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601.
Timothy G. Fisher Walter L. Loope William Pierce Harry M. Jol 《Journal of Paleolimnology》2007,37(3):365-382
We reconstruct postglacial lake-level history within the Lake Michigan basin using soil stratigraphy, ground-penetrating radar
(GPR), sedimentology and 14C data from the Silver Lake basin, which lies adjacent to Lake Michigan. Stratigraphy in nine vibracores recovered from the
floor of Silver Lake appears to reflect fluctuation of water levels in the Lake Michigan basin. Aeolian activity within the
study area from 3,000 years (cal yr. B.P.) to the present was inferred from analysis of buried soils, an aerial photograph
sequence, and GPR. Sediments in and around Silver Lake appear to contain a paleoenvironmental record that spans the entire
post-glacial history of the Lake Michigan basin. We suggest that (1) a pre-Nipissing rather than a Nipissing barrier separated
Silver Lake basin from the Lake Michigan basin, (2) that the Nipissing transgression elevated the water table in the Silver
Lake basin about 6,500 cal yr. B.P., resulting in reestablishment of a lake within the basin, and (3) that recent dune migration
into Silver Lake is associated with levels of Lake Michigan.
This is the fourth in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were
presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004), held at the University
of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M. Lewis were guest editors of this special issue. 相似文献
602.
While women own 25% of the acres rented out for farming, little has been done in terms of federal policy that focuses on these women. In this policy analysis, we detail how (1) lack of data on these women landowners and (2) the invisibility of these women to federal natural resource and agricultural agency staff contribute to women nonoperating landowners (WNOLs) not being on the federal policy radar. We discuss how the persistence of these factors continues to marginalize WNOLs in federal agricultural policy, despite the mandate of U.S. Department of Agriculture (USDA) agencies to be serving underserved populations such as WNOLs. Our study findings clearly illustrate a critical point: federal agricultural/conservation agencies are not fulfilling their mandate to reach WNOLs. Using data from USDA Production Regions in the United States, we detail how WNOLs are marginalized and provide specific policy recommendations to allow for intentional inclusion of these women. 相似文献
603.
Abstract— We demonstrate that the use of an established spectral deconvolution algorithm with mid‐infrared spectral libraries of mineral separates of varying grain sizes is capable of identifying the known mineral compositions and abundances of a selection of howardite, eucrite, and diogenite (HED) meteorite samples. In addition, we apply the same technique to mid‐infrared spectral emissivity measurements of Vesta that have been obtained from Cornell's Mid‐Infrared Asteroid Spectroscopy (MIDAS) Survey and the Infrared Space Observatory (ISO). Each Vesta measurement was made over a different range of longitudes. Our spectral deconvolution results to the Vesta spectra corroborate that Vesta's surface is howardite or eucrite‐like in composition and heterogeneous across its surface. The spectral fits produced by the linear deconvolution algorithm yields good results for the HED samples of known composition, thus giving us a high degree of confidence that our results for Vesta are valid. 相似文献
604.
605.
Martin J. SiegertDavid A. Fisher 《Icarus》2002,157(1):264-267
The surface of the northern martian ice cap is known to contain alternating white-dark scarp-trough features, and one method of their formation involves spatially coherent patterns of ice accumulation and ablation via sublimation. In this so-called “accublation” model, the internal ice sheet layers submerge into the ice sheet across the accumulation zone and emerge to the ice surface across the ablation region. Here we report on an Antarctic analogy to the martian accublation model, which demonstrates that surface mass balance conditions actually affect internal ice-sheet structure as predicted by D. A. Fisher (2000, Icarus144, 289-294). This analogy shows how it is possible for ancient ice to become exposed at the surface of an ice sheet, allowing the paleoclimate record stored within the ice to be measured without the need for deep ice coring. 相似文献
606.
A. Bregman F. Arnold V. Bürger H. Fisher J. Lelieveld B. A. Scheeren J. Schneider P. C. Siegmund J. Ström A. Waibel W. M. F. Wauben 《Journal of Atmospheric Chemistry》1997,26(3):275-310
In situ aircraft measurements of O3, CO,HNO3, and aerosol particles are presented,performed over the North Sea region in the summerlower stratosphere during the STREAM II campaign(Stratosphere Troposphere Experiments by AircraftMeasurements) in July 1994. Occasionally, high COconcentrations of 200-300 pbbv were measured in thelowermost stratosphere, together with relatively highHNO3 concentrations up to 1.6 ppbv. The particlenumber concentration (at standard pressure andtemperature) between 0.018-1 m decreased acrossthe tropopause, from >1000 cm-3 in the uppertroposphere to <500 cm-3 in the lowermoststratosphere. Since the CO sources are found in thetroposphere, the elevated CO mixing ratios areattributed to mixing of polluted tropospheric air intothe lowermost extratropical stratosphere. Further wehave used a chemical model to illustrate that nitrogenoxide reservoir species (mainly HNO3) determinethe availability of NOx (=NO + NO2) andtherefore largely control the total net O3production in the lower kilometers of thestratosphere. Model simulations, applying additionalNOx perturbations from aircraft, show that theO3 production efficiency of NOx is smallerthan previously assumed, under conditions withrelatively high HNO3 mixing ratios, as observedduring STREAM II. The model simulations furthersuggest a relatively high O3 productionefficiency from CO oxidation, as a result of therelatively high ambient HNO3 and NOxconcentrations, implying that upward transport of COrich air enhances O3 production in the lowermoststratosphere. Analysis of the measurements and themodel calculations suggest that the lowermoststratosphere is a transition region in which thechemistry deviates from both the upper troposphere andlower stratosphere. 相似文献
607.
Alexis Comber Peter Fisher Richard Wadsworth 《International journal of geographical information science》2013,27(7):691-708
Spatially coincident land-cover information frequently varies due to technological and political variations. This is especially problematic for time-series analyses. We present an approach using expert expressions of how the semantics of different datasets relate to integrating temporal time series land-cover information where the classification classes have fundamentally changed. We use land-cover mapping in the UK (LCMGB and LCM2000) as example data sets because of the extensive object-based meta-data in the LCM2000. Inconsistencies between the two datasets can arise from random, gross and systematic error and from an actual change in land cover. Locales of possible land-cover change are inferred by comparing characterizations derived from the semantic relations and meta-data. Field visits showed errors of omission to be 21% and errors of commission to be 28%, despite the accuracy limitations of the land-cover information when compared with the field survey component of the Countryside Survey 2000. 相似文献
608.
The stable longitudinal dunes in the northern Simpson Desert, Australia, were observed in satellite imagery to become more active after vegetation cover was reduced by fire and drought. Subsequent rainfall events also resulted in significant vegetation regrowth and dune stabilization. These switches between more active and stable conditions have not been previously described in the largely vegetated dune fields of central Australia. The observations, made on 12 dune sites, relied on high spatial resolution satellite imagery to observe dune crest activity, and seasonal Landsat fractional cover imagery to observe vegetation cover changes. The non-photosynthetic vegetation (NPV) component of the fractional vegetation cover images revealed significant changes in hummock grass cover on the dunes between 1988 and 2018, with a positive relationship with the three-year cumulative rainfall, disrupted by two periods of patchy burning. Only those sites that had burnt became active, and only after vegetation cover had remained low (NPV < 16%) during the ‘Millennium Drought’. There is no threshold in vegetation cover, below which dune crests become active, but active dune features require four-years of low NPV cover (< 16%) to develop. The large rainfall event that ended the drought increased NPV cover, stabilizing the dunes. Similar hummock grass covered dunes are present across large areas of the arid zone, and are likely to respond in similar ways, given that fire and drought are common occurrences in Australia. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd. 相似文献
609.
Hydraulic and geomorphic processes in an overbank flood along a meandering,gravel‐bed river: implications for chute formation 下载免费PDF全文
Hydraulic interactions between rivers and floodplains produce off‐channel chutes, the presence of which influences the routing of water and sediment and thus the planform evolution of meandering rivers. Detailed studies of the hydrologic exchanges between channels and floodplains are usually conducted in laboratory facilities, and studies documenting chute development are generally limited to qualitative observations. In this study, we use a reconstructed, gravel‐bedded, meandering river as a field laboratory for studying these mechanisms at a realistic scale. Using an integrated field and modeling approach, we quantified the flow exchanges between the river channel and its floodplain during an overbank flood, and identified locations where flow had the capacity to erode floodplain chutes. Hydraulic measurements and modeling indicated high rates of flow exchange between the channel and floodplain, with flow rapidly decelerating as water was decanted from the channel onto the floodplain due to the frictional drag provided by substrate and vegetation. Peak shear stresses were greatest downstream of the maxima in bend curvature, along the concave bank, where terrestrial LiDAR scans indicate initial floodplain chute formation. A second chute has developed across the convex bank of a meander bend, in a location where sediment accretion, point bar development and plant colonization have created divergent flow paths between the main channel and floodplain. In both cases, the off‐channel chutes are evolving slowly during infrequent floods due to the coarse nature of the floodplain, though rapid chute formation would be more likely in finer‐grained floodplains. The controls on chute formation at these locations include the flood magnitude, river curvature, floodplain gradient, erodibility of the floodplain sediment, and the flow resistance provided by riparian vegetation. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
610.
Ann M. Fletchall 《Geographical review》2016,106(4):539-566
Montana's craft brewing industry has grown astronomically in the last few decades and has spawned many breweries with local names and themes. Using Montana's craft breweries as a case study, this paper demonstrates that craft breweries play a significant role in contemporary place‐making. First, brewery and beer names are analyzed to extract several place‐based themes, and it is argued that these perpetuate a particular New West identity for the state. Then, through the lens of tourism and the quest for “authenticity,” surveys of brewery visitors are used to identify the various attractions that drinking craft beer and visiting breweries offer their patrons. Besides the taste of the beer, the local nature of breweries and their community focus prove to be an important draw for brewery visitors and provide the chance to experience the community in a more authentic way, and thus, offer an opportunity to make a meaningful connection with place. This research proves that craft breweries have become an important venue for place‐making, not only in Montana, but in other cities and states with a significant craft‐brewing industry 相似文献