Public Release: 

AGU journal highlights -- Jan. 31, 2012

American Geophysical Union

The following highlights summarize research papers that have been recently published in Journal of Geophysical Research-Solid Earth (JGR-B), Water Resources Research (WRR), Geophysical Research Letters (GRL), and Journal of Geophysical Research-Oceans (JGR-C).

In this release:

  1. Fine, jagged ash increased Eyjafjallajökull volcano's influence
  2. Geological evidence for past earthquakes in Tokyo region
  3. Much irrigation water comes from non-sustainable sources
  4. Greenland's pronounced glacier retreat not irreversible
  5. New record from stalagmites shows climate history in Central Asia
  6. Io's volcanism influences Jupiter's magnetosphere
  7. Massive swarm of tunicates tilts ocean's chemical balance

Anyone may read the scientific abstract for any already-published paper by clicking on the link provided at the end of each Highlight. You can also read the abstract by going to and inserting into the search engine the full doi (digital object identifier), e.g. 10.1029/2011JB008726. The doi is found at the end of each Highlight below.

Journalists and public information officers (PIOs) at educational or scientific institutions who are registered with AGU also may download papers cited in this release by clicking on the links below. Instructions for members of the news media, PIOs, and the public for downloading or ordering the full text of any research paper summarized below are available at

1. Fine, jagged ash increased Eyjafjallajökull volcano's influence

The 2010 eruption of Eyjafjallajökull volcano was not a large event. Over months of volcanic activity the ash plume never pushed above 10 kilometers (6.2 miles), and the mass flows peaked at 1 million kilograms per second (2.2 million pounds per second), feeble amounts compared to some other volcanic eruptions. In total, the volcano spewed out only 270 million cubic meters (353 million cubic yards) of ash-a single day's activity for some eruptions. By any conventional measure, Eyjafjallajökull lacked power. Yet the eruption had a powerful effect on society, leaving tens of thousands of people stranded as air traffic around Western Europe was shut down.

The eruption's widespread influence was due to the unusually large distribution and high residency time of volcanic ash particles. By analyzing ash samples collected across Iceland, Dellino et al. show how the eruptive mechanisms acting at the vent, and thus the ash's small-scale properties, changed throughout the eruption. A simple computer simulation let the authors estimate an ash grain's drag and terminal velocity, and hence residency time, from measurements of small-scale properties.

The authors find that upwelling magma reacted with water from a nearby glacier, and the rapid cooling caused it to contract and fragment into fine, irregularly shaped ash. Near the end of the eruption, equally fine ash was produced when small gas bubbles trapped in the magma expanded as the molten rock neared the surface. From their collected samples, the authors find that the median diameter of the ash grains is 1 millimeter (0.04 inches). Starting 10 km (6.2 miles) from the volcano's vent, particles smaller than 16 micrometers became an important portion of the mix. The authors argue that the violent fragmentation processes caused jagged and porous ash grains. These aspherical aberrations increased the ash grains' time aloft and, according to the authors, explain how a small eruption inconvenienced such a large area.

Source: Journal of Geophysical Research-Solid Earth, Doi:10.1029/2011JB008726, 2012

Title: Ash from the Eyjafjallajökull eruption (Iceland): Fragmentation processes and aerodynamic behavior

Authors: P. Dellino and D. Mele: Centro Interdipartimentale di Ricerca sul Rischio Sismico e Vulcanico, Dipartimento di Scienze della Terra e Geoambientali, Universita di Bari, Bari, Italy;

M. T. Gudmundsson and G. Larsen: Institute of Earth Sciences, University of Iceland, Reykjavik, Iceland;

J. A. Stevenson and T. Thordarson: School of Geosciences, University of Edinburgh, Edinburgh, UK;

B. Zimanowski: Physicalisch Vulkanologisches Labor, Universitaat Wurzburg, Wurzburg, Germany.

2. Geological evidence for past earthquakes in Tokyo region

In 1923, a magnitude 7.9 earthquake devastated the Tokyo area, resulting in more than 100,000 deaths. About 200 years earlier, in 1703, a magnitude 8.2 earthquake struck the same region, causing more than 10,000 deaths.

These earthquakes, which occurred just south of the area hit by the March 2011 Tohoku earthquake, were produced by slips on the boundary between the subducting Philippine Sea plate and the overlying plate.

To estimate the average recurrence time between earthquakes in this region, and thus learn more about earthquake hazard, scientists need to know when earthquakes occurred before 1703. There are few historical documents describing earlier earthquakes, though some records indicate that earthquakes occurred in 1293 and 1433.

To learn more about past earthquakes, Shimazaki et al. analyzed cores about 2 meters (6.6 feet) long from eight tidal flat sites on the Miura Peninsula in Japan. Their cores contained layers of shell-filled gravel that the researchers infer were deposited by tsunamis associated with the 1703 and 1923 earthquakes, as well as a third layer of tsunami-deposited material. The authors used radiocarbon dating to date the third event to sometime between 1060 C.E. and 1400 C.E. That is consistent with a large earthquake having occurred in 1293. If so, that indicates that the recurrence interval of these earthquakes varies from about 200 to about 400 years. The study could help scientists assess the earthquake and tsunami hazard in the Tokyo area.

Source: Journal of Geophysical Research-Solid Earth, doi:10.1029/2011JB008639, 2011

Title: Geological Evidence of Recurrent Great Kanto Earthquakes at the Miura Peninsula, Japan

Authors: K. Shimazaki and H. Y. Kim: Earthquake Research Institute, University of Tokyo, Tokyo, Japan;

T. Chiba: Graduate School of Frontier Science, University of Tokyo, Chiba, Japan;

K. Satake: Earthquake Research Institute, University of Tokyo, Tokyo, Japan.

3. Much irrigation water comes from non-sustainable sources

Some of the water used worldwide for irrigation comes from renewable sources such as local precipitation, rivers, lakes, and renewable groundwater. But some comes from nonrenewable groundwater sources. Because water supply for irrigation is so essential to the world's food supply, it is important to quantify how much water comes from sustainable sources. Wada et al. conducted a global assessment of how much water used for irrigation comes from non-sustainable groundwater sources. They used a global hydrological model to simulate the amount of water needed for optimal crop growth and the amount available from renewable sources. They combined this information with country-level data on groundwater use to estimate the amount of groundwater used for irrigation that comes from nonrenewable sources.

Their results show that about 20 percent, or 234 cubic kilometers per year (56 cubic miles per year), of the water used for irrigation worldwide in 2000 came from nonrenewable sources. The countries with the highest levels of nonrenewable groundwater use are India, Pakistan, the United States, Iran, China, Mexico, and Saudi Arabia. Furthermore, worldwide, the use of groundwater from nonrenewable sources more than tripled from 1960 to 2000.

Source: Water Resources Research, doi:10.1029/2011WR010562, 2012

Title: Nonsustainable groundwater sustaining irrigation: A global assessment

Authors: Yoshihide Wada and L. P. H. van Beek: Department of Physical Geography, Utrecht University, Utrecht, Netherlands;

Marc F. P. Bierkens: Department of Physical Geography, Utrecht University, Utrecht, Netherlands, and Soil and Groundwater Systems Unit, Deltares, Utrecht, Netherlands.

4. Greenland's pronounced glacier retreat not irreversible

In recent decades, the combined forces of climate warming and short-term variability have forced the massive glaciers that blanket Greenland into retreat, with some scientists worrying that deglaciation could become irreversible. The short history of detailed glacier observations, however, makes pinning the ice loss to either short-term dynamics or long-term change difficult. Research by Young et al. detailing the effects of two bouts of sudden and temporary cooling during an otherwise warm phase in Greenland's climate history could help answer that question by showing just how heavy a hand short-term variability can have in dictating glacier dynamics.

Along the western edge of Greenland, the massive Jakobshavn Isbræ glacier reaches out to the coast, its outflow dropping icebergs into Baffin Bay during the summer months. Flanking the glacier's tongue are the Tasiussaq and Marrait moraines-piles of rock marking the glacier's former extent. Researchers suspected the moraines were tied to two periods of abrupt cooling that hit Greenland 9,300 and 8,200 years ago, and the association was reinforced by the authors' radiocarbon and beryllium isotope analyses of the area surrounding the moraines. Beryllium-10 forms when cosmic radiation travels through the atmosphere and strikes the Earth's surface, with surface rock concentrations indicating how long it has been ice-free.

The authors' analyses show that the moraines were laid down 9,200 and 8,200 years ago, corresponding with periods of sudden cooling. They suggest that the Jakobshavn glacier, which had been retreating prior to the sudden temperature changes, started to grow. At the end of each cold phase, the glacier deposited a moraine before it resumed its retreat. In detailing the sensitivity of the Jakobshavn glacier to short-term temperature change, the study suggests that while the Greenland glaciers' current retreat is not necessarily irreversible, their extent is tightly bound to the variability of our warming world.

Source: Geophysical Research Letters, doi:10.1029/2011GL049639, 2011

Title: Response of a marine-terminating Greenland outlet glacier to abrupt cooling 8200 and 9300 years ago

Authors: Nicolas E. Young, Jason P. Briner, Beata Csatho and Greg S. Babonis: Department of Geology, University at Buffalo, Buffalo, New York, USA;

Yarrow Axford: Department of Earth and Planetary Sciences, Northwestern University, Evanston, Illinois, USA;

Dylan H. Rood: Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, California, USA, and Earth Research Institute, University of California, Santa Barbara, California, USA, and Scottish Universities Environmental Research Centre (SUERC), East Kilbride, UK;

Robert C. Finkel: Department of Earth and Planetary Sciences, University of California, Berkeley, California, USA.

5. New record from stalagmites shows climate history in Central Asia

The climate in Central Asia, currently a semiarid region, has varied over the past 500,000 years. An accurate record of the past climate can help scientists understand current climate and better predict how the climate may change in the future. Previous studies with paleoclimate records, such as lake sediments and ice cores, show changes in moisture in the region, but climate history in the region is debated, as some of those records are not high resolution or not well dated.

Cheng et al. describe a new high-resolution, well-dated record of oxygen isotopes in stalagmites from the Kesang cave in western China. The researchers dated the stalagmites using radioactive thorium dating and then looked at the oxygen isotope record, which provides information on past atmospheric circulation and precipitation.

The record shows how climate in the region varies with cyclical changes in the Earth's orbit over the past 500,000 years. The authors find that there were some wetter periods in the past, which the authors suggest were caused by moisture carried from the Indian Ocean or other Asian monsoon regions. Currently, moisture to the region mainly comes with westerly winds from the Atlantic Ocean and the Mediterranean and Caspian seas, not from Asian monsoons. These new observations contrast with interpretations based on nearby, but higher-elevation, ice core records. The authors suggest that based on their record, unless anthropogenic effects supersede natural processes, an arid climate will prevail in the region for the next several thousand years.

Source: Geophysical Research Letters, doi:10.1029/2011GL050202, 2012

Title: The climatic cyclicity in semiarid-arid central Asia over the past 500,000 years Authors: H. Cheng: Institute of Global Environmental Change, Xi'an Jiaotong University, Xi'an, China, and Department of Earth Sciences, University of Minnesota, Minneapolis, Minnesota, USA;

P. Z. Zhang: College of Earth and Environment Sciences, Lanzhou University, Lanzhou, China;

C. Spotl: Institut fur Geologie und Palaontologie, Leopold-Franzens-Universitat, Innsbruck, Austria;

R. L. Edwards: Department of Earth Sciences, University of Minnesota, Minneapolis, Minnesota, USA;

Y. J. Cai: Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China;

D. Z. Zhang and W. C. Sang: College of Earth and Environment Sciences, Lanzhou University, Lanzhou, China;

M. Tan: Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China;

Z. S. An: Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China.

6. Io's volcanism influences Jupiter's magnetosphere Volcanic emissions from Jupiter's moon Io supply plasma to the planet's magnetosphere and lead to its main auroral emissions. New observations show that the main auroral oval expanded and outer emissions brightened in spring 2007. Some studies have suggested that magnetospheric changes such as this could be caused by changes in the incoming solar wind. Bonfond et al. present several lines of evidence-including images from the Hubble Space Telescope and observations of a volcanic plume on Io from the New Horizons probe, along with measurements of increased emissions from Jupiter's sodium cloud-that indicate that Io's volcanism controls changes in Jupiter's magnetosphere.

Source: Geophysical Research Letters, doi: 10.1029/2011GL050253, 2012

Title: Auroral evidence of Io's control over the magnetosphere of Jupiter

Authors: B. Bonfond, D. Grodent, and J.-C. Gerard: Laboratoire de Physique Atmospherique et Planetaire, Universite de Liege, Liege, Belgium;

T. Stallard: Department of Physics and Astronomy, University of Leicester, Leicester, United Kingdom;

J. T. Clarke: Center for Space Physics, Boston University, Boston, Massachusetts, USA;

M. Yoneda: Planetary Plasma and Atmospheric Research Center, Graduate School of Science, Tohoku University, Sendai, Japan;

A. Radioti and J. Gustin: Laboratoire de Physique Atmospherique et Planetaire, Universite de Liege, Liege, Belgium.

7. Massive swarm of tunicates tilts ocean's chemical balance

A surge of nutrients to the warm waters off the southeastern coast of Australia during the highly productive austral spring can spark an explosion in the phytoplankton population. Where phytoplankton bloom, so do the predators that feed on them. Some of these predators, like the globally prevalent, barrel-shaped tunicate salp Thalia democratica, excel at capitalizing on the transient nature of phytoplankton blooms. Salps are tiny gelatinous creatures that feed on plankton and other microorganisms by straining them from the ocean water with a fine mesh sieve. A rarity among multicellular animals, salps retain the ability to reproduce by asexual budding, with one salp spawning a clone of itself. This budding, combined with sexual reproduction, enables salp populations to grow by up to 250 percent per day.

During early October 2008 the southbound waters of the East Australian Current entrained a column of nutrient-rich coastal water, spawning a self-contained clockwise-rotating cold water eddy. Within the eddy, nutrient-rich deep water mixed with warm surface waters, sparking a surge in phytoplankton and, consequently, salp populations. Using temperature, salinity, fluorescence, and nutrient concentration measurements, along with particulate matter concentration detections, Everett et al. describe the highest-density salp population ever recorded. Concentrated in a 15-kilometer by 20-meter (9-mile by 66-foot) disk, the authors estimate that roughly 40 trillion salps gorged on phytoplankton, with a peak density of more than 6,000 salps per cubic meter. Samples from the swarm showed individuals ranging from 0.5 to 5 millimeters (0.02 to 0.2 inches) in length. Stretched end to end, the swarm would stretch halfway to the Sun. Salp swarms can have a powerful temporary effect on localized biology, impinging other species' survivability by limiting carbon and nitrogen supplies. The authors estimate that this swarm would have tied up 264 metric tons (582,000 pounds) of carbon and 72 metric tons (159,000 pounds) of nitrogen.

Source: Journal of Geophysical Research-Oceans, doi:10.1029/2011JC007310, 2011

Title: Three-dimensional structure of a swarm of the salp Thalia democratica within a cold-core eddy off southeast Australia

Authors: J. D. Everett and I. M. Suthers: Evolution and Ecology Research Centre, University of New South Wales, Sydney, New South Wales, Australia, and Sydney Institute of Marine Science, Mosman, New South Wales, Australia;

M. E. Baird: Plant Functional Biology and Climate Change Cluster, Faculty of Science, University of Technology Sydney, Sydney, New South Wales, Australia, and Sydney Institute of Marine Science, Mosman, New South Wales, Australia.


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