Ice-marginal Environments Research Articles

Quaternary Geology of the Washington-Jasper Area

"Quaternary Geology of the Washington-Jasper Area" was created to present basic quaternary geologic information that contributes to the characterization of potential aggregate resources, characterization of bedrock aquifer systems, and analysis of the overlying predominantly glacial deposits. This map is based on data compiled from project field observations and project exploratory borings, complemented with IGWS cartographic (e.g., Gray, 1989) and archive borehole data, select Indiana Department of Natural Resources water well logs, and United States Department of Agriculture soil survey maps. Expert knowledge of fluvial, glacifluvial and ice-marginal environments was used to draw contacts between units. This geologic map was funded in part through the STATEMAP program supported by the U.S. Geological Survey under Cooperative Agreement No. G21AC10646. "Quaternary Geology of the Washington-Jasper Area" is a composite geodata set that conforms to "GeMS (Geologic Map Schema)--a standard format for the digital publication of geologic maps," available at http://ngmdb.usgs.gov/Info/standards/GeMS/. Metadata records associated with each element within the geodata set contain more detailed descriptions of their purposes, constituent entities, and attributes. An OPEN shapefile version of the data set is also available. It consists of shapefiles, DBF files, and delimited text files and retains all information in the native geodatabase, but some programming will likely be necessary to assemble these components into usable formats.

Surface deformation detection and attribution in the Mountain-Oasis-Desert Landscape in north Tianshan Mountains

ABSTRACT The Mountain-Oasis-Desert System (MODS) is the fundamental landscape component within the vast arid region of Central Asia. Human activities and natural processes cause surface displacement in the MODS, resulting in geoenvironmental issues and hazards. However, surface displacement and its driving mechanisms in the MODS are not understood. In this study, we used the time-series interferometric synthetic aperture radar (InSAR) method to detect deformation in the MODS in north Tianshan Mountain, Xinjiang and investigated its attribution from the geological conditions, groundwater level changes, and climate variability. The results along the vertical gradient indicate that decorrelation is severe in the high mountain areas with ice-marginal environments (over 3600 m above sea level (a.s.l.)) and the forest-covered mid-mountainous belt (1700–2800 m asl), rendering effective detection unfeasible. Dynamic characteristics are identified in subalpine areas with an elevation of 2800–3600 m asl, with maximum horizontal and vertical displacements of −80.2 mm/year and −58.6 mm/year, respectively. The seasonal acceleration is influenced by the combined effects of temperature and precipitation changes. We observed dense subsidence funnels and ground fissures associated with coal mining in the foreland hills (700–1700 m asl). Ground displacements here exceeded −50 mm/year two years after mining activities had ceased. Subsidence has expanded in the oases with elevations of less than 700 m asl, due to extensive groundwater extraction for agricultural irrigation. The correlation coefficient between groundwater level and displacement was 0.89 and 0.45 at wells in the agricultural and desert areas, respectively. The deformation exhibited seasonal variations associated with groundwater level. The deformation remains relatively stable in the surrounding oasis-affected desert areas, with weak fluctuations influenced by seasonal variations in groundwater level.

Chad's cabinet of icy curiosities: Sharpening the interpretation of subglacial and ice marginal environments during the LPIA glaciation of the Ennedi Plateau

The Ennedi Plateau in Chad in north-central Africa exposes an outstanding example of a palaeo-ice stream glacial landsystem of late Palaeozoic age, with an assemblage of geomorphological structures of comparable preservation quality to those found in Quaternary deglaciated landscapes. Satellite images and various methods to combine acquired satellite data (e.g. band-ratio technique) have been used to interpret proglacial, ice-marginal and subglacial structures. The main goal of the study is to produce a detailed and more in-depth analysis of newly found structures that enhance our understanding of ice sheet behaviour in the Ennedi Plateau during the LPIA.We report the first known evidence of soft-sediment striated surfaces from outcrop, testifying to the existence of a soft-deformable bed. This deformable bed interpretation can probably be upscaled to explain the extensive swarms of mega-scale glacial lineations mapped previously across the plateau. Furthermore, we identify the first known fully preserved grounding zone wedge (GZW), replete with three-dimensional geometry, in the rock record. This unique structure exhibits a well pronounced slope and a convex topography. Its presence allows the position of the former coastline to be reconstructed as it is assumed that ice streams terminated into a former ocean basin. Building on the studies by Le Heron (2018) and Kettler et al. (this issue), our analyses permit unprecedented insights into the behaviour of a significant, mid-latitude, marine-terminating ice sheet during the LPIA.

Environmental implication of geochemical record in the Arctic Ny-Ålesund glacial sediment, Svalbard (Norway)

Glacial sediments as an important end member of the global dust system, could indicate changes in global climate, aerosols sources, ocean elements, and productivity. With global warming, ice caps shrinking and glaciers retreat at high latitudes have attracted concern. To understand the response of glacier to environment and climate in modern high latitude ice-marginal environments, this paper investigated glacial sediments in the Ny-Ålesund region of the Arctic and clarified the response of polar environmental to global changes through geochemical characteristics of glacial sediments. The results showed that: 1) main factors affecting the elements distribution of the Ny-Ålesund glacial sediments were thought as soil formation, bedrock and weathering, and biological activity; 2) variations of SiO2/Al2O3 and SiO2/Al2O3 + Fe2O3, indicating low weathering of the soil. The ratio of Na2O/K2O indicating a weak chemical weathering, was negatively correlated to the CIA. With the average CIA of Ny-Ålesund glacial sediments for main minerals of quartz, feldspar, and muscovite as well as dolomite and calcite 50.13, which implied glacial sediments at the early stage of chemical weathering and depletion of Ca and Na; 3) the separating effect of stones and soils by stone circle formation due to thermal conductivity and frost heave makes sediments in stone circle have lower chemical weathering with only two main minerals, albite and quartz; 4) changes of carbonate content in sediments with glacier front retreating in different period implied that weathering rate of calcite averagely reached an estimate of 0.0792%wt/year in glacier A. The succession of vegetation made biological weathering become an important driving force for carbonate leaching from glacial sediments. These results and data provide scientifically significant archive for future global change studies.

Ice-marginal lakes associated with enhanced recession of the Greenland Ice Sheet

There has been a progressive increase in the number and area of ice-marginal lakes situated along the south-western margin of the Greenland Ice Sheet (GrIS) since the 1980s. The increased prevalence of ice-marginal lakes is notable because of their capacity to enhance mass loss and ice-margin recession through a number of thermo-mechanical controls. Although such effects have been extensively documented at alpine glaciers, an understanding of how ice-marginal lakes impact the dynamics of the GrIS has been limited by a sparsity of observational records. This study employs the Landsat archive to conduct a multi-decadal, regional-scale statistical analysis of ice-margin advance and recession along a ~ 5000 km length of the south-western margin of the GrIS, incorporating its terrestrial, lacustrine and marine ice-margins. We reveal an extended and accelerating phase of ice-margin recession in south-west Greenland from 1992 onwards, irrespective of margin type, but also observe considerable heterogeneity in the behaviour of the different ice-marginal environments. Marine ice-margins exhibited the greatest magnitude and variability in ice-margin change, however lacustrine termini were notable for a progressive increase in ice-margin recession rates from 1987 to 2015, which increasingly outpaced those measured at terrestrial ice-margins. Furthermore, significant correlations were identified between lake parameters and rates of lacustrine ice-margin recession, including lake area, latitude, altitude and the length of the lake – ice-margin interface. These results suggest that ice-marginal lakes have become increasingly important drivers of ice-margin recession and thus mass loss at the GrIS, however further research is needed to better parameterise the causal connections between ice-marginal lake evolution and enhanced ice-margin recession. More widely, a detailed understanding of the impacts of ice-marginal lakes on ice-margin dynamics across Greenland is increasingly necessary to accurately forecast the response of the ice sheet to enhanced ice-marginal lake prevalence and thus refine projections of recession, mass loss and sea level rise.

Ground ice, organic carbon and soluble cations in tundra permafrost soils and sediments near a Laurentide ice divide in the Slave Geological Province, Northwest Territories, Canada

Abstract. The central Slave Geological Province is situated 450–650 km from the presumed spreading centre of the Keewatin Dome of the Laurentide Ice Sheet, and it differs from the western Canadian Arctic, where recent thaw-induced landscape changes in Laurentide ice-marginal environments are already abundant. Although much of the terrain in the central Slave Geological Province is mapped as predominantly bedrock and ice-poor, glacial deposits of varying thickness occupy significant portions of the landscape in some areas, creating a mosaic of permafrost conditions. Limited evidence of ice-rich ground, a key determinant of thaw-induced landscape change, exists. Carbon and soluble cation contents in permafrost are largely unknown in the area. Twenty-four boreholes with depths up to 10 m were drilled in tundra north of Lac de Gras to address these regional gaps in knowledge and to better inform projections and generalizations at a coarser scale. Excess-ice contents of 20 %–60 %, likely remnant Laurentide basal ice, are found in upland till, suggesting that thaw subsidence of metres to more than 10 m is possible if permafrost were to thaw completely. Beneath organic terrain and in fluvially reworked sediment, aggradational ice is found. The variability in abundance of ground ice poses long-term challenges for engineering, and it makes the area susceptible to thaw-induced landscape change and mobilization of sediment, solutes and carbon several metres deep. The nature and spatial patterns of landscape changes, however, are expected to differ from ice-marginal landscapes of western Arctic Canada, for example, based on greater spatial and stratigraphic heterogeneity. Mean organic-carbon densities in the top 3 m of soil profiles near Lac de Gras are about half of those reported in circumpolar statistics; deeper deposits have densities ranging from 1.3–10.1 kg C m−3, representing a significant additional carbon pool. The concentration of total soluble cations in mineral soils is lower than at previously studied locations in the western Canadian Arctic. This study can inform permafrost investigations in other parts of the Slave Geological Province, and its data can support scenario simulations of future trajectories of permafrost thaw. Preserved Laurentide basal ice can support new ways of studying processes and phenomena at the base of an ice sheet.

Controls on jökulhlaup-transported buried ice melt-out at Skeiðarársandur, Iceland: Implications for the evolution of ice-marginal environments

High-magnitude jökulhlaups, glacier margin position and ice-thickness have been identified as key controls on sandur evolution. Existing models however have focused primarily on observations made during short windows of time and often do not account for the subsequent modification of proglacial landsystems by repeated jökulhlaups or post-depositional modification due to melt out over decadal time-scales. Digital Elevation Models (DEMs) were used to reconstruct the development of large depressions on Skeiðarársandur, an outwash plain in southeast Iceland. These depressions measure up to 1 km in width and up to 13 m in depth and are associated with ice bodies up to 1 km in length and up to 150 m in height emplaced during a high-magnitude jökulhlaup in 1903 and subsequently buried by jökulhlaups in 1913 and 1922. The continued melting of the Harðaskriða ice bodies over a century following their emplacement, together with subsequent repeated burial, by high-magnitude jökulhlaups demonstrates that jökulhlaups may continue to serve as important controls on sandur evolution on a decadal to centennial timescale (101–102 years). The Harðaskriða depressions developed only following the retreat of the glacier margin after 1945, which highlights the controls of margin position on the evolution of the sandur. Margin position and thickness of the glacier profile was seen to affect not only the distribution and thickness of sediment emplaced during jökulhaups but also the rate and pattern of melt in the decades following the decoupling of the margin from the sandur. The jökulhlaup landsystem model signatures identified at this site may provide a useful analogue for interpreting landforms and strata emplaced by glacier margin fluctuations, jökulhlaups and melt out generated by retreating continental Pleistocene ice sheets.

Radiocarbon chronology and environmental context of Last Glacial Maximum human occupation in Switzerland

Central Europe during the Last Glacial Maximum (LGM) was dominated by polar desert and steppe-tundra biomes. Despite this, a human presence during this time period is evident at several locations across the region, including in Switzerland, less than 50 km from the Alpine ice sheet margin. It has been hypothesised that such human activity may have been restricted to brief periods of climatic warming within the LGM, but chronological information from many of these sites are currently too poorly resolved to corroborate this. Here we present a revised chronology of LGM human occupation in Switzerland. AMS radiocarbon dating of cut-marked reindeer (Rangifer tarandus) bones from the sites of Kastelhöhle-Nord and Y-Höhle indicates human occupation of Switzerland was most likely restricted to between 23,400 and 22,800 cal. BP. This timeframe corresponds to Greenland Interstadial 2, a brief warming phase, supporting the hypothesis that human presence was facilitated by favourable climatic episodes. Carbon, nitrogen and sulphur stable isotope analysis of the fauna provides palaeoenvironmental information for this time period. These findings contribute to our understanding of human activity in ice-marginal environments and have implications for understanding cultural connections across central Europe during the LGM.

The local Last Glacial Maximum in McMurdo Sound, Antarctica: Implications for ice-sheet behavior in the Ross Sea Embayment

AbstractDuring the Last Glacial Maximum (LGM), a grounded ice sheet filled the Ross Sea Embayment in Antarctica and deposited glacial sediments on volcanic islands and peninsulas in McMurdo Sound and coastal regions of the Transantarctic Mountains. The flow geometry and retreat history of this ice are debated, with contrasting views yielding divergent implications for the interaction between and stability of the East and West Antarctic ice sheets during late Quaternary time. Here, we present terrestrial geomorphologic evidence and reconstruct former ice-marginal environments, ice sheet elevations, and ice-flow directions in McMurdo Sound. Fossil algae in ice-marginal sediments provide a coherent radiocarbon chronology of maximum ice extent and deglaciation. We integrate these data with marine records to reconstruct grounded ice dynamics in McMurdo Sound and the western Ross Sea. The combined data set suggests ice flow toward the Transantarctic Mountains in McMurdo Sound during peak glaciation, with thick, grounded ice at or near its maximum position between 19.6 and 12.3 ka. Persistent grounded ice in McMurdo Sound and across the western Ross Sea after Meltwater Pulse 1a (14.0–14.5 ka) suggests that this sector of Antarctica did not significantly contribute to this rapid sea-level rise event. Our data show no significant advance of locally derived ice from the Transantarctic Mountains into McMurdo Sound during the local LGM.

Potential sources of bacteria colonizing the cryoconite of an Alpine glacier.

We investigated the potential contribution of ice-marginal environments to the microbial communities of cryoconite holes, small depressions filled with meltwater that form on the surface of Forni Glacier (Italian Alps). Cryoconite holes are considered the most biologically active environments on glaciers. Bacteria can colonize these environments by short-range transport from ice-marginal environments or by long-range transport from distant areas. We used high throughput DNA sequencing to identify Operational Taxonomic Units (OTUs) present in cryoconite holes and three ice-marginal environments, the moraines, the glacier forefield, and a large (> 3 m high) ice-cored dirt cone occurring on the glacier surface. Bacterial communities of cryoconite holes were different from those of ice-marginal environments and hosted fewer OTUs. However, a network analysis revealed that the cryoconite holes shared more OTUs with the moraines and the dirt cone than with the glacier forefield. Ice-marginal environments may therefore act as sources of bacteria for cryoconite holes, but differences in environmental conditions limit the number of bacterial strains that may survive in them. At the same time, cryoconite holes host a few OTUs that were not found in any ice-marginal environment we sampled, thus suggesting that some bacterial populations are positively selected by the specific environmental conditions of the cryoconite holes.

Dynamics and palaeoclimatic significance of a Loch Lomond Stadial glacier: Coire Ardair, Creag Meagaidh, Western Highlands, Scotland

The extent, basal conditions and retreat history of a Loch Lomond Stadial glacier are reconstructed based on detailed geomorphological and sedimentological assessment. We present new evidence from the vicinity of Coire Ardair that supports the former existence of a warm-based, locally-fed valley glacier, with probable cold-based ice on the surrounding plateau. This is broadly consistent with modelled creep-dominated flow in the upper catchment and sliding-dominated flow throughout much of the valley. A dense suite of moraines, primarily formed in ice-marginal environments, records a multi-phase recessional history: (1) active and oscillatory retreat; (2) a prolonged ice stillstand; (3) partial ice stagnation with occasional minor readvances; (4) increased oscillatory retreat with a substantial readvance event; and (5) rapid and uninterrupted retreat. We propose that a Coire Ardair glacier responded to sub-centennial scale climate fluctuations, possibly associated with the periodic delivery of warmer air masses to the region, rather than to a single, prominent shift in climate.

Role of sediment in speleogenesis; sedimentation and paragenesis

Although the effects of sedimentation in caves have been recognised for many years, its role in speleogenesis is frequently overlooked. Influxes of sediment into a cave system fundamentally alter the way cave passages develop, either by alluviation in a vadose environment, forcing lateral corrosion and the development of notches, or by upwards dissolution in a phreatic environment through a process known as paragenesis. Sediment influxes affect the hydrological functioning of a karst aquifer by changing the way conduits behave and subsequently develop both in plan and long section.Here we give an overview of the mechanisms of cave sedimentation and describe how the process of alluviation and paragenesis affect speleogenesis. A characteristic suite of meso- and micro-scale dissolutional features can be used to recognise paragenetic development, which is reviewed here. In a vadose environment these include alluvial notches, whilst in a phreatic environment, half tubes, anastomoses and pendants, bedrock fins and paragenetic dissolution ramps result. Using these to identify phases of sedimentation and paragenesis is crucial for reconstructing denudation chronologies from cave deposits. We suggest that sedimentation and paragenesis are most likely to occur in certain geomorphological situations, such as ice marginal and periglacial environments, beneath thick residual soils and where rivers can transport fluvial sediment into a cave, either via stream sinks or back-flooding.

Biogeochemistry of snowmelt in an Antarctic glacial ecosystem

Solute mass balance, hydrochemical data, and hydrological process data are used to present the first detailed account of catchment biogeochemistry in an Antarctic melt season. The study was undertaken in a small glacial catchment in the maritime Antarctic (Signy Island, South Orkney Islands), where extreme ecosystem changes have been observed at the ice margin. Here melting caused a snowpack solute elution phase characterized by the production of extremely concentrated solutions just centimeters from the snow surface. These were equivalent to 2% marine water and dominated by sea‐salt aerosol. Nutrients were also present but were rapidly sequestered in snowpack and ice marginal environments. Thus the decoupling of nutrient dynamics from other snowpack solutes seems to occur almost immediately after melt and testifies to the presence of a glacial ecosystem. Although significant, the estimated rates of nutrient uptake were low (0.025 gNH4‐N/m2/yr and 0.0011 gPO4‐P/m2/yr, equivalent to 66 and 74% of total annual atmospheric inputs) and, in the case of NH4+, 2–3 orders of magnitude lower than those reported for temperate snowpacks. However, the data also demonstrated significant NO3− production (0.030 gNO3‐N/m2/yr or 3 times total atmospheric inputs) that appears to be associated with zones of high rock‐water contact at the ice margin. After the early snowpack elution phase, nutrient cycling was also greatly influenced by inputs from penguin and seal excreta. Thus local marine ecosystems enhance the nutrient content of meltwaters and fertilize the glacial, terrestrial, and aquatic ecosystems that are responding to climate change in the maritime Antarctic.

Problems associated with luminescence dating of Late Quaternary glacial sediments in the NW Scottish Highlands

Linking the timing of glacial episodes and behaviour to climatic shifts that are documented in ice and marine sedimentary archives is key to understanding ocean-land interactions. In the NW Scottish Highlands a large number of closely spaced (‘hummocky’) moraines formed at retreating glacier margins. Independent age control on one palaeo-glacier limit is consistent with the timing of Younger Dryas (YD) glaciation in the area, but adjacent glacier lobes have remained undated due to the lack of sites and material for 14C dating. Direct dating of ice-marginal moraines using optically stimulated luminescence (OSL) techniques has never been attempted before in Scotland, but if successful, they may be the most appropriate methods for constraining the age of sediment deposition in the absence of organic material. Coarse-grained quartz and K-feldspar minerals from supraglacial sheet flow deposits and glacilacustrine sediments within ice-marginal moraines were analysed using the single-aliquot regenerative-dose (SAR) protocol. Independent age control and clear geomorphological relationships indicate that all samples should yield YD or post-Last Glacial Maximum (LGM) ages. Quartz OSL shine down curves showed low luminescence sensitivity, significant medium-to-slow components, a weak fast component, and scattered SAR data; Linearly Modulated-OSL (LM-OSL) measurements confirmed that the fast component was weak or absent. In contrast, feldspar infrared stimulated luminescence (IRSL) was highly sensitive with excellent SAR data. However, SAR data from 3 mm diameter aliquots of feldspar (∼200 grains) give higher than expected equivalent doses ( D e) by an order of magnitude. SAR measurements of small clusters of feldspar grains (ranging from ∼1–8) considerably broaden the apparent D e distribution, but even the lowest value is about 2–3 times the expected D e. Two possibilities arise to explain the quartz and feldspar data: (1) that glacial sequences in the NW Highlands re-work inherited (older) glacial deposits and that some of the pre-Devensian existing glacial landforms have only been modified during Devensian glaciation; or (2) that the sedimentary processes operating in these ice-marginal environments are not conducive to adequate bleaching of quartz and feldspar grains. Our study implies that ice-proximal supraglacial sediments from this region in NW Scotland reflect older ages of deposition, but dating YD sediments has not been possible.

Evidence for Stagnation of the Harvard Sublobe (Lake Michigan Lobe) in Northeastern Illinois, U.S.A., from 24 000 to 17 600 BP and Subsequent Tundra-Like Ice-Marginal Paleoenvironments from 17 600 to 15 700 BP

Glacial deposits of the last glaciation associated with the Harvard sublobe (Lake Michigan lobe) in northeastern Illinois, U.S.A., occur between sediment with dateable organics. The lower organics include fragments ofPiceasp. as young as 24 000 ± 270 BP. The supraglacial organics occur sparsely in laminated silt and fine sand in landforms that are positioned relatively high on the landscape, such as deposits from ice-walled lakes. These terrestrial organics yield ages that are 2500 to 1300 14C years older than organics at the base of sediment successions in nearby kettle basins. Basal 14C ages from four upland sites range from 17 610 ± 270 to 16 120 ± 80 BP. Our revised time-distance diagram of the Harvard sublobe now reflects a period of stagnation from 24 000 to about 17 600 BP. The supraglacial lacustrine silt yielded plant macrofossil assemblages of primarily tundra plants, includingSalix herbaceaandDryas integrifolia. These plants likely grew in supraglacial and ice-marginal environments. The ostracode fauna includeCytherissa lacustrisandLimnocythere friabilis.Geomorphic relations and ostracode ecology indicate that more than 17 m of ice buttressed some of the supraglacial lakes.

About this title

The introduction of the term periglacial by Łoziński in 1909 to describe the cold-climate conditions in the zone adjacent to, but beyond, the Pleistocene glaciers encouraged the separate development of geocryological and glaciological research. Geological and geomorphological processes at the interface between glaciers and permafrost have, as a result, been given less attention than they warrant, and the influence of one on the other has in many respects been neglected. This book includes a collection of papers that emphasize glacier-permafrost interactions. Papers consider permafrost and its influence on glacitectonic processes, glacial meltwater systems and ground-ice development in proglacial and ice-marginal environments. In addition, recent research findings are reported on paraglacial processes, permafrost evolution, rock glaciers, the formation of ice-wedge casts and periglacial slope evolution. It is hoped that this book will stimulate interest in the interface between glacial and periglacial systems, and encourage further collaborative research involving glaciologists and glacial geologists on the one hand, and geocryologists and permafrost scientists on the other.

Interactions between glaciers and permafrost: an introduction

Abstract A consideration of the interactions between glaciers and permafrost is essential to many environmental studies of cold regions. This paper reviews how concepts, field data and experimental studies from glaciology and geocryology can provide a basis for improved understanding of some of the key glacier-permafrost interactions at scales ranging from continental ice sheets to small proglacial streams. Glacitectonic processes are strongly influenced by water pressures beneath subglacial and proglacial permafrost, and by the amount of unfrozen water within the permafrost. Burial of glacier ice and growth of intrasedimental ice also occur within sub- and proglacial permafrost, and together they produce a complex assemblage of ground ice in glaciated frozen lowlands. In mountain regions, rock glaciers are associated with the presence of ground ice, and represent a landform that stradles the semantic fence separating glacial features from permafrost features. In proglacial and ice-marginal environments, geomorphological activity reflects the combined effects of glacially- and periglacially-conditioned processes operating synchronously in adjacent areas, or in succession; such activity includes the transport of sediment in glacierized catchments and the calving of glacial ice in ice-marginal lakes. Interaction between permafrost and glacial phenomena depends largely on their proximity: where permafrost occurs close to glaciers, the thermal regime of the active layer is influenced in part by the surface covering of adjacent glacial ice through its effect on albedo and ground heat flux. Glacier-permafrost interactions are particularly important in recently deglaciated terrain, where permafrost may be aggrading. This ‘paraglacial’ zone often shows rapid geomorphological change. Thus, glacier-permafrost interactions are complex and occur over a wide range of temporal and spatial scales.

Geomorphic implications of subglacial drainage configuration: rates of basal sediment evacuation controlled by seasonal drainage system evolution

Although basal sediment evacuation by subglacial meltwater is widely assumed to dominate the sediment budget of most temperate glaciers and ice caps, its potential influence for glacial geomorphic processes and landforms has largely been overlooked in the glacial literature. Data collected at Haut Glacier d'Arolla, Switzerland during the 1998 ablation season are used to test theoretical predictions that subglacial drainage configuration should exert a primary control on rates of basal sediment evacuation by subglacial meltwater. Seasonal evolution of the subglacial drainage system enables observation of sediment evacuation from both distributed and channelised drainage systems. Daily suspended sediment load exhibits an extreme, nonlinear increase with respect to discharge between winter and summer periods, which correspond to periods of predominantly distributed and channelised subglacial drainage, respectively. These results suggest that subglacial drainage configuration should significantly impact upon: (a) rates of subglacial erosion and debris production; (b) the nature of debris transport and the proportion of sediment in glacial versus fluvioglacial transport pathways; and (c) rates and styles of ice-marginal sedimentation. In contrast to their distributed counterparts, channelised drainage configurations are predicted to encourage subglacial erosion through the removal of basal sediment from the ice–bedrock interface and, with the exception of supraglacial transport, will discourage sediment transport by alternative glacial mechanisms. Direct sedimentation at the glacier margin may therefore be reduced, resulting in smaller moraines despite an overall increase in sediment production. An appreciation of the coupling between glacier hydrology and geomorphic processes suggests new frameworks for the understanding of rates and styles of glacial erosion, sediment transfer and deposition, and the complex geomorphology of ice-marginal environments.

The hydrochemistry of Bayelva, a high Arctic proglacial stream in Svalbard

Major ion, silica and pH data from a high Arctic proglacial stream network are examined. Factor analysis shows that the major controls upon hydrochemistry in the basin include snowpack solute elution, rapid alteration of minerals via surface reactions and slow, incongruent silicate dissolution. The importance of chemical weathering is found to increase downstream at the expense of solute acquisition from the transient snowpack. Data from a series of snow pits show that snowpack solute elution is characterised by the preferential elution of SO42−. Evidence for the preferential elution of NO3− is equivocal. However, NO3− levels in proglacial runoff may be enhanced by the leaching of cryotic soils later in the ablation season.Chemical weathering is dominated by calcite dissolution at high elevations and a combination of calcite and dolomite dissolution in the downstream proglacial environment. Silicate weathering at high elevations is characterised by the enrichment of K+ relative to Si. Concentrated active layer soil waters show less enrichment of K+ and constitute a potentially important source of dissolved silica to the river system. Na+ is also produced by silicate weathering, but its mobility is believed to be largely governed by ion exchange with Ca2+ early in the ablation season.All chemical weathering environments are characterised by high p(CO2) due to either respiration within the soil or, at higher elevations within the catchment, H+ provision from acid aerosol and sulphide oxidation. However, rates of sulphide oxidation are limited because the cold-based thermal regime of the glaciers effectively prevents access of meltwaters to freshly comminuted sub-glacial sulphide minerals. The restricted sub-glacial weathering therefore means that ice marginal and proglacial environments are the most important zones of solute acquisition by meltwaters, causing significant enrichment of major ions, silica and dissolved CO2 within only a short distance of the contemporary ice margin.

Pleistocene climate change, natural environments and palaeolithic occupation of the Altai area, west-central Siberia

Diversity of the relief and the Pleistocene environments of the mountain areas of SW Siberia played a major role in the history of the palaeolithic peopling of this territory. The geographical and contextual distribution of the cultural records reflects a climatic instability in the Altai area. Palaeoenvironmental proxy data indicate that the natural conditions during the earlier stages were generally more favourable for early human occupation than during the later stages. The cyclic nature of the glacial and interglacial periods led to periodic landscape transformations and generation of specific ecosystems adjusted to particular topographic settings and responding to climatic variations. The initial occupation of the broader Altai region associated with “pebble-tool” industries from alluvial formations likely occurred during some of the Middle Pleistocene interglacials accompanying the northern expansion of the temperate zone and biota. Mixed coniferous and broadleaf forests established in the tectonically active mountain zone with elevations of 1500–2000 m and parklands in the adjacent plains and continental basins provided a wide range of occupation habitats. There is limited evidence for persistence of Early Palaeolithic inhabitation during glacial stages due to inhospitable periglacial conditions. The last interglacial warming, indicated by re-colonization of southern Siberia by coniferous taiga forests, is linked with the appearance of the Mousterian tradition. Changes in the relief configuration influenced the local climate regime and opened new habitats for the Middle Palaeolithic population concentrated in the transitional zones of 500–1000 m elevation in the karstic area of the NW Altai foothills. Occupation of the central and southern Altai during the early last glacial was impeded by harsh, ice-marginal environments and expansion of glaciers in the valleys filled by large proglacial lakes. Progressive warming during the early mid-last glacial interstadial stage (59–35 ka BP) caused wasting of the ice fields accompanied by cataclysmic releases of ice-dammed lakes and large-scale erosional processes. Periodic outbursts of the glacial basins had a dramatic impact on the regional ecosystems, also obliterating the earlier cultural records. Appearance of the transitional early Late Palaeolithic stone industries reflects adaptation to mosaic interstadial habitats, including sub-alpine forest, dark coniferous forest, mixed parklands and open steppe. The identical geographical distribution of the Middle and Late Palaeolithic sites and the time-transgressive lithic technologies suggest a regional cultural (and biological?) continuity in the broader Altai area during the Late Pleistocene. Re-establishment of cold tundra–steppe and tundra–forest habitats correlates with the Late Palaeolithic horizon with developed stone industries dominated by blade-flaking techniques. These techniques possibly survived in more protected locations characterized by warm microclimates in the northern Altai throughout the last glacial maximum (20–18 ka BP). Emergence of the microlithic assemblages with wedge-shape cores is linked with a new cultural adjustment in the final stage of the Palaeolithic development responding to transformations of the former periglacial ecosystems towards the end of the Pleistocene.