- Climate change could transform Venice Lagoon
- Fast, bright lights sketch sprites
- Eastern Amazon copiously emits greenhouse gas methane
- Winds flood an Arctic shelf with warm waters
- Human influence could rev up oceanic planetary waves by 35 percent
- Active volcanoes may mechanically interact
- Level of ancient Mediterranean Sea changed repeatedly
- Evaluating river discharge from space
- Black carbon pollutants scrutinized above Japan
- Southern Ocean simulation yields key details
- Energy goes down the tubes in North Atlantic
- Magnetism of ancient Amazon rocks illuminates early Earth
- Predicting sea surface temperatures with artificial neural networks
- Extreme drought parched ancient Upper Colorado River Basin
A new model that couples biotic and abiotic processes in intertidal zones predicts that salt marshes in Italy’s Venice Lagoon may not survive future climate changes. These projections of the model developed by study authors Marani et al. stem from current forecasts of sea-level rise. Tidal ecosystems and landforms in lagoons and estuaries manifest extremely high biodiversity and rates of primary productivity. Because these zones are associated with important socio-economic activities sustaining a large population worldwide, their evolution through different climate-change scenarios could bear important consequences for regional economies of several areas. Applying their new model, the authors find that vegetation type, disturbances to microbial biofilm, sediment availability, and marine transgressions or regressions drive evolution of such systems. Besides making specific predictions for the Venice Lagoon’s future, the model also reproduces empirical observations from the lagoon’s past, spanning the last five centuries.
Title: Biologically-controlled multiple equilibria of tidal landforms and the fate of the Venice Lagoon
Authors: Marco Marani, Andrea D'Alpaos, Stefano Lanzoni, Luca Carniello and Andrea Rinaldo: Dipartimento di Ingegneria Idraulica, Marittima, Ambientale e Geotecnica, and International Center for Hydrology, Università di Padova, Padova, Italy.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL030178, 2007 (in press, as of 7 June 2007)
Small but brilliant filaments of charged particles streaking at about a tenth the speed of light sketch out the fiery atmospheric patterns known as sprites, recent observations indicate. Sprites occur in the mesosphere and lower ionosphere above electrically active thunderstorms. In images collected in 2005 from the Langmuir Observatory in New Mexico, these sprite-sketching “streamer heads” blaze at up to five times the brightness of Venus, which typically outshines every object in the sky except the Sun and Moon. Lasting less than 1 millisecond, these bright objects have not been previously recognized. In sub-millisecond-resolution video sequences of sprites recorded by Stenbaek-Nielsen et al. with advanced high-frame-rate cameras, the authors find that many structures, such as branches and tendrils, actually represent trajectories of streamer heads. Because the heads’ physical sizes are less that the spatial resolution of the images, the researchers used theoretical models for streamer-head development and volume emission rates to infer the heads sizes to be 10 to 100 meters (33 to 330 feet).
Title: Observed emission rates in sprite streamer heads
Authors: H. C. Stenbaek-Nielsen, T. Kanmae, and D. D. Sentman: Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska, U.S.A.;
M. G. McHarg: U.S. Air Force Academy, Colorado Springs, Colorado, U.S.A.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL029881, 2007
Recent satellite and laboratory observations suggested that the Amazon rainforest emits large amounts of methane, a potent greenhouse gas. Yet, direct measurements of methane in the air high above the Amazon basin were lacking. Using a light aircraft above two sites in the central and eastern Amazon, Miller et al. collected air samples for four years along vertical profiles spanning four kilometers. Comparing those profiles with data collected at islands in the Atlantic Ocean, which represent background air entering the Amazon basin, the authors find large enhancements of methane over the eastern Amazon, averaging about 34 parts per billion each year. For comparison, the entire north-south, pole-to-pole difference in methane concentrations is about 150 parts per billion. Previous estimates of methane emissions from sources such as wetlands, fires, and aerobic processes in plants are not large enough to explain the observed concentrations above the Amazon. However, the authors suspect that wetlands may release the bulk of this added methane.
Title: Airborne measurements indicate large methane emissions from the eastern Amazon basin
Authors: John B. Miller, Andrew M. Crotwell, Edward. J. Dlugokencky, Peter Bakwin and Pieter P. Tans: National Oceanic and Atmospheric Administration Earth System Research Laboratory, Boulder, Colorado, U.S.A.;
Luciana V. Gatti and Monica T.S. d'Amelio: Divisao de Quimica Ambiental, Laboratorio de Quimica Atmosferica, Insituto de Pesquisas Energéticas e Nucleares, São Paulo, Brazil;
Paulo Artaxo: Instituto de Física, Universidade de São Paulo, São Paulo, Brazil.
Source: Geophysical Research Letters (GRL) paper 10.1029/2006GL029213, 2007
Many scientists expect that Arctic regions will experience amplified warming as the global climate changes, a prediction supported by models and recent observations. Cottier et al. studied interactions between warm Atlantic water carried by the West Spitsbergen Current (situated between Greenland and Norway's Svalbard Islands) and cold waters of the Arctic Front. Their examination reveals that, during the Arctic winter of 2005-2006, periods of sustained winds over Svalbard's West Spitsbergen Shelf caused extensive flooding of the typically cold coastal waters with warm Atlantic water from the West Spitsbergen Current. The winter temperature of water on the West Spitsbergen Shelf reverted to readings typical of Fall, interrupting the region’s normal cycle of sea-ice formation. Winds may also play an important role in distributing heat to other Arctic areas, the authors say.
Title: Wintertime warming of an Arctic shelf in response to large-scale atmospheric circulation
Authors: F. R. Cottier and M. E. Inall: Scottish Association for Marine Science, Oban, Scotland, United Kingdom;
F. Nilsen: University Centre in Svalbard, Longyearbyen, Norway; and Geophysical Institute, University of Bergen, Bergen, Norway;
S. Gerland and V. Tverberg: Norwegian Polar Institute, Tromsø, Norway;
H. Svendsen: Geophysical Institute, University of Bergen, Bergen, Norway.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL029948, 2007
By the end of the 21st century, human-induced ocean warming is likely to accelerate oceanic planetary wave speeds by 35 percent relative to pre-industrial times, a new study suggests. Oceanic planetary waves are long-wavelength, westward-traveling waves linked to Earth’s rotation and shape. Critical to transmitting energy and nutrients throughout the oceans, they can intensify western boundary currents such as the Gulf Stream and the Kuroshio Current. Theory predicts that the waves’ propagation speeds increase as density differences in the ocean's water column become more sharply delineated. Fyfe and Saenko note that human-induced ocean warming over the last 40 years has likely increased density contrast between surface and deep-ocean zones. Through analysis of climate models, they forsee the potentially large speed-up of oceanic planetary waves by century’s end as a result. Morever, they find that such warming may have already produced a detectable speed-up of low-latitude North Pacific oceanic planetary waves. These wave speed-ups, based on emissions scenarios from the Intergovernmental Panel on Climate Change, will have important effects on year-to-year climate variability, the authors say.
Title: Anthropogenic speed-up of oceanic planetary waves
Authors: John C. Fyfe and Oleg A. Saenko: Canadian Centre for Climate Modelling and Analysis, Environment Canada, Victoria, British Columbia, Canada.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL029859, 2007
Gudmundsson and Andrew test the possibility of mechanical interaction between eight volcanoes in the central part of the active Iceland rift zone. There, the average distance between the volcanoes is 30 kilometers (19 miles), and each volcano is thought to have a shallow magma chamber. Many of Earth’s active volcanoes occur in clusters. When assessing volcanic hazards and risks, it is important to know in what way, if any, volcanoes within a given cluster interact. The new results from various numerical models indicate that stress concentrations between neighboring volcanoes favor mechanical interactions. Furthermore, interactions between volcanoes in a pair, such as simultaneous dike emplacement, earthquakes, and deformation, may be common in the part of Iceland studied. Many observations there support this model prediction, the authors note.
Title: Mechanical interaction between active volcanoes in Iceland
Authors: Agust Gudmundsson and Ruth E. B. Andrew: Department of Structural Geology and Geodynamics, Geoscience Centre, University Göttingen, Göttingen, Germany.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL029873, 2007
New research indicates that water levels in the Mediterranean Sea rose and fell several times during a period in which the sea became separated from the Atlantic Ocean. During the so-called Messinian Salinity Crisis, believed to have begun about 6 million years ago, a combination of tectonic uplift and sea-level variation in the Atlantic Ocean progressively isolated the Mediterranean Sea. Under such conditions, the Mediterranean's water level is expected to have varied significantly (more than one thousand meters) depending on rates of river transport, rain, evaporation, and land uplift. Using seismic surveys, Gargani and Rigollet observed several surfaces of erosion in the Nile Delta. Based on their geometry, those features must have formed during the Messinian Salinity Crisis at a depth of 1500 to 2250 meters (4921 to 7382 feet) beneath the present-day water level of the Mediterranean. Using a numerical model that weighs hydrologic inputs and outputs to determine scenarios favoring basin isolation, the authors match these erosion horizons to likely formation scenarios. Their findings demonstrate that water levels in the Mediterranean did in fact rise and fall several times during the Messinian Salinity Crisis.
Title: Mediterranean Sea level variations during the Messinian Salinity Crisis
Authors: Julien Gargani: Laboratoire Géodynamique des Rifts et Marges Passives, Université du Maine, Le Mans, France; Now at Institut Français du Pétrole, Rueil-Malmaison, France;
Christophe Rigollet: Gaz de France, Saint-Denis, France.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL029885, 2007
A proposed joint U.S.-European satellite mission could provide global estimates of surface-water elevation within river channels. Although such a satellite would not directly observe river discharge, water-level observations could be assimilated into a hydrology/hydrodynamics model to provide spatially and temporally continuous fields of river discharge. Andreadis et al. evaluate such a system using synthetically generated satellite observations over a reach of the Ohio River. Using assumed satellite overpass frequencies of 8, 16, and 32 days, the study demonstrates significant error reductions in estimates of water-surface elevation and discharge relative to simulations without assimilation—especially during the period between satellite overpasses. While humans use 54 percent of accessible global stream runoff for agriculture, industry, and municipal consumption, estimates of river discharge globally remain highly uncertain due to limitations of direct observations, especially in developing countries and remote regions. The proposed WatER (Water Elevation Recovery) satellite would include an altimeter using a pair of synthetic aperture radar antennae.
Title: Prospects for river discharge and depth estimation through assimilation of swath-altimetry into a raster-based hydrodynamics model
Authors: Konstantinos M. Andreadis and Dennis P. Lettenmaier: Department of Civil and Environmental Engineering, University of Washington, Seattle, Washington, U.S.A.;
Elizabeth A. Clark: Department of Geological and Environmental Sciences, Stanford University, Stanford, California, U.S.A.;
Douglas E. Alsdorf: School of Earth Sciences, Ohio State University, Columbus, Ohio, U.S.A.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL029721, 2007
To better understand how an important atmospheric pollutant disperses and transforms, Moteki et al. used an airborne, single-particle, soot photometer to study urban plumes in the lower troposphere around Nagoya, Japan. The researchers observed particles of black carbon—an aerosol that is emitted from fossil-fuel combustion and biomass burning and known to efficiently absorb visible sunlight and heat the atmosphere. Many climate models include the effect of these particles on the atmosphere, but approach their dispersion in an idealized way. From the new observations of freshly emitted black-carbon particles, the authors conclude that those particles become well-mixed within the atmosphere 12 hours after emission. The observations also indicated changes in particle size. In the Nagoya plumes, the authors found that black carbon particles with a core diameter of 180 nanometers increased in size at a rate of 2.3 percent per hour. Larger particles increased at a slower rate of one percent per hour. Particles grew as sulfates and organic carbons coated them. Light absorption by black-carbon particles can almost double if the particles are coated by other pollutants.
Title: Evolution of mixing state of black carbon particles: Aircraft measurements over the western Pacific in March 2004
Authors: N. Moteki, Y. Kondo, Y. Miyazaki, N. Takegawa, and T. Miyakawa: Research Center of Advances Science and Technology, University of Tokyo, Tokyo, Japan;
Y. Komazaki: Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan;
G. Kurata: Department of Ecological Engineering, Toyohashi University of Technology, Toyohashi, Japan; now at Department of Urban and Environmental Engineering, Kyoto University, Kyoto, Japan;
T. Shirai: Earth Observation Research and Application Center, Japan Aerospace Exploration Agency; also at National Institute for Environmental Studies, Tsukuba, Japan;
D. R. Blake: Department of Chemistry, University of California, Irvine, California, U.S.A.;
M. Koike: Department of Earth and Planetary Science, University of Tokyo, Tokyo, Japan.
Source: Geophysical Research Letters (GRL) paper 10.1029/2006GL028943, 2007
In a new study, scientists have characterized parts of the Southern Ocean with unprecedented detail and tracked trends and disturbances of an important surface layer of water near Antarctica. Although general ocean circulation models increasingly produce realistic representations of the deep, well-mixed surface layer known as the Subantarctic Mode Water (SAMW), detailed distributions have been unreliable. Moreover, verification of such distributions is not always available for remote regions of the ocean during winter months. Aoki et al. investigate the layer during winter, when the SAMW forms from convection north of the Subantarctic Front of the Antarctic Circumpolar. The authors use an ocean general circulation model substantiated by floating-instrument measurements. They find that sudden transitions from a deep to shallow mixed layer were effected by near-surface flows associated with gravitational forces and the Earth's rotation. Underwater topography steers these flows, implying a link between underwater features and the formation of thick SAMW.
Title: Formation regions of Subantarctic Mode Water detected by OFES and Argo profiling floats
Authors: Shigeru Aoki and Humio Mitsudera: Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan;
Mieko Hariyama: Graduate School of Environmental Science, Hokkaido University, Sapporo, Japan; Now at NNT Communications, Tokyo, Japan;
Hideharu Sasaki: Earth Simulator Center, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan;
Yoshikazu Sasai: Frontier Research Center for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL029828, 2007
Ocean eddies can behave like inverted chimneys that drain a form of sea-borne energy, called near-inertial energy, into the watery depths, a new study finds. Near-inertial waves, such as Rossby waves, travel through the bulk of the ocean and respond to rotational forces. While theoretical studies characterize near-inertial waves in an idealized way, Zhai et al. sought to model them in a more realistic setting by using a model of the North Atlantic that is driven by varying wind forcing and that has 1/12-degree-of-longitude resolution. The authors find that near-inertial energy is strongly influenced by eddies. In particular, the interior of the subtropical gyre, an eddy system driven by the trade winds and westerly winds, shows very low levels of near-inertial energy, contrary to expectations.
Title: Spreading of near-inertial energy in a 1/12° model of the North Atlantic Ocean
Authors: Xiaoming Zhai and Richard J. Greatbatch: Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, Canada;
Carsten Eden: Leibniz Institute of Marine Sciences at the Christian-Albrechts University of Kiel (IFM-GEOMAR), Kiel, Germany.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL029895, 2007
New measurements of South American rocks indicate weakness of Earth’s magnetic field when the ancient rocks were made. Celino et al. scrutinized basalts and gabbros more than a billion years old from what’s known as the Amazon craton in Brazil. Cratons are stable parts of the continental crust containing Earth's oldest rocks. The researchers used paleomagnetic techniques that enable them to deduce from magnetic signatures in crystal grains imprints of the Earth’s magnetic field as it was when the rock formed. Comparing the results of two magnetic intensity extraction methods, the authors find that the magnetic intensity in billion-year-old rocks in the Amazon craton is below half that of the present magnetic field. Their measurements, which are the first such observations from South America, agree with similar data from cratons in Canada. The Amazon results also support the idea that increases in magnetic field strength during the Earth's first 3 billion years occurred gradually. This implies that growth of the solid inner core occurred later, in accordance with recent thermodynamic models.
Title: LTD-Thellier paleointensity of 1.2 Ga Nova Floresta mafic rocks (Amazon craton)
Authors: Klaydson R. Celino, Ricardo I. F. Trindade, and Eric Tohver: Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, São Paulo, Brazil.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL029550, 2007 (in press, as of 7 June 2007)
Scientists have now used sophisticated computational networks to generate sea surface temperature maps for a time period before widespread satellite data was available. Artificial neural networks—which are numerically complex modeling techniques inspired by biological nervous systems—operate by invoking 'training' algorithms whereby a set of input variables produces a specific set of output targets within a prescribed error level. Such networks have been previously used to identify ocean features in satellite imagery and to forecast sea surface temperatures. Using similar techniques, Garcia-Gorriz and Garcia-Sanchez have recently trained neural networks to compute sea surface temperatures in the western Mediterranean Sea using meteorological information as inputs and concurrent satellite-derived, sea surface temperatures as targets. Their networks predicted both the seasonal and interannual variability of sea surface temperatures, reproducing the impact of the 2003 European summer heat wave. Turning next to the western Mediterranean of 1960 to 1981, when satellite data were scarce, the authors applied the network technique to predict sea surface temperature maps for that period. Those are providing insights into sea circulation patterns through time and are contributing to the validation of circulation model results.
Title: Prediction of sea surface temperatures in the western Mediterranean Sea by neural networks using satellite observations
Authors: Elisa Garcia-Gorriz: European Comission-DG Joint Research Centre, Institute for Environment and Sustainability, Global Environment Monitoring Unit, Ispra, Italy;
Joan Garcia-Sanchez: Universitat de Barcelona, Departament d'Astronomia i Meteorologia, Barcelona, Spain; now at European Commission-DG Joint Research Centre, Institute for the Protection and Security of the Citizen, Ispra, Italy.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL029888, 2007
While reconstructing the precipitation history of the Upper Colorado River Basin back to the 8th century A.D., scientists have uncovered evidence of a six-decades-long drought in the mid-1100s. To estimate yearly streamflow in a region’s past, researchers can evaluate tree ring widths, where narrow rings mean dryer years. Previously, tree-ring analyses in the basin had determined annual streamflow patterns only back to the A.D. 1400s. Meko et al. have now used a newly developed network of tree-ring sites composed of living trees and dead remnant wood to extend the basin’s precipitation history back to A.D. 762. That expanded record includes a period of widespread drought known as the Medieval Climate Anomaly. The anomaly persisted sometime between A.D. 900 and A.D. 1300. It was accompanied by a 20 percent precipitation decline in areas of the western United States. The timing of the newfound extreme drought of the 12th century is consistent with Medieval Climate Anomaly conditions inferred from tree ring data elsewhere in the western United States. Understanding changes in streamflow in the Upper Colorado River Basin on long timescales is critical to water resources management in the United States' desert southwest.
Title: Medieval drought in the Upper Colorado River Basin
Authors:
David M. Meko, Christopher A. Baisan, Troy Knight, Malcolm K. Hughes, and Matthew W. Salzer: Laboratory of Tree-Ring Research, University of Arizona, Tucson, Arizona, U.S.A.;
Connie A. Woodhouse: Department of Geography and Regional Development, University of Arizona, Tucson, Arizona, U.S.A.;
Jeffrey J. Lukas: Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado, U.S.A.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL029988, 2007
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Geophysical Research Letters