sea level during the Last Interglacial was up to 8.5 meters higher than today,” McKay explained.

“We already knew that the vast majority came from the melting of the large ice sheets in Greenland and Antarctica, but how much could the expansion of seawater have added to that?”

Given that sea surface temperatures were about 0.7 degrees warmer than today, the team calculated that even if the warmer temperatures reached all the way down to 2,000 meters depth – more than 6,500 feet, which is highly unlikely – expansion would have accounted for no more than 40 centimeters, less than a foot and a half.

“That means almost all of the substantial sea level rise in the Last Interglacial must have come from the large ice sheets, with only a small contribution from melted mountain glaciers and small ice caps,” McKay said.

According to co-author Bette Otto-Bliesner, senior scientist at the National Center for Atmospheric Research (NCAR) in Boulder, Colo., getting the same estimate of the role ocean expansion played on sea level rise increases confidence in the data and the climate models.

“The models allow us to attribute changes we observe in the paleoclimate record to the physical mechanisms that caused those changes,” Otto-Bliesner said. “This helps tremendously in being able to distinguish mere correlations from cause-and-effect relationships.”

The authors cautioned that past evidence is not a prediction of the future, mostly because global temperatures during the Last Interglacial were driven by changes in the Earth’s orbit around the sun. However, current global warming is driven by increasing greenhouse gas concentrations.

The seasonal differences between the northern and the southern hemispheres were more pronounced during the Last Interglacial than they will be in the future.

“We expect something quite different for the future because we’re not changing things seasonally, we’re warming the globe in all seasons,” McKay said.

“The question is, when we think about warming on a global scale and contemplate letting the climate system change to a new warmer state, what would we expect for the ice sheets and sea levels based on the paleoclimate record? The Last Interglacial is the most recent time when sea levels were much higher and it’s a time for which we have lots of data,” McKay added.

“The message is that the last time glaciers and ice sheets melted, sea levels rose by more than eight meters. Much of the world’s population lives relatively close to sea level. This is going to have huge impacts, especially on poor countries,” he added.

“If you live a meter above sea level, it’s irrelevant what causes the rise. Whether sea levels are rising for natural reasons or for anthropogenic reasons, you’re still going to be under water sooner or later.”

Fast-shrinking Greenland glacier experienced rapid growth during cooler times

Large, marine-calving glaciers have the ability not only to shrink rapidly in response to global warming, but to grow at a remarkable pace during periods of global cooling, according to University at Buffalo geologists working in Greenland.

The conclusion stems from new research on Jakobshavn Isbrae, a tongue of ice extending out to sea from Greenland’s west coast. Through an analysis of adjacent lake sediments and plant fossils, the UB team determined that the glacier, which retreated about 40 kilometers inland between 1850 and 2010, expanded outward at a similar pace about 200 years ago, during a time of cooler temperatures known as the Little Ice Age.

A paper detailing the results is in press and available online in Quaternary Science Reviews, a top peer-reviewed journal in the field. (http://www.sciencedirect.com/science/article/pii/S0277379111001636)

“We know that Jakobshavn Isbrae has retreated at this incredible rate in recent years, and our study suggests that it advanced that fast, also,” said Jason Briner, the associate professor of geology who led the research. His team included master’s and PhD students from UB and Brown University.

“Our results support growing evidence that calving glaciers are particularly sensitive to climate change,” Briner added.

Jakobshavn Isbrae has been the focus of intense scientific interest because it is one of the world’s fastest-flowing glacier, releasing enormous quantities of Greenland’s ice into the ocean. Changes in the rate at which icebergs calve off from the glacier could influence global sea level rise.

The decline of Jakobshavn Isbrae between 1850 and 2010 has been well-documented through aerial photographs and satellite photographs by UB Associate Professor of Geology Bea Csatho, which show the ice shrinking rapidly from west to east along a narrow fjord.

To reconstruct the glacier’s advance from east to west during earlier, cooler years, Briner and his colleagues examined sediment samples from Glacial Lake Morten and Iceboom Lake, two glacier-fed lakes that sit along the glacier’s path of expansion.

As Jakobshavn Isbrae expanded seaward, it reached Glacial Lake Morten first, damming one side of the lake with ice and filling the basin, previously a tundra-covered valley, with meltwater.

To pinpoint the time in history when this happened, the researchers counted annual layers of overlying glacial sediments and used radiocarbon dating to analyze plant fossils at the lake bottom (the last vestiges of the old tundra). The team’s conclusion: Glacial Lake Morten formed between 1795 and 1800.

An analysis of sediment layers from the bottom of Iceboom Lake showed that Jakobshavn Isbrae reached Iceboom lake about 20 or 25 years later, around 1820.

Jakobshavn Isbrae’s rate of expansion from Glacial Lake Morten to Iceboom Lake, as documented by the UB team, matched the glacier’s rate of retreat between those two points. (Aerial imagery shows Iceboom Lake draining around 1965 and Glacial Lake Morten draining between 1986 and 1991.

Long distance: Research shows ancient rock under Haiti came from 1,000+ miles away

Earthquakes and volcanoes are known for their ability to transform Earth’s surface, but new research in the Caribbean has found they can also move ancient Earth rock foundations more than 1,000 miles.

Two University of Florida geologists are part of a team that found lavas on the Caribbean island of Hispaniola – home to Haiti and the Dominican Republic – that suggest the area is underlain by rocks almost a billion years older than previously believed. Until now geologists thought Hispaniola was relatively young from a geological perspective and rocks there should be no older than the Jurassic period, around 150 million to 160 million years ago.

An article published Sunday on the Nature Geoscience website reports the team found that unusual lavas resulting from relatively recent volcanic activity had occurred in the region of the same fault system that caused the January 2010 earthquake in Haiti. The existence of this volcanic activity, which probably occurred less than 1 million years ago, is unexpected as it postdates the previously known active volcanism in this part of the Caribbean by at least 40 million years, said Michael R. Perfit, a professor and chairman of UF’s department of geological sciences.

The most surprising discovery came from chemical analyses of the lavas which were found to have compositions similar to lavas found inside stable interior parts of continents. A detailed examination of the chemical data suggests that the source for these lavas is derived from mantle rock that originated at least 1,000 miles away.

“We can use the trace element and isotope information recorded in lavas and other environmental samples as sort of ‘inorganic DNA’ to trace their origin, migratory pathways and age,” said George D. Kamenov, a UF associate in geology. The department’s state-of-the-art plasma mass spectrometer was used to measure precisely the abundances of lead, strontium and neodymium isotopes in the lavas.

The team of geologists found the ratios of these isotopes did not match any rock substrate found nearby or anywhere else on the Caribbean islands. Instead the isotope ratios matched billion year old rocks like those existing in Central and South America today. These crustal fragments are likely surviving portions of an ancient supercontinent known as Gondwana. By contrast, lavas found in island arcs such as the Greater Antilles are formed by oceanic plates being thrust under other oceanic plates or continents similar to what is currently happening around the so called “Ring of Fire” around the Pacific Ocean.

Perfit said the findings suggest that as the Caribbean tectonic plate moved between North and South America it captured a rifted piece of ancient continent that had formed the foundation of Central America. Subsequently this fragment migrated eastward, likely for more than 1,000 miles, to its current position in Hispaniola. This implies that continental material can be transported in the upper mantle for thousands of miles and survive more or less intact for billions of years with such fragments serving as “cores” around which islands and eventually continents can grow.

The research suggests the possibility that the fault system in the region can be “leaky” and can be a place where volcanic activity occurs. Although it is uncommon, sometimes major transform faults (called leaky transform faults) penetrating tens of miles into the Earth’s crust serve as conduits for magma to reach the surface. One example of this is the southernmost boundary of the San Andreas Fault in the area of the Salton Sea in Southern California.

“In addition to earthquakes in such fault zones you may get volcanic activity, but we can’t use this to predict earthquakes or say there will be a volcano in Haiti in the near future,” Kamenov said. “Although the volcanism we found occurred only a million years ago, we can’t say if it will happen again or not. In addition, there are known hot springs and travertine deposits east of these volcanoes indicating that the geothermal activity continues today.”

Lie of the land beneath glaciers influences impact on sea levels

Fresh research into glaciers could help scientists better predict the impact of changing climates on global sea levels.

Scientists have shown for the first time that the terrain beneath glaciers influences how much glacier melt contributes to fluctuations in sea levels.

Researchers say the study will improve their understanding of how ice sheet movements have affected sea levels in the past, and will enable more accurate projections of future change.

Scientists from the University of Edinburgh studied the Slessor glacier in the Weddell Sea bay in Antarctica, and found surprising evidence that ice thickness in the region has not changed markedly since the past ice age.

Researchers say that this is because during the last ice age, sea levels were lower, which would be expected to extend the land over which the ice traveled slowly towards the sea, thickening as it went. However, a large trough in the land caused the glacier to float instead, moving more quickly and preventing its thickening.

This means the ice thickness has not varied markedly with climate or sea level change and has had little impact on sea levels or the volume of ice in Antarctica.

Being able to anticipate the dynamics of the ice sheet in response to changing climates helps scientists predict shifts in global sea levels.

The study, funded by the Natural Environment Research Council and Scottish Alliance for Geoscience, Environment and Society, was published in Earth and Planetary Science Letters and unveiled at the International Symposium of Antarctic Earth Sciences in Edinburgh.

Dr Andrew Hein, of the University of Edinburgh’s School of Geosciences, said: “This finding is remarkable. We expected to show that the Slessor glacier had thinned significantly since the last ice age, in common with other glaciers in Antarctica. But it is possible to step off the glacier and on to rocks that have been untouched by ice for more than 100,000 years. To understand the behavior of big glaciers, it is important to understand their landscapes.”