Public Release: 

AGU Journal Highlights -- July 3, 2008

American Geophysical Union

1. Carbon enters deep Arctic Ocean mainly from continent edges

Scientists predict that the consequences of human-induced climate change will be greatly amplified in the Arctic, both on the surrounding continents and in the ocean. Changes in nutrient supply and diminishing sea ice extent have the potential to alter primary production, ecological structure, and carbon cycling in the Arctic Ocean. Currently, little information exists on carbon export and associated biogeochemical processes in the central Arctic Ocean, hindering predictions of how this system will respond to change. To address this knowledge gap, Hwang et al. analyze organic matter on particles settling out from the waters within the Arctic Ocean above the Canada Abyssal Plain. They find strikingly old radiocarbon ages (averaging about 1900 years) for the organic carbon. This, along with a spike in abundances of sediment from continental sources rather than deep-sea sources, suggests that the majority of the particulate organic carbon entering the deep Canada Basin is supplied from surrounding continental margins.

Title: Lateral organic carbon supply to the deep Canada Basin

Authors: Jeomshik Hwang, Timothy I. Eglinton, Richard A. Krishfield. Steven J. Manganini, and Susumu Honjo: Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, U.S.A.

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL034271, 2008; http://dx.doi.org/10.1029/2008GL034271


2. Magnetic patterns around Venus revealed

Venus lacks an intrinsic magnetic field. Instead, Venus's ionosphere acts as an obstacle to the supersonic solar wind that carries the interplanetary magnetic field. The interplanetary field drapes around the ionosphere, forming an induced magnetosphere. Recent research has shown that distinct physical regions in this induced magnetosphere are recognizable from variations and fluctuations within the Venusian magnetic field. Using data from the Venus Express spacecraft, launched in 2006, Vörös et al. study the statistical properties of these fluctuations, particularly within the magnetosheath, terminator, and wake. Their research uncovers several new structures and turbulence patterns within these regions, which may help scientists build more refined theories on the evolution of Venus's induced magnetosphere.

Title: Magnetic fluctuations and turbulence in the Venus magnetosheath and wake

Authors: Z. Vörös and M. P. Leubner: Institute of Astro- and Particle Physics, University of Innsbruck, Innsbruck, Austria;

T. L. Zhang, M. Volwerk, M. Delva, and W. Baumjohann: Space Research Institute, Austrian Academy of Sciences, Graz, Austria;

K. Kudela: Institute of Experimental Physics, Slovakia Academy of Sciences, Kosice, Slovakia.

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL033879, 2008; http://dx.doi.org/10.1029/2008GL033879


3. How porous, organism-rich layers form in Antarctic sea ice

Sea ice in Antarctica that persists through the summer is a highly important polar habitat for unique polar species, such as algae, krill, seals, and penguins. Scientists worry that as climate warms, declining sea ice trends might devastate Antarctic ecosystems. Noting that during summer the temperature of air, sea ice, and ocean are in near equilibrium around the freezing point of seawater, Ackley et al. investigate the cause for a specific feature of Antarctic summer sea ice: partially melted honeycomb-like ice matrices filled with seawater that form below a surface layer of snow and ice. Called "gap layers," these features contain especially high algal and microbial content. Using a model of gap layer formation that takes into account the summer reversal in near-surface temperature gradients in the Antarctic sea ice and the thermal conductivity found in the upper ice column, the authors calculate that the gap layer forms at a rate of up to three fourths of a centimeter per day. Their analysis reveals why gap layers are common within Antarctic summer sea ice and that gap layers should be considered when analyzing melting scenarios, perhaps at both poles.

Title: Internal melting in Antarctic sea ice: Development of "gap layers"

Authors: S. F. Ackley and Hongjie Xie: Laboratory for Remote Sensing and Geoinformatics, University of Texas at San Antonio, San Antonio, Texas, U.S.A.;

M. J. Lewis: Laboratory for Remote Sensing and Geoinformatics, University of Texas at San Antonio, San Antonio, Texas, U.S.A.; Also at Southwest Research Institute, San Antonio, Texas, U.S.A.;

C. H. Fristen: Desert Research Institute, Reno, Nevada, U.S.A.

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL033644, 2008; http://dx.doi.org/10.1029/2008GL033644


4. Cold plasma plumes help generate aurora

The THEMIS (Time History of Events and Macroscale Interactions during Substorms) mission is NASA's five-satellite mission whose prime science objective is to measure the trigger mechanism and dynamics of substorms, explosive energy releases in near-Earth space that create spectacular eruptions of the auroras. During a 9-month coast phase before the prime mission, dayside studies of the magnetosphere, magnetopause, and bow shock were performed. During this period, McFadden et al. uncovered dense plumes of cold plasma that extend from the inner magnetosphere out to the magnetopause, the boundary where the Earth's magnetic field deflects the solar wind. THEMIS's multisatellite measurements resolve the layered structure and evolution of these plumes, and its high time resolution experiments allow definitive demonstrations that this dense, cold plasma participates in dayside magnetic reconnection. Such observations provide a much more extensive, high-resolution data set of in situ cold plasma observations than was previously available. These first results suggest that future missions to study the magnetopause should include cold plasma sensors to better quantify the role cold plasma plays in magnetic reconnection.

Title: Structure of plasmaspheric plumes and their participation in magnetopause reconnection: First results from THEMIS

Authors: J.P. McFadden, C. W. Carlson, D. Larson, J. Bonnell, and F.S. Mozer: Space Sciences Laboratory, University of California, Berkeley, California U.S.A.;

V. Angelopoulos: Space Sciences Laboratory, University of California, Berkeley, California U.S.A.; also at IGPP, University of California, Los Angeles, California, U.S.A.;

K.-H. Glassmeier and U. Auster: Technische Universität Braunschweig, Germany.

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL033677, 2008; http://dx.doi.org/10.1029/2008GL033677


5. Sea current near Norway gets cooled in Arctic

The Norwegian Atlantic Current passes water from the Atlantic Ocean through the Norwegian Sea and is thus the major source of oceanic heat and salt to the Arctic Ocean. Where the Norwegian Sea borders the Barents Sea, the Norwegian Atlantic Current splits and partially flows into the Barents Sea as the North Cape Current before it returns back to the Norwegian Sea through the Bear Island Trough. Using data from current meters and hydrographic sections in the area where the North Cape Current splits from the Norwegian Atlantic Current, Skagseth identifies rates of water flux into and out of the Barents Sea. Analysis of temperature and salinity indicates that North Cape Current waters return back to the Norwegian Sea only after 7 months. Using a mixing model, the author finds that the outflow water consists of about 80 percent of water derived from the Atlantic Ocean, cooled by 2.0��.5 degrees Celsius (3.6-4.5 degrees Fahrenheit), indicating that water returning to the Norwegian Sea has not been well mixed with water from the Arctic and that such cooling needs to be included in heat budgets for the Barents Sea.

Title: Recirculation of Atlantic Water in the western Barents Sea

Authors: Øystein Skagseth: Institute of Marine Research, Bergen, Norway; also at Bjerknes Centre for Climate Research, Bergen, Norway.

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL033785, 2008; http://dx.doi.org/10.1029/2008GL033785


6. Rock type may influence hill steepness and landslide frequency

Landslide models in active mountain belts are based predominantly on the idea that hillslopes are limited to a threshold inclination angle by the rate of landsliding. To investigate more about threshold angles, Korup takes a closer look at hillslopes and landslide occurrences in several active mountain ranges in New Zealand. These ranges are composed primarily of rocks that are derivatives of greywacke and schist. All of the mountain ranges studied share a high frequency of hillslope inclination angles despite wide variations in rates of rock uplift and precipitation, landslide density, and deformation due to alpine glaciation. Comparing these angles with those found in other active mountain belts composed of different rock types, the author finds that the hillslope angles in these New Zealand mountains are higher, perhaps diagnostic of particular properties inherent in greywacke and schist. On the basis of this, Korup hypothesizes that hillslope evolution may adjust to rock-mass strength irrespective of the intensity of tectonic and climatic forcing.

Title: Rock type leaves topographic signature in landslide-dominated mountain ranges

Author: Oliver Korup: Research Department Avalanches, Debris Flows, and Rock Falls, Swiss Federal Research Institutes WSL/SLF, Davos, Switzerland

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL034157, 2008; http://dx.doi.org/10.1029/2008GL034157


7. Permafrost risk from rapid melt of Arctic sea ice

Climate models and observational evidence suggest that Arctic sea ice may undergo abrupt periods of loss during the next 50 years. To study how this influences permafrost degradation, Lawrence et al. evaluate effects of rapid sea ice loss on terrestrial Arctic climate and ground thermal state. Using the Community Climate System Model developed by the U.S. National Center for Atmospheric Research (NCAR), the authors find that simulated, western Arctic land-warming trends are 3.5 times greater during 5- to 10-year-long, rapid-sea-ice-loss periods than the longer-term, projected, 21st-century Arctic warming rates. This accelerated warming penetrates up to 1500 kilometers (930 miles) inland and is apparent throughout most of the year, peaking in autumn. NCAR's Community Land Model, with improved permafrost dynamics, reveals that an accelerated warming period substantially increases ground heat accumulation. This leads to rapid degradation of surface permafrost and may increase the vulnerability to degradation of colder permafrost layers at depth.

See 10 June 2008 press release at: http://www.agu.org/sci_soc/prrl/2008-22.html .

Title: Accelerated Arctic land warming and permafrost degradation during rapid sea ice loss

Authors: David M. Lawrence, Robert A. Tomas, Marika M. Holland, and Clara Deser: Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, Colorado, U.S.A.;

Andrew G. Slater: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, U.S.A.

Source: Geophysical Research Letters (GRL) paper 10.1029/2008GL033985, 2008; http://dx.doi.org/10.1029/2008GL033985

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