Mesoscale Satellite Bioclimatology     

Bradley C. Rundquist  John A. Harrington  Jr.  Douglas G. Goodin 《The Professional geographer》2000,52(2):331-344

This paper examines the strength of relationships between the Normalized Difference Vegetation Index (NDVI) and climatic data, when examined at the mesoscale. Mean monthly AVHRR NDVI data for 1988‐1996 for the months of April through October for State of Kansas, its nine climatic divisions (CDs), and dominant land cover types within each CD were used. Corresponding climatic and water budget data were obtained or derived from National Climatic Data Center data. Temperature, precipitation, and NDVI deviations from normal were determined. Statistical analysis revealed significant relationships between NDVI and climatic variables, although strengths of the associations were modest. The highest correlation coefficient (r) for the state as a whole was 0.53, between NDVI and estimated actual evapotranspiration. When examined by climatic division or major land cover type, relationships between NDVI and a drought index were statistically significant in most cases and ranged from 0.30 to 0.56.  相似文献   

Geomorphic and pedogenic evidence for bioturbation of artifacts at a multicomponent site in Licking County,Ohio, U.S.A.     

Tod A. Frolking  Bradley T. Lepper 《Geoarchaeology》2001,16(3):243-262

The distribution of artifacts at the multi-component (Paleoindian through Middle Woodland) Munson Springs site (33Li251) is best explained by downward migration of objects through bioturbation processes rather than by a vertical sequence of occupation surfaces through a period of sediment accretion. At the noncultivated, 1800 m², footslope site, the distribution of glacial diamict, loess, and drift- and bedrock-derived colluvium indicate widespread slope erosion during the late-glacial period with general backslope and footslope stability during the Holocene. Diagnostic Paleoindian artifacts were recovered from a BE soil horizon lying directly below fill material of a small (8 × 10 m) Early Woodland mound. Based on soil fine clay distribution, these artifacts lay about 30 cm below the premound land surface. Woodland artifacts are concentrated at depths of 10–20 cm immediately down slope from the mound. Soil horizonation and total and fine clay distributions within footslope profiles indicate no significant sediment accretion through the period of soil genesis and prehistoric site occupation. © 2001 John Wiley & Sons, Inc.  相似文献   

Exploring the variability of argon loss in Apollo 17 impact melt rock 77135 using high‐spatial resolution 40Ar/39Ar geochronology     

Cameron M. Mercer  Kip V. Hodges  Bradley L. Jolliff  Matthijs C. Van Soest  Jo‐Anne Wartho  John R. Weirich 《Meteoritics & planetary science》2019,54(4):721-739

⁴⁰Ar/³⁹Ar incremental heating experiments on whole‐rock lunar samples commonly provide evidence of varying degrees of radiogenic ⁴⁰Ar (⁴⁰Ar*) loss. However, these experiments provide limited information about whether or not ⁴⁰Ar* is preferentially lost from specific glasses, minerals, or polyphase domains. Ultraviolet laser ablation microprobe (UVLAMP) ⁴⁰Ar/³⁹Ar dating and electron probe microanalysis of mineral clasts and polyphase melt assemblages in Apollo 17 poikilitic impact melt rock 77135 show evidence of geochemical controls on ⁴⁰Ar/³⁹Ar dates. Potassium‐rich glass and K‐feldspar in the mesostasis are the dominant sources for Ar released during low‐temperature steps of published ⁴⁰Ar/³⁹Ar release spectra for this rock, while pyroxene oikocrysts with enclosed plagioclase chadacrysts contribute Ar predominantly to intermediate‐ to high‐temperature steps. Additionally, UVLAMP analysis of a mm‐scale plagioclase clast demonstrates the potential to use stranded ⁴⁰Ar* diffusive loss profiles to constrain the thermal evolution of lunar impact melt deposits and indicates that the melt component of 77135 cooled quickly. While some submillimeter clasts of plagioclase are distinctly older than the melt, other small clasts yield dates younger than the oldest melt components in 77135, plausibly due to subgrain fast diffusion pathways and/or ⁴⁰Ar* loss during brief episodes of reheating at high temperatures. Our data suggest that integrated petrologic and microanalytical geochronologic studies are necessary complements to bulk sample geochronologic studies in order to fully evaluate competing models for the impactor flux during the first billion years of the Moon's evolution.  相似文献   

Local government perspectives on rural retirement migration and social sustainability     

Rachel Winterton  Andrew Butt  Bradley Jorgensen  John Martin 《The Australian geographer》2019,50(1):111-128

Within the policy and academic literature, the impact of rural retirement migration (RRM) on community sustainability has been questioned. This qualitative study investigated the perceived impact of retirement migration on rural social sustainability from a local government perspective. Focus groups were conducted with local government senior managers and community services staff (n = 39) across six rural local government areas in one Australian state. Data were analysed against the three components of rural social sustainability (equity, community and rurality) proposed by Jones and Tonts [1995. “Rural Restructuring and Social Sustainability: Some Reflections on the Western Australian Wheatbelt.” Australian Geographer 26: 133–140]. While RRM is perceived to benefit rural community capacity to facilitate or maintain equity, community and rurality, it also presents challenges for local government. Participants suggested that capacity to facilitate equity, community and rurality in contexts of RRM was impacted by uncertainty around future impacts of RRM on population ageing, increasing advocacy and expectations of older in-migrants, and the impact of RRM on rural heterogeneity. These issues required local governments to think critically about how to accommodate and manage the needs and expectations of older in-migrants, while mediating potential impacts associated with RRM.  相似文献   

Historical valley alluviation in mid-Wales     

J. Lewin  S. B. Bradley  M. G. Macklin 《Geological Journal》1983,18(4):331-350

Recent developments on a floodplain reach of the Afon Ystwyth are analysed with the aid of five sets of maps and ten of air photographs covering the period since 1800. The area has been subjected to around 3 m of aggradation and then incision in association with historic metal mining. Analysis of sediment texture and metal concentrations allows subdivision of the mining-associated sediments; C/M plots and shape analyses allow a distinction between proglacial, mining aggradation, and wandering river phases. The distinctive style of aggradation, involving overbank gravel splays and interfingering fines, and the lagged response of channel and sedimentation, relate largely to alterations in sediment supply rates. This has relevance for the interpretation of Quaternary fills and river terraces and for contemporary river management.  相似文献