AGU journal highlights -- Oct. 8 2013

The following highlights summarize research papers that have been recently published in Journal of Geophysical Research-Atmospheres (JGR-D), Journal of Geophysical Research-Earth Surface (JGR-F), Journal of Geophysical Research-Oceans (JGR-C), Geophysical Research Letters, and Paleoceanography.

In this release:

1. Measuring global sulfur dioxide emissions with satellite sensors
2. Seismic network detects landslides on broad area scale
3. Examining increasing potential for storms with global warming
4. Understanding oxygen depletion on the Oregon coastal shelf
5. A selective approach to draw data from altered foraminifera shells
6. West Antarctic Ice Sheet formed earlier than thought

Anyone may read the scientific abstract for any already-published paper by clicking on the link provided at the end of each Highlight. You can also read the abstract by going to http://onlinelibrary.wiley.com/ and inserting into the search engine the full doi (digital object identifier), e.g. doi: 10.1002/jgrd.50826. The doi is found at the end of each Highlight below.

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Atmospheric sulfur dioxide affects the weather by enhancing cloud formation, and long-term shifts in emissions can change the climate by increasing the planetary albedo. Sulfur dioxide emissions are the basis for acid rain, and the gas itself can cause respiratory problems. Despite its importance, the difficulties associated with accurately measuring sulfur dioxide mean that rates of emissions are generally not well understood. For readings made using satellite-borne spectrometers, the signal of sulfur dioxide is often swamped by that of ozone, which absorbs radiation at similar wavelengths. Using data filtering and analysis techniques, Fioletov et al. find that observations from three different satellites are consistent and could be used to detect large sources of sulfur dioxide emissions.

Satellites have previously been used to track emissions from individual point sources, such as volcanoes or large power plants. Global assessments have proven to be more elusive. By comparing observations from ultraviolet spectrometers carried by three different satellites, the authors identified 30 strong sources of sulfur dioxide emissions, ranging from smelters and oil refineries to factories, volcanoes, and power plants. With observations from 2004 to 2010, the authors calculated trends in emissions rates at these sites.

The development of an accurate method to remotely detect sulfur dioxide concentrations is important because otherwise scientists are reliant on reported emissions rates, which aren't always accurately disclosed.

Source: Journal of Geophysical Research-Atmospheres, doi:10.1002/jgrd.50826, 2013 http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50826/abstract

Title: Application of OMI, SCIAMACHY, and GOME-2 satellite SO2 retrievals for detection of large emission sources

Authors: V. E. Fioletov and C. A. McLinden: Environment Canada, Toronto, Ontario, Canada;

N. Krotkov: Laboratory for Atmospheric Chemistry and Dynamics, NASA Goddard Space Flight Center, Greenbelt, Maryland, U.S.A.;

K. Yang: Laboratory for Atmospheric Chemistry and Dynamics, NASA Goddard Space Flight Center, Greenbelt, Maryland, U.S.A., and Department of Atmospheric and Oceanic Sciences, University of Maryland, College Park, Maryland, U.S.A.;

D. G. Loyola and P. Valks: Deutsches Zentrum für Luft- und Raumfahrt (DLR), Wessling, Germany;

N. Theys and M. Van Roozendael: Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium;

C. R. Nowlan: Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada;

K. Chance and X. Liu: Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, U.S.A.;

C. Lee: National Institute of Meteorological Research, Korea Meteorological Administration, Seoul, South Korea;

R. V. Martin: Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada and Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, U.S.A.

From 1999 to 2006, Taiwan's Chenyoulan watershed experienced 48,000 landslides, rock avalanches, and other geomorphic events, the bulk of which are thought to be triggered by the powerful tropical cyclones that batter the island each summer. Rock slides and other geomorphic events are a natural hazard, but they're also the source for some of the raw sediment that ends up winding its way downstream, affecting watershed erosion and sedimentation dynamics. From both of these perspectives, having a handle on when and where these geomorphic events occur is important. However, the main method used to track landslides—optical satellite observations—has a low temporal resolution, has trouble discerning new activity at previously affected sites, and struggles to see through clouds or dense canopy cover. Using 14 seismic sensors installed from July to September 2010, Burtin et al. studied the skill of their network in detecting geomorphic activity in the Chenyoulan watershed.

The authors detected 314 separate geomorphic events during their study period. Using their moderately dense network of seismic sensors, the authors located the geographic source of each event, and a manual analysis let them categorize the cause of the signal. Different types of geomorphic events produce seismic signals with different shapes. Comparing their observations with rainfall records, they find that 69 percent of the events coincided with storms, with the timing of the landslide or other event often occurring during the period of peak precipitation. Tracking the source of the seismic signals, they find that 61 percent of the events occurred at sites of previous geomorphic events. The authors note that their seismic network approach still needs work, but that when fully developed, it could provide a means to automatically assess the occurrence, cause, and type of geomorphic events.

Source: Journal of Geophysical Research-Earth Surface, doi:10.1002/jgrf.20137, 2013 http://onlinelibrary.wiley.com/doi/10.1002/jgrf.20137/abstract

Title: Continuous catchment-scale monitoring of geomorphic processes with a 2-D seismological array

Authors: Arnaud Burtin, Niels Hovius, and Robert Emberson: GeoForschungsZentrum, Helmholtz Centre Potsdam, Potsdam, Germany;

David Milodowski: University of Edinburgh, School of Geosciences, Edinburgh, United Kingdom;

Yue-Gau Chen, Yih-Min Wu, and Hongey Chen: National Taiwan University, Department of Geosciences, Taipei, Taiwan ROC;

Ching-Weei Lin: National Cheng-Kung University, Department of Earth Sciences, Tainan, Taiwan ROC;

Peih-Lin Leu: Seismological Center, Central Weather Bureau, Taipei, Taiwan ROC.

Increases in convective available potential energy (CAPE)—the energy available to a parcel of air as it rises through a cloud that is warmer than its surroundings, causing it to rise—may increase the potential for severe storms. Model simulations have shown that global warming will increase CAPE in the tropics, but scientists do not fully understand why this occurs or what the implications may be for future precipitation intensity.

Providing a step toward better understanding of CAPE, Singh and O'Gorman show that the increase in tropical CAPE with warming occurs over a wide range of temperatures in simulations with different atmospheric carbon dioxide concentrations. Based on their simulations and radiosonde observations from the tropical western Pacific, the authors developed a simple model in which mixing of the surrounding dry air into the cloud reduces cloud buoyancy more in warmer atmospheres. They show that this model can account for the increase in CAPE with warming, suggesting that changes in CAPE may not necessarily reflect changes in cloud buoyancy and hence storm intensity.

Source: Geophysical Research Letters, doi:10.1002/grl.50796, 2013 http://onlinelibrary.wiley.com/doi/10.1002/grl.50796/abstract

Title: Influence of entrainment on the thermal stratification in simulations of radiative-convective equilibrium

Authors: Martin S. Singh and Paul A. O'Gorman: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, U.S.A.

Each spring, the winds off Oregon shift, changing ocean currents and spurring the onset of the upwelling season, an approximately 4 month period where cold, nutrient-rich, oxygen-depleted deep water is driven into the coastal region. In recent decades, measurements have shown that the concentration of oxygen in the waters off Oregon has been decreasing. More recently, seasonal hypoxia has become a concern. Although this long-term decline is well documented, the details of the annual and seasonal variability in the concentration of dissolved oxygen on the shelf are not. Using moored sensors installed off the coast of Oregon for three seasons, from 2009 to 2011, Adams et al. measured the properties of the water, including changes in the current as well as the temperature, salinity, and concentration of dissolved oxygen. They find that although the seasonal upwelling initiates the annual reduction in dissolved oxygen, it is also responsible for staving off widespread anoxia.

To understand the effect of upwelling on coastal conditions, the authors analyzed their observations for trends that occurred on a range of time scales, from subtidal to tidal to interannual. They find that because the cold deep water is low in dissolved oxygen and because the introduction of nutrients spurs biological productivity, the onset of upwelling leads to oxygen depletion. However, upwelling also causes enhanced flushing and mixing, which prevents the oxygen from dropping as low as it otherwise would. Upwelling-induced flushing and mixing limit the annual oxygen depletion to just 30 percent of what it should be if the infiltration of cold deep water and biological respiration were the only factors. The authors find that changes in the winds along the coast cause weekly variability in the concentration of dissolved oxygen, while monthly variability can be caused by fluctuations in the atmospheric jet stream.

Source: Journal of Geophysical Research-Oceans, doi:10.1002/jgrc.20361, 2013 http://onlinelibrary.wiley.com/doi/10.1002/jgrc.20361/abstract

Title: Temporal variability of near-bottom dissolved oxygen during upwelling off central Oregon

Authors: Katherine A. Adams and John A. Barth: College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, Oregon, U.S.A.;

Francis Chan: Department of Zoology, Oregon State University, Corvallis, Oregon, USA.

A sudden surge in the concentration of carbon dioxide in the air and the ocean 56 million years ago may have triggered the Paleocene-Eocene thermal maximum (PETM), a period of rapid and dramatic warming. In conjunction with the rising atmospheric temperature, ocean acidification significantly increased the dissolution, or "burndown," of carbonate sediments on the seafloor, destroying the preservation quality of seafloor foraminifera shells. Analyzing foraminifera shells is one of the main proxy measurements used by paleoclimatologists to reconstruct past ocean temperatures. Kozdon et al., however, find that by using two highly precise analytical techniques, they can draw useful data from foraminifera samples that were damaged by the burndown.

When single-celled foraminifera die, their calcite shells sink to the seafloor. Locked inside are records of the environmental conditions when the foraminifera formed their shells, indicated by the isotope ratios and the concentrations of various elements. The burndown caused many of these shells to fully or partially dissolve. When the warm period ended, the dissolved carbonate reprecipitated on the remaining shells, but with new, different isotope ratios.

Traditionally, researchers studying the isotope ratios of foraminifera shells use an analytical technique that consumes the whole shell. As such, the recrystallization from the PETM burndown would skew their results. The authors of the present study, however, used two highly selective techniques, secondary ion mass spectrometry and electron probe microanalysis, to measure the compositions of small preserved fragments of individual shells. The techniques allowed them to measure the isotope ratios of the parts of the shells that were unaffected by recrystallization and to compare original shell material against recrystallized regions within the same shell.

Source: Paleoceanography, doi:10.1002/palo.20048, 2013 http://onlinelibrary.wiley.com/doi/10.1002/palo.20048/abstract

Title: In situ δ18 O and Mg/Ca Analyses of Diagenetic and Planktic Foraminiferal Calcite Preserved in a Deep-Sea Record of the Paleocene-Eocene Thermal Maximum

Authors: Reinhard Kozdon, D. C. Kelly, K. Kitajima, A. Strickland, J. H. Fournelle, and J. W. Valley: WiscSIMS, Deptartment of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin, U.S.A.

About 34 million years ago, Earth transitioned from a warm "greenhouse" climate to a cold "icehouse" climate, marking the transition between the Eocene and Oligocene epochs. This transition has been associated with the formation of a large ice sheet on Antarctica.

However, as scientists tried to simulate the growing Antarctic ice sheet, they found that the models could not produce the large volume of ice that independent data suggested to have existed on Earth at that time. For these models, scientists suggested that although the East Antarctic Ice Sheet formed during the transition, the West Antarctic Ice Sheet formed during the middle Miocene, about 20 million years later. Another site was needed, possibly in the Northern Hemisphere, to accommodate the missing ice.

The previous simulations of growing ice at the Eocene-Oligocene transition assumed that West Antarctica was mostly below sea level, as it is today. In a new simulation, Wilson et al. take into account the long-term evolution of the landscape. They suggest that much of West Antarctica was above sea level during that time and was thus capable of supporting terrestrially grounded ice, even at a time when ocean temperatures were too warm to support an ice sheet grounded below sea level as today.

Their new ice sheet model shows how the predecessor to the modern West Antarctic Ice Sheet could have developed at the Eocene-Oligocene transition, 20 million years earlier than some scientists have supposed. Therefore, they conclude that Antarctica accommodated all of the ice that formed at the climate transition.

Source: Geophysical Research Letters, doi:10.1002/grl.50797, 2013 http://onlinelibrary.wiley.com/doi/10.1002/grl.50797/abstract

Title: Initiation of the West Antarctic Ice Sheet and estimates of total Antarctic ice volume in the earliest Oligocene

Authors: Douglas S. Wilson: Department of Earth Science and Marine Science Institute, University of California, Santa Barbara, California, U.S.A.;

David Pollard: Earth and Environmental Systems Institute, Pennsylvania State University, University Park, Pennsylvania, U.S.A.;

Robert M. DeConto: Department of Geosciences, University of Massachusetts Amherst, Amherst, Massachusetts, U.S.A.;

Stewart S.R. Jamieson: Department of Geography, University of Durham, Durham, U.K.;

Bruce P. Luyendyk: Department of Earth Science and Earth Research Institute, University of California, Santa Barbara, California, U.S.A.

Contact:

Mary Catherine Adams
Phone (direct): +1 202 777 7530
E-mail: mcadams@agu.org

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