AGU期刊一周Research Spotlight (Aug 17~Aug 24, 2017)

发布时间:2017-8-25 9:37:23 点击次数:94

I. Climate Change

1. Coastal Wetlands Effectively Sequester “Blue Carbon”

Mangrove forests, salt marshes, seagrass beds, and the like are carbon storage treasure troves.

2. On-the-Ground Measurements Overestimate Earth’s Albedo

Weather stations can be used to calibrate and validate albedo measurements from satellites, but they fail to account for variability across landscapes, overestimating how reflective our planet is.

II. Hazards & Disasters

1. Quakes Pack More Punch in Eastern Than in Central United States

A new finding rests on the recognition that fault types differ between the two regions. It helps explain prior evidence that human-induced quakes and natural ones behave the same in the nation’s center.

III. Science Policy

1. Physicist and Former Congressman Vernon Ehlers Dead at 83

A staunch supporter of science, Ehlers worked as a research scientist before going into politics.

IV. Hydrology, Cryosphere & Earth Surface

1. Small Streams Make Big Contribution to Carbon Cycle

A recent paper in Reviews of Geophysics discussed the carbon dynamics of headwater streams.

V. Space Science & Space Physics

1. Eclipse’s Last Major Stop Is Rich in Science and Amazement

Eclipse celebrations and scientific preparations abound in the final large U.S. population center to see Monday’s total eclipse.

VI. Geophysical Research Letters

1. Are we near the predictability limit of tropical Indo-Pacific sea surface temperatures?

The predictability of seasonal anomalies worldwide rests largely on the predictability of tropical sea surface temperature (SST) anomalies. Tropical forecast skill is also a key metric of climate models. We find, however, that despite extensive model development, the tropical SST forecast skill of the operational North American Multi-Model Ensemble (NMME) of eight coupled atmosphere-ocean models remains close both regionally and temporally to that of a vastly simpler linear inverse model (LIM) derived from observed covariances of SST, sea surface height, and wind fields. The LIM clearly captures the essence of the predictable SST dynamics. The NMME and LIM skills also closely track and are only slightly lower than the potential skill estimated using the LIM's forecast signal-to-noise ratios. This suggests that the scope for further skill improvement is small in most regions, except in the western equatorial Pacific where the NMME skill is currently much lower than the LIM skill.

2. The competition between coastal trace metal fluxes and oceanic mixing from the10Be/9Be ratio: Implications for sedimentary records

At an ocean margin site 37°S offshore Chile, we use the meteoric cosmogenic10Be/9Be ratio to trace changes in terrestrial particulate composition due to exchange with seawater. We analyzed the marine authigenic phase in surface sediments along a coast-perpendicular transect and compared to samples from their riverine source. We find evidence for growth of authigenic rims through coprecipitation, not via reversible adsorption, that incorporate an open ocean10Be/9Be signature from a deep water source only 30 km from the coast, overprinting terrestrial 10Be/9Be signatures. Together with increasing 10Be/9Be ratios, particulate-bound Fe concentrations increase, which we attribute to release of Fe-rich pore waters during boundary exchange in the sediment. The implications for the use of 10Be/9Be in sedimentary records for paleodenudation flux reconstructions are the following: in coast-proximal sites the authigenic record will likely preserve local riverine ratios unaffected by exchange with seawater, whereas sites beneath well-mixed seawater will preserve global flux signatures.

3. Modeling fracture propagation and seafloor gas release during seafloor warming-induced hydrate dissociation

The stability of marine methane hydrates and the potential release of methane gas to the ocean and atmosphere have received considerable attention in the past decade. Sophisticated hydraulic-thermodynamic models are increasingly being applied to investigate the dynamics of bottom water warming, hydrate dissociation, and gas escape from the seafloor. However, these models often lack geomechanical coupling and neglect how overpressure development and fracture propagation affect the timing, rate, and magnitude of methane escape. In this study we integrate a geomechanical coupling into the widely used TOUGH + Hydrate model. It is shown that such coupling is crucial in sediments with permeability ≤10−16 m2, as fracture formation dramatically affects rates of dissociation and seafloor gas release. The geomechanical coupling also results in highly nonlinear seafloor gas release, which presents an additional mechanism for explaining the widely observed episodic nature of gas flares from seafloor sediments in a variety of tectonic and oceanographic settings.

4. Large paleoearthquake timing and displacement near Damak in eastern Nepal on the Himalayan Frontal Thrust

An excavation across the Himalayan Frontal Thrust near Damak in eastern Nepal shows displacement on a fault plane dipping ~22° has produced vertical separation across a scarp equal to 5.5 m. Stratigraphic, structural, geometrical, and radiocarbon observations are interpreted to indicate that the displacement is the result of a single earthquake of 11.3 ± 3.5 m of dip-slip displacement that occurred 1146–1256 A.D. Empirical scaling laws indicate that thrust earthquakes characterized by average displacements of this size may produce rupture lengths of 450 to >800 km and moment magnitudes Mw of 8.6 to >9. Sufficient strain has accumulated along this portion of the Himalayan arc during the roughly 800 years since the 1146–1256 A.D. earthquake to produce another earthquake displacement of similar size.

VII. AGU Blogs

1. Regent landslide in Sierra Leone: the causes of the disaster

The latest tally of losses from the Regent landslide in Sierra Leone has been released by the coroner.  To date 499 bodies have been recovered, with about 600 people still reported missing.  As expected, this is now the worst landslide of the calendar year to date.

2. Scicomm & scipol are becoming integral parts of conferences

Last week I attended the annual Ecological Society of America (ESA) meeting. I’m an ecologist by training to this used to be my go-to meeting. I was there this time for a Story Collider show (my other job) but also to represent Sharing Science in various scicomm events/functions.