Instability of seawater pH in the South China Sea during the mid-late Holocene: Evidence from boron isotopic composition of corals   总被引：1，自引：0，他引：1  

Yi Liu  Weiguo Liu  Yingkai Xiao  Weidong Sun  Guijian Liu 《Geochimica et cosmochimica acta》2009,73(5):1264-1272

We used positive thermal ionization mass spectrometry (PTIMS) to generate high precision δ¹¹B records in Porites corals of the mid-late Holocene from the South China Sea (SCS). The δ¹¹B values of the Holocene corals vary significantly, ranging from 22.2‰ to 25.5‰. The paleo-pH records of the SCS, reconstructed from the δ¹¹B data, were not stable as previously thought but show a gradual increase from the Holocene thermal optimal and a sharp decrease to modern values. The latter is likely caused by the large amount of anthropogenic CO₂ emissions since the Industrial Revolution but variations of atmospheric pCO₂ cannot explain the pH change of the SCS before the Industrial Revolution. We suggest that variations of monsoon intensity during the mid-late Holocene may have driven the sea surface pH increase from the mid to late Holocene. Results of this study indicate that the impact of anthropogenic atmospheric CO₂ emissions may have reversed the natural pH trend in the SCS since the mid-Holocene. Such ocean pH records in the current interglacial period can help us better understand the physical and biological controls on ocean pH and possibly predict the long-term impact of climate change on future ocean acidification.  相似文献   

Inner-sphere complexation of cations at the rutile-water interface: A concise surface structural interpretation with the CD and MUSIC model     

Moira K. Ridley  Tjisse Hiemstra  Michael L. Machesky 《Geochimica et cosmochimica acta》2009,73(7):1841-715

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Galaxy colour, morphology and environment in the Sloan Digital Sky Survey     

N. M. Ball  J. Loveday  R. J. Brunner 《Monthly notices of the Royal Astronomical Society》2008,383(3):907-922

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Estimating Transmissivity from the Water Level Fluctuations of a Sinusoidally Forced Well   总被引：1，自引：0，他引：1  

E. Mehnert  A.J. Valocchi  M. Heidari  S.G. Kapoor  P. Kumar 《Ground water》1999,37(6):855-860

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Recharge and Groundwater Flow Within an Intracratonic Basin,Midwestern United States          下载免费PDF全文

Samuel V. Panno  Zohreh Askari  Walton R. Kelly  Thomas M. Parris  Keith C. Hackley 《Ground water》2018,56(1):32-45

The conservative nature of chloride (Cl^?) in groundwater and the abundance of geochemical data from various sources (both published and unpublished) provided a means of developing, for the first time, a representation of the hydrogeology of the Illinois Basin on a basin‐wide scale. The creation of Cl^? isocons superimposed on plan view maps of selected formations and on cross sections across the Illinois Basin yielded a conceptual model on a basin‐wide scale of recharge into, groundwater flow within and through the Illinois Basin. The maps and cross sections reveal the infiltration and movement of freshwater into the basin and dilution of brines within various geologic strata occurring at basin margins and along geologic structures. Cross‐formational movement of brines is also seen in the northern part of the basin. The maps and cross sections also show barriers to groundwater movement created by aquitards resulting in areas of apparent isolation/stagnation of concentrated brines within the basin. The distribution of Cl^? within the Illinois Basin suggests that the current chemical composition of groundwater and distribution of brines within the basin is dependent on five parameters: (1) presence of bedrock exposures along basin margins; (2) permeability of geologic strata and their distribution relative to one another; (3) presence or absence of major geologic structures; (4) intersection of major waterways with geologic structures, basin margins, and permeable bedrock exposures; and (5) isolation of brines within the basin due to aquitards, inhomogeneous permeability, and, in the case of the deepest part of the basin, brine density effects.  相似文献   

北京郊区居民日常生活方式的行为测度与空间—行为互动   总被引：7，自引：2，他引：5  

塔娜  柴彦威  关美宝 《地理学报》2015,70(8):1271-1280

郊区化及其对居民日常生活的影响成为近年来城市研究的重要议题。时空行为研究认为推动日常生活方式的郊区化是解决郊区化过程中出现的社会与空间问题的根本措施。从日常生活方式的角度出发,需要利用多维度时空行为指标刻画群体的生活方式类型以分析郊区居民的空间—行为互动机制。本文采用活动空间和出行频率指标构建个体日常生活方式的行为测度方法,并基于2012年在北京上地—清河地区进行的GPS调查数据将郊区居民划分为“空间排斥”、“本地化”、“郊区性”、“两极化”、“城市依赖”五种日常生活方式类型。研究发现不同日常生活方式群体在活动分布、活动频率和交通方式上存在差异;并通过多项logistic模型分析郊区化对于个体日常生活方式的影响,发现工作日居民的日常生活方式受到性别、收入、年龄和工作时长等社会经济属性的影响。同时郊区设施配置直接影响着居民对郊区空间的利用程度,土地混合利用、商业设施密度提高更有可能实现日常生活的郊区化。日常生活方式的行为测度方法有助于分析郊区居民日常行为的复杂性,为理解郊区化提供了独特的视角,为构建城市研究的空间—行为互动理论提供了有力的支持。  相似文献   

Advancing Groundwater Technology on the Prairie     

Gary D. Miller  Donald A. Keefer 《Ground water》2014,52(5):651-652

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A hybrid framework for improving recharge and discharge estimation for a three-dimensional groundwater flow model     

Meyer SC  Lin YF  Roadcap GS 《Ground water》2012,50(3):457-463

We employed the ArcGIS plug-in package PRO-GRADE (Lin et al. 2009), developed for zonation of recharge/discharge (R/D) for modeling two-dimensional aquifer systems, to develop alternative R/D zonations for an existing three-dimensional groundwater flow model of a complex hydrogeologic setting. Our process began by intersecting PRO-GRADE output with the existing model's 4-zone R/D representation to develop a model having 12 R/D zones (R12) and then calibrating the resulting model using PEST. We then revised the R12 zonation using supplementary GIS data to develop a 51-zone R/D zonation (R51). From R51, we developed a series of daughter models having 40, 30, 28, and 18 R/D zones by removing zones from R51 if calibration resulted in little change in the zone's starting R/D rate and/or if the model was insensitive to the zone's R/D rate. For these models (R40N, R30N, R28N, and R18N), we used the ArcGIS Nibble tool to rapidly and consistently reassign model cells within eliminated zones of R51 to the zone of the nearest model cell in a retained zone having the same starting value. R12, R51, R40N, R30N, R28N, and R18N are all more accurate than the original model (R4), although improvements relative to stream discharge targets exceeded improvements relative to head targets. The models also executed with better numerical stability and less mass balance discrepancy than R4. These improvements demonstrate that R/D estimation in a complex shallow three-dimensional steady-state model can be improved with PRO-GRADE estimates of R/D when guided by calibration statistics and supplemental geographic data.  相似文献   

Paleocurrent and fabric analyses of the imbricated fluvial gravel deposits in Huangshui Valley, the northeastern Tibetan Plateau, China   总被引：2，自引：0，他引：2  

Xiaodong Miao  Huayu Lu  Zhen Li  Guangchao Cao 《Geomorphology》2008,99(1-4):433-442

Gravel deposits on fluvial terraces contain a wealth of information about the paleofluvial system. In this study, flow direction and provenance were determined by systematic counts of more than 2000 clasts of imbricated gravel deposits in the Xining Region, northeastern Tibetan Plateau, China. These gravel deposits range in age from the modern Huangshui riverbed to Miocene-aged deposits overlain by eolian sediments. Our major objectives were not only to collect first-hand field data on the fluvial gravel sediments of the Xining Region, but also to the reconstruct the evolution of the fluvial system. These data may offer valuable information about uplift of the northeastern Tibetan Plateau during the late Cenozoic era. Reconstructed flow directions of the higher and lower gravel deposits imply that the river underwent a flow reversal of approximately 130–180°. In addition, the lithological compositions in the higher gravel deposits differ significantly from the lower terraces, suggesting that the source areas changed at the same time. Eolian stratigraphy overlying the gravel deposits and paleomagnetic age determination indicate that this change occurred sometime between 1.55 Ma and 1.2 Ma. We suggest that tectonic activity could explain the dramatic changes in flow direction and lithological composition during this time period. Therefore, this study provides a new scenario of fluvial response to tectonic uplift: a reversal of flow direction. In addition, field observation and statistical analyses reveal a strong relationship between rock type, size and roundness of clasts.  相似文献   

Influence of capillary-pressure models on CO2 solubility trapping     

《Advances in water resources》2013

The typical shape of a capillary-pressure curve is either convex (e.g., Brooks–Corey model) or S-shaped (e.g., van Genuchten model). It is not universally agreed which model reflects natural rocks better. The difference between the two models lies in the representation of the capillary entry pressure. This difference does not lead to significantly different simulation results for modeling CO₂ sequestration in aquifers without considering CO₂ dissolution. However, we observe that the van-Genuchten-type capillary-pressure model accelerates CO₂ solubility trapping significantly compared with the Brooks–Corey-type model. We also show that the simulation results are very sensitive to the slope of the van-Genuchten-type curve around the entry-pressure region. For the representative examples we study, the differences can be so large as to have complete dissolution of the CO₂ plume versus persistence of over 50% of the plume over a 5000-year period.The cause of such sensitivity to the capillary-pressure model is studied. Particularly, we focus on how the entry pressure is represented in each model. We examine the mass-transfer processes under gravity-capillary equilibrium, molecular diffusion, convective mixing, and in the presence of small-scale heterogeneities. Laboratory measurement of capillary-pressure curves and some important implementation issues of capillary-pressure models in numerical simulators are also discussed. Most CO₂ sequestration simulations in the literature employ one of the two capillary-pressure models. It is important to recognize that these two representations lead to very different predictions of long-term CO₂ sequestration.  相似文献