Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New Technique Dates Saharan Groundwater as Million Years Old

01.03.2004

The Mediterranean Sea was a desert, millions of years ago. In contrast, the Sahara Desert was once a lush, green landscape dotted with lakes and ponds. Evidence of this past verdancy lies hidden beneath the sands of Egypt and Libya, in the form of a huge aquifer of fresh groundwater. An international team of geologists and physicists has found that this groundwater has been flowing slowly northward (at about the rate grass grows) for the past million years. Their findings have been accepted for March publication in Geophysical Research Letters, published by the American Geophysical Union.

Determining residence times and flow velocities of groundwater in aquifers is a vexing challenge. The extremely rare radioactive isotope krypton-81 (half-life of 229,000 years), which is produced by cosmic rays in the atmosphere, could be an ideal groundwater chronometer on the million-year time scale, but it has been nearly impossible to measure because of its low abundance. There is only one atom of krypton-81 in a trillion atoms of atmospheric krypton, a rare gas to begin with, and krypton is absorbed only slightly by water.

Recently, scientists at Argonne National Laboratory developed a laser-based method to count individual atoms of krypton-81 and measure its abundance accurately. Known as ATTA, for Atom-Trap Trace Analysis, this new, ultrasensitive method could revolutionize the scientific study of such topics as continental groundwater flow, long-term glacier motion, and seawater circulation through the ocean floor, say the researchers.

In their Geophysical Research Letters paper, Neil C. Sturchio (University of Illinois at Chicago), Zheng-Tian Lu (Argonne National Laboratory), Roland Purtschert (University of Bern), Mohamed Sultan (State University of New York at Buffalo), and others report the most extensive measurements yet made for krypton-81 in groundwater. In the first application of the ATTA method to a groundwater investigation, this team visited the Western Desert of Egypt to sample krypton from the Nubian Aquifer groundwater, which was reputedly old but of unknown age.

To obtain a sufficient amount of krypton for the ATTA measurements, the team had to extract dissolved gases from thousands of liters [gallons] of groundwater in the field, using a device invented by the Swiss members of the team. The gas extracted from each well was compressed into steel containers and shipped to Bern, where the trace amount of krypton in each sample was purified and delivered to Argonne for analysis of krypton-81. ATTA measured the ratios of krypton-81 to ordinary krypton, which ranged from about five to 53 percent of that in the air, corresponding to groundwater ages of 200,000 to 1,000,000 years.

Based on these data, it is possible to estimate the direction and velocity of the groundwater flow, which is about one-to-two meters [yards] per year toward the north, and to determine the recharge location in southwest Egypt. This confirms results from some previous numerical hydrologic models, but refutes others. Isotopic characteristics of the water itself indicate that it was transported by air masses traveling long distances over North Africa from the Atlantic Ocean, thus reflecting climate conditions much different from the present during the past million years. Changing climate patterns turned this green oasis into today’s desert.

The research was funded primarily by the National Science Foundation and the Department of Energy.

Harvey Leifert | AGU

More articles from Earth Sciences:

nachricht Six-decade-old space mystery solved with shoebox-sized satellite called a CubeSat
15.12.2017 | National Science Foundation

nachricht NSF-funded researchers find that ice sheet is dynamic and has repeatedly grown and shrunk
15.12.2017 | National Science Foundation

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First-of-its-kind chemical oscillator offers new level of molecular control

DNA molecules that follow specific instructions could offer more precise molecular control of synthetic chemical systems, a discovery that opens the door for engineers to create molecular machines with new and complex behaviors.

Researchers have created chemical amplifiers and a chemical oscillator using a systematic method that has the potential to embed sophisticated circuit...

Im Focus: Long-lived storage of a photonic qubit for worldwide teleportation

MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...

Im Focus: Electromagnetic water cloak eliminates drag and wake

Detailed calculations show water cloaks are feasible with today's technology

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

Engineers program tiny robots to move, think like insects

15.12.2017 | Power and Electrical Engineering

One in 5 materials chemistry papers may be wrong, study suggests

15.12.2017 | Materials Sciences

New antbird species discovered in Peru by LSU ornithologists

15.12.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>