AGU Journal Highlights
17 December 2012
Highlights, including authors and their institutions
The following highlights summarize research papers that have been recently published in Geophysical Research Letters (GRL).
In this release:
- First satellite detection of volcanogenic carbon monoxide
- Antarctic sea ice thickness affects algae populations
- Central European Summer Temperature Variability to Increase
- Global ocean salinity changing due to anthropogenic climate change
- Chamber measurements find plants potentially important methane sink
- Low-frequency radio emissions from high-altitude sprite discharge
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 Search Options and inserting into the search engine the full doi (digital object identifier), e.g. 10.1029/2012GL053275. The doi is found at the end of each Highlight below.
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1. First satellite detection of volcanogenic carbon monoxide
Measuring and tracking the gases that vent from an erupting volcano is a project wrought with potential dangers and difficulties. On the ground measurements place researchers in harm's way, as do airborne sampling surveys. These approaches may also suffer from issues around accurately representing the spatial and temporal shifts in gas emissions rates. As such, satellite-based remote sensing techniques are becoming a favorite way to assess the dispersion and concentrations of various volcanic gases. Devising a functional remote sensing scheme, however, depends on identifying a satellite sensor that can reliably identify the chemical species in question and pick the volcanic emissions out from the background concentrations. Such efforts have so far been successful for only a few volcanic gases: sulfuric acid, hydrochloric acid, and hydrogen sulfide.
Working from satellite observational records from the 2010 Eyjafjallajökull and 2011 Grímsvötn eruptions, Martínez-Alonso et al.find that the Measurements of Pollution in the Troposphere sensor aboard NASA's Terra satellite and the Infrared Atmospheric Sounding Interferometer on the European Space Agency's Meteorological Operational satellite MetOp-A could be used to remotely detect volcanic carbon monoxide emissions. The two sensors measured atmospheric carbon monoxide in different ways and hence could be used to support the other’s observations. The authors find that the remotely sensed volcanogenic carbon monoxide is not a misdiagnosis of atmospheric water vapor or aerosols. Further, their concentration measurements aligned with airborne surveys.
Based on their detections, the authors estimate that the global emission of volcanic carbon monoxide is approximately 5.5 teragrams per year, a small but not insignificant fraction of total annual emissions.
Geophysical Research Letters, doi:10.1029/2012GL053275, 2012
“First satellite identification of volcanic carbon monoxide”
- Sara Martínez-Alonso, Merritt N. Deeter, Helen M. Worden, Debbie Mao, and John C. Gille
- Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado, USA;
- Cathy Clerbaux
- LATMOS, IPSL, CNRS/INSU, UPMC Université Paris 06, Université Versailles St.-Quentin, Paris, France.
2. Antarctic sea ice thickness affects algae populations
In the waters off Antarctica, algae grow and live in the sea ice that surrounds the southern continent—a floating habitat sure to change as the planet warms. As with most aquatic ecosystems, microscopic algae form the base of the Southern Ocean food web. Distinct algae populations reside in the sea ice surface layers, on the ice's underside, and within the floating ice itself. The algae that reside on the floating ice's underside are particularly important for the region's krill population, while those on the interior or surface layers are less accessible. How changing sea ice properties will affect the regional biology, then, depends on understanding how algae populations interact with the ice.
Drawing together samples collected by previous researchers, and through their own efforts, Meiners et al. developed the Antarctic Sea Ice Processes and Climate-Biology database, a collection of 1,300 Antarctic sea ice core samples collected from 1983 to 2008. By melting core samples and measuring the concentration of chlorophyll a,researchers can estimate the amount of algae living in the ice, with vertical profiles indicating where ice algal biomass peaks.
Using their database, the authors find that algae populations vary seasonally, peaking in the spring and late summer. They find that though algal biomass is distributed evenly among surface, interior, and underside populations, there is a distinct relationship between sea ice thickness and the likelihood of biomass maxima in different layers. They find that on thin ice, less than 0.4 meters (1.3 feet) thick, algae live on both the surface and the underside. For ice from 0.4 to 1 m (1.3 to 3.3 feet) thick, however, the majority of the algae were on the ice's underside. Thick ice, often formed by rafting of ice floes, showed a more homogeneous distribution of ice algal biomass.
Geophysical Research Letters, doi:10.1029/2012GL053478, 2012
“Chlorophyll a in Antarctic sea ice from historical ice core data”
- K. M. Meiners and B. Raymond
- Australian Antarctic Division, Department of Sustainability, Environment, Water, Population and Communities, Kingston, Tasmania, Australia, and Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, Tasmania, Australia;
- M. Vancoppenolle
- Laboratoire d'Océanographie et du Climat (CNRS/UPMC/IRD/MNHN), IPSL, Paris, France;
- S. Thanassekos
- Commission for the Conservation of Antarctic Marine Living Resources, Hobart, Tasmania, Australia;
- G. S. Dieckmann
- Alfred Wegener Institute for Polar and Marine Science, Bremerhaven, Germany;
- D. N. Thomas
- School of Ocean Sciences, Bangor University, Anglesey, UK, and Finnish Environment Institute, Helsinki, Finland and Arctic Centre, Aarhus University, Aarhus, Denmark;
- J.-L. Tison
- Laboratoire de Glaciologie, Université Libre de Bruxelles, Brussels, Belgium;
- K. R. Arrigo
- Department of Environmental Earth System Science, Stanford University, Stanford, California, USA;
- D. L. Garrison
- Biological Oceanography Program, Division of Ocean Sciences, National Science Foundation, Arlington, Virginia, USA;
- A. McMinn and K. M. Swadling
- Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia;
- D. Lannuzel and P. van derMerwe
- Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, Tasmania, Australia and Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia;
- W. O. Smith Jr.
- Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, Virginia, USA;
- I. Melnikov
- P. P. Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia.
3. Central European summer temperature variability to increase
More extreme heat waves have been observed in central Europe in recent years as summer temperature variability has increased on both daily and interannual timescales. Models project that as the climate warms throughout the 21st century, this increased variability will continue.
To evaluate the robustness of those previous findings, which are based on regional climate models from the Prediction of Regional Scenarios and Uncertainties for Defining European Climate Change Risks and Effects (PRUDENCE) project or a small sample of models from the ENSEMBLES project, Fischer et al. revisit model projections using the full set of ENSEMBLES regional climate models. These models cover a larger uncertainty range than previous studies. They note that PRUDENCE regional climate models are all driven by the same global climate model, while ENSEMBLES regional climate models are driven by six different global climate models.
They find that PRUDENCE models all projected a substantial increase in interannual summer temperature variability in central Europe by the end of the 21st century, while different ENSEMBLES models projected different amounts of interannual summer temperature variability, with the mean of ENSEMBLES models projecting no clear increase. However, those ENSEMBLES models that most realistically represented present-day interannual summer temperature variability did project an increase in temperature variability over central Europe by the end of the 21st century. Under the assumption that a model with a better representation of the present-day conditions provides a more credible estimate of future changes, the reduced set of well-performing models yields a robust projection.
The study also indicates that the largest increases in interannual summer temperature variability would occur mainly in the central European region that is a transition zone between dry climates in the south and moist climates in the north. They also find that all ENSEMBLES regional climate models project an increase in daily summer temperature variability over central Europe. They emphasize that hot extremes are expected to warm more strongly than the summer mean temperature.
Geophysical Research Letters, doi: 10.1029/2012GL052730, 2012
“Changes in European summer temperature variability revisited”
- E. M. Fischer, J. Rajczak, and C. Schär
- Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland.
4. Global ocean salinity changing due to anthropogenic climate change
Rising sea surface temperatures, climbing sea levels, and ocean acidification are the most commonly discussed consequences of anthropogenic climate change for the global oceans. They are not, however, the only potentially important shifts observed over recent decades. Drawing on observations from 1955 to 2004, Pierce et al. find that the oceans' salinity changed throughout the study period, that the changes were independent of known natural variability, and that the shifts were consistent with the expected effects of anthropogenic climate change.
The authors analyzed 50 years of salinity and temperature observations drawn from the National Oceanographic Data Center's records. The observations spanned the top 700 meters (2,300 feet) of the water column from 60 degrees North to 60 degrees South. Using 20 global general circulation models, they assessed whether the observed changes in ocean salinity and temperature could be explained by known natural cycles: the El Niño–Southern Oscillation, the Pacific Decadal Oscillation, the effects of volcanic eruptions, and changes in solar activity. They find that the observed trends, which varied regionally, did not relate to any of these forcings. However, the observed trends are consistent with model estimates of the effects of human-caused climate change.
The slowly shifting global salinity field is known to be affected by changes in the hydrological cycle, including changes in evaporation and precipitation rates, ocean currents, river discharge, and other forces. As such, the authors suggest that the observed human-driven trends in the global salinity field demonstrate an ongoing, long-term shift in the global hydrological cycle that is likely to continue into the future.
Geophysical Research Letters, doi:10.1029/2012GL053389, 2012
“The fingerprint of human-induced changes in the ocean's salinity and temperature fields”
- David W. Pierce and Tim P. Barnett
- Division of Climate, Atmospheric Sciences, and Physical Oceanography, Scripps Institution of Oceanography, La Jolla, California, USA;
- Peter J. Gleckler, Benjamin D. Santer and Paul J. Durack
- Program for Climate Model Diagnosis and Intercomparison, Lawrence Livermore National Laboratory, Livermore, California, USA.
5. Chamber measurements find plants potentially important methane sink
As a greenhouse gas, methane has a much higher heat-trapping potential than carbon dioxide when considered over the course of a few decades. In recent years, researchers discovered a potentially important new source of atmospheric methane—emissions from green plants. Though estimates of the extent of vegetative methane emissions vary greatly, previous research suggests they could amount to as much as a tenth of global annual emissions. The mechanism behind such emissions is a matter of considerable debate, with questions remaining regarding the effects of atmospheric or soil conditions, local hydrological influences, and variability for different plant species. Also under investigation are various potential plant methane uptake mechanisms, or the effects of methane-consuming bacteria—aspects of the methane cycle that could dampen plants' role as a methane source.
To determine the overall effect of some boreal tree species on atmospheric methane, Sundqvist et al.used branch chamber measurements to directly assess the net gas exchange for birch, spruce, pine, and rowan trees in a Swedish forest. The authors find that all four tree species were net absorbers of atmospheric methane, meaning they served as a sink rather than a source. The authors analyzed how the methane exchange varied with changes in the availability of photosynthetically active radiation (PAR), temperature, photosynthesis rate, and ultraviolet radiation levels. For birch, spruce and rowan trees, but not pine, they find that an increase in PAR caused the trees to take up more methane. They find that temperature changes had inconsistent effects on methane exchange. The authors suggest that plants could actually be an important global sink, rather than source, for atmospheric methane.
Geophysical Research Letters, doi:10.1029/2012GL053592, 2012
“Atmospheric methane removal by boreal plants”
- Elin Sundqvist, Meelis Mölder, Patrik Vestin and Anders Lindroth
- Department of Physical Geography and Ecosystem Science, Lund University, Lund, Sweden;
- Patrick Crill
- Department of Geological Sciences, Stockholm University, Stockholm, Sweden.
6. Low-frequency radio emissions from high-altitude sprite discharge
When lightning strikes from a towering cumulonimbus cloud down to the ground, the electrical discharge can perturb the atmosphere's electric field, potentially triggering a second event—sprite discharge. This more elusive type of electrical discharge, which produces lightning that is red in color, initiates from high altitudes, with streamers propagating down toward the top of the cumulonimbus cloud. Coincident with the dramatic displays, researchers have previously identified low-frequency radio emissions, which they suggest may be produced in association with the sprite discharge. Investigating this hypothesis, Qin et al. used a two-dimensional plasma model tocalculate the radio emissions that should be produced by a single sprite streamer.
The authors find the frequency of the radio emissions that should be produced by a sprite streamer depends on two main factors: the air density (which decreases with altitude) and the background electric field through which the streamer is propagating. The authors find that sprite streamers that initiate from 75 kilometers (47 miles) altitude emit radio waves with frequencies from 0 to 3 kilohertz (up to the “very low frequency” range). If the sprite streamers spawned at 40 kilometers (25 miles) altitude, they would emit low-frequency radiowaves, with frequencies up to 300 kilohertz. Further, the authors suggest that the sprite streamers branching mechanism could act as a band-pass filter, with the radio wave frequencies being lower at high altitudes than at low altitudes.
Geophysical Research Letters, doi:10.1029/2012GL053991, 2012
“Low frequency electromagnetic radiation from sprite streamers”
- Jianqi Qin, Sebastien Celestin, and Victor P. Pasko
- Communications and Space Sciences Laboratory, Department of Electrical Engineering, Pennsylvania State University, University Park, Pennsylvania, USA.