AGU journal highlights — Nov. 2, 2010

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

1. Toxic levels of chemicals found kilometers from Gulf spill site

Oil contains compounds known as polycyclic aromatic hydrocarbons (PAH), which can be toxic. These compounds were released into the water during the Deepwater Horizon oil spill, which was larger than any previously studied release of oil. The impacts of the oil spill on marine life are not yet certain. Diercks et al. present initial observations of the distributions of PAH in subsurface water near the site of the Deepwater Horizon oil spill. The researchers made the observations during 9-16 May, about 3 weeks after the oil rig sank. They found PAH concentrations as high as 189 micrograms per liter at depths greater than 1000 meters (3280 feet). PAH concentrations that would be toxic to marine organisms extended as far as 13 kilometers (8 miles) from the wellhead site.

Characterization of subsurface polycyclic aromatic hydrocarbons at the Deepwater Horizon site

Arne-R. Diercks, Vernon L. Asper: Department of Marine Science, University of Southern Mississippi, Stennis Space Center, Mississippi, USA, and National Institute for Undersea Science and Technology, University of Mississippi, Abbeville, Mississippi, USA;

Raymond C. Highsmith: National Institute for Undersea Science and Technology, University of Mississippi, Abbeville, Mississippi, USA;

DongJoo Joung, Zhengzhen Zhou, Laodong Guo, Steven E. Lohrenz, and Alan M. Shiller: Department of Marine Science, University of Southern Mississippi, Stennis Space Center, Mississippi, USA;

Samantha B. Joye: Department of Marine Sciences, University of Georgia, Athens, Georgia, USA;

Andreas P. Teske: Department of Marine Sciences, University of North Carolina,
Chapel Hill, North Carolina, USA;

Norman Guinasso and Terry L. Wade: Geochemical and Environmental Research Group, Texas A&M University, College Station, Texas, USA.


Geophysical Research Letters, doi:10.1029/2010GL045046, 2010

2. Europe’s 2010 winter was cold extreme in warming climate

Abnormally cold weather and unusually large amounts of snow fell on Europe during the winter of 2009-2010. Cattiaux et al. analyze records of temperature and atmospheric conditions to show that although the 2010 winter in Europe was very cold and snowy, it was not extreme relative to winters of the past six decades. The authors also find that the 2010 winter in Europe was actually warmer than expected given atmospheric circulation conditions, including a record persistence of the negative phase of the North Atlantic Oscillation. The 2010 winter is thus an example of a cold extreme in a warming climate.

Winter 2010 in Europe: A cold extreme in a warming climate

J. Cattiaux, V. Masson-Delmotte, R. Vautard, P. Yiou: LSCE, UMR 8212, IPSL, CEA-CNRS-UVSQ, Gif-sur-Yvette, France;

C. Cassou: Cerfacs, CNRS, Toulouse, France;

F. Codron: LMD, IPSL, CNRS-Ecole Polytechnique-ENS-UPMC, Paris, France.


Geophysical Research Letters, doi:10.1029/2010GL044613, 2010

3. Atmospheric dynamics, not ocean, could drive El Niño features

Scientists generally believe that ocean dynamics are the primary factor controlling El Niño sea surface temperature variability. However, new simulations show that atmospheric dynamics can account for many of the features of El Niño that were previously thought to be controlled by ocean dynamics. Dommenget uses a series of atmospheric model simulations coupled to a simple ocean model that contained no ocean dynamics. He finds that El Niño–like variations in sea surface temperature were produced in the simulations. Although ocean dynamics are a factor influencing El Niño events, the study suggests that atmospheric dynamics may be more important than previously thought in controlling El Niño. The study could change scientists’ understanding of the mechanisms driving El Niño.

The slab ocean El Niño

Dietmar Dommenget: School of Mathematical Sciences, Monash University, Clayton, Victoria, Australia.


Geophysical Research Letters, doi:10.1029/2010GL044888, 2010

4. New map of moisture recycling and global water resources

Water that falls as precipitation in one region may have originated in a distant region, or it may be recycled moisture that originated as evaporation within the region. Global wind patterns, topography, and land cover all play a role in moisture recycling patterns and the distribution of global water resources. Land use changes such as irrigation, dams, and deforestation can alter evaporation patterns in a region, potentially affecting water resources in distant regions.

Many studies of moisture recycling have had a regional focus. To provide a global perspective, van der Ent et al. create global maps showing the sources of atmospheric moisture for various regions. The researchers estimate that on average 40 percent of terrestrial precipitation originates from land evaporation and 57 percent of all terrestrial evaporation returns as precipitation over land. They find that some regions rely on recycled water from within the region, while others get moisture from different regions. For instance, water evaporating from Eurasia is responsible for 80 percent of China’s water resources, and the Rio de la Plata basin in South America gets 70 percent of its water from evaporation from the Amazon. The study suggests that land use changes in one region could have global effects on water resources.

Origin and fate of atmospheric moisture over continents

Rudi J. van der Ent, Hubert H. G. Savenije, Bettina Schaefli, and Susan C. Steele‐Dunne: Department of Water Management, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, Netherlands.


Water Resources Research,
doi:10.1029/2010WR009127, 2010

5. Satellite measurements show sources of sea level change

Sea level is rising as ice on continents melts and adds to the volume of the ocean. The Gravity Recovery and Climate Experiment (GRACE) satellites measure changes in Earth’s gravity field, which makes it possible to observe patterns of mass exchange between land and oceans and the resultant sea level change.

Riva et al. analyze GRACE measurements from 2003 to 2009 to trace sea level changes to mass sources. The researchers estimate that the total ice and water mass loss from the continents is leading to a global mean rate of sea level rise of about 1.0 mm/yr (0.04 inches/year). In particular, they find that ice movement and melting is the main contributor to global sea level change, while water movement is important to regional sea level rise in many coastal areas.

Sea-level fingerprint of continental water and ice mass change from GRACE

Riccardo E. M. Riva: DEOS, Delft University of Technology, Delft, Netherlands, Faculty of Geosciences, Utrecht University, Utrecht, Netherlands;

David A. Lavallée: DEOS, Delft University of Technology, Delft, Netherlands;

Jonathan L. Bamber, Bristol Glaciology Centre, School of Geographical Sciences, University of Bristol, Bristol, UK;

Bert Wouters, Royal Netherlands Meteorologic Institute, De Bilt, Netherlands.


Geophysical Research Letters, doi:10.1029/2010GL044770, 2010

6. Meltwater within glaciers speeds ice sheet warming

Ice sheets and glaciers have been observed to respond rapidly to climate warming. Cryohydrologic warming, a new mechanism proposed by Philips et al., could explain why.

Meltwater can flow through networks of crevasses and fractures that develop or expand within glaciers as the climate warms. Some liquid water can remain in a glacier without refreezing after the summer melt season ends. Heat exchange between this englacial water and the ice can accelerate warming of ice sheets, the authors explain. The magnitude of the warming effect depends on the spacing, surface area, and geometry of the englacial water features as well as the amount of meltwater percolation.

The researchers apply their model to a glacier on the Greenland ice sheet, showing that unusually warm ice temperatures can be explained only by invoking the role of cryohydrologic warming. The authors note that ice sheet models used within many climate models ignore this mechanism and thus may underestimate ice sheet temperatures in a warming climate.

Cryo-hydrologic warming: A potential mechanism for rapid thermal response of ice sheets

Thomas Phillips: Aerospace Engineering and Sciences, Department of Geography, University of Colorado at Boulder, Boulder, Colorado, USA;

Harihar Rajaram: Department of Civil, Environmental and Architectural Engineering, University of Colorado at Boulder, Boulder, Colorado, USA;

Konrad Steffen: Department of Geography, Cooperative Institute for Research in Environmental Science, University of Colorado at Boulder, Boulder, Colorado, USA.


Geophysical Research Letters, doi:10.1029/2010GL044397, 2010

7. Tropical cyclone size distribution characterized

A new climatology of tropical cyclone size was created by Chavas and Emanuel using near-surface wind measurements made during 1999-2008 using the QuikSCAT satellite microwave scatterometer. Their study shows that cyclone size follows an approximately lognormal distribution. The global mean outer radius of cyclones is 423 kilometers (263 miles), and the outer radius ranges from 341 km (212 mi) in the eastern Pacific to 488 km (303 mi) in the western Pacific. They also find that for most storms, the cyclone’s size expands very slowly early in the storm’s life, then stays approximately constant for the duration of the storm. The lognormal distribution could provide a clue to help scientists improve understanding of the mechanisms controlling the dynamics of tropical cyclones.

A QuikSCAT climatology of tropical cyclone size

D. R. Chavas and K. A. Emanuel: Department of Earth, Atmosphere, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.


Geophysical Research Letters, doi:10.1029/2010GL044558, 2010

8. Moon plucks electrons from Earth’s magnetic tail

For a few days around the time of each full Moon, the Moon passes through Earth’s plasma sheet, the plasma-filled region separating the two lobes of Earth’s magnetotail. In this region, plasma conditions are different from plasma conditions the Moon encounters in the solar wind, outside of Earth’s magnetosphere. Measurements made by the Japanese SELENE (Kaguya) spacecraft, reported by Harada et al., show that relatively high energy electrons gyrating in the magnetic field in the plasma sheet can be absorbed at the lunar surface. Their observations also suggest the presence of a relatively strong electric field around the Moon when it is inside Earth’s magnetosphere.

Interaction between terrestrial plasma sheet electrons and the lunar surface: SELENE (Kaguya) observations

Yuki Harada and Shinobu Machida: Department of Geophysics, Kyoto University, Kyoto, Japan;

Yoshifumi Saito, Shoichiro Yokota, Kazushi Asamura, Masaki N. Nishino, and Takaaki Tanaka:
Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan;

Hideo Tsunakawa, Futoshi Takahashi, and Masaki Matsushima: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, Japan;

Hidetoshi Shibuya: Department of Earth and Environmental Sciences, Kumamoto University,
Kumamoto, Japan;

Hisayoshi Shimizu: Earthquake Research Institute, University of Tokyo, Tokyo, Japan.


Geophysical Research Letters, doi:10.1029/2010GL044574, 2010

9. Assessing regional impacts of geoengineering

As the climate warms along with rising levels of atmospheric carbon dioxide, geoengineering has been suggested as an emergency option to cool the planet. One possibility is implementing a project to manage solar radiation, such as injecting sulphate aerosols into the stratosphere or deploying a solar “sunshade” to decrease the amount of sunlight that reaches Earth’s surface. Global interventions would have different regional impacts, however. Geoengineering could result in decreased precipitation and increased droughts in some regions, with serious consequences for some human populations.

Irvine et al. run climate model simulations to assess the regional effects of solar radiation management under scenarios in which carbon dioxide rises to four times pre-industrial levels. The authors consider various levels of solar radiation management to counteract some or all of the carbon dioxide induced warming.

The researchers find that it is possible to identify a level of solar radiation management that would meet several goals, such as maintaining the Greenland ice sheet and avoiding dramatic reductions in precipitation or creating unusual climate conditions for significant areas of the world. However, because of regional disparities in the impacts, there may be disagreements between countries over the ideal level of geoengineering. The study highlights the need for further study of the regional effects of geoengineering.

Assessing the regional disparities in geoengineering impacts

Peter J. Irvine and Andy Ridgwell: Bristol Research Initiative for the Dynamic Global Environment, School of Geographical Sciences, University of Bristol,
Bristol, UK;

Daniel J. Lunt: Bristol Research Initiative for the Dynamic Global Environment, School of Geographical Sciences, University of Bristol, Bristol, UK and British Antarctic Survey, Cambridge, UK.


Geophysical Research Letters, doi:10.1029/2010GL044447, 2010

10. Record warming in South Pacific associated with central Pacific El Niño

In 2009-2010, a record warming occurred in the South Pacific and western Antarctica. Lee et al. analyze satellite and in situ observations to document the oceanic and atmospheric conditions associated with the sea surface temperature anomalies. The anomalous warming in the south central Pacific region began in September 2009 and reached a record high in December, around the same time that the 2009� central Pacific El Niño peaked.

The amplitude of the South Pacific warming was larger than the usual variability in the region by more than five times and was substantially stronger than the concurrent El Niño. The spatial extent of the South Pacific warming was comparable to the size of the continental United States and was associated with an unusually strong and persistent high-pressure system.

The authors suggest that the strong central Pacific El Niño may have amplified the oceanic and atmospheric anomalies in the South Pacific and western Antarctica. Central Pacific El Niño events, which have become more common and more intense in recent decades, have maximum warming in the central Pacific, unlike the classic El Niño, which has maximum warming in the eastern equatorial Pacific. The authors note that if extreme events such as the 2009� south central Pacific anomaly become more common in the future, they could significantly affect the ocean-ice-atmosphere system around Antarctica.

Record warming in the South Pacific and western Antarctica associated with the strong central-Pacific El Niño in 2009-10

Tong Lee, William R. Hobbs, Joshua K. Willis, Daria Halkides, Ichiro Fukumori, Edward M. Armstrong, Akiko K. Hayashi, W. Timothy Liu, William Patzert, Ou Wang: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA.


Geophysical Research Letters, doi:10.1029/2010GL044865, 2010

11. Understanding the eruption of the Soufrière Hills volcano

When the Soufrière Hills volcano erupted in 1995, it wreaked havoc on the Caribbean island of Montserrat. Many scientists have since studied the eruption, but the internal structure of the volcano had not been well characterized until recently. Voight and Sparks introduce a special section of Geophysical Research Letters that contains 26 papers on the Soufrière Hills volcano, including papers on the eruption, on data from the Caribbean Andesite Lava Island Precision Seismo-geodetic Observatory (CALIPSO) borehole observatory network and surface monitoring stations, and on results from the Seismic Experiment with Airgun-source CALIPSO (SEA-CALIPSO) project, which imaged the arc crust and lithosphere around Montserrat.

Introduction to special section on the Eruption of Soufrière Hills Volcano, Montserrat, the CALIPSO Project, and the SEA-CALIPSO Arc-Crust Imaging Experiment

Barry Voight: College of Earth and Mineral Sciences, Pennsylvania State University, University Park, Pennsylvania, USA;

R. S. J. Sparks: Department of Earth Sciences, Bristol University, Bristol, UK.


Geophysical Research Letters (GRL) doi:10.1029/2010GL044254, 2010

12. Why do clouds prevent heat from escaping Earth in a warming climate?

Clouds affect Earth’s surface temperature in two key ways: They exert a cooling influence on the planet by reflecting solar (shortwave) radiation back to space and a warming influence on the planet by reducing the amount of infrared (longwave) radiation emitted to space. The balance between these two forces helps to govern climate conditions. A changing climate may influence cloud height, thickness, and frequency, which in turn could dramatically affect how clouds balance cooling and warming. All of the global climate models used in the recent assessment by the Intergovernmental Panel on Climate Change indicate that the warming influence of clouds becomes stronger as the climate warms, indicating that clouds exhibit robustly positive longwave feedbacks.

Zelinka and Hartmann pose this question: Why is longwave cloud feedback always positive in these models–that is, why do clouds in climate models increasingly prevent heat from escaping back to space as climate warms? The researchers determine that under warming conditions, tropical high clouds rise in such a way that temperatures at cloud tops remain about the same despite that the surface is warming. Because the clouds are not warming hand in hand with the surface temperature, the warming tropics become less efficient at emitting heat into space and thus the clouds exert a positive climate feedback. The authors go on to show that the amount that clouds rise is well predicted across models simply by considering the energy balance of the tropical atmosphere, and therefore the resultant positive feedback arises from relatively well understood physics.

Why is longwave cloud feedback positive?

Mark D. Zelinka and Dennis L. Hartmann: Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA.


Journal of Geophysical Research-Atmospheres (JGR-D) doi:10.1029/2010JD013817, 2010

13. Sediment transport distorts landscape record of environmental change

Over time, landscapes change in response to climate change, tectonic motion, and sea level changes. It is generally believed that these environmental changes are recorded in landscape patterns that scientists can use to interpret past changes. However, sediment transport can complicate the picture. New research by Jerolmack and Paola shows that sediment transport alters landscape patterns in nonlinear ways. The authors use a numerical model to show that sediment transport destroys most signals of environmental change. The study suggests that scientists may need to reconsider how they use landscape patterns to assess past environmental change.

Shredding of environmental signals by sediment transport

Douglas J. Jerolmack: Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, Pennsylvania, USA;

Chris Paola: St. Anthony Falls Laboratory, University of Minnesota, Minneapolis, Minnesota, USA.


Geophysical Research Letters, doi:10.1029/2010GL044638, 2010

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. 10.1029/2010GL045046. The doi is found at the end of each Highlight above.

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