Public Release:  AGU journal highlights -- March 25, 2009

American Geophysical Union

The following highlights summarize research papers that have been published in Geophysical Research Letters (GRL) and Journal of Geophysical Research-Atmospheres (JGR-D).

In this release:

  1. Coral reefs may start dissolving when atmospheric carbon dioxide doubles
  2. Ocean proximity aggravates Houston's ozone pollution
  3. Underground subatomic-particle measurements yield meteorological clues
  4. Airborne acid may help soot turn into cloud seeds
  5. Understanding sea temperature-atmospheric pressure links in North Atlantic
  6. New tool differentiates man-made from natural nitrogen-oxide pollution

Anyone may read the scientific abstract for these papers by clicking on the link provided at the end of each Highlight. You can also read the abstract by going to http://www.agu.org/pubs/search_options.shtml and inserting into the search engine the full doi (digital object identifier), e.g. 10.1029/2008GL036282. The doi is found at the end of each Highlight below.

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1. Coral reefs may start dissolving when atmospheric carbon dioxide doubles

Increasing levels of atmospheric carbon dioxide are known to result in reduced coral calcification because carbon dioxide alters ocean chemistry and decreases aragonite saturation because it contributes to ocean acidification. As the aragonite saturation decreases, corals precipitate their skeletons (composed of calcium carbonate) at a slower rate. Silverman et al. predict the future rate of global decline in the calcification of coral reefs resulting from rising sea surface temperature and ocean acidification. Unlike previous studies, which used results of laboratory experiments, they use measurements made on natural coral reef located in the Red Sea to develop relationships between coral reef calcification, temperature, carbonate ion concentrations, and live coral cover. Using these relationships, they find that most coral reefs are already calcifying more slowly than during preindustrial times. Further, when atmospheric carbon dioxide reaches 560 parts per million (double the preindustrial level), the authors predict that all coral reefs are likely to stop growing and start dissolving.

Title: Coral reefs may start dissolving when atmospheric carbon dioxide doubles

Authors: Jacob Silverman: Institute of Earth Sciences, Hebrew University of Jerusalem, Jerusalem, Israel; Department of Global Ecology, Carnegie Institution, Stanford, California, U.S.A.;

Boaz Lazar, and Jonathan Erez: Hebrew University of Jerusalem, Jerusalem, Israel;

Long Cao, Ken Caldeira: Department of Global Ecology, Carnegie Institution, Stanford, California, U.S.A.

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL036282, 2009; http://dx.doi.org/10.1029/2008GL036282


2. Ocean proximity aggravates Houston's ozone pollution

In Houston, Texas, understanding atmospheric processes that control pollution formation is complicated by both typical urban emissions and large industrial emissions sources--many of the nation's petrochemical facilities are located in southeastern Texas, and these sources release ground-level ozone precursors including nitrogen oxides and highly reactive organic compounds. Simon et al. determine that the pollution profile in Houston is further complicated by its proximity to the ocean. Nitryl chloride, a compound created by the reaction of sea salt with an oxide of nitrogen produced in urban atmospheres, can photodissociate into nitrogen dioxide and chlorine atoms. The former is a pollutant, and the latter has been shown to increase ground-level ozone formation. During the summer of 2006, nytril chloride mixing ratios of more than 1 part per billion (ppb) were measured in the Houston urban area. Through photochemical modeling, the authors find that nytril chloride increases the total reactive chlorine mass by 20 to 40 percent in the atmosphere of southeastern Texas. The nytril chloride caused widespread increases in ozone concentrations over Houston of 1 to 2 ppb; vertical dispersion and local atmospheric composition moderated the effect of nytril chloride on ozone mixing ratios.

Title: Modeling the impact of nitryl chloride on ozone formation in the Houston area

Authors: H. Simon: Center for Energy and Environmental Resources, University of Texas at Austin, Austin, Texas, U.S.A.; now at Atmospheric Modeling and Analysis Division, National Exposure Research Laboratory, Environmental Protection Agency, Research Triangle Park, North Carolina, U.S.A.;

Y. Kimura, G. McGaughey, and D. T. Allen: Center for Energy and Environmental Resources, University of Texas at Austin, Austin, Texas, U.S.A.;

S. S. Brown, J. M. Roberts: Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado U.S.A.;

H. D. Osthoff: Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado U.S.A.; now at Department of Chemistry, University of Calgary, Calgary, Alberta, Canada;

D. Byun: Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas, U.S.A.; now at Air Resources Laboratory, Office of Ocean and Atmospheric Research, NOAA, Silver Spring, Maryland, U.S.A.;

D. Lee: Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas, U.S.A.

Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2008JD010732, 2009; http://dx.doi.org/10.1029/2008JD010732


3. Underground subatomic-particle measurements yield meteorological clues

When high-energy cosmic rays interact with molecules in the atmosphere, they produce muons, negatively charged elementary particles that can be detected at ground level or underground. The rate of these muons detected by underground detectors has been found to correlate strongly with temperature changes in the upper air. Osprey et al. compare cosmic ray muon rates from the Main Injector Neutrino Oscillation Search (MINOS) underground neutrino detector in Soudan, Minnesota, with upper air temperature data from the European Centre for Medium Range Weather Forecasts during the winters from 2003 to 2007. They find a strong positive correlation between muon rate and temperature. For instance, both muon rate and temperature showed a sharp rise and fall over a period of about 2 weeks in February 2005, corresponding to a sudden stratospheric warming event. If other underground detectors show matching effects, the authors suggest that the correlation between muon rate and upper air temperature raises the possibility that cosmic ray muon data could potentially be useful for calibrating long-term temperature trends or independently measuring meteorological conditions.

Title: Sudden stratospheric warmings seen in MINOS deep underground muon data

Authors: S.Osprey: Department of Physics, University of Oxford, Oxford, UK, and collaborators (for complete list see online abstract at link below).

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL036359, 2009; http://dx.doi.org/10.1029/2008GL036359


4. Airborne acid may help soot turn into cloud seeds

Carbon soot aerosols from combustion of fossil fuels and forest fires directly influence the Earth-atmosphere heat balance by absorbing sunlight. Fresh soot particles repel water and hence have little effect on properties and lifetimes of clouds. As soot particles age, they are thought to undergo a weathering process that allows them to absorb water, potentially transforming particles into cloud condensation nuclei. To learn more about how soot develops an affinity for water, Khalizov et al. examine the properties of soot aerosols exposed to gaseous sulfuric acid. They find that although fresh soot does not change below water saturation, soot particles exposed to sulfuric acid increase in mass when relative humidity rises because the acid-coated soot absorbs water. An increase in particle mass is often accompanied by a decrease in size, suggesting that conventional measurement methods based on particle size may underestimate the impact of soot aging on clouds. Because sulfuric acid, a pollutant and the driving agent in acid rain, is increasing in the atmosphere due to industrial activities, the authors expect that this mechanism of water absorption by acid-coated soot significantly influences cloud formation.

Title: Formation of highly hygroscopic soot aerosols upon internal mixing with sulfuric acid vapor

Authors: Alexei F. Khalizov, Renyi Zhang, Dan Zhang, and Huaxin Xue: Department of Atmospheric sciences, Texas A&M University, College Station, Texas, U.S.A.;

Joakim Pagels: Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota, U.S.A.; also at Division of Ergonomics and Aerosol Technology, Faculty of Engineering, Lund University, Lund, Sweden;

Peter H. McMurry: Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota, U.S.A.

Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2008JD010595, 2009; http://dx.doi.org/10.1029/2008JD010595


5. Understanding sea temperature-atmospheric pressure links in North Atlantic

Feedback effects between the ocean and atmosphere are important to understanding the mechanisms affecting climate variations. Previous studies have found that atmospheric anomalies associated with a variation in atmospheric pressure above the North Atlantic Ocean called the North Atlantic Oscillation produce a three-part pattern (tripole) of sea surface temperature anomalies at midlatitudes. Scientists refer to such anomalies as the North Atlantic sea surface temperature tripole, and scientists have debated to what extent the atmosphere responds to these midlatitude sea surface temperature variations. Mochizuki et al. identify oceanic feedback signals poleward of the tropics, taking a new approach based on a model used in four-dimensional variational data assimilation to determine the sensitivity of the model to fluctuations in physical variables. Their results reveal that oceanic thermal feedback beyond the tropics is an important process influencing the North Atlantic Oscillation, providing a better understanding of the factors affecting climate variations in the North Atlantic.

Title: Possible oceanic feedback in the extratropics in relation to the North Atlantic SST tripole

Authors: Takashi Mochizuki, Toshiyuki Awaji, and Nozomi Sugiura: Frontier Research Center for Global Change, JAMSTEC, Yokohama, Japan; Awaji is also at Department of Geophysics, Kyoto University, Kyoto, Japan.

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL036781, 2009; http://dx.doi.org/10.1029/2008GL036781


6. New tool differentiates man-made from natural nitrogen-oxide pollution

Nitrogen oxides in the atmosphere, which are produced by lightning, biomass burning, and soil outgassing, are converted into atmospheric nitrate through oxidation reactions. Nitrogen oxide, itself a pollutant, controls the production of ozone, which in turn is a greenhouse gas and a pollutant at ground levels. Atmospheric nitrate contributes to the load of atmospheric particulate matter and, along with sulfate, to acid rain. Despite efforts to regulate and monitor emissions, nitrogen oxide and atmospheric nitrate burdens in the atmosphere are increasing in many regions. To learn more, Morin et al. study the stable isotopic composition of nitrate within aerosol samples, collected along a shipborne transect, in the lower atmosphere over the Atlantic Ocean from 65 degrees South to 79 degrees North. They find that in nonpolar regions, nitrate derived from anthropogenically emitted nitrogen oxide had isotopic properties distinct from locations influenced by natural nitrogen oxide sources. Further, air masses exposed to snow-covered areas have low nitrogen isotopic ratios, showing that snowpack emissions of nitrogen oxide from upwind regions can have a significant effect on the local surface budget of reactive nitrogen.

Title: Comprehensive isotopic composition of atmospheric nitrate in the Atlantic Ocean boundary layer form 65 degrees South to 79 degrees North

Authors: S. Morin, J. Savarino, and F. Domine: Institut National des Sciences de l'Univers, CNRS, Grenoble, France; also at Laboratoire de Glaciologie et Géophysique de l'Environnement, Université Josef Fourier, Grenoble, France;

M. M. Frey: Institut National des Sciences de l'Univers, CNRS, Grenoble, France; also at Laboratoire de Glaciologie et Géophysique de l'Environnement, Université Josef Fourier, Grenoble, France; now at British Antarctic Survey, Natural Environment Research Council, Cambridge, U.K.;

H.-W. Jacobi: Institut National des Sciences de l'Univers, CNRS, Grenoble, France; also at Laboratoire de Glaciologie et Géophysique de l'Environnement, Université Josef Fourier, Grenoble, France; Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany;

L. Kaleschke; ZMAW, Institute of Oceanography, University of Hamburg, Hamburg, Germany;

J. M. F. Martins: Institut National des Sciences de l'Univers, CNRS, Grenoble, France; also at Laboratoire d'Étude des Transferts en Hydrologie et Environnement, Université Josef Fourier, Grenoble, France.

Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2008JD010696, 2009; http://dx.doi.org/10.1029/2008JD010696

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