AGU 期刊一周Research Spotlights (Sep 22~Sep 28, 2016)

发布时间:2016-9-29 10:04:42 点击次数:701

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I. Atmospheric Sciences

1. Aquatic Plants May Accelerate Arctic Methane Emissions

About two thirds of the gas produced by a study area near Barrow, Alaska, came from increasingly abundant greenery covering only 5% of the landscape, researchers estimate.

2. What Drives Variation in the Ionosphere’s Electron Density?

The long-term trend in the electron density of the ionospheric F layer may be natural, not man-made.

II. Geology & Geophysics

1. The Gravity of Volcanic Eruptions

New research suggests that continually monitoring gravity changes near active volcanoes could provide insights into volcanic activity.

2Seismological Models Are Biased, But Scientists Have a Solution

Many seismic wave models are based on an erroneous assumption about the Earth's interior. A new technique corrects this by eliminating false signals produced by models.

3What Causes GPS Signal Loss on Satellites like Swarm?

Using data from the European Space Agency's Swarm mission, scientists find that abrupt drops in the ionosphere's electron density may cause low-orbiting satellites to lose contact with GPS satellites

4We Need a New Definition for “Magma”

Confusion over the meaning of "magma" can generate popular misperceptions, including a nonexistent molten sea underneath Yellowstone National Park. We propose a different definition.

III.Biogeosciences

1Rock-Chomping Bees Burrow into Sandstone

A previously unknown species of rock-excavating bees, discovered 40 years ago but not reported in the scientific literature, finally gets the spotlight.

IV. Climate Change

1. Candidates Have Dustup over Climate in First Debate

During the first presidential candidate debate Monday, Donald Trump denied saying that climate change is a hoax, but his own tweets show otherwise.

2White House: National Security Plans Must Consider Climate Risks

Along with the new policy directive, the administration released a report on how climate changes—from more extreme weather to sea level rise—can threaten national security.

3Comprehensive Earth System Models of the Last Glacial Cycle

Much of modern climate science fails to consider millennium-scale processes, many of which may prove to be important for predicting the climate trajectory in the shorter term.

4Top Arctic Science Diplomats Convene at White House Next Week

Precipitous transformations from climate change add impetus for this international meeting to guide cooperative research in the northern polar region, U.S. official says.

V.Science Policy & Funding

1.State Budgets, Geological Surveys, and the New Reality

As state geological surveys face budget cuts and reorganizations, scientists must step into political spheres to advocate for what they do.

VI. Earth and Space Science

1. New research explores how wetlands and agriculture could be causing a global rise in methane

New research shows recent rises in methane levels in the atmosphere are most likely driven by biological sources, such as swamp gas, cow burps, or rice fields, rather than fossil fuel emissions.

2. Ms. Callaghan’s Classroom: The Underwater Flying Glider

Earlier this week we deployed a glider that belongs to the University of Alaska at Fairbanks (UAF). What’s a glider? It is an underwater robot that “flies” around the sea going from the surface to the bottom of the seafloor collecting different types of science data.

VII. Geophysical Research Letters

1. Rapid reinflation following the 2011–2012 rhyodacite eruption at Cordón Caulle volcano (Southern Andes) imaged by InSAR: Evidence for magma reservoir refill

Cordón Caulle is a large fissural volcano that has erupted rhyodacitic magma of the same composition in its past three historical eruptions in 1921, 1960, and 2011–2012. There was significant ground deformation observed before and during the 2011–2012 eruption—here we use C and X band interferometric synthetic aperture radar (InSAR) time series results to document posteruptive uplift up to 0.8 m between March 2012 and May 2015, with line-of-sight rates up to 45 cm/yr that have been largely aseismic, along with subsidence in the 2011–2012 lava flow. The 2012 uplift rate is one of the largest for silicic systems and was likely produced by the intrusion of ~0.125 km3 of magma in the same tectonically controlled plumbing system that has been active during the historical eruptions. Nevertheless, the uplift ended before the reservoir refilled with the erupted volume, maybe due to a change in the pressure gradient produced by the 2011–2012 eruption.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070066/full

2. Peat bogs in northern Alberta, Canada reveal decades of declining atmospheric Pb contamination

Peat cores were collected from six bogs in northern Alberta to reconstruct changes in the atmospheric deposition of Pb, a valuable tracer of human activities. In each profile, the maximum Pb enrichment is found well below the surface. Radiometric age dating using three independent approaches (14C measurements of plant macrofossils combined with the atmospheric bomb pulse curve, plus 210Pb confirmed using the fallout radionuclides 137Cs and 241Am) showed that Pb contamination has been in decline for decades. Today, the surface layers of these bogs are comparable in composition to the “cleanest” peat samples ever found in the Northern Hemisphere, from a Swiss bog ~ 6000 to 9000 years old. The lack of contemporary Pb contamination in the Alberta bogs is testimony to successful international efforts of the past decades to reduce anthropogenic emissions of this potentially toxic metal to the atmosphere.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070952/full

3. Anthropogenic sources stimulate resonance of a natural rock bridge

The natural modes of vibration of bedrock landforms, as well as the sources and effects of stimulated resonance remain poorly understood. Here we show that seismic energy created by an induced earthquake and an artificial reservoir has spectral content coincident with the natural modes of vibration of a prominent rock bridge. We measured the resonant frequencies of Rainbow Bridge, Utah using data from two broadband seismometers placed on the span, and identified eight distinct vibrational modes between 1 and 6 Hz. A distant, induced earthquake produced local ground motion rich in 1 Hz energy, stimulating a 20 dB increase in measured power at the bridge's fundamental mode. Moreover, we establish that wave action on Lake Powell, an artificial reservoir, generates microseismic energy with peak power ~1 Hz, also exciting resonance of Rainbow Bridge. These anthropogenic sources represent relatively new energy input for the bridge with unknown consequences for structural fatigue.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070088/full

4. Subcircular conduits and dikes offshore the Somma-Vesuvius volcano revealed by magnetic and seismic data

We analyzed new magnetic, bathymetric, and seismic data acquired in the offshore sector of Somma-Vesuvius volcano (Italy). We detected a group of high-intensity, short wavelength magnetic anomalies corresponding to partly buried volcanic dome-like structures located by seismic data. The magnetic anomalies are aligned along a NW-SE strike that is the preferential orientation of an eruptive fracture of the pre-19 ka activity of Vesuvius. Three cones emplaced before the Last Glacial Maximum, whereas a fourth one emplaced after 19 ka suggesting a rejuvenation of the eruptive system offshore the volcano in historical times. We also identified a NE-SW elongated magnetic anomaly consistent with a dike-like body associated to an on-land tectonic structure that was active in recent times at Vesuvius. A delta-like area with diffuse low-intensity magnetic anomalies reflects the seaward fronts of lava flows that entered the sea mainly during the Middle Ages.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070271/full

5. Experimental evidence of reaction-induced fracturing during olivine carbonation

Mineral carbonation, a process that binds CO2 in the form of carbonates by silicate weathering, is widespread on the Earth's surface. Because of the abundance of silicate rocks and the permanence of the carbonated solids, sequestering CO2 via mineral carbonation has generated lots of interests. However, it is unclear how the fluid-rock reaction proceeds to completion in spite of an increasing solid volume. We conducted a mineral carbonation experiment in which a sintered olivine aggregate reacted with a sodium bicarbonate solution at reservoir conditions. Time-resolved synchrotron X-ray microtomographic images show cracks in polygonal patterns arising in the surface layers and propagating into the interior of the olivine aggregate. The nanotomography data reveal that the incipient cracks intersect at right angles. We infer that stretching due to nonuniform volume expansion generates polygonal cracking of the surfaces. Our data shed new lights on the processes that control hydration and carbonation of peridotite.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070834/full

6. A subsequent positive stroke developing in the channel of preceding negative stroke and containing bipolar continuing current

A bipolar cloud-to-ground lightning flash was observed to exhibit two types of polarity reversal associated with the first two strokes separated by a not unduly long time interval of 70 ms. The first stroke was negative and had a peak current of −101 kA. The second stroke was positive, had a peak current of 16 kA and was followed by a 122 ms long bipolar continuing current. The first two strokes, including the bipolar continuing current, occurred in the same channel to ground, whose imaged 2-D length was 4.2 km. The occurrence of positive stroke in the negative-stroke channel is highly unusual. The 2-D speed versus height profiles for the negative stepped leader of the first stroke and, for the first time, for the positive leader in the previously conditioned, first-stroke channel were examined and the average speeds were found to be 4.7 × 105 m/s and 7.2 × 105 m/s, respectively.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070475/full

7. Early growth dynamical implications for the steerability of stratospheric solar radiation management via sulfur aerosol particles

Aerosol growth dynamics may have implications for the steerability of stratospheric solar radiation management via sulfur particles. This paper derives a set of critical initial growth conditions that are analyzed as a function of two key parameters: the initial concentration of the injected sulfuric acid and its dilution rate with the surrounding air. Based upon this analysis, early aerosol growth dynamical regimes may be defined and classified in terms of their likelihood to serve as candidates for the controlled generation of a radiatively effective aerosol. Our results indicate that the regime that fulfills all critical conditions would require that airplane turbines be used to provide sufficient turbulence. The regime's parameter space is narrow and related to steep gradients, thus pointing to potential fine tuning requirements. More research, development, and testing would be required to refine our findings and determine their global-scale implications.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070701/full

8. Footprints of past earthquakes revealed in the afterslip of the 2010 Mw 7.8 Mentawai tsunami earthquake

The 2010 Mw 7.8 Mentawai tsunami earthquake marks one of the first tsunami earthquakes to have postseismic deformation observed by geodetic instruments. The Sumatran GPS Array has recorded the postseismic deformation following this event continuously for >5 years. The spatiotemporal evolution of the postseismic deformation is well explained by velocity-strengthening frictional sliding on the Sunda megathrust. Our results show that the 2010 afterslip progressed downdip relative to the 2010 coseismic rupture. The southeastern portion of the afterslip region overlaps the area that slipped during the main shock and afterslip of the 2007 Mw 8.4 Bengkulu earthquake, while the northwestern portion slipped an area without recent large earthquakes. By incorporating pre-earthquake stress conditions into quasi-dynamic models, we demonstrate that the preceding cumulative slip from the 2007 sequence might have caused a ~0.1 MPa difference in pre-earthquake Coulomb stress between the southeastern and northwestern portions of the afterslip region.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL069870/full

9. The size distribution of spatiotemporal extreme rainfall clusters around the globe

The scaling behavior of rainfall has been extensively studied both in terms of event magnitudes and in terms of spatial extents of the events. Different heavy-tailed distributions have been proposed as candidates for both instances, but statistically rigorous treatments are rare. Here we combine the domains of event magnitudes and event area sizes by a spatiotemporal integration of 3-hourly rain rates corresponding to extreme events derived from the quasi-global high-resolution rainfall product Tropical Rainfall Measuring Mission 3B42. A maximum likelihood evaluation reveals that the distribution of spatiotemporally integrated extreme rainfall cluster sizes over the oceans is best described by a truncated power law, calling into question previous statements about scale-free distributions. The observed subpower law behavior of the distribution's tail is evaluated with a simple generative model, which indicates that the exponential truncation of an otherwise scale-free spatiotemporal cluster size distribution over the oceans could be explained by the existence of land masses on the globe.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070692/full

10. An initial assessment of SMAP soil moisture retrievals using high-resolution model simulations and in situ observations

At the end of its first year of operation, we compare soil moisture retrievals from the Soil Moisture Active Passive (SMAP) mission to simulations from a land surface model with meteorological forcing downscaled from observations/reanalysis and in situ observations from sparse monitoring networks within continental United States (CONUS). The radar failure limits the duration of comparisons for the active and combined products (~3 months). Nevertheless, the passive product compares very well against in situ observations over CONUS. On average, SMAP compares to the in situ data even better than the land surface model and provides significant added value on top of the model and thus good potential for data assimilation. At large scale, SMAP is in good agreement with the model in most of CONUS with less-than-expected degradation over mountainous areas. Lower correlation between SMAP and the model is seen in the forested east CONUS and significantly lower over the Canadian boreal forests.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL069964/full  

VIII.AGU News

1. AMERICAN GEOPHYSICAL UNION’S CEO HONORED AS PROFESSIONAL SOCIETY CEO OF THE YEAR

WASHINGTON, DC – Chris McEntee, Executive Director and CEO of the American Geophysical Union (AGU), has been honored by CEO Update as the 2016 Professional Society CEO of the Year.

https://news.agu.org/press-release/american-geophysical-unions-ceo-honored-as-professional-society-ceo-of-the-year/