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1.
Seismic velocities from the Yaquina forearc basin off Peru: evidence for free gas within the gas hydrate stability zone 总被引：3，自引：0，他引：3
Gesa L. Netzeband Christian P. Hübscher Dirk Gajewski Jan W. G. Grobys Jörg Bialas 《International Journal of Earth Sciences》2005,94(3):420-432
Multichannel seismic (MCS) data from the Yaquina forearc basin off Peru reveal a complex distribution of gas and gas hydrate related reflections. Lateral variations of the reflection pattern at the assumed base of the gas hydrate stability zone in terms of continuity, amplitude, and signal attenuation underneath are observed, as well as the possible occurrence of paleo-bottom simulating reflectors (BSRs). Phase reversed reflections above the bottom simulating reflector point to free gas within the gas hydrate stability zone (GHSZ). To constrain the interpretation of the observed reflection pattern we calculated the velocity distribution along the MCS line from high-resolution ocean bottom hydrophone recordings with two independent methods. Heat flux values estimated on the basis of the velocity-depth functions increase with decreasing amplitude of the BSR and peak near chemoherms. These results suggest a model of the Yaquina Basin where free gas is trapped under parts of the BSR, and within the GHSZ, particularly under the seafloor and under an erosional unconformity. The hypothesis of a paleo-BSR that reflects the uplift of the base of the hydrate stability zone caused by the deposition of a particular sediment sequence is supported by the estimated heat flux values. 相似文献
2.
M. Focardi E. Pace M. Farina A. M. Di Giorgio J. Colomé Ferrer I. Ribas C. Sierra Roig L. Gesa Bote J. C. Morales J. Amiaux C. Cara J. L. Augurés E. Pascale G. Morgante V. Da Deppo M. Pancrazzi V. Noce S. Pezzuto M. Frericks F. Zwart G. Bishop K. Middleton P. Eccleston G. Micela G. Tinetti 《Experimental Astronomy》2018,45(1):1-20
In this paper we present the electromagnetic modeling and beam pattern measurements of a 16-elements ultra wideband sparse random test array for the low frequency instrument of the Square Kilometer Array telescope. We discuss the importance of a small array test platform for the development of technologies and techniques towards the final telescope, highlighting the most relevant aspects of its design. We also describe the electromagnetic simulations and modeling work as well as the embedded-element and array pattern measurements using an Unmanned Aerial Vehicle system. The latter are helpful both for the validation of the models and the design as well as for the future instrumental calibration of the telescope thanks to the stable, accurate and strong radio frequency signal transmitted by the UAV. At this stage of the design, these measurements have shown a general agreement between experimental results and numerical data and have revealed the localized effect of un-calibrated cable lengths in the inner side-lobes of the array pattern. 相似文献
3.
Katja K. Hirsch Magdalena Scheck-Wenderoth Jan-Diederik van Wees Gesa Kuhlmann Douglas A. Paton 《Marine and Petroleum Geology》2010
The Orange Basin offshore southwest Africa appears to represent a classical example of continental rifting and break up associated with large-scale, transient volcanism. The presence of lower crustal bodies of high seismic velocities indicates that large volumes of igneous crust formed as a consequence of lithospheric extension. 相似文献
4.
Evapotranspiration and canopy characteristics of two lodgepole pine stands following mountain pine beetle attack 总被引：1，自引：0，他引：1 
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下载免费PDF全文 Mathew G. Brown T. Andrew Black Zoran Nesic Vanessa N. Foord David L. Spittlehouse Arthur L. Fredeen Rebecca Bowler Nicholas J. Grant Philip J. Burton J. A. Trofymow Dominic Lessard Gesa Meyer 《水文研究》2014,28(8):3326-3340
Over the past decade, British Columbia (BC), has experienced the largest mountain pine beetle (MPB) outbreak on record. This study used the eddy‐covariance (EC) technique to examine the impact of the MPB attack on evapotranspiration (E) and associated canopy characteristics of two lodgepole pine stands with secondary structure (trees, saplings and seedlings surviving the attack) located in central BC. MPB‐06, an 85‐year‐old almost pure stand of pine trees, was first attacked in 2006, and by 2010, ~80% of the trees had been killed. MPB‐03, a 110‐year‐old stand with an overstory consisting of over 90% pine and a developed sub‐canopy, was first attacked in 2003 and by 2007 had > 95% pine canopy mortality. EC measurements began in August 2006 at MPB‐06 and in March 2007 at MPB‐03, and continued for four years. Annual total E ranged from 226 mm to 237 mm at MPB‐06, and from 280 to 297 mm at MPB‐03, showing relatively little year‐to‐year change at both sites over the four years. Increased E from the accelerated growth of the surviving vegetation (secondary structure, shrubs and herbs) compensated for reduction in E due to the death of the overstory. Monthly average daytime canopy conductance, the Priestley–Taylor (α), and the canopy–atmosphere decoupling coefficient (Ω) steadily increased during the growing season reaching approximate maximum values of 5 mm s?1, 0.75 and 0.12, respectively. Potential evapotranspiration was approximated using a vapour pressure deficit‐dependent α obtained at high soil water content. Calculated water deficits indicated some water‐supply limitation to the surviving trees and understory at both sites. Rates of root zone drainage during the growing season were low relative to precipitation. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Gesa Kuhlmann Selwyn Adams Curnell Campher David van der Spuy Rolando di Primio Brian Horsfield 《Marine and Petroleum Geology》2010,27(4):973-992
Using a 2D seismic dataset that covers part of the southern Orange Basin offshore South Africa, we reconstructed the geological evolution of the basin. This evolutionary model was then used to investigate the occurrence of natural gas within the sedimentary column and the distribution of gas leakage features in relation to the observed sedimentary and tectonic structures developed in the post-rift succession since the Early Cretaceous. The Cretaceous succession has been subdivided into five seismic units. The highest sedimentation rates occur within the Barremian/Aptian (unit C1) and the Turonian/Coniacian (unit C3). Two Cenozoic units (T1 and T2) have been distinguished. These show a sudden decrease in sedimentation rate for the whole of the Cenozoic. Three phases of gravitational tectonics, with two Late Cretaceous phases of mass movement in the northern study area and Cenozoic slumping in the southern study area, have been related to sedimentation rates, sea-level changes, paleoenvironmental evolution and regional tectonics. The occurrence of natural gas leakage follows a coast-parallel distribution within the study area. In the near shore part at water depths shallower than 400 m, massive gas chimneys penetrate through the sediment layers and reach the (near-) surface. Within an intermediate narrow band, between 300 and <500 m water depth, the gas migrates more diffusely through sub-vertical faulted Cretaceous sediments, while in the outer part of the basin, through the Cretaceous and Cenozoic gravitational wedges, only very few signs of gas accumulation and migration can be seen along the faults. A conceptual model has been established with the Aptian source rock generating gas in the outer part of the basin. This source rock underlies the Cenozoic wedge in the south and the thick Cretaceous wedge in the north and is a postulated source for the natural gas within the sedimentary column. This thermogenically generated gas does not migrate directly through the gravitational faults and the above lying sediments, but moves buoyancy driven up-dip along stratigraphic layers, to escape through the sediments to the sea-floor in the inner shelf area. 相似文献
7.
The entrainment of bottom deposits (silt and clay) into newly formed ice was investigated in the Amderma/Vaygach flaw lead in the southwestern Kara Sea, Siberian Arctic. Fine-grained bottom deposits and sea ice sediments (SIS) were analyzed by granulometry, scanning electron microscopy and X-ray diffractometry. On average, SIS contain by a factor of four times more silt than the shelf deposits (66.7% vs. 16.3%), and the SIS clay percentage is more than three-fold of the bottom value (31.2% vs. 9.1%). Sand-sized particles are significantly less abundant in SIS compared to bottom sediment (2.1% vs. 74.6%). The preferred entrainment of silt into ice is underpinned by the enhanced silt-to-clay-ratio in SIS compared to bottom deposits. Though silt is preferably entrained into SIS, no evidence was found for preferential ice-entrainment of any silt sub-fraction (coarse, medium or fine). However, sub-angular- and angular-discoidal silt particles are favorably entrained into local sea ice. Clay mineral assemblages in SIS and shelf surface sediments match very well revealing that no individual clay mineral is preferably enriched in SIS or reduced at the bottom. The general textural, compositional and statistical match of fine-grained shelf surface deposits and SIS proves that bottom sediment is the principle source for ice-entrained material in the study area. We propose e.g. wave action and thermohaline convection to take sediment particles upward from the bottom nepheloid layer into the well-mixed 10–40 m deep water column of the Amderma/Vaygach flaw lead, and the turbulent process of suspension freezing to bring sediment particles and frazil crystals into contact, finally leading to the formation of sediment-laden ice. The role of SIS entrainment and export for local/regional shelf erosion and coastal retreat is of minor importance in the SW Kara Sea compared to other circum-Arctic shelf seas. However, the characteristic clay mineral assemblage of local SIS and bottom deposits can help identify the origin of SIS both on regional and Arctic-wide scales. 相似文献
8.
Barbara J. Benson John J. Magnuson Olaf P. Jensen Virginia M. Card Glenn Hodgkins Johanna Korhonen David M. Livingstone Kenton M. Stewart Gesa A. Weyhenmeyer Nick G. Granin 《Climatic change》2012,112(2):299-323
Often extreme events, more than changes in mean conditions, have the greatest impact on the environment and human well-being.
Here we examine changes in the occurrence of extremes in the timing of the annual formation and disappearance of lake ice
in the Northern Hemisphere. Both changes in the mean condition and in variability around the mean condition can alter the
probability of extreme events. Using long-term ice phenology data covering two periods 1855–6 to 2004–5 and 1905–6 to 2004–5
for a total of 75 lakes, we examined patterns in long-term trends and variability in the context of understanding the occurrence
of extreme events. We also examined patterns in trends for a 30-year subset (1975–6 to 2004–5) of the 100-year data set. Trends
for ice variables in the recent 30-year period were steeper than those in the 100- and 150-year periods, and trends in the
150-year period were steeper than in the 100-year period. Ranges of rates of change (days per decade) among time periods based
on linear regression were 0.3−1.6 later for freeze, 0.5−1.9 earlier for breakup, and 0.7−4.3 shorter for duration. Mostly,
standard deviation did not change, or it decreased in the 150-year and 100-year periods. During the recent 50-year period,
standard deviation calculated in 10-year windows increased for all ice measures. For the 150-year and 100-year periods changes
in the mean ice dates rather than changes in variability most strongly influenced the significant increases in the frequency
of extreme lake ice events associated with warmer conditions and decreases in the frequency of extreme events associated with
cooler conditions. 相似文献
9.
Einfach sprachlos but not simply speechless: language(s), thought and practice in the social sciences 总被引：1，自引：1，他引：1
Based on the authors' experiences as German-language speakers working at different stages of their careers within Anglo-American human geography, this article reflects on the workings of (foreign) language, not only through academic publications but more widely in research contexts and everyday work. This is done by three personal observations, highlighting the relevance of (foreign) language interactions in terms of research practice as well as the poetics and politics of language. We argue that a wider recognition of language in the practical terms of academic work is called for in the light of an increasing 'internationalization' of academia. 相似文献
10.
Endoskarn assemblages involving the Ca-silicates ilvaite, epidoteand Ca-rich garnet occur along fracture zones in the persodicIlímaussaq intrusion, South Greenland. The 1·16Ga intrusion solidified at a depth of about 3–4 km, belowa cover of sandstones and pillow-basalts of the Eriksfjord Formation.In contrast to typical skarn assemblages, the Ilímaussaqendoskarns contain albite as a main phase and they did not formin metacarbonate rocks, as these are completely lacking in thevicinity of Ilímaussaq. Instead, they record late- topost-magmatic interaction of possibly external Ca-rich fluidswith the alkaline to agpaitic magmatic rocks. Accordingly, endoskarntextures clearly reflect the magmatic textures of the precursorrocks. Phase relations in two endoskarn varieties with epidote+ albite + andradite-rich garnet ± ilvaite ± retrogradeprehnite suggest their formation at about 500°C at highoxygen fugacities slightly above the hematite–magnetiteoxygen buffer [FMQ (fayalite–magnetite–quartz) +5 to FMQ + 7] with later small modifications as a result offluid influx or cooling of the original fluid at about 300–350°C(formation of prehnite) and at about 200–250°C (oxygenisotopic re-equilibration of the albite). One model for theformation of the observed assemblages is the decomposition ofCa-bearing minerals, such as primary eudialyte, clinopyroxeneor ternary feldspar, and redistribution of the Ca by a metasomatizinglate-magmatic fluid. Stable isotope (O, H) investigations, however,favour a model in which seawater was the metasomatizing fluid,which entered the Eriksfjord basalts above the intrusion, reactedwith them (spilitization) and brought about 10–3 mol/lCa along fractures into the metasomatized rocks. Fluid–rockinteraction in the Eriksfjord basalts is documented by abundantchlorite–epidote–quartz assemblages; high fluid/rockratios allowed the fluid to retain its seawater oxygen isotopecomposition. KEY WORDS: agpaite; endoskarn; Ilímaussaq; ilvaite; metasomatism; seawater 相似文献