Quaternary vegetation history of the Mississippi embayment     

Paul A. Delcourt  Hazel R. Delcourt  Ronald C. Brister  Laurence E. Lackey 《Quaternary Research》1980,13(1):111-132

Nonconnah Creek, located in the loess-mantled Blufflands along the eastern wall of the Lower Mississippi Alluvial Valley in Tennessee displays a sedimentary sequence representing the Altonian Substage through the Woodfordian Substage of the Wisconsinan Stage. The site has a biostratigraphic record for the Altonian and Farmdalian Substages that documents warm-temperate upland oak-pine forest, prairie, and bottomland forest. At 23,000 yr B.P., white spruce and larch migrated into the Nonconnah Creek watershed and along braided-stream surfaces in the Mississippi Valley as far as southeastern Louisiana. The pollen and plant-macrofossil record from Nonconnah Creek provides the first documentation of a full-glacial locality in eastern North America for beech, yellow poplar, oak, history, black walnut, and other mesic deciduous forest taxa. During the full and late glacial, the Mississippi Valley was a barrier to the migration of pine species, while the adjacent Blufflands provided a refuge for mesic deciduous forest taxa. Regional climatic amelioration, beginning about 16,500 yr B.P., is reflected by increases in pollen percentages of cooltemperate deciduous trees at Nonconnah Creek. The demise of spruce and jack pine occurred 12,500 yr B.P. between 34° and 37° N in eastern North America in response to postglacial warming.  相似文献   

Evaluating Errors in a Digital Vegetation Map with Forest Inventory Data and Accuracy Assessment Using Fuzzy Sets   总被引：1，自引：0，他引：1  

Janet Franklin  Dena K. Simons  Debby Beardsley  John M. Rogan  & Hazel Gordon 《Transactions in GIS》2001,5(4):285-304

In large-area mapping projects, existing reference data, often collected for a different purpose, are increasingly being used for map accuracy assessment. Multi-attribute digital vegetation maps have been developed for all National Forest lands in California (8.1 million ha). We developed decision rules that could be applied to quantitative Forest Inventory and Analysis (FIA) plot data in order to score the fuzzy membership of plot locations in all possible map classes. We compare the accuracy of the vegetation map attributes estimated using this method to accuracy estimated from fuzzy class membership scores assigned by experts (inventory crews) during field work. Accuracy of the vegetation life form attribute was estimated to be higher when expert label assignments were used as reference data (76–87%), instead of FIA plot data (62–79%). This suggests that automated decision rules applied to detailed data from FIA plots, which have smaller area than map polygons, may systematically underestimate map accuracy. However, assignment of the actual map labels to FIA plot locations by inventory crews appears to be a robust method for using the FIA data for accuracy assessment.  相似文献   

Late-Holocene Formation of Lake Michigan Beach Ridges Correlated with a 70-yr Oscillation in Global Climate     

Paul A. Delcourt  William H. Petty  Hazel R. Delcourt 《Quaternary Research》1996,45(3):321-326

A radiocarbon-dated series of 75 beach ridges, formed at regular intervals averaging 72 yr over the past 5400 yr, provides further support for the existence of a 70-yr oscillation in Northern Hemisphere climate, postulated recently from instrument data representing less than two cycles of this climate oscillation. Results from this study lend support to the interpretation that internal variations in the ocean–atmosphere system are an important factor in climate fluctuations on a decadal–centennial time scale. A temperature oscillation with a period of about 70 yr has been a previously unrecognized but fundamental part of the global climate system since at least the middle Holocene.  相似文献   

Comment on “Update on terrestrial ages of Antarctic meteorites” by K. Nishiizumi, D. Elmore and P.W. Kubik     

Derek W.G. Sears  Fouad A. Hasan  Benjamin M. Myers  Hazel Sears 《Earth and Planetary Science Letters》1990,99(4)

  相似文献   

Living with volcanoes     

Hazel Rymer 《Geology Today》2000,16(1):26-31

The 1990s were designated the International Decade of Natural Disaster Reduction (IDNDR) by the United Nations and considerable research effort has gone into achieving a better understanding of volcanic processes and public understanding of volcanic phenomena. Some eruptions have been predicted successfully and thousands of lives have been saved through evacuation and well co-ordinated aid programmes.  相似文献   

Discrediting the late Eocene microspherule layer at Cynthia,Mississippi     

Gary R. Byerly  Joseph E. Hazel  Charles McCabe 《Meteoritics & planetary science》1990,25(2):89-92

Abstract— Glassy microspherules recently reported from the late Eocene of central Mississippi are physically and chemically similar to impact-produced microspherules, especially those from Molino de Cobo, Spain, leading several investigators to conclude that these samples document another late Eocene impact event. A careful evaluation of the sample site and spherule compositions, however, suggests that these glasses are modern contaminants. Similar contaminants could be widespread throughout industrialized countries.  相似文献   

Effects of some environmental parameters on the reproduction and development of a tropical marine harpacticoid copepod Nitocra affinis f. californica Lang     

Matias-Peralta H  Yusoff FM  Shariff M  Arshad A 《Marine pollution bulletin》2005,51(8-12):722-728

The effects of salinity, temperature, and light conditions on the reproduction and development of harpacticoid copepod, Nitocra affinis f. californica under controlled laboratory conditions were determined. Seven different salinity levels (5, 10, 15, 20, 25, 30, 35 ppt), four temperatures (20, 25, 30, 35 °C), three different light intensities (25, 56, 130 μmol m⁻² s⁻¹) and photoperiods (24 h:0 h, 1 h:23 h, 12 h:12 h LD cycle) were employed in this study. The highest (p < 0.05) overall reproduction and fastest development time were achieved by copepods reared under 30–35 ppt salinity. The optimum temperature required for the maximum reproduction was 30 °C while under 30 °C and 35 °C the copepod development time was shortest (p < 0.05) compared to other temperature levels. The overall reproduction was highest (p < 0.05) and development rate of N. affinis was shortest (p < 0.05) under lowest light intensity (25 μmol m⁻² s⁻¹). Continuous light (24 h:0 h LD) inhibited the egg production while, continuous darkness (1 h:23 h LD) and 12 h:12 h LD significantly favoured the overall reproductive activity of the female. Photoperiods 1 h:23 h and 12 h:12 h LD yielded highest total (p < 0.05) offspring female⁻¹ coupled with highest (p < 0.05) survival percentage. This study illustrated that although N. affinis can tolerate wide range of environmental conditions, prolonged exposure to subnormal environments affect its reproduction and development. This study showed that this species can be mass cultured for commercial purposes and has a potential to be used for toxicity studies due to its high reproductive performance fast development and a wide range of tolerance to environmental conditions.  相似文献   

Simulation of summer storms of differing recurrence intervals in a semiarid environment using a kinematic routing scheme     

Hazel Faulkner 《水文研究》1992,6(4):397-416

A kinematic flood routing procedure has been devised for a small dendritic headwater gully network on the Western slope of Colorado. the program is spatially-distributed, incorporating lateral inflows from 103 field sites on the network for which channel geometry variables are known. This model, in which a lateral inflow algorithm for the sideslopes between each channel site is convoluted into a Freeze-type (1978) numerical scheme, is fully developed in this paper. Although the field basis of the lateral inflow algorithm has been tested elsewhere (Faulkner, 1990), sensitivity tests were needed for the roughness and hillslope velocity estimates used in the routing procedure. After these successful tests, a suitably precalibrated run of the model was compared with a field-monitored runoff event on the watershed, and results again were encouraging. However, peak attentuation downstream was more pronounced in reality than on the simulation, so the model was also modified by inclusion of allowances for transmission loss. the tendency that the model had displayed for peak size attenuation downstream was considerably enhanced. Using the model, the geomorphic role of the flashfloods which affect the watershed in the summer months is briefly considered by applying the model to existing records of local summer storm rainfall events as a basis for event simulation. These simulations show that downstream attenuation of the flood wave on concave networks in steep semiarid terrain was likely to be a common occurrence, possibly resulting in down-net deposition and differences in geomorphic behaviour between upstream and downstream sites. the discussion is finally broadened to consider the relative importance of ‘common’ as compared to ‘freak’ watershed events in maintaining these differences.  相似文献   

The short term climatic sensitivity of carbonate and silicate weathering fluxes: Insight from seasonal variations in river chemistry   总被引：2，自引：0，他引：2  

Edward T. Tipper  Mike J. Bickle  A. Joshua West  Hazel J. Chapman 《Geochimica et cosmochimica acta》2006,70(11):2737-2754

Large seasonal variations in the dissolved load of the headwater tributaries of the Marsyandi river (Nepal Himalaya) for major cations and ⁸⁷Sr/⁸⁶Sr ratios are interpreted to result from a greater dissolution of carbonate relative to silicate at high runoff. There is up to a 0.003 decrease in strontium isotope ratios and a factor of 3 reduction in the Si(OH)₄/Ca ratio during the monsoon. These variations, in small rivers sampling uniform lithologies, result from a different response of carbonate and silicate mineral dissolution to climatic forcing. Similar trends are observed in compiled literature data, from both Indian and Nepalese Himalayan rivers. Carbonate weathering is more sensitive to monsoonal runoff because of its faster dissolution kinetics. Silicate weathering increases relative to carbonate during the dry season, and may be more predominant in groundwater with longer water-rock interaction times. Despite this kinetic effect, silicate weathering fluxes are dominated by the monsoon flux, when between 50% and 70% of total annual silicate weathering flux occurs.  相似文献   

Reply to discussion of “late-Quaternary vegetational dynamics and community stability reconsidered”     

Paul A. Delcourt  Hazel R. Delcourt 《Quaternary Research》1984,22(2):263-265

  相似文献