Discovery of Antarctic subglacial rivers may challenge excavation plans

Plans to drill deep beneath the frozen wastes of the Antarctic, to investigate subglacial lakes where ancient life is thought to exist, may have to be reviewed following a discovery by a British team led by UCL (University College London) scientists at the Natural Environment Research Council (NERC)Centre for Polar Observation and Modelling (CPOM).

In a Letter to Nature they report that rivers the size of the Thames have been discovered which are moving water hundreds of miles under the ice. The finding challenges the widely held assumption that the lakes evolved in isolated conditions for several millions years and thus may support microbial life that has evolved "independently". It has been suggested that if microbes exist in the lakes, they could function in the same way as those in the subsurface ocean of Jupiter’s moon Europa or within subsurface water pockets on Mars.

Professor Duncan Wingham, of UCL, Director of CPOM and who led the team, says: "Previously, it was thought water moves underneath the ice by very slow seepage. But this new data shows that, every so often, the lakes beneath the ice pop off like champagne corks, releasing floods that travel very long distances."

"A major concern has been that by drilling down to the lakes new microbes would be introduced. Our data shows that any contamination will not be limited to one lake, but will over time extend down the length of the network of rivers. We had thought of these lakes as isolated biological laboratories. Now we are going to have to think again."

The discovery, which came as a great surprise to the team, also raises the possibility that large flood waters from deep within the interior may have reached the ocean in the past and may do so again.

Subglacial lakes in Antarctica were first identified in the 1960s. Since then over 150 have been discovered but it is thought thousands may exist, as much of the bed of Antarctica remains un-surveyed. The team focused on the Dome Concordia region in East Antarctica, where more than 40 lakes are known to exist.

Ultra-precise measurements were taken using radars on the European Space Agency ERS-2 satellite to examine in detail small changes in the surface of some of the oldest, thickest ice in Antarctica. The satellite found synchronous changes in the surface height separated by 290 kilometres.

The scientists argue that the only possible explanation of these changes is that a large flow of water must have occurred beneath the ice from one subglacial lake into several others. The finding re-invigorates old speculations that Lake Vostok, which contains 5,400 cubic kilometres of water (equivalent to London’s water consumption over 5000 years), may have generated huge floods that could reach the coast.

"The lakes are like a set of beads on a string, where the lakes are the beads connected by a string or river of water,” explains Professor Wingham."

"For the most part, there is very little flow along the string. Then, one of the lakes over pressurises and a flood occurs that fills the next "bead" down the string. The lakes must be pressurising until the pressure is high enough to force the water under the surrounding ice. Once it starts to flow, it melts the ice, and there is a run-away effect."

"Whether that could start an immediate "chain reaction" down the string (and hence to the coast), or whether that bead would "go off" sometime later is a vital question to which we don’t know the answer yet. But, sooner or later, the system will be flushed throughout."

Professor Martin Siegert, of the University of Bristol and a co-author of the study, says: "Currently we don’t know how full Lake Vostok is or the length of time it will take to fill – it might be thousands or even tens of thousands of years. Whether such a discharge could affect the ocean circulation around Antarctica is an open question at this stage."

The study was funded by NERC and the ERS-2 satellite was funded by the European Space Agency.

The story can be read at the University College London

- posted by Affenhänger @ 4/30/2006 08:17:00 PM 0 comments links to this post

 
New Properties of the Very Deep Earth Discovered

Washington, DC. To truly understand some of the movement we see at the Earth’s surface, scientists have to probe deep into the interior. A region near the planet’s core, about 1,800 miles down called the core-mantle boundary, is particularly intriguing. Through novel experiments mimicking high-pressures and temperatures there, scientists at Los Alamos National Laboratory (LANL) and the Carnegie Institution’s Geophysical Laboratory* may have solved a longstanding mystery about why certain seismic waves called shear waves move so sluggishly through clumpy patches (ultralow velocity zones) at these incredible depths. The team found that when lots of iron is added to the most prevalent mineral in that region (post-perovskite), shear waves move in slow motion. Their discovery offers an alternative to the prevailing idea that these regions are partially melted, and it has important implications for understanding how volcanoes, located in places such as Hawaii and Iceland, may originate. The research is published in the April 28, 2006, issue of Science.

Seismologists learn about the deep Earth, in part, by observing different seismic waves from earthquakes as they travel through the planet. Shear waves wiggle at right angles to the direction of their movement, but they don’t move through liquid at all and are thus useful for understanding aspects of the Earth’s composition. The team, including the daughter/father duo Wendy Mao (LANL) and Carnegie’s Ho-kwang (Dave) Mao, used a novel technique to measure the velocity of shear waves in the lab, moving through the most abundant mineral in that region (post-perosvkite).

"The major mineral in Earth’s mantle is iron-magnesium silicate perosvkite," explained Dave Mao. "Post-perosvkite, discovered a couple years ago, is a different phase of the mineral at the core-mantle boundary and scientists have been fascinated by its properties. Understanding the mineral and the intrigue of the ultralow velocity zones led us to these experiments," he continued.

Ultralow velocity zones exist as patches between the solid mantle and liquid core, and are very different from the mantle above and material on the sides. Since shear waves can’t propagate through a liquid, a prevailing view has been that the zone contains some liquid, or melts, which would slow the waves down. Scientists have noticed that the ultralow velocity patches could also give rise to mantle plumes, eventually sparking volcanoes in places like Hawaii and Iceland.

The researchers subjected post-perosvkite, containing 40% iron, to pressures as high as 1.6 million times the pressure at sea level (170 Gigapascals) and 3,100 °F (2,000K). Although the researchers can add as much as 80% iron in the post-perovskite, only 40% is needed to match the ultralow velocity zones.

"With our new techniques we were able to determine the shear velocity of this material," stated Wendy Mao. "We were amazed that adding iron dramatically slowed the velocities to levels that seismologists have observed in the ultralow velocity zones. Iron-rich post-perosvkite, formed by reactions between the mantle and the core, could be what these thin, patchy regions are made of."

In addition to offering an alternative explanation to partial melting of the ultralow velocity zones, the dense material would sink instead of rising with the convection at hot spots. This behavior would explain why these zones are clumped and not uniformly distributed and why the clumps are associated with the hot spots and contribute to the volcanic activity at the surface.

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* Wendy Mao is with Los Alamos National Laboratory. Ho-Kwang (Dave) Mao is with Carnegie’s Geophysical Laboratory and HPCAT. Yingwei Fei and Russell Hemley are also with Carnegie.

This work was supported by Earth Sciences Research and the National Science Foundation. The HPCAT facility is supported by the Department of Energy, the W. M. Keck Foundation, and Carnegie Institution of Washington.

The Carnegie Institution of Washington (www.carnegieinstitution.org) has been a pioneering force in basic scientific research since 1902. It is a private, nonprofit organization with six research departments throughout the U.S. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.

- posted by Affenhänger @ 4/29/2006 04:34:00 AM 0 comments links to this post

 
New e-journals portal
Bruno Granier, whom some of you may know from Carnets de Géologie/Notebooks on Geology fame, is in the process of transforming a former webring into a genuine e-journals portal covering the earth sciences in general (palaeontology, geography, etc.). The majority of the journals offer published material in open access, although some still offer only a limited number of papers. You are invited to bookmark the following URL: paleopolis.rediris.es/geosciences/. Please also feel free to forward this information to your friends and colleagues (do not forget your librarians!).
- posted by Affenhänger @ 4/22/2006 10:00:00 PM 1 comments links to this post

 
Hartlepool webcams

I recently discovered that Hartlepool has a number of webcams. They can be viewed at Digital Hartlepool dot com and then by clicking at the bottom on "View Webcams". A separate window opens with four webcam options: Hartlepool Marina Sea Lock; Hartlepool Historic Quay/HMS Trincomalee; Town Skyline from Hartlepool College; and Webcam Timelapse Demo: "Marina Sunset". My favourite is the sea lock. It'll give you a picture like this:


Hartlepool Marina Sea Lock

- posted by Affenhänger @ 4/22/2006 09:28:00 PM 0 comments links to this post