AGU Journal highlights - 8 April 2004

04/08/04

The following highlights summarize research papers in Geophysical Research Letters (GL), Journal of Geophysical Research-Oceans (JC), Journal of Geophysical Research- Atmospheres (JD), and Paleoceanography (PA). The papers related to these Highlights are printed in the next paper issue of the journal following their electronic publication.

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1. Warming in the Arctic could release ancient carbon into ocean

Though global warming is expected to increase future permafrost melting and carbon transport in Arctic rivers, the carbon currently found in the Arctic Ocean indicates that such melting has not yet occurred. Benner et al. report that the vast majority of land-derived dissolved organic carbon in the Arctic Ocean and rivers is young and is only recently removed from soil transported by high-latitude rivers. The authors used the half-life of radiocarbon to perform the first predictions of its age in the Arctic waters and suggest that the carbon's terrestrial characteristics show that it is likely recently removed from the upper soil. They indicate that million-year-old carbon from melting permafrost would be readily identifiable in the polar surface waters. Such melting would release ancient carbon in freshwater runoff that would significantly affect the biogeochemical cycles of the Arctic Ocean, which have the highest carbon levels of any ocean basin.

Title: Export of young terrigenous dissolved organic carbon from rivers to the Arctic Ocean

Authors:
Ronald Benner, Bryan Benitez-Nelson, Karl Kaiser, University of South Carolina, Columbia, South Carolina;
Rainer M. W. Amon, Alfred Wegener Institute for Marine and Polar Research, Bremerhaven, Germany.

Source: Geophysical Research Letters (GL) paper
10.1029/2003GL019251, 2004

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2. Cause of plasmasphere corotation lag

Researchers compared satellite images of long-lived "notches" used to track the rotation of the plasmasphere [a doughnut-shaped region of ionized hydrogen and helium gas that surrounds the Earth in space, extending out to three or four Earth radii] to the movement of the Earth and suggest that the recently observed plasmaspheric co-rotation is caused by a corresponding corotation lag in the upper ionosphere. Burch et al. propose that ionospheric movement causes a 10-15 percent lag between the plasmasphere and Earth. Such a delay would have a significant effect on models that simulate Earth's plasmaspheric dynamics and its response to solar and interplanetary events. They note that previous models assumed that the plasmasphere and the Earth corotated together. Although a similar rotational lag was seen in Jupiter's magnetosphere, the authors report that the likely cause--effects from its moon Io--do not apply to the effect seen on Earth. They suggest that the rotation delay can affect model interpretations of Earth's shielding magnetic field and should be included in future analyses of planetary convection.

Title: Cause of plasmasphere corotation lag

Authors:
Jim L. Burch, J. Goldstein, Southwest Research Institute, San Antonio, Texas;
B. R. Sandel, University of Arizona, Tucson, Arizona.

Source: Geophysical Research Letters (GL) paper
10.1029/2003GL019164, 2004

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3. Modeling the North Atlantic on a laptop

A detailed numerical model of the North Atlantic Ocean that once required supercomputing power can now be run on a personal computer. Dietrich et al. used a PC to simulate the interacting Gulf Stream and deep current systems that link the North Atlantic, northern seas and Arctic Ocean climate. They suggest that the increased computing power, combined with improved modeling techniques, permits the reliable assessment of a variety of ocean-related climate change theories, including abrupt climate change. The authors show that dissipation processes, although small, strongly affect these climatologically important systems on a decadal time scale. Their low dissipation results compare well with previous observations of Gulf Stream behavior near Cape Hatteras, a well-studied yet poorly understood section of the Atlantic. The researchers note that the deep current system is critical to climate change risk assessments, because of its contact with methane hydrate deposits on the ocean floor that can significantly affect ocean currents and climate change.

Title: Dissipation effects in North Atlantic Ocean modeling

Authors:
David E. Dietrich, AcuSea Inc., Albuquerque, New Mexico;
A. Mehra, Geo Resources Institute, Mississippi State University, Stennis Space Center, Mississippi;
R. L. Haney, Naval Postgraduate School, Monterey, California;
M. J. Bowman, State University of New York at Stony Brook, New York;
Y. H. Tseng, Johns Hopkins University, Baltimore, Maryland.

Source: Geophysical Research Letters (GL) paper 10.1029/2003GL019015, 2004

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4. Unusual emissions associated with lightning

Two papers by Dwyer et al. provide new information on unexpected emissions observed in rocket-triggered lightning that could affect scientific understanding of natural lightning dynamics. The first article notes the frequent occurrence of very brief, unusually strong x-ray bursts coming from the lightning channel close to the ground. The researchers observed the source of the x-rays moving downward as the lightning propagated from the cloud to the ground. They note that the lightning appeared to flicker in x-rays, emitting rapid bursts with energies up to about twice that found in a chest x-ray.

The second article reports an intense gamma ray burst observed on the ground in association with the initial stage of rocket-triggered lightning. The gamma rays, which were 50 times more energetic than the x-rays, may represent a new kind of event originated from thunderclouds several miles overhead. In both cases, the study results provide new insight into how large-scale lightning discharges occur, including their initiation and propagation.

Titles:
1. Measurements of x-ray emission from rocket-triggered lightning;
2. A ground level gamma-ray burst observed in association with rocket-triggered lightning

Authors:
Joseph R. Dwyer, H. K. Rassoul, M. Al-Dayeh, L. Caraway, B. Wright, A. Chrest, Florida Institute of Technology, Melbourne, Florida;
M. A. Uman, V. A. Rakov, K. J. Rambo, D. M. Jordan, J. Jerauld, C. Smyth, University of Florida, Gainesville, Florida.

Source: Geophysical Research Letters (GL) papers 10.1029/2003GL018770, 2004 and 10.1029/2003GL018771, 2004

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5. New method to estimate groundwater age

A new method to measure the age of groundwater sources finds that water inside an Egyptian aquifer is approximately one million years old. Sturchio et al. used a laser-based atom-counting method to measure a radioactive krypton isotope with a known half-life in deep groundwater sources. Kryton-81 is produced nearly constantly in the upper atmosphere and is uniformly deposited on the Earth surface, including the oceans and surface waters. Unlike other isotopes used to date groundwater, such as chlorine-36, krypton-81 can be used in saline and briney waters, because it has no other natural or manmade sources that could contaminate a water sample. The authors used the krypton-81 technique to measure the age of water in the Nubian Aquifer in southwest Egypt, finding that groundwater there may have originated as precipitation derived from moisture transported across North Africa from the Atlantic during the Pleistocene epoch.

Title: One million year old groundwater in the Sahara revealed by krypton-81 and chlorine-36

Authors:
Neil C. Sturchio, L. J. Patterson, University of Illinois at Chicago, Illinois;
X. Du, Physics Division, Argonne National Laboratory, Argonne, Illinois, and Northwestern University, Evanston, Illinois;
R. Purtschert, B. E. Lehmann, T. Bigler, R. Lorenzo, Institute of Physics, University of Bern, Switzerland;
M. Sultan, R. Becker, University of New York at Buffalo, New York;
Z.-T. Lu, P. Muller, K. Bailey, T. P. O'Connor, L. Young, Argonne National Laboratory, Argonne, Illinois;
Z. El Alfy, Egyptian Geological Survey and Mining Authority, Cairo, Egypt;
B. El Kaliouby, Y. Dawood, A. M. A. Abdallah, Ain Shams University, Cairo, Egypt.

Source: Geophysical Research Letters (GL) paper 10.1029/2003GL019234, 2004

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6. Environmental impact of switch to hydrogen economy

Switching from the current fossil fuel-driven economy to one powered by hydrogen could significantly influence the chemical composition of the atmosphere, although a new study finds that such a change would likely have little effect on concentrations of stratospheric ozone. Warwick et al. created a two-dimensional model to simulate the effects from a worldwide transfer to a hydrogen economy, including using hydrogen technology for power and transportation systems, and analyzed the atmospheric effects from varying manmade emissions. They report that hydrogen leaks and resulting increases in stratospheric water vapor are expected to be smaller than previous estimates. The researchers also note that the largest environmental changes would come from reduced carbon gases and nitrogen oxides in the atmosphere, because of a decrease in fossil fuel burning. They suggest that the results from such chemical and radiative changes are potentially more important than hydrogen emissions and should be studied with three-dimensional models.

Title: Impact of a hydrogen economy on the stratosphere and troposphere studied in a 2-D model

Authors:
Nicola J. Warwick, Centre for Atmospheric Science, Cambridge University, Cambridge, United Kingdom;
S. Bekki, Pierre-Simon Laplace Institute, University of Paris VI, Paris, France;
E. G. Nisbet, University of London, Egham, United Kingdom;
J. A. Pyle, Centre for Atmospheric Science, Cambridge University, Cambridge, United Kingdom, and NCAS Atmospheric Chemical Modeling Support Unit, Cambridge, United Kingdom.

Source: Geophysical Research Letters (GL) paper
10.1029/2003GL019224, 2004

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7. Analysis of a harmful algal bloom

A study analyzing the harmful effects of algal blooms in Vietnam may help researchers better understand the cause of the increasingly common worldwide phenomenon. Tang et al. observed a 2002 bloom in the warm Vietnamese waters for approximately six weeks, using satellites to detect the ocean color and other instruments to track the ocean temperature and wind velocity. The plankton blooms and associated algal toxins, thought to be primarily caused by nutrient- and mineral-rich waters and moved by the wind, remove the dissolved oxygen in estuaries and coastal areas, killing fish and biological life in its path. The researchers found that the bloom was induced and supported by nutrients transported from the deep ocean to the surface by strong winds that created a cold-water plume from the coast to the open sea. They suggest that the study provides one of the first assessments of the formation and movement of a bloom, which can be used to predict and track the biogeochemical impacts from such events.

Title: Remote sensing oceanography of a harmful algal bloom off the coast of southeastern Vietnam

Authors:
Danling Tang, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China, and Fudan University, Shanghai, China, and Tohoku University, Sendai, Japan;
Hiroshi Kawamura, Tohoku University, Sendai, Japan;
Hai Doan-Nhu, Institute of Oceanography, Nha Trang, Vietnam;
Wataru Takahashi, Japan NUS Co., Ltd., Tokyo, Japan.

Source: Journal of Geophysical Research-Oceans (JC) paper: 10.1029/2003JC002045, 2004

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8. Canadian smoke pollutes Washington, D.C., air

An analysis of the unusual high-altitude transport of smoke and pollutants from Canadian forest fires to Washington, D.C., in 2002 may help explain the long-range movement and distribution of similar pollutants downstream. Colarco et al. examined ground, air, and space-based data of smoke from fires in Quebec that were carried by winds in 2002 to the upper atmosphere to Washington, where they descended to the surface. Similar instances have been observed worldwide where pollutants are transported over long distances and affect the air quality in locations far removed from the source. The authors followed the path of the Canadian smoke and used a meteorological model to infer the mechanism for moving the pollutants from higher altitudes to the surface. They report that now that the mechanism is understood, it can be used to predict when smoke or pollutants moving overhead will impact surface air quality.

Title: Transport of smoke from Canadian forest fires to the surface near Washington, D.C.: Injection height, entrainment, and optical properties

Authors:
Peter R. Colarco, B. G. Doddridge, L. T. Marufu, University of Maryland, College Park, Maryland;
M. R. Schoeberl, E. J. Welton, NASA Goddard Space Flight Center, Greenbelt, Maryland;
O. Torres, University of Maryland Baltimore County, Baltimore, Maryland.

Source: Journal of Geophysical Research-Atmospheres (JD) paper: 10.1029/2003JD004248, 2004

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9. Global response to tropical volcanic eruptions

A four-century record of the climate's response to tropical volcanic eruptions indicates that the events have a significant global impact that may be possible to estimate. Shindell et al. used a combination of historical climate reconstructions and modern instrumental records to analyze the climate patterns following large tropical eruptions since the early 17th century. Their research found anomalously warm temperatures throughout northern Eurasia and cooling over northern Africa and the Middle East after tropical eruptions. The authors note that the northern portion of North America also cooled, creating a broad pattern of alternating warm and cool zones similar to changes expected from the North Atlantic Oscillation (NAO). They caution, however, that the climate response varies between eruptions and suggest that including the average response could improve forecasts following a future eruption. The researchers propose that the ash injected into the stratosphere from each volcanic blast can cause a shift in the normal NAO and affect the surface climate.

Title: Dynamic winter climate response to large tropical volcanic eruptions since 1600

Authors:
Drew T. Shindell, Gavin A. Schmidt, NASA Goddard Institute for Space Studies and Columbia University, New York, New York;
Michael E. Mann, University of Virginia, Charlottesville, Virginia;
G. Faluvegi, Columbia University, New York, New York.

Source: Journal of Geophysical Research-Atmospheres (JD) paper: 10.1029/2003JD004151, 2004

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10. Predicting the effects from an ancient El Nino

Fossilized coral from the tropical Pacific Ocean may allow researchers to measure ancient sea surface temperatures and salinities possibly influenced by El Nino. Kilbourne et al. measured the oxygen isotopic composition and the strontium/calcium ratios of a 350,000-year-old coral in the southwestern Pacific to identify the possible influence of El Nino during a time of lower sea level and possibly cooler tropical waters. The authors compared geochemical variations in the fossil coral with modern samples to investigate the background climate from the time and determine whether there was evidence of El Nino activity in the distant past. Large corals contain annual bands, much like tree rings, that record seasonal and annual changes in the tropical ocean, making it an ideal proxy for reconstructing climate variability and estimating seawater conditions before measurements were available. The researchers suggest that El Nino-like variations were present in the tropical Pacific between 335,000-374,000 years ago, although likely at a reduced amplitude relative to the current version.

Title: A fossil coral perspective on western tropical Pacific climate ~350 ka

Authors:
Kelly Halimeda Kilbourne, Terrence M. Quinn, Frederick W. Taylor, University of South Florida, St. Petersburg, Florida.

Source: Paleoceanography (PA) paper: 10.1029/2003PA000944, 2004

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