AGU journals highlights – 11 February 2003

Highlights, including authors and their institutions

The following highlights summarize research papers in Geophysical Research Letters (GL), Journal of Geophysical Research – Solid Earth (JB), Journal of Geophysical Research – Atmospheres (JD), and Journal of Geophysical Research – Planets (JE). The papers related to these Highlights are printed in the next paper issue of the journal following their electronic publication.

1. Another Great Salinity Anomaly?

An exceptionally pronounced dip in the North Atlantic Oscillation (NAO) was associated with a recent spate of freshwater seen in the coastal Labrador Sea during summer that could have been caused by icebergs that flowed further south than usual during the past decade. Sirpa Hakkinen suggests that the freshening observed over the past 10 years is part of a decadal shift similar to a period known as the Great Salinity Anomaly, when another freshwater trend originated in the 1970s. That incident was widely attributed to effects from the lowest NAO recorded in the past 50 years. Her analysis posits that the reduction in saltwater is caused by a weakened transport of saline waters to the area, evidenced by weak westerly winds that changed the oceanic overturning patterns and affect the spread of saltwater to the region.

Title: Freshening of the Labrador Sea surface waters in the 1990s:
Another great salinity anomaly?

Author:
Sirpa Hakkinen, NASA Goddard Space Flight Center, Greenbelt,
Maryland.

Source: Geophysical Research Letters (GRL) paper
10.1029/2002GL015243, 2002

2. Mixing of water temperatures may prevent El Nino

Combining warm and cool waters in the Pacific may prevent the initiation of an El Nino weather event, which requires the separation of temperature layers to begin the circulation pattern. Maes et al. used a coupled ocean and atmospheric circulation model, finding that cool surface waters in the Pacific confine the warm westerly winds needed to warm the ocean and initiate an El Nino. Consequently, the lack of winds prevents the overturning oceanic waves that bring cooler, saltier water to the surface and drive the atmospheric pattern. The authors suggest that remotely measuring changes to the ocean’s salinity, which can help identify oceanic temperature anomalies, can help estimate the atmospheric and climate precursors to weather patterns like El Nino.

Title: Salinity barrier layer and onset of El Nino in a Pacific coupled model
Authors:
Christophe Maes, Joel Picaut, School of Geophysical and Oceanographic Sciences (LEGOS), Toulouse, France; Sophie Belamari, National Center for Meteorological Research, Toulouse, France.

Source: Geophysical Research Letters (GRL) paper 10.1029/2002GL06029, 2002

3. Speculating on the cause of high Arctic ozone loss

Ozone loss over the Arctic is occurring faster than can be accounted for by standard models during exceptionally cold winters, leading researchers to suggest a possible new source for the difference. Rex et al. analyzed the ozone depletion rate in the northern pole during four particularly frigid winter seasons. Typically, ozone loss can be calculated from the activation of chlorine and the actions of normal atmospheric dynamics. The researchers confirm previous speculation that the chemical depletion is happening faster than could be predicted and propose that although the existing models and theory remain accurate during other parts of the year, the ozone loss may be caused by a sunlight-induced chemical breakdown during the Arctic twilight period when the sun is just returning after the polar night, but is still very weak.

Title: On the unexplained stratospheric ozone losses during cold Arctic Januaries

Authors:
Markus Rex, Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany;
R. J. Salawitch, M. L. Santee, J. W. Waters, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California;
K. Hoppel, R. Bevilacqua, Naval Research Laboratory, Washington, DC.

Source: Geophysical Research Letters (GRL) paper 10.1029/2002GL016008, 2003

4. Martian methane may provide evidence of life

Finding elevated methane in the Martian atmosphere might be a good indicator of subsurface life on the Red Planet, according to Summers et al. Methane, a gas produced by certain bacteria on Earth, is a byproduct of terrestrial metabolism from carbon monoxide and hydrogen, compounds that are found on Mars and could diffuse into the ground, providing energy sources for underground life. The researchers suggest that such biota may have evolved in early Martian history when the planet was warmer and wetter, moving underground over time as they were exposed to its predominantly carbon dioxide atmosphere. Methane produced by subterranean bacteria would emerge from the ground and, because the gas can survive approximately 300 years in Martian conditions, would spread uniformly in the atmosphere. The authors conclude that remote detection of such methane could offer an estimate of a possible subsurface biosphere on Mars.

Title: Atmospheric biomarkers of subsurface life on Mars

Authors:
Michael E. Summers, B. Joseph Lieb, Emily Chapman, George Mason University, Fairfax, Virginia;
Yuk L. Yung, California Institute of Technology, Pasadena, California.

Source: Geophysical Research Letters (GRL) paper 10.1029/2002GL015377, 2002

5. Combination method to date deepwater

Simultaneously measuring chlorofluorocarbons and sulfur hexaflouride in water can provide a better estimate of deepwater renewal rates than single tracer measurements. These compounds’ atmospheric concentrations have varied over time, which allows researchers to estimate the length of time since the water was exposed to the surface, but interpreting this time is difficult, because the individual tracer compounds mix at various depths in the water. Waugh et al. present a method to analyze simultaneous measurements of the two compounds that accounts for the effects of mixing and provides the deepwater ages more accurately. Using measurements from a deep central Asian lake, they were able to predict the mean time since the waters were exposed to the atmosphere and show the variability of the lake’s deepwater renewal. The authors conclude that their approach can also be used for oceans and groundwater.

Title: Transit time distributions in Lake Issyk-Kul

Authors:
Darryn W. Waugh, Thomas W. N. Haine, Johns Hopkins University, Baltimore, Maryland;
Martin K. Vollmer, Max Planck Institute for Chemistry, Mainz, Germany;
Ray F. Weiss, Scripps Institution of Oceanography, University of California-San Diego, La Jolla, California;
Timothy M. Hall, NASA Goddard Institute for Space Studies, New York, New York.

Source: Geophysical Research Letters (GRL) paper 10.1029/2002GL016201, 2002

6. Tracking the evolution of “trapped waves”

A 2001 hurricane off the western Mexico coast has allowed researchers to report the first complete life cycle of coastally trapped waves, which generate cyclonic and anticyclonic eddies in their wake, as opposed to normally propagating ocean waves. Zamudio et al. present the results from a global ocean forecasting system that followed the wave as it propagated northward toward the Baja California peninsula, induced by winds from Hurricane Juliette. The study documents the evolution of two such waves and was confirmed by sea level monitors along the coast and numerical models that predict the generation and path of such waves.

Title: On the evolution of coastally trapped waves generated by Hurricane Juliette along the Mexican West Coast

Authors:
Luis Zamudio, Florida State University, Tallahassee, Florida;
Harley E. Hurlburt, E. Joseph Metzger, Naval Research Laboratory, Stennis Space Center, Mississippi;
Ole Martin Smedstad, Planning Systems Incorporated, Stennis Space Center, Mississippi.

Source: Geophysical Research Letters (GRL) paper 10.1029/2002GL014769, 2002

7. Improved method for estimating electrical properties of minerals

A new method to measure the electrical intensity and conductivity of minerals may improve the currently used remote sensing techniques for such applications as oil prospecting or estimating the surface water content in sandy deserts. Robinson and Friedman created a novel way to measure the electrical potential of materials, which can be used to estimate the porosity and water content of soils, sediments and rocks. The new method could, for example, allow researchers to more accurately determine the electrical properties of solid matter and could require reference books to revise their existing dielectric constant values. Unlike existing mineral electrical intensity (permittivity) measures that are based on information that approximates the material’s dielectric constant value, the proposed method would immerse a sample in dielectric fluids and add new fluids until the two reach equilibrium.

Title: A method for measuring the solid particle permittivity or electrical conductivity of rocks, sediments and granular materials

Authors:
David A. Robinson, S. P. Friedman, Institute of Soil, Water and Environmental Sciences, ARO, Bet Dagan, Israel.
(Note: Robinson is now at the US Salinity Laboratory, U.S. Department of Agriculture, Riverside, California.

Source: Journal of Geophysical Research-Solid Earth (JGR-B) paper 10.1029/2001JB000691, 2003

8. Photochemical effects of aerosols

A new model that accounts for previously unrecognized photochemical processes of aerosols suggests that efforts to control particulate matter air pollution may have the unintended consequence of increasing surface ozone. Martin et al. predict that surface ozone over Europe and other industrialized regions will increase if aerosol emissions are reduced without also reducing ozone precursors. The authors examined the difference between model predictions from existing gas-phase models and other models that include aerosols like black carbon and found an unexpectedly large aerosol contribution from the unexpected photochemical processes. The researchers suggest that aerosols help the atmosphere remove pollution by increasing sun-driven atmospheric oxidation, which breaks down polluting gases like carbon monoxide, fluorocarbons and other greenhouse gases, by nearly twice the amount previously expected.

Title: Global and regional decreases in tropospheric oxidants from photochemical effects of aerosols

Authors:
Randall V. Martin, Daniel J. Jacob, Robert M. Yuantosca, Harvard University, Cambridge, Massachusetts;
Mian Chin, Paul Ginoux, Georgia Institute of Technology, Atlanta, Georgia.

Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2002JD002622, 2003

9. Meteor strikes may create biotic conditions on icy moons

Meteorites crashing into Jupiter’s icy moon Europa at hypersonic speeds have likely triggered electrical impulses that could change the chemistry of that frigid world. Borucki et al. report for the first time that electrical discharges result from the impact of a projectile striking a block of ice at high speed. The authors speculate that Europa’s colored ice, seen by the Galileo spacecraft, may result from yellow-brown organic molecules created by impact-induced electrical impulses passing through the icy surface. The researchers propose that meteor impacts could also generate organic matter in the outer Solar System, but that Europa, with its widely conjectured underground ocean, might contain organic material under its craters where complex living matter can seep onto the surface from cracks in the ice.

Title: A new energy source for organic synthesis in Europa’s surface ice

Authors:
Jerome G. Borucki, Dale P. Cruikshank, NASA Ames Research Center, Moffett Field, California;
Bishun Khare, SETI Institute, NASA Ames Research Center, Moffett Field, California.

Source: Journal of Geophysical Research-Planets (JGR-E) paper 10.1029/2002JE001841, 2002