Postglacial climatic conditions were inferred from cores taken from Big Lake in southern British Columbia. Low concentrations of nonarboreal pollen and pigments near the base of the core suggest that initial conditions were cool. Increases in both aquatic and terrestrial production suggest warmer and moister conditions until 8500 cal yr B.P. Hyposaline diatom assemblages, increases in nonarboreal pollen, and increased concentrations of pigments suggest the onset of arid conditions from 8500 to 7500 cal yr B.P. Slightly less arid conditions are inferred from 7500 until 6660 cal yr B.P. based on the diatoms, small increases and greater variability in biogenic silica and pigments, and higher percentages of arboreal pollen. At 6600 cal yr B.P., changes in diatoms, pigments, biogenic silica, and organic matter suggest that Big Lake became fresh, deep, and eutrophic until 3600 cal yr B.P., when water levels and nutrients decreased slightly. Our paleoclimatic inferences are similar to pollen-based studies until 6600 cal yr B.P. However, unlike these studies, our multiple lines of evidence from Big Lake imply large changes in effective moisture since 6000 cal yr B.P. 相似文献
A sample preparation technique was developed to isolate and separate two classes of combustion-produced pollutants: three- to six-ring polycyclic aromatic hydrocarbons (PAH) and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F), from sediment samples for interference-free analyses by gas chromatography/mass spectrometry (GC/MS). The method involves soxhlet extraction with methylene chloride, sulfur removal with activated copper powder, gel filtration chromatography with Sephadex LH-20, polarity separations of PAH and PCDD/F with prepacked silica gel solid-phase extraction columns, and isolation of PCDD/F from polychlorinated biphenyls with microalumina columns. Stringent procedural controls were established to achieve clean isolations and recoveries of 70% or better for each step in the method. The prepared sample extracts were analyzed by capillary GC and GC/MS. Electron impact ionization was used for PAH, and negative chemical ionization with methane as a reagent gas was used for PCDD/F. Reproducible results were obtained. The method is simple and has the advantage of conserving sample consumption since two classes of compounds can be analyzed from the same sample. This can be critical in sediment core analyses where sample size is usually limited. 相似文献
This paper compares monthly and seasonal rain rates derived from the Version 5 (V5) and Version 6 (V6) TRMM Precipitation Radar (TPR, TSDIS reference 2A25), TRMM Microwave Imager (TMI, 2A12), TRMM Combined Instrument (TCI, 2B31), TRMM calibrated IR rain estimates (3B42) and TRMM merged gauge and satellite analysis (3B43) algorithms over New Mexico (NM) with rain gauge analyses provided by the New Mexico water districts (WD). The average rain rates over the NM region for 1998–2002 are 0.91mmd?1 for WD and 0.75, 1.38, 1.49, 1.27, and 1.07mmd?1 for V5 3B43, 3B42, TMI, PR and TCA; and 0.74, 1.38, 0.87 and 0.97 mm d?1 for V6 3B43, TMI, TPR and TCA, respectively. Comparison of V5 3B43 with WD rain rates and the daily TRMM mission index (TPR and TMI) suggests that the low bias of V5 3B43 for the wet months (summer to early fall) may be due to the non-inclusion of some rain events in the operational gauge analyses that are used in the production of V5 3B43. Correlation analyses show that the WD rain rates vary in phase, with higher correlation between neighboring WDs. High temporal correlations (>0.8) exist between WD and the combined algorithms (3B42, 3B43 and TCA for both V5 and V6) while satellite instrument algorithms (PR, TMI and TCI) are correlated best among themselves at the monthly scale. Paired t-tests of the monthly time series show that V5 3B42 and TMI are statistically different from the WD rain rates while no significant difference exists between WD and the other products. The agreements between the TRMM satellite and WD gauge estimates are best for the spring and fall and worst for winter and summer. The reduction in V6 TMI (?7.4%) and TPR (?31%) rain rates (compared to V5) results in better agreement between WD estimates and TMI in winter and TPR during summer. 相似文献
By a detailed comparison of annual and sub-annual components of EUV absorption heat input with those of the Jacchia density models, we consider the importance of EUV heating in the annual and sub-annual variations of the upper atmosphere. When all the geometrical effects of EUV heat input have been taken into account, it is found that a remarkable correspondence exists between properties of each harmonic component of EUV heat input and Jacchia model temperature and densities. Equinoctial latitude independence of diurnal averaged annual and sub-annual components of heat input and density is proposed as a test of the significance of the EUV heat input. The Jacchia model is found to satisfy this test rigourously. 相似文献
This paper adopts the logarithmic mean Divisia index in the family of spatial index decomposition analysis to decompose the driving effect of spatial differences of water intensity in China into intensity effect and structure effect employing data spanning 2000–2017. The results show that water use efficiency of the eastern provinces was always higher than that of the central provinces and western provinces except for Jiangsu and Hainan, and in the central and western regions, only Shanxi, Henan, Chongqing, and Shaanxi had higher efficiency levels than the national average level. Over that 17-year time period, the gap in water intensity exhibits a decreasing trend between the provincial level and average level (except for Heilongjiang and Chongqing). For industry water intensity, those provinces with a lower than average level were mainly in the eastern region. Except for Shanghai, Jiangsu, and Guangdong, the primary industry water intensity of the eastern provinces was always lower than the average level. Except for Fujian, Shanghai, Jiangsu, and Hainan, the secondary industry water intensity of the eastern provinces was always lower than the average level. Except for Guangdong, Fujian, and Hainan, the tertiary industry water intensity of the eastern provinces was always lower than average level. The water intensity of the secondary and tertiary industries in Shanxi and Inner Mongolia in the central and western regions was always lower than the average level. Lastly, the provinces in which the provincial proportion of the primary industry was lower than the average level were mainly in the eastern region, while conversely the same proportion of the primary industry among central and western provinces was generally high. Therefore, provinces should formulate and implement water resource policies that are different and pertinent to their own actual conditions.
