Natural Hazards - In moderate-to-low seismic hazard regions, estimating the socio-economic consequences of an earthquake on the regional scale is a costly and difficult task. This study analyses... 相似文献
This study contributes to identifying and spatializing the different types of nitrate sources by combining hydrogeochemical and isotopic data with principal component analysis (PCA) and t-distributed stochastic neighbor embedding (t-SNE) multicriteria statistical methods. The methodology is applied to the strategic Mons Basin chalk aquifer (Belgium). The results are based on a whole dataset containing 72 water samples with analyses of the hydrogeochemical parameters (temperature, pH, electrical conductivity (EC), redox potential, dissolved O2), alkalinity, total organic carbon (TOC), silica (SiO2), major and minor ions (NO3–, NH4+, Ca2+, dissolved Fe and Mn, K+, Mg2+, Na+, Sr2+, Cl–, F–, SO4–, B) and multiple stable isotope ratios (δ11B, δ15N–NO3–, δ18O–NO3–). Compared to classical PCA, the recently developed t-SNE method, which considers nonlinear relationships between variables and preserves local-scale similarities in a low-dimensional space, showed much better performance in discriminating different groups of samples and related zones in the aquifer. t-SNE results combined with isotope ratios highlighted four zones in the aquifer (grouped as A–D) and the presence of denitrification fronts. Group A presents a manure signature (δ15N–NO3– – mean (μ) +12.78‰, standard deviation (σ) 6.48‰; δ11B – μ 29.96‰, σ 6.91‰). Group B exhibits both manure and inorganic fertilizer signatures (δ15N–NO3– – μ 6.27‰, σ 2.55‰; δ11B – μ 15.86‰, σ 9.69‰). Group C shows a contamination by sewage (δ15N–NO3– – μ 12.67‰, σ 5.60‰; δ11B – μ 9.97‰, σ 7.08‰). Group D presents a mixed signature (δ15N–NO3– – μ 9.25‰, σ 2.94‰; δ11B – μ 20.00‰, σ 6.70‰).
We present in this article a rapid method for B extraction, purification and accurate B concentration and δ11B measurements by ID‐ICP‐MS and MC‐ICP‐MS, respectively, in different vegetation samples (bark, wood and tree leaves). We developed a rapid three‐step procedure including (1) microwave digestion, (2) cation exchange chromatography and (3) microsublimation. The entire procedure can be performed in a single working day and has shown to allow full B recovery yield and a measurement repeatability as low as 0.36‰ (± 2s) for isotope ratios. Uncertainties mostly originate from the cation exchange step but are independent of the nature of the vegetation sample. For δ11B determination by MC‐ICP‐MS, the effect of chemical impurities in the loading sample solution has shown to be critical if the dissolved load exceeds 5 μg g?1 of total salts or 25 μg g?1 of DOC. Our results also demonstrate that the acid concentration in the sample loading solution can also induce critical isotopic bias by MC‐ICP‐MS if chemistry of the rinsing‐, bracketing calibrator‐ and sample solutions is not thoroughly adjusted. We applied this method to provide a series of δ11B values of vegetal reference materials (NIST SRM 1570a = 25.74 ± 0.21‰; NIST 1547 = 40.12 ± 0.21‰; B2273 = 4.56 ± 0.15‰; BCR 060 = ?8.72 ± 0.16‰; NCS DC73349 = 16.43 ± 0.12‰). 相似文献
The stratigraphy of the last deglaciation sequence is investigated in Lake Saint‐Jean (Québec Province, Canada) based on 300 km of echo‐sounder two dimensional seismic profiles. The sedimentary archive of this basin is documented from the Late Pleistocene Laurentidian ice‐front recession to the present‐day situation. Ten seismic units have been identified that reflect spatio‐temporal variations in depositional processes characterizing different periods of the Saint‐Jean basin evolution. During the postglacial marine flooding, a high deposition rate of mud settling, from proglacial glacimarine and then prodeltaic plumes in the Laflamme Gulf, produced an extensive, up to 50 m thick mud sheet draping the isostatically depressed marine basin floor. Subsequently, a closing of the water body due to glacio‐isostatic rebound occurred at 8.5 cal. ka BP, drastically modifying the hydrodynamics. Hyperpycnal flows appeared because fresh lake water replaced dense marine water. River sediments were transferred towards the deeper part of the lake into river‐related sediment drifts and confined lobes. The closing of the water body is also marked by the onset of a wind‐driven internal circulation associating coastal hydrodynamics and bottom currents with sedimentary features including shoreface deposits, sediment drifts and a prograding shelf‐type body. The fingerprints of a forced regression are well expressed by mouth‐bar systems and by the shoreface–shelf system, the latter unexpected in such a lacustrine setting. In both cases, a regressive surface of lacustrine erosion (RSLE) has been identified, separating sandy mouth‐bar from glaciomarine to prodeltaic muds, and sandy shoreface wedges from the heterolithic shelf‐type body, respectively. The Lake Saint‐Jean record is an example of a regressive succession driven by a glacio‐isostatic rebound and showing the transition from late‐glacial to post‐glacial depositional systems. 相似文献
The Atlantic Meridional Overturning Circulation (AMOC) is a key feature of the climate system. However, its role during climate change is still poorly constrained particularly during an Interglacial to Glacial climate transition and the associated global cooling. We present here the first reconstruction of the evolution of the vertical structure of the rate of the AMOC from the Last Interglaciation to the subsequent glaciation (128,000–60,000 years ago) based on sedimentary (231Pa/230Th) records. We show a deep AMOC during the interglacial warmth Marine Isotope Stage (MIS) 5.5 and a shallower glacial one during glacial MIS 4. The change between these two patterns occurred mostly during the glacial inception, i.e. the transition from MIS 5.5 to MIS 5.4. Our data show that AMOC was enhanced during this latter transition as a consequence of a large increase of the overturning rate of the Intermediate Waters, above 2500 m. We suggest that this AMOC pattern required a reinforced Gulf Stream-North Atlantic Current system that ultimately supported ice-sheet growth by providing heat and moisture to the Northern high latitudes. From MIS 5.4 to MIS 5.1, the AMOC was broadly continuous below 2000 m and supported periods of ice-sheet growth. As a result, a glacial AMOC is triggered at the beginning of MIS 4 due to the extension of ice-sheet and the subsequent reorganization of deep-water formation. This study highlights the role of intermediate waters as a major player during climate change. 相似文献
The geometric correction process is a crucial step in remote sensing applications. This process is frequently manually performed-which is a laborious task in many situations-as automatic image registration methods are still far from being broadly applied. One of the reasons that justify the absence of a broad application of automatic image registration methods is the lack of measures for an objective and automated analysis of the image registration process quality. The root mean square (RMS) of the residuals is the only quantitative evaluation which is generally used in this process, with the final validation of the geometric correction process being a qualitative analysis. Therefore, in both ldquohumanrdquo and automatic image registration processes, an objective evaluation of its quality is required. In this letter, we propose several measures for an objective evaluation of the geometric correction process, as a complement to the traditional RMS of the residuals and visual inspection. Two scenarios of control point distribution and the most common residual distributions were considered. With the proposed measures, we intend to cover the most common qualitative analysis aspects. This has particular importance under the scope of automatic image registration methods, where an automatic evaluation of the results is also required. 相似文献