Drainage beneath ice sheets: groundwater–channel coupling,and the origin of esker systems from former ice sheets

The nature of the drainage system beneath ice sheets is crucial to their dynamic behaviour but remains problematic. An experimentally based theory of coupling between groundwater and major channel systems is applied to the esker systems in the area occupied the last ice sheet in Europe, which we regard as a fossil imprint of major longitudinal drainage channels. We conclude that the large-scale distribution and spacing of major eskers is consistent with the theory of groundwater control, in which esker spacing is partly controlled by the transmissivity of the bed.It is concluded that esker patterns reflect the large-scale organisation of the subglacial drainage pattern in which channel development is coupled to groundwater flow and to the ice sheet's dynamic regime. The theory is then used to deduce: basal meltwater recharge rates and their spatial variability from esker spacing in an area in which the ice sheet was actively streaming during its final retreat; patterns of palaeo-groundwater flow and head distribution; and the seasonally varying magnitude of discharge from stream tunnels at the retreating ice sheet margin. Major channel/esker systems appear to have been stable at least over several hundred of years during the retreat of the ice sheet, although major dynamic events are demonstrably associated with major shifts in the hydraulic regime.Modelling suggests: that glaciation can stimulate deep groundwater circulation cells that are spatially linked to channel locations, with groundwater flow predominantly transverse to ice flow; that the circulation pattern has the potential to create large-scale anomalies in groundwater chemistry; and that the spacing of channels will change through the glacial cycle, influencing water pressures in stream tunnels, subglacial hydraulic gradients and effective pressure. If the latter is reduced sufficiently, it could trigger enhanced bed deformation, thus coupling drainage to ice sheet movement. It suggests the possibility of distinctive phases of sediment deformation and drumlin mobilisation during a glacial cycle.     

Regional groundwater flow in an area mapped as continuous permafrost, NE Alaska (USA)

Fundamental knowledge of groundwater systems in areas of permafrost is often lacking. The likelihood of finding good quality groundwater resources of acceptable quantities generally decreases as the areal coverage of permafrost increases. In areas of continuous permafrost, the probability of finding areas of groundwater recharge and discharge are minimal. Still, in northeastern Alaska (USA), the presence of numerous springs and associated downstream aufeis formations clearly indicates that there has to be a groundwater system with the required complementary areas of groundwater recharge and transmission. Recharge zones and transmission pathways in this area of extensive permafrost, however, are essentially unknown. This study shows that the recharge occurs on the south side of the Brooks Range in northeastern Alaska, where extensive limestone outcrops are found. The transmission zone is beneath the permafrost, with discharge occurring through the springs via taliks through the permafrost (where faults are present) and also likely at the northern edge of the permafrost along the Beaufort Sea coast.     

Groundwater flow modeling of periods with periglacial and glacial climate conditions for the safety assessment of the proposed high-level nuclear waste repository site at Forsmark,Sweden

The impact of periglacial and glacial climate conditions on groundwater flow in fractured crystalline rock is studied by means of groundwater flow modeling of the Forsmark site, which was recently proposed as a repository site for the disposal of spent high-level nuclear fuel in Sweden. The employed model uses a thermal-hydraulically coupled approach for permafrost modeling and discusses changes in groundwater flow implied by the climate conditions found over northern Europe at different times during the last glacial cycle (Weichselian glaciation). It is concluded that discharge of particles released at repository depth occurs very close to the ice-sheet margin in the absence of permafrost. If permafrost is included, the greater part discharges into taliks in the periglacial area. During a glacial cycle, hydraulic gradients at repository depth reach their maximum values when the ice-sheet margin passes over the site; at this time, also, the interface between fresh and saline waters is distorted the most. The combined effect of advances and retreats during several glaciations has not been studied in the present work; however, the results indicate that hydrochemical conditions at depth in the groundwater flow model are almost restored after a single event of ice-sheet advance and retreat.     

Exchange and pathways of deep and shallow groundwater in different climate and permafrost conditions using the Forsmark site, Sweden, as an example catchment

This study simulates and quantifies the exchange and the pathways of deep and shallow groundwater flow and solute transport under different climate and permafrost conditions, considering the example field case of the coastal Forsmark catchment in Sweden. A number of simulation scenarios for different climate and permafrost condition combinations have been performed with the three-dimensional groundwater flow and transport model MIKE SHE. Results show generally decreasing vertical groundwater flow with depth, and smaller vertical flow under permafrost conditions than under unfrozen conditions. Also the overall pattern of both the vertical and the horizontal groundwater flow, and the water exchange between the deep and shallow groundwater systems, change dramatically in the presence of permafrost relative to unfrozen conditions. However, although the vertical groundwater flow decreases significantly in the presence of permafrost, there is still an exchange of water between the unfrozen groundwater system below the permafrost and the shallow groundwater in the active layer, via taliks. ‘Through taliks’ tend to prevail in areas that constitute groundwater discharge zones under unfrozen conditions, which then mostly shift to net recharge zones (through taliks with net downward flow) under permafrost conditions.     

A 40 ka record of temperature and permafrost conditions in northwestern Europe from noble gases in the Ledo‐Paniselian Aquifer (Belgium)

The Ledo‐Paniselian Aquifer in Belgium offers unique opportunities to study periglacial groundwater recharge during the Last Glacial Maximum (LGM), as it was located close to the southern boundary of the ice sheets at that time. Groundwater residence times determined by ¹⁴C and ⁴He reveal a sequence of Holocene and Pleistocene groundwaters and a gap between about 14 and 21 ka, indicating permafrost conditions which inhibited groundwater recharge. In this paper, a dataset of noble gas measurements is used to study the climatic evolution of the region. The derived recharge temperatures indicate that soil temperatures in the periods just before and after the recharge gap were only slightly above freezing, supporting the hypothesis that permafrost caused the recharge gap. The inferred glacial cooling of 9.5°C is the largest found so far by the noble gas method. Yet, compared to other palaeoclimate reconstructions for the region, recharge temperatures deduced from noble gases for the cold periods tend to be rather high. Most likely, this is due to soil temperatures being several degrees higher than air temperatures during periods with extended snow cover. Thus the noble‐gas‐derived glacial cooling of 9.5°C is only a lower limit of the maximum cooling during the LGM. Some samples younger than the recharge gap are affected by degassing, possibly related to gas production during recharge in part of the recharge area, especially during times of melting permafrost. The findings of this study, such as the occurrence of a recharge gap and degassing related to permafrost and its melting, are significant for groundwater dynamics and geochemistry in periglacial areas. Copyright © 2010 John Wiley & Sons, Ltd.     

Implications of subsurface thermal–hydraulic–mechanical processes associated with glaciation on Shield flow system evolution and performance assessment

A deep geologic repository (DGR) situated on the Canadian Shield will be subject to long-term climate change that will markedly alter surface conditions as a result of glaciation and permafrost penetration. Systematic, two-dimensional and three-dimensional coupled thermal–hydraulic–mechanical finite-element simulations with varying degrees of coupling, including depth-dependent salinity (represented as a change in groundwater density) and temperature-dependent density and viscosity, were undertaken to address the implications of glaciation on groundwater flow system dynamics as it could affect DGR performance. The modelling domain consisted of a 1.6-km deep sub-regional scale (≈100 km²) fractured Shield flow system. Initial and transient thermal, hydraulic and mechanical boundary conditions were developed from two realizations of the University of Toronto Glacial Systems Model of the last Laurentide glaciation. Results indicate that during the glacial loading/unloading cycle, for this particular conceptual model, there is limited penetration of glacial meltwaters to depth and small residual anomalous hydraulic head. During glacial coverage, the mechanical factor of safety increases in the moderately fractured and sparsely fractured rock mass, but principal effective stress reorientation also occurs. Given the assumed nonglacial in situ state of stress and mechanical properties, the fracture zones were predicted to be less stable under glacial conditions.

青藏高原多年冻土区地下水及其变化

青藏高原的高海拔多年冻土的分布格局及其动态变化、季节冻结融化作用与地下水的补给、径流和排泄关系密切,对各种尺度的水文地质环境具有控制或重要影响。作为一个隔水层或弱透水层,冻土层在地下水形成、演化、运移和水动力过程方面具有抑制作用,从而对地下水的分布、动态和水循环产生重要影响。而且,冻土可通过其中的水分迁移、冰分凝和地下冰结构重组等方式,形成和改变地下冰储量及地下水动静储量,调节水文地质循环。气候变暖显著和人类活动日益增加,冻土退化显著,已经普遍影响到了高原冻土生态水文地质环境,并引发了一系列水文（地质）、生态和环境问题,亟待系统、长期和细致的观测、试验和模型研究。     

Quantitative analysis of springs

Growing demand for groundwater resources and stringent environmental concerns has led to large groundwater investigations, including characterization of aquifer systems that are hydraulically connected to springs. A pumping test is one of the most reliable means of quantifying hydraulic characteristics and the response of natural springs to pumping because it yields results that, in general, are representative of a larger area than are results from a single point observation. Recharge to the aquifer sustaining discharge from springs must be evaluated prior to the utilization of springs. The spring hydrograph is analyzed, as the shape of a hydrograph is a reflection of the response of the aquifer to recharge. The form and rate of recession provide significant information on the storage, lithological composition, and structural characteristics of the aquifer system sustaining the spring. Water tracing techniques have been developed and used over a period of centuries to delineate catchment boundaries, estimate groundwater flow velocities, determine areas of recharge, and identify sources of pollution of spring water.     

川藏铁路格聂山和察雅段构造岩溶发育规律及岩溶地下水循环模式研究

Construction of the Sichuan-Tibet Railway may face significant geological safety risks of water inrush and mud inrush in the plateau tectonic karst region. It is of great scientific and practical significance to carry out research on the evolution regularity of the plateau tectonic karst and the relevant karst groundwater circulation mode for the early prediction and identification of the water inrush and mud inrush disaster in the railway tunnel to be built. Based on the field survey and published literatures, this paper makes an in-depth analysis and draws some conclusions. The tectonic karst development shows obvious sequence characteristics and elevation zonation. The first level to fourth level karst development areas were formed before Miocene, late Miocene to Pliocene, Pliocene and Pliocene to Pleistocene, and occur in the elevation range of 4900?5300 m, 4000?4300 m, 3700?3800 m and 2900?3200 m, respectively. Active faults obviously control the distribution and enrichment of karst groundwater. Since the late Pleistocene, active faults have connected different karst areas and formed unique storage conditions for the tectonic karst groundwater in the plateau region. Karst groundwater system can be divided into high recharge area, remote pipeline flow area and concentrated discharge area. The high recharge area occurs in the first-level karst evaluation area, and the third-level and fourth-level are the concentrated discharge area which generally contain the outcropping springs with a discharge of more than 100 L/s. The groundwater system is appropriately divided into shallow and deep groundwater flow system. Karst springs are mainly supplied by ice and snow melting water, and exhibits the dynamic characteristics of the high water pressure, long flow path and deep water groundwater circulation. High CO₂ saturation concentration of the melting water and the salt effect of sulfate promote the formation of high TDS sulfuric acid karst groundwater of low temperature.     

Noble gas and isotope geochemistry in western Canadian Arctic watersheds: tracing groundwater recharge in permafrost terrain

In Canada’s western Arctic, perennial discharge from permafrost watersheds is the surface manifestation of active groundwater flow systems with features including the occurrence of year-round open water and the formation of icings, yet understanding the mechanisms of groundwater recharge and flow in periglacial environments remains enigmatic. Stable isotopes (δ¹⁸O, δD, δ¹³C_DIC), and noble gases have proved useful to study groundwater recharge and flow of groundwater which discharges along rivers in Canada’s western Arctic. In these studies of six catchments, groundwater recharge was determined to be a mix of snowmelt and precipitation. All systems investigated show that groundwater has recharged through organic soils with elevated P_CO2, which suggests that recharge occurs largely during summer when biological activity is high. Noble gas concentrations show that the recharge temperature was between 0 and 5 °C, which when considered in the context of discharge temperatures, suggests that there is no significant imbalance of energy flux into the subsurface. Groundwater circulation times were found to be up to 31 years for non-thermal waters using the ³?H-³He method.     

Glaciotectonised Quaternary sediments at Cape Shpindler,Yugorski Peninsula,Arctic Russia: implications for glacial history,ice movements and Kara Sea Ice Sheet configuration

The coastal cliffs of Cape Shpindler, Yugorski Peninsula, Arctic Russia, occupy a key position for recording overriding ice sheets during past glaciations in the Kara Sea area, either from the Kara Sea shelf or the uplands of Yugorski Peninsula/Polar Urals. This study on Late Quaternary glacial stratigraphy and glaciotectonic structures of the Cape Shpindler coastal cliffs records two glacier advances and two ice‐free periods older than the Holocene. During interglacial conditions, a sequence of marine to fluvial sediments was deposited. This was followed by a glacial event when ice moved southwards from an ice‐divide over Novaya Zemlya and overrode and disturbed the interglacial sediments. After a second period of fluvial deposition, under interstadial or interglacial conditions, the area was again subject to glacial overriding, with the ice moving northwards from an inland ice divide. The age‐control suggests that the older glacial event could possibly belong to marine oxygen isotope stage (MOIS) 8, Drenthe (300–250 ka), and that the underlying interglacial sediments might be Holsteinian (>300 ka). One implication of this is that relict glacier ice, buried in sediments and incorporated into the permafrost, may survive several interglacial and interstadial events. The younger glacial event recognised in the Cape Shpindler sequence is interpreted to be of Early‐to‐Middle Weichselian age. It is suggested to correlate to a regional glaciation around 90 or 60 ka. The Cape Shpindler record suggests more complex glacial dynamics during that glaciation than can be explained by a concentric ice sheet located in the Kara Sea, as suggested by recent geological and model studies. Copyright © 2003 John Wiley & Sons, Ltd.     

Recharge and discharge controls on groundwater travel times and flow paths to production wells for the Ammer catchment in southwestern Germany

Travel times and flow paths of groundwater from its recharge area to drinking-water production wells will govern how the quality of pumped groundwater responds to contaminations. Here, we studied the 180 km² Ammer catchment in southwestern Germany, which is extensively used for groundwater production from a carbonate aquifer. Using a 3-D steady-state groundwater model, four alternative representations of discharge and recharge were systematically explored to understand their impact on groundwater travel times and flow paths. More specifically, two recharge maps obtained from different German hydrologic atlases and two plausible alternative discharge scenarios were tested: (1) groundwater flow across the entire streambed of the Ammer River and its main tributaries and (2) groundwater discharge via a few major springs feeding the Ammer River. For each of these scenarios, the groundwater model was first calibrated against water levels, and subsequently travel times and flow paths were calculated for production wells using particle tracking methods. These computed travel times and flow paths were indirectly evaluated using additional data from the wells including measured concentrations of major ions and environmental tracers indicating groundwater age. Different recharge scenarios resulted in a comparable fit to observed water levels, and similar estimates of hydraulic conductivities, flow paths and travel times of groundwater to production wells. Travel times calculated for all scenarios had a plausible order of magnitude which were comparable to apparent groundwater ages modelled using environmental tracers. Scenario with groundwater discharge across the entire streambed of the Ammer River and its tributaries resulted in a better fit to water levels than scenario with discharge at a few springs only. In spite of the poorer fit to water levels, flow paths of groundwater from the latter scenario were more plausible, and these were supported by the observed major ion chemistry at the production wells. We concluded that data commonly used in groundwater modelling such as water levels and apparent groundwater ages may be insufficient to reliably delineate capture zones of wells. Hydrogeochemical information relating only indirectly to groundwater flow such as the major ion chemistry of water sampled at the wells can substantially improve our understanding of the source areas of recharge for production wells.     

Reassessment of mid-Carboniferous glacial extent in southwestern Gondwana (Rio Blanco Basin,Argentina) inferred from paleo-mass transport of diamictites

Late Paleozoic glacial diamictites occur in many localities in western Argentina, indicating that the region was strongly affected by glaciation during the mid-Carboniferous (late Serpukhovian–early Bashkirian). In most instances these diamictites are found in steeply walled paleovalley settings in the Andean Precordillera. This study presents new data from a locality north of the Precordillera that suggests an additional, distinct, volume of ice existed in the region during the Carboniferous. The glacigenic diamictites in the Rio Blanco Basin were ultimately emplaced as gravity flows, precluding inferences of paleo-ice volume. Fold nose orientation and soft-sediment groove orientations within the diamictites indicate that the deposits were emplaced from north to south, suggesting that glacial ice was most likely not sourced from the proto-Precordillera at this locality, requiring the need for another ice center to the north of the basin. Diamictite facies indicates that the sediment was initially supplied to the study area by a warm-based glacier.     

Aquifer response to regional climate variability in a part of Kashmir Himalaya in India

Forty major perennial springs, under different lithological controls, in a part of Kashmir Himalaya in India were studied to understand the response of spring discharges to regional climate variability. The average monthly spring discharge is high in Triassic Limestone-controlled springs (karst springs) and low in alluvium- and Karewa-controlled springs. In general, the measured monthly spring discharges show an inverse relation with the monthly precipitation data. However, a direct correlation exists between the spring discharges and the degree of snow/ice melt. The results suggest that the creation of a low and continuous (but stable) recharge from the Triassic Limestone and Panjal Trap aquifers, due to blockage of groundwater flow between strata with contrasting hydraulic conductivity, attenuates the discharge and gives rise to small fluctuations in the alluvium- and Karewa-controlled springs. The average monthly discharge of the karst and alluvial springs showed an overall decreasing trend for two and a half decades, with the lowest discharge recorded in 2001. The study revealed that the regional/global warming and below-normal precipitation in the period of snow accumulation (PSA) has triggered the receding of glaciers and attenuation of spring discharges.     

Groundwater flow systems in turbidites of the Northern Apennines (Italy): natural discharge and high speed railway tunnel drainage

Turbidites crop out extensively in the Northern Apennine mountains (Italy). The huge amounts of groundwater drained by tunnels, built for the high speed railway connection between Bologna and Florence, demonstrate the aquifer-like behaviour of these units, up to now considered as aquitards. A conceptual model of groundwater flow systems (GFS) in fractured aquifers of turbidites is proposed, taking into account both system natural state and the perturbation induced by tunnel drainage. Analysis of hydrological data (springs, streams and tunnel discharge), collected over 10 years, was integrated with analysis of hydrochemical and isotopic data and a stream-tunnel tracer test. Hydrologic recession analysis of undisturbed conditions is a key tool in studying turbiditic aquifer hydrogeology, permitting the discrimination of GFS, the estimation of recharge relative to the upstream reach portion and the identification of springs most vulnerable to tunnel drainage impacts. The groundwater budgeting analysis provides evidence that the natural aquifer discharge was stream-focused through GFS, developed downslope or connected to main extensional tectonic lineaments intersecting stream beds; now tunnels drain mainly active recharge groundwater and so cause a relevant stream baseflow deplenishment (approximately two-thirds of the natural value), possibly resulting in adverse effects on local ecosystems.     

示踪试验在岩溶大泉修复中的应用——以丽江黑龙潭为例

为查明云南丽江黑龙潭泉域九子海洼地补给区地下水与周边泉水的连通关系,提供泉水修复的科学依据,采用人工化学示踪方法,选取碘化钾作为示踪剂,开展了一次大型地下水示踪试验。根据试验数据计算地下水渗流速度,并分析黑龙潭泉域地下水系统结构特征。结果表明:九子海洼地补给区地下水与黑龙潭泉群和古城泉群具有显著的连通关系,与清溪泉群和白浪花泉群不存在连通关系,九子海至黑龙潭和古城的地下水渗流速度分别为405.86~1 077.84 m·d-1、349.96~629.09 m·d-1。九子海洼地为黑龙潭泉域地下水系统的主要补给区,同时也可作为黑龙潭泉水修复的有效注水点,接受补给后,主要通过深层岩溶管道向南运移至黑龙潭—古城方向,其中黑龙潭泉群为系统的排泄天窗。      

The maximum ice extent on island groups in the Scotia sea,Antarctica

Evidence is presented for a more extensive ice cover over South Georgia, the South Orkney Islands, the South Shetland Islands, and the tip of the Antarctic Peninsula. Ice extended across the adjacent submarine shelves to a depth of 200 m below present sea level. Troughs cut into the submarine shelves by ice streams or outlet glaciers and ice-scoured features on the shelf areas suggest that the ice caps were warm-based. The South Shetland Islands appear not to have been overrun by continental ice. Geomorphological evidence in two island groups suggests that the maximum ice cover, which was responsible for the bulk of glacial erosion, predates at least one full glaciation. Subsequently there was a marine interval and then a glaciation which overran all of the lowlying peninsulas. The Falkland Islands, only 2° of latitude north of South Georgia, were never covered by an ice cap and supported only a few slightly enlarged cirque glaciers. This suggests that the major oceanographic and atmospheric boundary represented by the Antarctic Convergence, which is presently situated between the Falkland Islands and South Georgia, has remained in a similar position throughout the glacial age. Its position is probably bathymetrically controlled.     

Insights into palaeorecharge conditions for European deep aquifers

Climatic instability during the late Pleistocene has been reflected in the pattern of groundwater recharge. This report summarizes palaeoclimate knowledge during the late Weichselian in Europe. During this period the majority of northern Europe was covered by thick ice sheets and permafrost, preventing aquifers from recharging. In contrast, southern Europe was generally free of these palaeoclimatic features. Palaeoclimatic information has been combined with isotope data to better understand the palaeorecharge conditions and recharge timing across the European continent. The ¹⁸O and ²H relationship shows latitudinal plus climatic influences. Radiocarbon data show that while southern European aquifers have generally been recharged continuously during the last 40,000 years, northern European aquifers typically show a recharge gap during the Last Glacial Maximum. Areas that underwent continuous recharge during the entire late Pleistocene period can also be distinguished from areas where recharge to aquifers was prevented during the Last Glacial Maximum. Finally, several examples are presented of melt-water recharge or subglacial recharge. The identification of such diversity in the groundwater palaeorecharge in Europe is of great importance for modellers developing management schemes for groundwater resources.     

Hirnantian glacial and deglacial record in SW Djado Basin (NE Niger).

Pluridisciplinary fieldwork highlights features generated by an extended ice-sheet in the Djado Basin during the Hirnantian. Two glacial palaeovalley systems associated with glacial pavements and separated by thin glaciomarine interstadial series are revealed. Rigid glacial pavements characterised by abrasion erosion are differentiated from soft glacial pavements characterised by soft-bed deformation. Glacial pavements are associated with subglacial bedforms such as megaflutes, flutes and meltwater channels. They are also associated with clastic dykes and glaciotectonic structures such as deformed flutes, subglacial folds and duplex structures. This record demonstrates that ice was warm-based and flowed rapidly on the highfluid- pressure soft substrate, as for ice streams. The erosional glacial landscape is typical of areal scouring, and the depositional sediment-landform assemblage corresponds to subglacial processes. These data afford a reconstruction of glacial events which is consistent with the two polyphased low-frequency glacial cycles inferred in previous studies. During interstadial and postglacial stages, grabens, normal faults, radial extensional microfaults and extensional dihedrons were generated by extensional tectonics during glacio-isostatic rebound. In sectors highly affected by this tectonics, doleritic dykes reflect a basal crust fusion increase induced by adiabatic decompression.     

Subglacial bed conditions during Late Pleistocene glaciations and their impact on ice dynamics in the southern North Sea

Passchier, S., Laban, C., Mesdag, C.S. & Rijsdijk, K.F. 2010: Subglacial bed conditions during Late Pleistocene glaciations and their impact on ice dynamics in the southern North Sea. Boreas, Vol. 39, pp. 633–647. 10.1111/j.1502‐3885.2009.00138.x. ISSN 0300‐9483. Changes in subglacial bed conditions through multiple glaciations and their effect on ice dynamics are addressed through an analysis of glacigenic sequences in the Upper Pleistocene stratigraphy of the southern North Sea basin. During Elsterian (MIS 12) ice growth, till deposition was subdued when ice became stagnant over a permeable substrate of fluvial sediments, and meltwater infiltrated into the bed. Headward erosion during glacial retreat produced a dense network of glacial valleys up to several hundreds of metres deep. A Saalian (MIS 6) glacial advance phase resulted in the deposition of a sheet of stiff sandy tills and terminal moraines. Meltwater was at least partially evacuated through the till layer, resulting in the development of a rigid bed. During the later part of the Saalian glaciation, ice‐stream inception can be related to the development of a glacial lake to the north and west of the study area. The presence of meltwater channels incised into the floors of glacial troughs is indicative of high subglacial water pressures, which may have played a role in the onset of ice streaming. We speculate that streaming ice flow in the later part of the Saalian glaciation caused the relatively early deglaciation, as recorded in the Amsterdam Terminal borehole. These results suggest that changing subglacial bed conditions through glacial cycles could have a strong impact on ice dynamics and require consideration in ice‐sheet reconstructions.