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91.
There is a need to identify measurable characteristics of stream channel morphology that vary predictably throughout stream networks and that influence patterns of hyporheic exchange flow in mountain streams. In this paper we characterize stream longitudinal profiles according to channel unit spacing and the concavity of the water surface profile. We demonstrate that: (1) the spacing between zones of upwelling and downwelling in the beds of mountain streams is closely related to channel unit spacing; (2) the magnitude of the vertical hydraulic gradients (VHGs) driving hyporheic exchange flow increase with increasing water surface concavity, measured at specific points along the longitudinal profile; (3) channel unit spacing and water surface concavity are useful metrics for predicting how patterns in hyporheic exchange vary amongst headwater and mid‐order streams. We use regression models to describe changes in channel unit spacing and concavity in longitudinal profiles for 12 randomly selected stream reaches spanning 62 km2 in the H.J. Andrews Experimental Forest in Oregon. Channel unit spacing increased significantly, whereas average water surface concavity (AWSC) decreased significantly with increasing basin area. Piezometer transects installed longitudinally in a subset of stream reaches were used to measure VHG in the hyporheic zone, and to determine the location of upwelling and downwelling zones. Predictions for median pool length and median distance between steps in piezometer reaches bracketed the median distance separating zones of upwelling in the stream bed. VHG in individual piezometers increased with increasing water surface concavity at individual points in the longitudinal profile along piezometer transects. Absolute values of VHG, averaged throughout piezometer transects, increased with increasing AWSC, indicating increased potential for hyporheic exchange flow. These findings suggest that average hyporheic flow path lengths increase—and the potential for hyporheic exchange flow in stream reaches decreases—along the continuum from headwater to mid‐order mountain streams. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
92.
Hanna NEKVASIL Justin FILIBERTO Francis M. McCUBBIN Donald H. LINDSLEY 《Meteoritics & planetary science》2007,42(6):979-992
Abstract Detailed analysis of cumulate and melt inclusion assemblages in the chassignites provide important constraints on the nature of the melt trapped as inclusions in cumulus olivine (and, by extension, parental magma compositions), the pressures of crystallization, and magmatic volatile contents. These mineral assemblages show strong similarities to the experimental fractionation assemblages that produce the sodic silica‐saturated alkalic lavas on Earth (e.g., Ascension Island, Azores, the Nandewar volcano of Australia). The experimental assemblages were produced from silica‐saturated hawaiite at pressures above 4.3 kbar with dissolved water contents above 0.5 wt%. Such pressures are consistent with Ti:Al ratios of the melt‐inclusion pyroxenes in the Chassigny meteorite. Pyroxene compositions suggest early high crystallization temperatures and thus relatively low initial water and F contents. Feldspars indicate that melt evolution proceeded to rhyolite compositions both within the interstices of the cumulate olivine and within the melt inclusions, even though rhyolitic glass is only found within olivine‐hosted polyphase melt inclusions. The observed rhyolite glass is compositionally similar to the alkali‐rich rhyolite of Ascension Island which is produced experimentally by crystallization of hawaiite. It is proposed that the melt trapped in cumulus olivine of the Chassigny dunite was similar to a terrestrial silica‐saturated hawaiite, while that trapped in olivine of the Northwest Africa (NWA) 2727 dunite was less evolved, perhaps mildly alkalic basalt. Melts similar to terrestrial intra‐plate tholeiite could be parental to the cumulus minerals and evolve upon crystallization at pressures above 4.3 kbar and water contents above ?0.4 wt% to mildly alkalic basalt, silica‐saturated hawaiite, and alkali‐rich rhyolite. The melt inclusion assemblages are inconsistent with either crystallization of a low‐Al, high‐Fe basalt, or low‐pressure crystallization of a terrestrial‐like tholeiite. 相似文献
93.
Colm
Cofaigh Justin Taylor Julian A. Dowdeswell Carol J. Pudsey 《Boreas: An International Journal of Quaternary Research》2003,32(1):37-55
The classical model of trough mouth fan (TMF) formation was developed in the Polar North Atlantic to explain large submarine fans situated in front of bathymetric troughs that extend across continental shelves to the shelf break. This model emphasizes the delivery of large volumes of subglacial sediment to the termini of ice streams flowing along troughs, and subsequent re‐deposition of this glacigenic sediment down the continental slope via debris‐flow processes. However, there is considerable variation in terms of the morphology and large‐scale sediment architecture of continental slopes in front of palaeo‐ice streams. This variability reflects differences in slope gradient, the relative contributions of meltwater sedimentation compared with debris‐flow deposition, and sediment supply/geology of the adjacent continental shelf. TMF development is favoured under conditions of a low (<1°) slope gradient; a passive‐margin tectonic setting; abundant, readily erodible sediments on the continental shelf ‐ and thus associated high rates of sediment delivery to the shelf edge; and a wide continental shelf. The absence of large sediment fans on continental slopes in front of cross‐shelf troughs should not, however, be taken to indicate the former absence of palaeo‐ice streams in the geological record. 相似文献
94.
Igneous and shock processes affecting chassignite amphibole evaluated using chlorine/water partitioning and hydrogen isotopes
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Paul A. Giesting Susanne P. Schwenzer Justin Filiberto Natalie A. Starkey Ian A. Franchi Allan H. Treiman Andy G. Tindle Monica M. Grady 《Meteoritics & planetary science》2015,50(3):433-460
Amphibole in chassignite melt inclusions provides valuable information about the volatile content of the original interstitial magma, but also shock and postshock processes. We have analyzed amphibole and other phases from NWA 2737 melt inclusions, and we evaluate these data along with published values to constrain the crystallization Cl and H2O content of phases in chassignite melt inclusions and the effects of shock on these amphibole grains. Using a model for the Cl/OH exchange between amphibole and melt, we estimate primary crystallization OH contents of chassignite amphiboles. SIMS analysis shows that amphibole from NWA 2737 currently has 0.15 wt% H2O. It has lost ~0.6 wt% H2O from an initial 0.7–0.8 wt% H2O due to intense shock. Chassigny amphibole had on average 0.3–0.4 wt% H2O and suffered little net loss of H2O due to shock. NWA 2737 amphibole has δD ≈ +3700‰; it absorbed Martian atmosphere‐derived heavy H in the aftermath of shock. Chassigny amphibole, with δD ≤ +1900‰, incorporated less heavy H. Low H2O/Cl ratios are inferred for the primitive chassignite magma, which had significant effects on melting and crystallization. Volatiles released by the degassing of Martian magma were more Cl‐rich than on Earth, resulting in the high Cl content of Martian surface materials. 相似文献
95.
Fundamental differences between SPH and grid methods 总被引:1,自引:0,他引:1
Oscar Agertz Ben Moore Joachim Stadel Doug Potter Francesco Miniati Justin Read Lucio Mayer Artur Gawryszczak rey Kravtsov Åke Nordlund Frazer Pearce Vicent Quilis Douglas Rudd Volker Springel James Stone Elizabeth Tasker Romain Teyssier James Wadsley Rolf Walder 《Monthly notices of the Royal Astronomical Society》2007,380(3):963-978
96.
97.
Ian J. W. Giesbrecht William C. Floyd Suzanne E. Tank Ken P. Lertzman Brian P. V. Hunt Maartje C. Korver Allison A. Oliver Ray Brunsting Paul Sanborn Santiago G. Gonzalez Arriola Gordon W. Frazer Kyra A. St. Pierre Shawn Hateley James McPhail Colby Owen Stewart Butler Bryn Fedje Emma Myers Lucy Quayle Emily Haughton Isabelle Desmarais Rob White David J. Levy-Booth Colleen T. E. Kellogg Jennifer M. Jackson William W. Mohn Steven J. Hallam Justin Del Bel Belluz 《水文研究》2021,35(6):e14198
The Kwakshua Watersheds Observatory (KWO) is an integrative watersheds observatory on the coastal margin of a rain-dominated bog-forest landscape in British Columbia (BC), Canada. Established in 2013, the goal of the KWO is to understand and model the flux of terrestrial materials from land to sea – the origins, pathways, processes and ecosystem consequences – in the context of long-term environmental change. The KWO consists of seven gauged watersheds and a network of observation sites spanning from land to sea and along drainage gradients within catchments. Time-series datasets include year-round measurements of weather, soil hydrology, streamflow, aquatic biogeochemistry, microbial ecology and nearshore oceanographic conditions. Sensor measurements are recorded every 5 min and water samples are collected approximately monthly. Additional observations are made during high-flow conditions. We used remote sensing to map watershed terrain, drainage networks, soils and terrestrial ecosystems. The watersheds range in size from 3.2 to 12.8 km2, with varying catchment characteristics that influence hydrological and biogeochemical responses. Despite local variation, the overall study area is a global hotspot for yields of dissolved organic carbon, dissolved organic nitrogen and dissolved iron at the coastal margin. This observatory helps fill an important gap in the global network of observatories, in terms of spatial location (central coast of BC), climate (temperate oceanic), hydrology (very high runoff, pluvial regime), geology (igneous intrusive, glacially scoured), vegetation (bog rainforest) and soils (large stores of organic carbon). 相似文献
98.
Elsa S. Culler Andrew M. Badger Justin Toby Minear Kristy F. Tiampo Spencer D. Zeigler Ben Livneh 《水文研究》2021,35(7):e14260
Extreme precipitation can have profound consequences for communities, resulting in natural hazards such as rainfall-triggered landslides that cause casualties and extensive property damage. A key challenge to understanding and predicting rainfall-triggered landslides comes from observational uncertainties in the depth and intensity of precipitation preceding the event. Practitioners and researchers must select from a wide range of precipitation products, often with little guidance. Here we evaluate the degree of precipitation uncertainty across multiple precipitation products for a large set of landslide-triggering storm events and investigate the impact of these uncertainties on predicted landslide probability using published intensity–duration thresholds. The average intensity, peak intensity, duration, and NOAA-Atlas return periods are compared ahead of 177 reported landslides across the continental United States and Canada. Precipitation data are taken from four products that cover disparate measurement methods: near real-time and post-processed satellite (IMERG), radar (MRMS), and gauge-based (NLDAS-2). Landslide-triggering precipitation was found to vary widely across precipitation products with the depth of individual storm events diverging by as much as 296 mm with an average range of 51 mm. Peak intensity measurements, which are typically influential in triggering landslides, were also highly variable with an average range of 7.8 mm/h and as much as 57 mm/h. The two products more reliant upon ground-based observations (MRMS and NLDAS-2) performed better at identifying landslides according to published intensity–duration storm thresholds, but all products exhibited hit ratios of greater than 0.56. A greater proportion of landslides were predicted when including only manually verified landslide locations. We recommend practitioners consider low-latency products like MRMS for investigating landslides, given their near-real time data availability and good performance in detecting landslides. Practitioners would be well-served considering more than one product as a way to confirm intense storm signals and minimize the influence of noise and false alarms. 相似文献
99.
The Wave GliderTM wave-powered unmanned maritime vehicle represents a novel and unique approach to persistent ocean presence. Wave Glider is
a hybrid sea-surface and underwater vehicle in that it is comprised of a submerged “glider” attached via a tether to a surface
float. The Wave Glider vehicle is propelled by the purely mechanical conversion of ocean wave energy into forward thrust,
independent of wave direction. In this paper, we provide an overview of the design of this new platform and present results
from the engineering sea trials conducted with several prototype and production versions of the vehicle. In addition to the
Wave Glider technology, we present results from ongoing scientific demonstration programs. Results from test deployments of
a conductivity–temperature–depth sensor and its applicability to oceanography are discussed. An evaluation of horizontal current
profiles and current velocity estimation from a Wave Glider operating in Monterey Bay (California, USA) are presented. 相似文献
100.
A physicochemical framework for interpreting the biological calcification response to CO2-induced ocean acidification 总被引:2,自引:0,他引:2
Justin B. Ries 《Geochimica et cosmochimica acta》2011,75(14):4053-4064
A generalized physicochemical model of the response of marine organisms’ calcifying fluids to CO2-induced ocean acidification is proposed. The model is based upon the hypothesis that some marine calcifiers induce calcification by elevating pH, and thus ΩA, of their calcifying fluid by removing protons (H+). The model is explored through two end-member scenarios: one in which a fixed number of H+ is removed from the calcifying fluid, regardless of atmospheric pCO2, and another in which a fixed external-internal H+ ratio ([H+]E/[H+]I) is maintained. The model is able to generate the full range of calcification response patterns observed in prior ocean acidification experiments and is consistent with the assertion that organisms’ calcification response to ocean acidification is more negative for marine calcifiers that exert weaker control over their calcifying fluid pH. The model is empirically evaluated for the temperate scleractinian coral Astrangia poculata with in situ pH microelectrode measurements of the coral’s calcifying fluid under control and acidified conditions. These measurements reveal that (1) the pH of the coral’s calcifying fluid is substantially elevated relative to its external seawater under both control and acidified conditions, (2) the coral’s [H+]E/[H+]I is approximately the same under control and acidified conditions, and (3) the coral removes fewer H+ from its calcifying fluid under acidified conditions than under control conditions. Thus, the carbonate system dynamics of A. poculata’s calcifying fluid appear to be most consistent with the fixed [H+]E/[H+]I end-member scenario. Similar microelectrode experiments performed on additional taxa are required to assess the model’s general applicability. 相似文献