Public Release: 

AGU: Journal highlights 17 Dec., 2012

American Geophysical Union

Highlights, including authors and their institutions


In this release:

1. First satellite detection of volcanogenic carbon monoxide
2. Antarctic sea ice thickness affects algae populations
3. Central European Summer Temperature Variability to Increase
4. Global ocean salinity changing due to anthropogenic climate change
5. Chamber measurements find plants potentially important methane sink
6. 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 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.


1. First satellite detection of volcanogenic carbon monoxide




Source: Geophysical Research Letters, doi:10.1029/2012GL053275, 2012

Title: First satellite identification of volcanic carbon monoxide

Authors: 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


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.

Source: Geophysical Research Letters, doi: 10.1029/2012GL053478, 2012

Title: Chlorophyll a in Antarctic sea ice from historical ice core data

Authors: 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.

Source: Geophysical Research Letters, doi:10.1029/2012GL052730, 2012

Title: Changes in European summer temperature variability revisited

Authors: 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.

Source: Geophysical Research Letters, doi:10.1029/2012GL053389, 2012

Title: The fingerprint of human-induced changes in the ocean's salinity and temperature fields

Authors: 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.

Source: Geophysical Research Letters, doi: 10.1029/2012GL053592, 2012

Title: Atmospheric methane removal by boreal plants

Authors: 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.


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 to calculate 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.

Source: Geophysical Research Letters, doi:10.1029/2012GL053991, 2012

Title: Low frequency electromagnetic radiation from sprite streamers

Authors: Jianqi Qin, Sebastien Celestin, and Victor P. Pasko: Communications and Space Sciences Laboratory, Department of Electrical Engineering, Pennsylvania State University, University Park, Pennsylvania, USA.


Kate Ramsayer
Phone (direct): +1 202 777 7524

