Oceanographers develop method for measuring the pace of life in deep sediments

Life deep in the seabed proceeds very slowly. But the slow-growing bacteria living many meters beneath the seafloor play an important role in the global storage of organic carbon and have a long-term effect on climate.
A team of scientists from Aarhus University (Denmark) and the University of Rhode Island have developed a new method for measuring this slow life deep down in the seabed.

Their findings were published last week in the journal Nature.

According to URI Oceanography Professor Arthur Spivack, the relative abundance of amino acids that are mirror images of each other in subseafloor sediment reflects the activity of microorganisms. The research team used this signature to calculate how active microorganisms are in the deepest layers of the seabed.

The deep seafloor samples were collected during an international drilling program led by the URI and Danish researchers. Advanced laboratory techniques were used to obtain the data. The researchers found that the metabolism of organic carbon takes place at a much slower rate in the deep seabed compared with all other known ecosystems.

“This study goes far beyond previous studies by showing that microbes in subseafloor sediment replace their biomass thousands of times more slowly than microbes in the surface world,” said URI Oceanography Professor Steven D’Hondt. The mean generation time of bacterial cells in the sediment is correspondingly long – 1,000 to 3,000 years. In comparison, the bacteria that have previously been studied in the laboratory or in nature typically reproduce in a number of hours.

“Seventy percent of our planet is covered by ocean, which means that seventy percent of the planet is made up of seabed consisting of sediment that stores old organic matter,” said Aarhus University Associate Professor Bente Lomstein. “In some places the deposits are more than one hundred meters thick. Several percent of the total living biomass on Earth is actually found in the mud in the seabed. The bacteria in the seabed convert the carbon of organic matter to CO2, and if we add it all up, the metabolism down there plays a crucial role in the global carbon cycle, even if it happens very slowly.”

One reason for the slow pace of life in the seabed is the challenging environment the bacteria lives in.

“Extremely high pressure, total darkness and very little nutrition – those are the conditions under which microorganisms live in the seabed,” added Alice Thoft Langerhuus, another Aarhus University researcher. “At the bottom of the deep ocean, the pressure reaches several hundred atmospheres.”

The research team has also showed how many of the bacteria survive under such extreme conditions. The scientists succeeded for the first time in demonstrating that there are just as many dormant cells as there are active ones. The dormant bacteria have formed endospores, which have a solid shell to protect themselves against the harsh environment.

The researchers said that their new method for calculating the pace of life in the seabed can also be used to measure the pace of life in other ancient environments with extremely low biological activity, like permafrost soils.

Geologists correct a rift in Africa

The huge changes in the Earth’s crust that influenced human evolution are being redefined, according to research published today in Nature Geoscience.

The Great Rift Valley of East Africa – the birthplace of the human species – may have taken much longer to develop than previously believed.

“”We now believe that the western portion of the rift formed about 25 million years ago, and is approximately as old as the eastern part, instead of much younger as other studies have maintained,” said Michael Gottfried, Michigan State University associate professor of geological sciences. “The significance is that the Rift Valley is the setting for the most crucial steps in primate and ultimately human evolution, and our study has major implications for the environmental and landscape changes that form the backdrop for that evolutionary story.”

Gottfried worked with an international team led by Eric Roberts at Australia’s James Cook University who added that the findings have important implications for understanding climate change models, animal evolution and the development of Africa’s unique landscape.

The Rukwa Rift (a segment of the western branch) is an example of a divergent plate boundary, where the Earth’s tectonic forces are pulling plates apart and creating new continental crust. The East African Rift system is composed of two main segments: the eastern branch that passes through Ethiopia and Kenya, and a western branch that forms a giant arc from Uganda to Malawi, interconnecting the famous rift lakes of eastern Africa.

Traditionally, the eastern branch is considered much older, having developed 15 to 25 million years earlier than the western branch.

This study provides new evidence that the two rift segments developed at about the same time, nearly doubling the initiation age of the western branch and the timing of uplift in this region of East Africa.

“A key piece of evidence in this study is the discovery of approximately 25 million-year-old lake and river deposits in the Rukwa Rift that preserve abundant volcanic ash and vertebrate fossils,” Roberts said.

These deposits include some of the earliest anthropoid primates yet found in the rift, added Nancy Stevens of Ohio University.

The findings imply that around 25 to 30 million years ago, the broad uplift of East Africa occurred and re-arranged the flow of large rivers such as the Congo and the Nile to create the distinct landscapes and climates that mark Africa today.

Signs of thawing permafrost revealed from space

Permafrost is ground that remains at or below 0┬░C for at least two consecutive years and usually appears in areas at high latitudes such as Alaska, Siberia and Northern Scandinavia, or at high altitudes like the Andes, Himalayas and the Alps. About half of the world’s underground organic carbon is found in northern permafrost regions. This is more than double the amount of carbon in the atmosphere in the form of the greenhouse gases carbon dioxide and methane.

The effects of climate change are most severe and rapid in the Arctic, causing the permafrost to thaw. When it does, it releases greenhouse gases into the atmosphere, exacerbating the effects of climate change.

Although permafrost cannot be directly measured from space, factors such as surface temperature, land cover and snow parameters, soil moisture and terrain changes can be captured by satellites.

The use of satellite data like from ESA’s Envisat, along with other Earth-observing satellites and intensive field measurements, allows the permafrost research community to get a panoptic view of permafrost phenomena from a local to a Circum-Arctic dimension.

“Combining field measurements with remote sensing and climate models can advance our understanding of the complex processes in the permafrost region and improve projections of the future climate,” said Dr Hans-Wolfgang Hubberten, head of the Alfred Wegner Institute Research Unit (Germany) and President of the International Permafrost Association.

Last month, more than 60 permafrost scientists and Earth observation specialists came together for the Third Permafrost User Workshop at the Alfred Wegener Institute in Potsdam, Germany, to discuss their latest findings.

“The already available Permafrost products provide researchers with valuable datasets which can be used in addition to other observational data for climate and hydrological modelling,” said Dr Leonid Bobylev, the director of the Nansen Centre in St. Petersburg.

“However, for climate change studies – and in particular for evaluation of the climate models’ performance – it is essential to get a longer time series of satellite observational data.

“Therefore, the Permafrost related measurements should be continued in the future and extended consistently in the past.”

ESA will continue to monitor the permafrost region with its Envisat satellite and the upcoming Sentinel satellite series for Europe’s Global Monitoring for Environment and Security (GMES) programme.

Expedition to undersea mountain yields new information about sub-seafloor structure

This is a map of Atlantis Massif, showing the fault that borders this Atlantic Ocean seamount. -  NOAA
This is a map of Atlantis Massif, showing the fault that borders this Atlantic Ocean seamount. – NOAA

Scientists recently concluded an expedition aboard the research vessel JOIDES Resolution to learn more about Atlantis Massif, an undersea mountain, or seamount, that formed in a very different way than the majority of the seafloor in the oceans.

Unlike volcanic seamounts, which are made of the basalt that’s typical of most of the seafloor, Atlantis Massif includes rock types that are usually only found much deeper in the ocean crust, such as gabbro and peridotite.

The expedition, known as Integrated Ocean Drilling Program (IODP) Expedition 340T, marks the first time the geophysical properties of gabbroic rocks have successfully been measured directly in place, rather than via remote techniques such as seismic surveying.

With these measurements in hand, scientists can now infer how these hard-to-reach rocks will “look” on future seismic surveys, making it easier to map out geophysical structures beneath the seafloor.

“This is exciting because it means that we may be able to use seismic survey data to infer the pattern of seawater circulation within the deeper crust,” says Donna Blackman of the Scripps Institution of Oceanography in La Jolla, Calif., co-chief scientist for Expedition 340T.

“This would be a key step for quantifying rates and volumes of chemical, possibly biological, exchange between the oceans and the crust.”

Atlantis Massif sits on the flank of an oceanic spreading center that runs down the middle of the Atlantic Ocean.

As the tectonic plates separate, new crust is formed at the spreading center and a combination of stretching, faulting and the intrusion of magma from below shape the new seafloor.

Periods of reduced magma supplied from the underlying mantle result in the development of long-lived, large faults. Deep portions of the crust shift upward along these faults and may be exposed at the seafloor.

This process results in the formation of an oceanic core complex, or OCC, and is similar to the processes that formed the Basin and Range province of the Southwest United States.

“Recent discoveries from scientific ocean drilling have underlined that the process of creating new oceanic crust at seafloor spreading centers is complex,” says Jamie Allan, IODP program director at the U.S. National Science Foundation (NSF), which co-funds the program.

“This work significantly adds to our ability to infer ocean crust structure and composition, including predicting how ocean crust has ‘aged’ in an area,” says Allan, “thereby giving us new tools for understanding ocean crust creation from Earth’s mantle.”

Atlantis Massif is a classic example of an oceanic core complex.

Because it’s relatively young–formed within the last million years–it’s an ideal place, scientists say, to study how the interplay between faulting, magmatism and seawater circulation influences the evolution of an OCC within the crust.

“Vast ocean basins cover most of the Earth, yet their crust is formed in a narrow zone,” says Blackman. “We’re studying that source zone to understand how rifting and magmatism work together to form a new plate.”

The JOIDES Resolution first visited Atlantis Massif about seven years ago; the science team on that expedition measured properties in gabbro.

But they focused on a shallower section, where pervasive seawater circulation had weathered the rock and changed its physical properties.

For the current expedition, the team did not drill new holes.

Rather, they lowered instruments into a deep existing hole drilled on a previous expedition, and made measurements from inside the hole.

The new measurements, at depths between 800 and 1,400 meters (about 2,600-4,600 feet) below the seafloor, include only a few narrow zones that had been altered by seawater circulation and/or by fault slip deformation.

The rest of the measurements focused on gabbroic rocks that have remained unaltered thus far.

The properties measured in the narrow zones of altered rock differ from the background properties measured in the unaltered gabbroic rocks.

The team found small differences in temperature next to two sub-seafloor faults, which suggests a slow percolation of seawater within those zones.

There were also significant differences in the speed at which seismic waves travel through the altered vs. unaltered zones.

“The expedition was a great opportunity to ground-truth our recent seismic analysis,” says Alistair Harding, also from the Scripps Institution of Oceanography and a co-chief scientist for Expedition 340T.

“It also provides vital baseline data for further seismic work aimed at understanding the formation and alteration of the massif.”

The Integrated Ocean Drilling Program (IODP) is an international research program dedicated to advancing scientific understanding of the Earth through drilling, coring and monitoring the subseafloor.

The JOIDES Resolution is a scientific research vessel managed by the U.S. Implementing Organization of IODP (USIO). Texas A&M University, Lamont-Doherty Earth Observatory of Columbia University and the Consortium for Ocean Leadership comprise the USIO.

Seismic survey at the Mariana trench will follow water dragged down into the Earth’s mantle

After the cruise some of the scientists set sail on a smaller boat to install seismometers on five islands surrounding the trench. The volcano that created one of these islands, Pagan, has erupted several times over the past 30 years. Fortunately it was only moderately active when the team was there, expelling steam that reflects the setting sun in this photo. -  Heather Relyea
After the cruise some of the scientists set sail on a smaller boat to install seismometers on five islands surrounding the trench. The volcano that created one of these islands, Pagan, has erupted several times over the past 30 years. Fortunately it was only moderately active when the team was there, expelling steam that reflects the setting sun in this photo. – Heather Relyea

Last month, Doug Wiens, PhD, professor of earth and planetary science at Washington University in St. Louis, and two WUSTL students were cruising the tropical waters of the western Pacific above the Mariana trench aboard the research vessel Thomas G. Thompson.

The trench is a subduction zone, where the ancient, cold and dense Pacific plate slides beneath the younger, lighter high-riding Mariana Plate, the leading edge of the Pacific Plate sinking deep into the Earth’s mantle as the plates slowly converge.

Taking turns with his shipmates, Wiens swung bright-yellow ocean bottom seismometers and hydrophones off the fantail, and lowered them gently to the water’s surface, as the ship laid out a matrix of instruments for a seismic survey on the trench.

The survey, which Wiens leads together with Daniel Lizarralde, PhD, of the Woods Hole Oceanographic Institution, will follow the water chemically bound to the down-diving Pacific Plate or trapped in deep faults that open in the plate as it bends. The work is funded by the National Science Foundation.

Scientists have only recently begun to study the subsurface water cycle, which promises to be as important as the more familiar surface water cycle to the character of the planet.

Hydration reactions along the subducting plate are thought to carry water deep into the Earth, and dehydration reactions at greater depths release fluids into the overlying mantle that promote melting and volcanism.

The water also plays a role in the strong earthquakes characteristic of subduction zones. Hydrated rock and water under high pressure are thought to lubricate the boundary between the plates and to permit sudden slippage.

Dropping the instruments

Between Jan. 26 and Feb. 9, working day and night, watch-on and watch-off, the Thompson laid down 80 ocean bottom seismometers and five hydrophones.

The hydrophones, which detect pressure waves and convert them into electrical signals, provide less information than the seismometers, which register ground motion, but they can be tethered four miles deep in the water column where the bottom is so far down seismometers would implode as they sank.

The Thompson sailed over some of the most famous real estate in the world, the Mariana trench, which includes the bathtub-shaped depression called the Challenger Deep, to which Avatar director James Cameron plans to plunge in a purpose-built one-man submersible called the Deep Challenger.

Seven miles down, the pressure in the Deep is 1,000 atmospheres (1,000 times the pressure at sea level on dry land) or roughly 8 tons per square inch. Seismometers, says Wiens, only go down four miles.

The trench is created by the subduction of some of the world’s oldest oceanic crust, which plunges underneath the Mariana Isalnds so steeply at places that it is going almost straight down.

The active survey

After the Thompson returned to Guam and Wiens flew back to St. Louis to resume his less romantic duties as chair of the Department of Earth and Planetary Sciences, the research vessel Marcus G. Langseth began to sail transects above the matrix of seismometers, firing the 36-airgun array on its back deck.

The sound blasts reflected from the boundaries between rock layers a few miles beneath the ocean floor were picked up by an five-mile-long “streamer,” or hose containing many hydrophones, towed just beneath the surface behind the ship.

This was the “active” stage of a seismic survey with a “passive” stage yet to come.

After the seismic survey, the Langseth returned to pick up 60 seismometers, leaving behind 20 broadband seismometers and the hydrophones that will listen for a year to the reverberations from distant earthquakes, allowing the seismologists to map structures as deep as 60 miles beneath the surface.

In the meantime Patrick Shore, a research scientist in earth and planetary science, and two Washington University students had set sail across the ocean in a tiny vessel, the Kaiyu III, to install seismometers on the Mariana islands that will also supply data for the “passive” stage of the survey.

Water, water everywhere

Water plays a completely different role at depth than it does on the surface of the Earth. Water infiltrating the mantle through faults hydrates the mantle rock on either side of the fault.

In a low temperature process called serpentinization, it transforms mantle rock such as the green periodotite into serpentinite, a rock with a dark scaly surface like a serpent’s skin.

As the slab plunges yet deeper, dehydration reactions release water, which at such great pressure and temperature exists as a supercritical fluid that can drift through materials like a gas and dissolve them like a fluid. The fluid rises into the overlying mantle where it lowers the melting point of rock and triggers the violent eruptions of magma that created the Mariana Islands, to which Shore was sailing.

“We think that much of the water that goes down at the Mariana trench actually comes back out of the earth into the atmosphere as water vapor when the volcanos erupt hundreds of miles away,” Wiens says.

The scientists will map the distribution of serpentinite in the subducting plate and overlying mantle, by looking for regions where certain seismicwaves travel more slowly than usual.

Tracing the water cycle within subduction zones will allow the scientists to better understand island-arc volcanism and subduction-zone earthquakes, which are among the most powerful in the world

But the role of subsurface water is not limited to these zones. Scientists don’t know how subduction got started in the first place, but water may be a necessary ingredient. Venus, which is in many ways similar to Earth, has volcanism but no plate tectonics, probably because it is bone dry.

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Seismologists have just returned from a cruise in the Western Pacific to lay the instruments for a seismic survey that will follow the water chemically bound to or trapped in the down-diving Pacific Plate at the Mariana trench, the deep trench to which Avatar director James Cameron is poised to plunge. This video combines an interview of co-PI Doug Wiens of Washington University in St. Louis and the videos he took on the cruise. – Doug Wiens/Clark Bowen/WUSTL

Discovery sheds new light on wandering continents

This diagram represents a cross-section of the Earth beneath the ocean, with the layers labeled on the right. It illustrates the paths of earthquake waves (white lines) from an earthquake source (white star) through the Earth to a seismometer location (blue triangle). Halfway through their journey, the waves can reflect off of the surface or a melt layer. The longer path goes all the way to the surface before the waves are reflected. A shorter path is possible if the waves get reflected off of a melt layer at the lithosphere-asthenosphere boundary (represented by the yellow-orange area beneath the hotspot). Waves taking this shorter path will arrive several tens of seconds before waves that miss the melt layer and have to travel to the surface. -  Credit: Nicholas Schmerr
This diagram represents a cross-section of the Earth beneath the ocean, with the layers labeled on the right. It illustrates the paths of earthquake waves (white lines) from an earthquake source (white star) through the Earth to a seismometer location (blue triangle). Halfway through their journey, the waves can reflect off of the surface or a melt layer. The longer path goes all the way to the surface before the waves are reflected. A shorter path is possible if the waves get reflected off of a melt layer at the lithosphere-asthenosphere boundary (represented by the yellow-orange area beneath the hotspot). Waves taking this shorter path will arrive several tens of seconds before waves that miss the melt layer and have to travel to the surface. – Credit: Nicholas Schmerr

A layer of partially molten rock about 22 to 75 miles underground can’t be the only mechanism that allows continents to gradually shift their position over millions of years, according to a NASA-sponsored researcher. The result gives insight into what allows plate tectonics – the movement of the Earth’s crustal plates – to occur.

“This melt-rich layer is actually quite spotty under the Pacific Ocean basin and surrounding areas, as revealed by my analysis of seismometer data,” says Dr. Nicholas Schmerr, a NASA Postdoctoral Program fellow. “Since it only exists in certain places, it can’t be the only reason why rigid crustal plates carrying the continents can slide over softer rock below.” Schmerr, who is stationed at NASA’s Goddard Space Flight Center in Greenbelt, Md., is author of a paper on this research appearing in Science on March 23.

The slow slide of Earth’s continents results from plate tectonics. Our planet is more than four billion years old, and over this time, the forces of plate tectonics have carried continents many thousands of miles, forging mountain ranges when they collided and valleys that sometimes filled with oceans when they were torn apart. This continental drift could also have changed the climate by redirecting currents in the ocean and atmosphere.

The outermost layer of Earth, the lithosphere, is broken into numerous tectonic plates. The lithosphere consists of the crust and an underlying layer of cool and rigid mantle. Beneath the oceans, the lithosphere is relatively thin (about 65 miles), though beneath continents, it can be as thick as 200 miles. Lying beneath the lithosphere is the asthenosphere, a layer of rock that is slowly deforming and gradually flowing like taffy. Heat in Earth’s core produced by the radioactive decay of elements escapes and warms mantle rocks above, making them softer and less viscous, and also causes them to convect. Like the circulating blobs in a lava lamp, rock in the mantle rises where it is warmer than its surroundings, and sinks where it’s cooler. This churn moves the continental plates above, similar to the way a raft of froth gets pushed around the surface of a simmering pot of soup.

Although the basic process that drives plate tectonics is understood, many details remain a mystery. “Something has to decouple the crustal plates from the asthenosphere so they can slide over it,” says Schmerr. “Numerous theories have been proposed, and one of those was that a melt-rich layer lubricates the boundary between the lithosphere and the asthenosphere, allowing the crustal plates to slide. However, since this layer is only present in certain regions under the Pacific plate, it can’t be the only mechanism that allows plate tectonics to happen there. Something else must be letting the plate slide in areas where the melt doesn’t exist.”

Other possible mechanisms that would make the boundary between the lithosphere and the asthenosphere flow more easily include the addition of volatile material like water to the rock and differences in composition, temperature, or the grain size of minerals in this region. However, current data lacks the resolution to distinguish among them.

Schmerr made the discovery by analyzing the arrival times of earthquake waves at seismometers around the globe. Earthquakes generate various kinds of waves; one type has a back-and-forth motion and is called a shear wave, or S-wave. S-waves traveling through the Earth will bounce or reflect off material interfaces inside the Earth, arriving at different times depending on where they interact with these interfaces.

One type of S-wave reflects from Earth’s surface halfway between an earthquake and a seismometer. An S-wave encountering a deeper melt layer at the lithosphere-asthenosphere boundary at this location will take a slightly shorter path to the seismometer and therefore arrive several tens of seconds earlier. By comparing the arrival times, heights, and shapes of the primary and the melt-layer-reflected waves at various locations, Schmerr could estimate the depth and seismic properties of melt layers under the Pacific Ocean basin.

“Most of the melt layers are where you would expect to find them, like under volcanic regions like Hawaii and various active undersea volcanoes, or around subduction zones – areas at the edge of a continental plate where the oceanic plate is sinking into the deep interior and producing melt,” said Schmerr. “However, the interesting result is that this layer does not exist everywhere, suggesting something other than melt is needed to explain the properties of the asthenosphere.”

Understanding how plate tectonics works on Earth could help us figure out how other rocky planets evolved, according to Schmerr. For example, Venus has no oceans, and no evidence of plate tectonics, either. This might be a clue that water is needed for plate tectonics to work. One theory proposes that without water, the asthenosphere of Venus will be more rigid and unable to sustain plates, suggesting internal heat is released in some other way, maybe through periodic eruptions of global volcanism.

Schmerr plans to analyze data from other seismometer networks to see if the same patchy pattern of melt layers exists under other oceans and the continents as well. The research was supported by the NASA Postdoctoral Program and the Carnegie Institution of Washington Department of Terrestrial Magnetism Postdoctoral Fellowship.

Everything you always wanted to know about exploring Earth with seismology

A new addition to The Geological Society of America’s Memoir series, this comprehensive volume presents the worldwide history (1850 to 2005) of seismological studies of Earth’s crust. Authors Claus Prodehl of Universit├Ąt Karlsuhe, Germany, and Walter D. Mooney of the U.S. Geological Survey have achieved the Herculean task of compiling into this one volume the results of all major field projects, land and sea, that have used man-made seismic energy sources to explore Earth’s crust.

First is a general synthesis of all major seismic projects on land as well as the most important oceanic projects during the time period 1850 to 1939, with more detailed coverage from 1940 onward. After the initial overview, history and results are subdivided into a separate chapter for each decade, with the material ordered by geographical region. Each chapter highlights the major advances achieved during that decade in terms of data acquisition, processing technology, and interpretation methods.

For all major seismic projects, Prodehl and Mooney provide specific details regarding the field observations, interpreted crustal cross section, and key references. They conclude the memoir with global and continental scale maps of all field measurements and interpreted Moho contours. An accompanying DVD contains important out-of-print publications and an extensive collection of controlled-source data, location maps and crustal cross sections.

Polycrystalline diamond drill bits open up options for geothermal energy

Elton Wright shows a torsional spring that's used to simulate the rotational vibration of the drill string in a Sandia experiment. -  Photo by Randy Montoya
Elton Wright shows a torsional spring that’s used to simulate the rotational vibration of the drill string in a Sandia experiment. – Photo by Randy Montoya

Nearly two-thirds of the oil we use comes from wells drilled using polycrystalline diamond compact (PDC) bits, originally developed nearly 30 years ago to lower the cost of geothermal drilling. Sandia and the U.S. Navy recently brought the technology fullcircle, showing how geothermal drillers might use the original PDC technology, incorporating decades of subsequent improvements by the oil and gas industry.

Sandia and the Navy’s Geothermal Program Office (USN GPO) conducted the Phase One demonstration tests as part of a geothermal resources evaluation at the Chocolate Mountains Aerial Gunnery Range in Imperial Valley, Calif.

Sandia has a long history in geothermal research and drill bit technology development. Three decades ago, Sandia played a large role in developing PDCs for geothermal drilling. That work focused on resolving issues with materials, devising laboratory tests and developing data and design codes that now form the basis of the bit industry. Recently, Sandia received American Recovery and Reinvestment Act (ARRA) funding to improve PDC bits, potentially increasing access to geothermal resources in the continental U.S. by enabling the drilling of deeper, hotter geothermal resources in hard, basement rock formations.

Geothermal drilling more demanding

Because oil and gas drilling is generally less complicated than geothermal drilling, PDCs were first used to drill for oil and gas, said principal investigator David Raymond.

“Oil and gas drilling is normally done in softer and less-fractured rock, resulting in fewer problems with fluid circulation to remove debris and cool the bit,” he said. “Oil and gas drilling also doesn’t usually involve the higher temperatures that geothermal wells exhibit.”

But as the oil and gas industry looks for new sustained resources in deeper reservoirs, it encounters more difficult drilling conditions similar to those found in geothermal drilling.

“Oil and gas drilling must now go deeper into the ground, into harder and sometimes fractured rocks, and in hotter environments,” said Raymond.

Raymond said geothermal resources are typically associated with igneous and metamorphic rocks, which are harder than the sedimentary rocks through which most oil and gas wells are drilled. Igneous and metamorphic rocks also can contain large amounts of abrasives such as quartz, which can cause vibration and accelerated wear that damages drill bits. These types of rocks are often fractured, which can change the impact loading on drills and cause more damage.

“Drilling for geothermal energy is still the most difficult drilling on a cost-per-foot basis,” said Raymond. “You have to go through the hardest rock, sometimes at high temperatures and pressures. The DOE (Department of Energy) vision for advanced geothermal development is to drill to great depths, up to 30,000 feet, to access heat for geothermal.”

The economic risk for oil and gas wells also is different. Because many more oil and gas wells are drilled per year, that industry has the resources and can invest significantly in research and testing to improve the ability to drill under increasingly difficult conditions.

The geothermal industry has advanced far more slowly. Because geothermal drillers create only a small number of new wells each year, the drilling service industry finds it difficult and expensive to support innovation, since each well represents a substantial risk.

The Sandia/Navy demonstration project called for a test hole to evaluate geothermal resources in the Camp Billy Machen/Hot Mineral Spa region that would have been otherwise undetectable at the surface. The basement rock at the Chocolate Mountains includes granite and andesite, formations typically encountered during geothermal drilling.

A key part of the demonstration project was to test and evaluate PDC bits and related technologies in a real-world drilling environment. Sandia worked with PDC bit manufacturer National Oilwell Varco (NOV) of Houston to find specific solutions for the company’s ReedHycalog PDC bits. NOV provided commercially available drill bits and on-site experts to counsel the drilling contractor during the demonstration drill runs.

Sandia worked with the Navy’s geothermal drilling contractor, Barbour Well Inc. of Henderson, Nev., in evaluating drilling technologies during production drilling.

Sandia also formed partnerships with Albuquerque’s Prime Core Systems, and the Barbour Well mud logging company, Prospect Geotech, to field instruments to monitor the Barbour drill rig during the drilling process.

In the tests, two bits drilled 1,291 feet of the overall well depth of 3,000 feet. The two bits were in the well just over four days, penetrating approximately 30 feet per hour throughout their drilling interval, nearly three times better than standard roller bits used for comparison. The team retrieved and downloaded downhole data from both bits for analysis.

In a planned second phase of the project, Sandia will continue work with NOV to evaluate drill performance and improve the bit design and materials.

Cooperative work between the Navy and Sandia was covered by a memorandum of understanding between the Department of Defense and the DOE on collaborative development of renewable energy resources.

The demonstrations and planned phase two drilling are funded through an American Recovery and Reinvestment Act project, “Technology Development and Field Trials of EGS Drilling Systems,” under the supervision of DOE.

How PDC cutters are made

Polycrystalline diamond compact cutters on the cutting faces of bits allow more aggressive drilling than bits traditionally used for geothermal drilling. They are created by a sintering process. Graphite powder is applied to the leading face of a cutter made of tungsten carbide. The material assembly is compressed in three directions at pressures of 1 million pounds per square inch. When heated to a transition temperature, the graphite converts a to a 1-millimeter layer of synthetic diamond.

New study lowers estimate of ancient sea-level rise

Scientists offer a new explanation for why ancient beach deposits on these cliff tops in Eleuthera, Bahamas, are nearly 70 feet above present day sea level. -  Paul Hearty
Scientists offer a new explanation for why ancient beach deposits on these cliff tops in Eleuthera, Bahamas, are nearly 70 feet above present day sea level. – Paul Hearty

The seas are creeping higher as the planet warms. But how high will they go? Projections for the year 2100 range from inches to several feet, or more. The sub-tropical islands of Bermuda and the Bahamas contain important sites where researchers have gone looking for answers; by pinpointing where shorelines stood on cliffs and reefs there during an extremely warm period 400,000 years ago, they hope to narrow the range of global sea-level projections for the future.

After correcting for what they say were the sinking of the islands at that time, a new study in the journal Nature estimates the seas rose 20 to 43 feet higher than today-up to a third less than previous estimates, but still a drastic change. The new study infers that Greenland and West Antarctica ice sheets collapsed at that time, but not the even bigger East Antarctic Ice Sheet.

“Our study provides a simple explanation for these high beach deposits,” said study lead author Maureen Raymo, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory.

Average global sea level has risen eight inches since the 1880s. It is currently rising an inch per decade, driven by thermal expansion of seawater and melting of glaciers and ice sheets, including the still mostly intact ice sheets of Greenland and West Antarctica. In its most recent report, the Intergovernmental Panel on Climate Change estimated that the seas could rise up to two feet by 2100; but that number could go higher depending on the amount of polar ice melt, and quantity of greenhouse gas emissions by humans. The United Nations estimates that five feet of sea-level rise would be enough to swamp 17 million people in low-lying Bangladesh alone.

The cliffs and ancient reefs on Bermuda and the Bahamas have attracted fossil hunters for decades, and more recently, scientists investigating global sea level. In a 1999 study in the journal Geology, Paul Hearty, a scientist at the University of North Carolina, Wilmington, estimated that during the period 400,000 years ago, the seas rose nearly 70 feet, in between glacial periods. He hypothesized that the East Antarctic ice sheet must have partly melted to produce such a rise. In 2007, University of Hawaii scientist Gary McMurtry offered a competing hypothesis in the journal Sedimentary Geology: that a mega-tsunami generated by a collapsing volcano off the Canary Islands created the high-water mark.

The new study comes up with a different take. It factors in the loading and unloading of ice from North America during the ice ages preceding the sea-level rise. As the ice sheets grew, their weight pushed down the land beneath them, while causing land at the edges of the continent-including Bermuda and the Bahamas–to bulge up, says Raymo. When the ice pulled back, the continent rebounded, and the islands sank.

“Bermuda and the Bahamas are not a pristine measure of the volumes of ice that melted in the past, because they’re contaminated by effects left over from the ice ages,” said study coauthor Jerry Mitrovica, a geophysicist at Harvard University.

The new study infers that the huge Greenland and West Antarctic ice sheets indeed collapsed at the time, but that loss from the even vaster East Antarctic Ice Sheet was negligible. Today, both Greenland and West Antarctica are losing mass in a warming world, but signals from East Antarctica-about eight times bigger than the other two combined–are less clear. Raymo said the study helps show that “catastrophic collapse” of the East Antarctic ice is probably not a threat today. “However, we do need to worry about Greenland and West Antarctica,” she said.

The study’s revised estimate of 20 to 43 feet makes sense, said sea-level rise expert Mark Siddall, a climate scientist at the University of Bristol who was not involved in the study. But, he added, it would probably take hundreds to thousands of years for such a rise to occur again. “We’re moving from a place of disagreement about sea level estimates from this past period to one consistent theory that reconciles data from diverse geographic areas,” he said.

Millions of Americans at risk of flooding as sea levels rise

Nearly four million Americans, occupying a combined area larger than the state of Maryland, find themselves at risk of severe flooding as sea levels rise in the coming century, new research suggests.

A new study, published today, 14 March, in IOP Publishing’s journal Environmental Research Letters, asserts that around 32,000 km2 of US land lies within one vertical meter of the high tide line, encompassing 2.1 million housing units where 3.9 million people live.

For this study, the researchers created a new model to identify the areas of US mainland that are at risk of flooding and, with a predicted sea level rise of 1 meter or more by the end of the century, suggest that the US Government’s currently designated flood zones should not be considered stable.

A second study, also published today in Environmental Research Letters, corroborates evidence of the risk, showing that a majority of US locations, from the 55 studied, will see a substantially higher frequency of storm-driven high water levels by the middle of the century; water levels that have previously been encountered only once-a-century.

Many locations would be expected to experience such high flooding every decade or more often.

Two ways in which global warming is causing sea levels to rise are thermal expansion – the expanding of water as it warms – and the melting of glaciers.

The first study, undertaken by researchers at Climate Central and the University of Arizona, shows that at a state level, areas surrounding the Gulf appear to be the most vulnerable, whilst in terms of population, Florida is the most vulnerable, closely followed by Louisiana, California, New York and New Jersey, illustrating significant exposure on every coast.

The researchers pick out greater Los Angeles as a largely-populated city of great concern, as previous research suggests that flooding may reach rare heights more swiftly in southern California than in any other mainland US area.

The second study examined the effect of heavy storms on past water levels at 55 stations across the US and combined these with estimates of future global sea level rises to predict the frequency and extent of future flooding.

The researchers, from Climate Central, the National Center for Atmospheric Research and the National Oceanic and Atmospheric Administration, liken the type of annual flooding that we may come to expect to the infamous high water levels brought about in New York in 1992, which managed to flood the subway system, as a result of a violent nor’easter (a storm coming in off the Atlantic).

Co-author of both papers, Ben Strauss, researcher at Climate Central, said: “The sea level rise taking place right now is quickly making extreme coastal floods more common, increasing risk for millions of people where they live and work. Sea level rise makes every single coastal storm flood higher. With so many communities concentrated on US coasts, the odds for major damage get bigger every year.”