AGU期刊一周Research Spotlight (April 21~ April 27, 2017)

发布时间:2017-4-28 10:48:28 点击次数:291

I. Science Policy

1. Thousands March Worldwide in Support of Science

Science enthusiasts descended on the National Mall in Washington, D. C., and demonstrated in more than 600 cities and other places globally in support of science and evidence-based decision-making.

2. Acquiring a Taste for Advocacy

A scientist rethinks his distrust of political engagement.

II. Ocean Sciences

1. What Happens When Ocean Eddies Hit a Wall?

A new study tracks two ocean eddies passing over the Pacific Ocean's Izu-Ogasawara Ridge.

2. Dam Discharge Events Alter Water Flow in an Estuary in Spain

Three-year observations suggest that increased sediment concentrations inhibit vertical transfer of momentum between water layers for more than 2 months after a high-discharge event.

III. Hazards & Disasters

1. What Causes Rock Avalanches?

Experimental studies of frictional weakening beneath a deadly rock avalanche in China help to clarify the mechanisms that cause these devastating natural disasters.

IV. Climate Change

1. Could Stratospheric Ozone Depletion Make Hadley Cells Expand?

Convection-driven Hadley cells are expanding poleward. Scientists now may have uncovered part of the reason why.

V. Planetary Sciences

1. New Study Ranks Asteroid Effects from Least to Most Destructive

Violent winds, shock waves from impacts pose greatest threat to humans, study finds.

2. What to Expect from Cassini's Final Views of Titan

Cassini will fly close to Saturn's largest moon one last time. Here's a look back at what the spacecraft has revealed and ahead to scientists' final close glimpses of the moon.

VI. Space & Planets

1. Hydrogen Molecules Hint at Habitability of Enceladus's Ocean

Scientists suggest that the hydrogen could be evidence of hydrothermal activity on the ocean floor of Saturn's sixth largest moon.

VII. Geophysical Research Letters

1. Shallow episodic tremor near the Nankai Trough axis off southeast Mie prefecture, Japan

We analyzed long-term continuous seismic records (from September 2015 to April 2016) of Dense Ocean-floor Network System for Earthquake and Tsunamis, an ocean-floor observation system deployed around the fore-arc slope of the Nankai subduction zone to investigate shallow tremor near the trough axis. We found that the activity of shallow tremor was concentrated in two time periods: 6 days in October 2015 and 2 weeks in April 2016. During the episode in April 2016, migration and triggering of tremor were observed. These characteristics are similar to those of tremor in the deeper part of the subduction zone. The triggering of tremor indicates that the tremor activity is very sensitive to nearby stress perturbation in the area of this study, which is near the initiation points of past large earthquakes along the Nankai Trough. Therefore, it is very important to monitor tremor activity in this region for understanding the stress accumulation process of megathrust earthquakes.

2. Global warming and ocean stratification: A potential result of large extraterrestrial impacts

The prevailing paradigm for the climatic effects of large asteroid or comet impacts is a reduction in sunlight and significant short-term cooling caused by atmospheric aerosol loading. Here we show, using global climate model experiments, that the large increases in stratospheric water vapor that can occur upon impact with the ocean cause radiative forcings of over +20 W m−2 in the case of 10 km sized bolides. The result of such a positive forcing is rapid climatic warming, increased upper ocean stratification, and potentially disruption of upper ocean ecosystems. Since two thirds of the world's surface is ocean, we suggest that some bolide impacts may actually warm climate overall. For impacts producing both stratospheric water vapor and aerosol loading, radiative forcing by water vapor can reduce or even cancel out aerosol-induced cooling, potentially causing 1–2 decades of increased temperatures in both the upper ocean and on the land surface. Such a response, which depends on the ratio of aerosol to water vapor radiative forcing, is distinct from many previous scenarios for the climatic effects of large bolide impacts, which mostly account for cooling from aerosol loading. Finally, we discuss how water vapor forcing from bolide impacts may have contributed to two well-known phenomena: extinction across the Cretaceous/Paleogene boundary and the deglaciation of the Neoproterozoic snowball Earth.

3. Air-Sea exchange of biogenic volatile organic compounds and the impact on aerosol particle size distributions

We report simultaneous, underway eddy covariance measurements of the vertical flux of isoprene, total monoterpenes, and dimethyl sulfide (DMS) over the Northern Atlantic Ocean during fall. Mean isoprene and monoterpene sea-to-air vertical fluxes were significantly lower than mean DMS fluxes. While rare, intense monoterpene sea-to-air fluxes were observed, coincident with elevated monoterpene mixing ratios. A statistically significant correlation between isoprene vertical flux and short wave radiation was not observed, suggesting that photochemical processes in the surface microlayer did not enhance isoprene emissions in this study region. Calculations of secondary organic aerosol production rates (PSOA) for mean isoprene and monoterpene emission rates sampled here indicate that PSOA is on average <0.1 μg m−3 d−1. Despite modest PSOA, low particle number concentrations permit a sizable role for condensational growth of monoterpene oxidation products in altering particle size distributions and the concentration of cloud condensation nuclei during episodic monoterpene emission events from the ocean.

4. Interplate locking condition derived from seafloor geodetic observation in the shallowest subduction segment at the Central Nankai Trough, Japan

We monitored seafloor crustal deformation at two observation stations on opposite sides of the Nankai Trough from 2013 to 2016 in order to investigate the interplate locking condition along the Central Nankai Trough. We estimated the seafloor crustal deformation with respect to the Amurian Plate based on five observations. The results for two stations, TCA and TOA, were 38±25 mm/yr toward N78°W and 57±21 mm/yr toward N69°W (1σ), respectively. The displacement rate at TOA is consistent with the motion of the Philippine Sea Plate with respect to the Amurian Plate using the Euler vector of the REVEL model. The displacement rate at TCA is similar to that at other seafloor geodetic stations, e.g., 48±10 mm/yr at KUM2 station, on the Kumano Basin. The interplate coupling rate was estimated to be roughly 70±40% (1σ) in the shallowest segment of the Nankai Trough.

5. Productivity diagnosed from the diel cycle of particulate carbon in the North Pacific Subtropical Gyre

The rate of primary production (PP) in the ocean is a critical ecosystem function that contributes to the regulation of air-sea CO2 exchange. Historically, oceanographers have relied primarily on in vitro measurements of 14C uptake (14C-PP) as a proxy for PP. Yet it can be difficult to reconcile PP rates measured in vitro with in situ rates such as those based on oxygen. Here we present diel cycles of optically derived particulate organic carbon (POC) measured in the North Pacific Subtropical Gyre. We have calculated gross production (OPTGP) from the daytime increase and nighttime decrease of optically derived POC, assuming that the observed change in POC represents the sum of PP and community losses. We have compared these estimates to parallel 14C-PP incubations and considered sources of difference. We find that OPTGP is strongly related to 14C-PP in this region and that growth and loss rates of POC are tightly coupled.

6. Global observations of magnetospheric high-m poloidal waves during the 22 June 2015 magnetic storm

We report global observations of high-m poloidal waves during the recovery phase of the 22 June 2015 magnetic storm from a constellation of widely spaced satellites of five missions including Magnetospheric Multiscale (MMS), Van Allen Probes, Time History of Events and Macroscale Interactions during Substorm (THEMIS), Cluster, and Geostationary Operational Environmental Satellites (GOES). The combined observations demonstrate the global spatial extent of storm time poloidal waves. MMS observations confirm high azimuthal wave numbers (m ~ 100). Mode identification indicates the waves are associated with the second harmonic of field line resonances. The wave frequencies exhibit a decreasing trend as L increases, distinguishing them from the single-frequency global poloidal modes normally observed during quiet times. Detailed examination of the instantaneous frequency reveals discrete spatial structures with step-like frequency changes along L. Each discrete L shell has a steady wave frequency and spans about 1 RE, suggesting that there exist a discrete number of drift-bounce resonance regions across L shells during storm times.

7. Direct determination of the air-sea CO2gas transfer velocity in Arctic sea ice regions

The Arctic Ocean is an important sink for atmospheric CO2. The impact of decreasing sea ice extent and expanding marginal ice zones on Arctic air-sea CO2exchange depends on the rate of gas transfer in the presence of sea ice. Sea ice acts to limit air-sea gas exchange by reducing contact between air and water but is also hypothesized to enhance gas transfer rates across surrounding open-water surfaces through physical processes such as increased surface-ocean turbulence from ice-water shear and ice-edge form drag. Here we present the first direct determination of the CO2 air-sea gas transfer velocity in a wide range of Arctic sea ice conditions. We show that the gas transfer velocity increases near linearly with decreasing sea ice concentration. We also show that previous modeling approaches overestimate gas transfer rates in sea ice regions.


1. Study finds pond expansion a significant factor in loss of Mississippi delta land

Wind-driven expansion of marsh ponds on the Mississippi River Delta is a significant factor in the loss of crucial land in the Delta region, according to new research. The study found 17 percent of land loss in the area resulted from pond expansion, much of it caused by waves that eroded away the edges of the pond.

2. Thousands Stand Up for Mankind’s Greatest Invention- Science

Thousands of scientists from around the world did something that seemed unimaginable a few years ago. They stood up and made their voices heard in defense of science. Thousands of scientists braved a steady light rain and cool temperatures to gather on the Mall in Washington today and then marched toward the Capitol. The rain was not a surprise because the forecast for the day was nearly spot-on (thanks to …

IX. AGU News


Joint Release

The undersigned scientific societies and associations applaud Saturday’s March for Science, which generated an unparalleled global voice to stand up for science, the role of evidence in policymaking, and the conditions science needs to thrive. In more than 600 locations worldwide, thousands of people marched for science as citizens and scientists, parents and children, technicians and teachers, workers and retirees, doctors and patients. They marched to say our collective future is more hopeful with science – and at risk without it. They affirmed that science is exciting, essential to human well-being and economic prosperity, and a foundation for sound policy.


WASHINGTON, DC — The American Geophysical Union (AGU) today published acollection of more than 25 essays as commentaries in its scientific journals highlighting the important role Earth and space science research plays in society.