Modeling studies of the bioluminescence potential dynamics in a high Arctic fjord during polar night     

Shulman  Igor  Cohen  Jonathan H.  Moline  Mark A.  Anderson  Stephanie  Metzger  E. Joseph  Rowley  Clark 《Ocean Dynamics》2022,72(1):37-48

Ocean Dynamics - During polar nights in January 2012 and 2017, significantly higher bioluminescence (BL) potential emissions in the upper 50 m were observed in the fjord Rijpfjorden...  相似文献   

Influence of bedrock structures on the spatial pattern of erosional landforms in small alpine catchments     

Alexandre Loye  Andrea Pedrazzini  Joshua I. Theule  Michel Jaboyedoff  Frédéric Liébault  Richard Metzger 《地球表面变化过程与地形》2012,37(13):1407-1423

Structural settings and lithological characteristics are traditionally assumed to influence the development of erosional landforms, such as gully networks and rock couloirs, in steep mountain rock basins. The structural control of erosion of two small alpine catchments of distinctive rock types is evaluated by comparing the correspondences between the orientations of their gullies and rock couloirs with (1) the sliding orientations of potential slope failures mechanisms, and (2) the orientation of the maximum joint frequency, this latter being considered as the direction exploited primarily by erosion and mass wasting processes. These characteristic orientations can be interpreted as structural weaknesses contributing to the initiation and propagation of erosion. The morphostructural analysis was performed using digital elevation models and field observations. The catchment comprised of magmatic intrusive rocks shows a clear structural control, mostly expressed through potential wedges failure. Such joint configurations have a particular geometry that encourages the development of gullies in hard rock, e.g. through enhanced gravitational and hydrological erosional processes. In the catchment underlain by sedimentary rocks, penetrative joints that act as structural weaknesses seem to be exploited by gullies and rock couloirs. However, the lithological setting and bedding configuration prominently control the development of erosional landforms, and influence not only the local pattern of geomorphic features, but the general morphology of the catchment. The orientations of the maximum joint frequency are clearly associated with the gully network, suggesting that its development is governed by anisotropy in rock strength. These two catchments are typical of bedrock‐dominated basins prone to intense processes of debris supply. This study suggests a quantitative approach for describing the relationship between bedrock jointing and geomorphic features geometry. Incorporation of bedrock structure can be relevant when studying processes governing the transfer of clastic material, for the assessment of sediment yields and in landforms evolution models. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Comment on “Are there connections between the Earth's magnetic field and climate?” by V. Courtillot,Y. Gallet,J.-L. Le Mouël,F. Fluteau,A. Genevey EPSL 253, 328, 2007     

Edouard Bard  Gilles Delaygue 《Earth and Planetary Science Letters》2008,265(1-2):302-307

  相似文献   

Simulated asteroid materials based on carbonaceous chondrite mineralogies     

Daniel T. Britt  Kevin M. Cannon  Kerri Donaldson Hanna  Joanna Hogancamp  Olivier Poch  Pierre Beck  Dayl Martin  Jolantha Escrig  Lydie Bonal  Philip T. Metzger 《Meteoritics & planetary science》2019,54(9):2067-2082

A set of high‐fidelity simulated asteroid materials, or simulants, was developed based on the mineralogy of carbonaceous chondrite meteorites. Three varieties of simulant were developed based on CI1 chondrites (typified by Orgueil), CM2 chondrites (typified by Murchison), and CR2/3 chondrites (multiple samples). The simulants were designed to replicate the mineralogy and physical properties of the corresponding meteorites and anticipated asteroid surface materials as closely as is reasonably possible for bulk amounts. The simulants can be made in different physical forms ranging from larger cobbles to fine‐grained regolith. We analyzed simulant prototypes using scanning electron microscopy, X‐ray fluorescence, reflectance spectroscopy at ambient conditions and in vacuum, thermal emission spectroscopy in a simulated asteroid environment chamber, and combined thermogravimetry and evolved gas analysis. Most measured properties compare favorably to the reference meteorites and therefore to predicted volatile‐rich asteroid surface materials, including boulders, cobbles, and fine‐grained soils. However, there were also discrepancies, and mistakes were made in the original mineral formulations that will be updated in the future. The asteroid simulants are available to the community from the nonprofit Exolith Lab at UCF, and the mineral recipes are freely published for other groups to reproduce and modify as they see fit.  相似文献   

Vegetation impacts soil water content patterns by shaping canopy water fluxes and soil properties          下载免费PDF全文

Johanna Clara Metzger  Thomas Wutzler  Nicolas Dalla Valle  Janett Filipzik  Christoph Grauer  Robert Lehmann  Martin Roggenbuck  Danny Schelhorn  Josef Weckmüller  Kirsten Küsel  Kai Uwe Totsche  Susan Trumbore  Anke Hildebrandt 《水文研究》2017,31(22):3783-3795

Soil water content is a key variable for biogeochemical and atmospheric coupled processes. Its small‐scale heterogeneity impacts the partitioning of precipitation (e.g., deep percolation or transpiration) by triggering threshold processes and connecting flow paths. Forest hydrologists frequently hypothesized that throughfall and stemflow patterns induce soil water content heterogeneity, yet experimental validation is limited. Here, we pursued a pattern‐oriented approach to explore the relationship between net precipitation and soil water content. Both were measured in independent high‐resolution stratified random designs on a 1‐ha temperate mixed beech forest plot in Germany. We recorded throughfall (350 locations) and stemflow (65 trees) for 16 precipitation events in 2015. Soil water content was measured continuously in topsoil and subsoil (210 profiles). Soil wetting was only weakly related to net precipitation patterns. The precipitation‐induced pattern quickly dissipates and returns to a basic pattern, which is temporally stable. Instead, soil hydraulic properties (by the proxy of field capacity) were significantly correlated with this stable soil water content pattern, indicating that soil structure more than net precipitation drives soil water content heterogeneity. Also, both field capacity and soil water content were lower in the immediate vicinity of tree stems compared to further away at all times, including winter, despite stemflow occurrence. Thus, soil structure varies systematically according to vegetation in our site. We conclude that enhanced macroporosity increases gravity‐driven flow in stem proximal areas. Therefore, although soil water content patterns are little affected by net precipitation, the resulting soil water fluxes may strongly be affected. Specifically, this may further enhance the channelling of stemflow to greater depth and beyond the rooting zone.  相似文献   

The orientations of molecular clouds in the outer Galaxy: evidence for the scale of the turbulence driver?     

Sami Dib  C. Jakob Walcher  Mark Heyer  Edouard Audit  Laurent Loinard 《Monthly notices of the Royal Astronomical Society》2009,398(3):1201-1206

Supernova (SN) explosions inject a considerable amount of energy into the interstellar medium (ISM) in regions with high-to-moderate star formation rates. In order to assess whether the driving of turbulence by supernovae is also important in the outer Galactic disc, where the star formation rates are lower, we study the spatial distribution of molecular cloud (MC) inclinations with respect to the Galactic plane. The latter contains important information on the nature of the mechanism of energy injection into the ISM. We analyse the spatial correlations between the position angles (PAs) of a selected sample of MCs (the largest clouds in the catalogue of the outer Galaxy published by Heyer et al). Our results show that when the PAs of the clouds are all mapped to values into the  [0°, 90°]  interval, there is a significant degree of spatial correlation between the PAs on spatial scales in the range of 100–800 pc. These scales are of the order of the sizes of individual SN shells in low-density environments such as those prevailing in the outer Galaxy and where the metallicity of the ambient gas is of the order of the solar value or smaller. These findings suggest that individual SN explosions, occurring in the outer regions of the Galaxy and in likewise spiral galaxies, albeit at lower rates, continue to play an important role in shaping the structure and dynamics of the ISM in those regions. The SN explosions we postulate here are likely associated with the existence of young stellar clusters in the far outer regions of the Galaxy and the ultraviolet emission and low levels of star formation observed with the Galaxy Evolution Explorer (GALEX) satellite in the outer regions of local galaxies.  相似文献   

Neutron-rich freeze-out in viscously spreading accretion discs formed from compact object mergers     

B. D. Metzger  A. L. Piro  E. Quataert 《Monthly notices of the Royal Astronomical Society》2009,396(1):304-314

  相似文献   

Rural property size drives patterns of upland and riparian forest retention in a tropical deforestation frontier     

Fernanda Michalski  Jean Paul Metzger  Carlos A. Peres 《Global Environmental Change》2010,20(4):705-712

Deforestation in Brazilian Amazonia accounts for a disproportionate global scale fraction of both carbon emissions from biomass burning and biodiversity erosion through habitat loss. Here we use field- and remote-sensing data to examine the effects of private landholding size on the amount and type of forest cover retained within economically active rural properties in an aging southern Amazonian deforestation frontier. Data on both upland and riparian forest cover from a survey of 300 rural properties indicated that 49.4% (SD = 29.0%) of the total forest cover was maintained as of 2007, and that property size is a key regional-scale determinant of patterns of deforestation and land-use change. Small properties (≤150 ha) retained a lower proportion of forest (20.7%, SD = 17.6) than did large properties (>150 ha; 55.6%, SD = 27.2). Generalized linear models showed that property size had a positive effect on remaining areas of both upland and total forest cover. Using a Landsat time-series, the age of first clear-cutting that could be mapped within the boundaries of each property had a negative effect on the proportion of upland, riparian, and total forest cover retained. Based on these data, we show contrasts in land-use strategies between smallholders and largeholders, as well as differences in compliance with legal requirements in relation to minimum forest cover set-asides within private landholdings. This suggests that property size structure must be explicitly considered in landscape-scale conservation planning initiatives guiding agro-pastoral frontier expansion into remaining areas of tropical forest.  相似文献   

Micrometeorological Conditions for Dust-Devil Occurrence in the Atacama Desert     

Michael V. Kurgansky  Aldo Montecinos  Victor Villagran  Stephen M. Metzger 《Boundary-Layer Meteorology》2011,138(2):285-298

We report on field observations in January 2009 (austral summer) of atmospheric dust devils in the northern part of the Atacama Desert in South America (≈20^◦S). An extremely high level of dust-devil activity over the study site has been observed, dependent on local meteorological conditions. We found a high correlation between the dust-devil frequency of occurrence and the Obukhov length scale, L, calculated from meteorological gradient measurements, with a clear tendency for this frequency to increase with decreasing −L. The upper threshold values of −L ≈ 20–30 m, and the 2-m mean wind speed, V ₂ ≈ 8m s⁻¹, for dust-devil occurrence have been found, but the minimal V ₂ threshold was not observed. Parallel routine meteorological measurements enabled us to calculate the main constituents of the surface energy balance, to obtain direct estimates of the surface albedo (α ≈ 0.21 at the solar noon) and to summarize the local conditions.  相似文献   

An Antarctic view of Beryllium-10 and solar activity for the past millennium   总被引：1，自引：1，他引：0  

Gilles Delaygue  Edouard Bard 《Climate Dynamics》2011,36(11-12):2201-2218

Beryllium-10 in ice provides a valuable proxy of solar activity. However, complex production pathways, atmospheric transport, and deposition processes impede its quantitative interpretation. Here, we examine the influence of deposition processes on two Be-10 ice core records from Central Antarctica (South Pole and Dome Fuji stations), covering the last millennium. We try to quantify how Be-10 variations in ice relate to variations in Be-10 production, and the bias associated to this relationship. An independent bias estimation is provided by comparing atmospheric radiocarbon variations reconstructed from tree rings and deduced from Be-10 variations. Both techniques suggest an uncertainty of the order of 10% in Be-10 production. This uncertainty estimate does not account for the geographical origin of Be-10, which remains a major issue. Because both Be-10 records are so similar, we propose to average them as a means to decrease the unshared (non solar) variability. This average record provides a new reconstruction of solar modulation parameter ?? and total solar irradiance over the last ~1,300?years. The lowest solar activity is found during the so-called Sp?rer Minimum (around AD 1450). The highest activities are found during the 8th century and over the last decades: as shown in previous studies, our results suggest that the recent solar activity is not exceptionally high for the last millennium.  相似文献