Highlights Collection

A compilation of AGU journal content that has been featured as Research Spotlights, Press Releases, Editors’ Highlights, Editors’ Vox, and GeoSpace blog posts (most recent listed first)

Editors' Highlight, 15 September 2017 in Paleoceanography

Cores reveal ocean circulation changes during the last deglaciation

This paper discusses the complexity of changes in the Atlantic Meridional Overturning Circulation as reconstructed from cores in the western equatorial Atlantic Ocean. Understanding feedbacks between climate change and Atlantic circulation is of major importance in attempts to evaluate the regional pattern and magnitude of future climate change due to increased greenhouse gas concentration.

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Editors' Highlight, 15 September 2017 in JGR: Biogeosciences

Observations on the role of microbes in nontronite mineralization

This manuscript presents textural, microbiological and geochemical characteristics of hydrothermal nontronite deposits from a recently discovered vent field at the South Mid-Atlantic Ridge. The authors aim to resolve whether microorganisms play a role in nontronite mineralization and determine how nontronites relate to co-occurring iron- and manganese-oxides. By combining textural, geochemical and molecular data, the paper has the potential to provide new insights into the origin of nontronite deposits in seafloor hydrothermal settings.

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Editors' Highlight, 15 September 2017 in JGR: Biogeosciences

Integrating the activities of soil microorganisms into mathematical models

This paper examines the ramifications of incorporating specific microbial controls on decomposition processes. At the core of this work is the integration of two previous models, DAMM and MCNiP, combining the more realistic effects of temperature and moisture on the kinetics of microbial-mediated decay from the former, with microbial characteristics controlling substrate catalysis from the latter. The work is timely in response to growing calls for more mechanism, particularly microbial activities, in global carbon models. It also focuses on some of the most pressing issues-climate change directly (soil temperature and moisture) and indirectly (timing and quality of plant products), as well as including biochemical mechanisms of microbial responses (metabolism, stoichiometry). The overall goal of inferring microbial processes rather than predicting decomposition, per se, by selecting model parameters to produce observed carbon dioxide efflux provided considerable insight to the various model assumptions. In other words, this is a modeler’s study of models.

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Editors' Highlight, 15 September 2017 in JGR: Atmospheres

A coupled snow-atmosphere modeling study

Snow-atmosphere interactions is an important but under-appreciated field. Snow is a critical natural water reservoir yet we do not have a good understanding of what controls its distribution, particularly in alpine environments where it is most important. This paper presents a fully-coupled model simulation attempting to grapple with this process. The authors ran high-resolution model simulations with and without a snow redistribution parameterization enabled over a region of complex terrain. They then contrasted the spatial variability of snow accumulation on the surface with and without the redistribution model component, finding that redistribution substantially increases the spatial variability, particularly for shorter length scales. This work is important because the variability of snowpack has important implications for hydrology, ecosystems, and avalanches. This paper should be of interest to the atmospheric community, which has thus far been relatively absent from this research field.

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Editors' Highlight, 15 September 2017 in JGR: Solid Earth

New insights in to the strength of rocks

This paper presents new high-resolution analyses of dislocation microstructures in deformed single crystals. The authors apply techniques that provide new insights into dislocation interactions during viscous deformation that have the potential to significantly improve our understanding of rate-limiting processes during creep. The manuscript should be of interest to a wide range of scientists interested in mantle dynamics. While results for only two samples were presented, the analysis is extensive and could pave the way for more extensive studies in the future.

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Editors' Highlight, 15 September 2017 in JGR: Solid Earth

Analysis of injection-induced seismicity related to wastewater disposal

This study provides a comprehensive analysis of the 2015 Mw 4.0 Venus, Texas earthquake sequence and its links to the injection of wastewater. The authors examine seismicity prior to the Mw 4.0 earthquake using a matched filter technique. They demonstrate that seismicity begins years before the event, and initiates only months after injection begins at one of the injection wells local to the sequence. The study also evaluates the impact of changing injection rates on reservoir pressure and stress perturbation at the fault.

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Editors' Highlight, 15 September 2017 in JGR: Solid Earth

New type of guided acoustic waves revealed

This paper addresses the existence and nature of waves that travel on intersections between objects arranged in three dimensions, such as fractures is a rock mass. By combining theoretical and experimental results, the authors show the existence of various modes of seismic wave propagation and contribute to a better understanding of attenuation through fractured media.

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Editors' Highlight, 15 September 2017 in JGR: Solid Earth

Modeling the spatiotemporal variation of earthquake rates

This paper investigates a time series of seismicity associated with the 2010 El Mayor-Cucapah earthquake and subsequent Octillo aftershock in the Yuha Desert, California. Dividing the affected rea in two three regions, the authors find that the seismicity rate in two regions agrees well with the static Coulomb stress changes induced by the Ocotillo mainshock, while the third region, which experienced static Coulomb stress decrease, had clear seismicity rate increase immediately after the mainshock and delayed stress shadow. They therefore suggest that the coupled Coulomb Rate-State model is able to explain a very complex spatiotemporal seismicity rate pattern, and that static Coulomb stress changes are very important in seismic hazard estimation. This case study is a nice illustration of how static Coulomb stress influences seismicity patterns, and shows how a generally complicated pattern of seismicity can be explained and could even be relatively easily predicted.

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Editors' Highlight, 15 September 2017 in JGR: Oceans

Challenging predictions about ocean surface warming trends

This paper challenges predictions from the Intergovernmental Panel on Climate Change about ocean surface warming. The authors find that observations of the surface layer of the ocean at established sites in the North Pacific and North Atlantic contradict the assertion that global warming leads to necessarily shallower mixed layers, even though the surface temperature is steadily increasing. This has implications for the response of biochemical ocean models to global warming. If the physics is not correctly represented in the model(s) then the biochemical processes will also be wrong.

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Editors' Highlight, 15 September 2017 in JGR: Oceans

Exploring the role of slope water in altering the characteristics of bottom water

This study examines interannual variability of dissolved oxygen and physical water properties in the northern California Current System (CSS) using a 25-year numerical hindcast. Focusing primarily on the continental slope, the study uses the hindcast fields to examine how winds, alongshore transport and water masses affect long-term trends and year-to-year anomalies in dissolved oxygen. The model results show that a trend of increasing Pacific Equatorial Water is partially responsible for long-term declines in oxygen. In addition to upwelling-favorable wind stress, the strength of the California Undercurrent is found to influence the magnitude and cross-shelf structure of dissolved oxygen anomalies. Interestingly, wintertime downwelling is also shown to affect subsurface oxygen anomalies during the following summer under certain conditions. This study contributes a new perspective to the subject of hypoxia in the northern CCS because historical observations are limited, and previous modeling studies of dissolved oxygen in this region have not extended this far back in time. The paper should be of interest to scientists across multiple disciplines, as well as both modelers and observational oceanographers.

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Editors' Highlight, 15 September 2017 in JGR: Oceans

Long-term observation data provides insights into current flow in East China Sea

Using Ferryboat Acoustic Doppler Current Profiler (ADCP) technology is ready to become an essential contribution to the Global Ocean Climate Observing System. This paper presents an analysis of nearly 10 years of ferryboat ADCP data collected along the northern part of the Ryukyu Island Chain that lies midway between Taiwan and Japan. These long-term data provide new insights into the complex flow patterns and current structure, particularly tidal and residual currents. They could contribute to improving numerical models to better reproduce water exchange between the East China Sea and the North Pacific.

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Editors' Highlight, 8 September 2017 in WRR

Modeling choices about stormwater investments

This paper applies game theory to examine individual landowner investment in green infrastructure stormwater control investments. Because of location-dependent drainage effects, which landowners (and where) have a large effect on overall benefits and the cost effectiveness of alternative policies. The authors have developed a relatively small scale but easy-to-follow application. Too often, people present game theory applications at a general, abstract level, then move on to very large problems with many moving parts which makes it hard to understand and interpret results. This paper strikes a nice balance between transparency and realism in modeling. The authors have also tied analysis to very real and practical policy options. At the end, they discuss applying the approach to a larger scale, such as home owner associations which could be a promising direction for future research.

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Editors' Highlight, 8 September 2017 in Space Weather

Ground-based solar monitoring and energetic particle event warning

The Mauna Loa Solar Observatory (MLSO) located on a mountain top in Hawaii, USA, uses an instrument called K-Cor that creates artificial eclipse images for daily observations of the sunlight scattered by electrons in the inner solar corona. The polarized light from the solar limb is processed by K-Cor to provide information on the density and magnetic field of the Sun’s corona. This paper presents a simple algorithm that has been developed to detect the onset of coronal mass ejections (CMEs) using ground-based observations from the observatory. Fast CMEs moving through the lower corona have been associated with significant solar energetic particle events, which with high enough flux can inhibit polar communications at Earth and be dangerous for astronauts and for airline crew and passengers traveling polar routes. The new algorithm automatically recognizes CMEs in MLSO K-Cor images in near real time while the eruption is still forming. The authors demonstrate that their observations and detection algorithms can provide advanced warning (1 to 3 hours) of fast CMEs moving through the inner corona. Currently bright CMEs are the most easily detected. The authors propose further work to warn of less bright CMEs more typical of solar minimum. This promising detection scheme is limited by cloudy weather conditions, limited observing time at a single observatory during daytime hours. They also note that daily observing duration is similar to that for solar observing spacecraft that must maintain contact with the NASA deep space network.

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Editors' Highlight, 8 September 2017 in JGR: Space Physics

Iron ions discovered in the Earth’s magnetosphere

Apparently the Earth’s magnetosphere is iron-fortified, just like your breakfast cereal. Not only does this paper present the discovery of singly-charged iron ions but also tests three possible sources for these ions, concluding that they originate from the Earth’s ionosphere. The count rates are very small, but the instrument on Geotail is capable of distinguishing them, and approximately 21 years of Geotail data provide a large timeline of statistics about their characteristics. The counts for other charge states of iron is inconsistent with a solar source, and comparison with the flyby of Cassini/CHEMS, a nearly identical instrument, shows the values to be inconsistent with an interplanetary dust source. The variation of the Fe+ count rate with solar extreme ultraviolet radiation photon flux is dramatic and supports the claim that they come from the Earth’s upper atmosphere.

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Press Release, 8 September 2017 in GRL

Ship exhaust makes oceanic thunderstorms more intense

Thunderstorms directly above two of the world’s busiest shipping lanes are significantly more powerful than storms in areas of the ocean where ships don’t travel, according to new research.

A new study mapping lightning around the globe finds lightning strokes occur nearly twice as often directly above heavily-trafficked shipping lanes in the Indian Ocean and the South China Sea than they do in areas of the ocean adjacent to shipping lanes that have similar climates.

The difference in lightning activity can’t be explained by changes in the weather…More

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AGU Blog Post, 8 September 2017 in GRL

Heat stress escalates in cities under global warming

Heatwaves are intensifying in cities due to the double whammy of the urban heat island effect and global warming, according to a new study.

The study’s authors used computer models to simulate with unprecedented detail the temperature changes through the mid-21st century in Belgian cities. They found that heatwaves become hotter, longer and more frequent because of greenhouse gas emissions, and that temperature above the heat stress alarm level increases by a factor of between 1.4 and 15 by the middle of this century.

“The trends are very harmful to an increasing share of people living in the cities, since hot temperatures lead to excessive mortalities, hospital admissions, energy usage and economic loss, which are exacerbated by the urban heat island,” said Hendrik Wouters, of Belgium’s Katholieke Universiteit Leuven and Ghent University.

More deaths from future heat waves could make heat waves the most deadly type of natural disaster in the near future, he added…More

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Editors' Highlight, 8 September 2017 in GRL

How microorganisms drive water convection

Biomixing in natural bodies of water is a controversial topic. The initial excitement about organisms mixing oceans with their swimming motions has subsided, and biomixing is now regarded as insignificant in the context of ocean mixing. But bioconvection driven by density difference between organisms and surrounding water, with vertical motions by organisms providing the necessary energy input to maintain convection, is conceptually more sound. This paper is an excellent example of combining field work with numerical experiments to test out a hypothesis.

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Editors' Highlight, 8 September 2017 in GRL

Determining the cause of an earthquake in a seismically quiet zone

The April 2017 earthquake at Moiyabana, Botswana, was unusual in that it occurred in an area with little previously known seismicity. This paper integrates a range of data sets (including magnetic, seismic, and InSAR data) to determine the likely cause of this earthquake. The nature of intraplate earthquakes, including their causes and source faults, are poorly constrained so this approach provides a foundation for future studies of other such seismic events.

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Editors' Highlight, 8 September 2017 in GRL

Experimental work presents new insights into magnetic energy in the solar atmosphere

In a field dominated by semi-empirical, empirical models and numerical experiments, this paper represents one of the very few experimental efforts. It provides an alternative explanation of why coronal loops have constant cross-section and are over-dense, through a single mechanism. It has the potential to be a model for future research on plasmas such as those on the Sun.

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Press Release, 8 September 2017 in GRL

Researchers find direct evidence of sea level ‘fingerprints’

Researchers have reported the first observation of sea level “fingerprints,” tell-tale differences in sea level rise around the world in response to changes in continental water and ice sheet mass. The team’s findings have been accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.

“Scientists have a solid understanding of the physics of sea level fingerprints, but we’ve never had a direct detection of the phenomenon until now,” said Isabella Velicogna, professor of Earth system science at the University of California, Irvine and research scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, who was a co-author of the new study…More

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