Estimating surface sublimation losses from snowpacks in a mountain catchment using eddy covariance and turbulent transfer calculations

Sublimation is a critical component of the snow cover mass balance. Although sublimation can be directly measured using eddy covariance (EC), such measurements are relatively uncommon in complex mountainous environments. The EC measurements of surface snowpack sublimation from three consecutive winter seasons (2004, 2005 and 2006) at a wind‐exposed and wind‐sheltered site were analysed to characterise sublimation in mountainous terrain. During the 2006 snow season, snow surface and near‐surface air temperature, humidity and wind were also measured, permitting the calculation of sublimation rates and a comparison with EC measurements. This comparison showed that measured and simulated sublimation was very similar at the exposed site but less so at the sheltered site. Wind speeds at the exposed site were nearly four times than that at the sheltered site, and the exposed site yielded measured sublimation that was two times the magnitude of that at the sheltered site. The time variation of measured sublimation showed diurnal increases in the early afternoon and increased rates overall as the snow season progressed. Measured mean daily sublimation rates were 0.39 and 0.15 mm day^?1 at the exposed and sheltered sites, respectively. At the exposed site, measured sublimation accounted for 16% and 41% of the maximum snow accumulation in 2006 and 2005, respectively. At the sheltered site, measured seasonal sublimation was approximately 4% in 2004 and 2006 and 8% in 2005 of the maximum snow water equivalent. Simulated sublimation was only available for 2006 and suggested smaller but comparable percentages to the sublimation estimated from observations. At the exposed site, a total of 42 mm sublimated for the snow season, which constituted 12% of the maximum accumulation. At the sheltered site, 17 mm (2.2% of maximum accumulation) was sublimated over the snow season. Copyright © 2011 John Wiley & Sons, Ltd.     

Organic matter from the Callovian (Middle Jurassic) deposits of Lithuania: Compositions,sources and depositional environments

This study presents the first organic geochemical and petrographical investigation of the Callovian deposits of the eastern part of the Central European Basin. It is shown that in both the terrigenous Papil? Formation (Lower Callovian) and shallow- to deeper-marine facies of the Papartin? and Skinija formations (Middle and Upper Callovian, respectively), terrestrial organic matter predominates. This is reflected by the carbon preference index values higher than 1.2 for all samples and in some cases higher than 2, as well as the occurrence of characteristic higher plant biomarkers like cadalene, dehydroabietane, simonellite and retene. Moreover, in the case of the Papil? Formation, sugiol – a natural product terpenoid produced by distinct conifer families, has been detected in clay sediments. The occurrence of such a biomolecule in the Middle Jurassic clays is reported for the first time. Its occurrence is probably connected with the presence of small wood debris in the clay sediments. In samples of the Papil? Formation, charcoal fragments co-occurring with unsubstituted polycyclic aromatic hydrocarbons were detected, indicating that wildfires took place during the Early Callovian of Lithuania and/or neighbouring areas. In the Middle and Upper marine Callovian sediments of Lithuania there is no evidence of anoxic conditions occurring in the water column. However, periodic anoxic or strongly dysoxic episodes may have occurred, most probably below the photic zone, during the deepest phase of the Late Callovian transgression, as is evidenced from pyrite framboid diameter distribution and general impoverishment of benthic fauna. Huminite reflectance (R_r) values for the investigated area are in the range of 0.21–0.31%, suggesting the occurrence of immature organic matter. Such values indicate that these investigated deposits were close to the surface during their whole diagenetic history, and the thickness of younger cover did not exceed ca. 500 m. This is also supported by a biomarker analysis in which less thermally stable ββ-hopanes and hopenes significantly dominated.     

Effect of injected CO2 on geochemical alteration of the Altmark gas reservoir in Germany

Capturing CO₂ from point sources and storing it in geologic formations is a potential option for allaying the CO₂ level in the atmosphere. In order to evaluate the effect of geological storage of CO₂ on rock-water interaction, batch experiments were performed on sandstone samples taken from the Altmark reservoir, Germany, under in situ conditions of 125 °C and 50 bar CO₂ partial pressure. Two sets of experiments were performed on pulverized sample material placed inside a closed batch reactor in (a) CO₂ saturated and (b) CO₂ free environment for 5, 9 and 14 days. A 3M NaCl brine was used in both cases to mimic the reservoir formation water. For the “CO₂ free” environment, Ar was used as a pressure medium. The sandstone was mainly composed of quartz, feldspars, anhydrite, calcite, illite and chlorite minerals. Chemical analyses of the liquid phase suggested dissolution of both calcite and anhydrite in both cases. However, dissolution of calcite was more pronounced in the presence of CO₂. In addition, the presence of CO₂ enhanced dissolution of feldspar minerals. Solid phase analysis by X-ray diffraction and Mössbauer spectroscopy did not show any secondary mineral precipitation. Moreover, Mössbauer analysis did not show any evidence of significant changes in redox conditions. Calculations of total dissolved solids’ concentrations indicated that the extent of mineral dissolution was enhanced by a factor of approximately 1.5 during the injection of CO₂, which might improve the injectivity and storage capacity of the targeted reservoir. The experimental data provide a basis for numerical simulations to evaluate the effect of injected CO₂ on long-term geochemical alteration at reservoir scale.     

Role of temporal resolution of meteorological inputs for process‐based snow modelling

Accurate snow accumulation and melt simulations are crucial for understanding and predicting hydrological dynamics in mountainous settings. As snow models require temporally varying meteorological inputs, time resolution of these inputs is likely to play an important role on the model accuracy. Because meteorological data at a fine temporal resolution (~1 hr) are generally not available in many snow‐dominated settings, it is important to evaluate the role of meteorological inputs temporal resolution on the performance of process‐based snow models. The objective of this work is to assess the loss in model accuracy with temporal resolution of meteorological inputs, for a range of climatic conditions and topographic elevations. To this end, a process‐based snow model was run using 1‐, 3‐, and 6‐hourly inputs for wet, average, and dry years over Boise River Basin (6,963 km²), which spans rain dominated (≤1,400 m), rain–snow transition (>1,400 and ≤1,900 m), snow dominated below tree line (>1,900 and ≤2,400 m), and above tree line (>2,400 m) elevations. The results show that sensitivity of the model accuracy to the inputs time step generally decreases with increasing elevation from rain dominated to snow dominated above tree line. Using longer than hourly inputs causes substantial underestimation of snow cover area (SCA) and snow water equivalent (SWE) in rain‐dominated and rain–snow transition elevations, due to the precipitation phase mischaracterization. In snow‐dominated elevations, the melt rate is underestimated due to errors in estimation of net snow cover energy input. In addition, the errors in SCA and SWE estimates generally decrease toward years with low snow mass, that is, dry years. The results indicate significant increases in errors in estimates of SCA and SWE as the temporal resolution of meteorological inputs becomes coarser than an hour. However, use of 3‐hourly inputs can provide accurate estimates at snow‐dominated elevations. The study underscores the need to record meteorological variables at an hourly time step for accurate process‐based snow modelling.     

Linking hydrological variations at local scales to regional climate teleconnection patterns

Climate patterns over preceding years affect seasonal water and moisture conditions. The linkage between regional climate and local hydrology is challenging due to scale differences, both spatially and temporally. In this study, variance, correlation, and singular spectrum analyses were conducted to identify multiple hydroclimatic phases during which climate teleconnection patterns were related to hydrology of a small headwater basin in Idaho, USA. Combined field observations and simulations from a physically based hydrological model were used for this purpose. Results showed statistically significant relations between climate teleconnection patterns and hydrological fluxes in the basin, and climate indices explained up to 58% of hydrological variations. Antarctic Oscillation (AAO), North Atlantic Oscillation (NAO), and Pacific North America (PNA) patterns affected mountain hydrology, in that order, by decreasing annual runoff and rain on snow (ROS) runoff by 43% and 26% during a positive phase of NAO and 25% and 9% during a positive phase of PNA. AAO showed a significant association with the rainfall-to-precipitation ratio and explained 49% of its interannual variation. The runoff response was affected by the phase of climate variability indices and the legacy of past atmospheric conditions. Specifically, a switch in the phase of the teleconnection patterns of NAO and PNA caused a transition from wet to dry conditions in the basin. Positive AAO showed no relation with peak snow water equivalent and ROS runoff in the same year, but AAO in the preceding year explained 24 and 25% (p < 0.05) of their variations, suggesting that the past atmospheric patterns are equally important as the present conditions in affecting local hydrology. Areas sheltered from the wind and acted as a source for snow transport showed the lowest (40% below normal) ROS runoff generation, which was associated with positive NAO that explained 33% (p < 0.01) of its variation. The findings of this research highlighted the importance of hydroclimatic phases and multiple year variations that must be considered in hydrological forecasts, climate projections, and water resources planning.     

Interpreting geology at Portreath, Cornwall: a resource for geological education

The geology of Portreath preserved both in the natural outcrop and as building stones is assessed as a potential resource for visiting educational groups. Portreath is a former mining port, its expansion and historical development being closely associated with local and regional geology. A fieldwork programme and complementary literature search revealed that this location contains a wide range of accessible rock types suitable for student analysis.     

Optimal use of high‐resolution topographic data in flood inundation models

In this paper we explore the optimum assimilation of high‐resolution data into numerical models using the example of topographic data provision for flood inundation simulation. First, we explore problems with current assimilation methods in which numerical grids are generated independent of topography. These include possible loss of significant length scales of topographic information, poor representation of the original surface and data redundancy. These are resolved through the development of a processing chain consisting of: (i) assessment of significant length scales of variation in the input data sets; (ii) determination of significant points within the data set; (iii) translation of these into a conforming model discretization that preserves solution quality for a given numerical solver; and (iv) incorporation of otherwise redundant sub‐grid data into the model in a computationally efficient manner. This processing chain is used to develop an optimal finite element discretization for a 12 km reach of the River Stour in Dorset, UK, for which a high‐resolution topographic data set derived from airborne laser altimetry (LiDAR) was available. For this reach, three simulations of a 1 in 4 year flood event were conducted: a control simulation with a mesh developed independent of topography, a simulation with a topographically optimum mesh, and a further simulation with the topographically optimum mesh incorporating the sub‐grid topographic data within a correction algorithm for dynamic wetting and drying in fixed grid models. The topographically optimum model is shown to represent better the ‘raw’ topographic data set and that differences between this surface and the control are hydraulically significant. Incorporation of sub‐grid topographic data has a less marked impact than getting the explicit hydraulic calculation correct, but still leads to important differences in model behaviour. The paper highlights the need for better validation data capable of discriminating between these competing approaches and begins to indicate what the characteristics of such a data set should be. More generally, the techniques developed here should prove useful for any data set where the resolution exceeds that of the model in which it is to be used. Copyright © 2002 John Wiley & Sons, Ltd.     

Thermo-mechanical facies representative of fast and slow flowing ice sheets: the Weichselian ice sheet,a central west Poland case study

This study deals with an issue of thermo-mechanical facies, reflecting specific thermal and mechanical properties of the subglacial environment. The main objective of this study was to develop a model of glacitectionic deformation and its sedimentary record beneath fast and slow flowing ice sheets, based on investigations conducted in Wielkopolska (west central Poland). Sedimentary structures, mainly at the contact between subglacial tills and glacifluvial sediments, were recognized to delineate typical facies associations in a Weichselian glacigenic succession. Each association was interpreted as a record of the different depositional environments related to different subglacial conditions. Those investigations suggest the substratum was composed of frozen and dry, and wet and mobile spots, and four thermo-mechanical facies were distinguished: A – is representative of slower ice flow, dry and cold subglacial conditions, where driving stresses and normal effective pressure were high; B – is also related to slow ice flow and occurrence of cold subglacial permafrost, but with little amount of unfrozen water (however, higher than in facies A), with similar physical characteristics of the ice sheet as facies A; thermo-mechanical facies C and D represent wet and warm ice sole, with low normal effective pressure and driving stresses, thus lowering sediments’ shear strength and enabling high ice-flow velocities. We suggest that these facies have specific and non-random location, thereby revealing the relationship between subglacial thermo-mechanical conditions and ice sheet dynamics. Slow moving, cold-based ice occurred along ice sheet margins and inter-stream areas, whereas fast-moving, warm-based, well-lubricated ice, was typical of the axial parts of ice streams.