Active hydrate destabilization in Lake Baikal,Siberia?   总被引：1，自引：0，他引：1  

Marc De Batist  Jan Klerkx  Pieter Van Rensbergen  Maarten Vanneste  Jeffrey Poort  Alexander Y. Golmshtok  rei A. Kremlev  Oleg M. Khlystov  Petr Krinitsky 《地学学报》2002,14(6):436-442

ABSTRACT In this paper, we present new seismic and heat-flow data that show the base of the hydrate stability zone (BHSZ) in Lake Baikal to be locally characterized by abnormal variations in depth, with distinct regions of deeper-than-normal and regions of shallower-than-normal BHSZ. These variations are related to strong lateral variations in heat flow, and occur in close association with important rift-basin faults. Areas of shallow BHSZ are also characterized by the presence of several methane seeps and mud volcanoes at the lake floor. We infer that the seeps are the surface expression of escape pathways for overpressured fluids generated by the dissociation of pre-existing hydrates, in response to a thermal pulse caused by an upward flow of hydrothermal fluids towards the BHSZ. It thus seems that present-day hydrate dissociation in Lake Baikal is modulated by the tectonic activity in the rift rather than by – climatically controlled – changes in lake level or water temperature.  相似文献   

Late Holocene fire impact and post-fire regeneration from the Bereket basin, Taurus Mountains, southwest Turkey     

David Kaniewski  Etienne Paulissen  Marc Waelkens 《Quaternary Research》2008,70(2):228-239

The 800 cm long sequence from the Bereket provides the first detailed fire history in the western Taurus Mountains for the last three millennia. The main disturbances occurred during the Bey?ehir Occupation Phase (BO Phase), a period of intensive polyculture and dated at Bereket from ca. 2230 to 1550 cal yr BP. Four phases of local and extra-local fire periods have been recorded at 2320-2240, 1985-1970, 1865-1820 cal yr BP and post-AD 1950. The fire history established for the BO Phase is complex, with fire periods alternating with periods without local fires, as is the case for the late BO Phase from 1820 until 1550 cal yr BP. It is suggested that the past agricultural practices including fires cause a higher soil erodibility than agricultural practices without fires. A climatic shift towards aridity during Roman times may have triggered the observed change in fire regime but local processes, mainly human disturbances, appear to be the proximal cause of all recorded changes. In the Bereket surroundings, fires led to a simplification of the vegetation structure, favouring soil erosion, pastures and intensive cultivation.  相似文献   

Multibeam bathymetry and sidescan imaging of the Rivera Transform–Moctezuma Spreading Segment junction, northern East Pacific Rise: New constraints on Rivera–Pacific relative plate motion     

William L. Bandy  Franois Michaud  Jrme Dyment  Carlos A. Mortera-Gutirrez  Jacques Bourgois  Thierry Calmus  Marc Sosson  Jose Ortega-Ramirez  Jean-Yves Royer  Bernard Pontoise  Bertrand Sichler 《Tectonophysics》2008,454(1-4):70-85

To better understand the recent motion of the Pacific plate relative to the Rivera plate and to better define the limitations of the existing Rivera–Pacific plate motion models for accurately predicting this motion, total-field magnetic data, multibeam bathymetric data and sidescan sonar images were collected during the BART and FAMEX campaigns of the N/O L'Atalante conducted in April and May 2002 in the area surrounding the Moctezuma Spreading Segment of the East Pacific Rise, located offshore of Manzanillo, Mexico, at 106°16′W, between 17.8°N and 18.5°N. Among the main results are: (1) the principle transform displacement zone of the Rivera Transform is narrow and well defined east of 107o15′W and these azimuths should be used preferentially when deriving new plate motion models, and (2) spreading rates along the Moctezuma Spreading Segment should not be used in plate motion studies as either seafloor spreading has been accommodated at more than one location since the initiation of seafloor spreading in the area of the Moctezuma Spreading Segment, or this spreading center is not a Rivera–Pacific plate boundary as has been previously assumed. Comparison of observed transform azimuths with those predicted by the best-fit poles of six previous models of Rivera–Pacific relative motion indicate that, in the study area, a significant systematic bias is present in the predictions of Rivera–Pacific motion. Although the exact source of this bias remains unclear, this bias indicates the need to derive a new Rivera–Pacific relative plate motion model.  相似文献   

Contamination of surface waters by mining wastes in the Milluni Valley (Cordillera Real,Bolivia): Mineralogical and hydrological influences     

Matías Miguel Salvarredy-Aranguren  Anne Probst  Marc Roulet  Marie-Pierre Isaure 《Applied Geochemistry》2008

This study is one of very few dealing with mining waste contamination in high altitude, tropical-latitude areas exploited during the last century. Geochemical, mineralogical and hydrological characterizations of potentially harmful elements (PHEs) in surface waters and sediments were performed in the Milluni Valley (main reservoir of water supply of La Paz, Bolivia, 4000 m a.s.l.), throughout different seasons during 2002–2004 to identify contamination sources and sinks, and contamination control parameters. PHE concentrations greatly exceeded the World Health Organization water guidelines for human consumption. The very acidic conditions, which resulted from the oxidation of sulfide minerals in mining waste, favoured the enrichment of dissolved PHEs (Cd > Zn ? As ? Cu ∼ Ni > Pb > Sn) in surface waters downstream from the mine. Stream and lake sediments, mining waste and bedrock showed the highest PHE content in the mining area. With the exception of Fe, the PHEs were derived from specific minerals (Fe, pyrite; Zn, Cd, sphalerite, As, Fe, arsenopyrite, Cu, Fe, chalcopyrite, Pb, galena, Sn, cassiterite), but the mining was responsible for PHEs availability. Most of the PHEs were extremely mobile (As > Fe > Pb > Cd > Zn ∼ Cu > Sn) in the mining wastes and the sediments downstream from the mine. pH and oxyhydroxides mainly explained the contrasted availability of Zn (mostly in labile fractions) and As (associated with Fe-oxyhydroxides). Unexpectedly, Pb, Zn, As, and Fe were significantly attenuated by organic matter in acidic lake sediments.  相似文献   

Inference of the structure of karst conduits using quantitative tracer tests and geological information: example of the Swiss Jura   总被引：2，自引：0，他引：2  

Jérôme Perrin  Marc Luetscher 《Hydrogeology Journal》2008,16(5):951-967

Karst aquifers are known for being particularly heterogeneous with highly transmissive conduits embedded in low permeability volumes of rock matrix. Artificial tracer experiments have been carried out in a complex karst aquifer of the folded Jura Mountains in Switzerland with the aim of deciphering the conduit organisation. It is shown that tracer experiments with multiple injection points under different flow conditions can lead to useful information on the conduits’ structure. This information has been combined with data from structural geology, spring hydrology, and speleological observations. A conceptual model of the conduit network shows that a detailed inference of the conduit organisation can be reached: geology controls conduit location and orientation; spring hydrology, including temporary springs, constrains conduit elevations and relative hydraulic heads in the aquifer subsystems; and tracer tests identify major flow paths and outlets of the system and dilution caused by non-traced tributaries, as well as the presence of secondary flow routes. This understanding of the Aubonne aquifer structure has important implications for the future management of the groundwater resource. Similar approaches coupling geological information, spring hydrology, and multi-tracer tests under various flow conditions may help to characterise the structure of the conduit network in karst aquifers.  相似文献   

Tracking and orbit determination performance of the GRAS instrument on MetOp-A   总被引：8，自引：3，他引：5  

Oliver Montenbruck  Yago Andres  Heike Bock  Tom van Helleputte  Jose van den Ijssel  Marc Loiselet  Christian Marquardt  Pierluigi Silvestrin  Pieter Visser  Yoke Yoon 《GPS Solutions》2008,12(4):289-299

The global navigation satellite system receiver for atmospheric sounding (GRAS) on MetOp-A is the first European GPS receiver providing dual-frequency navigation and occultation measurements from a spaceborne platform on a routine basis. The receiver is based on ESA’s AGGA-2 correlator chip, which implements a high-quality tracking scheme for semi-codeless P(Y) code tracking on the L1 and L2 frequency. Data collected with the zenith antenna on MetOp-A have been used to perform an in-flight characterization of the GRAS instrument with focus on the tracking and navigation performance. Besides an assessment of the receiver noise and systematic measurement errors, the study addresses the precise orbit determination accuracy achievable with the GRAS receiver. A consistency on the 5 cm level is demonstrated for reduced dynamics orbit solutions computed independently by four different agencies and software packages. With purely kinematic solutions, 10 cm accuracy is obtained. As a part of the analysis, an empirical antenna offset correction and preliminary phase center correction map are derived, which notably reduce the carrier phase residuals and improve the consistency of kinematic orbit determination results.

Oliver MontenbruckEmail:

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SPIRIT. SPOT 5 stereoscopic survey of Polar Ice: Reference Images and Topographies during the fourth International Polar Year (2007–2009)     

Jérôme Korona  Etienne Berthier  Marc Bernard  Frédérique Rémy  Eric Thouvenot 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(2):204-212

Monitoring the evolution of polar glaciers, ice caps and ice streams is of utmost importance because they constitute a good indicator of global climate change and contribute significantly to ongoing sea level rise. Accurate topographic surveys are particularly relevant as they reflect the geometric evolution of ice masses. Unfortunately, the precision and/or spatial coverage of current satellite missions (radar altimetry, ICESat) or field surveys are generally insufficient. Improving our knowledge of the topography of Polar Regions is the goal of the SPIRIT (SPOT 5 stereoscopic survey of Polar Ice: Reference Images and Topographies) international polar year (IPY) project. SPIRIT will allow (1) the acquisition of a large archive of SPOT 5 stereoscopic images covering most polar ice masses and, (2) the delivery of digital terrain models (DTM) to the scientific community.Here, we present the architecture of this project and the coverage achieved over northern and southern polar areas during the first year of IPY (July 2007 to April 2008). We also provide the first accuracy assessments of the SPIRIT DTMs. Over Jakobshavn Isbrae (West Greenland), SPIRIT elevations are within ±6 m of ICESat elevations for 90% of the data. Some comparisons with ICESat profiles over Devon ice cap (Canada), St Elias Mountains (Alaska) and west Svalbard confirm the good overall quality of the SPIRIT DTMs although large errors are observed in the flat accumulation area of Devon ice cap. We then demonstrate the potential of SPIRIT DTMs for mapping glacier elevation changes. The comparison of summer-2007 SPIRIT DTMs with October-2003 ICESat profiles shows that the thinning of Jakobshavn Isbrae (by 30–40 m in 4 years) is restricted to the fast glacier trunk. The thinning of the coastal part of the ice stream (by over 100 m) and the retreat of its calving front (by up to 10 km) are clearly depicted by comparing the SPIRIT DTM to an ASTER April-2003 DTM.  相似文献   

Role of particle size in till-fabric characteristics: systematic variation in till fabric from Vestari-Hagafellsjökull, Iceland     

Simon J. Carr  Marc A. Goddard 《Boreas: An International Journal of Quaternary Research》2007,36(4):371-385

Till-fabric analysis has often been used to interpret glacier flow directions and subglacial dynamics using vector-based statistics, but recent data suggest that such analysis may also effectively indicate former glacier dynamics. The results of a fabric investigation of subglacially strained till deposited during a surge of Vestari-Hagafellsjökull, Iceland, are presented. Till fabric was collected at four sites within a limited area where ice-flow direction during deposition was known from subglacial bedforms at the site. Analysis was carried out on elongate grains (axial ratio <1.5:1) at seven size fractions, with the a-axis length ranging from 0.25 to 32 mm. The largest grains tend to be parallel to ice flow, whereas smaller grains reflect a mix of parallel and transverse orientations. The implications of these data for the role and validity of till-fabric analysis are discussed, with reference to vector analyses and the compilation of fabric shape envelopes. It is noted that, in contrast to laboratory experimental data, neither March nor Jeffery mechanisms explain the fabric configurations reported. It is concluded that a standardized approach is necessary for collecting fabric data, and in many situations analysis of data populations at a range of particle sizes is desirable.  相似文献   

Pattern recognition in photogrammetry and remote sensing: PRRS 2006 in conjunction with ICPR 2006     

Marc  Bartels Hong  Wei 《The Photogrammetric Record》2007,22(117):97-99

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10Be dating of boulders on moraines from the last glacial period in the Nyainqentanglha mountains,Tibet     

DONG GuoCheng  YI ChaoLu  Marc CAFFEE 《中国科学:地球科学(英文版)》2014,57(2):221-231

Chronologies of glacial advances during the last glacial period in the Nyainqentanglha mountain range may provide constraints on the past climate in a transition zone of the Asian monsoon.We present 15 new10Be exposure ages from two moraines in the Payuwang valley,on the north slope of the range.The inner moraine has exposure ages ranging from 18.0±1.7 to 30.6±2.8 ka(n=10),with a mean age of 23.8±4.0 ka,corresponding to the global Last Glacial Maximum(LGM).The outer moraine yields exposure ages ranging from 18.0±1.6 to 39.9±3.7 ka(n=5).Evidence for weathering leads us to view the oldest age as a minimum age,placing moraine formation during MIS3.Chronologies from the last glacial period from south slope of the Nyainqentanglha support this interpretation.Thus,there appears to have been a local LGM(LLGM)during MIS3 and a more limited glacial advance during the global LGM.Glacial advances during MIS3 in the Nyainqentanglha may correlate with millennial-scale climate change(Heinrich events).  相似文献