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1.
Mineral magnetic signatures in a long core from Lake Qarun, Middle Egypt   总被引：1，自引：0，他引：1  
The analysis and interpretation of changes in mineral magnetic signatures from a long (ca. 8.2 m) sedimentary sequence recovered from Lake Qarun, Middle Egypt in 2003 spanning a timescale of approximately the last 2,000 years is reported. A suite of mass specific susceptibility and magnetic remanence measurements were made at irregular intervals downcore on 39 samples. These samples were selected on the basis of trends and abrupt changes in whole-core magnetic susceptibility measured using a Bartington® MS2E sensor and were analysed for low and high temperature loss on ignition and their particle size distribution. Trends in all mineral magnetic concentration parameters are remarkably similar and were initially used to divide the core into three magnetically distinct zones. The upper and lower sections of the core (0–119 cm and 445–822 cm depth) are characterised by low values for all magnetic concentration parameters. Between 153 and 380 cm depth, concentration parameters are considerably higher, although somewhat variable. The S ratio and percentage loss of remanence after 24 h (IRMloss) follow a different trend and are inversely related to each other. A low S ratio (<0.7) is associated with a loss of remanence of >4%. On the basis of these parameters, the core can be divided into four zones, and differences in magnetic mineralogy between these four zones were confirmed by measurement of IRM acquisition curves. The major difference between concentration parameters and ratios or percentage loss of IRM lies in the identification of an additional zone below 619 cm depth where the S ratio is high and IRMloss is low. There is little evidence to suggest that the magnetic signatures are controlled by particle size or by trends in organic matter and/or carbonate content. The signatures appear to be predominantly detrital and show little evidence of post-depositional alteration through dissolution or authigenic addition of bacterial magnetite or greigite. Analysis of Saharan dust deposition rates in Northern Egypt suggests that atmospheric fallout is likely to make only a very minor contribution (<1%) to sedimentation rates in Lake Qarun. The downcore trends therefore appear to reflect major changes in fluvial sediment sources over the ca. 2,000 year time period spanned by this ～8 m core. Preliminary mineral magnetic characterisations of potential local sources suggest that these cannot account for the range of signatures recorded in the Qarun sediments and it is hypothesised that these sediments are derived from Nile river floods.  相似文献   

2.
Subfossil Cladocera were sampled and examined from the surface sediments of 35 thermokarst lakes along a temperature gradient crossing the tree line in the Anabar-river basin in northwestern Yakutia, northeastern Siberia. The lakes were distributed through three environmental zones: typical tundra, southern tundra and forest tundra. All lakes were situated within the continuous permafrost zone. Our investigation showed that the cladoceran communities in the lakes of the Anabar region are diverse and abundant, as reflected by taxonomic richness, and high diversity and evenness indices (H = 1.89 ± 0.51; I = 0.8 ± 0.18). CONISS cluster analysis indicated that the cladoceran communities in the three ecological zones (typical tundra, southern tundra and forest-tundra) differed in their taxonomic composition and structure. Differences in the cladoceran assemblages were related to limnological features and geographical position, vegetation type, climate and water chemistry. The constrained redundancy analysis indicated that TJuly, water depth and both sulphate (SO4 2?) and silica (Si4+) concentrations significantly (p ≤ 0.05) explained variance in the cladoceran assemblage. TJuly featured the highest percentage (17.4 %) of explained variance in the distribution of subfossil Cladocera. One of the most significant changes in the structure of the cladoceran communities in the investigated transect was the replacement of closely related species along the latitudinal and vegetation gradient. The results demonstrate the potential for a regional cladoceran-based temperature model for the Arctic regions of Russia, and for and Yakutia in particular.  相似文献   

3.
Holocene lake level fluctuations were reconstructed from a 2.7-m sediment core from Nam Co, Central Tibet, China dating to >7.2 cal ka BP. Results were compared to existing lake records from the Tibetan Plateau to infer variations in the strength of the Asian Monsoon. Geomorphological features in the Nam Co catchment, such as beach ridges and lake terraces, indicate high lake stands during the late Glacial. A major low stand is suggested for the Last Glacial Maximum (LGM). Sands and sandy silts at the base of the core are transgressive facies, with material transported by melt water and deposited under rising lake level conditions that followed the LGM low stand. Variations in grain size, major elements, biomarker stable isotopes and minerals in the core suggest a climate evolution reflected in at least five depositional units and subunits. Sediments in Unit I (~7.2 to ~5.4 cal ka BP) were deposited at highest lake levels. Large amounts of allogenic minerals and allochthonous organic matter suggest high precipitation and melt water input, implying positive water balance. Increasing aquatic productivity points to favourable environmental conditions. Unit II (~5.4 to ~4.0 cal ka BP) marks a transition between favourable, stable hydrological conditions and lake level decrease. Lower lake levels were a consequence of drier climate with less monsoonal precipitation, higher evaporation rates, and increased moisture recycling in the catchment. Unit III (~4.0 to ~1.4 cal ka BP) reflects the driest periods recorded, at ~3.7 cal ka BP and 1.6 cal ka BP. Lake shrinkage and salinization was interrupted as suggested by the deposition of Unit IV (~1.4 to ~0.8 cal ka BP), when increased precipitation and runoff that might be related to the Medieval Warm Period, led to a stable, but still low lake level. Unit V (800 cal years BP—present) is characterized by progressive lake shrinkage due to intense evaporation. Large fluctuations in geochemical variables indicate humid and arid periods, respectively, at Nam Co between ~450 and ~200 cal years BP, with the latter assumed to correspond to the Little Ice Age. Modern hydrological data indicate the lake level is rising. Comparison of the Nam Co record with other lake records from the Tibetan Plateau suggests general agreement with the broader picture of Holocene environmental evolution. The timing of dry and wet climate conditions at lake sites across Tibet indicates a gradually decreasing influence of the southern monsoon during the Holocene, from NW to SE. Nevertheless, further research is needed to improve our understanding of Holocene spatio-temporal hydrological variations across the Asian continent.  相似文献   

4.
Assessing the thermal evolution of sedimentary basins over time is a major aspect of modern integrated basin analysis. While the behavior of clay minerals and organic matter with increasing burial is well documented in different geological and thermal settings, these methods are often limited by the temperature ranges over which they can be precisely applied and by the available material. Here, we explore the emergent Δ47 clumped isotope geospeedometry (based on the diffusional redistribution of carbon and oxygen isotopes in the carbonate lattice at elevated temperatures) to refine time‐temperature paths of carbonate rocks during their burial evolution. This study provides a reconstruction of the thermal and exhumation history of the Upper Cretaceous thrust belt series in the western subalpine massifs (Bauges and Bornes, French Alps) by a new approach combining for the first time available data from three independent geothermometers. The investigated area presents two zones affected by contrasting thermal histories. The most external zone has undergone a relatively mild thermal history (T < 70°C) and does not record any significant clay mineral diagenetic transformation. By contrast, the internal zone has experienced tectonic burial (prealpine nappes) in response to thrusting, resulting in overheating (T > 160–180°C) that induced widespread clay mineral diagenetic transformations (progressive illitization from R0 to R1 and R3 illite‐smectite mixed‐layers), organic matter maturation (oil window) and Δ47 thermal resetting with apparent equilibrium temperatures above 160°C. The three employed geothermal indicators conjointly reveal that the investigated Upper Cretaceous rocks have suffered a wide range of burial temperatures since their deposition, with a thermal maximum locally up to 160–180°C. High temperatures are associated with the tectonic emplacement of up to 4 km of prealpine nappes in the northern part of the studied area. Finally, a forward thermal modeling using Δ47, vitrinite reflectance and clay mineral data, is attempted to precisely refine the burial and exhumation histories of this area.  相似文献   

5.
Multivariate statistical methods and geochemical modeling were used to assess spatial variation of water quality of the Soummam basin, Algeria. The application of hierarchical cluster analysis (HCA) showed three main groups of samples. Group 1 samples are exclusively composed of surface water. Groups 2 and 3 samples consist of groundwater. Discriminant analysis assigned about 98.6% of the cases grouped by HCA. All groups are super-saturated with Ca-montmorillonite, dolomite, gibbsite, K-mica, kaolinite, and quartz, and all these groups are under-saturated with albite, anhydrite, anorthite, CO2(g), gypsum, halite, melanterite, and smithsonite. The results of analysis of variance indicate that the saturation indices of each of the mineral phases are significant except for chalcedony and quartz (p > 0.05). The results obtained by inverse geochemical modeling show the dissolution of albite, which justifies Na enrichment during the chemical evolution of groundwater. Calcite, dolomite, Ca-montmorillonite, kaolinite, illite, gibbsite, and K-mica are shown to have always precipitated.  相似文献   

6.

A thorough study on understanding of groundwater recharge sources and mechanisms was attempted by integrating the hydrogeological, geochemical and isotopic information along with groundwater dating and end-member mixing analysis (EMMA). This study was necessitated due to prolonged dryness and unavailability of freshwater in semi arid Deccan trap regions of Central India. In addition, groundwater resources are not characterized well in terms of their geochemical nature and recharge sources. The hydrogeochemical inferences suggest that aquifer I consists of recently recharged water dominated by Ca–Mg–HCO3 facies, while groundwater in aquifer II shows water–rock interaction and ion exchange processes. Presence of agricultural contaminant, nitrate, in both aquifers infers limited hydraulic interconnection, which is supported by unconfined to semi-confined nature of aquifers. Groundwater in both aquifers is unsaturated with respect to carbonate and sulfate minerals indicating lesser water–rock interaction and shorter residence time. This inference is corroborated by tritium age of groundwater (aquifer I: 0.7–2 years old and aquifer II: 2–4.2 years old). Stable water isotopes (δ2H, δ18O) suggest that groundwater is a mixture of rainwater and evaporated water (surface water and irrigation return flow). EMMA analysis indicates three groundwater recharge sources with irrigation return flow being the dominant source compared to others (rainwater and surface waters). A conceptual model depicting groundwater chemistry, recharge and dynamics is prepared based on the inferences.

  相似文献   

7.
Two seismic facies were recognized in the sedimentary sequence overlying acoustic basement in Lake Winnipeg. The upper facies, which overlies a regional unconformity, is termed the Lake Winnipeg Sequence. Based on the seismostratigraphy, lithostratigraphy, and radiocarbon dates of approximately 4000 and 7000 yr BP from material collected directly over the unconformity in the southern and northern parts of the lake, respectively, this facies has been interpreted as representing Holocene sedimentation. Results of compositional and textural analyses of the Holocene sediment (Winnipeg sediment) from thirteen long (>2 m) cores indicate a transgressional sequence throughout the basin. In the South Basin, the generally fining upward sequence is characterized at the base by silt-sized detrital carbonate minerals, quartz and feldspar which decrease in concentration upward. In this basin, the high carbonate content and V/Al and Zn/Al ratios are indicative of a Paleozoic and Cretaceous provenance for sediment derived from glacial deposits through shoreline erosion and fluvial transport, via the Red River. Sedimentation in the central part of the lake and the North Basin is attributed to shoreline erosion of sand and gravel beaches. Consequently, the texture of these sediments is generally coarser than in the South Basin, and the composition primarily reflects a Paleozoic and Precambrian provenance. The basin-wide decrease in Ca, total carbonate minerals, dolomite and calcite concentrations upward in the cores is reflected by a decrease in the detrital carbonate component in all but the most northern cores. Other basin-wide trends show an upward increase in organic content in all cores. An increase in grain size near the top of most cores suggests a major, basin-wide change in sedimentation within the last, approximately 900 years in the South Basin.  相似文献   

8.
在野外考察采样的基础上,对泥河湾盆地马圈沟剖面更新世河湖相沉积序列进行了XRD矿物组分和磁性矿物分析。研究发现,剖面沉积矿物主要由碎屑矿物和碳酸盐矿物组成,碎屑矿物主要为石英、钠长石、白云母和斜绿泥石,其平均含量分别为38.77%、17.16%、29.63%和4.11%,是剖面沉积矿物组成主体,且各矿物之间基本没有相关性;相对于碎屑矿物,碳酸盐矿物在整个剖面中含量较低,主要为方解石和白云石,其平均含量分别为4.72%、3.59%,文石在剖面中零星出现。对剖面典型样品进行热磁分析,确定了沉积物中磁性矿物的种类以及加热过程中的变化和产物,并对其来源进行了探讨。同时发现,含绿泥石较高的灰绿色粉砂样品加热后磁化率的升幅比灰黄色样品高,而绿泥石的相对含量与该地区化学风化密切相关,进一步说明κ-T曲线的变化特征可以用来反应盆地化学风化作用强度的变化,具有重要的古环境意义。  相似文献   

9.
The euryhaline ostracod Cyprideis torosa lives in Akyatan Lagoon, Turkey, which is exposed to large spatial and seasonal variations in water salinity, δ18O, and temperature. Hydrogen and oxygen isotope measurements of waters reveal that the large range of salinity (15–80 g L?1) in the lagoon results from a combination of evaporation and mixing between Mediterranean seawater and Seyhan River input. Round sieve-pore relative abundance in C. torosa provides a robust proxy for water salinity (S) from 15 to 80 g L?1, according to the equation: S = 161.41 (±4.52) * log10(% rounded pores) ? 94.04 (±3.44) (R2 = 0.937; p = 10?31). Seasonal sampling and isotope analysis of C. torosa in waters of known δ18O values (?4.7 to +6.9 ‰ V-PDB) and temperatures (15–35 °C) yielded a weak positive correlation (r = 0.71) between 1000 lnα(calcite–water) ‰ V-SMOW) and 103 * T?1. Specimens of C. torosa collected during the mild and warm seasons have oxygen isotope compositions close to those of inorganic calcite precipitated in equilibrium with ambient water. The large oxygen-isotope variability observed during any season of the year most likely results from shell calcification in water bodies of highly variable salinity, alkalinity, Mg/Ca and water saturation relative to calcite. Indeed, distinct water bodies in the Akyatan Lagoon are generated by mixing of fresh and marine waters, which are exposed to different evaporation rates at the seasonal scale.  相似文献   

10.
王国华  张妍  缑倩倩  张仲伍  孙九林 《地理科学》2022,42(10):1818-1828
以黑河流域中游典型绿洲边缘地表水（水库水、河流水）和地下水为研究对象,选取2005—2013年地下水和地表水水化学离子连续监测数据,综合运用描述性统计、Piper图、Gibbs图、离子相关性等方法,对水化学类型及其控制因素进行系统分析。结果表明：① 在2005—2013年地下水总溶解固体（TDS）呈上升趋势,而地表水（河流水和水库水）TDS呈下降趋势,同时,地下水TDS显著高于地表水;② 在年际尺度,地下水离子浓度均随时间增加而显著升高,而河流水和水库水离子整体呈下降趋势;在年内尺度,地下水NO3?离子浓度呈现8月显著高于5月的特征,河流水Ca2+、SO42?离子浓度8月高于5月,而水库水所有离子含量5月高于8月;③ 在2005—2013年,地表水和地下水水化学类型变化：地表水水化学类型在2005—2009年由HCO3?-SO42?-Ca2+-Mg2+ 转变为HCO3?-Ca2+-Na+,而2009—2013年水库水转变为HCO3?-SO42?-Ca2+-Mg2+,河水转变为HCO3?-SO42?-Ca2+-Na+;地下水水化学类型由HCO3?-SO42?-Ca2+-Mg2+ 型转变为SO42?-HCO3?-Ca2+-Na+-Mg2+ 型;地表水和地下水中SO42?、NO3?变异系数最大,是随环境因素变化的最主要敏感离子;④ Gibbs图表明,地表水和地下水中离子主要来源于岩石风化作用,方解石、白云岩等碳酸盐岩或硅酸盐岩矿物的风化溶解是该地区离子主要来源。  相似文献   

11.
We investigated oxygen and carbon isotopes of bulk carbonate and of benthic freshwater ostracods (Candona candida) in a sediment core of Lago Piccolo di Avigliana that was previously analyzed for pollen and loss-on-ignition, in order to reconstruct environmental changes during the late glacial and early Holocene. The depth–age relationship of the sediment core was established using 14 AMS 14C dates and the Laacher See Tephra. While stable isotopes of bulk carbonates may have been affected by detrital input and, therefore, only indirectly reflect climatic changes, isotopes measured on ostracod shells provide unambiguous evidence for major environmental changes. Oxygen isotope ratios of ostracod shells (δ18OC) increased by ～6‰ at the onset of the Bølling (～14,650 cal BP) and were ～2‰ lower during the Younger Dryas (～12,850 to 11,650 cal BP), indicating a temporal pattern of climate changes similar to the North Atlantic region. However, in contrast to records in that region, δ18OC gradually decreased during the early Holocene, suggesting that compared to the Younger Dryas more humid conditions occurred and that the lake received gradually increasing input of 18O-depleted groundwater or river water.  相似文献   

12.
The river Narmada is a major source of fresh water for the highly populated areas, predominantly the rural populations in Madhya Pradesh (Central India) and Gujarat (Western India). Modernization and industrialization in these areas have become a matter of concern due to changing environment and increasing social activities that influence the quality of water directly or indirectly. This investigation was undertaken to evaluate the quality of water along the banks of the river Narmada at different sampling sites using physico-chemical and bacteriological methods. The samples collected were analyzed per standard method parameters and were measured in situ. The correlation matrix indicated strong mutual dependency between the measured parameters (P < 0.05). Principal components analysis of the data indicates that two components (PC1 and PC2) influence the water quality to the extent of 57.4, 64.5 and 61.0% during rainy, winter and summer seasons, respectively. The mean values of the physico-chemical parameters of the river water samples were consistently higher than the levels certified by the World Health Organization and other regulatory bodies as polluted water. The presence of coliform bacteria in the water samples warrants for proper measures to reduce the pollution at point sources and requires proper remediation strategies to combat contamination in the river water.  相似文献   

13.
We sampled modern chironomids at multiple water depths in Lake Annecy, France, before reconstructing changes in chironomid assemblages at sub-decadal resolution in sediment cores spanning the last 150 years. The lake is a large, deep (zmax = 65 m), subalpine waterbody that has recently returned to an oligotrophic state. Comparison between the water-depth distributions of living chironomid larvae and subfossil head capsules (HC) along three surface-sediment transects indicated spatial differences in the influence of external forcings on HC deposition (e.g. tributary effects). The transect with the lowest littoral influence and the best-preserved, depth-specific chironomid community characteristics was used for paleolimnological reconstructions at various water depths. At the beginning of the twentieth century, oxygen-rich conditions prevailed in the lake, as inferred from M. contracta-type and Procladius sp. at deep-water sites (i.e. cores from 56 to 65 m) and Paracladius sp. and H. grimshawi-type in the core from 30 m depth. Over time, chironomid assemblages in cores from all three water depths converged toward the dominance of S. coracina-type, indicating enhanced hypoxia. The initial change in chironomid assemblages from the deep-water cores occurred in the 1930s, at the same time that an increase in lake trophic state is inferred from an increase in total organic carbon (TOC) concentration in the sediment. In the 1950s, an assemblage change in the core from 30 m water depth reflects the rapid expansion of the hypoxic layer into the shallower region of the lake. Lake Annecy recovered its oligotrophic state in the 1990s. Chironomid assemblages, however, still indicate hypoxic conditions, suggesting that modern chironomid assemblages in Lake Annecy are decoupled from the lake trophic state. Recent increases in both TOC and the hydrogen index indicate that changes in pelagic functioning have had a strong indirect influence on the composition of the chironomid assemblage. Finally, the dramatic decrease in HC accumulation rate over time suggests that hypoxic conditions are maintained through a feedback loop, wherein the accumulation of (un-consumed) organic matter and subsequent bacterial respiration prevent chironomid re-colonization. We recommend study of sediment cores from multiple water depths, as opposed to investigation of only a single core from the deepest part of the lake, to assess the details of past ecological changes in large deep lakes.  相似文献   

14.
A significant relationship between the distribution and abundance of chironomids and water depth has long been recognized. Few studies on this topic, however, have been carried out in arid regions where the chironomid community is usually controlled by water salinity. Bosten Lake, northwest China, the largest inland freshwater lake (~1,260 km2) in the country, provides a unique opportunity to investigate this relationship in an arid region. A total of 42 surface sediment samples from water depths of 0.9–17.0 m, and 12 chironomid taxa, were used in the analysis. The first principal component analysis (PCA) axis explained 59.3 % of the variance in the chironomid assemblage and there was a significant correlation between PCA axis 1 scores and water depth (R2 = 0.84, P < 0.001). The chironomid assemblages change significantly at 8.0 m water depth. This threshold corresponds to an abrupt change in the basin slope and the spatial distribution of aquatic vascular plants. Redundancy analysis showed that abundances of Chironomus plumosus-type, Microchironomus and Cryptochironomus are positively correlated with water depth, whereas abundances of Tanytarsus, Polypedilum nubifer-type, Cricotopus and Psectrocladius sordidellus-type are negatively correlated with water depth. These ecological relationships are supported by published data. Qualitative chironomid-inferred changes in lake level and diatom-inferred changes in salinity from sediment core BSTC001 were compared. Close agreement in trends for these two variables validates the use of chironomid assemblages to study palaeo-hydrological variability in this westerlies-dominated, arid region of central Asia.  相似文献   

15.
黑河上游夏半年河水化学组成及年内过程   总被引：4，自引：2，他引：2  
2006年5月至2006年10月在黑河上游扎马什克、祁连及莺落峡水文站逐日采集河水样,同期在七一冰川冰采集融水样,研究水化学组成、演化特征及其影响因素。样品分析结果表明：黑河上游山区,受人类活动影响较少,水中可溶性无机离子的含量比较低,主要受水岩作用过程影响。水文因素,特别是降水是控制水中化学物质含量季节变化的主要因素。受流域地理-地貌特征及水文差异影响,祁连水文站样品中Cl-,NO-3,SO2-4和Na+的含量相对较高,札马什克样品中Ca2+,Mg2+和HCO-3浓度较大,莺落峡的水化学组成介于扎马什克与祁连之间。在流域范围内,气候差异是引起水化学组成变化的主要因素。上游河水中的化学物质主要来源于碳酸盐溶解,也有部分硫酸盐的贡献,随径流演化,岩盐和硫酸盐的贡献逐渐占主要地位。  相似文献   

16.
The study investigates the possibility of using carbonatite in the production of precipitated calcium carbonate (PCC). We made use of fresh apatite-rich carbonatites found at the phosphate mining sites at Eppawala, Sri Lanka. Analyses of the fresh carbonatite were performed with the aid of optical microscopy, powder X-ray diffraction (XRD), atomic absorption spectrophotometry (AAS), UV/visible spectrophotometry (UVVS), and thermo gravimetric analysis (TGA). Quicklime obtained from calcinations of carbonatites was used in synthesizing PCC via a lime-soda process. The end product was analyzed with XRD, TGA, AAS, and UVVS. Results revealed that the most common CO3 2? phase available in fresh carbonatites is calcite (>65%). The Ca-rich CO3 2? phase can be distinguished easily from other available minerals because its mode of occurrence in carbonatite matrix is different to that of other minerals. The results of TGA show that the decomposition of CO3 2? phase initiates at about 340°C, which leads to lower energy consumption during calcinations. Post-magmatic hydrothermal process may have been the cause of the formation of thermally unstable CO3 2? phases. Hydration of quicklime from the carbonatite yields much higher Ca2+ in the solution than from marble under the same experimental conditions. The synthesized PCC particles are in the calcite polymorphic form. The purity of PCC varies from 96 to 98 wt%. The maximum precipitable CaCO3 from 1 g of quicklime is about 1.1 g. Hence, fresh carbonatites has great economic potential for the production of PCC.  相似文献   

17.
塔里木盆地水汽含量的计算与特征分析   总被引：3，自引：0，他引：3  
杨青  刘晓阳  崔彩霞  李军  刘蕊 《地理学报》2010,65(7):853-862
利用1976-2009 年塔里木盆地的和田、库车、若羌、喀什和民丰5 个探空站的实测资料计算了逐月平均水汽含量,并建立了与地面水汽压的关系式;利用这种关系式计算了盆地及周边地区28 个站水汽含量,进行了EOF分解,得出了水汽分布形式;分析了地表水汽压随高度的变化;对在盆地腹地及周边地区进行的GPS观测资料进行了水汽含量的反演,并与探空计算值进行了对比。结果表明：盆地内水汽含量有两个高值区,主要分布在盆地西部和北部的边缘地带,中心水汽含量在13~14 mm,均位于塔里木河干流、叶尔羌河流域、阿克苏河支流周围的绿洲地区。塔克拉玛干沙漠腹地是水汽的低值区中心,水汽含量仅为7~8 mm,塔中是所有站中水汽量最少的,由中心向外逐渐增加,在环塔里木盆地的西部、北部绿洲区达到最高,然后由于海拔高度的影响又逐渐减小。塔里木盆地地基GPS反演水汽数据与探空计算值存在良好的线性关系。  相似文献   

18.
High-resolution, well-calibrated records of lake sediments are critically important for quantitative climate reconstructions, but they remain a methodological and analytical challenge. While several comprehensive paleotemperature reconstructions have been developed across Europe, only a few quantitative high-resolution studies exist for precipitation. Here we present a calibration and verification study of lithoclastic sediment proxies from proglacial Lake Oeschinen (46°30′N, 7°44′E, 1,580 m a.s.l., north–west Swiss Alps) that are sensitive to rainfall for the period AD 1901–2008. We collected two sediment cores, one in 2007 and another in 2011. The sediments are characterized by two facies: (A) mm-laminated clastic varves and (B) turbidites. The annual character of the laminae couplets was confirmed by radiometric dating (210Pb, 137Cs) and independent flood-layer chronomarkers. Individual varves consist of a dark sand-size spring-summer layer enriched in siliciclastic minerals and a lighter clay-size calcite-rich winter layer. Three subtypes of varves are distinguished: Type I with a 1–1.5 mm fining upward sequence; Type II with a distinct fine-sand base up to 3 mm thick; and Type III containing multiple internal microlaminae caused by individual summer rainstorm deposits. Delta-fan surface samples and sediment trap data fingerprint different sediment source areas and transport processes from the watershed and confirm the instant response of sediment flux to rainfall and erosion. Based on a highly accurate, precise and reproducible chronology, we demonstrate that sediment accumulation (varve thickness) is a quantitative predictor for cumulative boreal alpine spring (May–June) and spring/summer (May–August) rainfall (rMJ = 0.71, rMJJA = 0.60, p < 0.01). Bootstrap-based verification of the calibration model reveals a root mean squared error of prediction (RMSEPMJ = 32.7 mm, RMSEPMJJA = 57.8 mm) which is on the order of 10–13 % of mean MJ and MJJA cumulative precipitation, respectively. These results highlight the potential of the Lake Oeschinen sediments for high-resolution reconstructions of past rainfall conditions in the northern Swiss Alps, central and eastern France and south-west Germany.  相似文献   

19.
A fully allocated surface water supply in the Upper Deschutes Basin, Oregon, intensifies concern for the watershed's response to climate change. Such concern provides the impetus for this case study of the basin under a potential doubling of atmospheric trace gas concentrations (2 × CO2). Modeling the watershed as four sectors incorporates climate and landscape heterogeneity and defines a control climate that closely simulates adjusted gaged runoff. Monthly temperature and precipitation from a limited area model nested in a global circulation model define changes for modeling the watershed 2 × CO2 climate. Precipitation increases are greatest in the Wickiup sector and least in the Little Deschutes sector for a 2 × CO2 climate, but snow-water equivalent decreases substantially in all sectors. Summer water deficits are extended and magnified in all sectors and increase by 175% in the Wickiup sector. Water surplus increases range from 34% for Wickiup to 5% for Benham Falls. Average monthly runoff for the Upper Deschutes Basin increases by 7 mm or 24% in the 2 × CO2 climate, but the greatest monthly runoff differences are for the Crescent Lake sector, where February and March runoff increase by 68% and May runoff decreases by 10%. The earlier occurrence of maximum and minimum 2 × CO2 climate runoff of one to five months significantly alters the Upper Deschutes Basin runoff regime. [Key words: mesoscale hydroclimate model, climate change, Deschutes River Basin.]  相似文献   

20.
分布式水文模型全局敏感性高效分析方法研究(英文)   总被引：4，自引：0，他引：4  
Sensitivity analysis of hydrological model is the key for model uncertainty quantification. However, how to effectively validate model and identify the dominant parameters for distributed hydrological models is a bottle-neck to achieve parameters optimization. For this reason, a new approach was proposed in this paper, in which the support vector machine was used to construct the response surface at first. Then it integrates the SVM-based response surface with the Sobol’ method, i.e. the RSMSobol’ method, to quantify the parameter sensitivities. In this work, the distributed time-variant gain model (DTVGM) was applied to the Huaihe River Basin, which was used as a case to verify its validity and feasibility. We selected three objective functions (i.e. water balance coefficient WB, Nash-Sutcliffe efficiency coefficient NS, and correlation coefficient RC) to assess the model performance as the output responses for sensitivity analysis. The results show that the parameters g1 and g2 are most important for all the objective functions, and they are almost the same to that of the classical approach. Furthermore, the RSMSobol method can not only achieve the quantification of the sensitivity, and also reduce the computational cost, with good accuracy compared to the classical approach. And this approach will be effective and reliable in the global sensitivity analysis for a complex modelling system.  相似文献   

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