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Richard J. Cooper Thomas M. Melvin Ian Tyers Rob J. S. Wilson Keith R. Briffa 《Climate Dynamics》2013,40(3-4):1019-1039
We present an annually resolved reconstruction of spring-summer precipitation variability in East Anglia, UK (52–53°N, 0–2°E) for the period AD 900–2009. A continuous regional network of 723 living (AD 1590–2009) and historical (AD 781–1790) oak (Quercus sp.) ring-width series has been constructed and shown to display significant sensitivity to precipitation variability during the March-July season. The existence of a coherent common growth signal is demonstrated in oaks growing across East Anglia, containing evidence of near-decadal aperiodic variability in precipitation throughout the last millennium. Positive correlations are established between oak growth and precipitation variability across a large region of northwest Europe, although climate-growth relationships appear time transgressive with correlations significantly weakening during the early twentieth century. Examination of the relationship between oak growth, precipitation, and the North Atlantic Oscillation (NAO), reveals no evidence that the NAO plays any significant role in the control of precipitation or tree growth in this region. Using Regional Curve Standardisation to preserve evidence of low-frequency growth variability in the East Anglian oak chronology, we produce a millennial length reconstruction that is capable of explaining 32–35% of annual-to-decadal regional-scale precipitation variance during 1901–2009. The full length reconstruction indicates statistically significant anomalous dry conditions during AD 900–1100 and circa-1800. An apparent prolonged wetter phase is estimated for the twelfth and thirteen centuries, whilst precipitation fluctuates between wetter and drier phases at near centennial timescales throughout the fourteenth to seventeenth centuries. Above average precipitation reconstructed for the twenty-first century is comparable with that reproduced for the 1600s. The main estimated wet and dry phases reconstructed here appear largely coherent with an independent tree-ring reconstruction for southern-central England. 相似文献
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Peter J. Melvin 《Celestial Mechanics and Dynamical Astronomy》1985,35(4):345-355
Deprit's approach to the summation of the Legendre series in the geopotential evaluation problem is modified to accomodate normalized spherical harmonics and coefficients. Normalization avoids the floating point overflow encountered with high order geopotential models when the computer floating point arithmetic does not provide for large enough exponent. Deprit's algorithm is then appropriate for trajectory generation on-board an autonomous satellite system or for gravity compensation in an inertial navigation system. 相似文献
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The electrical conductivity and water soluble Na, K, Ca, and Mg of aqueous solutions of terrestrial soils and finely divided igneous and metamorphic rocks were determined. Soils from dry terrestrial basins with a history of water accumulation as well as soils from the topographic lows of valleys accumulated water soluble cations, particularly Na and Ca. These soils as a group can be distinguished from the rocks or a second group of soils (leached upland soils and soils from sites other than the topographic lows of valleys) by significant differences in their mean electrical conductivity and water soluble Na + Ca content. Similar measurements on multiple samples from the surface of Mars, collected by an automated long-range roving vehicle along a highlands to basin transect at sites with morphological features resembling dry riverlike channels, are suggested to determine the fluvial history of the planet. 相似文献
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The content of 11 heavy metals in the sediments of a stream system was determined by atomic absorption analysis. Geochemical phases were investigated using a sequential extraction scheme, and bulk contents were assessed with a single HNO3 extraction. Certain heavy metals were associated with different geochemical phases. Co, Mn, and Ba concentrated primarily in the carbonate and Mn phases, while all the remaining metals concentrated in the Fe and remnant phases. Features located along the stream system influenced the content of heavy metals. Results from the geochemical phases indicated Cu, Pb, Zn, Cd and Ag were emitted by one landfill, while Cd, Ba, and Ag were emitted by a second landfill. A wastewater treatment facility appeared to emit Ni and Cu. A stream draining a reservoir and joining the study stream resulted in dilution of the heavy metals in the sediments. A populated area along the study stream appeared to emit Mn. The single HNO3 extraction procedure is quicker to perform than the sequential extraction but does not indicate the phase associations. 相似文献
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Mumbfu Ernestine Mimba Takeshi Ohba Salomon César Nguemhe Fils Melvin Tamnta Nforba Nozomi Numanami Tasin Godlove Bafon Festus Tongwa Aka Cheo Emmanuel Suh 《Geochemical transactions》2018,19(1):11
The distribution of trace metals in active stream sediments from the mineralized Lom Basin has been evaluated. Fifty-five bottom sediments were collected and the mineralogical composition of six pulverized samples determined by XRD. The fine fraction (<?150 µm) was subjected to total digestion (HClO4?+?HF?+?HCl) and analyzed for trace metals using a combination of ICP-MS and AAS analytical methods. Results show that the mineralogy of stream sediments is dominated by quartz (39–86%), phyllosilicates (0–45%) and feldspars (0–27%). Mean concentrations of the analyzed metals are low (e.g. As?=?99.40 µg/kg, Zn?=?573.24 µg/kg, V?=?963.14 µg/kg and Cr?=?763.93 µg/kg). Iron and Mn have significant average concentrations of 28.325 and 442 mg/kg, respectively. Background and threshold values of the trace metals were computed statistically to determine geochemical anomalies of geologic or anthropogenic origin, particularly mining activity. Factor analysis, applied on normalized data, identified three associations: Ni–Cr–V–Co–As–Se–pH, Cu–Zn–Hg–Pb–Cd–Sc and Fe–Mn. The first association is controlled by source geology and the neutral pH, the second by sulphide mineralization and the last by chemical weathering of ferromagnesian minerals. Spatial analysis reveals similar distribution trends for Co–Cr–V–Ni and Cu–Zn–Pb–Sc reflecting the lithology and sulphide mineralization in the basin. Relatively high levels of As were concordant with reported gold occurrences in the area while Fe and Mn distribution are consistent with their source from the Fe-bearing metamorphic rocks. These findings provide baseline geochemical values for common and parallel geological domains in the eastern region of Cameroon. Although this study shows that the stream sediments are not polluted, the evaluation of metal composition in environmental samples from abandoned and active mine sites for comparison and environmental health risk assessment is highly recommended. 相似文献
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The potential rapid development of tidal energy and accompanying structures in the coastal waters in several regions of Canada, and the world, will require subsurface sampling tools to monitor and evaluate the biological and environmental effects of this new industry. Proposed development sites are characterized by large tidal ranges, strong tidal flows, extreme turbulence, and in some cases sediment-laden water restricting visibility, imposing monitoring challenges. Turbulence-induced acoustic backscatter typically occurs in the top 10–20 m, but can extend from the surface to bottom during some phases of the tide. In Minas Passage, turbulence accounted for 78 % of the total water column backscatter making the separation of fish difficult if not impossible at times. In this paper, we examine operational capabilities of two high-frequency multibeam sonars to meet these monitoring challenges in the nearshore high-flow shallow coastal waters (1–100 m). Observations from proposed sites are used to illustrate the challenges as well as the advantages, and limitations, of multibeam sonars compared to conventional split beam technology in strong tidal currents and turbulent waters. Acoustic multibeam hardware necessary to meet the monitoring demands is currently available, but the processing and analytical software required to advance their application is insufficient to meet the requirements for effects and impact monitoring. It is anticipated that the required advancements will be available within the next 5 years. Challenges associated with equipment deployment, power supply, and communications are also discussed. 相似文献
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