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AGU Media ContactsAGU Journal Highlights
15 November 2011
Highlights, including authors and their institutions
The following highlights summarize research papers that have been recently published in Geophysical Research Letters (GRL), Journal of Geophysical Research-Biogeosciences (JGR-G) Journal of Geophysical Research-Solid Earth (JGR-B) and Journal of Geophysical Research-Oceans (JGR-C).
In this release:
- Winds drive dune movement on Mars
- Amazon lakes release more carbon dioxide than previously thought
- Post-fire debris flows occur quickly after rainfall starts
- Reassessing satellite-observed color as clue to ocean's biological activity
- Fractures on curved rocks: A classic problem solved
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 Search Options and inserting into the search engine the full doi (digital object identifier), e.g. doi:10.1029/2011GL048955. 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 — see “Access to AGU Papers”.
1. Winds drive dune movement on Mars
Sand dunes, a common feature on the surface of Mars, can provide a record of recent and past changes. Some dunes near Mars’ polar areas have been observed to move recently due to carbon dioxide ice sublimation, but it has not been confirmed whether dunes are still active all over Mars. Winds contribute to dune movement on Earth, but wind tunnel and atmospheric computer simulations have suggested that strong winds would be rare in the current Martian atmosphere.
In a new study, Silvestro et al. observe recent dune movement in Mars' tropical regions, which are not affected by seasonal changes in carbon dioxide frost. Focusing on the Arabia Terra and Meridiani region on Mars, the researchers analyze images from the High Resolution Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter as well as other sources of data. They measure migration rates of two groups of ripples in the sand in a dune field in Meridiani Planum and find that dunes advanced about 0.4–1 meter (1.31-3.28 feet) in a Martian year. The study shows clear evidence that wind-driven dune activity occurs regularly on Mars today. This suggests that carbon dioxide ice sublimation is not necessary for Martian sand movement, as had previously been thought, and that wind tunnel measurements and computer simulations showing that strong winds are rare on Mars need to be reconsidered.
Source:
Geophysical Research Letters, doi:10.1029/2011GL048955, 2011
Title:
“Active aeolian processes on Mars: A regional study in Arabia and Meridiani Terrae”
Authors:
- S. Silvestro
- Carl Sagan Center, SETI Institute, Mountain View, California, USA;
- D. A. Vaz Centre for Geophysics, University of Coimbra, Coimbra, Portugal;
- L. K. Fenton Carl Sagan Center, SETI Institute, Mountain View, California, USA and NASA Ames Research Center, Moffett Field, California, USA;
- P. E. Geissler U.S. Geological Survey, Flagstaff, Arizona, USA.
2. Amazon lakes release more carbon dioxide than previously thought
Lakes in the Amazon basin contain large amounts of organic carbon derived from primary production in the lakes and on land bordering them. Biological oxidation of this organic carbon leads to waters supersaturated in carbon dioxide (CO2) and evasion of the CO2 to the atmosphere. The total amount of carbon released to the atmosphere from Amazon lakes, rivers, and wetlands is estimated to be similar to the amount sequestered by Amazon forests. Complementing other measurements, Rudorff et al. measure the seasonal and spatial variability of the dissolved CO2 concentration and estimate CO2 emission from a large lake in the Amazon floodplain. They find that CO2 concentrations in the lake varied in space, with higher concentrations in the zones near the shore and lower concentrations in offshore regions with phytoplankton blooms. They also find seasonal changes in lake water mixing patterns that affect gas production and emission from the lake. On the basis of their observations, the researchers suggest that current regional calculations underestimate the amount of CO2 released into the atmosphere from large Amazon lakes by as much as 2 to 4 times.
Source:
Journal of Geophysical Research-Biogeosciences, doi:10.1029/2011JG001699, 2011
Title:
“Seasonal and spatial variability of CO2 emission from a large floodplain lake in the lower Amazon”
Authors:
- Conrado M. Rudorff and John M. Melack
- Bren School of Environmental Science and Management, University of California, Santa Barbara, California, USA;
- Sally MacIntyre
- Marine Science Institute, University of California, Santa Barbara, California, USA;
- Cláudio C. F. Barbosa and Evlyn M. L. M. Novo
- Coordenação de Observação da Terra, Instituto Nacional de Pesquisas Espaciais, S;ão José dos Campos, Brazil.
3. Post-fire debris flows occur quickly after rainfall starts
Areas damaged by forest fires can be vulnerable to debris flows because vegetation is no longer holding dirt and rocks in place, and debris flows in burnt areas can be triggered by much less rainfall than would be needed to trigger a debris flow in an unburned area. Such debris flows are common in burned steep terrain in southern California and sometimes cause significant damage to property and even loss of life—for instance, 16 people died in debris flows above San Bernardino on 25 December 2003.
To better understand the conditions that lead to debris flows, Kean et al. measured properties including rainfall, channel bed pore fluid pressure, and hillslope soil water content for 24 debris flow events that occurred in five different watersheds that burned in the 2009 Station and Jesusita fires in the San Gabriel and Santa Ynez mountains.
They look at the timing of rainfall and debris flow events. Although there were differences between the sites and between different events at the same site, the researchers consistently find that debris flow events began very quickly—within 30 min—after the onset of a rainstorm. Debris flow is not found to be correlated with soil moisture, and debris flows are primarily initiated by surface water runoff rather than by landslides. This is true across sites of different size and different geologic material.
The data could be useful in constraining future models of debris flow following fires, but more important, they show that to give enough practical lead time, early warning of debris flow must rely on weather forecasts—once a heavy rain starts, it is too late to warn people of an impending debris flow.
Source:
Journal of Geophysical Research-Earth Surface, doi: 10.1029/2011JF002005, 2011
Title:
"In situ measurements of post-fire debris flows in southern California: Comparisons of the timing and magnitude of 24 debris-flow events with rainfall and soil moisture conditions"
Authors:
- Jason W. Kean, Dennis M. Staley, and Susan H. Cannon
- U.S. Geological Survey, Denver, Colorado, USA.
4. Reassessing satellite-observed color as clue to ocean’s biological activity
Determining the level of biological activity in the ocean is a task not readily suited to satellite-based remote sensing techniques. After all, many important markers of ocean ecosystem health, like nutrient concentrations or population counts of indicator species, are difficult to assess from space. In the past few decades, however, researchers have developed a technique that uses satellite observations of the ocean's visible color to track changes in biological activity, treating color as a proxy for chlorophyll concentrations and thus for phytoplankton populations. Interpretations of these chlorophyll concentration estimates have been used to assess, to varying degrees of success, the ocean's salinity and temperature, gas fluxes, nutrient availability, and the overall level of biosphere activity. Yet the algorithms used to convert ocean color into chlorophyll have remarkably large errors, sometimes in excess of 50 percent, when compared against direct measurements of chlorophyll concentrations.
Combing through chlorophyll concentration estimates provided by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) satellite, Szeto et al. see the large errors disappear when the relationship is assessed for different ocean basins rather than for the full global ocean. By comparing the algorithm-derived chlorophyll concentrations against samples collected in the field, they find that chlorophyll concentrations are being seriously underestimated for the Pacific, Indian, and Southern oceans and overestimated for the Atlantic Ocean. The authors attribute the discrepancies between the satellite-based observations and the direct measurements to systematic differences they see in terms of the different ocean basins’ concentrations of colored detrital matter and in the light-absorbing properties of their differing phytoplankton communities.
Source:
Journal of Geophysical Research-Oceans, doi: 10.1029/2011JC007230, 2011
Title
"Are the world's oceans optically different?"
Authors:
- M. Szeto, T. S. Moore and J. W. Campbell
- Ocean Process Analysis Laboratory, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire, USA;
- P. J. Werdell
- Ocean Biology Processing Group, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA.
5. Fractures on curved rocks: A classic problem solved
Sheeting joints, large fractures parallel to a curved rock surface, are common in many locations on Earth, such as the iconic Half Dome in Yosemite National Park in California. Explaining how these fractures form has been a classic unsolved problem in geology. Martel solves the problem by reformulating the static equilibrium equations in a curvilinear reference frame. His analysis shows that compression along a curved surface can induce tension perpendicular to the surface, which can cause subsurface cracks to open. He finds that the curvature of a rock surface plays a key role in the formation of fractures.
The author tests his theoretical findings and shows that his analysis accurately predicts where sheeting joints would be abundant and where they would be scarce in Yosemite National Park. Sheeting joints weaken a rock mass, so knowing where a rock mass is vulnerable to such cracks is valuable. Furthermore, the method of analysis applies not only to rock surfaces but also to any curved surface and thus should be useful in a broad variety of engineering and scientific applications, especially those addressing failure mechanisms.
Source:
Geophysical Research Letters, doi:10.1029/2011GL049354, 2011
Title:
"Mechanics of curved surfaces, with application to surface-parallel cracks"
Authors:
- Stephen J. Martel
- Department of Geology and Geophysics, University of Hawaii, Honolulu, Hawaii, USA.