News Release

AGU journal highlights -- June 22, 2010

Peer-Reviewed Publication

American Geophysical Union

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

In this release:

  1. El Niño explanation for global warming flawed
  2. Less warming risk from permafrost thaw?
  3. Drill site targeted for subglacial Antarctic lake
  4. Aerosols strongly influence cloud properties
  5. Realistic models of aquifer conduits

Anyone may read the scientific abstract for any of these papers 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. 10.1029/2009JD012960. 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 .Please note that papers not yet published (i.e. "in press") are available only to journalists and public information officers.

1. El Niño explanation for global warming flawed

About every 4 years, faltering easterly trade winds over the tropical Pacific Ocean cause warm waters to linger, generating an anomalously warm wet period in the eastern Pacific for about 6 months. During these times the western Pacific becomes cooler and drier. A few years later, a reversal of these conditions occurs when trade winds amplify, pushing warm waters even farther west, leading to unusually cool waters across a broad expanse of the equatorial Pacific.

This seesaw effect is called the El Niño-Southern Oscillation (ENSO). Scientists know that ENSO is important to climate studies, playing a key role in determining average global temperature. But to what extent does it influence these temperatures?

A recently published paper by McLean et al. (Influence of the Southern Oscillation on tropospheric temperature, J. Geophys. Res., 114, D14104, doi:10.1029/2008JD011637, 2009) claimed that more than two thirds of the decadal and longer-term variation in large-scale tropospheric temperatures—including recent global warming—can be explained solely by ENSO. However, Foster et al. use a simple model to show that McLean et al. reached invalid conclusions because of inappropriate filtering of data. This caused McLean et al. to overstate the influence of ENSO in their study; in actuality, ENSO contributes less than a third of the signal. Thus the general acknowledgment that recent temperature rise is likely due to human-induced greenhouse emissions is not refuted by McLean et al.'s study.

Title: Comment on "Influence of the Southern Oscillation on tropospheric temperature" by J. D. McLean, C. R. de Freitas, and R. M. Carter

Authors: G. Foster: Tempo Analytics, Westbrook, Maine, USA.; J. D. Annan: Research Institute for Global Change, JAMSTEC, Yokohama, Japan; P. D. Jones: Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norwich, UK; M. E. Mann: Department of Meteorology and Earth and Environmental Systems Institute, Pennsylvania State University, University Park, Pennsylvania, USA.; B. Mullan and J. Renwick: Climate Variability group, NIWA, Wellington, New Zealand; J. Salinger: School of Environment, University of Auckland, Auckland, New Zealand; G. A. Schmidt: NASA Goddard Institute for Space Studies, New York, New York, USA; K. E. Trenberth: Climate Analysis Section, NCAR, Boulder Colorado, USA.

Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper 10.1029/2009JD012960, 2010

2. Less warming risk from permafrost thaw?

Soil found in the Arctic stores half of the world's soil organic carbon (SOC) and twice as much carbon as is in the atmosphere. Rising temperatures in the Arctic are thawing the permafrost; some of the soil carbon then degrades into greenhouse gases that are remobilized into the carbon cycle, exerting positive feedback on global warming.

Vonk et al.'s objective was to find out what happens to terrestrial SOC after it is released from Arctic landmasses to coastal waters. The authors chose northernmost Scandinavia to conduct their study due to its sensitivity to the warming climate.

The molecular radiocarbon fingerprint of suspended particulate matter and surface sediments collected during spring flood 2005 in the Kalix River-Bothnian Bay system reveals that there are two distinct SOC pools, which exhibit different susceptibilities to degradation upon settling from the surface water to the underlying sediments. The exported SOC distributed by rivers and streams consists of a young pool that is released from recent plant material and the upper soil layers of peatlands and an older pool that originates from deeper mineral soil layers.

The data reveal that the young pool, with an inferred high degradation rate, would be expected to add greenhouse gases to the atmosphere, while the carbon from the older pool, which is tightly bound to mineral particles that protect it from degradation, would resettle in coastal sediments. Therefore, thaw-released mineral organic carbon may, relative to peat organic carbon, preferentially end up in coastal sediments instead of the atmosphere. The results suggest that researchers should reevaluate the assumption that there is a simple direct link between thawing of permafrost and the addition of greenhouse gases to the atmosphere.

Title: Selective preservation of old organic carbon fluvially released from sub-Arctic soils

Authors: Jorien E. Vonk, Bart E. van Dongen, and Örjan Gustafsson: Department of Applied Environmental Science and Bert Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden.

Source: Geophysical Research Letters (GRL) paper 10.1029/2010GL042909, 2010

3. Drill site targeted for subglacial Antarctic lake

Since the discovery in 1996 that Lake Vostok, a subglacial (hidden under a glacier) lake in Antarctica, possessed a water column of more than 500 meters (1640 feet), scientists have come to believe that subglacial lakes are feasible habitats for life and may contain records of ice sheet and climate history within the sediments on their floors. So far, however, no subglacial lakes have been directly sampled.

To determine a good location for direct measurements, Woodward et al. study subglacial Lake Ellsworth, in West Antarctica. The area is ideal for access because freezing and water circulation rates are low and are not affected by inflow of sediment with base water. Over the course of 2007� and 2008�, researchers collected geophysical data from the lake using towed radar, seismics, the Global Positioning System (GPS), and stake measurements. The scientists also created a three-dimensional numerical fluid dynamics model to simulate not only water circulation within the lake but also the interaction between the water and the overlying ice.

The results point to an optimal location for future studies to access Lake Ellsworth to reduce the risk of drilling into a zone of basal freezing and recover undisturbed sediment.

This location will allow researchers to search for microbial life and sample sublake sediments that may reveal climate history.

Title: Location for direct access to subglacial Lake Ellsworth: An assessment of geophysical data and modeling

Authors: J. Woodward: School of Applied Sciences, Northumbria University, Newcastle-upon-Tyne, UK; A. M. Smith, H. F. J. Corr and E. C. King: British Antarctic Survey, Natural Environment Research Council, Cambridge, UK; N. Ross, M. J. Siegert: School of Geosciences, University of Edinburgh, Edinburgh, UK; M. Thoma: Commission for Glaciology, Bavarian Academy of Sciences, Munich, Germany; Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany; M. A. King: School of Civil Engineering and Geosciences, Newcastle University, Newcastle-upon-Tyne, UK; K. Grosfeld: Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany; M. Tranter: School of Geographical Sciences, University of Bristol, Bristol, UK.

Source: Geophysical Research Letters (GRL) paper 10.1029/2010GL042884, 2010

4. Aerosols strongly influence cloud properties

The interaction of aerosol and clouds is one significant uncertainty in studies of anthropogenic forcing of climate. To learn more about the effects of fine aerosols on cloud microphysics, Constantino and Bréon perform a multisensor analysis of the atmosphere off the coast of Namibia and Angola. The authors chose this particular area because it is often affected by smoke from burning biomass. The aerosol particles from this smoke are transported by trade winds into the atmosphere, where they come in contact with low-level stratocumulus clouds.

The authors analyze cloud droplet radii (CDR), aerosol index (AI), and vertical profiles of aerosols and clouds using measurements from three different satellites. One satellite measured CDR, a second one detected active fires in the area and allowed estimates of aerosol loads around the clouds, and a third was used to distinguish between separate layers of clouds and aerosols and mixed layers.

Previous studies have shown that the concentration of aerosol particles in a cloud affects the cloud droplet radius. Adding to those studies, the authors now report that near-simultaneous measurements from the three satellites show no specific relationship between CDR and AI for separated aerosol and cloud layers. But, when aerosol and cloud layers mix, there is a strong correlation between CDR and aerosol concentration, with higher levels of aerosols resulting in smaller cloud droplets.

The results confirm that aerosols have a strong impact on cloud microphysics. The size of cloud droplets affects the amount of solar radiation that is reflected by clouds, which influences climate.

Title: Analysis of aerosol-cloud interaction from multi-sensor satellite observations

Authors: Lorenzo Costantino and François-Marie Bréon: Laboratoire des Sciences du Climat et de l'Environnement, Unité Mixte de Recherche, UVSQ, CEA, CNRS, Gif-sur-Yvette, France.

Source: Geophysical Research Letters (GRL) paper 10.1029/2009GL041828, 2010

5. Realistic models of aquifer conduits

The spatial distribution of underground rock units and geologic structures governs the flow of groundwater and thus any pollutant plumes within this groundwater. Such information is critical to water resources managers and to those drilling for oil and natural gas. However, simulating these units and structures in fine detail is difficult, relying on a knowledge of basic geology, erosion, and the physical processes that produce sedimentary deposits in a given space.

Michael et al. approach subsurface simulation by using a method that incorporates multiple techniques of modeling, playing on each technique's strengths. Though the authors are not the first to use a multiple model approach, they are the first to attempt simulations involving process-based models with direct conditioning to local geologic data. The inherent uncertainties are handled by the probabilistic nature of their model and the ability to generate multiple alternate subsurface scenarios. The authors feel that their approach is promising because it simulates realistic aquifer structures, including interwoven flow conduits and barriers connected in a manner consistent with the deposition and erosion that form geological systems.

Title: Combining geologic-process models and geostatistics for conditional simulation of 3-D subsurface heterogeneity

Authors: H. A. Michael: Department of Geological Sciences, University of Delaware, Newark, Delaware, USA; H. Li and T. Sun: ExxonMobile Upstream Research Company, Houston, Texas, USA; A. Boucher and S. M. Gorelick: Department of Environmental Earth System Science, Stanford University, Stanford, California, USA; J. Caers: Department of Energy Resources Engineering, Stanford University, Stanford, California, USA.

Source: Water Resources Research, doi:10.1029/2009WR008414, 2010


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