[ Back to EurekAlert! ] Public release date: 15-Jun-2012
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Contact: Mary Catherine Adams
mcadams@agu.org
202-777-7530
American Geophysical Union

AGU Journal highlights - June 15, 2012

The following highlights summarize research papers that have been recently published in Geophysical Research Letters (GRL), and Journal of Geophysical Research-Oceans (JGR-C).

In this release:

1. Measuring currents between North Atlantic and Nordic Seas

2. For first time, entire thermal infrared spectrum observed

3. Changing El Nino could reshape Pacific Ocean biology

4. Italian super-eruption larger than thought

5. Langmuir circulation inhibits near-surface water turbulence

6. Seasonal algae plays critical role in North Pacific carbon uptake

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://www.agu.org/pubs/search_options.shtml and inserting into the search engine the full doi (digital object identifier), e.g. 10.1029/2012GL051269. The doi is found at the end of each Highlight below.

Journalists and public information officers (PIOs) at educational or scientific institutions who are registered with AGU also may download papers cited in this release by clicking on the links below. Instructions for members of the news media, PIOs, and the public for downloading or ordering the full text of any research paper summarized below are available at http://www.agu.org/news/press/papers.shtml.


1. Measuring currents between North Atlantic and Nordic Seas

The fluxes of water from the North Atlantic to the Nordic Seas provide a measure of the water that flows into and out of the global ocean as part of the meridional overturning circulation. The meridional overturning circulation, which carries warm water in the Atlantic from the tropics northward and brings cold dense water back southward, is a key part of global ocean circulation and a strong influence on climate; some research has suggested that the meridional overturning circulation could slow down as the global climate warms. Using an acoustic Doppler current profiler mounted in the high seas ferry Norrona to repeatedly measure the currents in the Faroe-Shetland Channel and over the Iceland-Faroe Ridge, Rossby and Flagg report on three years of weekly measurements that provide a new, accurate measure of the exchange of water between the North Atlantic to the Nordic Seas. The observations will be useful in understanding the meridional overturning circulation.

Source: Geophysical Research Letters, doi:10.1029/2012GL051269, 2012 http://dx.doi.org/10.1029/2012GL051269

Title: Direct measurement of volume flux in the Faroe-Shetland Channel and over the Iceland-Faroe Ridge

Authors: T. Rossby: Graduate School of Oceanography, University of Rhode Island, Kingston, Rhode Island, USA;

C. N. Flagg: Marine Sciences, Stony Brook University, Stony Brook, New York, USA.


2. For first time, entire thermal infrared spectrum observed

The driving mechanism of the greenhouse effect, and the underpinning of modern anthropogenic warming, is the absorption, emission, and transmission of infrared radiation by atmospheric gases. The heat-trapping ability of a gas depends on its chemical composition, and each type of gas absorbs infrared radiation of different energies. The amount of infrared radiation that escapes into space depends on the net effect of the myriad gases in the atmosphere, with water vapor being the primary gaseous absorber of infrared radiation. Water vapor absorbs a wide range of infrared radiation, masking the effects of other gases. In fact, in many spectral regions (or infrared radiation energy bands), water vapor is so strongly absorbing that it makes testing the accuracy of infrared radiation absorption parameterizations used in general circulation models difficult.

To surmount this obstacle, Turner et al. headed to a 5.3-kilometer (3.3-mile) altitude site in the Atacama Desert in northern Chile, where the air is extremely dry. Using a broad suite of spectroscopic equipment, they produce the first ground-based measurement of the entire atmospheric infrared radiation absorption spectrum-from 3.3 to 1000 micrometers-including spectral regions that are usually obscured by strong water vapor absorption and emission. Though the data collected will likely be valuable for a broad range of uses, the authors use their measurements to verify the water vapor absorption parameterizations used in the current generation of climate models.

Source: Geophysical Research Letters, doi:10.1029/2012GL051542, 2012 http://dx.doi.org/10.1029/2012GL051542

Title: Ground-based high spectral resolution observations of the entire terrestrial spectrum under extremely dry conditions

Authors: D. D. Turner: National Severe Storms Laboratory, NOAA, Norman, Oklahoma, USA;

E. J. Mlawer and J. S. Delamere: Atmospheric and Environmental Research, Inc., Lexington, Massachusetts, USA;

G. Bianchini and L. Palchetti: Istituto di Fisica Applicata "Nello Carrara, " Consiglio Nazionale delle Ricerche, Sesto Fiorentino, Italy;

M. P. Cadeddu: Argonne National Laboratory, Argonne, Illinois, USA;

S. Crewell and G. Maschwitz: Institut fur Geophysik und Meteorologie, University of Cologne, Cologne, Germany;

R. O. Knuteson and D. C. Tobin: Space Science and Engineering Center, University of Wisconsin-Madison, Madison, Wisconsin, USA;

M. Mlynzcak: NASA Langley Research Center, Hampton, Virginia, USA;

S. Paine: Smithsonian Astrophysical Observatory, Cambridge, Massachusetts, USA.


3. Changing El Nino could reshape Pacific Ocean biology

Over the past few decades, the scientific understanding of El Nino has grown increasingly complex. Traditionally viewed as a periodic warming focused largely in the eastern equatorial Pacific Ocean, El Nino is associated with reduced productivity in South American fisheries and changing temperature, pressure, and rainfall patterns around the world. In the 1990s, however, researchers started to notice a new kind of El Nino, one where anomalous ocean temperatures were concentrated mainly in the central equatorial Pacific Ocean. This previously unknown mode of variability, now termed the Central Pacific (CP) El Nino, in contrast to the classical Eastern Pacific (EP) El Nino, has increased in frequency and intensity over the past 30 years. Some scientists expect CP El Ninos to become the dominant El Nino variant in response to global warming, so understanding their differing effects is a pressing concern.

Comparing the major 1997-98 EP and 2009-10 CP El Nino events, Gierach et al. determined the effect of each on surface ocean biology. Using a satellite-based proxy measurement for phytoplankton biomass, they find that the EP event brought about a strong decrease in both eastern and central Pacific biomass. The CP event ties to a larger decline in central Pacific phytoplankton biomass but has little effect on eastern Pacific activity. They find that during the CP event, strong westerly winds brought warm nutrient-depleted waters to the central Pacific from the west. For the EP El Nino, westerly winds weakened upwelling and vertical mixing in the eastern Pacific, inhibiting the supply of nutrients from the subsurface ocean. In both cases, a reduction in nutrient supply caused a drop in productivity in the near-surface tropical waters. The authors suggest that a shift to more frequent CP El Ninos in the future could alter ecosystem dynamics in the equatorial Pacific Ocean, enhancing productivity in the eastern basin while reducing it in the central basin.

Source: Geophysical Research Letters, doi:10.1029/2012GL051103, 2012 http://dx.doi.org/10.1029/2012GL051103

Title: Biological response to the 1997-98 and 2009-10 El Nino events in the equatorial Pacific Ocean

Authors: Michelle M. Gierach and Tong Lee: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA;

Daniela Turk: Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, Canada and Lamont-Doherty Earth Observatory, Earth Institute at Columbia University, Palisades, New York, USA;

Michael J. McPhaden: Pacific Marine Environmental Laboratory, NOAA, Seattle, Washington, USA.


4. Italian super-eruption larger than thought

Recent research suggested that the super-eruption of the Campi Flegrei caldera volcano in southern Italy about 40,000 years ago may have played a part in wiping out, or forcing the migration of, the Neanderthal and modern human populations in the eastern Mediterranean regions that were covered in ash. Now a new modeling study by Costa et al. suggests that this eruption may have been even larger than previously thought. This Campi Flegrei eruption produced a widespread ash layer known as Campanian Ignimbrite (CI). Using ash thickness measurements collected at 115 sites and a three-dimensional ash dispersal model, the authors find that the CI super-eruption would have spread 250-300 cubic kilometers (60-72 cubic miles) of ash across a 3.7-million-square-kilometer (1.4- million-square-mile) region-2 to 3 times previous ash volume estimates.

The updated values stem from a new method of modeling what the wind would have been like during the eruption. Traditionally, models assume a consistent wind field for the entire duration of an eruption. The authors, however, incorporate wind fields into the model that are based on 15 years of recent measurements, using the modern wind field that best accounts for the ash deposit measurements.

On the basis of their updated estimates, the authors calculate that up to 450 million kilograms (990 million pounds) of sulfur dioxide would have been spread into the atmosphere, driving down temperatures by 1-2 degrees Celsius (1.8-3.6 degrees Fahrenheit) for 2 to 3 years. Further, sulfur dioxide and chloride emissions would have triggered acidic rains, and fluorine-laden ash would have become incorporated into plant matter, potentially inducing fluorosis, replete with eye, tooth, and organ damage, in animal populations.

Source: Geophysical Research Letters, doi:10.1029/2012GL051605, 2012 http://dx.doi.org/10.1029/2012GL051605

Title: Quantifying volcanic ash dispersal and impact of the Campanian Ignimbrite super-eruption

Authors: A. Costa: Environmental Systems Science Centre, University of Reading, Reading, UK and Istituto Nazionale di Geofisica e Vulcanologia, sezione "Osservatorio Vesuviano," Napoli, Italy;

A. Folch: Barcelona Supercomputing Center - Centro Nacional de Supercomputacion, Barcelona, Spain;

G. Macedonio and R. Isaia: Istituto Nazionale di Geofisica e Vulcanologia, sezione "Osservatorio Vesuviano," Napoli, Italy;

B. Giaccio: Istituto di Geologia Ambientale e Geoingegneria, CNR, Rome, Italy;

V. C. Smith: Research Laboratory for Archaeology and the History of Art, University of Oxford, Oxford, UK.


5. Langmuir circulation inhibits near-surface water turbulence

In the surface ocean, breaking waves are a major source of air bubbles and turbulent kinetic energy. During the presence of a consistent surface wind, these wave-generated bubbles, along with other surface material like seaweed or foam, can be drawn into long rows along the surface. Driving this organization is Langmuir circulation, a phenomenon in which the wind and waves cause surface waters to rotate helically, moving like a wire wrapped around a pole in the windward direction. These spiral currents oscillate between left-handed and right- handed rotations, such that in some places the surface waters are pushed together and in others they are pulled apart. Researchers have previously found that at sites of convergence the bubbles produced by breaking waves are pushed to depths of 15 meters (49 feet) or more, with important implications for air-sea gas mixing and other processes.

Of interest to Gemmrich, however, is whether Langmuir circulation-induced convergence also affects near-surface turbulent kinetic energy, the other product of breaking waves. Using measurements taken from aboard the R/P Floating Instrument Platform, a unique ship designed to deliberately flood itself to turn into a stable floating research station, the author finds that Langmuir circulation convergence zones suppressed turbulence in the near-surface ocean. The author suggests that in convergence zones the wave-generated bubbles that had been forced to depth would rise at varying rates, with large bubbles rising faster than small bubbles. This would cause the ocean waters to become stratified by air fraction. This stable stratification would, in turn, inhibit turbulence close to the surface. The results suggest that in a convergence zone, buoyant particles originating from a surface source-such as oil from a tanker spill-would get trapped in the near-surface waters rather than be mixed to depth, the opposite of what would have been previously assumed.

Source: Geophysical Research Letters, doi:10.1029/2012GL051691, 2012 http://dx.doi.org/10.1029/2012GL051691

Title: Bubble-induced turbulence suppression in Langmuir circulation

Authors: Johannes Gemmrich: Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia, Canada.


6. Seasonal algae plays critical role in North Pacific carbon uptake

The role of the North Pacific Ocean as a net carbon sink may prove to be more precarious than previously thought as researchers work to isolate the contributions of biological and physical processes to air-sea gas exchange. Scientists have long known that physical processes, such as the seasonally changing solubility of carbon dioxide in seawater, combine with a biological pump driven by seasonal shifts in phytoplankton growth to control the carbon dioxide flux in the region. A dearth of on-site evidence regarding biological pump function, however, has prevented researchers from assessing the relative importance of either mechanism to known carbon uptake rates. From data collected during four cruises from 2003 to 2008, Juranek et al. determined the strength of the biological pump, finding that for the northern Pacific Ocean it was strong enough to counteract solubility induced outgassing in summer, turning a net source region into a carbon sink.

The North Pacific is split into three sections: an anticyclonic subtropical gyre, a cyclonic subarctic gyre, and a transition zone sandwiched between. Superimposed on these largely stationary features, the transition zone chlorophyll front (TZCF) travels from 30 degrees North in winter to 40 degrees North in summer. Using dissolved gas concentration and isotope ratio detections, satellite measurements of chlorophyll concentrations, and other data sources, the authors map the oxygen and carbon dioxide budgets of the different North Pacific regions. They find that in the TZCF, biological productivity was 2-4 times higher than in adjacent regions. This spike was driven by the confluence of enhanced ocean mixing, increased nutrient availability, and a change in the TZCF's algal ecosystem composition. Owing to the newly realized power of the biological pump, the authors suggest that understanding how North Pacific algal populations could be affected by changing climate or hydrological conditions is a pressing concern.

Source: Journal of Geophysical Research-Oceans, doi:10.1029/2011JC007450, 2012 http://dx.doi.org/10.1029/2011JC007450

Title: Biological production in the NE Pacific and its influence on air-sea CO2 flux: Evidence from dissolved oxygen isotopes and O2/Ar

Authors: L. W. Juranek: College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon, USA;

P. D. Quay and D. Lockwood: School of Oceanography, University of Washington, Seattle, Washington, USA;

R. A. Feely: NOAA Pacific Marine Environmental Laboratory, Seattle, Washington, USA;

D. M. Karl and M. J. Church: School of Ocean and Earth Science and Technology, University of Hawai'i at Manoa, Honolulu, Hawaii, USA.

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Contact:
Mary Catherine Adams
Phone (direct): +1 202 777 7530
Email: mcadams@agu.org



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