Topics. Viking iron-smelting in Dublin's Temple Bar West     

Chris Stillman  Robert Barklie†  Cathy Johnson‡ 《Geology Today》2003,19(6):216-218

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Transpiration in Quercus suber trees under shallow water table conditions: the role of soil and groundwater          下载免费PDF全文

Clara A. Pinto  Nadezhda Nadezhdina  Jorge S. David  Cathy Kurz‐Besson  Maria C. Caldeira  Manuel O. Henriques  Fernando G. Monteiro  João S. Pereira  Teresa S. David 《水文研究》2014,28(25):6067-6079

Water is one of the major environmental factors limiting plant growth and survival in the Mediterranean region. Quercus suber L. woodlands occupy vast areas in the Iberian Peninsula, frequently under shallow water table conditions. The relative magnitude of soil and groundwater uptake to supply transpiration is not easy to evaluate under these circumstances. We recently developed a conceptual framework for the functioning of the root system in Q. suber that simulates well tree transpiration, based on two types of root behaviour: shallow connected and deep connected. Although this significantly improved knowledge on the functional traits of Mediterranean Q. suber, the approach has the limitation of requiring root sap flow data, which are seldom available. In this work, we present alternative methodologies to assess if trees are connected to groundwater and to estimate the soil and groundwater contributions to tree transpiration. We provide evidence on the tree unrestricted access to groundwater solely based on meteorological, stem sap flow and leaf water potential data. Using a soil mass balance approach, we estimated the yearly soil and groundwater contributions to tree transpiration: 69.7% and 30.3%, respectively. Groundwater uptake became dominant in the dry summer: 73.2% of tree transpiration. Results reproduce extremely well those derived from root modelling. Because of its simplicity both in formulation and data requirements, our approach is potentially liable to be adapted to other groundwater‐dependent Mediterranean oak sites, where interactions between land use and water resources may be relevant. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Do young martian ray craters have ages consistent with the crater count system?     

William K. Hartmann  Cathy Quantin  Olga Popova 《Icarus》2010,208(2):621-21

McEwen et al. (McEwen, A.S., Preblich, B.S., Turtle, E.P., Artemieva, N.A., Golombek, M.P., Hurst, M., Kirk, R.L., Burr, D.M., Christensen, P. [2005]. Icarus 176, 351-381) developed a useful test for the internal consistency of crater-count chronometry systems. They argued that certain multi-kilometer, fresh-looking martian craters with prominent rays should be the youngest or near-youngest craters in their size range. The “McEwen et al. test” is that the ages determined from crater densities of the smallest superimposed craters (typically diameter D ∼ 5-20 m) should thus be comparable to the expected formation intervals of the host primary. McEwen et al. concluded from MOC data that crater chronometry failed this test by factors of 700-2000. We apply HiRISE and other imagery to eight different young craters in order to re-evaluate their arguments. We use existing crater chronology systems as well as the reported observed production rate of 16 m craters (Malin, M.C., Edgett, K., Posiolova, L., McColley, S., Noe Dobrea, E. [2006]. Science 314, 1573-1557; Hartmann, W.K., Quantin, C., Mangold, N. [2007]. Icarus 186, 11-23; Kreslavsky [2007]. Seventh International Conference on Mars, 3325). Every case passes the McEwen et al. test. We conclude that the huge inconsistencies suggested by McEwen et al. are spurious. Many of these craters show evidence of impact into ice-rich material, and appear to have ice-flow features and sublimation pits on their floors. As production rate data improve, decameter-scale craters will provide a valuable way of dating these young martian geological formations and the processes that modify them.  相似文献   

Late Quaternary vegetation and fire history in the northernmost Nothofagus forest region: Mallín Vaca Lauquen,Neuquén Province,Argentina     

Vera Markgraf  Cathy Whitlock  R. Scott Anderson  Adriana García 《第四纪科学杂志》2009,24(3):248-258

The last 16 000 cal. a of vegetation, fire and limnological history are described from the steppe‐forest ecotone in the northernmost Nothofagus forest region east of the Andes (Mallín Vaca Lauquen, Neuquén Province, Argentina, latitude 36° 51.336′ S, longitude 71° 02.538′ W). Between 16 000 and 14 800 cal. a BP, scrub steppe with substantial open ground expanded in formerly glaciated valleys, whereas Nothofagus–Prumnopitys andina woodland covered mountain slopes. The site was a relatively deep and unproductive small lake at this time. After 14 800 cal. a BP, both steppe and woodland vegetation became denser, indicating increased moisture and temperatures, although not to present levels. The lake was still relatively deep and dystrophic, but became more alkaline by 10 000 cal. a BP. Between 8900 and 5500 cal. a BP, conditions were markedly drier than before; a Cyperaceae marsh developed and disturbance taxa increased. After 5500 cal. a BP, moisture increased but varied greatly, as evidenced by fluctuating water levels and high fire activity from 5500 to 4400 cal. a BP and from 2300 to 1000 cal. a BP. Human activity, in terms of forest clearance and livestock grazing, is documented in the uppermost levels. The evidence of high environmental variability in the middle and late Holocene is consistent with the onset or strengthening of the El Niño–Southern Oscillation, but differences in the timing of fire activity among sites on the west and east sides of the Andes suggest that fuel conditions were important in determining the local occurrence of fire. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Geographers doing household research: intrusive research and moral accountability   总被引：1，自引：0，他引：1  

Cathy Bailey 《Area》2001,33(1):107-110

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Late-Glacial Vegetation and Climate Change in Western Oregon     

Laurie D. Grigg  Cathy Whitlock 《Quaternary Research》1998,49(3):287-298

Pollen records from two sites in western Oregon provide information on late-glacial variations in vegetation and climate and on the extent and character of Younger Dryas cooling in the Pacific Northwest. A subalpine forest was present at Little Lake, central Coast Range, between 15,700 and 14,850 cal yr B.P. A warm period between 14,850 and 14,500 cal yr B.P. is suggested by an increase inPseudotsugapollen and charcoal. The recurrence of subalpine forest at 14,500 cal yr B.P. implies a return to cool conditions. Another warming trend is evidenced by the reestablishment ofPseudotsugaforest at 14,250 cal yr B.P. Increased haploxylonPinuspollen between 12,400 and 11,000 cal yr B.P. indicates cooler winters than before. After 11,000 cal yr B.P. warm dry conditions are implied by the expansion ofPseudotsuga.A subalpine parkland occupied Gordon Lake, western Cascade Range, until 14,500 cal yr B.P., when it was replaced during a warming trend by a montane forest. A rise inPinuspollen from 12,800 to 11,000 cal yr B.P. suggests increased summer aridity.Pseudotsugadominated the vegetation after 11,000 cal yr B.P. Other records from the Pacific Northwest show an expansion ofPinusfrom ca. 13,000 to 11,000 cal yr B.P. This expansion may be a response either to submillennial climate changes of Younger Dryas age or to millennial-scale climatic variations.  相似文献   

An Atlas of past and present pollen maps for Europe: 0–13,000 years ago: By B. Huntley and H. J. B. Birks. Cambridge Univ. Press. Cambridge, 1983, 650 pp., $175.00     

Cathy W. Barnosky 《Quaternary Research》1985,24(1):133-135

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Stability of Holocene Climate Regimes in the Yellowstone Region     

Cathy Whitlock  Patrick J. Bartlein  Kelli J. Van Norman 《Quaternary Research》1995,43(3)

A 12,500-yr pollen record from Loon Lake, Wyoming provides information on the climate history of the southwestern margin of Yellowstone National Park. The environmental reconstruction was used to evaluate hypotheses that address spatial variations in the Holocene climate of mountainous regions. Loon Lake lies within the summer-dry/winter-wet climate regime. An increase in xerophytic pollen taxa suggests drier-than-present conditions between ca. 9500 and 5500 ¹⁴ C yr B.P. This response is consistent with the hypothesis that increased summer radiation and the expansion of the east Pacific subtropical high-pressure system in the early Holocene intensified summer drought at locations within the summer-dry/winter-wet regime. This climate history contrasts with that of nearby sites in the summer-wet/winter-dry region, which were under the influence of stronger summer monsoonal circulation in the early Holocene. The Loon Lake record implies that the location of contrasting climate regimes did not change in the Yellowstone region during the Holocene. The amplitude of the regimes, however, was determined by the intensity of circulation features and these varied with temporal changes in the seasonal distribution of solar radiation.  相似文献   

An investigation of the sensitivity of a land surface model to climate change using a reduced form model   总被引：1，自引：0，他引：1  

A. H. Lynch  S. McIlwaine  J. Beringer  G. B. Bonan 《Climate Dynamics》2001,17(8):643-652

 In an illustration of a model evaluation methodology, a multivariate reduced form model is developed to evaluate the sensitivity of a land surface model to changes in atmospheric forcing. The reduced form model is constructed in terms of a set of ten integrative response metrics, including the timing of spring snow melt, sensible and latent heat fluxes in summer, and soil temperature. The responses are evaluated as a function of a selected set of six atmospheric forcing perturbations which are varied simultaneously, and hence each may be thought of as a six-dimensional response surface. The sensitivities of the land surface model are interdependent and in some cases illustrate a physically plausible feedback process. The important predictors of land surface response in a changing climate are the atmospheric temperature and downwelling longwave radiation. Scenarios characterized by warming and drying produce a large relative response compared to warm, moist scenarios. The insensitivity of the model to increases in precipitation and atmospheric humidity is expected to change in applications to coupled models, since these parameters are also strongly implicated, through the representation of clouds, in the simulation of both longwave and shortwave radiation. Received: 27 March 2000 / Accepted: 11 September 2000  相似文献   

Toxicity of 1,4-dichlorobenzene in sediments to juvenile polychaete worms   总被引：1，自引：0，他引：1  

McPherson CA  Tang A  Chapman PM  Taylor LA  Gormican SJ 《Marine pollution bulletin》2002,44(12):1405-1414

Investigation of sediment contamination associated with a marine sewage outfall in Victoria (BC, Canada) found elevated concentrations of 1,4-dichlorobenzene (1,4-DCB). Juvenile polychaete worm (Neanthes) growth was significantly reduced at or near the outfall, roughly corresponding to elevated 1,4-DCB concentrations. There are few data on 1,4-DCB toxicity to marine organisms and no published literature on its toxicity to benthic marine organisms. To determine whether reduced polychaete growth (measured as dry weight) was due to 1,4-DCB exposure, a laboratory investigation was conducted. Uncontaminated marine sediment was spiked with 1,4-DCB and juvenile Neanthes were exposed in 20-d sublethal toxicity tests. There were no adverse effects on survival at any test concentration; mean survival was 80–100%. Statistically significant decreases in average dry weight only occurred at the highest 1,4-DCB concentration (19,900 μg/kg, dry weight); this represented a 1,4-DCB concentration more than 10 times higher than previously measured at the outfall (1710 μg/kg, dry weight). There were no adverse effects on survival or dry weight at the range of concentrations previously measured in sediments from the vicinity of the outfall.  相似文献