JOURNAL HIGHLIGHTS(202) 777-7507
hleifert@agu.org
| American Geophysical Union JOURNAL HIGHLIGHTS |
Contact: Harvey Leifert (202) 777-7507 hleifert@agu.org |
| 12 June 2003 |
The following highlights summarize research papers in
Geophysical Research Letters (GL), Journal of Geophysical
Research-Atmospheres (JD), Global Biogeochemical Cycles (GB), and Water
Resources Research (WR). The papers related to these Highlights are
printed in the next paper issue of the journal following their
electronic publication.
1. Increased vegetation in Africa may indicate recovery from drought 1. Increased vegetation in Africa may indicate recovery from drought A trend toward increased vegetation in sub-Saharan Africa may indicate the slow reversal of decades-long droughts that negatively influenced the local human, plant, and animal populations. Eklundh and Olsson analyzed satellite observations that show the greenness of vegetation in the Sahel, which covers a large part of Africa and ranges from the Atlantic Ocean to the Red Sea. The authors found strong positive trends in the region during a 17-year period ending in 1999 and interpreted their findings as a recovery from the drought years during the mid 1980s. Such a recovery may also have significant impacts on water and carbon cycles in Africa, as well as global climate systems. They note that rainfall has slightly increased during the recent years, but say that other factors, such as improved land management and migration during and after the droughts may also have contributed to the increasing vegetation trend. Title: Vegetation index trends for the African Sahel 1982-1999 Authors: Lars Eklundh, Lennart Olsson, Lund University, Lund, Sweden. Source: Geophysical Research Letters (GRL) paper 10.1029/2002GL016772, 2003
2. New method to measure seismic anomalies A case study of an unusual example of wave propagation through solids was used to infer the nature of a formation at the base of the mantle beneath Central America and could also be helpful in resolving other types of wave anomalies identified during seismological experiments. Fisher et al. created images of a small region at the bottom of the lower mantle in Central America, revealing a relationship between wave velocities and damping at the core-mantle boundary. The relationship displayed in their study can allow researchers to distinguish between chemical and thermal origins of anomalous structures deep within the Earth. The study concluded that the unknown formation approximately 3,000 kilometers [2,000 miles] below the Central American study area was most likely a thermal anomaly and was perhaps the birth of a small mantle plume. Title: Small-scale lateral variations in D" attenuation and velocity structure Authors: Jesse L. Fisher, Michael E. Wysession, Washington University, St. Louis, Missouri; Karen M. Fischer, Brown University, Providence, Rhode Island. Source: Geophysical Research Letters (GRL) paper 10.1029/2002GL016179, 2003
3. Plankton produce tropical ocean surface temperature anomalies The growth of plankton blocks sunlight penetration into the upper part of the oceans, a finding that could to explain unusual variations in sea surface temperatures in the tropical Pacific. Gildor et al. propose that shifts in oceanic plankton growth influence the opacity of the near-surface ocean and can induce seasonal changes in sea surface temperatures that affect regional atmospheric conditions. The authors observed long-term satellite images of biota [the ensemble of living organisms] growth in the Western Pacific and suggest that their simple model can present an accurate measure of surface conditions in the area. The researchers present a new model that includes the interactions of living systems with the air and sea, finding that oceanic biology may play a role in the tropical intraseasonal oscillation, an atmospheric phenomenon that affects weather conditions throughout the tropics and over North America. Title: A role for ocean biota in tropical intraseasonal atmospheric variability Authors: Hezi Gildor, Raymond N. Sambrotto, Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York; Adam H. Sobel, Mark A. Cane, Columbia University, New York, New York. Source: Geophysical Research Letters (GRL) paper 10.1029/2002GL016759, 2003
4. Antarctic climate patterns extend to the ocean floor New research suggests that climate fluctuations in the Antarctic reach from the stratosphere to the ocean floor. Hughes et al. report data recorded by a series of tidal gauges that measured the underwater pressure along the continental shelf to depths of 1,000 meters [3,000 feet], finding that ocean pressure variations are driven by the region's climate. Two other climatic indicators, known as the Antarctic Oscillation and the Southern Hemisphere Annular Mode, are also associated with circulation changes in the stratosphere. The authors found that the ocean pressure variations they observed are a measure of the changing strength of the Antarctic Circumpolar Current, the world's largest current, and show that such pressure fluctuations are forced by climate changes. The researchers conclude that the climate conditions of the entire Antarctic continent, from the stratosphere to the ocean floor, respond to changes within the atmospheric circulation. Title: Coherence of Antarctic sea levels, Southern Hemisphere Annular Mode, and flow through Drake Passage Authors: Chris W. Hughes, Philip L. Woodworth, Michael P. Meredith, Vladimir Stapanov, Proudman Oceanographic Laboratory, Bidston, Merseyside, United Kingdon; Thomas Whitworth, Texas A&M University, College Station, Texas; Alexander R. Pyne, Victoria University of Wellington, Wellington, New Zealand. Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017240, 2003
5. Composition of Jupiter-family comets A measurement from inside the plume of an inner solar system comet suggests that the chemical content of its plasma is similar to that predicted by cometary evolution models, but has some significant differences that may prompt a re-examination of solar-system comets. Nordholt et al. present data from a mass spectrometer aboard Deep Space 1 during its 2001 flyby near comet Borrelly, a Jupiter-family comet that was considered significantly more evolved, compared to those from the Halley family. The authors found a preponderance of heavy ions within the comet's plume, including a concentration of oxygen, water and the methyl radical CH3, similar to that previously seen in the Halley class. However, their observations showed some important differences between the two types of comet that leave the researchers unable to conclusively determine whether the there is a fundamental difference in the composition of the comets, which have vast variation among their orbital periods and proximity to the Sun. Title: Deep Space 1 encounter with Comet 19P/Borrelly: Ion composition measurements by the PEPE mass spectrometer Authors: Jane E. Nordholt, D. B. Reisenfeld, R. C. Wiens, S. P. Gary, D. M. Delapp, R. C. Elphic, H. O. Funsten, D. J. Lawrence, M. Shappirio, J. T. Steinberg, Los Alamos National Laboratory, Los Alamos, New Mexico; F. Crary, University of Michigan, Ann Arbor, Michigan; J. J. Hanley, D. J. McComas, D. T. Young, Southwest Research Institute, San Antonio, Texas; J. Wang, Virginia Polytechnic Institute and State University, Blacksburg, Virginia. Source: Geophysical Research Letters (GRL) paper 10.1029/2002GL016840, 2003
6. Radon levels can provide early warning for earthquakes Evidence from a strong earthquake in the Philippines provides new information to help confirm a link between radon levels in the ground and the onset of a seismic event. Richon et al. continuously monitored the soil-gas concentrations near the Taal volcano, finding peak levels of radon approximately three weeks before the massive 1994 Mindoro earthquake. Previous research had suggested that elevated concentrations of a radon isotope could serve as a useful predictor of seismic events and provide an effective method of early warning, but researchers had been unable to provide such a direct correlation between the two or create a method to discern the timing and location of a seismic event from radon signatures. The authors' study of the volcanically and tectonically active area found a near-sixfold increase in radon levels prior to the quake. Title: Radon anomaly in the soil of Taal volcano, the Philippines: A likely precursor of the M 7.1 Mindoro earthquake (1994) Authors: Patrick Richon, Atomic Energy Commission, Bruyeres-le-Chatel, France; J.-C. Sabroux, National Institute of Radiation and Nuclear Safety, Gif-sur-Yvette, France; M. Halbwachs, University of Savoie, Le Bourget du Lac, France; J. Vandemeulebrouck, N. Poussielgue, National Center of Scientific Research, University of Savoie, Chambery, France; J. Tabbagh, Pierre and Marie Curie University, Paris, France; R. Punongbayan, Philippine Institute of Volcanology and Seismology, Manila, Philippines. Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL016902, 2003
7. Ancient El Nino may have warmed equatorial Pacific A new analysis of sediment records from the western equatorial Pacific suggests that the waters there continued to warm for another millennium after other ocean temperatures reached their modern levels. Rosenthal et al. used sediment records to report the sea surface temperatures in the equatorial Sulu Sea and compared their findings to ice core records in Greenland, specifically examining the size and timing of climate change shifts between the equatorial Pacific and the rest of the world. They note that modern sea surface temperatures, combined with larger weather patterns like El Nino, significantly affect atmospheric circulation patterns and global climate conditions. Although some previous studies had argued against the formation of modern El Nino-like weather patterns on the ancient seas, the researchers conclude that external forces, like tropical winds, are the most likely source of the continued warming in the western Pacific. Title: The amplitude and phasing of climate change during the last deglaciation in the Sulu Sea, western equatorial Pacific Authors: Yair Rosenthal, Rutgers University, New Brunswick, New Jersey; Delia W. Oppo, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts; Braddock K. Linsley, State University of New York-Albany, Albany, New York. Source: Geophysical Research Letters (GRL) paper 10.1029/2002GL016612, 2003
8. Map of Earth's crust helps estimate global carbon exchange The first map of Earth's rocky crust can help researchers monitor weathering conditions that transfer carbon dioxide from the atmosphere into the world's oceans. Suchet et al. present a finely detailed lithological map of the Earth, which they used to examine the type and distribution of various rock formations on all the continents. They found that the composition of stone outcroppings near all of the world's major river systems was, on average, approximately the same as the surface of the continents. The authors suggest that such information can be used to link the biosphere, the lithosphere, and the oceans to simulate carbon transfer between the land and water. They conclude that their study will also be useful to analyze the overall global carbon cycle and to provide information for regulating atmospheric carbon dioxide concentrations. Title: Worldwide distribution of continental rock lithology: Implications for the atmospheric/soil CO2 uptake by continental weathering and alkalinity river transport to the oceans Authors: Philippe Amiotte Suchet, National Research Institute/Univeristy of Bourgogne, Dijon, France; Jean-Luc Probst, National Research Institute/Paul Sabatier University, Toulouse, France; Wolfgang Ludwig, University of Perpignan, Perpignan, France. Source: Global Biogeochemical Cycles (GBC) paper 10.1029/2002GB001891, 2003
9. Airborne mercury can spread worldwide Data collected from airborne mercury level measurements in Canada provide insights into the element's distribution in the atmosphere and how the toxic metal can spread to the global food chain in regions far from the original sources. Banic et al. report results from a method that allowed the first continuous monitoring of mercury levels suspended aloft at various altitudes. They recorded the quantity of gaseous elemental mercury in three locations during three seasons that represented various meteorological conditions. Previous mercury observations often gave conflicting information because of the complexities inherent in estimating the conditions at high altitudes, the authors noted. Their findings provide additional evidence for a vast pool of airborne mercury that can be drawn to the Earth's surface by atmospheric mixing, even in remote regions. The researchers conclude that mercury's long lifetime in the atmosphere, combined with wind and cloud transport, could lead to long-range transport of mercury. Title: Vertical distribution of gaseous elemental mercury in Canada Authors: Cathy M. Banic, W. H. Schroeder, A. Steffen, K. A. Anlauf, Meteorological Service of Canada, Toronto, Ontario, Canada; S. T. Beauchamp, R. J. Tordon, Meteorological Service of Canada, Dartmouth, Nova Scotia, Canada; H. K. T. Wong, National Water Research Institute, Burlington, Ontario, Canada. Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2002JD002116, 2003
10. Local analysis helps avoid arsenic-contamination well water An analysis of arsenic in groundwater near the capital of Bangladesh shows that detailed mapping is necessary to determine which wells pose a serious health hazard in many parts of South Asia. Van Geen et al. determined the location, depth, and the arsenic levels for a large number of tube wells distributed in a cluster of closely spaced villages. The authors found that the depth required for wells to consistently reach low-arsenic aquifers ranges from 30-120 meters [100-400 feet] within their study area and related the information to geological features that guide the arsenic concentrations. They suggest that their study could be used to better identify the toxic element and trace the health problems that affect much of the local population, noting that the arsenic distribution in wells shallower than 30 meters [100 feet] was highly variable. While their study examines only a tiny fraction of the total wells in the nation, the authors conclude that the local-scale investigations should be used in other areas to guide residents to potable water. Title: Spatial variability of arsenic in 6,000 tube wells in a 25 square kilometer [10 square mile] area of Bangladesh Authors: Alexander Van Geen, M. Steckler, C. Small, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York; Y. Zheng, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, and Queens College, City University of New York, Flushing, New York; R. Versteeg, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, and Idaho National Environmental and Engineering Laboratory, Idaho Falls, Idaho; M. Stute, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, and Barnard College, New York, New York; A. Horneman, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, and Columbia University, New York, New York; R. Dhar, Queens College, City University of New York, Flushing, New York; A. Gelman, H. Ahsan, Columbia University, New York, New York; I. Hussein, National Institute of Preventive and Social Medicine, Dhaka, Bangladesh; K. M. Ahmed, Dhaka University, Dhaka, Bangladesh. Source: Water Resources Research (WRR) paper 10.1029/2002WR001617, 2003 ***** Journalists and public information officers of educational and scientific institutions (only) may receive one or more of the papers cited in the Highlights by sending a message to Emily Crum at ecrum@agu.org, indicating which one(s). Include your name, the name of your publication, and your phone and fax number. State whether you prefer to receive the paper(s) as pdf attachments by email or as a fax. Others should send a request to service@agu.org, citing the doi of the paper (number beginning 10.1029/....), to order a copy of the paper. The Highlights and the papers to which they refer are not under AGU embargo. Contact: Phone (direct): +1 (202) 777-7513 |
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