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AGU Research Spotlight (Mar 08-Mar 14, 2018)

2018-03-16 15:08:13

I. Climate Change

1. How Earthquakes Start and Stop

Earthquakes: Nucleation, Triggering, Rupture, and Relationships to Aseismic Processes; Cargèse, Corsica, France, 2–6 October 2017


2. Understanding High-Latitude Methane in a Warming Climate

Climate change could spur greenhouse gas release from the Arctic. A new project will synthesize existing data to improve uncertain predictions.


3. New Maps Highlight Antarctica’s Flowing Ice

The maps focus on surface ice velocity, showing how Antarctica’s frozen surface changed over a 7-year period.


II. Hazards & Disasters

1. Scientists Capture Sounds of Volcanic Thunder

Microphones set out to detect eruptions in Alaska’s Aleutian Islands recorded sounds of volcanic thunder for the first time.


2. U.S. Scientists Safely Retrieved from Ice-Bound Antarctic Island

Argentineans came to the aid of stranded scientists.


III. Ocean Sciences

1. Dead Sea Provides Unique Insights on Water Evaporation

Scientists study the impacts of sunlight and wind on evaporation at one of Earth’s most unusual lakes.


2. Chaos Beneath a Calm Sea

Seismic data help reveal fine-scale wave breaking, instability and turbulence in the ocean interior.


IV. Biogeosciences

1. What Would Earth Be Like Without Life?

Workshop on a Cosmic Perspective of Earth: A Planet Permeated and Shaped by Life—Implications for Astrobiology; Tokyo, Japan, 13–15 September 2017


V. Geology & Geophysics

1. Widespread Mantle Upwelling Beneath Oceanic Transform Faults

A global characterization of mantle flow patterns beneath active oceanic transforms suggests pervasive upwelling stabilizes divergent plate boundaries by warming and weakening these enigmatic features.


VI. Geophysical Research Letters

1. Continuous Gravity and Tilt Reveal Anomalous Pressure and Density Changes Associated With Gas Pistoning Within the Summit Lava Lake of Kīlauea Volcano, Hawai‘i

Gas piston events within the summit eruptive vent of Kīlauea Volcano, Hawai‘i, are characterized by increases in lava level and by decreases in seismic energy release, spattering, and degassing. During 2010–2011, gas piston events were especially well manifested, with lava level rises of tens of meters over the course of several hours, followed by a sudden drop to preevent levels. The changes in lava level were accompanied by directly proportional changes in gravity, but ground deformation determined from tilt was anticorrelative. The small magnitude of the gravity changes, compared to the large changes in volume within the vent during gas pistons, suggests that pistoning involves the accumulation of a very low-density (100–200 kg/m3) foam at the top of the lava column. Co-event ground tilt indicates that rise in lava level is paradoxically associated with deflation (the opposite is usually true), which can be modeled as an increase in the gas content of the magma column between the source reservoir and the surface. Gas pistoning behavior is therefore associated with not only accumulation of a shallow magmatic foam but also more bubbles within the feeder conduit, probably due to the overall decrease in gas emissions from the lava lake during piston events.


2. Storm Time Evolution of Outer Radiation Belt Relativistic Electrons by a Nearly Continuous Distribution of Chorus

During the 13–14 November 2012 storm, Van Allen Probe A simultaneously observed a 10 h period of enhanced chorus (including quasi-parallel and oblique propagation components) and relativistic electron fluxes over a broad range of L = 3–6 and magnetic local time = 2–10 within a complete orbit cycle. By adopting a Gaussian fit to the observed wave spectra, we obtain the wave parameters and calculate the bounce-averaged diffusion coefficients. We solve the Fokker-Planck diffusion equation to simulate flux evolutions of relativistic (1.8–4.2 MeV) electrons during two intervals when Probe A passed the location L = 4.3 along its orbit. The simulating results show that chorus with combined quasi-parallel and oblique components can produce a more pronounced flux enhancement in the pitch angle range ~45°–80°, consistent well with the observation. The current results provide the first evidence on how relativistic electron fluxes vary under the drive of almost continuously distributed chorus with both quasi-parallel and oblique components within a complete orbit of Van Allen Probe.


3. Age of the Subducting Philippine Sea Slab and Mechanism of Low-Frequency Earthquakes

Nonvolcanic low-frequency earthquakes (LFEs) usually occur in young and warm subduction zones under condition of near-lithostatic pore fluid pressure. However, the relation between the LFEs and the subducting slab age has never been documented so far. Here we estimate the lithospheric age of the subducting Philippine Sea (PHS) slab beneath the Nankai arc by linking seismic tomography and a plate reconstruction model. Our results show that the LFEs in SW Japan take place in young parts (~17–26 Myr) of the PHS slab. However, no LFE occurs beneath the Kii channel where the PHS slab is very young (~15 Myr) and thin (~29 km), forming an LFE gap there. According to the present results and previous works, we think that the LFE gap at the Kii channel is caused by joint effects of several factors, including the youngest slab age, high temperature, low fluid content, high permeability of the overlying plate, a slab tear, and hot upwelling flow below the PHS slab.


4. Seasonal Variability of Magnetotactic Bacteria in a Freshwater Pond

Nonvolcanic low-frequency earthquakes (LFEs) usually occur in young and warm subduction zones under Magnetotactic bacteria (MTB) synthesize ferrimagnetic crystals that contribute to the remanent magnetization in sediments, yet knowledge of how MTB populations vary in natural environments over time remains limited. We report abundances of three MTB morphotypes from nine sites collected and measured every month over a two-year period from a natural pond near Munich, Germany. Morphotype populations underwent coherent temporal trends among the nine sites—especially at proximal sites with similar water depths. MTB populations varied independently of bottom water oxygen concentrations or temperature over the two-year period, except for spirilla, which flourished during the summer at some sites. Magnetic properties of the sediments did not reflect living MTB abundances, but instead varied with water depth. Deeper sites, which were also lower in organic carbon, nitrogen, and oxygen concentrations than shallower sites, had higher saturation magnetizations and were richer in single-domain particles.


5. Abyssal Upwelling in Mid-Ocean Ridge Fracture Zones

Turbulence in the abyssal ocean plays a fundamental role in the climate system by sustaining the deepest branch of the overturning circulation. Over the western flank of the Mid-Atlantic Ridge in the South Atlantic, previously observed bottom-intensified and tidally modulated mixing of abyssal waters appears to imply a counterintuitive densification of deep and bottom waters. Here we show that inside fracture zones, however, turbulence is elevated away from the seafloor because of intensified downward propagating near-inertial wave energy, which decays below a subinertial shear maximum. Ray-tracing simulations predict a decay of wave energy subsequent to wave-mean flow interactions. The hypothesized wave-mean flow interactions drive a deep flow toward lighter densities of up to 0.6 Sv over the mid-ocean ridge flank in the Brazil Basin, and the same process may also cause upwelling of abyssal waters in other ocean basins with mid-ocean ridges with fracture zones.


6. Does Southern Ocean Surface Forcing Shape the Global Ocean Overturning Circulation?

Paleoclimate proxy data suggest that the Atlantic Meridional Overturning Circulation (AMOC) was shallower at the Last Glacial Maximum (LGM) than its preindustrial (PI) depth. Previous studies have suggested that this shoaling necessarily accompanies Antarctic sea ice expansion at the LGM. Here the influence of Southern Ocean surface forcing on the AMOC depth is investigated using ocean-only simulations from a state-of-the-art climate model with surface forcing specified from the output of previous coupled PI and LGM simulations. In contrast to previous expectations, we find that applying LGM surface forcing in the Southern Ocean and PI surface forcing elsewhere causes the AMOC to shoal only about half as much as when LGM surface forcing is applied globally. We show that this occurs because diapycnal mixing renders the Southern Ocean overturning circulation more diabatic than previously assumed, which diminishes the influence of Southern Ocean surface buoyancy forcing on the depth of the AMOC.


7. Change in Dense Shelf Water and Adélie Land Bottom Water Precipitated by Iceberg Calving

Antarctic Bottom Water supplies the deep limb of the global overturning circulation and ventilates the abyssal ocean. Antarctic Bottom Water has warmed, freshened, and contracted in recent decades, but the causes remain poorly understood. We use unique multiyear observations from the continental shelf and deep ocean near the Mertz Polynya to examine the sensitivity of this bottom water formation region to changes on the continental shelf, including the calving of a large iceberg. Postcalving, the seasonal cycle of Dense Shelf Water (DSW) density almost halved in amplitude and the volume of DSW available for export reduced. In the deep ocean, the density and volume of Adélie Land Bottom Water decreased sharply after calving, while oxygen concentrations remained high, indicating continued ventilation by DSW. This natural experiment illustrates how local changes in forcing over the Antarctic continental shelf can drive large and rapid changes in the abyssal ocean.


VII. AGU Blogs

1. Underwater volcano behavior captured by timely scientific expedition

Researchers got a rare opportunity to study an underwater volcano in the Caribbean when it erupted while they were surveying the area. The research, published online in the journal Geochemistry, Geophysics, Geosystems, a journal of the American Geophysical Union, provides new insight into the little-studied world of underwater volcanoes. It investigated a volcano named Kick-‘em-Jenny (KeJ), which is thought to be named after the turbulent waters nearby.

2.How much snow accumulates in North America each year? More than scientists thought

There’s a lot more snow piling up in the mountains of North America than anyone knew, according to a first-of-its-kind study. Scientists have revised an estimate of snow volume for the entire continent, and they’ve discovered that snow accumulation in a typical year is 50 percent higher than previously thought.

3. Mexico’s 2017 earthquake emerged from a growing risk zone

Under Mexico, where the Cocos Plate from the Pacific Ocean slides under the North American Plate, a bending line of hills, created when the seafloor first formed, sits atop a flattened area of subduction. That newly recognized combination has created a fault that likely explains last September’s Puebla earthquake, scientists report in a new study.

4. Llusco, Peru: a dramatic landslide has destroyed 100 houses

A major landslide at Llusco in the Cusco region of Peru over the last few days has led to the destruction of over 100 houses, and the declaration of a state of emergency by the government.  The local authorities have stated that the landslide was caused by high pore water pressures, rather than by seismic activity. The landslide is reported to cover an area of about 30 hectares.  The best images that I have seen of the landslide reside in a Youtube video that was shot by a drone by Fameco Films and Art.  This should be visible below.

5. Papua New Guinea earthquake – continued landslide impacts

The continued scandalous response (or, more precisely, non-response) of the international community to the Papua New Guinea earthquake is highlighted in this article on the New Zealand website stuff.co.nz.  The article includes this telling section.


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