HYDROCHEMISTRY AS AN INDICATOR OF SUBGLACIAL DRAINAGE SYSTEM STRUCTURE: A COMPARISON OF ALPINE AND SUB-POLAR ENVIRONMENTS

The anion compositions (SO²₄, HCO⁻₃ and Cl⁻) of runoff from the Haut Glacier d'Arolla, Switzerland and Austre Brøggerbreen, Svalbard are compared to assess whether or not variations in water chemistry with discharge are consistent with current understanding of the subglacial drainage structure of warm- and polythermal-based glaciers. These glacial catchments have very different bedrocks and the subglacial drainage structures are also believed to be different, yet the range of anion concentrations show considerable overlap for SO²⁻₄ and HCO⁻₃. Concentrations of Cl⁻ are higher at Austre Brøggerbreen because of the maritime location of the glacier. Correcting SO²⁻₄ for the snowpack component reveals that the variation in non-snowpack SO²⁻₄ with discharge and with HCO⁻₃ is similar to that observed at the Haut Glacier d'Arolla. Hence, if we assume that the provenance of the non-snowpack SO²⁻₄ is the same in both glacial drainage systems, a distributed drainage system also contributes to runoff at Austre Brøggerbreen. We have no independent means of testing the assumption at present. The lower concentrations of non-snowpack SO²⁻₄ at Austre Brøggerbreen may suggest that a smaller proportion of runoff originates from a distributed drainage system than at the Haut Glacier d'Arolla.     

Evidence for seasonal subglacial outburst events at a polythermal glacier,Finsterwalderbreen, Svalbard

Bulk runoff and meteorological data suggest the occurrence of two meltwater outburst events at Finsterwalderbreen, Svalbard, during the 1995 and 1999 melt seasons. Increased bulk meltwater concentrations of Cl^? during the outbursts indicate the release of snowmelt from storage. Bulk meltwater hydrochemical data and suspended sediment concentrations suggest that this snowmelt accessed a chemical weathering environment characterized by high rock:water ratios and long rock–water contact times. This is consistent with a subglacial origin. The trigger for both the 1995 and 1999 outbursts is believed to be high rates of surface meltwater production and the oversupply of meltwater to areas of the glacier bed that were at the pressure melting point, but which were unconnected to the main subglacial drainage network. An increase in subglacial water pressure to above the overburden pressure lead to the forcing of a hydrological connection between the expanding subglacial reservoir and the ice‐marginal channelized system. The purging of ice blocks from the glacier during the outbursts may indicate the breach of an ice dam during connection. Although subglacial meltwater issued continually from the glacier terminus via a subglacial upwelling during both melt seasons, field observations showed outburst meltwaters were released solely via an ice‐marginal channel. It is possible that outburst events are a seasonal phenomenon at this glacier and reflect the periodic drainage of meltwaters from the same subglacial reservoir from year to year. However, the location of this reservoir is uncertain. A 100 m high bedrock ridge traverses the glacier 6·5 km from its terminus. The overdeepened area up‐glacier from this is the most probable site for subglacial meltwater accumulation. Copyright © 2001 John Wiley & Sons, Ltd.     

High resolution mapping of supra‐glacial drainage pathways reveals link between micro‐channel drainage density,surface roughness and surface reflectance

This paper reports on the use of a small unmanned aerial vehicle (sUAV) carrying a standard compact camera, to construct a high resolution orthomosaic (OM) and digital elevation model (DEM) over the lower reaches of the glacier Midtre Lovénbreen, Svalbard. Structure from Motion (SfM) techniques were used to build the OM and DEM, and together these reveal insights into the nature of supra‐glacial drainage. Major meandering supra‐glacial drainage pathways show clear dynamism, via meander cutoffs and abandoned channels. In addition, the imagery reveals a very extensive network of smaller channels that may well carry substantial amounts of water. This network of channels is in part controlled by the structure of the glacier, but in turn, these channels have a significant impact on the ice surface. Roughness of the ice surface is higher where channels are most extensive. In addition, we find a relationship between channel density and surface reflectance, such that greater channel density is associated with lower reflectance values. Given the role of surface reflectance and roughness in the energy balance of glaciers, it is therefore apparent that extensive networks of small supra‐glacial channels across such glaciers have the potential to have an important impact on energy exchanges between the atmosphere and the ice surface. Copyright © 2015 John Wiley & Sons, Ltd.     

Improved discrimination of subglacial and periglacial erosion using 10Be concentration measurements in subglacial and supraglacial sediment load of the Bossons glacier (Mont Blanc massif,France)

Deciphering the complex interplays between climate, uplift and erosion is not straightforward and estimating present‐day erosion rates can provide useful insights. Glaciers are thought to be powerful erosional agents, but most published ‘glacial’ erosion rates combine periglacial, subglacial and proglacial erosion processes. Within a glaciated catchment, sediments found in subglacial streams originate either from glacial erosion of substratum or from the rock walls above the glacier that contribute to the supraglacial load. Terrestrial cosmogenic nuclides (TCN) are produced by interactions between cosmic ray particles and element targets at the surface of the Earth, but their concentration becomes negligible under 15 m of ice. Measuring TCN concentrations in quartz sand sampled in subglacial streams and in supraglacial channels is statistically compliant with stochastic processes (e.g. rockfalls) and may be used to discriminate subglacial and periglacial erosion. Results for two subglacial streams of the Bossons glacier (Mont Blanc massif, France) show that the proportion of sediments originating from glacially eroded bedrock is not constant: it varies from 50% to 90% (n = 6). The difference between the two streams is probably linked to the presence or absence of supraglacial channels and sinkholes, which are common features of alpine glaciers. Therefore, most of the published mean catchment glacial erosion rates should not be directly interpreted as subglacial erosion rates. In the case of catchments with efficient periglacial erosion and particularly rockfalls, the proportion of sediments in the subglacial stream originating from the supraglacial load could be considerable and the subglacial erosion rate overestimated. Here, we estimate warm‐based subglacial and periglacial erosion rates to be of the same order of magnitude: 0.39 ± 0.33 and 0.29 ± 0.17 mm a^?1, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

Fluvial suspended sediment transport from cold and warm-based glaciers in Svalbard

An analysis of temporal variability in proglacial suspended sediment concentration is undertaken using time series data collected from three Svalbard basins which include one largely cold-based glacier (Austre Brøggerbreen), one largely warm-based glacier (Finsterwalderbreen) and one intermediate polythermal glacier (Erdmannbreen). The temporal variability in proglacial suspended sediment concentration is analysed using multiple regression techniques in which discharge is supplemented by other predictors acting as surrogates for variability in sediment supply at diurnal, medium-term and seasonal timescales. These multiple regression models improve upon the statistical explanation of suspended sediment concentration produced by simple sediment rating curves but need to account for additional stochastic elements within the time series before they may be considered successful. An interpretation of the physical processes which are responsible for the regression model characteristics is offered as a basis for comparing the different arctic glaciofluvial suspended sediment transport systems with that of their better known temperate glaciofluvial counterparts. It is inferred that the largely warm-based glacier is dominated by sediment supply from subglacial reservoirs which evolve in a similar manner to temperate glaciers and which cause a pronounced seasonal exhaustion of suspended sediment supply. The largely cold-based glacier, however, is dominated by sediment supply from marginal sources which generate a responsive system at short time scales but no significant seasonal pattern. The intermediate polythermal glacier basin, which was anticipated to be similar to the warm-based glacier, instead shows a highly significant seasonal increase in suspended sediment supply from an unusual subglacial reservoir emerging under pressure in the glacier foreland. The temperate model of glaciofluvial suspended sediment transport is therefore found to be of limited use in an arctic context. Copyright © 1999 John Wiley & Sons, Ltd.     

Impact of post-mixing chemical reactions on the major ion chemistry of bulk meltwaters draining the haut glacier d'arolla,valais, Switzerland

Until now, alpine glacial meltwaters have been assumed to consist of two components, dilute quickflow and concentrated delayed flow, the mixing of which has been regarded as chemically conservative for the major dissolved ions and electrical conductivity. Dye tracing results suggest that this two-component model adequately represents the sub-glacial hydrology of the Haut Glacier d'Arolla, Switzerland. However, laboratory dissolution experiments in which various concentrations of glacial rock flour are placed in dilute solutions show that this rock flour is highly reactive and suggest that bulk meltwaters may acquire significant amounts of solute through rapid chemical reactions with suspended sediment which occur after mixing of the two components. This view is supported by detailed analysis of variations in the hydrochemistry of meltwaters draining from the Haut Glacier d'Arolla over three diurnal cycles during the 1989 melt season. Variations in the composition of bulk meltwaters are controlled by two main factors: dilution of the delayed flow component by quickflow, and the extent of post-mixing reactions. The latter depends on the suspended sediment concentration in bulk meltwaters and on the duration of contact between these waters and suspended sediment. Seasonal changes in the magnitude of these factors result in changes in the character and causes of diurnal variations in meltwater chemistry. In June, these variations reflect discharge-related variations in residence time within a distributed subglacial drainage system; in July, when a channelized drainage system exists beneath the lower glacier, they primarily reflect the dilution of delayed flow by quickflow; in August, when suspended sediment concentrations are particularly high, they reflect varying degrees of solute acquisition by post-mixing reactions with suspended sediment that take place in arterial channels at the glacier bed.     

Suspended sediment yield and transfer processes in a small High-Arctic glacier basin,Svalbard

Observations of suspended sediment concentration and discharge at two sites on the proglacial river network draining from a predominantly cold-based, High-Arctic glacier (Austre Brøggerbreen) are described. Analysis of these observations illustrates: (i) the relatively low suspended sediment yield from this basin in comparison with many other glacier basins reported in the open literature; (ii) sustained and possibly increasing availability of suspended sediment to the fluvial system as the ablation season progresses; and (iii) the role of the proglacial sandur as both a sediment source and sink. Field observations coupled with the results of the data analysis are used to make inferences concerning the changing nature and relative importance of sediment sources within the basin. © 1998 John Wiley & Sons, Ltd.     

Subglacial processes from drumlins in Clew Bay,western Ireland

Interpretation of subglacial processes and environments can be usefully informed by the stratigraphy and structures of sediments preserved within drumlins, and the down‐ice variability of these sediments. Drumlins in Clew Bay, western Ireland, were formed by westward late Pleistocene ice flow onto the Atlantic shelf, but the depositional processes and environments of these sediments remain uncertain. This study describes and interprets the drumlin stratigraphy and sediment properties and structures from two drumlins on the south side of Clew Bay. Drumlin sediments are dominated by massive to stratified diamicton deposited subglacially by deformation of flows of varying rheology. Folds, shears and clastic dikes within the sediments suggest active subglacial water flow related to variations in ice flow and ice‐bed coupling. The distal ends of the drumlins are dominated by stratified diamicton and gravel units with sandy interbeds. These sediments reflect deposition in a leeside subglacial cavity formed coevally with bedform development. A model is proposed that can account for sediment stratigraphic patterns and drumlin formation. Copyright © 2015 John Wiley & Sons, Ltd.     

Meltwater discharge through the subglacial bed and its land‐forming consequences from numerical experiments in the Polish lowland during the last glaciation

Numerical experiments suggest that the last glaciation severely affected the upper lithosphere groundwater system in NW Poland: primarily its flow pattern, velocities and fluxes. We have simulated subglacial groundwater flow in two and three spatial dimensions using finite difference codes for steady‐state and transient conditions. The results show how profoundly the ice sheet modifies groundwater pressure heads beneath and some distance beyond the ice margin. All model runs show water discharge at the ice forefield driven by ice‐sheet‐thickness‐modulated, down‐ice‐decreasing hydraulic heads. In relation to non‐glacial times, the transient 3D model shows significant changes in the groundwater flow directions in a regionally extensive aquifer ca. 90 m below the ice–bed interface and up to 40 km in front of the glacier. Comparison with empirical data suggests that, depending on the model run, only between 5 and 24% of the meltwater formed at the ice sole drained through the bed as groundwater. This is consistent with field observations documenting abundant occurrence of tunnel valleys, indicating that the remaining portion of basal meltwater was evacuated through a channelized subglacial drainage system. Groundwater flow simulation suggests that in areas of very low hydraulic conductivity and adverse subglacial slopes water ponding at the ice sole was likely. In these areas the relief shows distinct palaeo‐ice lobes, indicating fast ice flow, possibly triggered by the undrained water at the ice–bed interface. Owing to the abundance of low‐permeability strata in the bed, the simulated groundwater flow depth is less than ca. 200 m. Copyright © 2009 John Wiley & Sons, Ltd.     

Proglacial sediment dynamics from daily to seasonal scales in a glaciated Alpine catchment (Bossons glacier,Mont Blanc massif,France)

The sediment yields of Alpine catchments are commonly determined from streamload measurements made some distance downstream from glaciers. However, this approach indiscriminately integrates erosion processes occurring in both the glacial and proglacial areas. A specific method is required to ascertain the respective inputs from (i) subglacial and supraglacial sediments, (ii) proglacial hillslopes and (iii) proglacial alluvial areas or sandurs. This issue is addressed here by combining high‐resolution monitoring (2 min) of suspended sediment concentrations at different locations within a catchment with discharge gauging and precipitation data. This methodological framework is applied to two proglacial streams draining the Bossons glacier (Mont Blanc massif, France): the Bossons and Crosette streams. For the Bossons stream, discharge and suspended load data were acquired from June to October 2013 at 1.15 and 1.5 km from the glacial terminus, respectively upstream and downstream from a small valley sandur. These hydro‐sedimentary data are compared with the Crosette stream dataset acquired at the outlet of the Bossons glacier subglacial drainage system. A fourfold analysis focusing on seasonal changes in streamload and discharge, multilinear regression modelling, evaluation of the sandur flux balance and probabilistic uncertainty assessment is used to determine the catchment sediment budget and to explain the proglacial sediment dynamics. The seasonal fluctuation of the sediment signal observed is related to the gradual closing of the subglacial drainage network and to the role of the proglacial area in the sediment cascade: the proglacial hillslopes appear to be disconnected from the main channel and the valley sandur acts as a hydrodynamic sediment buffer both daily and seasonally. Our findings show that an understanding of proglacial sediment dynamics can help in evaluating paraglacial adjustment and subglacial erosion processes. Copyright © 2017 John Wiley & Sons, Ltd.     

Influence of the hyporheic zone on the phosphorus dynamics of a large gravel‐bed river,Garonne River,France

Phosphorus (P) concentrations in sediments and in surface and interstitial water from three gravel bars in a large river (Garonne River, southern France) were measured daily, downstream of a wastewater treatment plant for a city of 740 000 inhabitants (Toulouse). Measurements were made of vertical hydraulic gradient (VHG), total dissolved phosphorus (TDP), soluble reactive phosphorus (SRP) and total phosphorus (TP) in water and of three extractable forms of phosphorus (water extractable, NaOH extractable and H₂SO₄ extractable) in hyporheic sediments from the gravel bars. Dissolved phosphorus was the major contributor to TP (74–79%) in both interstitial and surface waters on all sampling dates, and in most cases surface water P concentrations were significantly higher than interstitial concentrations. Hyporheic sediment TP concentrations ranged between 269 and 465 µg g^?1 and were highest in fine sediment fractions. Acid‐extractable P, a non‐bioavailable form, represented at least 95% of sediment TP. A positive relationship was observed between VHG and TP in two of the gravel bars, with wells that were strongly downwelling having lower TP concentrations. These results suggest that in downwelling zones, hyporheic sediments can trap surface‐derived dissolved P, and that much of this P becomes stored in refractory particulate forms. Bioavailable P is mainly present in dissolved form and only occupies a small fraction of total P, with particulate P comprising the majority of total P. Copyright © 2009 John Wiley & Sons, Ltd.     

Phosphorus Buildup and Release Risk Associated with Agricultural Intensification in the Estuarine Sediments of Chaohu Lake Valley,Eastern China

Phosphorus (P) accumulation and the risk of P release were studied in the estuarine sediments of the Chaohu Lake Valley in Eastern China. Rapid agricultural intensification has occurred in this area since the 1980s, resulting in the extensive use of phosphate fertilizers. This extensive use of phosphate has affected P processes throughout the valley and resulted in the total phosphorus (TP) contents in the substrates and surface sediments increasing from 374 to 537 mg/kg, on average. Of all the forms of P evaluated in this study, residual P (Res‐P) was present at the highest levels and accounted for 19.8–74.0% of the TP. Conversely, the lowest contents were observed for KCl‐extracted P (KCl‐P), which accounted for only 0.602% of the TP. Additionally, aluminum/iron‐bound P (NaOH‐Pi), which accounted for 16.0–53.1% of the TP, was an important factor that caused the TP to increase due to long‐term P fertilization. However, calcium‐bound P (Ca‐P) was maintained at a relatively stable level. Furthermore, the degree of P saturation (DPS) and the P‐induced lake eutrophication risk index (ERI) were investigated to determine the risk of release of P from the sediments. The average DPS and ERI values were found to range from 3.92–21.4% and from 12.6–33.6%, respectively. These results suggest that almost half of the estuarine sediments posed a potential risk of eutrophication. Moreover, these findings indicate that estuarine sediments that have been enriched with P are likely the sources of P that lead to the formation of algal blooms in Chaohu Lake.     

Pressure‐driven,shoreline currents in a perennially ice‐covered,pro‐glacial lake in Antarctica,identified from a LiCl tracer injected into a pro‐glacial stream

The distribution of streamwater within ice‐covered lakes influences sub‐ice currents, biological activity and shoreline morphology. Perennially ice‐covered lakes in the McMurdo Dry Valleys, Antarctica, provide an excellent natural laboratory to study hydrologic–limnologic interactions under ice cover. For a 2 h period on 17 December 2012, we injected a lithium chloride tracer into Andersen Creek, a pro‐glacial stream flowing into Lake Hoare. Over 4 h, we collected 182 water samples from five stream sites and 15 ice boreholes. Geochemical data showed that interflow travelled West of the stream mouth along the shoreline and did not flow towards the lake interior. The chemistry of water from Andersen Creek was similar to the chemistry of water below shoreline ice. Additional evidence for Westward flow included the morphology of channels on the ice surface, the orientation of ripple marks in lake sediments at the stream mouth and equivalent temperatures between Andersen Creek and water below shoreline ice. Streamwater deflected to the right of the mouth of the stream, in the opposite direction predicted by the Coriolis force. Deflection of interflow was probably caused by the diurnal addition of glacial runoff and stream discharge to the Eastern edge of the lake, which created a strong pressure gradient sloping to the West. This flow directed stream momentum away from the lake interior, minimizing the impact of stream momentum on sub‐ice currents. It also transported dissolved nutrients and suspended sediments to the shoreline region instead of the lake interior, potentially affecting biological productivity and bedform development. Copyright © 2014 John Wiley & Sons, Ltd.     

Glacial conditions that contribute to the regeneration of Fountain Glacier proglacial icing,Bylot Island,Canada

Proglacial icings are one of the most common forms of extrusive ice found in the Canadian Arctic. However, the icing adjacent to Fountain Glacier, Bylot Island, is unique due to its annual cycle of growth and decay, and perennial existence without involving freezing point depression of water due to chemical characteristics. Its regeneration depends on the availability of subglacial water and on the balance between ice accretion and hydro‐thermal erosion. The storage and conduction of the glacial meltwater involved in the accretion of the icing were analyzed by conducting topographic and ground penetrating radar surveys in addition to the modelling of the subglacial drainage network and the thermal characteristics of the glacier base. The reflection power analysis of the geophysical data shows that some areas of the lower ablation zone have a high accumulation of liquid water, particularly beneath the centre part of the glacier along the main supraglacial stream. A dielectric permittivity model of the glacier – sediment interface suggests that a considerable portion of the glacier is warm based; allowing water to flow through unfrozen subglacial sediments towards the proglacial outwash plain. All these glacier‐related characteristics contribute to the annual regeneration of the proglacial icing and allow for portions of the icing to be perennial. Copyright © 2013 John Wiley & Sons, Ltd.     

The mixed-bed glacial landform imprint of the North Sea Lobe in the western North Sea

During the last glacial cycle an intriguing feature of the British-Irish Ice Sheet was the North Sea Lobe (NSL); fed from the Firth of Forth and which flowed south and parallel to the English east coast. The controls on the formation and behaviour of the NSL have long been debated, but in the southern North Sea recent work suggests the NSL formed a dynamic, oscillating terrestrial margin operating over a deforming bed. Further north, however, little is known of the behaviour of the NSL or under what conditions it operated. This paper analyses new acoustic, sedimentary and geomorphic data in order to evaluate the glacial landsystem imprint and deglacial history of the NSL offshore from NE England. Subglacial tills (AF2/3) form a discontinuous mosaic interspersed with bedrock outcrops across the seafloor, with the partial excavation and advection of subglacial sediment during both advance and retreat producing mega-scale glacial lineations and grounding zone wedges. The resultant ‘mixed-bed’ glacial landsystem is the product of a dynamic switch from a terrestrial piedmont-lobe margin with a net surplus of sediment to a partially erosive, quasi-stable, marine-terminating, ice stream lobe as the NSL withdrew northwards. Glaciomarine sediments (AF4) drape the underlying subglacial mixed-bed imprint and point to a switch to tidewater conditions between 19.9 and 16.5 ka cal BP as the North Sea became inundated. The dominant controls on NSL recession during this period were changing ice flux through the Firth of Forth ice stream onset zone and water depths at the grounding line; the development of the mixed-bed landsystem being a response to grounding line instability. © 2018 John Wiley & Sons, Ltd.     

Basal sediment evacuation by subglacial meltwater: suspended sediment transport from Haut Glacier d'Arolla,Switzerland

Proglacial suspended sediment transport was monitored at Haut Glacier d'Arolla, Switzerland, during the 1998 melt season to investigate the mechanisms of basal sediment evacuation by subglacial meltwater. Sub‐seasonal changes in relationships between suspended sediment transport and discharge demonstrate that the structure and hydraulics of the subglacial drainage system critically influenced how basal sediment was accessed and entrained. Under hydraulically inefficient subglacial drainage at the start of the melt season, sediment availability was generally high but sediment transport increased relatively slowly with discharge. Later in the melt season, sediment transport increased more rapidly with discharge as subglacial meltwater became confined to a spatially limited network of channels following removal of the seasonal snowpack from the ablation area. Flow capacity is inferred to have increased more rapidly with discharge within subglacial channels because rapid changes in discharge during highly peaked diurnal runoff cycles are likely to have been accommodated largely by changes in flow velocity. Basal sediment availability declined during channelization but increased throughout the remainder of the monitored period, resulting in very efficient basal sediment evacuation over the peak of the melt season. Increased basal sediment availability during the summer appears to have been linked to high diurnal water pressure variation within subglacial channels inferred from the strong increase in flow velocity with discharge. Basal sediment availability therefore appears likely to have been increased by (1) enhanced local ice‐bed separation leading to extra‐channel flow excursions and[sol ]or (2) the deformation of basal sediment towards low‐pressure channels due to a strong diurnally reversing hydraulic gradient between channels and areas of hydraulically less‐efficient drainage. Copyright © 2005 John Wiley & Sons, Ltd.     

Sulphide oxidation under partially anoxic conditions at the bed of the Haut Glacier d'Arolla,Switzerland

Oxygen isotopic data are presented for bulk glacial meltwaters draining the Haut Glacier d'Arolla, Valais, Switzerland and for the sulphate contained within them in an attempt to assess the redox status of the subglacial chemical weathering environment. The sulphate derived from subglacial chemical weathering is so depleted in ¹⁸O that it must have formed, at least partially, in an anoxic environment. Under these conditions, Fe³⁺ can act as an oxidizing agent and oxygen atoms incorporated into sulphate are derived from ¹⁸O‐depleted water molecules (by contrast, dissolved O₂ is strongly enriched in ¹⁸O). These data therefore support the hypothesis that sectors of the glacier bed are anoxic and that Fe³⁺ may act as a significant oxidizing agent under these conditions. Copyright © 2002 John Wiley & Sons, Ltd.     

A comparison of solute fluxes and sources from glacial and non‐glacial catchments over contrasting melt seasons

Solute and runoff fluxes from two adjacent alpine streams (one glacial and one non‐glacial) were investigated to determine how the inorganic solute chemistry of runoff responded to seasonal and interannual changes in runoff sources and volume, and to differences in physical catchment properties. Intercatchment differences in solute composition were primarily controlled by differences in catchment geology and the presence of soils, whereas differences in total solute fluxes were largely dependent on specific discharge. The glacial stream catchment had higher chemical denudation rates due to the high rates of flushing (higher specific discharge). The non‐glacial Bow River had higher overall concentrations of solutes despite the greater prevalence of more resistant lithologies in this catchment. This is likely the result of both longer average water–rock contact times, and a greater supply of protons from organic soils and/or pyrite oxidation. Increases in snowpack depth/snowmelt runoff reduced the retention of nitrate in the Bow River catchment (i.e. increased nitrate export), probably by reducing net biological uptake, or by reducing the proportion of runoff that had contact with biologically active soil horizons that tend to remove nitrate. The two streams exhibited opposite solute flux responses to climate perturbations over three melt seasons (1998, 1999, and 2000). The 1998 El Niño event resulted in an unusually thin winter snowpack, and increased runoff and solute fluxes from the glacial catchment, but decreased fluxes from the Bow River catchment. Solute fluxes in the Bow River increased proportionally to discharge, indicating that increased snowmelt runoff in this catchment resulted in a proportional increase in weathering rates. In contrast, the proportional variation in solute flux in the glacial stream was only ∼70–80% of the variation in water flux. This suggests that increased ablation of glacier ice and the development of subglacial channels during the 1998 El Niño year apparently reduced the average water–rock contact time in the glacial catchment relative to seasons when the subglacial drainage system was primarily distributed in character. Copyright © 2005 John Wiley & Sons, Ltd.     

Supraglacial weathering crust dynamics inferred from cryoconite hole hydrology

Water levels in cryoconite holes were monitored at high resolution over a 3‐week period on Austre Brøggerbreen (Svalbard). These data were combined with melt and energy balance modelling, providing insights into the evolution of the glacier's near‐surface hydrology and confirming that the hydrology of the near‐surface, porous ice known as the ‘weathering crust’ is dynamic and analogous to a shallow‐perched aquifer. A positive correlation between radiative forcing of melt and drainage efficiency was found within the weathering crust. This likely resulted from diurnal contraction and dilation of interstitial pore spaces driven by variations in radiative and turbulent fluxes in the surface energy balance, occasionally causing ‘sudden drainage events’. A linear decrease in water levels in cryoconite holes was also observed and attributed to cumulative increases in near‐surface ice porosity over the measurement period. The transport of particulate matter and microbes between cryoconite holes through the porous weathering crust is shown to be dependent upon weathering crust hydraulics and particle size. Cryoconite holes therefore yield an indication of the hydrological dynamics of the weathering crust and provide long‐term storage loci for cryoconite at the glacier surface. This study highlights the importance of the weathering crust as a crucial component of the hydrology, ecology and biogeochemistry of the glacier ecosystem and glacierized regions and demonstrates the utility of cryoconite holes as natural piezometers on glacier surfaces. Copyright © 2015 John Wiley & Sons, Ltd.     

An erosional origin for drumlins of NW Poland

Drumlins are landforms essential to understanding of ice sheet movement over soft beds, sediment transport along the ice/bed interface, and the formation of a wide range of glacial deposits. Although investigated more than any other glacial landform, the origin of drumlins remains contentious. Using high-resolution LiDAR imagery and field data, we investigate the geomorphology and internal composition of one of the biggest drumlin fields in the North European Lowland. The Stargard drumlin field consists of over 1300 drumlins and related streamlined subglacial bedforms in a terminal part of a major Weichselian palaeo-ice stream of the southern Scandinavian Ice Sheet. The drumlins are typically 600-800 m long, 200-250 m wide, 3-6 m high and have axial elongation ratios ~2 but in some cases exceeding 15. Several subzones inferred from drumlin morphometry exist reflecting different ice flow dynamics. The most elongated drumlins occur in areas where ice moved down-slope and where thick fine-grained deposits of low hydraulic conductivity occur in the substratum. The largest portion of land occupied by drumlins and the greatest frequency density of drumlins occur where the ice moved up-slope. Stargard drumlins are composed of a wide variety of glacial deposits including various types of tills and meltwater sediments, which range from undisturbed to heavily deformed. There is no correlation between the deposits in the drumlins and the drumlin forms indicating that the deposits pre-date the drumlinizing process. It is suggested that the drumlin field was generated by a combination of direct glacial erosion and subglacial meltwater erosion by removing antecedent material from the inter-drumlin areas and streamlining the resultant bumps. Our data support the search for a unifying theory of drumlin formation and suggest erosion as the most plausible single mechanism generating drumlin landscapes. © 2019 John Wiley & Sons, Ltd.