Glaciological Research Articles

New perspectives on paleoglaciology

Paleoglaciology deals with glaciation cycles of the Quaternary Ice Age. It combines the dynamics of present-day ice sheets deduced from glaciology with the history of former ice sheets deduced from glacial geology. Cosmogenic dating now makes a detailed chronology of a cycle possible. Radiocarbon dating has provided a detailed chronology for Termination of the last cycle, but cannot date how the cycle began. Here we identify the central challenge in applying paleoglaciology to Quaternary glaciation cycles in general, and initiation of these cycles in particular. The challenge is the role of thickening sea ice in the Arctic Ocean, possibly becoming thick ice shelves floating over deep Arctic basins and high marine ice sheets grounded on shallow Arctic continental shelves. In that case, an Arctic Ice Sheet existed that was larger and less stable than the Antarctic Ice Sheet is now or in the past. Two approaches to this problem are presented as Part 1 and Part 2. In Part 1, the height of these former ice sheets is linked primarily to the strength of ice-bed coupling, which is deduced from glacial geology. It provides “snapshots” of ice sheets that give ice elevations independent of the past history and largely independent of ice-surface conditions, temperatures and the mass balance in particular. In Part 2, heights of former ice sheets depend on both their past history, particularly initial conditions, and changing surface conditions during the glaciation cycle. This provides a “motion picture” of ice sheets during the full cycle. The challenge is to establish a “mind meld” of these two approaches. They allow new perspectives on paleoglaciology.

Glacitectonics – a key approach to examining ice dynamics, substrate rheology and ice-bed coupling

The role of ice masses within the Earth's climate system and in landscape change is increasingly being recognised within regions that are either currently glaciated or were glaciated during the geological past. There are many different remote and field-based approaches to studying the products of glaciation. One approach – that of glacitectonics, focuses on the styles of deformation and tectonic imprint (folds, fractures, fabrics, foliations and lineations) produced as ice overrides or pushes into pre-existing rocks or sediment. This approach, when used in combination with other types of evidence, can be used to infer ice-dynamics, substrate rheology and ice-bed coupling. Of equal significance is the influence of glacitectonic structure upon the applied properties of glaciated terranes such as ground stability, hydrogeology and fluid migration (e.g. water, gas hydrates and hydrocarbons). This paper provides an introduction to this Special Issue on Glacitectonics, outlining the significance and historical development of this field of glacial geology, before introducing and summarising the contributions that make up the volume.

Glacial geology of North Lithuanian ice marginal ridge and surrounding plains

Glacial geology of North Lithuanian ice marginal ridge and surrounding plains

Late Pleistocene glacial stratigraphy of the Kumara-Moana region, West Coast of South Island, New Zealand

On the South Island of New Zealand, large piedmont glaciers descended from an ice cap on the Southern Alps onto the coastal plain of the West Coast during the late Pleistocene. The series of moraine belts and outwash plains left by the Taramakau glacier are used as a type section for interpreting the glacial geology and timing of major climatic events of New Zealand and also as a benchmark for comparison with the wider Southern Hemisphere. In this paper we review the chronology of advances by the Taramakau glacier during the last or Otira Glaciation using a combination of exposure dating using the cosmogenic nuclides 10Be and 36Cl, and tephrochronology. We document three distinct glacial maxima, represented by the Loopline, Larrikins and Moana Formations, separated by brief interstadials. We find that the Loopline Formation, originally attributed to Oxygen Isotope Chronozone 4, is much younger than previously thought, with an advance culminating around 24,900 ± 800 yr. The widespread late Pleistocene Kawakawa/Oruanui tephra stratigraphically lies immediately above it. This Formation has the same age previously attributed to the older part of the Larrikins Formation. Dating of the Larrikins Formation demonstrates there is no longer a basis for subdividing it into older and younger phases with an advance lasting about 1000 years between 20,800 ± 500 to 20,000 ± 400 yr. The Moana Formation represents the deposits of the last major advance of ice at 17,300 ± 500 yr and is younger than expected based on limited previous dating. The timing of major piedmont glaciation is restricted to between ∼25,000 and 17,000 yr and this interval corresponds to a time of regionally cold sea surface temperatures, expansion of grasslands at the expense of forest on South Island, and hemisphere wide glaciation.

The influence of ground disturbance and gap position on understory plant diversity in upland forests of southern New England

The forest understory contains the majority of vascular plant diversity in eastern temperate forests, and its diversity, composition, and dynamics contribute directly to ecosystem function. Forest managers have traditionally viewed the understory as primarily affecting forest regeneration or wildlife habitat, but the growing recognition of goods and services the understory provides (e.g., ecosystem function, ecological resiliency, non-timber forest products) has increased concerns about the impacts of forest management on understory diversity. We monitored response of understory diversity to microsite position and degree of ground-level disturbance within experimental gaps for 10years. We did this at four sites with distinct soil types and topographic positions of a glacial geology in southern New England that were categorized as (i) mesic, (ii) mid-slope, (iii) outwash, and (iv) sandy-skeletal. We analyzed differences in patterns of species richness, Shannon diversity, and evenness across sites and through time. Understory species richness was generally enhanced by gap formation. Gap position was the primary factor influencing species richness across all sites, but the patterns of diversity and evenness within gaps was site specific. Ground-disturbance was influential on drier sandy sites, and more pronounced earlier in the experiment. Temporal differences were also evident across sites, with richness stabilizing at all sites 10years after gap creation. The one exception was the sandy-skeletal site, which was still increasing in richness. Resource managers interested in protecting and enhancing understory species diversity need to consider underlying site, specifically soil type when planning silvicultural treatments, as the response of the understory community to disturbance can vary greatly with site.

Microbial Communities in Antarctic Subglacial Aquatic Environments

Glaciological processes under ice masses, including ice sheets, produce conditions favorable for microbes by forming subglacial aquatic environments (SAE) through basal melting and providing nutrients and energy for microbes from bedrock comminution. The abundance and interconnectivity of water beneath the Antarctic Ice Sheet, largely demonstrated through remote sensing techniques, indicates significant and varied SAE including lakes, saturated sediments and channelized and linked cavity drainage systems. Microbes have been detected in the two Antarctic SAE sampled to date; accreted ice from Vostok Subglacial Lake in East Antarctica and saturated till from beneath ice streams draining the West Antarctic Ice Sheet. Heterotrophic activity has been measured in these samples at temperatures close to freezing in the laboratory, demonstrating that in situ microbial activity in subglacial environments is plausible. Phylogenetic analysis of 16S rRNA gene sequences suggests that organisms with Fe and S oxidizing metabolisms may also be important members of the microbial community in these environments. This is consistent with the geochemistry of the accreted ice and till pore waters that indicates biologically driven sulfide oxidation coupled to carbonate and silicate mineral weathering as a significant solute source. Exploration of Antarctic SAE is in its infancy, and in a number of the unexplored SAE, the lack of connectivity between oxygenated surface waters and the subglacial environment and the extended water flow paths and water-rock residence times may lead to anoxic conditions. Such anoxic conditions would favor anaerobic microbial metabolisms similar to those documented in other deep terrestrial subsurface environments.

Siple Coast Subglacial Aquatic Environments: The Whillans Ice Stream Subglacial Access Research Drilling Project

The Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project is a 6-year (2009-2015) integrative study of ice sheet stability and subglacial geobiology in West Antarctica, funded by the Antarctic Integrated System Science Program of National Science Foundation's Office of Polar Programs, Antarctic Division. The overarching scientific objective of WISSARD is to assess the role of water beneath a West Antarctic Ice Stream in interlinked glaciological, geological, microbiological, geochemical, hydrological, and oceanographic systems. The WISSARD's important science questions relate to (1) the role that subglacial and ice shelf cavity waters and wet sediments play in ice stream dynamics and mass balance, with an eye on the possible future of the West Antarctic Ice Sheet and (2) the microbial metabolic and phylogenetic diversity in these subglacial environments. The study area is the downstream part of the Whillans Ice Stream on the Siple Coast, specifically Subglacial Lake Whillans and the part of the grounding zone across which it drains. In this chapter, we provide background on the motivation for the WISSARD project, detail the key scientific goals, and describe the new measurement tools and strategies under development that will provide the framework for conducting an unprecedented range of scientific observations.

10Be exposure age constraints on the Late Weichselian ice‐sheet geometry and dynamics in inter‐ice‐stream areas, western Svalbard

The Late Weichselian ice sheet of western Svalbard was characterized by ice streams and inter‐ice‐stream areas. To reconstruct its geometry and dynamics we investigated the glacial geology of two areas on the island of Prins Karls Forland and the Mitrahalvøya peninsula. Cosmogenic 10Be surface exposure dating of glacial erratics and bedrock was used to constrain past ice thickness, providing minimum estimates in both areas. Contrary to previous studies, we found that Prins Karls Forland experienced a westward ice flux from Spitsbergen. Ice thickness reached >470 m a.s.l., and warm‐based conditions occurred periodically. Local deglaciation took place between 16 and 13 ka. At Mitrahalvøya, glacier ice draining the Krossfjorden basin reached >300 m a.s.l., and local deglaciation occurred at c. 13 ka. We propose the following succession of events for the last deglaciation. After the maximum glacier extent, ice streams in the cross‐shelf troughs and fjords retreated, tributary ice streams formed in Forlandsundet and Krossfjorden, and, finally, local ice caps were isolated over both Prins Karls Forland and Mitrahalvøya and their adjacent shelves.

Glacial geology: Ice sheets and landforms, 2nd edition, by Matthew R. Bennett and Neil F.Glasser. Wiley‐Blackwell, Chichester, UK, 2009. No. of pages: xiii + 385. (paperback). ISBN: 978‐0‐470‐51691‐1

Glacial geology: Ice sheets and landforms, 2nd edition, by Matthew R. Bennett and Neil F.Glasser. Wiley‐Blackwell, Chichester, UK, 2009. No. of pages: xiii + 385. (paperback). ISBN: 978‐0‐470‐51691‐1

Palaeoglaciology of Bayan Har Shan, NE Tibetan Plateau: exposure ages reveal a missing LGM expansion

The Bayan Har Shan, a prominent upland area in the northeastern sector of the Tibetan Plateau, hosts an extensive glacial geological record. To reconstruct its palaeoglaciology we have determined 10Be exposure ages based on 67 samples from boulders, surface pebbles, and sediment sections in conjunction with studies of the glacial geology (remote sensing and field studies) and numerical glacier modelling. Exposure ages from moraines and glacial sediments in Bayan Har Shan range from 3 ka to 129 ka, with a large disparity in exposure ages for individual sites and within the recognised four morphostratigraphical groups. The exposure age disparity cannot be explained by differences in inheritance without using unrealistic assumptions but it can be explained by differences in post-depositional shielding which produces exposure ages younger than the deglaciation age. We present a palaeoglaciological time-slice reconstruction in which the most restricted glaciation, with glaciers less than 10 km long, occurred before 40–65 ka. More extensive glaciations occurred before 60–100 ka and 95–165 ka. Maximum glaciation is poorly constrained but probably even older. The Bayan Har Shan exposure age dataset indicates that glaciers on the northeastern Tibetan Plateau have remained surprisingly restricted for at least 40 ka, including the global last glacial maximum (LGM). This case of a missing LGM is further supported by high-resolution glacier modelling experiments.

Sublimation and surface energy budget of Taylor Glacier, Antarctica

AbstractTaylor Glacier, an outlet of the East Antarctic ice sheet, flows through the Transantarctic Mountains and terminates in the Dry Valleys. Understanding how this glacier fluctuates is important for studies of glacial geology, paleoclimate, ice dynamics and ecology. Sublimation is the primary mass-loss process for most of the glacier. Four years of specific balance measurements from the ablation zone show sublimation rates up to 40 cm a−1. We used data from an array of weather stations as inputs to a model for latent heat flux and hence sublimation rate. Calculated and measured ablation rates agree to within uncertainties, indicating that wind speed and vapour pressure gradient (a function of temperature and humidity) are the governing variables, as expected from theory. Measurements and model results together allowed us to examine the spatial and temporal variations of sublimation on the glacier. On average, sublimation is about two times faster in summer than winter. Rapid sublimation occurs during storms and katabatic wind events, but such periods contribute less to the annual total than do slow, persistent losses. Spatially, sublimation reaches a maximum midway along the glacier, where descending surface air currents are focused by the topography of the aptly named tributary, Windy Gully.

M. R. Bennett & N. F. Glasser 2009. Glacial Geology. Ice Sheets and Landforms, 2nd ed. xii + 385 pp. Wiley-Blackwell. Price £85.00, €97.80, US $129.95 (hard covers); £29.95, €34.50, US$ 54.95 (paperback). ISBN 978 0 470 51690 4; 978 0 470 51691 1 (pb).

M. R. Bennett & N. F. Glasser 2009. Glacial Geology. Ice Sheets and Landforms, 2nd ed. xii + 385 pp. Wiley-Blackwell. Price £85.00, €97.80, US 54.95 (paperback). ISBN 978 0 470 51690 4; 978 0 470 51691 1 (pb). - Volume 147 Issue 6

History of ice sheet elevation in East Antarctica: Paleoclimatic implications

Abstract The multi-disciplinary study of past ice surface elevations in the Grove Mountains of interior East Antarctica provides direct land-based data on the behavior of the East Antarctic Ice Sheet since the Pliocene. The glacial geology, the ages of cold desert soils, the depositional environment of younger moraine sedimentary boulders and their spore–pollen assemblages combine to imply a possible significant shrinkage of the Ice Sheet before the Middle Pliocene Epoch, with the Ice Sheet margin retreating south of the Grove Mountains (∼ 450 km south from its present coastal position). Exposure age measurements of bedrock indicate that the elevation of the ice surface in the Grove Mountains region subsequently rose at about mid-Pliocene to at least 200 m higher than today's levels. The ice surface then progressively lowered, with some minor fluctuations. Middle to Late Pleistocene exposure ages found on the lowest samples, at the ice/bedrock contact line, indicate a long period with ice surface elevations kept at the current level or complex fluctuation history during the Quaternary Epoch.

Life, death and afterlife of the extrusion flow theory

Abstract‘Extrusion flow’ describes any velocity field where maximum horizontal velocity occurs below the surface. By 1914, viscous flow and basal sliding over rough beds were accepted concepts. Between the world wars, there was little communication between naturalists describing complicated ice sheets, and physicists studying fundamental processes controlling flow. Max Demorest brought concepts from mechanics into glaciology and glacial geology; however, his extrusion flow theory, to explain how ice flowed out of central Greenland, overlooked force imbalance. Rudolf Streiff-Becker found an apparent large imbalance between ice flux discharged through a gate and net accumulation in the upstream catchment at Claridenfirn, Switzerland. Because he underestimated uncertainty in ice depth, he had to propose a strong undercurrent (extrusion flow) to evacuate the excess mass. Reassessment of his assumptions shows that extrusion was actually unnecessary. However, confluence of two lines of evidence for extrusion flow added stature to the concept. In 1952, John Nye showed that free extrusion flow was impossible due to force imbalance. Two forms of extrusion flow survive: capped extrusion flow is possible on local scales where longitudinal stress gradients allow upper ice to move slowly, and rigid- body rotational flow can allow deeper ice to move faster without strain.

Digital surface models and the landscape: interaction between bedrock and glacial geology in the Ullapool area

Synopsis The front cover image for this volume is a hill-shaded digital surface model (DSM) of the Ullapool area, created using NEXTMap Britain elevation data from Intermap Technologies. This is a classic area for bedrock geology, transected by the Moine Thrust Zone, and in recent years it has also been studied in detail for its glacial history. Perhaps equally important, this is one of Scotland's most iconic landscapes. The geology of the area comprises a number of distinct sequences, each of which has a characteristic landscape expression as illustrated by the DSM. This paper considers the influence of the bedrock geology on the glacial geomorphology, and shows that the interplay of the two has led to the development of the different landscape elements of this spectacular area. Surprisingly, it is not always the major geological features – such as the Moine Thrust – that have the strongest topographic expression.

Lateglacial ice-cap dynamics in NW Scotland: evidence from the fjords of the Summer Isles region

The seaboard of western Scotland is a classic fjord landscape formed by glaciation over at least the last 0.5 Ma. We examine the glacial geology preserved in the fjords (or sea lochs) of the Summer Isles region of NW Scotland using high-resolution seismic data, multibeam swath bathymetry, seabed sediment cores, digital terrain models, aerial photographs, and field investigations. Detailed analyses include seismic facies and lithofacies interpretations; sedimentological and palaeoenvironmental analyses; and radiocarbon dating of selected microfauna. Our results indicate that the Pleistocene sediments of the Summer Isles region, on- and offshore, can be subdivided into several lithostratigraphic formations on the basis of seismic character, geomorphology and sedimentology. These are: subglacial tills; ice-distal and glacimarine facies; ice-proximal and ice-contact facies; moraine assemblages; and Holocene basin fill. The submarine landscape is also notable for its large-scale mass-movement events – the result of glaciodynamic, paraglacial or seismotectonic processes. Radiocarbon dating of marine shells indicate that deglaciation of this part of NW Scotland was ongoing between 14 and 13 ka BP – during the Lateglacial Interstadial (Greenland Interstadial 1) – consistent with cosmogenic surface-exposure ages from previous studies. A sequence of numerous seafloor moraine ridges charts oscillatory retreat of the last ice sheet from a buoyant calving margin in The Minch to a firmly grounded margin amongst the Summer Isles in the early part of Lateglacial Interstadial (GI-1) (pre-14 ka BP). Subsequent, punctuated, frontal retreat of the ice mass occurred in the following ∼1000 years, during which time ice-cap outlet glaciers became topographically confined and restricted to the fjords. A late-stage readvance of glaciers into the inner fjords occurred soon after 13 ka BP, which calls into question the accepted limits of ice extent during the Younger Dryas Stadial (Greenland Stadial 1). We examine the wider implications of our chronostratigraphic model, discussing the implications for British Ice Sheet deglaciation, Lateglacial climate change, and the style and rates of fjord sedimentation.

Palaeoglaciation of Bayan Har Shan, northeastern Tibetan Plateau: glacial geology indicates maximum extents limited to ice cap and ice field scales

AbstractKey locations within an extensive area of the northeastern Tibetan Plateau, centred on Bayan Har Shan, have been mapped to distinguish glacial from non‐glacial deposits. Prior work suggests palaeo‐glaciers ranging from valley glaciers and local ice caps in the highest mountains to a regional or even plateau‐scale ice sheet. New field data show that glacial deposits are abundant in high mountain areas in association with large‐scale glacial landforms. In addition, glacial deposits are present in several locations outside areas with distinct glacial erosional landforms, indicating that the most extensive palaeo‐glaciers had little geomorphological impact on the landscape towards their margins. The glacial geological record does indicate extensive maximum glaciation, with local ice caps covering entire elevated mountain areas. However, absence of glacial traces in intervening lower‐lying plateau areas suggests that local ice caps did not merge to form a regional ice sheet on the northeastern Tibetan Plateau around Bayan Har Shan. No evidence exists for past ice sheet glaciation. Copyright © 2009 John Wiley & Sons, Ltd.

Glacial geology and chronology of Bishop Creek and vicinity, eastern Sierra Nevada, California

The valley of Bishop Creek, which drains part of the eastern flank of the Sierra Nevada, California, contains an unusually well-preserved set of middle to late Quaternary moraines. These deposits have been mapped by previous investigators, but they have not been quantitatively dated. We used the accumulation of cosmogenic 36 Cl to assign a chronology to the maximal glacial positions mapped in the valley. Our results indicate that the terminal moraines mapped by previous investigators as Tahoe were all deposited between ca. 165 and ca. 135 ka, during marine isotope stage (MIS) 6. Moraines mapped as Tioga were deposited between 28 and 14 ka, during MIS 2. These can be subdivided into Tioga 1 (28–24 ka), Tioga 3 (18.5–17.0 ka), and Tioga 4 (16.0–14.5 ka) advances (no moraines dated to Tioga 2 [21–19 ka] were found, presumably because the Tioga 3 advance either overrode or fluvially eroded them). At 15.0–14.5 ka, the Tioga 4 glacier retreated abruptly to the crest of the range. This was followed by the brief and fairly minor Recess Peak advance at ca. 13.4 ka. No Holocene advances extended beyond the very restricted limits of ice during the Matthes (Little Ice Age) advance. All preserved terminal moraines at lower elevations were deposited during either the Tahoe or Tioga stades. The Tahoe terminal moraines are extensive and voluminous, whereas the Tioga moraines are relatively narrow and have small volumes. However, this notable difference may be more a result of idiosyncrasies in the local glacial history than the result of differences in the length or intensity of glaciation between the two glacial episodes. The history of glacial advances at Bishop Creek exhibits a strong correspondence to global climate cycles, and to paleoclimate events in the North Atlantic in particular.

Progress and Prospect of Ice Radar in Investigating and Researching Antarctic Ice Sheet

The Antarctic ice sheet is the largest continental ice on the earth and its mass budget and stability has an important influence on global climate change and sea level rise.Ice radar,or radio-echo sounding(RES),constitutes the principal means by which glaciologists investigate the subsurface properties of the Antarctic ice sheet.In the past fifty years,ice radar has been widely applied to measure ice sheet thickness,internal structure and subglacial morphology.These parameters are fundamental for the calculation of ice volume and mass balance as well as the reconstruction of past snow accumulation and melting rates,ice dynamics and deposition process.Now,RES has covered most regions in Antarctica and provided significant understanding of the interactions between ice sheet and global system.We briefly introduced ice radar and its technical development firstly and then mainly reviewed the progress of ice radar in investigating and researching Antarctic ice sheet thickness and subglacial topography,internal reflecting horizons,subglacial lakes and water systems,subglacial bedrock roughness and crystal orientation fabrics(COF).Finally,the prospect of ice radar in investigating and researching Antarctic ice sheet in the future and our present situation was proposed.

Quaternary glaciation of Muztag Ata and Kongur Shan: Evidence for glacier response to rapid climate changes throughout the Late Glacial and Holocene in westernmost Tibet

The glacial geology of two massifs, Muztag Ata and Kongur Shan, in western Tibet was examined to help define the timing and style of glaciation in the semiarid regions of western Tibet. Remote sensing, geomorphic mapping, and 10Be terrestrial cosmogenic nuclide (TCN) surface-exposure dating of boulders on the moraines and sediment in depth profiles show that glaciers advanced at least 12 times during at least the last two glacial cycles. Over this time, the style of glaciation changed progressively from one that produced ice caps to one that produced less extensive and more deeply entrenched valley glaciers. The timing of the two earliest glaciations is poorly defined, but they likely occurred prior to the penultimate glacial cycle (the Karasu glacial stage) and the early part of the last glacial cycle or during the penultimate glacial cycle (the Subaxh glacial stage). In contrast, the timing of later glacial advances (the Olimde glacial stage) is relatively well defined showing quasiperiodical oscillations on millennial time scales (17.1 ± 0.3 ka, 13.7 ± 0.5 ka, 11.2 ± 0.1 ka, 10.2 ± 0.3 ka, 8.4 ± 0.4 ka, 6.7 ± 0.2 ka, 4.2 ± 0.3 ka, 3.3 ± 0.6 ka, 1.4 ± 0.1 ka, and a few hundred years before the present). These data suggest that since the global Last Glacial Maximum (LGM), the glaciers in western Tibet likely responded to Northern Hemisphere climate oscillations (rapid climate changes), with minor influences from the south Asian monsoon. This study provides the first well-defined glacial geologic evidence to suggest that glaciers in western Tibet respond to rapid climate changes on millennial time scales throughout the Late Glacial and Holocene.