Highlights, including authors and their institutions
The following highlights summarize research papers that have been recentlypublished in Geophysical Research Letters (GRL).
In this release:
1. First satellite detection of volcanogenic carbon monoxide2. Antarctic sea ice thickness affects algae populations3. Central European Summer Temperature Variability to Increase4. Global ocean salinity changing due to anthropogenic climate change5. Chamber measurements find plants potentially important methane sink6. Low-frequency radio emissions from high-altitude sprite discharge
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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 projectwrought with potential dangers and difficulties. On the ground measurementsplace researchers in harm's way, as do airborne sampling surveys. Theseapproaches may also suffer from issues around accurately representing the spatialand temporal shifts in gas emissions rates. As such, satellite-based remote sensingtechniques are becoming a favorite way to assess the dispersion andconcentrations of various volcanic gases. Devising a functional remote sensingscheme, however, depends on identifying a satellite sensor that can reliablyidentify the chemical species in question and pick the volcanic emissions out fromthe background concentrations. Such efforts have so far been successful for only afew volcanic gases: sulfuric acid, hydrochloric acid, and hydrogen sulfide.
Working from satellite observational records from the 2010 Eyjafjallajökull and2011 Grímsvötn eruptions, Martínez-Alonso et al. find that the Measurements ofPollution in the Troposphere sensor aboard NASA's Terra satellite and theInfrared Atmospheric Sounding Interferometer on the European Space Agency'sMeteorological Operational satellite MetOp-A could be used to remotely detectvolcanic carbon monoxide emissions. The two sensors measured atmosphericcarbon monoxide in different ways and hence could be used to support the other'sobservations. The authors find that the remotely sensed volcanogenic carbonmonoxide 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 ofvolcanic carbon monoxide is approximately 5.5 teragrams per year, a small butnot insignificant fraction of total annual emissions.
Source:Geophysical Research Letters, doi:10.1029/2012GL053275, 2012http://dx.doi.org/10.1029/2012GL053275
Title:First satellite identification of volcanic carbon monoxide
Authors:Sara Martínez-Alonso, Merritt N. Deeter, Helen M. Worden, Debbie Mao, andJohn C. Gille: Atmospheric Chemistry Division, National Center for AtmosphericResearch, 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 thesouthern continent-a floating habitat sure to change as the planet warms. As withmost aquatic ecosystems, microscopic algae form the base of the Southern Oceanfood web. Distinct algae populations reside in the sea ice surface layers, on theice's underside, and within the floating ice itself. The algae that reside on thefloating 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 seaice properties will affect the regional biology, then, depends on understandinghow algae populations interact with the ice.
Drawing together samples collected by previous researchers, and through theirown efforts, Meiners et al. developed the Antarctic Sea Ice Processes andClimate-Biology database, a collection of 1,300 Antarctic sea ice core samplescollected from 1983 to 2008. By melting core samples and measuring theconcentration of chlorophyll a, researchers can estimate the amount of algaeliving 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 isdistributed evenly among surface, interior, and underside populations, there is adistinct relationship between sea ice thickness and the likelihood of biomassmaxima in different layers. They find that on thin ice, less than 0.4 meters (1.3feet) thick, algae live on both the surface and the underside. For ice from 0.4 to 1m (1.3 to 3.3 feet) thick, however, the majority of the algae were on the ice'sunderside. Thick ice, often formed by rafting of ice floes, showed a morehomogeneous distribution of ice algal biomass.
Source:Geophysical Research Letters, doi: 10.1029/2012GL053478, 2012http://dx.doi.org/10.1029/2012GL053478
Title:Chlorophyll a in Antarctic sea ice from historical ice core data
Authors:K. M. Meiners and B. Raymond: Australian Antarctic Division, Department ofSustainability, Environment, Water, Population and Communities, Kingston,Tasmania, Australia, and Antarctic Climate and Ecosystems Cooperative ResearchCentre, 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 LivingResources, 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, andFinnish Environment Institute, Helsinki, Finland and Arctic Centre, AarhusUniversity, Aarhus, Denmark;
J.-L. Tison: Laboratoire de Glaciologie, Université Libre de Bruxelles, Brussels,Belgium;
K. R. Arrigo: Department of Environmental Earth System Science, StanfordUniversity, 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 EcosystemsCooperative 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 andMary, Gloucester Point, Virginia, USA;
I. Melnikov: P. P. Shirshov Institute of Oceanology, Russian Academy ofSciences, Moscow, Russia.
3. Central European summer temperature variability to increase
More extreme heat waves have been observed in central Europe in recent years assummer temperature variability has increased on both daily and interannualtimescales. 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 onregional climate models from the Prediction of Regional Scenarios andUncertainties for Defining European Climate Change Risks and Effects(PRUDENCE) project or a small sample of models from the ENSEMBLESproject, Fischer et al. revisit model projections using the full set of ENSEMBLESregional climate models. These models cover a larger uncertainty range thanprevious studies. They note that PRUDENCE regional climate models are alldriven by the same global climate model, while ENSEMBLES regional climatemodels are driven by six different global climate models.
They find that PRUDENCE models all projected a substantial increase ininterannual summer temperature variability in central Europe by the end of the21st century, while different ENSEMBLES models projected different amounts ofinterannual summer temperature variability, with the mean of ENSEMBLESmodels projecting no clear increase. However, those ENSEMBLES models thatmost realistically represented present-day interannual summer temperaturevariability did project an increase in temperature variability over central Europeby the end of the 21st century. Under the assumption that a model with a betterrepresentation of the present-day conditions provides a more credible estimate offuture changes, the reduced set of well-performing models yields a robustprojection.
The study also indicates that the largest increases in interannual summertemperature variability would occur mainly in the central European region that isa transition zone between dry climates in the south and moist climates in thenorth. They also find that all ENSEMBLES regional climate models project anincrease in daily summer temperature variability over central Europe. Theyemphasize that hot extremes are expected to warm more strongly than the summermean temperature.
Source:Geophysical Research Letters, doi:10.1029/2012GL052730, 2012http://dx.doi.org/10.1029/2012GL052730
Title:Changes in European summer temperature variability revisited
Authors:E. M. Fischer, J. Rajczak, and C. Schär: Institute for Atmospheric and ClimateScience, ETH Zurich, Zurich, Switzerland.
4. Global ocean salinity changing due to anthropogenic climate change
Rising sea surface temperatures, climbing sea levels, and ocean acidification arethe most commonly discussed consequences of anthropogenic climate change forthe global oceans. They are not, however, the only potentially important shiftsobserved 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 shiftswere consistent with the expected effects of anthropogenic climate change.
The authors analyzed 50 years of salinity and temperature observations drawnfrom the National Oceanographic Data Center's records. The observationsspanned the top 700 meters (2,300 feet) of the water column from 60 degreesNorth to 60 degrees South. Using 20 global general circulation models, theyassessed whether the observed changes in ocean salinity and temperature could beexplained by known natural cycles: the El Niño-Southern Oscillation, the PacificDecadal Oscillation, the effects of volcanic eruptions, and changes in solaractivity. They find that the observed trends, which varied regionally, did not relateto any of these forcings. However, the observed trends are consistent with modelestimates of the effects of human-caused climate change.
The slowly shifting global salinity field is known to be affected by changes in thehydrological cycle, including changes in evaporation and precipitation rates,ocean currents, river discharge, and other forces. As such, the authors suggest thatthe observed human-driven trends in the global salinity field demonstrate anongoing, long-term shift in the global hydrological cycle that is likely to continueinto the future.
Source:Geophysical Research Letters, doi:10.1029/2012GL053389, 2012http://dx.doi.org/10.1029/2012GL053389
Title:The fingerprint of human-induced changes in the ocean's salinity and temperaturefields
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 ClimateModel 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 thancarbon dioxide when considered over the course of a few decades. In recent years,researchers discovered a potentially important new source of atmosphericmethane-emissions from green plants. Though estimates of the extent ofvegetative methane emissions vary greatly, previous research suggests they couldamount to as much as a tenth of global annual emissions. The mechanism behindsuch emissions is a matter of considerable debate, with questions remainingregarding the effects of atmospheric or soil conditions, local hydrologicalinfluences, and variability for different plant species. Also under investigation arevarious potential plant methane uptake mechanisms, or the effects of methane-consuming bacteria-aspects of the methane cycle that could dampen plants' roleas a methane source.
To determine the overall effect of some boreal tree species on atmosphericmethane, Sundqvist et al. used branch chamber measurements to directly assessthe 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 atmosphericmethane, meaning they served as a sink rather than a source. The authors analyzedhow the methane exchange varied with changes in the availability ofphotosynthetically active radiation (PAR), temperature, photosynthesis rate, andultraviolet radiation levels. For birch, spruce and rowan trees, but not pine, theyfind that an increase in PAR caused the trees to take up more methane. They findthat temperature changes had inconsistent effects on methane exchange. Theauthors suggest that plants could actually be an important global sink, rather thansource, for atmospheric methane.
Source:Geophysical Research Letters, doi: 10.1029/2012GL053592, 2012http://dx.doi.org/10.1029/2012GL053592
Title:Atmospheric methane removal by boreal plants
Authors:Elin Sundqvist, Meelis Mölder, Patrik Vestin and Anders Lindroth: Department ofPhysical 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, potentiallytriggering a second event-sprite discharge. This more elusive type of electricaldischarge, which produces lightning that is red in color, initiates from highaltitudes, with streamers propagating down toward the top of the cumulonimbuscloud. Coincident with the dramatic displays, researchers have previouslyidentified low-frequency radio emissions, which they suggest may be produced inassociation with the sprite discharge. Investigating this hypothesis, Qin et al. useda two-dimensional plasma model to calculate the radio emissions that should beproduced by a single sprite streamer.
The authors find the frequency of the radio emissions that should be produced bya sprite streamer depends on two main factors: the air density (which decreaseswith altitude) and the background electric field through which the streamer ispropagating. 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 tothe "very low frequency" range). If the sprite streamers spawned at 40 kilometers(25 miles) altitude, they would emit low-frequency radiowaves, with frequenciesup to 300 kilohertz. Further, the authors suggest that the sprite streamersbranching mechanism could act as a band-pass filter, with the radio wavefrequencies being lower at high altitudes than at low altitudes.
Source:Geophysical Research Letters, doi:10.1029/2012GL053991, 2012http://dx.doi.org/10.1029/2012GL053991
Title:Low frequency electromagnetic radiation from sprite streamers
Authors:Jianqi Qin, Sebastien Celestin, and Victor P. Pasko: Communications and SpaceSciences Laboratory, Department of Electrical Engineering, Pennsylvania StateUniversity, University Park, Pennsylvania, USA.
Contact:
Kate RamsayerPhone (direct): +1 202 777 7524E-mail: kramsayer@agu.org
Source: American Geophysical Union