JOURNAL HIGHLIGHTS(202) 777-7507
hleifert@agu.org
| American Geophysical Union JOURNAL HIGHLIGHTS |
Contact: Harvey Leifert (202) 777-7507 hleifert@agu.org |
| 25 August 2003 |
| Contents I. Highlights, including authors and their institutions II. Ordering information for science writers |
| I. Highlights, including authors and their institutions
The following highlights summarize research papers in Geochemistry,
Geophysics, Geosystems (GC), Geophysical Research Letters (GL), Journal
of Geophysical Research - Space Physics (JA), Journal of Geophysical
Research - Oceans (JC), Journal of Geophysical Research - Planets (JE),
Paleoceanography (PA), and Reviews of Geophysics (RG).. The papers related
to these Highlights are printed in the next paper issue of the journal 1. Dust from Northern Hemisphere influences Southern Ocean 1. Dust from Northern Hemisphere influences Southern Ocean The majority of lead found in the Southern Ocean comes from dust that originated in the Saharan desert, according to a newly published report. Sanudo-Wilhelmy and Flegal examined the composition of lead in Antarctic waters and report that the atmospheric dust that originated in the north African desert is transferred from the central Atlantic Ocean via deepwater circulation to the Southern Ocean. The authors provide the first analysis to pinpoint the dominant source of the fertilizing element in the southern polar region's surface waters, although their study found that additional lead can come from industrial emissions and natural rock weathering in other parts of the world. They conclude that environmental changes in the Northern Hemisphere can have a significant influence on the chemical composition of waters in remote regions of the Southern Hemisphere and may impact climate change scenarios. Title: Potential influence of Saharan dust on the chemical composition of the Southern Ocean Authors: Source: Geochemistry, Geophysics, Geosystems (GC) paper 10.1029/2003GC000507, 2003
2. Special section on unusually cold California Current The 1 August issue of Geophysical Research Letters features a collection of papers reporting the strong enhancement of subarctic waters entering the California Current system in the summer of 2002. Adriana Huyer provides a preface to the eight papers that analyze the possible causes and effects from the rare phenomenon. The condition brought exceptionally cold and fresh water to the upper layer of the ocean between Vancouver Island and Southern California that was unprecedented in several decades of temperature records that span El Nino, La Nina and Pacific decadal oscillation shifts. The researchers suggest that unusual winds over the northeastern Pacific during the preceding winter and spring initiated stronger eastward and southward currents and supplied more subarctic water to the California system. Title: Preface to special section on enhanced Subarctic influence in the California Current, 2002 Author: Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017724, 2003
3. Atmospheric bromine reductions are good news for stratospheric ozone A reduction in the ozone-depleting gas methyl bromide has reduced the amount of atmospheric bromine worldwide. Montzka et al. report a nearly five percent reduction in tropospheric bromine that they suggest was driven by a reduction in industrial production of chemicals that release the element. Halons, mostly used in fire extinguishing equipment, and methyl bromine were among the gases targeted for restrictions in the Montreal Protocol for mitigating damage to the ozone layer. The authors analyzed the results from 10 globally distributed ground-based sampling sites and found that the global load of gaseous bromine from halons and methyl bromide peaked in 1998 and has dropped ever since. They note that the bromine reduction results in a much larger decline in the atmospheric burden of ozone-depleting halogens like chlorine and bromine than predicted, which may result in a need for new ozone predictions. [Note: See also AGU press release 03-23: http://www.agu.org/sci_soc/prrl/prrl0323.html] Title: A decline in tropospheric organic bromine Authors: Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017745, 2003
4. Regional records make the best temperature reconstructions A small number of natural temperature "gauges" can provide the most accurate data to reconstruct past environmental conditions. Pauling et al. show that the best sources used to assemble historical temperature records can vary by region and season, from tree-ring records as an optimal measure of summertime temperatures in Europe to cave deposits as a proxy for large areas of the North Atlantic Ocean and land areas bordering the water during all seasons. Similarly, the results from conclusive documentary evidence like ice core samples and oceanic coral analysis can provide information that is often more reliable than records kept by local residents. The authors propose that a combination of only a few data sets from the best measures at each location would provide more precise information to estimate historical temperatures worldwide than global averages. Title: Evaluation of proxies for European and North Atlantic temperature field reconstructions Authors: Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017589, 2003
5. Rocket plumes shed light on lower thermosphere transport An analysis of water vapor in the upper atmosphere injected by space shuttle and unmanned rocket launches may allow researchers to better understand the poorly understood processes in the lower thermosphere [highest part of Earth's atmosphere]. Siskind et al. report from an extensive set of plumes observed by satellite and make some of the first hypotheses about the transport and circulation at the approximately 110-kilometer [70-mile] thermospheric altitude. They suggest that unexpectedly strong winds move the water vapor faster than implied by previous satellite estimates, which is consistent with the proposal that shuttle exhaust can be rapidly transported and may affect the formation of Polar Mesospheric Clouds. The authors also propose a correlation between the time of a launch and the direction of the plume motion, noting that the plumes from mid-day launches traveled to the north while those from late afternoon and evening launches moved south. Title: Signatures of shuttle and rocket exhaust plumes in TIMED/SABER radiance data Authors: Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017627, 2003
6. Modern temperatures warmest in 2,000 years A look over the past 2,000 years of Earth's surface temperature history indicates that the average warmth of the late 20th century is unprecedented in the Northern Hemisphere and likely the entire world. Mann and Jones present mean surface temperature reconstructions in both hemispheres based on previous data and a new global average temperature estimate. The authors averaged previous temperature reconstructions that used ice core samples, tree-ring records and other indicators taken from multiple regions worldwide to examine long-term variations in global temperatures. They note that not enough information was available to make any accurate conclusions in the Southern Hemisphere. The researchers suggest that the anomalously warm conditions in the modern environment are unprecedented at least back to 200 AD. Title: Global surface temperatures over the past two millennia Authors: Source: Geophysical Research Letters (GRL) paper 10.1029/2003GL017814, 2003
7. Simulation can help understand upper atmospheric changes A new study provides evidence suggesting that the cause of upper atmospheric cooling is related to the presence of oxygen atoms in the region rather than to the element's concentration. Rashid A. Akmaev ran numerical simulations of the atmospheric response to various levels of carbon dioxide movement in the upper atmosphere and found surprisingly little reaction in the thermosphere to faster movements by atomic oxygen. Previous research had found that increasing amounts of manmade greenhouse gases in the lower atmosphere led to elevated carbon dioxide higher in the sky, which reacted with oxygen and produced lower temperatures at the Earth-space boundary in an effect known as greenhouse cooling. Akmaev's study showed, contrary to expectation, that neither the amount of cooling nor the related near-Earth space density decline was affected by the increased efficiency of molecular collisions or higher oxygen levels at the top of the atmosphere. Title: Thermospheric resistance to "greenhouse cooling": Effect of the collisional excitation rate by atomic oxygen on the thermal response to CO2 forcing Author: Source: Journal of Geophysical Research-Space Physics (JGR-A) paper 10.1029/2003JA009896, 2003
8. Modeling the effects from asteroid impacts on Earth The dust injected into the atmosphere following a collision between the Earth and even a medium-sized asteroid would block the Sun's radiation and lower surface and ocean temperatures enough to threaten all living species. Luder et al. modeled the short- and long-term effects from asteroid collisions and report the details of dust suspension and the possibility of oceanic modification because of sea surface temperature changes. The authors suggest that while the dust would remain suspended in the atmosphere for only approximately six months, the climactic consequences could last for nearly a thousand years. Such effects are dependent on the size of a space rock, although an asteroid greater than three kilometers [two miles] in diameter would stir up enough dust to essentially block all incoming sunlight and heat. The researchers conclude that meter-sized [three foot-sized] object collisions occur on a near-monthly basis, while larger asteroids are estimated to hit the planet's surface approximately once per millennia. Title: A model for long-term climatic effects of impacts Authors: T. Luder, W. Benz, T. F. Stocker, University of Bern, Bern, Switzerland. Source: Journal of Geophysical Research-Planets (JGR-E) paper 10.1029/2002JE001894, 2003
9. New method estimates less ice coverage during glacial maximum A new measure to estimate historical sea ice levels indicates that ice cover during the last glacial maximum was much less extensive than previously reported. Sarnthein et al. applied a newly devised method to sediment records in the northern high latitudes and suggest that the northern North Atlantic and Nordic seas were largely ice-free during the glacial summer and provided atmospheric moisture that allowed continental-sized ice sheets to build up further to the south during wintertime. The ice cover associated with the glacial period significantly affected the global climate system and the exchange of heat and radiation during the historical Ice Age. Most previous indicators of sea ice cover measured in the Southern Ocean estimated the concentration of single-celled plant plankton in deep-sea sediment cores; the authors found that hardly any of the cells were present in glacial-age sediments in the Northern Atlantic. Instead, they created a method to measure calcium deposits found in microorganism shells in marine sediment cores. Title: Past extent of sea ice in the northern North Atlantic inferred from foramineferal paleotemperature estimates Authors: Source: Paleoceanography (PA) paper 10.1029/2002PA000771, 2003
10. Current technology could improve volcano warnings Modern geodetic monitoring tools such as ground-sensing radar and global positioning systems might enable scientists to extend the warning period for volcanic eruptions. Daniel Dzurisin suggests that such systems could detect ground deformation caused by magma accumulation earlier than is possible with other techniques and could provide a better monitor for the world's active volcanoes. More advanced equipment would permit observations of eruption precursors like deep earthquakes and the carbon dioxide emission rate from volcanoes and provide more accurate eruption forecasts and allow greater warning before unexpected and catastrophic eruptions strike. Dzurisin proposes that more thorough monitoring of the world's volcanoes with InSAR radar and continuous sensors could allow researchers to better understand a volcano's magmatic plumbing system and processes and to provide more specific alerts to residents living near active volcanoes. Title: A comprehensive approach to monitoring volcano deformation as a window on the eruption cycle Author: Source: Review of Geophysics (RG) paper 10.1029/2001RG000107, 2003 ***** Others should send a request to service@agu.org, citing the doi of The Highlights and the papers to which they refer are not under Contact: Phone (direct): +1 (202) 777-7507 |
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