AGU 期刊一周Research Spotlights (Dec 1 ~Dec 7, 2016)

发布时间:2016-12-9 10:50:44 点击次数:716

I. Science Policy

1. Climate Efforts Will Continue Despite Rhetoric, Officials Say

Secretary of the Interior says that citizens can help hold the Trump administration accountable for what they want to see happen in terms of action on climate change.

https://eos.org/articles/climate-efforts-will-continue-despite-rhetoric-officials-say

2. Take the Long View on Environmental Issues in the Age of Trump

Although climate and environmental regulations are at risk in the short term, Trump's disruption of traditional party positions could help to break decades of stalled efforts to address climate change.

https://eos.org/opinions/take-the-long-view-on-environmental-issues-in-the-age-of-trump

II.Biogeosciences

1. From Science to Storytelling: An Experiment in Journalism

From ominous deadlines to Internet trolls, AGU's 2016 AAAS Mass Media Fellow recounts his experience writing for National Geographic as a science journalist.

https://eos.org/agu-news/from-science-to-storytelling-an-experiment-in-journalism

III. Climate Change

1. Understanding Tectonic Processes Following Great Earthquakes

Scientists parse out the processes underlying tectonic signals detected by GPS networks.

https://eos.org/research-spotlights/understanding-tectonic-processes-following-great-earthquakes

IV.Ocean Sciences

1. East of Japan, Upper Ocean Waves Follow a Seasonal Cycle

The seasonality of fine-scale, near-surface ocean dynamics raises important considerations for an upcoming satellite mission to measure global sea surface height.

https://eos.org/research-spotlights/east-of-japan-upper-ocean-waves-follow-a-seasonal-cycle


V. Geophysical Research Letters

1. Evidence for a biological pump driver of atmospheric CO2 rise during Heinrich Stadial 1

The initial trigger of the atmospheric CO2 rise during Heinrich Stadial 1 (HS1: 14.5–17.5 kyr B.P.) remains elusive. We present a compilation of four paired surface and intermediate-depth foraminiferal δ13C records to test whether reduced biological pump efficiency led to the initial CO2 rise during the last deglaciation. Surface ocean δ13C decreased across HS1 while intermediate-depth δ13C increased, leading to a reduction in the upper ocean δ13C gradient. Our compilation also suggests the δ13C gradient increased during the Bølling-Allerød (12.9–14.5 kyr B.P.) and decreased during the Younger Dryas (YD: 11.7–12.9 kyr B.P.). The HS1 and YD data are consistent with reduced biological export of isotopically light carbon from the surface ocean and its remineralization at depth. Our results support the idea that a weaker Atlantic Meridional Overturning Circulation decreased biological pump efficiency by increasing the overall fraction of preformed nutrients in the global ocean, leading to an increase in atmospheric CO2.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070723/full

2. Multidecadal increases in the Yukon River Basin of chemical fluxes as indicators of changing flowpaths, groundwater, and permafrost

The Yukon River Basin, underlain by discontinuous permafrost, has experienced a warming climate over the last century that has altered air temperature, precipitation, and permafrost. We investigated a water chemistry database from 1982 to 2014 for the Yukon River and its major tributary, the Tanana River. Significant increases of Ca, Mg, and Na annual flux were found in both rivers. Additionally, SO4 and P annual flux increased in the Yukon River. No annual trends were observed for dissolved organic carbon (DOC) from 2001 to 2014. In the Yukon River, Mg and SO4 flux increased throughout the year, while some of the most positive trends for Ca, Mg, Na, SO4, and P flux occurred during the fall and winter months. Both rivers exhibited positive monthly DOC flux trends for summer (Yukon River) and winter (Tanana River). These trends suggest increased active layer expansion, weathering, and sulfide oxidation due to permafrost degradation throughout the Yukon River Basin.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070817/full

3. Effects of unstable flow on solute transport in the marsh soil and exchange with coastal water

Recent studies of marsh hydraulics have focused on tide-induced pore water circulation as the main drive for solute transport in the marsh soil and exchange with coastal water. Our study revealed another important mechanism provided by unstable fingering flow, which largely modified solute transport paths. In the marsh interior, downward penetration of salt fingers forced ambient pore water and solute plumes to move upward and exit the marsh soil through marsh platform at relatively high concentrations, up to 2 orders of magnitude higher than exit solute concentrations at the tidal creek bed. The mixing of solute with ambient pore water in the marsh interior was intensified greatly by fingering flow. A critical distance to the creek was determined based on a field-scale model simulation to distinguish tidal circulation-dominated and fingering flow-dominated solute transport zones. The new transport mechanism has implications for understanding the fate of solutes in particularly salt marshes of low creek densities.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070576/full

4. Work done by atmospheric winds on mesoscale ocean eddies

Mesoscale eddies are ubiquitous in the ocean and dominate the ocean's kinetic energy. However, physical processes influencing ocean eddy energy remain poorly understood. Mesoscale ocean eddy-wind interaction potentially provides an energy flux into or out of the eddy field, but its effect on ocean eddies has not yet been determined. Here we examine work done by atmospheric winds on more than 1,200,000 mesoscale eddies identified from satellite altimetry data and show that atmospheric winds significantly damp mesoscale ocean eddies, particularly in the energetic western boundary current regions and the Southern Ocean. Furthermore, the large-scale wind stress curl is found to on average systematically inject kinetic energy into anticyclonic (cyclonic) eddies in the subtropical (subpolar) gyres while mechanically damps anticyclonic (cyclonic) eddies in the subpolar (subtropical) gyres.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL071275/full

5. The global infrared energy budget of the thermosphere from 1947 to 2016 and implications for solar variability

We present an empirical model of the global infrared energy budget of the thermosphere over the past 70 years. The F10.7, Ap, and Dst indices are used in linear regression fits to the 14.5 year time series of radiative cooling by carbon dioxide and nitric oxide measured by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the TIMED satellite. Databases of these indices are used to develop the radiative cooling time series from 1947. No consistent relation between the occurrence of peak sunspot number and peak infrared cooling is found over the past six solar cycles. The total infrared energy radiated by the thermosphere, integrated over a solar cycle, is nearly constant over five complete solar cycles studied. This is a direct consequence of the geoeffective solar energy also being nearly constant over the same intervals. These results provide a new metric for assessing the terrestrial context of the long-term record of solar-related indices.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070965/full

6. Regional and stress drop effects on aftershock productivity of large megathrust earthquakes

The total number of aftershocks increases with main shock magnitude, resulting in an overall well-defined relationship. Observed variations from this trend prompt questions regarding influences of regional environment and individual main shock rupture characteristics. We investigate how aftershock productivity varies regionally and with main shock source parameters for large (Mw ≥ 7.0) circum-Pacific megathrust earthquakes within the past 25 years, drawing on extant finite-fault rupture models. Aftershock productivity is found to be higher for subduction zones of the western circum-Pacific than for subduction zones in the eastern circum-Pacific. This appears to be a manifestation of differences in faulting susceptibility between island arcs and continental arcs. Surprisingly, events with relatively large static stress drop tend to produce fewer aftershocks than comparable magnitude events with lower stress drop; however, for events with similar coseismic rupture area, aftershock productivity increases with stress drop and radiated energy, indicating a significant impact of source rupture process on productivity.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL071104/full

7. Moment rate scaling for earthquakes 3.3 ≤ M ≤ 5.3 with implications for stress drop

We have determined a scalable apparent moment rate function (aMRF) that correctly predicts the peak ground acceleration (PGA), peak ground velocity (PGV), local magnitude, and the ratio of PGA/PGV for earthquakes 3.3 ≤ M ≤ 5.3. Using the NGA-West2 database for 3.0 ≤ M ≤ 7.7, we find a break in scaling of LogPGA and LogPGV versus M around M ~ 5.3 with nearly linear scaling for LogPGA and LogPGV for 3.3 ≤ M ≤ 5.3. Temporal parameters tp and td—related to rise time and total duration—control the aMRF. Both scale with seismic moment. The Fourier amplitude spectrum of the aMRF has two corners between which the spectrum decays ~ f− 1. Significant attenuation along the raypath results in a Brune-like spectrum with one corner fC. Assuming that fC ≅ 1/td, the aMRF predicts non-self-similar scaling  and weak stress drop scaling . This aMRF can explain why stress drop is different from the stress parameter used to predict high-frequency ground motion.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL071433/full

VI.AGU News

1. AGU FALL MEETING: PRESS CONFERENCE SCHEDULE; BRIEFINGS STREAMED ONLINE; BADGE PICKUP

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 from Monday through Friday, Dec. 12-16, 2016 at the Moscone Center, 747 Howard St., San Francisco, California.

https://news.agu.org/press-release/agu-fall-meeting-press-conference-schedule-briefings-streamed-online-badge-pickup-3/

VII.AGU Blogs

1.We’ve Been Waiting for this Whopper, and It Has Arrived!

We all knew it was coming, and this week it was delivered, just in time for Christmas. It’s the post El Nino, “The globe is cooling and climate change has stopped” myth.  First an explanation: During an El Nino event, very warm water covers much of the Equatorial Pacific, warming the air while cooling the oceans. Because of this, the hottest years globally are almost always El Nino years, and …

http://blogs.agu.org/wildwildscience/2016/12/02/weve-waiting-whopper-arrived/

2. Another Smoking Gun that the Earth’s Thermostat is Going Haywire

While those who do not live in the world of facts share fake news stories about the planet’s temperature dropping, the real data is far different. We will almost certainly set a new hottest year on record this year, breaking the previous record, last year, and the current second place holder, the year before that! Meteorologist Guy Walton keeps close track of the number of record highs versus record lows …

http://blogs.agu.org/wildwildscience/2016/12/06/another-smoking-gun-earths-thermostat-going-haywire/

3. The Icy Bay landslide in Alaska: a nice video describing the link with glacial melting

A very nice video has been posted on Youtube describing the link between the giant Icy Bay landslide in Alaska in 2015 (this landslide is also variously known as the Taan Fjord landslide and the Tyndall Glacier landslide), which is the largest known recent landslide in North America, and the melting of the adjacent glacier.  The video features Dr Michael Loso, physical scientist at Wrangell-St. Elias National Park.  The landslide, pictured above, occurred on 17th October 2015 occurred on the flanks of Taan Fjord in Icy Bay in Alaska.  I featured this landslide, which was detected via the seismic detection system developed by Goran Ekstrom and Colin Stark, in a blog post at the start of this year.  As noted above, this is the largest recorded landslide in North America, with a volume of about 72 million cubic metres and a mass of about 180 million tonnes.  The landslide generated a large tsunami that caused extensive damage along the flanks of Taan Fjord.

http://blogs.agu.org/landslideblog/2016/12/07/icy-bay-landslide/