Water and Radioactive Tracer Flow in a Heterogeneous Field-Scale System   总被引：1，自引：0，他引：1  

Frank M. Dunnivant  Meredith E. Newman  Carolyn W. Bishop  Dave Burgess  John R. Giles  Brian D. Higgs  Joel M. Hubbell  Erick Neher  Greg T. Norrell  M. Cathy Pfiefer  Indrek Porro  Robert C. Starr  Allan H. Wylie 《Ground water》1998,36(6):949-958

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Fire and Vegetation History from the Coastal Rain Forest of the Western Oregon Coast Range     

Colin J. Long  Cathy Whitlock 《Quaternary Research》2002,58(3):215

High-resolution charcoal and pollen analyses were used to reconstruct a 4600-yr-long history of fire and vegetation near Taylor Lake in the wettest forests of coastal Oregon. Today, fires in these forests are rare because the season of ignition does not coincide with months of dry fuels. From ca. 4600 to 2700 cal yr B.P. fire episodes occurred at intervals of 140±30 yr while forest vegetation was dominated by disturbance-adapted taxa such as Alnus rubra. From ca. 2700 cal yr B.P. to the present, fire episodes have become less common, occurring at intervals of 240±30 yr, and fire-sensitive forest taxa, such as Tsuga heterophylla and Picea sitchensis, have become more prominent. Fire occurrence during the mid-Holocene was similar to that of the more xeric forests in the eastern Coast Range and suggests that summer drought was widespread. After ca. 2700 cal yr B.P., a decrease in fire episode frequency suggests that cooler conditions and possibly increased summer fog allowed the establishment of present-day Picea sitchensis forests within the watershed. These results provide evidence that fire has been an important disturbance agent in the Coast Range of Oregon, and variations in fire frequency and climate have led to the establishment of present-day forests.  相似文献   

Temporal and spatial pattern of thermokarst lake area changes at Yukon Flats,Alaska          下载免费PDF全文

Min Chen  Joel C. Rowland  Cathy J. Wilson  Garrett L. Altmann  Steven P. Brumby 《水文研究》2014,28(3):837-852

To better understand the linkage between lake area change, permafrost conditions and intra‐annual and inter‐annual variability in climate, we explored the temporal and spatial patterns of lake area changes for a 422 382‐ha study area within Yukon Flats, Alaska using Landsat images of 17 dates between 1984 and 2009. Only closed basin lakes were used in this study. Among the 3529 lakes greater than 1 ha, closed basin lakes accounted for 65% by number and 50% by area. A multiple linear regression model was built to quantify the temporal change in total lake area with consideration of its intra‐annual and inter‐annual variability. The results showed that 80.7% of lake area variability was attributed to intra‐annual and inter‐annual variability in local water balance and mean temperature since snowmelt (interpreted as a proxy for seasonal thaw depth). Another 14.3% was associated with long‐term change. Among 2280 lakes, 350 lakes shrank, and 103 lakes expanded. The lakes with similar change trends formed distinct clusters, so did the lakes with similar short term intra‐annual and inter‐annual variability. By analysing potential factors driving lake area changes including evaporation, precipitation, indicators for regional permafrost change, and flooding, we found that ice‐jam flooding events were the most likely explanation for the observed temporal pattern. In addition to changes in the frequency of ice jam flooding events, the observed changes of individual lakes may be influenced by local variability in permafrost distributions and/or degradation. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Stratigraphic record of continental breakup,offshore NW Australia—Discussion     

Tiago M. Alves  Marcos Fetter  Cathy Busby  Tiago A. Cunha  Nathalia H. Mattos 《Basin Research》2023,35(1):470-482

Reeve et al. (2022) address the stratigraphic record of continental breakup by focusing on a set of stratigraphic unconformities from a proximal sector of the NW Australian continental margin, inboard from the Exmouth Plateau. They suggest that such unconformities can potentially document a well-defined three-stage process: end of the syn-rift phase, formation of a wide continent-ocean transition zone (COTZ) and generation of ‘true’ Penrose-type oceanic crust. We counterargue that continental breakup is a protracted event that can only be understood via seismic- and chronostratigraphic correlations of strata, and their composing sequences, across and along rifted margins. Tying proximal stratigraphic unconformities to magnetic anomalies outboard from the study area in Reeve et al. (2022) is open to question. In parallel, we suggest that age resolutions of ca. 1 Ma are not achievable using the micropaleontological data presented in Reeve et al. (2022), with an important reworking of microfossil assemblages potentially occurring during the erosional process forming local and regional unconformities. Our discussion addresses these points in more detail.  相似文献   

The signature of dark energy on the local Hubble flow     

Andrea V. Macciò  Fabio Governato  Cathy Horellou 《Monthly notices of the Royal Astronomical Society》2005,359(3):941-948

Using N -body simulations of flat, dark energy-dominated cosmologies, we show that galaxies around simulated binary systems resembling the Local Group (LG) have low peculiar velocities, in good agreement with observational data. We have compared results for LG-like systems selected from large, high-resolution simulations of three cosmologies: a ΛCDM model, a ΛWDM model with a 2-keV warm dark matter candidate, and a quintessence (QCDM) model with an equation-of-state parameter   w =−0.6  . The Hubble flow is significantly colder around LGs selected in a flat, Λ-dominated cosmology than around LGs in open or critical models, showing that a dark energy component manifests itself on the scales of nearby galaxies, cooling galaxy peculiar motions. Flows in the ΛWDM and QCDM models are marginally colder than in the ΛCDM one.
The results of our simulations have been compared to existing data and to a new data set of 28 nearby galaxies with robust distance measures (Cepheids and surface brightness fluctuations). The measured line-of-sight velocity dispersion is given by  σ_H= (88 ± 20  km s⁻¹) × ( R /7 Mpc)  . The best agreement with observations is found for LGs selected in the ΛCDM cosmology in environments with  −0.1 < δρ/ρ < 0.6  on scales of 7 Mpc, in agreement with existing observational estimates on the local matter density. These results provide new, independent evidence for the presence of dark energy on scales of a few megaparsecs, corroborating the evidence gathered from observations of distant objects and the early Universe.  相似文献   

Staging the Local: rethinking scale in farmers' markets     

Bethaney Turner  Cathy Hope 《The Australian geographer》2015,46(2):147-163

Local food has become a significant focus of food studies analysis in recent years with much of this work identifying the potential environmental, social and economic benefits of food localisation. However, a growing body of literature destabilises these assumed benefits with research now questioning the utility of scale in assessing food system outcomes. This paper explores this destabilisation by examining how concepts associated with the ‘local’ have been deployed by the Capital Region Farmers Market (CRFM) in the Australian Capital Territory (ACT). This leads to two key conclusions: firstly, the practical case study confirms theoretical insights highlighting the instability of the local, identifying how it is animated in multiple and sometimes contradictory ways often in response to conventional market forces; and secondly, we argue that the role of farmers' markets may not be best understood through the lens of the local but, rather, through their role in facilitating citizen engagement with the food system via the direct consumer–producer relationship at markets and the characteristics of the food purchased there (i.e. freshness and quality). In these ways, farmers' markets can disrupt conventional forms of engagement with the food system, creating a space that enhances social embeddedness and which may promote new forms of consumer understanding of food systems.  相似文献   

Extension and magmatism in the Cerocahui basin,northern Sierra Madre Occidental,western Chihuahua,Mexico     

Bryan P. Murray  Cathy J. Busby  María de los Angeles Verde Ramírez 《International Geology Review》2015,57(5-8):893-918

The Sierra Madre Occidental of northwestern Mexico is the biggest silicic large igneous province of the Cenozoic, yet very little is known about its geology due to difficulties of access to much of this region. This study presents geologic maps and two new U-Pb zircon laser ablation inductively coupled plasma mass spectrometry ages from the Cerocahui basin, a previously unmapped and undated ~25 km-long by ~12 km-wide half-graben along the western edge of the relatively unextended core of the northern Sierra Madre Occidental silicic large igneous province. Five stratigraphic units are defined in the study area: (1) undated welded to non-welded silicic ignimbrites that underlie the rocks of the Cerocahui basin, likely correlative to Oligocene-age ignimbrites to the east and west; (2) the ca. 27.5–26 Ma Bahuichivo volcanics, comprising mafic-intermediate lavas and subvolcanic intrusions in the Cerocahui basin; (3) alluvial fan deposits and interbedded distal non-welded silicic ignimbrites of the Cerocahui clastic unit; (4) basalt lavas erupted into the Cerocahui basin following alluvial deposition; and (5) silicic hypabyssal intrusions emplaced along the eastern margin of the basin and to a lesser degree within the basin deposits.

The main geologic structures in the Cerocahui basin and surrounding region are NNW-trending normal faults, with the basin bounded on the east by the syndepositional W-dipping Bahuichivo–Bachamichi and Pañales faults. Evidence of syndepositional extension in the half-graben (e.g. fanning dips, unconformities, coarsening of clastic deposits toward basin-bounding faults) indicates that normal faulting was active during deposition in the Cerocahui basin (Bahuichivo volcanics, Cerocahui clastic unit, and basalt lavas), and may have been active earlier based on regional correlations.

The rocks in the Cerocahui basin and adjacent areas record: (1) the eruption of silicic outflow ignimbrite sheets, likely erupted from caldera sources to the east during the early Oligocene pulse of the mid-Cenozoic ignimbrite flare-up, mostly prior to synextensional deposition in the Cerocahui basin (pre-27.5 Ma); (2) synextensional late Oligocene mafic-intermediate composition magmatism and alluvial fan sedimentation (ca. 27.5–24.5 Ma), which occurred during the lull between the Early Oligocene and early Miocene pulses of the ignimbrite flare-up; and (3) post-extensional emplacement of silicic hypabyssal intrusions along pre-existing normal faults, likely during the early Miocene pulse of the ignimbrite flare-up (younger than ca. 24.5 Ma). The timing of extensional faulting and magmatism in the Cerocahui basin and surrounding area generally coincides with previous models of regional-scale middle Eocene to early Miocene southwestward migration of active volcanism and crustal extension in the northern Sierra Madre Occidental controlled by post-late Eocene (ca. 40 Ma) rollback/fallback of the subducted Farallon slab.  相似文献   

Last glacial–interglacial environments in the southern Rocky Mountains,USA and implications for Younger Dryas-age human occupation     

Christy E. Briles  Cathy Whitlock  David J. Meltzer 《Quaternary Research》2012,77(1):96-103

The last glacial-interglacial transition (LGIT; 19–9 ka) was characterized by rapid climate changes and significant ecosystem reorganizations worldwide. In western Colorado, one of the coldest locations in the continental US today, mountain environments during the late-glacial period are poorly known. Yet, archaeological evidence from the Mountaineer site (2625 m elev.) indicates that Folsom-age Paleoindians were over-wintering in the Gunnison Basin during the Younger Dryas Chronozone (YDC; 12.9–11.7 ka). To determine the vegetation and fire history during the LGIT, and possible explanations for occupation during a period thought to be harsher than today, a 17-ka-old sediment core from Lily Pond (3208 m elev.) was analyzed for pollen and charcoal and compared with other high-resolution records from the southern Rocky Mountains. Widespread tundra and Picea parkland and low fire activity in the cold wet late-glacial period transitioned to open subalpine forest and increased fire activity in the Bølling–Allerød period as conditions became warmer and drier. During the YDC, greater winter snowpack than today and prolonged wet springs likely expanded subalpine forest to lower elevations than today, providing construction material and fuel for the early inhabitants. In the early to middle Holocene, arid conditions resulted in xerophytic vegetation and frequent fire.  相似文献   

Use of the SHMAK clarity tube for measuring water clarity: Comparison with the black disk method     

Cathy Kilroy  Barry J. F. Biggs 《新西兰海洋与淡水研究杂志》2013,47(3):519-527

A metre‐long transparent tube for measuring visual water clarity was developed as part of the New Zealand Stream Health Monitoring and Assessment Kit (SHMAK) for use by non‐scientists. Water clarity measured using the tube (the horizontal sighting range of a black target) was compared with that measured using the standard “black disk” method (in which a black target is viewed horizontally underwater) to determine the feasibility of estimating black disk clarities from clarity tube readings. Readings using the two methods showed good agreement for waters with clarity <c. 50 cm. In clearer waters the slope of the relationship depends on the reflectivity of the background material used in the clarity tube. With a reflective background (white, reflectance c. 75%; or grey, reflectance c. 55%), the clarity tube readings are directly proportional and approximately equal to the black disk readings. With a black background (reflectance c. 5.5%), clarity tube readings >c. 50 cm are lower than the black disk visibility and follow a logarithmic relationship with visibility, which enables useful readings to be made in clearer water. Independent testing of the relationship showed that black disk visibilities may be predicted with reasonable confidence in waters that contain very low concentrations of dissolved humic materials (yellow substance). In waters that are noticeably brown‐coloured, the relationship is less consistent especially at black disk visibilities of more than 1.5 m. Recommendations are given for the use of the clarity tube.  相似文献   

The missing half of the subduction factory: shipboard results from the Izu rear arc,IODP Expedition 350     

Cathy J. Busby  Yoshihiko Tamura  Peter Blum  Gilles Guèrin  Graham D. M. Andrews  Abigail K. Barker 《International Geology Review》2017,59(13):1677-1708

IODP Expedition 350 was the first to be drilled in the rear part of the Izu-Bonin, although several sites had been drilled in the arc axis to fore-arc region; the scientific objective was to understand the evolution of the Izu rear arc, by drilling a deep-water volcaniclastic section with a long temporal record (Site U1437). The Izu rear arc is dominated by a series of basaltic to dacitic seamount chains up to ~100-km long roughly perpendicular to the arc front. Dredge samples from these are geochemically distinct from arc front rocks, and drilling was undertaken to understand this arc asymmetry. Site U1437 lies in an ~20-km-wide basin between two rear arc seamount chains, ~90-km west of the arc front, and was drilled to 1804 m below the sea floor (mbsf) with excellent recovery. We expected to drill a volcaniclastic apron, but the section is much more mud-rich than expected (~60%), and the remaining fraction of the section is much finer-grained than predicted from its position within the Izu arc, composed half of ashes/tuffs, and half of lapilli tuffs of fine grain size (clasts <3 cm). Volcanic blocks (>6.4 cm) are only sparsely scattered through the lowermost 25% of the section, and only one igneous unit was encountered, a rhyolite peperite intrusion at ~1390 mbsf. The lowest biostratigaphic datum is at 867 mbsf (~6.5 Ma), the lowest palaeomagnetic datum is at ~1300 mbsf (~9 Ma), and the rhyolite peperite at ~1390 mbsf has yielded a U–Pb zircon concordia intercept age of (13.6 + 1.6/?1.7) Ma. Both arc front and rear arc sources contributed to the fine-grained (distal) tephras of the upper 1320 m, but the coarse-grained (proximal) volcaniclastics in the lowest 25% of the section are geochemically similar to the arc front, suggesting arc asymmetry is not recorded in rocks older than ~13 Ma.  相似文献