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NanoSIMS digs deep to study microorganisms in soil
Scientists may soon be able to examine microhabitats within soils using Livermore’s nanometer-scale secondary-ion mass spectrometer (NanoSIMS). This precise tool can determine the elemental and isotopic content of soil with a resolution of 50 nanometers. Results from a collaborative study, published in the August 2007 issue of Soil Biology & Biochemistry, showed that NanoSIMS can qualitatively determine how nitrogen and carbon isotopes assimilate into soil microorganisms. Researchers at the University of Western Australia also found that the high-resolution tool can detect isotopically enriched bacterial cells in soil.

Soils are highly complex porous mixtures that are structurally heterogeneous. Microorganisms act as go-betweens for a range of reactions occurring between the physical, chemical, and other biotic components of the soil environment. Because soils and the microorganisms in them are so small, a precise instrument such as NanoSIMS is required to evaluate these interactions.

“NanoSIMS shows promise for studying the heterogeneity and microbial activity in soil’s microhabitats,” says Jennifer Pett-Ridge, a postdoctoral researcher on the Livermore team. “However, this application is still at a very early stage.” The Livermore research also indicates that NanoSIMS could trace the uptake of fertilizer and other organics, track the stabilization of organic matter in soil, determine the spatial distribution of active microorganisms, distinguish the microorganisms associated with specific minerals, and establish the role of fungi in soil.

Contact: Jennifer Pett-Ridge (925) 424-2882 (pettridge2@llnl.gov).

Simulations indicate laser is on track
Computer simulations based on data from the National Ignition Facility (NIF) 2003–2004 Early Light Campaign produced results that mirror experimental measurements to an unprecedented degree. The simulations, which are discussed in the October 2007 edition of Nature Physics, indicate that NIF’s laser beams will propagate effectively in plasma-filled targets designed to produce the world’s first laboratory demonstration of inertial confinement fusion. “Getting agreement on that scale is something new,” says Livermore scientist Siegfried Glenzer, who led the simulation team.

The Nature Physics paper examined two experimental situations. In one simulation, an unsmoothed laser beam entering the target stalled in the hot plasma. As a result, about 30 percent of the laser’s light backscattered and failed to reach the target’s center. The second simulation tracked a smoothed laser beam as the beam moved through a 7-millimeter-long tube of carbon dioxide. In the inertial confinement fusion experiments planned for NIF, laser beams must pass through a large volume of plasma to reach the target center and ignite a sustained fusion reaction.

The computer simulation tracked 3.5 nanoseconds of laser beam pulse, more than 1,000 times longer than the pulse usually modeled by a laser–plasma code. The results showed how the target and beam geometry changed over time, revealing details down to the wavelength scale—a few hundred nanometers, or billionths of a meter. Livermore researchers are using simulations such as these to design upcoming NIF experiments.

Contact: Siegfried Glenzer (925) 422-7409 (glenzer1@llnl.gov).

Global warming increases atmospheric moisture
A collaboration involving researchers from Lawrence Livermore and eight other institutions has confirmed that human-induced global warming is affecting the total moisture content of the atmosphere. The study, which appeared in the September 25, 2007, Proceedings of the National Academy of Sciences, combined observational data from the satellite-based Special Sensor Microwave Imager with results from 22 climate models.

During the past 20 years, the total atmospheric moisture content over oceans has increased each decade by 0.41 kilogram per square meter, an amount that cannot be explained by natural variation alone. The research team, led by Livermore scientist Benjamin Santer, found that this increase in water vapor is not caused by solar forcing or the gradual recovery from particulates ejected by the 1991 Mount Pinatubo volcanic eruption. Instead, the research results showed that the primary driver for this atmospheric moistening is the increased levels of carbon dioxide caused by burning fossil fuels.

“When you heat the planet, you increase the ability of the atmosphere to hold moisture,” says Santer, who works in the Laboratory’s Program for Climate Model Diagnosis and Intercomparison. Water vapor is itself a greenhouse gas, so increasing amounts of water vapor will amplify the warming effect from carbon dioxide buildup. The team’s results indicate that the increase in water vapor is about 6 to 7.5 percent per °C of warming in the lower atmosphere.

When combined with similar studies of continental-scale river runoff, zonal mean rainfall, and surface-specific humidity, these findings point toward a human-caused signal in the cycling of moisture between the atmosphere, land, and ocean. “This work shows that the climate system is telling us a consistent story,” says Santer. “The observed changes in temperature, moisture, and atmospheric circulation fit together in an internally and physically consistent way.”

Contact: Benjamin Santer (925) 422-2486 (santer1@llnl.gov).

 


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