AGU 期刊一周Research Spotlights (Nov 18 ~Nov 24, 2016)

发布时间:2016-11-25 9:59:27 点击次数:641

I. Natural Hazards

1. Plate Boundaries and Natural Hazards

The editors of a new book on tectonics discuss the origins of the science and its importance in a new millennium.

2. Fighting Fire with Satellite Data

As climate change worsens wildfire impact, scientists use satellites to study climate-fire interactions.

3. Cores from Crater Tied to Dinosaur Demise Validate Impact Theory

Drilling into the famous, deeply buried Chicxulub crater off Mexico, researchers found deformed and porous granite that opens new avenues of research.

II.Hazards & Disasters

1. Complex Earthquake Raises Complex Questions

A devastating earthquake has hit New Zealand, but this unusual event, with long duration slip on several faults, will also provide an astounding data set for understanding a complex tectonic region.

2. A Significantly Hotter Mantle Beneath Iceland

Estimates of crystallization temperatures from four eruptions in northern Iceland offer improved constraints on the mantle's temperature beneath this anomalous divergent plate boundary.

III. Climate Change

1. Science Is Bipartisan Issue, White House Science Adviser Says

Holdren said that investing in climate change science and policy measures is good for the economy, national security, and the environment.

2. A Wetter Climate Increases Methane Production in Peat

As northern Minnesota's climate got wetter, precipitation drove mobile forms of young carbon deeper into peatlands, doubling the size of methane-producing strata.

IV. Geology & Geophysics

1. Navigating the 2016 AGU Fall Meeting: Part I

AGU editors and staff provide recommendations if you are looking for exciting science or learning opportunities outside your normal discipline.

2. Largest Ever U.S. Shale Oil Deposit Identified in Texas

The Wolfcamp shale, which underlies a large swath of Texas roughly centered on the city of Midland, contains 20 billion barrels of oil that could be recovered with current technology.

3. Scientists Offer New Explanation for Island's Unexpected Uplift

Researchers developed a new timeline for the rise, fall, and rise again of a puzzling island in the Azores.

V. Geophysical Research Letters

1. Mean Antarctic Circumpolar Current transport measured in Drake Passage

The Antarctic Circumpolar Current is an important component of the global climate system connecting the major ocean basins as it flows eastward around Antarctica, yet due to the paucity of data, it remains unclear how much water is transported by the current. Between 2007 and 2011 flow through Drake Passage was continuously monitored with a line of moored instrumentation with unprecedented horizontal and temporal resolution. Annual mean near-bottom currents are remarkably stable from year to year. The mean depth-independent or barotropic transport, determined from the near-bottom current meter records, was 45.6 sverdrup (Sv) with an uncertainty of 8.9 Sv. Summing the mean barotropic transport with the mean baroclinic transport relative to zero at the seafloor of 127.7 Sv gives a total transport through Drake Passage of 173.3 Sv. This new measurement is 30% larger than the canonical value often used as the benchmark for global circulation and climate models.

2. Drift paths of ions composing multiple-nose spectral structures near the inner edge of the plasma sheet

We present a case study of the H+, He+, and O+ multiple-nose structures observed by the Helium, Oxygen, Proton, and Electron instrument on board Van Allen Probe A over one complete orbit on 28 September 2013. Nose structures are observed near the inner edge of the plasma sheet and constitute the signatures of ion drift in the highly dynamic environment of the inner magnetosphere. We find that the multiple noses are intrinsically associated with variations in the solar wind. Backward ion drift path tracings show new details of the drift trajectories of these ions; i.e., multiple noses are formed by ions with a short drift time from the assumed source location to the inner region and whose trajectories (1) encircle the Earth different number of times or (2) encircle the Earth equal number of times but with different drift time, before reaching the observation site.

3. Evaporation estimates using weather station data and boundary layer theory

Global estimates of evapotranspiration remain a challenge. In this study, we show that the daily course of air temperature and specific humidity available at routine weather stations can be used to estimate evapotranspiration and the evaporative fraction, the ratio of latent heat flux to available energy at the surface. Indeed, the diurnal increase in air temperature reflects the magnitude of the sensible heat flux and the increase of specific humidity after sunrise reflects the amplitude of evapotranspiration. The method is physically constrained and based on the budget of heat and moisture in the boundary layer. Unlike land surface-based estimates, the proposed boundary layer estimate does not rely on ad hoc surface resistance parameterizations (e.g., Penman-Monteith). The proposed methodology can be applied to data collected at weather stations to estimate evapotranspiration and evaporative fraction under cloudy conditions and in the pre–remote sensing era.

4. Stratospheric control of planetary waves

The effects of imposing at various altitudes in the stratosphere zonally symmetric circulation anomalies associated with a stratospheric sudden warming are investigated in a mechanistic circulation model. A shift of the tropospheric jet is found even when the anomalies are imposed only above 2 hPa. Their influence is communicated downward through the planetary wave field via three distinct mechanisms. First, a significant fraction of the amplification of the upward fluxes of wave activity prior to the central date of the warming is due to the coupled evolution of the stratospheric zonal mean state and the wave field throughout the column. Second, a downward propagating region of localized wave, mean-flow interaction is active around the central date but does not penetrate the tropopause. Third, there is deep, vertically synchronous suppression of upward fluxes following the central date. The magnitude of this suppression correlates with that of the tropospheric jet shift.

5. Individual particle morphology, coatings, and impurities of black carbon aerosols in Antarctic ice and tropical rainfall

Black carbon (BC) aerosols are a large source of climate warming, impact atmospheric chemistry, and are implicated in large-scale changes in atmospheric circulation. Inventories of BC emissions suggest significant changes in the global BC aerosol distribution due to human activity. However, little is known regarding BC's atmospheric distribution or aged particle characteristics before the twentieth century. Here we investigate the prevalence and structural properties of BC particles in Antarctic ice cores from 1759, 1838, and 1930 Common Era (C.E.) using transmission electron microscopy and energy-dispersive X-ray spectroscopy. The study revealed an unexpected diversity in particle morphology, insoluble coatings, and association with metals. In addition to conventionally occurring BC aggregates, we observed single BC monomers, complex aggregates with internally, and externally mixed metal and mineral impurities, tar balls, and organonitrogen coatings. The results of the study show BC particles in the remote Antarctic atmosphere exhibit complexity that is unaccounted for in atmospheric models of BC.

6. Assessing the level of spatial homogeneity of the agronomic Indian monsoon onset

Over monsoon regions, such as the Indian subcontinent, the local onset of persistent rainfall is a crucial event in the annual climate for agricultural planning. Recent work suggested that local onset dates are spatially coherent to a practical level over West Africa; a similar assessment is undertaken here for the Indian subcontinent. Areas of coherent onset, defined as local onset regions or LORs, exist over the studied region. These LORs are significant up to the 95% confidence interval and are primarily clustered around the Arabian Sea (adjacent to and extending over the Western Ghats), the Monsoon Trough (north central India), and the Bay of Bengal. These LORs capture regions where synoptic scale controls of onset may be present and identifiable. In other regions, the absence of LORs is indicative of regions where local and stochastic factors may dominate onset. A potential link between sea surface temperature anomalies and LOR variability is presented. Finally, Kerala, which is often used as a representative onset location, is not contained within an LOR suggesting that variability here may not be representative of wider onset variability.

7. Rapid ice flow rearrangement induced by subglacial drainage in West Antarctica

Ice streams are corridors of rapid ice flow draining the ice sheets. They can exhibit astonishing spatial variability on annual to centennial time scales. We propose that changes in the subglacial drainage of meltwater could induce these sudden rearrangements of ice streams. We develop a two-dimensional, thermomechanical model representing an ice stream cross section and couple it to a plastically deforming bed with spatially variable meltwater influx. We find that where ice flows over deformable sediments and lacks significant topographic control, the efficiency of subglacial water drainage exerts direct control on the velocity, location, and width of ice streams. This implies that meltwater percolation at the meter scale could have a significant effect on the short-term variability in ice loss from a continental-scale ice sheet. We verify our model against previous analytical results and validate it against surface observations from the Siple Coast of West Antarctica.

8. Decadal variability of European sea level extremes in relation to the solar activity

This study investigates the relationship between decadal changes in solar activity and sea level extremes along the European coasts and derived from tide gauge data. Autumn sea level extremes vary with the 11 year solar cycle at Venice as suggested by previous studies, but a similar link is also found at Trieste. In addition, a solar signal in winter sea level extremes is also found at Venice, Trieste, Marseille, Ceuta, Brest, and Newlyn. The influence of the solar cycle is also evident in the sea level extremes derived from a barotropic model with spatial patterns that are consistent with the correlations obtained at the tide gauges. This agreement indicates that the link to the solar cycle is through modulation of the atmospheric forcing. The only atmospheric regional pattern that showed variability at the 11 year period was the East Atlantic pattern.

9. Wetland shoreline recession in the Mississippi River Delta from petroleum oiling and cyclonic storms

We evaluate the relative impact of petroleum spill and storm surge on near-shore wetland loss by quantifying the lateral movement of coastal shores in upper Barataria Bay, Louisiana (USA), between June 2009 and October 2012, a study period that extends from the year prior to the Deepwater Horizon spill to 2.5 years following the spill. We document a distinctly different pattern of shoreline loss in the 2 years following the spill, both from that observed in the year prior to the spill, during which there was no major cyclonic storm, and from change related to Hurricane Isaac, which made landfall in August 2012. Shoreline erosion following oiling was far more spatially extensive and included loss in areas protected from wave-induced erosion. We conclude that petroleum exposure can substantially increase shoreline recession particularly in areas protected from storm-induced degradation and disproportionally alters small oil-exposed barrier islands relative to natural erosion.

10. Diagnostic sea ice predictability in the pan-Arctic and U.S. Arctic regional seas

This study assesses sea ice predictability in the pan-Arctic and U.S. Arctic regional (Bering, Chukchi, and Beaufort) seas with a purpose of understanding regional differences from the pan-Arctic perspective and how predictability might change under changing climate. Lagged correlation is derived using existing output from the Community Earth System Model Large Ensemble (CESM-LE), Pan-Arctic Ice-Ocean Modeling and Assimilation System, and NOAA Coupled Forecast System Reanalysis models. While qualitatively similar, quantitative differences exist in Arctic ice area lagged correlation in models with or without data assimilation. On regional scales, modeled ice area lagged correlations are strongly location and season dependent. A robust feature in the CESM-LE is that the pan-Arctic melt-to-freeze season ice area memory intensifies, whereas the freeze-to-melt season memory weakens as climate warms, but there are across-region variations in the sea ice predictability changes with changing climate.



WASHINGTON, DC — Discover the latest Earth and space science news at the 49th annual AGU Fall Meeting this December, when about 24,000 attendees from around the globe are expected to assemble for the largest worldwide conference in the Earth and space sciences. This year, the meeting runs Monday through Friday, Dec. 12-16, 2016 at the Moscone Center, 747 Howard St., San Francisco, California.


WASHINGTON, DC — Icebergs contribute more meltwater to Greenland’s fjords than previously thought, losing up to half of their volume as they move through the narrow inlets, according to new research.

VII.Earth and Space Science

1. Older Mayan pyramid detected within Chichén Itzá

Scientists in Mexico have found evidence for a third and earlier—more purely Mayan—pyramid inside of the famous and iconic Pyramid of El Castillo at Chichén Itzá, in Yucatán. Using a non-destructive technique that employed hundred of electrodes deployed on the surface of the pyramid, the researchers also confirmed previous discoveries of a second pyramid, as well as their own 2014 discovery of a partially water-filled sinkhole beneath the pyramid.

2. Study finds widespread land losses from Gulf oil spill

A new study shows dramatic, widespread shoreline loss in Louisiana marshlands most heavily coated with oil during the 2010 BP Deepwater Horizon oil spill in the Gulf of Mexico. Following the spill, the length of shoreline that receded more than 13 feet (4 meters) a year quadrupled compared to the year before the spill. The land losses occurred mainly in areas where oil had washed ashore during the spill.