The application of COSI‐Corr to determine dune system dynamics in the southern Namib Desert using ASTER data     

Stephen P. Scheidt  Nick Lancaster 《地球表面变化过程与地形》2013,38(9):1004-1019

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Can in situ geochemical measurements be more fit-for-purpose than those made ex situ?     

Michael H. Ramsey  Katy A. Boon 《Applied Geochemistry》2012

It is argued that the selection of the most appropriate geochemical measurement technique should be based upon the fitness of its measurement results for any specified purpose, regardless of whether the measurement are made in situ or ex situ. Using this approach, in situ measurements made in the field are shown to have some definite advantages over those made ex situ in a laboratory. A case study is used to show that there are cases where in situ measurements can be more fit-for-purpose than their ex situ equivalents. This is primarily because the uncertainty of both types of measurement is usually limited by the uncertainty arising from the field sampling process. That uncertainty is mainly caused by small-scale heterogeneity (in space or time) in the analyte concentration within the environmental material (e.g. soil, water or air).  相似文献   

A method for activity calculations in saline and mixed solvent solutions at elevated temperature and pressure: A framework for geological phase equilibria calculations     

Katy Evans  Roger Powell 《Geochimica et cosmochimica acta》2006,70(22):5488-5506

Quantitative thermodynamic calculations that involve aqueous fluids have proved difficult because of the complexity of the interactions that occur within the fluids. Existing thermodynamic models are difficult to apply to mixed solvent or highly saline solutions at P > 0.3 GPa and T > 300 °C. This work constructs a method for activity-composition calculations in saline, mixed solvent, supercritical aqueous solutions. Mixing is formulated on a mole-fraction scale in terms of a set of independent end-members that describe composition and speciation within the solution. The ideal mixing term takes speciation into account and avoids problems with the common ion effect. Non-ideal interactions are represented by an activity coefficient term that combines a limited form of Debye-Hückel and a van Laar formulation. This approach, referred to as the DH-ASF model, is thermodynamically valid over a wide range of P, T and fluid composition. The value of the model lies in its broad applicability, and small number of calibration parameters. Experimental data from the literature for the systems NaCl-H₂O, KCl-H₂O, H₂O-SiO₂-CO₂, H₂O-NaCl-CO₂, H₂O-NaCl-SiO₂ and for H₂O-albite melts have been used to calibrate the DH-ASF model. Calculations were performed using Thermocalc, computer software that calculates equilibria for mineral-based chemical systems.¹ The model represents the data to within experimental error in most cases. Conditions modelled include pressures between 0.2 and 1.4 GPa, temperatures between 500 and 900 °C, and x_H2O from 0.1 to 1. Calibrated parameters are consistent with expectations based on the conceptual model for the fluid, and are relatively insensitive to changes in pressure and temperature for most examples. The DH-ASF model is thermodynamically valid for a range of P-T conditions that includes pressures from 0.1 to 2 GPa and temperatures from 200 to 1000 °C. A lack of experimental data restricts calibration of the model for many end-members. However, it may be possible to neglect parameters associated with end-members present in small amount. In this case, or with new experimental data for calibrations, the DH-ASF model allows previously inaccessible geological systems and processes to be modelled.  相似文献   

Improving fluorometry as a source tracking method to detect human fecal contamination     

Peter G. Hartel  Jennifer L. McDonald  Lisa C. Gentit  Sarah N. J. Hemmings  Karen Rodgers  Katy A. Smith  Carolyn N. Belcher  Robin L. Kuntz  Yaritza Rivera-Torres  Ernesto Otero  Eduardo C. Schröder 《Estuaries and Coasts》2007,30(3):551-561

In a continuing effort to develop inexpensive source tracking methods to detect human fecal contamination in environmental waters, targeted sampling was combined with fluorometry. Targeted sampling works by identifying hot spots of fecal contamination through multiple samplings over ever-decreasing distances. Fluorometry identifies human fecal contamination by detecting optical brighteners, primarily from laundry detergents. Because organic matter fluoresces and interferes with fluorometry, two locations were chosen for sampling: waters relatively low in organic matter at Mayagüez Bay, Puerto Rico, and waters relatively high in organic matter at St. Simons Island, Georgia. In Puerto Rico, targeted sampling and fluorometry quickly and easily identified two hot spots of human fecal contamination in the Yagüez River, which flows through the city of Mayagüez. Another source tracking method, detection of theesp gene, confirmed their human origin. On St. Simous Island, targeted sampling and fiuorometry identified two hot spots of potential human fecal contamination. Detection of theesp gene confirmed the human origin of one site but not the other, most likely because background organic matter fluorescence interfered with fhiorometry. A separate experiment showed that adding a 436-um emission filter to the fluorometer reduced this background fluorescence by > 50%. With the 436-nm Filter in place, another sampling was conducted on St. Simons Island, and the second hot spot was identified as fecal contamination from birds. As long as the fluorometer was equipped with a 436-nm filter and organic matter concentrations were considered, targeted sampling combined with fluorometry was a relatively inexpensive method for identifying human fecal contamination in water.  相似文献   

Response of eolian geomorphic systems to minor climate change: examples from the southern Californian deserts   总被引：2，自引：0，他引：2  

Nicholas Lancaster   《Geomorphology》1997,19(3-4)

Eolian processes and landforms are sensitive to changes in atmospheric parameters and surface conditions that affect sediment supply and mobility. The response of eolian geomorphic systems to minor climate change can be examined through process-response models based on a combination of relations between short-term changes in climatic variables and eolian activity and the geologic and geomorphic record of Holocene eolian activity.At both time scales, eolian activity in southern Californian deserts is strongly controlled by variations in precipitation. Wind energy is not a limiting factor in this region. Formation of eolian deposits is a product of climatic changes that increase sediment supply from fluvial and lacustrine sources and may, therefore, be closely tied to periods of channel cutting and geomorphic instability. During intervening periods, eolian deposits migrate away from sediment source areas and are reworked, modified, and degraded. Remobilization of existing dormant dunes is a product of reduced vegetation cover and soil moisture in periods of drier climates. The major control on these processes is decadal to annual changes in rainfall that determine vegetation cover and soil moisture content.  相似文献   

Sedimentology and paleohydrology of Late Quaternary lake deposits in the northern Namib Sand Sea, Namibia     

James T. Teller  Nat Rutter  N. Lancaster 《Quaternary Science Reviews》1990,9(4)

The Namib Sand Sea is the largest active desert dunefield in southern Africa, and is comprised mainly of large north-south linear dunes. In the interdune areas of the northern Sand Sea eleven small areas of calcareous lacustrine sediment have been studied. These beds are typically less than a metre thick and are dominantly comprised of calcareous sandstones to mudstones and sandy limestones. The carbonates are mainly magnesian calcites (1–14% MgCO₃) with some protodolomite and aragonite. Calcified reed casts and fresh to brackish water gastropods, diatoms, and ostracods are present in some beds. δ¹⁸O values indicate a hot and dry climate. A number of enriched δ¹³C values may reflect high salinity, low organic populations, or carbonate recrystallization.These carbonate-rich lacustrine deposits are indicative of increased periods of moisture availability in this normally hyperarid region during the Late Quaternary. The origin of the water responsible for depositing these sediments may be: (1) ponding at the end point of the Tsondab River, which at one time extended farther west into the Sand Sea; (2) flooding into interdune corridors when water levels rose in rivers such as the Kuiseb; (3) groundwater seepage into depressions either through dunes that border rivers or from the underlying Tsondab Sandstone; and (4) increased rainfall. We do not believe that there is evidence to support a major increase in precipitation over the region. However, even a small increase in precipitation in the headwaters of valleys that drain toward the Sand Sea might: (1) generate enough additional runoff to extend the terminal point of rivers such as the Tsondab farther into the dunes; (2) cause lateral flooding from major valleys into interdune corridors; and (3) recharge aquifers. The sedimentary records at Narabeb, Ancient Tracks, and West Pan, which lie along the old course of the Tsondab River, favor a ponded river origin for them, whereas groundwater seepage is favored at other sites. The chronology of deposition, based on radiocarbon dates, suggests that ponding and recharge occurred earlier in the lower, western part of the area, and later in the east. This is in harmony with the view that the end point of the Tsondab River progressively retreated eastward between about 30 and 14 ka BP, as dunes blocked its route.  相似文献   

The kalahari environment,by David S. G. Thomas and Paul A. Shaw,Cambridge University Press,Cambridge, 1991. Number of pages: 284. Price $55 ($95.00) (hardback). ISBN 0-521-37080-9     

Nick Lancaster 《地球表面变化过程与地形》1992,17(5):539-539

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Aeolian sand and sand dunes,by Kenneth Pye and Haim Tsoar,Unwin Hyman,London, 1990. Number of pages: 396. Price: £70.00. ISBN 004 551125X HB     

Nick Lancaster 《地球表面变化过程与地形》1992,17(5):541-542

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南极Lambert, Mellor和Fisher冰川的物质平衡及Amery冰架底部物质通量的估算     

温家洪  Kenneth C.Jezek  Beata M.Csathó  Ute C.Herzfeld  Katy L.Farness 《中国科学D辑》2007,37(9):1192-1204

利用现场观测与遥感数据对Lambert, Mellor和Fisher冰川的物质平衡及其在Amery冰架的底部融化与冻结状况进行了估算. 结果表明, 澳大利亚组织的Lambert冰川盆地(LGB)考察路线的上游地区, Lambert与Mellor冰川分别为(3.9±2.1)和(2.1±2.4) Gt·a^-1的正平衡, 而Fisher冰川基本处于平衡状态. 上游地区总的正平衡为(5.9±4.9) Gt·a^-1. 考察路线以下, 3条冰川均处于负平衡, 总的负平衡为(-8.5±5.8) Gt·a^-1. 整个Lambert, Mellor和Fisher冰川均接近于平衡状态. 3条冰川总净平衡为(-2.6±6.5) Gt·a^-1. 前人认为GL线(1970年代初澳大利亚在LGB建立的冰川运动观测点的连线)以上的内陆盆地处于显著正平衡, 可能是因为过高地估算了总积累量, 并低估了穿过GL线的冰通量. 靠近Amery冰架南端着地线, 冰架底部的平均融化速率为(-23.0±3.5) m冰·a^-1, 向下游方向快速减小, 并在距冰架最南端约300 km处过渡为底部冻结. 沿3条冰川在Amery冰架的冰流带(flowband), 冻结速率约介于(0.5±0.1)~(1.5±0.2) m 冰·a^-1. 由于冰流带底部的融化, 流入冰架的内陆冰损失了大约80%±5%. 3条冰流带底部总融化和总冻结分别为(50.3±7.5)和(7.0±1.1) Gt 冰·a^-1, 这要比前人通过模拟和海洋观测估算的整个Amery冰架底部总融化和总冻结还要大很多.  相似文献   

Relations between aerodynamic and surface roughness in a hyper‐arid cold desert: McMurdo Dry Valleys,Antarctica     

Nicholas Lancaster 《地球表面变化过程与地形》2004,29(7):853-867

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