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Data Mining Reveals the Dynamics of Auroral Substorms

Fri, 05/31/2019 - 11:32

Space physicists have long known that solar flares hurl vast amounts of charged particles into space that can cause magnetic storms on Earth—a days-long period of enhanced activity in the planet’s magnetic field that can create spectacular auroras and take down power grids on continental scales.

But the dynamics of how the Sun interacts with Earth’s magnetic field during such storms remain mysterious, especially the brief periods of peak intensity, which last just a few hours.

In the mid-1900s, scientists realized that there are distinct phases to these events, now called auroral substorms. First, the solar wind buffets and stretches out Earth’s magnetic field, which stores energy like a rubber band. Next, the field’s tail rebounds, jetting charged particles back toward the planet’s nightside and causing a surge of aurora that sweeps west across the planet. Finally, the magnetic field recovers to a quieter state.

This picture emerged in the 1970s, but it’s hard to piece together a comprehensive picture of Earth’s magnetic field during any given substorm because of the limited number of satellites making observations.

Now Stephens et al. have taken a new approach: mining and merging the archives of 15 satellites from NASA, the National Oceanic and Atmospheric Administration, the European Space Agency, and the Japan Aerospace Exploration Agency spanning 5 decades to create a unified data set. The resulting models behave as if 11,000 to 50,000 virtual satellites were observing a single representative substorm, making the simulation the most comprehensive view yet of substorms and their distinct phases.

As every substorm is unique and unfolds at its own pace, the researchers needed to synchronize all of them. To do this, the team turned to magnetic field readings from ground monitoring stations and satellite observations of the solar wind. These observations track the phases of the storm in the form of calculated indices, which act as a sort of time code that allows the spacecraft data to be matched to the correct phase of the substorm.

This unified data set is powerful and flexible. It can be used to construct a model of a representative, “average” substorm. But it can also be used to reconstruct any individual substorm in greater detail by starting with data for that event and filling in the rest of Earth’s magnetic field with closely matched data from the general data set.

This process allowed the team to track the system of currents that pulse around the planet as a substorm grows, expands, and recovers, including the wedge of current in the magnetic field’s nightside tail, the ring current above the planet’s equator (which is enhanced during a substorm), and the jets of particles that arc toward the poles to generate the aurora.

This global picture could help scientists better understand substorms on Earth, including their risk to infrastructure. It could also help scientists understand similar processes that have been observed in the magnetic fields of other planets and stars. (Journal of Geophysical Research: Space Physics, https://doi.org/10.1029/2018JA025843, 2019)

—Mark Zastrow, Freelance Writer

Damselfish in Distress?

Fri, 05/31/2019 - 11:30

Humans are changing the face of the planet. We’ve had sufficient impact on the surface that scientists have proposed a new geologic age, the Anthropocene, and we’re also changing the hydrosphere. In addition to toxins and plastics, the oceans are increasingly filled with human-generated noise pollution. Scientists first realized that this noise pollution affects marine mammals 3 decades ago, but now new research is highlighting its effects on species lower down on the food chain.Heightened noise was associated with increased heart rates and physical changes to the fishes’ bodies.

A study in Marine Pollution Bulletin looking at the effects of boat noise on the early life development of two types of damselfish found that heightened noise was associated with increased heart rates and physical changes to the fishes’ bodies. The results suggest that growing up in a noisy reef could affect the fishes’ long-term survival rates.

Noise pollution in the ocean has increased fourfold since the 1950s, largely because of commercial shipping, and the effects are noticeable. Previous work has shown that noise pollution changes the behavior, communication, and movements of marine wildlife and also induces stress in fish, but there is little research to date on noise’s impact on early development.

The new research looked at the development of two species of damselfish, cinnamon clownfish and spiny chromis, as they grew from embryos to hatchlings in tanks. Half of the embryos were exposed to normal levels of marine sounds, and the other half were exposed to the additional noise of motorboats. The researchers noted that the boat noise increased the fishes’ heart rates by 10% in both species, indicating they were stressed by the noise.

After hatching, the spiny chromis exposed to boat noise were slightly larger and had bigger eyes and smaller egg yolk sacs. The fish are sustained by yolk until they’re able to find their own food, so noise pollution may affect the way fish develop into adults.

In the lab, both noise groups had similar survival rates at birth, but in natural environments it is possible that increased stress could make the fish more vulnerable to predation. The differences between the two species further suggest that some fish might be more resilient to noise pollution.

“With the fish, [scientists] are just starting to touch the surface of who might be vulnerable and who are the more resilient species,” said Lauren McWhinnie, a researcher at the University of Victoria in Canada who was not involved with the new study. “We’ve looked before with climate and acidification, seeing that there are certain species that will be more resilient to those things, but noise is quite a new factor.”

—Mara Johnson-Groh, Freelance Science Writer and Photographer

Modeling Tsunamis with Social Media

Fri, 05/31/2019 - 11:30

A devastating tsunami occurred in Palu Bay on Sulawesi, Indonesia, following the 2018 Palu earthquake. This tsunami was unusually large according to conventional wisdom, because it was generated by a strike slip event. Carvajal et al. [2019] present a fascinating new approach to construct modeled tsunami waveforms using social media video footage shared by people who experienced the tsunami and recording from local CCTV cameras. These videos were analyzed to quantify the timing, amplitude, and period of the tsunami at different locations around Palu Bay.

Results show that either current rupture models of the earthquake underestimate the seafloor displacement it caused, or that non-tectonic sources were involved in generating the tsunami. This analysis also reveals significant short period tsunami waves which were not recorded by the local tide gauge because the sampling rate at the station was too large. This demonstrates that data obtained from unconventional devices can be extremely useful to better understand tsunami phenomena.

Citation: Carvajal, M., Araya‐Cornejo, C., Sepúlveda, I., Melnick, D., & Haase, J. S. [2019]. Nearly instantaneous tsunamis following the Mw 7.5 2018 Palu earthquake. Geophysical Research Letters, 46. https://doi.org/10.1029/2019GL082578

—Gavin P. Hayes, Editor, Geophysical Research Letters

Senator Rips Trump on Anniversary of Plan to Leave Climate Pact

Thu, 05/30/2019 - 18:03

Two years after President Donald Trump announced his intention to withdraw the United States from the Paris climate accord, Sen. Chris Murphy (D-Conn.) lambasted that decision but said that significant progress on climate change is being made despite the administration’s “open and proud hostility to taking climate change seriously.”

Murphy, who participated with several environmental leaders in a 29 May briefing, called the 2-year mark “an ignominious anniversary.” Trump announced on 1 June 2017 his controversial decision to plan to withdraw from the accord.

“Every single month that goes by that we don’t make the decisions necessary to save this planet from existential harm is a month that we get closer to the point of no return.”“It is a disaster for the United States to remove itself voluntarily from the international conversation around global warming pollutant reduction, even for 2 years,” Murphy said. “We don’t have 2 years to sit on our hands. We don’t have 2 years to fail to lead [on this issue]. Every single month that goes by that we don’t make the decisions necessary to save this planet from existential harm is a month that we get closer to the point of no return” from the impacts of climate change.

The agreement, which was adopted by 195 countries in 2015, aims to hold the increase in global average temperature to well below 2°C above preindustrial levels and to pursue efforts to limit the increase to 1.5°C. It also calls for boosting climate change adaptation measures, among other efforts. An October 2018 report by the Intergovernmental Panel on Climate Change states that limiting global warming to 1.5°C above preindustrial levels would require rapid and far-reaching transitions in energy and other systems that “are unprecedented in terms of scale.”

Assuming that Trump formally notifies the United Nations in November that the United States will be withdrawing from the Paris accord, the earliest effective date of that withdrawal is 4 November 2020, the day after the 2020 U.S. presidential election.

Building a Climate Coalition

Murphy said that action needs to be taken on climate change despite the administration’s intransigence on the issue.

“We’ll continue to fight the president’s attacks on Paris and attacks on climate science every single day of the week.”“Our focus now is on making sure that we build a political coalition in this country such that no one ever gets elected president of the United States again who isn’t 100% committed to the issue of climate,” commented Murphy.

“It is just heartbreaking to me that this administration is so, so hostile to the issue of climate change that they feel it necessary to use as a litmus test for selections to top administration posts the outright denial of science on this important issue,” he said. “So we’ll continue to fight the president’s attacks on Paris and attacks on climate science every single day of the week.”

Standing Up to the President

Murphy said that it is “good news” that the Democratically controlled House of Representatives “is willing to stand up to the president on climate.” He pointed to the House’s action on the issue, including its recent passage, mostly along party lines, of the Climate Action Now Act to require the country to remain a party to the Paris agreement.

Although there are not enough votes to pass the legislation in the Senate, Murphy said that “at least it paints for the American people a picture of the big difference that exists right now on this issue in Washington.”

He added that there are a number of Republican senators who understand that it is bad policy and bad politics “to follow Trump down this hard line on climate.” However, Murphy said that Senate Majority Leader Mitch McConnell (R-Ky.) so far has kept them in line.

Progress Despite the White House

Murphy and others at the briefing also noted progress on climate change at state and local levels and in the private sector. Murphy said, for instance, that many companies in the U.S. Chamber of Commerce either are climate leaders or are moving toward “more responsible” climate policy, although the chamber itself has been “the chief climate denial cheerleader for most of the last decade.”

“As unfortunate as it was that our administration chose to suggest we are not in the Paris accord, I would argue much of the country believes we are.”Mindy Lubber, CEO and president of Ceres, a sustainability advocacy organization based in Boston, said that despite Trump’s plan to withdraw from the Paris accord, many people and groups in the country are still striving to adhere to the goals of the agreement. “As unfortunate as it was that our administration chose to suggest we are not in the Paris accord, I would argue much of the country believes we are. Perhaps not literally. They are not the ones that signed the piece of paper. But they are in there looking at getting to the goals of the Paris agreement, and I think we are making progress despite an administration [that] has tried to do otherwise.”

Lubber pointed to the We Are Still In coalition of about 3,800 organizations in the United States—including states, cities, and businesses—committed to meeting the Paris goals. Ceres is one of the groups coordinating the coalition effort, along with the World Resources Institute (WRI) and other environmental and civic organizations.

“Americans Have Suffered”

Andrew Light, a senior fellow in WRI’s climate program and former senior adviser on climate change at the U.S. State Department, said at the briefing that the biggest impact of the United States planning to withdraw from the accord is that “Americans have suffered.”

Light said that America once was “the undisputed global leader on aggressive climate action” but that now the United States has lost influence with some other countries—including countries where the United States has critical security interests—that are looking to withstand climate impacts and reduce the causes of climate change.

The plan to withdraw from the accord “is hurting American security, and it is hurting American competitiveness overseas in what is now a multi-trillion-dollar market that’s been created by the pledges that countries have put forward under the Paris Agreement,” he said.

—Randy Showstack (@RandyShowstack), Staff Writer

The Quaking, Shrinking Moon

Thu, 05/30/2019 - 11:43

Between 1969 and 1977, lunar seismometers at four Apollo landing sites recorded 28 shallow moonquakes. However, the data transmitted by those seismometers were low resolution by current standards, making it difficult to locate the moonquakes’ epicenters.

Decades later, analysis of high-resolution images taken by the Lunar Reconnaissance Orbiter Camera (LROC) “revealed a vast, global network of lobate fault scarps,” researchers wrote in a study published on 13 May in Nature Geoscience. These formations likely resulted from thrust faults left behind as the Moon shrank like a raisin because of its interior cooling. The new study presents compelling evidence that the Moon is still tectonically active.

Arrows point to one of thousands of lobate fault scarps discovered in Lunar Reconnaissance Orbiter Camera images. Credit: NASA/GSFC/Arizona State University/Smithsonian

Researchers used a new algorithm designed for sparse seismic networks to constrain the epicenter locations of these moonquakes. The relocation algorithm used uncertainties in the arrival time of body waves to generate a cloud of possible epicenter locations for each moonquake.

The team also created what might be the first shake map of the Moon, according to lead author Thomas Watters, a coinvestigator on the LROC and director of the Smithsonian Regional Planetary Image Facility at the National Air and Space Museum in Washington, D.C. The epicenters of eight of the quakes were located within 30 kilometers of fault scarps, a distance at which strong shaking likely occurred, according to the shake map.

The orbital timing of these quakes was also significant. Seven of them occurred at near apogee, when compression of the Moon is near its maximum and fault slip events are likely to occur, according to the study. The team concluded, on the basis of the nearness of the moonquakes to the thrust faults, along with the presence of regolith disturbance and boulder movement on and near the geologically young fault scarps, that the Moon is probably tectonically active.

“Overall, this is an interesting study because it presents evidence for a potential link between seismicity and faulting on a planetary body other than Earth,” Christian Klimczak, a structural geologist at the University of Georgia in Athens who was not involved with the study, wrote in an email.

Need for More Data, More Maps, More Research

Still, more data are needed “before we have the smoking gun” that the moonquakes and the lobate scarps are related, said Nicholas Schmerr, a coauthor on the study and a planetary seismologist at the University of Maryland in College Park.

Although these results illustrate an exciting discovery, they also show the need for putting modern seismometers on the Moon.Analyzing the Apollo era data on the shallow moonquakes shows that “not all of them are well above the noise,” Schmerr said. Therefore, although these results illustrate an exciting discovery that is the product of combining decades-old Apollo data with images collected by the LROC, they also show the need for putting modern seismometers on the Moon.

Some of the moonquakes “did not have a strong association with a lobate scarp,” Schmerr said. In the future, researchers want to investigate whether those quakes are instead associated with wrinkle ridges. However, they first need to create a comprehensive map of the ridges and better constrain the ages of those features, he said.

Researchers still need to find and image more of the faults, Watters said. This will help them better plan to avoid seismic activity on future extended missions. When humans are ready to build lunar outposts, having data on the locations of faults will also help scientists decide whether to place them in areas where strong shaking is unlikely or to create structures that can withstand the shaking, he said.

“With the recent landing on Mars of the InSight mission, we’ve shown that it’s possible to remotely land and operate a seismometer on another world, and it’s far easier (and faster) to get to the Moon than to Mars,” Paul Byrne, a planetary geologist at North Carolina State University in Raleigh who was not involved with the study, wrote in an email. “So hopefully we’ll see, within the next few years, more seismic data being collected for the Moon, which can be used to bolster this kind of work and tell us just how seismically active our nearest neighbor is,” he added.

—Rachel Crowell (@writesRCrowell), Science Writer

In Appreciation of AGU’s Outstanding Reviewers of 2018

Thu, 05/30/2019 - 11:42

Today in Eos, American Geophysical Union (AGU) Publications recognizes outstanding reviewers for their work in 2018. Honored reviewers were selected by the editors of each AGU journal.

Peer-reviewed literature plays an important role in advancing science. In addition, there is growing use of peer-reviewed literature in our legal systems and governments as a basis for regulations, policies, and laws. This literature also provides reliable scientific information for advisory groups such as the Intergovernmental Panel on Climate Change and the National Academies.

Quality peer review is thus a critical part of the social contract between science and society. As the uses for this literature have grown, so has the complexity of papers, which now typically include more authors bringing more techniques, data, simulations, and results.

This increase in complexity, in turn, has increased the challenge and role of reviewing. The outstanding reviewers listed here have all provided in-depth evaluations that greatly improved the final published papers, often over multiple rounds of revision.

Many Reviewers: A Key Part of AGU Journals

While we note these few outstanding reviewers, we also acknowledge the broad efforts by the many AGU reviewers in helping ensure the quality, timeliness, and reputation of AGU journals. In 2018, AGU received over 15,600 submissions (up from the 14,300 submissions received in 2017) and published nearly 6,600 articles (up from 6,400 in 2017). Many of these submissions were reviewed multiple times—in all, 17,242 reviewers completed 37,674 reviews in 2018 compared to the 34,000 reviews completed in 2017.

This has happened in the past year while every AGU journal worked to shorten the time from submission to first decision and publication or maintained already industry-leading standards. Several AGU journals regularly return first decisions within 1 month of submission, and most others now do so within 2 months. Reviewers represent a key part of this improvement.

Our thanks are a small recognition of the large responsibility that reviewers shoulder in improving our science and its role in society. Editorials (some already published, some upcoming), along with recognition lists, express our appreciation.

Additional Thanks

In addition, we are working to highlight the valuable role of reviewers through events at the Fall Meeting and other meetings.

We are extending subscription benefits to those reviewers who repeatedly provide quality reviews. Each reviewer also receives a discount on AGU and Wiley books. We will continue to work with the Open Researcher and Contributor Identification network (ORCID) to provide official recognition of reviewers’ efforts, so that reviewers receive formal credit there. To date we have over 49,000 ORCIDs linked to GEMS user accounts, compared to 39,000 at this time last year.

Getting Your Feedback

We are working to improve the peer-review process itself, using new online tools. We have designed a short questionnaire for reviewers to provide feedback and will send a link after each review is completed.

We value your feedback, including ideas about how we can recognize your efforts even more, help improve your experience, and increase your input on the science.

We look forward to hearing from you. If you’d like to respond directly, feel free to take our survey.

Once again, thanks!

—Matt Giampoala (mgiampoala@agu.org), VP, Publications, AGU; and Lisa Tauxe, Chair, AGU Publications Committee

 

 

 

 

 

 

Benjamin W. Abbott Brigham Young University Cited by JGR: Biogeosciences editors JGR: Biogeosciences

 

 

 

 

 

Nicholas Achilleos University College London Cited by JGR: Space Physics editors JGR: Space Physics

 

 

 

 

 

James D. Allan University of Manchester Cited by Minghua Zhang JGR: Atmospheres

 

 

 

 

 

Antoine Aubeneau Lyles School of Civil Engineering, Purdue University Cited by Martyn Clark Water Resources Research

 

 

 

 

Maxim D. Ballmer University College London; Institute of Geophysics, ETH Zurich; and Earth-Life Science Institute, Tokyo Institute of Technology Cited by Geochemistry, Geophysics, Geosystems editors Geochemistry, Geophysics, Geosystems

 

 

 

 

 

Sylvain Barbot University of Southern California Cited by Uri ten Brink JGR: Solid Earth

 

 

 

 

 

Luke Barnard University of Reading Cited by Space Weather editors Space Weather

 

 

 

 

 

Rebecca Bendick University of Montana Cited by Uri ten Brink JGR: Solid Earth

 

 

 

 

Ross A. Beyer Carl Sagan Center, SETI Institute; and NASA Ames Research Center Cited by Earth and Space Science editors Earth and Space Science

 

 

 

 

 

Daniele Bianchi University of California, Los Angeles Cited by Global Biogeochemical Cycles editors Global Biogeochemical Cycles

 

 

 

 

Peter Blossey University of Washington Cited by Journal of Advances in Modeling Earth Systems (JAMES) editors Journal of Advances in Modeling Earth Systems (JAMES)

 

 

 

 

 

Edoardo Borgomeo Environmental Change Institute, University of Oxford Cited by Earth’s Future editors Earth’s Future

 

 

 

 

 

Nicolas Brantut University College London Cited by Uri ten Brink JGR: Solid Earth

 

 

 

 

 

Maryjo Brounce University of California, Riverside Cited by Geochemistry, Geophysics, Geosystems editors Geochemistry, Geophysics, Geosystems

 

 

 

 

 

Tamma Carleton Energy Policy Institute at the University of Chicago Cited by Noah Diffenbaugh Geophysical Research Letters

 

 

 

 

 

Ingrid Cnossen British Antarctic Survey Cited by JGR: Space Physics editors JGR: Space Physics

 

 

 

 

 

Giacomo Corti Consiglio Nazionale delle Ricerche Cited by Tectonics editors Tectonics

 

 

 

 

 

Beth Covitt University of Montana Cited by Carol A. Stein Eos

 

 

 

 

 

Hugh Daigle University of Texas at Austin Cited by Uri ten Brink JGR: Solid Earth

 

 

 

 

 

Sylvia Genevieve Dee Rice University Cited by Valerie Trouet Geophysical Research Letters

 

 

 

 

 

Kristine DeLong Louisiana State University Cited by Paleoceanography and Paleoclimatology editors Paleoceanography and Paleoclimatology

 

 

 

 

 

Kerri Donaldson Hanna University of Central Florida and University of Oxford Cited by JGR: Planets editors JGR: Planets

 

 

 

 

 

Eric Dunham Stanford University Cited by Uri ten Brink JGR: Solid Earth

 

 

 

 

 

William H. Farmer U.S. Geological Survey Cited by Martyn Clark Water Resources Research

 

 

 

 

 

David Ferreira University of Reading Cited by Andy Hogg Geophysical Research Letters

 

 

 

 

Paul Fiedler Southwest Fisheries Science Center, National Oceanic and Atmospheric Administration Cited by Peter Brewer JGR: Oceans

 

 

 

 

 

Christian Frankenberg California Institute of Technology Cited by Joel Thornton Geophysical Research Letters

 

 

 

 

 

Daniel A. Frost University of California Cited by Jeroen Ritsema Geophysical Research Letters

 

 

 

 

 

Martin Füllekrug University of Bath Cited by Sana Salous Radio Science

 

 

 

 

 

Jason C. Furtado University of Oklahoma School of Meteorology Cited by Suzana J. Camargo Geophysical Research Letters

 

 

 

 

 

Eric L. Geist U.S. Geological Survey Cited by Uri ten Brink JGR: Solid Earth

 

 

 

 

P. Joseph Gibson Richard M. Fairbanks School of Public Health, Indiana University Cited by Gabriel Filippelli GeoHealth

 

 

 

 

 

Evan B. Goldstein University of North Carolina at Greensboro Cited by JGR: Earth Surface editors JGR: Earth Surface

 

 

 

 

 

Janet Green Space Hazards Applications LLC Cited by Space Weather editors Space Weather

 

 

 

 

Sjoerd Groeskamp School of Mathematics and Statistics, University of New South Wales Cited by Andy Hogg Geophysical Research Letters

 

 

 

 

 

Yves Gueguen École Normale Supérieure Cited by Uri ten Brink JGR: Solid Earth

 

 

 

 

 

Bo Guo University of Arizona Cited by Martyn Clark Water Resources Research

 

 

 

 

 

Angela Gurnell School of Geography, Queen Mary University of London Cited by Martyn Clark Water Resources Research

 

 

 

 

 

Christos Haldoupis University of Crete Cited by Gang Lu Geophysical Research Letters

 

 

 

 

 

Alexa J. Halford The Aerospace Corporation Cited by Fabio Florindo Reviews of Geophysics

 

 

 

 

 

Lars Hansen University of Oxford Cited by Uri ten Brink JGR: Solid Earth

 

 

 

 

Trevor Harris Defence Science and Technology Group, Australian Department of Defence; and University of Adelaide Cited by Sana Salous Radio Science

 

 

 

 

 

Michael Hartinger Virginia Polytechnic Institute and State University Cited by JGR: Space Physics editors JGR: Space Physics

 

 

 

 

 

Carynelisa Haspel Hebrew University of Jerusalem Cited by Minghua Zhang JGR: Atmospheres

 

 

 

 

 

Jonathan D. Herman University of California, Davis Cited by Martyn Clark Water Resources Research

 

 

 

 

 

Vladimir Ivanov Lomonosov State University Cited by Andrey Proshutinsky JGR: Oceans

 

 

 

 

 

C. Rhett Jackson University of Georgia Cited by Martyn Clark Water Resources Research

 

 

 

 

Catherine L. Johnson University of British Columbia, Vancouver; and Planetary Science Institute Cited by JGR: Planets editors JGR: Planets

 

 

 

 

 

Brian Kahn Jet Propulsion Laboratory, California Institute of Technology Cited by Minghua Zhang JGR: Atmospheres

 

 

 

 

 

Scott D. King Virginia Polytechnic Institute and State University Cited by Carol A. Stein Eos

 

 

 

 

 

Randolph Kirk U.S. Geological Survey Cited by Earth and Space Science editors Earth and Space Science

 

 

 

 

 

Angela N. Knapp Florida State University Cited by Global Biogeochemical Cycles editors Global Biogeochemical Cycles

 

 

 

 

 

Inga Monika Koszalka Stockholm University Cited by Meghan Cronin Geophysical Research Letters

 

 

 

 

 

Marina Kubyshkina Saint Petersburg State University Cited by JGR: Space Physics editors JGR: Space Physics

 

 

 

 

Robin Lacassin Institut de Physique du Globe de Paris, Centre National de la Recherche Scientifique Cited by Tectonics editors Tectonics

 

 

 

 

 

Jessica R. Lacy Pacific Coastal and Marine Science Center, U.S. Geological Survey Cited by Ryan Lowe and Robert Hetland JGR: Oceans

 

 

 

 

Carol Ladd Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration Cited by Nadia Pinardi JGR: Oceans

 

 

 

 

 

Jason Leach Canadian Forest Service, Natural Resources Canada Cited by Martyn Clark Water Resources Research

 

 

 

 

 

Olivier Lengliné Université de Strasbourg Cited by Uri ten Brink JGR: Solid Earth

 

 

 

 

 

Steven Lentz Woods Hole Oceanographic Institution Cited by Ryan Lowe and Marjy Friedrichs JGR: Oceans

 

 

 

 

 

Peirong Lin Princeton University Cited by M. Bayani Cardenas Geophysical Research Letters

 

 

 

 

 

Xiaohong Liu University of Wyoming Cited by Zhanqing Li JGR: Atmospheres

 

 

 

 

 

Ning Ma Institute of Tibetan Plateau Research, Chinese Academy of Sciences Cited by Martyn Clark Water Resources Research

 

 

 

 

 

Roger Marchand University of Washington Cited by Minghua Zhang JGR: Atmospheres

 

 

 

 

 

Raleigh L. Martin American Association for the Advancement of Science Cited by JGR: Earth Surface editors JGR: Earth Surface

 

 

 

 

 

Yukio Masumoto University of Tokyo Cited by Leo Oey JGR: Oceans

 

 

 

 

 

Sergey Matrosov Cooperative Institute for Research in Environmental Sciences Cited by Minghua Zhang JGR: Atmospheres

 

 

 

 

Astrid Maute High Altitude Observatory, National Center for Atmospheric Science Cited by JGR: Space Physics editors JGR: Space Physics

 

 

 

 

 

Vivian Menezes Woods Hole Oceanographic Institution Cited by Janet Sprintall Geophysical Research Letters

 

 

 

 

 

Benjamin B. Mirus U.S. Geological Survey Cited by Valeriy Ivanov and M. Bayani Cardenas Geophysical Research Letters

 

 

 

 

 

Hamed Moftakhari University of Alabama Cited by Earth’s Future editors Earth’s Future

 

 

 

 

 

Richard H. Moore NASA Langley Research Center Cited by Minghua Zhang JGR: Atmospheres

 

 

 

 

Timothy Morin College of Environmental Science and Forestry, State University of New York Cited by JGR: Biogeosciences editors JGR: Biogeosciences

 

 

 

 

 

Morgan Moschetti U.S. Geological Survey Cited by Gavin Hayes Geophysical Research Letters

 

 

 

 

Rolf Müller Institute of Energy and Climate Research, Forschungszentrum Jülich Cited by Bill Randel JGR: Atmospheres

 

 

 

 

 

Paul G. Myers University of Alberta Cited by Andrey Proshutinsky JGR: Oceans

 

 

 

 

Allison Myers-Pigg Memorial University of Newfoundland; and Marine Sciences Laboratory, Pacific Northwest National Laboratory Cited by JGR: Biogeosciences editors JGR: Biogeosciences

 

 

 

 

 

Takuma Nakamura Space Research Institute, Austrian Academy of Sciences Cited by JGR: Space Physics editors JGR: Space Physics

 

 

 

 

 

Frantisek Nemec Charles University Cited by JGR: Space Physics editors JGR: Space Physics

 

 

 

 

 

Binbin Ni Wuhan University Cited by Andrew Yau Geophysical Research Letters

 

 

 

 

Sidao Ni Institute of Geodesy and Geophysics, Chinese Academy of Sciences Cited by Uri ten Brink JGR: Solid Earth

 

 

 

 

 

Fabian Nippgen University of Wyoming Cited by Martyn Clark Water Resources Research

 

 

 

 

 

Kiwamu Nishida Earthquake Research Institute, University of Tokyo Cited by Jeroen Ritsema Geophysical Research Letters

 

 

 

 

 

Robert L. Nowack Purdue University Cited by Uri ten Brink JGR: Solid Earth

 

 

 

 

 

Maitane Olabarrieta University of Florida Cited by Robert Hetland JGR: Oceans

 

 

 

 

Yoshiharu Omura Research Institute for Sustainable Humanosphere, Kyoto University Cited by Gang Lu Geophysical Research Letters

 

 

 

 

 

Yuichi Otsuka Nagoya University Cited by Sana Salous Radio Science

 

 

 

 

 

Brianna Rita Pagán Ghent University Cited by JGR: Biogeosciences editors JGR: Biogeosciences

 

 

 

 

Simon Parry Centre for Ecology & Hydrology, United Kingdom; and Loughborough University Cited by Martyn Clark Water Resources Research

 

 

 

 

Sarah Perkins-Kirkpatrick Climate Change Research Centre, University of New South Wales Cited by Earth’s Future editors Earth’s Future

 

 

 

 

 

David Pitchford SES Cited by Space Weather editors Space Weather

 

 

 

 

 

Riwal Plougonven École Polytechnique Cited by Bill Randel JGR: Atmospheres

 

 

 

 

 

Yadu Pokhrel Michigan State University Cited by M. Bayani Cardenas Geophysical Research Letters

 

 

 

 

 

Jeffrey Priest Schulich School of Engineering, University of Calgary Cited by Uri ten Brink JGR: Solid Earth

 

 

 

 

 

Philip Pritchett University of California, Los Angeles Cited by Andrew Yau Geophysical Research Letters

 

 

 

 

 

Julianne D. Quinn University of Virginia Cited by Martyn Clark Water Resources Research

 

 

 

 

Patricia Quinn Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration Cited by Lynn Russell JGR: Atmospheres

 

 

 

 

 

Thomas Reimann Technische Universität Dresden Cited by Martyn Clark Water Resources Research

 

 

 

 

Lorraine Remer Joint Center for Earth Systems Technology, University of Maryland Baltimore County Cited by Joel Thornton Geophysical Research Letters

 

 

 

Catherine Rio Centre National de Recherches Météorologiques, Université de Toulouse; and Centre National de la Recherche Scientifique Cited by Journal of Advances in Modeling Earth Systems (JAMES) editors Journal of Advances in Modeling Earth Systems (JAMES)

 

 

 

 

 

Alexander Robel Georgia Institute of Technology Cited by Journal of Advances in Modeling Earth Systems (JAMES) editors Journal of Advances in Modeling Earth Systems (JAMES)

 

 

 

 

 

Justin S. Rogers Stanford University Cited by Ryan Lowe JGR: Oceans

 

 

 

 

 

Virginia Ruiz-Villanueva Institute for Environmental Sciences, University of Geneva Cited by Martyn Clark Water Resources Research

 

 

 

 

 

Christopher Russoniello Syracuse University Cited by Martyn Clark Water Resources Research

 

 

 

 

Alexander Ryzhkov Cooperative Institute for Mesoscale Meteorological Studies, University of Oklahoma Cited by Minghua Zhang JGR: Atmospheres

 

 

 

 

Andrew Sayer Goddard Earth Sciences Technology and Research; Universities Space Research Association; and NASA Goddard Space Flight Center Cited by Minghua Zhang JGR: Atmospheres

 

 

 

 

 

 

Brandon Schmandt University of New Mexico Cited by Uri ten Brink JGR: Solid Earth

 

 

 

 

 

Viktor Sergeev Saint Petersburg State University Cited by JGR: Space Physics editors JGR: Space Physics

 

 

 

 

 

Guoyin Shen Argonne National Laboratory Cited by Steven D. Jacobsen Geophysical Research Letters

 

 

 

 

Isla Ruth Simpson Climate and Global Dynamics Laboratory, National Center for Atmospheric Research Cited by Gudrun Magnusdottir Geophysical Research Letters

 

 

 

 

 

Isobel Simpson University of California, Irvine Cited by Minghua Zhang JGR: Atmospheres

 

 

 

 

 

Arvind Singh University of Central Florida Cited by M. Bayani Cardenas Geophysical Research Letters

 

 

 

 

 

Deepti Singh Washington State University Vancouver Cited by Suzana J. Camargo Geophysical Research Letters

 

 

 

 

 

Murugesu Sivapalan University of Illinois at Urbana-Champaign Cited by Martyn Clark Water Resources Research

 

 

 

 

 

Alexander Soloviev Nova Southeastern University Cited by Chidong Zhang JGR: Atmospheres

 

 

 

 

 

Mohamad Reza Soltanian University of Cincinnati Cited by Martyn Clark Water Resources Research

 

 

 

 

 

Paolo Sossi Institut de Physique du Globe de Paris Cited by Geochemistry, Geophysics, Geosystems editors Geochemistry, Geophysics, Geosystems

 

 

 

 

 

Laura A. Stevens Lamont-Doherty Earth Observatory, Columbia University Cited by Julienne Stroeve Geophysical Research Letters

 

 

 

 

Samantha Stevenson Bren School of Environmental Science and Management, University of California, Santa Barbara Cited by Meghan Cronin Geophysical Research Letters

 

 

 

 

 

Benjamin Sulman Environmental Sciences Division, Oak Ridge National Laboratory Cited by JGR: Biogeosciences editors JGR: Biogeosciences

 

 

 

 

 

Abigail L. S. Swann University of Washington Cited by Rose M. Cory Geophysical Research Letters

 

 

 

 

 

Nicoletta Tambroni University of Genoa Cited by JGR: Earth Surface editors JGR: Earth Surface

 

 

 

Adriaan J. (Ryan) Teuling Hydrology and Quantitative Water Management Group, Wageningen University and Research Cited by M. Bayani Cardenas Geophysical Research Letters

 

 

 

 

 

 

Jessica Tierney University of Arizona Cited by Paleoceanography and Paleoclimatology editors Paleoceanography and Paleoclimatology

 

 

 

 

 

Darin W. Toohey University of Colorado Boulder Cited by José D. Fuentes Eos

 

 

 

 

Tomoki Tozuka University of Tokyo and Japan Agency for Marine-Earth Science and Technology Cited by Leo Oey JGR: Oceans

 

 

 

 

 

 

Marissa Tremblay Scottish Universities Environmental Research Centre Cited by Geochemistry, Geophysics, Geosystems editors Geochemistry, Geophysics, Geosystems

  

 

 

 

Roderik van de Wal Institute for Marine and Atmospheric Research, Utrecht University Cited by Julienne Stroeve Geophysical Research Letters

 

 

 

 

 

 

Douwe Van Hinsbergen Utrecht University Cited by Tectonics editors Tectonics

 

 

 

 

 

Vytenis M. Vasyliunas Max Planck Institute for Solar System Research Cited by JGR: Space Physics editors JGR: Space Physics

 

 

 

 

 

Marissa F. Vogt Boston University Cited by Andrew Yau Geophysical Research Letters

 

 

 

 

 

Dong-Ping Wang Stony Brook University Cited by Leo Oey JGR: Oceans

 

 

 

 

 

Kelin Wang Pacific Geoscience Centre, Geological Survey of Canada Cited by Geochemistry, Geophysics, Geosystems editors Geochemistry, Geophysics, Geosystems

 

 

 

 

 

Rongsheng Wang University of Science and Technology of China Cited by JGR: Space Physics editors JGR: Space Physics

 

 

 

 

Shengji Wei Earth Observatory of Singapore, Asian School of the Environment, Nanyang Technological University Cited by Gavin Hayes Geophysical Research Letters

 

 

 

 

Ensheng Weng Center for Climate Systems Research, Columbia University; and NASA Goddard Institute for Space Studies Cited by Rose M. Cory Geophysical Research Letters

 

 

 

William Wieder National Center for Atmospheric Research and Institute of Arctic and Alpine Research, University of Colorado Cited by JGR: Biogeosciences editors JGR: Biogeosciences

 

 

 

 

 

Earle R. Williams Massachusetts Institute of Technology Cited by Zhanqing Li JGR: Atmospheres

 

 

 

 

 

Ryan Woosley Massachusetts Institute of Technology Cited by Global Biogeochemical Cycles editors Global Biogeochemical Cycles

 

 

 

 

Zhiyong Xiao China University of Geosciences, Wuhan; and Macau University of Science and Technology Cited by JGR: Planets editors JGR: Planets

 

 

 

 

Shiqing Xu National Research Institute for Earth Science and Disaster Resilience Cited by Uri ten Brink JGR: Solid Earth

 

 

 

 

 

Huije Xue School of Marine Sciences, University of Maine Cited by Marjy Friedrichs and Robert Hetland JGR: Oceans

 

 

 

 

 

Elowyn M. Yager University of Idaho Cited by JGR: Earth Surface editors JGR: Earth Surface

 

 

 

 

William Yeck National Earthquake Information Center, U.S. Geological Survey Cited by Gavin Hayes Geophysical Research Letters

 

 

 

Hannah Zanowski Joint Institute for the Study of the Atmosphere and Ocean, University of Washington Cited by Janet Sprintall Geophysical Research Letters

 

 

 

 

 

 

Stephanie E. Zick Virginia Polytechnic Institute and State University Cited by Chidong Zhang JGR: Atmospheres

 

 

 

 

 

Robert W. Zimmerman Imperial College London Cited by Uri ten Brink JGR: Solid Earth

 

 

2018 Cited Referees Not Pictured

 

Gina DiBraccio NASA Goddard Space Flight Center Cited by Andrew Dombard Geophysical Research Letters

 

Ian Joseph Hewitt University of Oxford Cited by Julienne Stroeve Geophysical Research Letters

 

Frances C. Moore University of California, Davis Cited by Noah Diffenbaugh Geophysical Research Letters

 

Cory Morin University of Washington Cited by Gabriel Filippelli GeoHealth

 

Daniele Pedretti Università degli Studi di Milano Cited by Martyn Clark Water Resources Research

 

Barbara Romanowicz Collège de France, Paris; and University of California, Berkeley Cited by Uri ten Brink JGR: Solid Earth

 

Jack Scudder University of Iowa Cited by JGR: Space Physics editors JGR: Space Physics

 

Liangsheng Shi Wuhan University Cited by Martyn Clark Water Resources Research

 

Satoshi Takahama École Polytechnique Fédérale de Lausanne Cited by Lynn Russell JGR: Atmospheres

 

Kluge Tobias University of Heidelberg Institute of Environmental Physics Cited by Geochemistry, Geophysics, Geosystems editors Geochemistry, Geophysics, Geosystems

 

Hengmao Tong China University of Petroleum–Beijing Cited by Tectonics editors Tectonics

 

Jingfeng Wang Georgia Institute of Technology Cited by Valeriy Ivanov Geophysical Research Letters

 

Hui Wu East China Normal University Cited by Lei Zhou JGR: Oceans

Answer to California Landscape Riddle Lies Underground

Thu, 05/30/2019 - 11:41

A sharp divide lies in Northern California. Near the coast, moderate temperatures and plentiful annual rainfall give rise to a lush forest. But then there’s an abrupt break—suddenly, the forest opens into a wide savanna, a grass-dominated biome typical of drier climates. These two areas experience nearly identical temperatures and rainfall. What accounts for the sudden shift to open grassland far out of its normal climatic range? A team of researchers looked below the surface for answers.

These two landscapes are in a Mediterranean climate: Precipitation falls in winter, and the Sun shines most intensely over a dry summer. That means that plants don’t have access to rain when they most need it. In climates like this, plants depend on water stored in the ground during the wet season to make it through dry times.

The Eel River passes through an oak savanna. Credit: Jesse Hahm

Hahm et al. propose that the sharp landscape change in Northern California is chiefly due to differences in the critical zone, the layer spanning from the top of the vegetation canopy downward to fresh bedrock, where plants can access stored water. The critical zone includes the soil, as well as weathered bedrock that contains clay and has been fractured and cracked enough to store water.

The researchers monitored water dynamics at representative sites in the forested and savanna regions, drilling boreholes and installing wells in each area and remotely sensing vegetation patterns across the larger landscapes. They found that the vegetation differences could be linked to the type of rock beneath each region, in particular to the depth and extent of weathering of the bedrock.

The forested swath grew over a belt of sedimentary bedrock that is weathered up to 30 meters deep. During the rainy part of the year, water finds its way deep into the weathered bedrock and remains through the dry season, ready for plants to draw up as they need it.

The dry savanna landscape, in contrast, lies over bedrock of similar composition that has been severely mechanically sheared during tectonic processes such that the rocks do not weather easily and may even seal up their own cracks. Fresh, unweathered bedrock rests just 2 to 4 meters below the surface. During the rainy winter, the critical zone is saturated with water to the point of flooding. In the summer, it does not take long for the thin critical zone to dry out. The grasses and deciduous oaks of the savanna are better adapted to survive in the floods and dryness of this zone than the evergreen trees of the neighboring forest, but there are also a few pockets of sandstone within the savanna that support evergreens just like the lush forest nearby.

According to the researchers, bedrock can form the base of an ecosystem, even defying dominant factors like climate. The plants and animals that depend on a landscape, as well as the humans who live and use water in the area, rely on the interactions of rock and water that shape their world. (Water Resources Research, https://doi.org/10.1029/2018WR023760, 2019)

—Elizabeth Thompson, Freelance Writer

Gauging in the Rain

Thu, 05/30/2019 - 11:40

How much did we get today?

It seems like a simple question to answer after a rainy day or a rainstorm.

Putting a bucket or other container out to measure the amount of rainfall is a gauging method that may be as old as agriculture itself and, at least in India, was known at least 2 millennia ago: “The quantity of rain that falls in the country of Jángala is 16 dronas; half as much more in moist countries,” it says in the Arthashastra, a Sanskrit treatise on politics, economics, and military strategy. The text goes on to instruct, “According as the rainfall is more or less, the superintendent shall sow the seeds which require either more or less water.”

In today’s measurements, a drona represents about 50 millimeters of precipitation, according to a history of rain gauges by Ian Strangeways found in the journal Weather. But did those ancient instruments, to be positioned “in front of the storehouse” according to the Arthashastra, always record the right amount of dronas? Great care has to be taken lest gauges of that type are fooled by water splashing in or out or by wind preventing rain from falling nicely and vertically into a round opening.

At the annual General Assembly of the European Geosciences Union in Vienna, Austria, in April, three methods were discussed to improve or extend the measurement of rainfall. They nicely complemented one another: One would work best in an urban environment, one would work in an agricultural setting, and one would work out at sea.

Gauging Umbrellas

“There are no good places for rain gauges in cities.”In urban areas, measuring rainfall is a pain, said Marie-Claire ten Veldhuis, a hydrometeorologist at Delft University of Technology (TU Delft) in the Netherlands. “All the rain gauges we use now are way outside towns, because they have to be far from buildings. There are no good places for rain gauges in cities.”

That doesn’t mean there are no rain gauges there: lots of people like to install their own weather stations in their yard or on their roof. And these could be useful.

“But you need a great many of them to establish the pattern of rainfall in the city,” ten Veldhuis said.

Information from rain gauges would be very valuable for city authorities, for instance, to anticipate or possibly prevent flooding.

To help gather this information, ten Veldhuis’s group in the Water Management Department at TU Delft is developing portable rain gauges of a kind most people presumably wouldn’t mind carrying around for science—umbrella-mounted ones. A prototype shown in Vienna sports a piezoelectric sensor on its top. The umbrella would report its data and GPS-calculated position to a central server, so that city authorities would know how much rain is really falling at any given moment at many locations.

Live demo of rain measuring umbrella at #MacGyver session at #EGU19 @EuroGeosciences @EGU_HS pic.twitter.com/s7uI8arJsF

— Rolf Hut (@RolfHut) April 8, 2019

For the first feasibility study, the umbrella was installed in an open area, with a traditional rain gauge nearby, to see if counting rain droplets impacting the sensor would lead to a correct estimate of the amount of precipitation. As an alternative to drop counting, the circuitry also detected the general sound level generated by the rain.

In the first trial, both techniques worked, although both had issues. During counting, small drops would go undetected. With the sound measurement, wind noise could be a problem.

All in all, the measurements were most reliable when drops were counted in heavier rain. That makes the method already suitable for cities with a tropical climate, ten Veldhuis noted. “In many of those countries, alternatives like high-resolution radar aren’t available yet.” Her group is working with a number of cities in Africa, such as Dar es Salaam in Tanzania, Kumasi and Accra in Ghana, and Narok in Kenya, to develop “sensor-based weather services,” she said. “These umbrellas could be very useful there.”

The Delft group is working with NASA to turn the rain-gauging umbrellas into a citizen science project.

Radioactive Rain

Even those who would gladly carry an umbrella for science might recoil at being asked to help measure radioactivity after a rainstorm. The experiment isn’t as dangerous as it might sound.

Every bout of precipitation brings a tiny uptick in gamma radiation from the ground, and that fact can be exploited for gauging purposes, said Marica Baldoncini, a physicist at the University of Ferrara and the National Institute of Nuclear Physics in Italy.

The gamma radiation boost results from the transport of a series of radioactive elements first up and then down. The process starts with uranium and thorium deep in the earth. In a sequence of radioactive decay steps, a number of other unstable elements are produced, among which is radium, which produces radon, which as a gas escapes into the atmosphere. There it decays into unstable isotopes of lead and bismuth. It’s these isotopes that enter into the hydrologic cycle.

“Radon is chemically inert,” Baldoncini explained, “but when it decays, the daughter products are typically produced in a positively charged state and for that reason have high chemical reactivity. They attach to aerosols.”

Within clouds, these aerosols are “scavenged” by water drops circulating in them and are eventually brought to the ground when the drops fall as rain. There, the decay of the lead and bismuth produces the gamma radiation that Baldoncini has been measuring.

“You see a sharp increase in the count rate, and the height of that peak is essentially proportional to the amount of water that is going to the ground,” she said.

Baldoncini’s goal is to turn this phenomenon into an alternative way to gauge rainfall, one that would work particularly well in rural areas, in combination with satellite measurements. From satellites, falling rain itself is not detected, but the water content of soil is. Indirectly, these data can deliver an accurate estimate of rainfall, except when other sources of moisture are active, such as irrigation. A ground-based rain gauge that records spikes of gamma radiation above the natural background could fill that gap and would also need less human intervention than a conventional gauge.

At the Vienna meeting, Baldoncini reported measurements of a dozen rainfall events with both conventional rain gauges and sodium iodide scintillators that detect gamma radiation. This comparison allowed her to develop an algorithm to connect both measurements.

The gamma ray gauge could both improve local precipitation information and make satellite data more useful.In Baldoncini’s experiments, the hydrology of the location, an agricultural field near Budrio in the north of Italy, was exactly known. “There were people taking care of all that information, such as the amount of water added, the frequency, when the plants were sown. Typically, you don’t know this, because people don’t maintain a database about the irrigation frequency.”

Once the algorithm is fully developed, the gamma ray gauge could both improve local precipitation information and make satellite data more useful. “We plan to merge all the information from this proximal remote sensing that works at the scale of half a hectare with satellite measurements. And then [we] can tell in the satellite data: this is irrigation, and this is precipitation.”

Drops and Bubbles

If, eventually, cities are covered by umbrellas and the countryside is covered by gamma ray detectors, that leaves the world’s oceans as an underserved area for rain gauges.

Conventional gauges are used on islands, of course, and it is possible to mount them on buoys. But in the latter case, they are easily damaged by waves and are even sometimes stolen by the crews of passing ships, said Dimitrios Galanis, an undergraduate student at the School of Civil Engineering of the National Technical University of Athens, Greece.

Underwater rain gauges would record both the noise that raindrops make as they strike the water surface and the noise that emanates from the air bubbles that the raindrops create.Instead, meteorologists would like to develop rain gauges for use underwater. These instruments would be essentially hydrophones, anchored to the seafloor. They would record both the noise that raindrops make as they strike the water surface and also the noise that emanates from the air bubbles that the raindrops create. These bubbles resonate at specific frequencies depending on their size.

Although the idea is straightforward, making the connection between noise and rainfall rate turns out to be difficult, Galanis said. And the work he presented at the Vienna meeting hasn’t cracked the problem just yet.

Galanis analyzed published data from measurements in the Gulf of Mexico from both sound and conventional rain gauges, extracting two statistical characteristics from them, the power spectrum and the climacogram, to see which one would correlate best with the actual rainfall rate.

The power spectrum is a widely used measure and can be visualized as a plot of the relative strength of different frequencies in the sound. The climacogram is less common and plots whether sound is more constant or variable as it is averaged over shorter or longer timescales.

So far, the climacogram seems to work best.

“But it is still very preliminary,” Galanis cautioned.

Rain gauging may have progressed a great deal since precipitation was measured in dronas, but so far it hasn’t quite gotten its sea legs.

—Bas den Hond, Freelance Writer

Ammonia Ice Deposits on Pluto Hint at Recent Cryovolcanism

Wed, 05/29/2019 - 18:02

A deep red scar on Pluto’s surface may be spraying ammonia-rich water onto surrounding ice. A study published today in Science Advances presents the first detection of ammonia’s chemical signature on the reddish ices west of Pluto’s “heart.”

New Horizons measured the distribution of ammonia-rich ice near Elliot crater. (a) The hemisphere of Pluto seen by New Horizons on its 14 July 2015 flyby. (b) A close-up of Elliot crater to the west of Sputnik Planitia and the bright red slash of Virgil Fossa. (c) The distribution of (left color legend) ammonia-rich water ice and (right color legend) other ammonia-bearing molecules near Virgil Fossa. Dark blue pixels indicate areas with the highest concentrations of ammonia overlapping with water ice signatures, and yellow pixels indicate the lowest concentrations. Each pixel is 2,700 meters on each side. Credit: Dalle Ore et al., 2019, https://doi.org/10.1126/sciadv.aav5731

The researchers believe that the ammonia-rich water originates below Pluto’s surface. “The most likely emplacement mechanism…is that the ammonia–water liquid mixture found its way from the interior and was ‘sprayed’ in a neighborhood of about 200 kilometers from each ‘vent,’” lead author Cristina Dalle Ore, an astrophysicist at the SETI Institute in Mountain View, Calif., told Eos. “We call this mechanism cryovolcanism.”

“Ammonia mixed in water acts like an antifreeze,” she explained, but is short-lived once it is exposed on a planetary surface. Because of that, this detection of ammonia-rich water ice can tell scientists how old Pluto’s surface is, what lies beneath, and how the two interact.

Valley of Ammonia and Ice

Dalle Ore and her team analyzed spectral data of Pluto’s surface collected by NASA’s New Horizons spacecraft when it flew through the Pluto system on 14 July 2015. The researchers focused their analysis on the Virgil Fossae, a series of deep valleys near Elliot crater. These scars are tinted a dark brown-red by substantial amounts of non-ice material and are thought to be the result of geologic activity.

New Horizons measured the near-infrared spectrum of Pluto’s surface at a spatial resolution of 2,700 meters per pixel. The researchers analyzed the spectra of a 5,000-square-kilometer stretch of land encompassing Virgil Fossa, the area’s most prominent valley.

They found several patches that had strong signatures of ammonia ice overlapping the signature of water ice. Other nearby areas also showed evidence of ammonia-bearing molecules without water ice being present. The spatial distribution of ammonia suggests that it came from several cryovolcanic vents in and near Virgil Fossa, the team said.

What’s more, the ammonia must have been deposited on Pluto’s surface relatively recently. “The ammonia molecule is fragile,” Dalle Ore explained, especially when mixed into water. “When exposed to ultraviolet or cosmic ray irradiation, [it] lasts only on the order of millions of years, a short time compared to the age of Pluto itself.”

“Having found ammonia mixed in water ice on the surface of Pluto implies that in the fairly recent past it was emplaced there,” she said.

What Lies Beneath

Despite Pluto’s frigid surface, a balmy –230°C, liquid water can still exist beneath its surface. Radioactive decay of its rocky core heats Pluto from the inside. Chemical mix-ins could also lower the ocean’s freezing temperature.

This new discovery supports the existing theory that “there might be a submerged ocean, or at least some pockets of liquid water, under Pluto’s icy crust in correspondence of Sputnik Planitia,” Dalle Ore said. “We still don’t know the extent of the ocean, if it is a large body of water, or a few disjointed ones.”

—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer

Pacific Carbon Uptake Accelerating Faster Than Expected

Wed, 05/29/2019 - 12:05

The massive Pacific Ocean breathes slowly, exposing its deepest waters to the atmosphere only every few thousand years. Still, its sheer size enables it to absorb roughly 10% of global anthropogenic carbon dioxide emissions, as much as or more than any other ocean on the planet. New research shows that the Pacific has ramped up its carbon dioxide uptake in recent decades, in large part because of shifting ocean currents.

In the new study, Carter et al. took advantage of 3 decades of ocean observations in the Pacific Ocean conducted by the Global Ocean Ship-Based Hydrographic Investigations Program (GO-SHIP) oceanography survey. GO-SHIP scientists sail the world’s oceans collecting measurements of dissolved inorganic carbon, which serves as an indicator of how much carbon dioxide the water has absorbed from the atmosphere. GO-SHIP also measures other factors driving the exchange of carbon dioxide between the air and the sea surface, such as the availability of nutrients that feed carbon-capturing photosynthetic algae.

The team compared the Pacific Ocean’s absorption of carbon dioxide between two decades: 1995 to 2005 and 2005 to 2015. Between the first and second decades, carbon dioxide accumulation increased from 8.8 to 11.7 petagrams, or gigatons, of carbon. Although the biggest increase in carbon dioxide was due to mounting levels of the greenhouse gas in the atmosphere, variations in the rate of accumulation depended on the behavior of a system of ocean currents called the Southern Hemisphere Subtropical Gyre, they found.

This large counterclockwise eddy, which circulates between South America and Australia, appears to be responsible for the unexpected acceleration in carbon dioxide accumulation, the team writes. Careful, continued decadal surveys of the ocean’s interior are key to tracking ocean carbon in the future and understanding the ocean’s role in climate change, they say. (Global Biogeochemical Cycles, https://doi.org/10.1029/2018GB006154, 2019)

—Emily Underwood, Freelance Writer

Big Data Help Paint a New Picture of Trace Element Cycling

Wed, 05/29/2019 - 12:00

Although trace metals such as iron, copper, and zinc occur in only extremely low concentrations in the world’s oceans, they play an essential role in regulating photosynthesis and the global carbon cycle. But the difficulties inherent in measuring such minute concentrations, as well as the large uncertainties that exist regarding micronutrients’ sources and sinks—including their uptake and release from particulate phases—have made it challenging for scientists to quantify these complex biogeochemical cycles.

Now Ohnemus et al. present a novel conceptual framework for interpreting and understanding particulate trace metal data. Using extensive measurements of trace element distributions extracted from GEOTRACES biogeochemical data sets, the researchers show that simple statistical regressions—the conventional approach for modeling ocean particulate distributions—don’t accurately represent most trace metal cycles in the South Pacific and North Atlantic Oceans. They then demonstrate how alternative statistical techniques such as factor analysis, which allows scientists to examine biogeochemical processes that affect multiple trace elements at the same time, are much more effective at meaningfully interpreting large data sets.

The results indicate that although no two trace metals respond in the same way to the processes controlling their cycling, key processes such as biological uptake and remineralization do affect groups of trace elements in predictable ways. The factor analysis is especially successful at demonstrating shared associations, such as the increasing coaccumulation of copper, iron, and lanthanum with depth, as well as a concurrent accumulation of iron and nickel just below the South Pacific’s local oxygen minimum zone.

Collectively, these techniques paint a much clearer picture of how trace metals cycle through the world’s oceans and help illuminate the suite of interacting biogeochemical processes that affect multielement distributions. In the current era of burgeoning big data, these types of analyses are crucial for learning how to maximize the information that can be extracted from GEOTRACES and other large data sets. (Global Biogeochemical Cycles, https://doi.org/10.1029/2018GB006145, 2019)

—Terri Cook, Freelance Writer

Australia–New Zealand Plan for Future Scientific Ocean Drilling

Wed, 05/29/2019 - 11:52

A multidisciplinary community workshop has defined scientific themes and challenges for the next decade (2023–2033) of scientific ocean drilling using the capabilities of current and anticipated platforms of the International Ocean Discovery Program (IODP).

The workshop, attended by 75 mostly early-career and midcareer participants from Australia, New Zealand, Japan, and the United States, featured nine keynote presentations. Working groups identified important themes and challenges that are fundamental to understanding the Earth system and are addressable only by scientific ocean drilling.

IODP is the largest international program in the ocean and Earth sciences and among the largest international scientific research programs in any discipline. IODP explores Earth’s history and dynamics using oceangoing research platforms to recover geological, geobiological, and microbiological information preserved in seabed sediment and rock and to monitor subseafloor environments through the global ocean.

Australia and New Zealand are 2 of 23 member nations of IODP—led by the United States, Japan, and Europe—and participate via the Australian–New Zealand IODP Consortium (ANZIC). ANZIC comprises 16 universities and four publicly funded research agencies in the two countries.

The ANZIC Ocean Planet Workshop program was built around five scientific themes: Biosphere Frontiers, Earth Dynamics: Core to Crust, Global Climate, Natural Hazards, and Ocean Health Through Time.The ANZIC Ocean Planet Workshop program was built around five scientific themes: Biosphere Frontiers, Earth Dynamics: Core to Crust, Global Climate, Natural Hazards, and Ocean Health Through Time. Workshop sessions focused on these themes and 19 associated scientific challenges. Underpinning the themes and challenges are legacy samples and data, technology, engineering, education, public outreach, big data, and societal impact.

Although all challenges are important, the asterisks that follow denote those of particular relevance and interest to ANZIC.

Biosphere Frontiers addresses the habitable limits for life*; the composition, complexity, diversity, and mobility of subseafloor communities*; the sensitivity of ecosystems to environmental changes; and how the signatures of life are preserved through time and space*.

Earth Dynamics: Core to Crust encompasses the controls on the life cycle of ocean basins and continents*; how the core and mantle interact with Earth’s surface*; the rates, magnitudes, and pathways of physicochemical transfer among the geosphere, hydrosphere, and biosphere*; and the composition, structure, and dynamics of Earth’s upper mantle.

Global Climate entails coupling between the climate system and the carbon cycle; the drivers, rates, and magnitudes of sea level change in a dynamic world*; the extremes, variations, drivers, and impacts of Earth’s hydrologic cycle*; and cryosphere dynamics*.

Natural Hazards involves the mechanisms and periodicities of destructive earthquakes*; the impacts of submarine and coastal volcanism; the consequences of submarine slope failures for coastal communities and critical infrastructure*; and the magnitudes, frequencies, and impacts of natural disasters*.

Ocean Health Through Time comprises the ocean’s response to natural perturbations in biogeochemical cycles*; the lateral and vertical influence of human disturbance on the ocean floor; and the drivers and proxies of evolution, extinction, and recovery of life*.

A workshop report is in preparation, to be made available on the ANZIC website. This workshop is one of several held in 2019 by IODP member nations and consortia. Together, these workshops aim to formulate the next decadal science plan for scientific ocean drilling, which in turn will guide the focused planning of specific drilling, logging, and monitoring projects.

—Millard F. Coffin (mike.coffin@utas.edu.au), Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia; Joanna Parr, Commonwealth Scientific and Industrial Research Organisation, North Ryde, New South Wales, Australia; and Leanne Armand, ANZIC Office, Australian National University, Canberra, ACT, Australia

Join the Effort to Improve the Health of Our Oceans

Tue, 05/28/2019 - 16:47

Susan Lozier, AGU’s President-elect, encapsulated the forward-looking spirit and dialogue of global ocean experts earlier this month:

As an oceanographer, I view the upcoming United Nations Decade of Ocean Science for Sustainable Development as an incredibly important opportunity for the global community to focus on the health of Earth’s oceans. Many recent studies have revealed the negative effects humans have had on the oceans, from the sea surface to the deepest trenches. I look forward to learning how our collective scientific understanding, research, and innovation, discussed at the first Global Planning Meeting in Copenhagen, will help advance ocean sustainability. 

From 13 to 15 May, I was fortunate to attend the first Global Planning Meeting convened by the Intergovernmental Oceanographic Commission (IOC) of the United Nations Educational, Scientific and Cultural Organization (UNESCO) in preparation for the United Nations Decade of Ocean Science for Sustainable Development, 2021–2030. It was hosted by the National Museum of Denmark in Copenhagen. Also in attendance was Margaret Leinen, AGU past president and director of the Scripps Institution of Oceanography at the University of California, San Diego.Our collective goal was to find concrete ways that key stakeholders might work across disciplines and sectors to achieve the decade’s six key societal objectives that align perfectly with AGU’s mission.

The meeting aimed to present “a once-in-a-lifetime opportunity to deliver scientific knowledge, foster technological innovation, and build capacity to achieve the 2030 Agenda and reverse the decline of ocean health.” The meeting brought together approximately 200 thought leaders from around the world, who discussed issues as diverse as ocean science and technology, ocean policy and sustainable development, the role of business and industry in ocean conservation, and the interplay of nongovernmental organizations and civil society. Our collective goal was to find concrete ways that key stakeholders might work across disciplines and sectors to achieve the decade’s six key societal objectives that align perfectly with AGU’s mission of science for the benefit of humanity:

a safe ocean a sustainable and productive ocean a transparent and accessible ocean a clean ocean a healthy and resilient ocean a predicted ocean

I found the meeting incredibly inspirational—there were excitement, passion, and hope that significant progress can be made within a decade, through science, to ensure a healthy, resilient, safe ocean for all. This spirit of collaboration was summed up by Craig McLean, acting chief scientist and assistant administrator of the National Oceanic and Atmospheric Administration, who spoke of the importance of partnerships “to do more together than we ever could alone.”

These themes from the meeting especially resonated with me:

the need for a robust, diverse research agenda—drawing upon the knowledge of those working in the natural and physical sciences, social sciences, and indigenous and traditional knowledge—to best address the challenges facing the world’s oceans the need for mechanisms that encourage cooperation and innovative problem solving that break down traditional silos of expertise the imperative to have a better understanding of ecosystem restoration that works in concert with Earth observation systems to help recognize, monitor, and respond to critical environmental “tipping points” the need for integrated systems to disseminate ocean data and information to the public and key decision makers at all levels: local, regional, national, and global the imperative to build and develop a broad bench of talented experts who can interpret and share important conclusions, resources, technology, and infrastructure a pledge to keep the momentum that was initiated at the meeting going beyond 2030

This is an “all hands on deck” moment. I hope you take up this challenge and join the global science community in this effort to improve the health of our oceans.The challenges facing the world’s oceans can seem insurmountable. Thus, the collaboration of researchers across disciplines and with a diversity of communities will be essential to realize the promise and hope from transformations envisioned by the United Nations Decade of Ocean Science for Sustainable Development. AGU members are already contributing to this effort. For example, AGU past president Margaret Leinen and The Oceanography Society president, Martin Visbeck, are deeply involved in the IOC executive planning group. AGU members can also take part in regional workshops and stakeholder forums in which you will have the opportunity to engage and share your ideas about the design and planning of the decade. This is an “all hands on deck” moment. I hope you take up this challenge and join the global science community in this effort to improve the health of our oceans.

—Chris McEntee (agu_execdirector@agu.org), Executive Director/CEO, AGU

Mapping Subglacial Meltwater Channels

Tue, 05/28/2019 - 12:29

The bottoms of glaciers are riddled with conduits that drain meltwater and form hidden lakes and rivers. Scientists know these subglacial tunnels affect the speed at which glaciers slide, but the process is poorly understood because the channels are so hard to access. Now the first study of a real conduit beneath a glacier in Svalbard, Norway, reveals that the friction exerted on the water within the channel is orders of magnitude higher than previously thought.

Subglacial conduits affect the speed at which ice sheets slide in complex ways, including increasing the resistance of the surface glaciers travel over and lubricating their flow with water. Computer models need high-resolution data on a channel’s roughness, width, and curvature to accurately simulate these dynamics, but such data usually aren’t available because conduits are buried under thick slabs of ice.

To address that gap, Chen et al. mapped out a section of a real conduit beneath Hansbreen glacier in the ice archipelago of Svalbard. The conduit has an accessible outlet, so the researchers could climb inside and take photographs. They used them to build a 3-D computer model of its interior, including a 10-meter section of the conduit at millimeter-scale resolution and a less detailed, 125-meter-long section.

The Hansbreen conduit travels through a jumble of sharp rocks, widens and narrows, and makes several turns, a measure known as sinuosity. Using their detailed, 3-D model of the channel, the researchers ran computer simulations of the friction between the conduit and water flowing within it and found it was 1 to 2 orders of magnitude higher than estimates typically used in such studies.

In the past, researchers calculating how much resistance such conduits present to the water flowing through them have focused on the channels’ surface roughness, paying little attention to changes in conduit sinuosity or variations in width. But these neglected factors were far more important than roughness in generating resistance, the team found.

Together, the variations in channel width and sinuosity contributed 94% of the total friction between the water and conduit. The findings suggest that future glaciology models must account for how subglacial channels widen, narrow, and meander if they are to accurately predict how ice sheets slide and melt. (Geophysical Research Letters,  https://doi.org/10.1029/2018GL079590, 2018)

—Emily Underwood, Freelance Writer

Deciphering the Fate of Plunging Tectonic Plates in Borneo

Tue, 05/28/2019 - 12:24

Walking around Kota Kinabalu, the capital of the Malaysian state of Sabah in northern Borneo, one cannot help noticing the imposing bulk of Mount Kinabalu. Rising to an elevation of 4,095 meters (13,435 feet), it is among the highest mountains in Southeast Asia; it towers over the surrounding Crocker Range (Figure 1), which reaches higher than 2,000 meters.

Fig. 1. Map of Sabah showing topography and bathymetry in the background. Yellow and red squares indicate CMG-6TD and CMG-3ESPD seismic sensors, respectively, deployed by the nBOSS research team. The top right inset shows the location of Malaysia (green), with the blue lines depicting the tectonic plate boundaries. The top left inset is a close-up of the black rectangle, which shows the Maliau Basin (MB). CR = Crocker Range; MK = Mount Kinabalu.

Mount Kinabalu is made of granite that was emplaced within Earth’s crust between 7 and 8 million years ago [Cottam et al., 2010, 2013]. The mountain is a sheeted laccolith-like body; that is, it initially formed when a mass of magma intruded between two existing rock strata, causing the overlying layers to rise into a dome shape. After the granite was emplaced, it cooled rapidly; scientists have interpreted this cooling as a reflection of both the granite’s adjustment to ambient crustal temperatures and its relatively rapid exhumation toward Earth’s surface. The processes responsible for this rapid cooling and how this granitoid body rose so quickly to such spectacular heights remain enigmatic.

Mount Kinabalu is not the only puzzling geological landform in Sabah. Travel across the Crocker Range to the southeast of the state, and you will encounter circular basins that rise up from the surrounding landscape. The most spectacular of these is the Maliau Basin (Figure 1), which is around 30 kilometers in diameter and is encircled by an imposing ridge up to 1,500 meters high. The basin’s shape, clearly visible in satellite imagery and digital elevation maps, may at first suggest an impact crater, but closer inspection reveals that the interior contains a thick sequence of river delta sediments that were deposited at sea level 10–15 million years ago. What caused the uplift of southeast Sabah and the preceding 10 million years of subsidence, and how were these unusual basins formed?

Mount Kinabalu towers over Kota Kinabalu, the capital of the Malaysian state of Sabah in northern Borneo. Credit: Amy Gilligan

The answers to these questions may be found in the postsubduction setting of northern Borneo. As recently as 5 million years ago, subduction stopped along the eastern margin of Sabah for reasons we do not fully understand. The mantle processes and changes in the regional stress field associated with such an event likely conspired with surface processes to help shape the landforms we observe today. Clearly, we require detailed images of the crust and underlying mantle to understand why subduction ceased and how the landforms of Sabah may be related to deeper processes in the mantle.

This is where the North Borneo Orogeny Seismic Survey (nBOSS) project, which involves Borneo’s first temporary seismic network, comes into play. The nBOSS project is the result of a collaboration between the University of Cambridge, University of Aberdeen, Universiti Malaysia Sabah, and the Malaysian Meteorology Department. In March 2018, we deployed a network of 46 broadband seismic stations, spaced about 45 kilometers apart, throughout Sabah (Figure 1). This dense cluster of stations complements the more widely spaced stations in Malaysia’s regional seismic network.

Sabah’s Complex Tectonic History

Sabah lies near the northeastern edge of present-day Sundaland, the continental core of Southeast Asia, and is separated from the Philippines by the Sulu and Celebes Seas. Like much of Borneo, it formed by accretion of continental and oceanic material onto the eastern margin of Sundaland during the Late Cretaceous to early Miocene times (~70–20 million years ago).

Sabah is an ideal location to study the process of subduction termination, which is one of the more poorly understood stages of the global subduction cycle.During the Paleogene (which spans from ~60 to 25 million years ago), the proto–South China Sea was subducted beneath what is now the northwest continental margin of Sabah. This subduction process came to an end ~20 million years ago with the collision of two continents that resulted in the formation of the Crocker Range. Subsequently, there was a separate system of northward subduction of the Celebes Sea beneath eastern Sabah, which ended 5–6 million years ago.

The lithosphere that is now northern Borneo thus bears the signature of a southeast directed subduction system, followed by a northwest directed subduction system. Consequently, Sabah is an ideal location to study the process of subduction termination, which is one of the more poorly understood stages of the global subduction cycle.

Borneo’s First Dense Seismic Network Installing the seismometer network required the team to hike to remote locations, including the dense jungles in the Maliau Basin. Credit: Amy Gilligan

The nBOSS network, the first of its kind in Borneo, is supplemented by 24 permanent broadband seismic stations that form part of the Malaysian National Seismic Network. To install the instruments in our network, we used four-wheel drive vehicles to make use of all possible roads and fast motor boats to reach islands in the South China Sea. We dodged leeches as we trekked into the interior of the Maliau Basin and scaled Mount Kinabalu to install an instrument high on the mountain. The first batch of data was successfully recovered in September 2018, and now the data analysis has begun.

The network will be recording for a period of nearly 2 years. This time frame will allow us to record a sufficient number of distant earthquakes (Figure 2) for the application of a variety of seismic imaging techniques, including teleseismic tomography and receiver function and shear wave splitting analyses. We will extract further surface wave information from continuous ambient noise signals. The velocity and anisotropy models from this work will provide a number of critical constraints, including crustal thickness, mantle flow patterns, locations of lithospheric-scale faults, and discontinuities, that will feed into subsequent geodynamic modeling.

Fig. 2. Vertical component seismograms recorded by the nBOSS network from an M6.6 earthquake that occurred at about 8,000 kilometers (~5,000 miles) away from the seismic sensors in the Aleutian Islands (Alaska) on 15 August 2018. The colored stripes highlight the time periods in which body and surface waves are expected to arrive. What Happens When Subduction Stops?

Recent tectonic activity in Sabah, such as the rapid uplift and exhumation of Mount Kinabalu [Cottam et al., 2013], may be related to subduction termination. However, the extent to which postsubduction processes have dictated the evolution of the surface geology in the past 5–6 million years and whether those processes continue to do so now are unknown.

Several models have been proposed for the crustal evolution of the region. One such model posits that localized uplift and detachment faulting have caused gravitational collapse—mountain ranges collapsing under their own weight—in the Crocker Range, resulting in the formation of the fold-and-thrust belt offshore of northwest Sabah [Hall, 2013]. Confirming that gravitational collapse is happening requires obtaining constraints on the geographic distribution and rates of uplift and linking these to mantle structure and processes.

Although several models all have merit, the picture is incomplete without some understanding of how they couple with mantle processes. Another model says that continental extension has caused orogen collapse and produced a core complex [e.g., Lister and Davis, 1989] with the associated granite intrusion manifested by Mount Kinabalu. This model would explain both offshore subsidence and onshore uplift.

A third model says that a regional compressive stress field has localized strain in a foreland fold-and-thrust belt. This model can also explain onshore mountain building and does not require ongoing subduction or underthrusting.

The lack of constraints on mantle structure and dynamics beneath Sabah means that published models tend to focus on the crust, and even then, middle to lower crustal structure and processes are often largely based on speculation. Although the aforementioned models all have merit, the picture is incomplete without some understanding of how they couple with mantle processes.

On the basis of the presence of recent (~5 million years old) basalts with ocean island character in southeast Sabah, Hall [2013] proposed three models to explain the underlying cause for deformation of the lithosphere and vertical movements of the surface:

detachment of the descending slab from the rest of the plate (slab break off) delamination and sinking of the dense root of the lithosphere into the mantle below gravitational instability due to a lithospheric drip (a sinking plume of cold, dense lithospheric material)

For instance, uplift and extension caused by slab break off could induce or enhance orogen collapse. Alternatively, if regional compression has localized strain, then there is no requirement for any significant mantle anomaly. Clearly, to properly understand the link between mantle and crustal processes, a multidisciplinary and multiscale approach is essential.

Linking Field Data and Models

The crust and upper mantle beneath Sabah have yet to be targeted by geophysical imaging studies. The only evidence to date comes in the form of global seismic tomography, which shows a distinct high-velocity anomaly in the upper mantle beneath northern Borneo [Hall and Spakman, 2015]. Although this evidence is potentially consistent with a remnant slab or mantle drip, the lack of resolution (>250 kilometers) precludes any further analysis.

The new tomographic and geodynamic models will provide valuable insight into how continents evolve.Through the nBOSS project, we will use a multidisciplinary approach to address four specific aims: to understand mantle dynamics in a postsubduction setting; to determine the existence, cause, and extent of orogen collapse; to develop a model for postsubduction evolution of the continental crust-mantle system; and to unravel the cause of subduction termination in northern Borneo.

The new tomographic and geodynamic models will provide valuable insight into how continents evolve. The models we construct for the Sabah region can be compared with other recent postsubduction continental environments, including Europe’s east Carpathian-Pannonian region, North America’s Baja California, the Betic-Rif orogen in the western Mediterranean, and the Antarctic Peninsula.

Acknowledgments

S.P. acknowledges support from Natural Environmental Research Council (NERC) grant NE/R013500/1 and from the European Union’s Horizon 2020 research and innovation program under Marie Skłodowska-Curie grant agreement 790203. A.G. is supported by a Royal Astronomical Society Research Fellowship. Ten nBOSS seismometers were provided through NERC Geophysical Equipment Facility load 1038. We thank the Malaysian Meteorology Department, Sabah Foundation, and Sabah Parks for logistical support and assistance in the field. We also appreciate support from Guralp Systems Ltd., including provision of additional instruments for deployment on Mount Kinabalu and in Danum Valley.

Hiroshima Bomb Created Asteroid Impact–Like Glass

Tue, 05/28/2019 - 12:21

When a 10-kilometer-wide asteroid hit Earth about 66 million years ago, the ensuing blast annihilated the dinosaurs. When the United States dropped an atomic bomb on the city of Hiroshima, Japan, on 6 August 1945, the ensuing blast killed over 100,000 people.

Hiroshimaites like this one come in different shapes and sizes. Many are clear, with air bubbles trapped inside, whereas others are black, like obsidian. Credit: Mario Wannier

When the asteroid struck, it turned the rock that it hit into molten glass. That glass, while whizzing through the air as ejecta, formed and solidified into little beads, or spherules, that rained down over parts of the planet around the impact site.

When the atomic bomb detonated over Hiroshima, according to new research published in the journal Anthropocene, it turned parts of the city itself into molten glass. That glass formed spherules that rained down around the city, and the scientists that discovered the beads have called them “Hiroshimaites.”

Mario Wannier, a retired geologist who led the new research, retrieved 17 samples of beach sand from six beaches around Motoujina Peninsula and Miyajima Island in Hiroshima. Wannier initially set out to find the shells of tiny marine organisms because he wanted to study the health of the local marine ecosystem. But when he looked under a microscope at the samples, he saw spherules sitting alongside the shells.

“The main discovery is the elephant in the room that we’ve never seen before,” said Wannier, who explained that he immediately recognized the spherules for what they are, as they look very much like the spherules made by the dinosaur-killing asteroid. Wannier thinks the beads survived for so long without being washed away because the waters around the beaches he sampled tend to be relatively calm.

Miyajima Island in Hiroshima is one place where scientists found tiny glass spheres they think formed during the atomic bomb explosion. Credit: Mario Wannier

To turn material into glass—that is, to vitrify it—temperatures need to soar to heights of about 1,800°C, Wannier explained. The atomic bomb, codenamed Little Boy, caused sand and rocks in Hiroshima Bay to reach such hellish temperatures.

The rocks that form Hiroshima Bay are Cretaceous-aged granite, and crystals from this granite, including quartz and feldspar, form the majority of the sand grains at the beaches that Wannier and his team sampled. But these are not the only materials that went into forming the beads.

This Hiroshimaite is actually three conjoined spherules. Credit: Mario Wannier

The spherules also have pieces of Hiroshima itself. Some of the beads, Wannier explains, contain iron and steel—material that likely came from the city’s buildings.

One thing the spherules do not have and which Christian Koeberl, a geochemist at the University of Vienna who was not involved in the work, thinks they ought to have is some kind of radioactivity. Spherules collected from Alamogordo, N.M., the test site of the 1945 Trinity atomic explosion, are radioactive, so one would expect the Hiroshima beads to be similar, says Koeberl.

The ultimate proof that this really is Hiroshima fallout isn’t there yet.“The ultimate proof that this really is Hiroshima fallout isn’t there yet,” Koeberl said. “[Wannier and other researchers] make a reasonable interpretation of what they have. Further studies clearly are necessary.”

It could be, Koeberl mused, that the Hiroshima beads, collected several kilometers south and southwest from the hypocenter of the atomic blast, were cast too far afield to acquire much of a dose of radiation.

Although the Hiroshimaites appear to lack radioactivity, this absence does not negate the idea that they formed during the atomic blast. To be sure, researchers need to find and study more spherule samples.

Wannier thinks that there could be more such spherules in sediment either at different sites around Hiroshima or, perhaps, at the only other place where an atomic bomb was dropped on humans: Nagasaki.

—Lucas Joel, Freelance Journalist

Crystals Connect Bubbles in Explosive Magmas

Tue, 05/28/2019 - 11:30

Volcanic eruptions of hydrous and silica-rich (intermediate-felsic) magmas can cycle between Vulcanian-style explosions, lava dome extrusions, and dome collapse. The processes through which magmas degas during ascent depend on many factors, but the connectivity of bubble pathways ultimately controls how rapidly pressurized gas escapes. The critical threshold of gas permeability (the percolation threshold) in ascending intermediate to felsic magmas can be influenced by mineral crystallization.

Through laboratory experiments on crystal-bearing synthetic magmas, deGraffenried et al. [2019] show that at as little as 20 per cent crystallization can reduce the percolation threshold to just over 50 per cent porosity of the magma volume, creating connected bubble pathways that enhance degassing. That lowered threshold likely plays an important role in transitions between effusive and explosive eruption styles in hydrous, crystal-bearing magmas.

Citation: deGraffenried, R. L., Larsen, J. F., Graham, N. A., & Cashman, K. V. [2019]. The influence of phenocrysts on degassing in crystal‐bearing magmas with rhyolitic groundmass melts. Geophysical Research Letters, 46. https://doi.org/10.1029/2018GL081822

—Steven Jacobsen, Editor, Geophysical Research Letters

The Diversity and Complexity of Atmospheric Aerosol

Fri, 05/24/2019 - 13:25

Aerosols are microscopic particles suspended in the atmosphere. Studying their characteristics and behavior is a rapidly developing area of atmospheric chemistry. A recent paper in Reviews of Geophysics focuses on aerosol mixing state, describing methods for measuring and modeling, as well as understanding the impacts on climate. Here, two of the authors of the paper give an overview of our understanding and recent developments in this scientific field.

What different sources of particles and atmospheric processes combine to form overall aerosol in the atmosphere?

There are countless sources for aerosols, but to keep it from being overwhelming, we can roughly categorize them as coming from combustion processes (soot, biomass burning, and industrial particles), from mechanical processes (mineral dust, sea salt, car brake dust), and forming directly from low-volatility gases.

The challenge we face is that particles are not simply emitted and remain the same through their lifetime.The challenge we face is that particles are not simply emitted and remain the same through their atmospheric lifetime. Instead, various gases condense on or evaporate from the particles, and new species can form within the particles. Also, particles randomly collide with each other and form aggregates.

Thus, understanding the aerosol at any given time resembles hitting a moving target. The experimental methods and modeling approaches discussed in our review try to get a handle on this moving target.

What is ‘aerosol mixing state’ and what are the main factors that influence it?

At its simplest, aerosol mixing state is trying to say which chemical species are mixed with each other in individual particles and understanding how that contributes to the overall aerosol.

There are two extremes to mixing state, external and internal mixing. An external mixture means that all particles consist of just one chemical species, meaning a soot particle is just soot, a dust particle is just dust, etc. An internal mixture on the other hand means that every particle contains all the species in the overall aerosol in the same proportions (so a soot particle may also contain organic carbon, sulfate, nitrate, etc.).

The challenge is that it is very rare to have a perfectly externally mixed or internally mixed aerosol and usually we are somewhere in between. Aerosol mixing state is evolving in the atmosphere and a reflection of the processes that act on the particles during their lifetime.

Evolution of aerosol mixing state of an aerosol that is transported in the atmosphere. The line graph at the top illustrates how aerosol mixing state changes qualitatively between a more or less internally mixed state and how different aerosol processes contribute to that change. Adding new types of aerosol particles makes the population more externally mixed (steps 2 and 4), while aerosol aging processes (step 3) or the addition of one dominate particle type (step 5) moves the population toward a more internally mixed state. DMS = dimethyl sulfide. Credit: Riemer et al. [2019], Figure 2 How could you describe this in simpler language for a non-expert?

I like to think about my son’s plate at dinner, with each bite he takes as an aerosol particle. His plate starts as externally mixed, with green beans, chicken, squash and rice all separated on his plate, just like the aerosol particles as they enter the atmosphere from different sources.

Within a few minutes some of the green beans are in the squash, while some bites contain chicken and green beans. Then we add barbeque sauce (representing secondary species), which ends up on pretty much everything.

The bites are not an internal mixture, which would be the equivalent of the plate being put in a blender, with each bite having the same amount of everything. Thus, the plate and bites are each unique, but neither fully externally nor internally mixed. Various methods and models help us understand that complexity.

What techniques are used to measure aerosol mixing state?

Scanning electron microscopy (SEM) image and energy dispersive X-ray spectroscopy (EDX) maps of particles and the elements contained within them from the Southern Oxidant and Aerosol (SOAS) field campaign in 2013. Each of the elemental map panels corresponds to two elements overlaid to show the elemental distributions from the SEM image. The following particle types are shown: (a–d) dust, (e–f) aged sea salt aerosol, and (g) primary biological aerosol. Credit: Amy Bondy

Any technique that can provide single-particle composition data can help us understand the mixing state of the atmospheric aerosol. The key is that a method has to be able to analyze in situ or collected samples particle-by-particle, so that the different distinct particle chemical compositions don’t get smeared together within an average.

The methods have been used the most to study aerosol mixing state each provide their own flavor of information: single particle mass spectrometry (molecules and fragments), electron microscopy with X-ray spectroscopy (elemental) and microspectroscopy (functional groups).

Researchers are constantly pushing to understand more about the physicochemical properties of individual particles, which are enabling us to probe even variations within particles in composition, surface properties, acidity, and more.

These advances are enabling us to learn more than ever about the mixing state of the overall aerosol.

What impact does aerosol mixing state have on the atmospheric properties that influence climate?

Aerosols influence climate because they impact the Earth’s radiative balance.Aerosols influence climate because they impact the Earth’s radiative balance. This can happen directly as the particles scatter or absorb sunlight, or indirectly as the particles provide nuclei that help form cloud droplets and ice particles, thereby changing the reflectivity and lifetime of clouds. The magnitude of these effects depends on the make-up of the individual particles and how they are assembled in a population.

For example, soot particles that are coated with organic material absorb light differently than a situation where soot and organics reside in separate particles. This changes the heating of the atmosphere where the aerosol resides. Similarly, the propensity to form cloud droplets or ice particles is different for coated soot particles compared to bare soot. These differences in the initial formation process of clouds propagate and determine how much sunlight clouds reflect back into space, a key process in determining the Earth’s energy budget.

What are some of the unresolved questions where additional research is needed?

Despite the very sophisticated measurement methods that are currently available, there is no single instrument that can capture aerosol mixing state in its entirety.Despite the very sophisticated measurement methods that are currently available, there is no single instrument that can capture aerosol mixing state in its entirety. We therefore need to use multiple instruments that simultaneously sample the same aerosol and combine them in a way that yields a complete picture of aerosol mixing state. How to exactly do this, and how to connect these measurements to model output is challenging – but necessary for building a quantitative understanding of the aerosol mixing state in the ambient atmosphere.

Another important unresolved question is how to predict aerosol climate impacts – that is the aerosol impact on cloud properties and the aerosol interaction with light – from a known aerosol mixing state. The largest unknowns presently are associated with the formation of ice particles.

—Nicole Riemer (email: nriemer@illinois.edu), University of Illinois at Urbana‐Champaign; and Andrew Ault, University of Michigan

Shifting Winds Drive Ocean Temps Along South African Coast

Fri, 05/24/2019 - 13:24

The hazardous, turbulent waters around Africa’s southern tip have sunk countless ships, but they also sustain plentiful fisheries, including abundant sardine and anchovy populations. Fish populations in the region have fluctuated sharply in the past, possibly because of changing ocean temperatures. Now, a study shows that shifting winds are the main driver of long-term temperature shifts in the shallow coastal waters, a finding that could improve fisheries management.

Two powerful ocean currents, the Agulhas Current and the Benguela Current, collide around the southernmost promontory of South Africa, creating the dangerous conditions that once earned the region the moniker “Graveyard of Ships.” The currents swirl over a shallow, triangular shelf called the Agulhas Bank, churning up nutrients that feed plankton blooms and a rich spawning ground for sardines and anchovies.

Fish populations in this area have fluctuated dramatically over the past century, but scientists aren’t entirely sure why. One possibility is changing temperatures along the coast: In 1996, for example, the anchovy population shifted rapidly east when temperatures around the Agulhas Bank dropped by 0.5°C. However, long-term observations of this ocean region are rare, making answers hard to find.

In the new study, Malan et al. used a computer simulation of atmospheric conditions, ocean currents, and wind patterns in the Agulhas Bank to investigate what factors might affect water temperatures from decade to decade. As they tweaked different variables in the model, they found that shifting wind belts, not ocean currents or heating from the atmosphere, were the most important driver of coastal temperatures.

As winds shift direction, their angle relative to the coastline changes. When the wind blows parallel to the coastline, cold, nutrient-dense water gets pushed up toward the ocean surface, a phenomenon called upwelling. When winds blow toward the shore, warm surface water is forced toward the coastline, causing temperatures to rise.

In the simulated model of the Agulhas Bank, altering wind direction forced the boundary of warm water—demarcated by the 17°C isotherm—to shift toward or away from the coastline by up to 100 kilometers, the team found.

The Southern Annular Mode, the north–south wobbling of a massive, westerly wind belt, has a profound impact on local wind patterns in this region. Understanding how large-scale wind belts may affect temperatures in the Agulhas Bank could help fisheries experts manage marine protected areas in the region, the scientists note. (Journal of Geophysical Research: Oceans, https://doi.org/10.1029/2018JC014614, 2019)

—Emily Underwood, Freelance Writer

Seismic Clues to Surging Glaciers

Fri, 05/24/2019 - 13:16

Far from being static features of the landscape, glaciers are dynamic rivers of ice, flowing and carving earth beneath them in a diverse range of rates. There are fast-flowing glaciers, slow or stagnant glaciers, and surging glaciers that periodically accelerate and slow down again.

Understanding glacier movement is essential for accurate modeling of future climate.

“Their physics are critical for our understanding sea level change,” says Zhongwen Zhan, a professor of geophysics at the California Institute of Technology, “because that is where you are draining the ice sheets into the oceans.”

It’s long been thought, Zhan notes, that liquid water at the base of glaciers might be acting as a lubricant, speeding glaciers up and along, but it is difficult to fully characterize what is taking place under many meters of ice. In a recent study published in Geophysical Research Letters, Zhan details the results of a new approach that offers a work-around.

Zhan’s insight was to make use of two seismological stations set up astride the surging Bering Glacier in Alaska. Zhan examined station data for a 12-year period, which included a surge that lasted from 2008 to 2010, measuring changes in the speed of background seismic waves as they passed through the glacier. He found that waves slowed down during the surge, indicating they were traveling though softer material—water rather than ice or rock.

“This sort of geological observation and seismological observation are coming together and showing the same phenomenon.”Zhan thinks that the bottom 10 or 20 meters of a glacier crack during a surge, with those cracks running perpendicular to the direction of the glacier’s flow. Water, he says, rather than simply pooling at the base of the ice, fills these cracks. Zhan measured two types of seismic waves, Rayleigh and Love waves, to reach this conclusion.

“You have waves oscillating in the vertical direction, and another one in the horizontal direction, they are polarized,” he says. “Based on those differences in behavior of the polarization of the wave, we found that we need to have the cracks aligned perpendicular to the ice movement.”

Zhan’s research matches field observations of ridges of fine sediment left at the front of retreating surging glaciers, hinting at just these types of transverse cracks at the glacier base. “This sort of geological observation and seismological observation are coming together and showing the same phenomenon,” he says.

Zhan’s work is a step forward both in understanding surging glaciers and in furthering techniques for future studies, according Timothy Bartholomaus, a glaciologist and assistant professor in the University of Idaho’s Department of Geological Sciences.

“I think that it’s a very clever use of existing data and another really nice example of the ways by which people are applying techniques from seismology,” Bartholomaus says. “Over the last 5 or 10 years or so, there’s been a really major push by seismologists, oftentimes in collaboration with experts in other fields, to apply those same techniques to understand a whole range of other processes.”

An earlier study published in Geophysical Research Letters, for instance, used a network of 34 seismology stations in Antarctica to characterize high-frequency, wind-generated waves in ice shelves and correlated changes in the waves with a coming thaw.

Zhan would also like to extend his technique in future studies, perhaps adding additional seismological stations at different orientations across the glacier to better test his hypothesis.

“Our pair is aligned parallel to the cracks we are proposing. If we have a pair that’s perpendicular or 45° to the cracks, then we should see a change that’s very different,” he says. In the long term, with an array of sensors, a study could be like “the hospital people using X-ray or MRI [magnetic resonance imaging] to do tomography to show what the structure looks like and where something is changing.”

—Jon Kelvey (@JonKelvey), Science Writer

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