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The advance of the Cordilleran Ice Sheet (CIS) towards its Last Glacial Maximum (LGM) configuration and its subsequent retreat remain poorly understood. We use the glacial landform record to determine ice dynamics for the central sector of the CIS in northern British Columbia, Canada, beneath the LGM ice divide. We classify seventy ice-flow indicator flowsets based on morphology, elevation, orientation and cross-cutting relationships into one of three stages, whereby stage 1 is oldest and stage 3 youngest. Combined with ice-contact geomorphology, our reconstruction highlights complex changes in ice flow over time as a result of ice divide migrations through the LGM and deglacial phases. The orientation and distribution of landforms indicates active post-LGM ice retreat westward through the Cassiar and Omineca mountains. We map the regional distribution of independent mountain glaciers, ice caps, and ice fields that regrew during a cooling event in the Late Glacial and show that some of these readvance glaciers were subsequently overrun by advancing outlet glaciers of the CIS. We use the cross-cutting relationship between readvance glaciers and CIS outlet glaciers and available chronological data to reconstruct the eastern CIS margin during the Late Glacial for the first time.Key words: Pleistocene, paleoglaciology, North America, glacial geomorphology.

The Marine Isotope Substage 11c (MIS11c) interglacial (425 – 395 thousand years before present) is a useful analogue to climate conditions that can be expected in the near future, and can provide insights on the natural response of the Antarctic ice sheets to a moderate, yet long lasting warming period. However, its response to the warming of MIS11c and consequent contribution to global sea level rise still remains unclear. We explore the dynamics of the Antarctic ice sheets during this period using a numerical ice-sheet model forced by MIS11c climate conditions derived from climate model outputs scaled by three ice core and one sedimentary proxy records of ice volume. We identify a tipping point beyond which oceanic warming becomes the dominant forcing of ice-sheet retreat, and where collapse of the West Antarctic Ice Sheet is attained when a threshold of 0.4 oC oceanic warming relative to Pre-Industrial levels is sustained for at least 4 thousand years. Conversely, its eastern counterpart remains relatively stable, as it is mostly grounded above sea level. Our results suggest a total sea level contribution from the East and West Antarctic ice sheets of 4.0 – 8.2 m during MIS11c. In the case of a West Antarctic Ice Sheet collapse, which is the most probable scenario according to far-field sea-level reconstructions, this range is reduced to 6.7 – 8.2 m, and mostly reflects uncertainties regarding the initial configuration of the East Antarctic Ice Sheet.

Studying the response of the Antarctic ice sheets to past climate conditions similar to the present day can provide important insights for understanding its current changes and help identify natural drivers of ice sheet retreat. The Marine Isotope Substage 11c (MIS11c) interglacial is one of the best candidates for an in-depth analysis given that at its later portion orbital parameters were close to our current interglacial. However, Antarctic ice core data indicate that although MIS11c CO2 levels were close to Pre Industrial, warmer-than-present temperatures (of about 2 °C) lasted for much longer than during other interglacials. Since the global mean sea level is thought to have been 6‐13 m higher than today, there should have been some contribution from Antarctica. While substantial work has been conducted regarding the response of the Greenland Ice Sheet to the MIS11c climate, which is believed to have contributed with 3.9–7.0 m to global sea level, both configurations of the Antarctic ice sheets and their contribution to sea level rise remain poorly constrained. We use a numerical ice-sheet model to shed light on the response of the Antarctic ice sheets to MIS11c climate conditions obtained from a combination of a suite of Antarctic ice cores and the LR04 global stack of deep-sea sediment records and climate model outputs, while assessing the model sensitivity to the uncertainties in sea level reconstructions, ice sheet initial configuration, and multi-centennial climate variability. We found that the regional climate signal of the MIS11c peak warming in Antarctica captured by the ice core records is necessary for the recorded sea level highstand to be reproduced, and that warming length was more important than magnitude. However, there is a threshold for a West Antarctic Ice Sheet collapse that lies within an envelope of 1.6 and 2.1 °C warmer-than-pre-industrial regional climate conditions. Sea level forcing and multi-centennial variability were found to have played virtually no role in driving ice sheet contraction, but the choice of initial configuration of the East Antarctic Ice Sheet provided a large source of uncertainty in the quantification of MIS11c Antarctic peak sea level contribution, which falls between 6.4 and 8.8 m.

Landscape system components interact in ways which are not yet fully understood, and in tectonically active regions it is of particular interest whether endogenic or exogenic factors are the main drivers of landscape evolution. For example, fluvial terraces may form in response to exogenic disturbances like climatic changes or to endogenic forces like tectonic uplift. This study explores how temporal and spatial correlations between end moraines (denoting the advance of glaciers due to climate change) and fluvial terraces can yield insights about exogenic-endogenic processes determining landscape evolution during the Quaternary on the southern margin of the Shaluli Shan plateau, SE Tibet, a formerly glaciated and tectonically active region. A high-resolution TanDEM-X Digital Elevation Model (12 m) was used to produce detailed geomorphological maps of glacial valleys, marginal moraines, glacial lineations, and fluvial terraces. The geomorphological mapping was complemented with geomorphological and sedimentological field observations. Samples for Optically Stimulated Luminescence dating were taken from extensive and distinct terraces located in pull-apart basins bordering the plateau and samples for cosmogenic nuclide exposure dating were collected from selected boulders on end moraines formed by valley glaciers draining the Mt Genie massif on the Shaluli Shan plateau. Infrared stimulated luminescence (IRSL) signals from feldspar multi grains aliquots, and 10Be and 26Al concentrations from quartz, were used to determine depositional ages of terraces and moraines, respectively. In combining both dating techniques, we compare the timing of glacial expansions with the depositonal ages of the terraces to tease out the effects of exogenic and endogenic drivers on terrace formation and to formulate a conceptual model of landscape evolution.

Reconstructing past ice surface changes is key to test and improve ice-sheet models. Yet, data constraining the past behaviour of the East Antarctic Ice Sheet are sparse, limiting our understanding of its response to past and future climate changes. Here, we attempt to test whether the ice-sheet margin in western Dronning Maud Land has thinned since the last glacial maximum or whether it perhaps thickened in places due to increased precipitation associated with warmer climates. We report cosmogenic multi-nuclide (10Be, 26Al, 36Cl, 21Ne) data from bedrock and erratics on nunataks along Jutulstraumen ice stream and the Penck Trough in western Dronning Maud Land, East Antarctica. Spanning elevations between 751-2387 m above sea level, and between 5 and 450 m above the contemporaneous local ice sheet surface, the samples record apparent exposure ages between 2 ka and 5 Ma. The highest bedrock sample indicates (near-) continuous exposure since at least the Pliocene, with a very low apparent erosion rate of 15±3 cm Ma-1. However, there are also clear indications of a thicker-than-present ice sheet within the last glacial cycle, thinning ~35-120 m at several nunataks during the Holocene (~2-11 ka). Owing to difficulties in retrieving suitable sample material from the often rugged and quartz-poor mountain summits, and due to the presence of inherited nuclides in many of our samples, we are unable to present robust thinning estimates from elevational profiles. Nevertheless, the results clearly indicate ice-surface fluctuations of several hundred meters within the last glacial cycle in this sector of the EAIS, between the current grounding line and the edge of the polar plateau. Finally, inverse modelling of the cosmogenic multi-nuclide inventories in bedrock yields estimates of total erosion and ice cover across multiple glacial cycles. Our results show that the EAIS in western Dronning Maud Land was thicker than present during most of the Quaternary, covering sample sites up to 200 m above the present-day ice sheet for ~80 % of this period. Thinning of the ice since the last glacial maximum, combined with a long-term record of thicker-than-present ice, indicate that the ice sheet below the polar plateau in western Dronning Maud Land generally expands and thickens during climate cooling, despite decreasing precipitation associated with a cooler Southern Ocean.

We use a domain-wide geomorphometric analysis to investigate spatial patterns of glacial landforms. We focus or analysis on glacial depositional landforms (e.g. marginal moraines), as well as larger erosional landforms (e.g. glacial valleys), because our aim is to quantify long-term and time-integrated glaciation patterns. Our area of interest includes two large orogens in Central Asia; the Tian Shan and Altai mountains, both located in the continental interior of Central Asia. Our analysis is crucial as it can reveal the importance of 1) topographic barriers, 2) precipitation gradients and 3) rain-shadow effects on former glaciation patterns. We focus our analysis on six different physiographic regions (n=6), defined by major drainage divides, as well as for formerly glaciated catchments (n=21)—selected because they are intersected by cosmogenic-nuclide glacial-chronological datasets. We mine published datasets on the distribution of glaciers and glacial landforms, and use these datasets, together with freely available digital elevation models, to extract landform-specific hypsometric (area—elevation) distributions. Hypsometric peaks for modern glaciers (i.e. median glacier elevations) show pronounced spatial gradients; increasing elevations from the northern to the southern Tian Shan, and increasing median elevations from the northern to both the southeastern and southwestern Altai Mountains. This is interpreted to reflect topographic barrier effects and decreasing modern precipitation rates (i.e. increasing continentality), as a result of a weakening of the Mid-latitude Westerlies, across the main axes of the two mountain systems. A similar pattern can be observed in the paleorecord; reconstructed long-term and time-integrated glaciation patterns, also show pronounced spatial gradients, equivalent to modern median glacier elevation patterns. This observation indicates that during former periods of glaciation, maximum paleoglacier extents—reconstructed by delineating the extent of glacial depositional and erosional landforms (formed over one-to-several glacial cycles, over >100 thousand years)—were correspondingly controlled by a westerly-sourced moisture supply, and was thus affected by precipitation patterns similar to those of today.

Paleoglaciological data is a crucial source of information towards insightful paleoclimate reconstructions by providing vital boundary conditions for regional and global climate models. In this context, the Third Pole Environment is considered a key region because it is highly sensitive to global climate change and its many glaciers constitute a diminishing but critical supply of freshwater to downstream communities in SE Asia. Despite its importance, extents of past glaciation on the Tibetan Plateau remain poorly documented or controversial largely because of the lack of well define glacial chronostratigraphies and reconstructions of former glacier extent. This study contributes to a better documentation of the extent and improved resolution of the timing of past glaciations on the southeastern margin of the Tibetan Plateau. We deploy a high-resolution TanDEM-X Digital Elevation Model (12 m resolution) to produce maps of glacial and proglacial fluvial landforms in unprecedented detail. Geomorphological and sedimentological field observations complement the mapping while cosmogenic nuclide exposure dating of quartz samples from boulders on end moraines detail the timing of local glacier expansion. Additionally, samples for optically stimulated luminescence dating were taken from extensive and distinct terraces located in pull-apart basins downstream of the end moraines to determine their formation time. We compare this new dataset with new and published electron spin resonance ages from terraces. Temporal coherence between the different chronometers strengthens the geochronological record while divergence highlights limitations in the applicability of the chronometers to glacial research or in our conceptual understanding of landscape changes in tectonic regions. Results highlight our current understanding of paleoglaciation, landscape development, and paleoclimate on the SE Tibetan Plateau.

In low relief Precambrian gneiss terrain in eastern Sweden, abraded bedrock surfaces were ripped apart by the Fennoscandian Ice Sheet. The resultant boulder spreads are covers of large, angular boulders, many with glacial transport distances of 1–100 m. Boulder spreads occur alongside partly disintegrated roches moutonnées and associated fracture caves, and are associated with disrupted bedrock, which shows extensive fracture dilation in the near surface. These features are distributed in ice-flow parallel belts up to 10 km wide and extend over distances of >500 km. Our hypothesis is that the assemblage results from (1) hydraulic jacking and bedrock disruption, (2) subglacial ripping and (3) displacement, transport and final deposition of boulders. Soft sediment fills indicate jacking and dilation of pre-existing bedrock fractures by groundwater overpressure below the ice sheet. Overpressure reduces frictional resistance along fractures. Where ice traction overcomes this resistance, the rock mass strength is exceeded, resulting in disintegration of rock surfaces and ripping apart into separate blocks. Further movement and deposition create boulder spreads and moraines. Short boulder transport distances and high angularity indicate that glacial ripping operated late in the last deglaciation. The depths of rock mobilized in boulder spreads are estimated as 1–4 m. This compares with 0.6–1.6 m depths of erosion during the last glaciation derived from cosmogenic nuclide inventories of samples from bedrock surfaces without evidence of disruption. Glacially disrupted and ripped bedrock is also made ready for removal by future ice sheets. Hence glacial ripping is a highly effective process of glacial erosion.

Quantifying glacial erosion contributes to our understanding of landscape evolution and topographic relief production in high altitude and high latitude areas. Combining in situ Be-10 and Al-26 ana ...

Spanning the northern sector of High Asia, the Altai region contains a rich landform record of glaciation. We report the extent, chronologies, and dynamics of two paleoglaciers on opposite flanks of the Ikh Turgen mountains (In Russian: Chikhacheva Range), straddling the border between Russia and Mongolia, using a combination of remote sensing-based glacial geomorphological mapping, 10Be surface exposure dating, and geomorphometric analysis. On the eastern side (Mongolia), the Turgen-Asgat paleoglacier, with its potential for developing a large accumulation area (∼257 km2), expanded 40 km down valley, and mean ages from a latero-frontal moraine indicate deglaciation during marine oxygen isotope stage (MIS) 3 (45.1 ± 1.8 ka, n = 4) and MIS 2 (22.8 ± 3.3 ka, n = 5). These minimum age constraints are consistent with other 10Be glacial chronologies and paleoclimate records from the region, which indicates glacier culmination during cold and wet conditions coinciding with MIS 3 (piedmont-style glaciation; inferred for a few sites across the region) and glacier culmination during cold and dry conditions coinciding with MIS 2 (mainly valley-style glaciation; inferred from several sites across the region). On the western side (Russia), the Boguty paleoglacier had a smaller accumulation area (∼222 km2), and advanced 30 km down valley across a low gradient forefield. Surface exposure ages from two moraine complexes on this side of the mountains exhibit wide scatter (∼14–53 ka, n = 8), making paleoclimate inferences and comparison to other proxies difficult. Ice surface profile reconstructions imply that the two paleoglaciers likely shared an ice divide.

Previous investigations observed a period of major glacial advances in Central Asia during marine oxygen isotope stage (MIS) 3 (57-29 ka), out of phase with global ice volume records. We have re-ex ...

To provide a new reconstruction of the deglaciation of the Fennoscandian Ice Sheet, in the form of calendar-year time-slices, which are particularly useful for ice sheet modelling, we have compiled and synthesized published geomorphological data for eskers, ice-marginal formations, lineations, marginal meltwater channels, striae, ice-dammed lakes, and geochronological data from radiocarbon, varve, optically-stimulated luminescence, and cosmogenic nuclide dating. This is summarized as a deglaciation map of the Fennoscandian Ice Sheet with isochrons marking every 1000 years between 22 and 13 cal kyr BP and every hundred years between 11.6 and final ice decay after 9.7 cal kyr BP. Deglaciation patterns vary across the Fennoscandian Ice Sheet domain, reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins. For example, the ice sheet margin in the high-precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and other ice-marginal deposits in many fjords and coastal valleys. Retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern Sweden and rapid retreat of the calving ice margin in the Baltic Basin. Our reconstruction is consistent with much of the published research. However, the synthesis of a large amount of existing and new data support refined reconstructions in some areas. For example, the LGM extent of the ice sheet in northwestern Russia was located far east and it occurred at a later time than the rest of the ice sheet, at around 17–15 cal kyr BP. We also propose a slightly different chronology of moraine formation over southern Sweden based on improved correlations of moraine segments using new LiDAR data and tying the timing of moraine formation to Greenland ice core cold stages. Retreat rates vary by as much as an order of magnitude in different sectors of the ice sheet, with the lowest rates on the high-elevation and maritime Norwegian margin. Retreat rates compared to the climatic information provided by the Greenland ice core record show a general correspondence between retreat rate and climatic forcing, although a close match between retreat rate and climate is unlikely because of other controls, such as topography and marine versus terrestrial margins. Overall, the time slice reconstructions of Fennoscandian Ice Sheet deglaciation from 22 to 9.7 cal kyr BP provide an important dataset for understanding the contexts that underpin spatial and temporal patterns in retreat of the Fennoscandian Ice Sheet, and are an important resource for testing and refining ice sheet models. Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Cosmogenic exposure dating of glacial boulders is commonly used to estimate the timing of past glaciations because the method enables direct dating of the duration a boulder has been exposed to cos ...

Reconstructing past ice-sheet surface changes is key to testing and improving ice-sheet models. Data constraining the past behaviour of the East Antarctic Ice Sheet are sparse, limiting our understanding of its response to past, present and future climate change. Here, we report the first cosmogenic multi-nuclide (10Be, 26Al, 36Cl) data from bedrock and erratics on nunataks along the Jutulstraumen and Penck Trough ice streams in western Dronning Maud Land, East Antarctica. Spanning elevations between 741 and 2394 m above sea level, the samples have apparent exposure ages between 2 ka and 5 Ma. The highest-elevation bedrock sample indicates (near-) continuous minimum exposure since the Pliocene, with a low apparent erosion rate of 0.15 ± 0.03 m Ma−1, which is similar to results from eastern Dronning Maud Land. In contrast to studies in eastern Dronning Maud Land, however, our data show clear indications of a thicker-than-present ice sheet within the last glacial cycle, with a thinning of ∼35–120 m during the Holocene (∼2–11 ka). Difficulties in separating suitable amounts of quartz from the often quartz-poor rock-types in the area, and cosmogenic nuclides inherited from exposure prior to the last deglaciation, prevented robust thinning estimates from elevational profiles. Nevertheless, the results clearly demonstrate ice-surface fluctuations of several hundred meters between the current grounding line and the edge of the polar plateau for the last glacial cycle, a constraint that should be considered in future ice-sheet model simulations.

Geomorphological mapping is a well-established method for examining earth surface processes and landscape evolution in a range of environmental contexts. In glacial research, it provides crucial data for a wide range of process-oriented studies and palaeoglaciological reconstructions; in the latter case providing an essential geomorphological framework for establishing glacial chronologies. In recent decades, there have been significant developments in remote sensing and Geographical Information Systems (GIS), with a plethora of high-quality remotely-sensed datasets now (often freely) available. Most recently, the emergence of unmanned aerial vehicle (UAV) technology has allowed sub-decimetre scale aerial images and Digital Elevation Models (DEMs) to be obtained. Traditional field mapping methods still have an important role in glacial geomorphology, particularly in cirque glacier, valley glacier and icefield/ice-cap outlet settings. Field mapping is also used in ice sheet settings, but often takes the form of necessarily highly-selective ground-truthing of remote mapping. Given the increasing abundance of datasets and methods available for mapping, effective approaches are necessary to enable assimilation of data and ensure robustness. This paper provides a review and assessment of the various glacial geomorphological methods and datasets currently available, with a focus on their applicability in particular glacial settings. We distinguish two overarching ‘work streams’ that recognise the different approaches typically used in mapping landforms produced by ice masses of different sizes: (i) mapping of ice sheet geomorphological imprints using a combined remote sensing approach, with some field checking (where feasible); and (ii) mapping of alpine and plateau-style ice mass (cirque glacier, valley glacier, icefield and ice-cap) geomorphological imprints using remote sensing and considerable field mapping. Key challenges to accurate and robust geomorphological mapping are highlighted, often necessitating compromises and pragmatic solutions. The importance of combining multiple datasets and/or mapping approaches is emphasised, akin to multi-proxy approaches used in many Earth Science disciplines. Based on our review, we provide idealised frameworks and general recommendations to ensure best practice in future studies and aid in accuracy assessment, comparison, and integration of geomorphological data. These will be of particular value where geomorphological data are incorporated in large compilations and subsequently used for palaeoglaciological reconstructions. Finally, we stress that robust interpretations of glacial landforms and landscapes invariably requires additional chronological and/or sedimentological evidence, and that such data should ideally be collected as part of a holistic assessment of the overall glacier system.

An important constraint on the reliability of cosmogenic nuclide exposure dating is the rigorous determination of production rates. We present a new dataset for Be-10 production rate calibration from Mount Billingen, southern Sweden, the site of the final drainage of the Baltic Ice Lake, an event dated to 11,620 +/- 100 cal yr BP. Five samples of flood-scoured bedrock surfaces (58.5 degrees N, 13.7 degrees E, 105-120 m a.s.I.) unambiguously connected to the drainage event yield a reference Be-10 production rate of 4.19 +/- 0.20 atoms g(-1) yr(-1) for the CRONUS-Earth online calculator Lm scaling and 4.02 +/- 0.18 atoms g(-1) yr(-1) for the nuclide specific LSDn scaling. We also recalibrate the reference Be-10 production rates for four sites in Norway and combine three of these with the Billingen results to derive a tightly clustered Scandinavian reference Be-10 production rate of 4.13 +/- 0.11 atoms g(-1) yr(-1) for the CRONUS Lm scaling and 3.95 +/- 0.10 atoms g(-1) yr(-1) for the LSDn scaling scheme. (C) 2015 Elsevier B.V. All rights reserved. (Less)

The Eurasian ice sheet complex (EISC) was the third largest ice mass during the Last Glacial Maximum with a span of over 4500 km and responsible for around 20 m of eustatic sea-level lowering. Whilst recent terrestrial and marine empirical insights have improved understanding of the chronology, pattern and rates of retreat of this vast ice sheet, a concerted attempt to model the deglaciation of the EISC honouring these new constraints is conspicuously lacking. Here, we apply a first-order, thermomechanical ice sheet model, validated against a diverse suite of empirical data, to investigate the retreat of the EISC after 23 ka BP, directly extending the work of Patton et al. (2016) who modelled the build-up to its maximum extent. Retreat of the ice sheet complex was highly asynchronous, reflecting contrasting regional sensitivities to climate forcing, oceanic influence, and internal dynamics. Most rapid retreat was experienced across the Barents Sea sector after 17.8 ka BP when this marine-based ice sheet disintegrated at a rate of ∼670 gigatonnes per year (Gt a−1) through enhanced calving and interior dynamic thinning, driven by oceanic/atmospheric warming and exacerbated by eustatic sea-level rise. From 14.9 to 12.9 ka BP the EISC lost on average 750 Gt a−1, peaking at rates >3000 Gt a−1, roughly equally partitioned between surface melt and dynamic losses, and potentially contributing up to 2.5 m to global sea-level rise during Meltwater Pulse 1A. Independent glacio-isostatic modelling constrained by an extensive inventory of relative sea-level change corroborates our ice sheet loading history of the Barents Sea sector. Subglacial conditions were predominately temperate during deglaciation, with over 6000 subglacial lakes predicted along with an extensive subglacial drainage network. Moreover, the maximum EISC and its isostatic footprint had a profound impact on the proglacial hydrological network, forming the Fleuve Manche mega-catchment which had an area of ∼2.5 × 106 km2 and drained the present day Vistula, Elbe, Rhine and Thames rivers through the Seine Estuary. During the Bølling/Allerød oscillation after c. 14.6 ka BP, two major proglacial lakes formed in the Baltic and White seas, buffering meltwater pulses from eastern Fennoscandia through to the Younger Dryas when these massive proglacial freshwater lakes flooded into the North Atlantic Ocean. Deglaciation temporarily abated during the Younger Dryas stadial at 12.9 ka BP, when remnant ice across Svalbard, Franz Josef Land, Novaya Zemlya, Fennoscandia and Scotland experienced a short-lived but dynamic re-advance. The final stage of deglaciation converged on present day ice cover around the Scandes mountains and the Barents Sea by 8.7 ka BP, although the phase-lagged isostatic recovery still continues today.

Reply to comment received from J. Herget et al. regarding "Complex patterns of glacier advances during the late glacial in the Chagan Uzun Valley, Russian Altai" by Gribenski et al. (2016), Quaternary Science Reviews 149, 288-305

In this article, we present a map of the glacial geomorphology of the Altai andWestern Sayan Mountains, covering an area of almost 600,000 km2. Although numerous studies provide evidence for restricted Pleistocene glaciations in this area, others have hypothesized the past existence of an extensive ice sheet. To provide a framework for accurate glacial reconstructions of the Altai and Western Sayan Mountains, we present a map at a scale of 1:1,000,000 based on a mapping from 30 m resolution ASTER DEM and 15 m/30 mresolution Landsat ETM+ satellite imagery. Four landform classes have been mapped: marginal moraines, glacial lineations, hummocky terrain, and glacial valleys. Our mapping reveals an abundance of glacial erosional and depositional landforms. The distribution of these glacial landforms indicates that the Altai and Western Sayan Mountains have experienced predominantly alpine-style glaciations, with some small ice caps centred on the higher mountain peaks. Large marginal moraine complexes mark glacial advances in intermontane basins. By tracing the outer limits of present-day glaciers, glacial valleys, and moraines, we estimate that the past glacier coverage have totalled to 65,000 km2 (10.9% of the mapped area), whereas present-day glacier coverage totals only 1300 km2 (0.2% of the mapped area). This demonstrates the usefulness of remote sensing techniques for mapping the glacial geomorphology in remote mountain areas and for quantifying the past glacier dimensions. The glacial geomorphological map presented here will be used for further detailed reconstructions of the paleoglaciology and paleoclimate of the region. Central Asia Paleoglaciology Project (CAPP)

The Cordilleran Ice Sheet (CIS) covered most of British Columbia and southern Yukon Territory at the local Last Glacial Maximum (lLGM) during Marine Oxygen Isotope Stage 2. However, its subsequent demise is not well understood, particularly at high elevations east of its ocean-terminating margin. We present 10Be exposure ages from two high-elevation sites in southern and central British Columbia that help constrain the time of initial deglaciation at these sites. We sampled granodiorite erratics at elevations of 2126–2230 m a.s.l. in the Marble Range and 1608–1785 m a.s.l. in the Telkwa Range at the western margin of the Interior Plateau. The erratics at both sites are near ice-marginal meltwater channels that delineate the local ice surface slope and thus the configuration of the ice sheet during deglaciation. The locations of the erratics and their relations to meltwater channels ensure that the resulting 10Be ages date CIS deglaciation and not the retreat of local montane glaciers. Our sample sites emerged above the surface of the CIS as its divide migrated westward from the Interior Plateau to the axis of the Coast Mountains. Two of the four samples from the summit area of the Marble Range yielded apparent exposure ages of 14.0 ± 0.7 and 15.2 ± 0.8 ka. These ages are 1.8–3.0 ka younger than the well-established lLGM age of ca 17 ka for the Puget lobe of the CIS in Washington State; they are 1.7 ka younger than the lLGM age for the Puget lobe if a snow-shielding correction to their uncertainty-weighted mean age is applied. The other two samples yielded much older apparent exposure ages (20.6 ± 1.4 and 33.0 ± 1.5 ka), indicating the presence of inherited isotopes. Four samples collected from the summit area of the Telkwa Range in the Hazelton Mountains yielded well clustered apparent exposure ages of 10.1 ± 0.6, 10.2 ± 0.7, 10.4 ± 0.5, and 11.5 ± 1.1 ka. Significant present-day snow cover introduces a large uncertainty in the apparent exposure ages from this site. A snow-shielding correction based on present-day snow cover data increases the uncertainty-weighted mean exposure age of the Telkwa Range erratics to 12.4 ± 0.7 ka, consistent with deglacial 14C ages from areas near sea level to the west. Our exposure ages show a thinning of the southern portion of the CIS shortly after the lLGM and persistence of a remnant mountain ice cap in the central Coast Mountains into the Younger Dryas Chronozone. Our data also show that the summit area of the Marble Range was ice-covered during the lLGM. The presence of an ice body of considerable dimension in north-central British Columbia until, or possibly even after, the Younger Dryas highlights the need for geomorphological and geochronological studies of the ice dispersal centre over the Skeena Mountains in northwest British Columbia and the need for better understanding of the response of the CIS to Lateglacial climate fluctuations.

Reconstructing glacial chronologies with consistent methods is critical for efforts to examine the timing and pattern of past climate change. Cosmogenic 10Be surface exposure dating has been widely used to constrain the timing of glacial events on the Tibetan Plateau and in Central Asia. However, few such studies have been conducted in the Chinese Tian Shan and available 10Be ages from this region have only provided evidence for glacial events during the global Last Glacial Maximum (gLGM) and Lateglacial. Here, we present 45 10Be surface exposure ages from glacial landforms in the Ala and Daxi valleys, two formerly glaciated valleys draining the Tianger Range, eastern Tian Shan. Combined with previously published 10Be surface exposure ages from the Daxi Valley in the source area of the Urumqi River, the new ages record five major glacial events during Marine Oxygen Isotope Stages (MIS) 6 or older, 4, 3, 2, and 1 (during the Little Ice Age, LIA). Landforms from glacial events since MIS 2 are found on the northern slope of the Tianger Range (Daxi Valley), whereas evidence for the older glacial events is only preserved on its southern slope (Ala Valley). This disparity may be caused by different preservation- and micro-climatic conditions on the northern and southern slopes of this mountain range, due to differences in gradient and aspect. The LIA glacial advances are apparently the only Holocene glacial event recorded in this area. Earlier Holocene glacial events were probably so restricted in extent that they were destroyed by subsequent LIA advances.

Quantifying long-term erosion rates across the Tibetan Plateau and its bordering mountains is of critical importance to an understanding of the interaction between climate, tectonic movement, and landscape evolution. We present a new dataset of basin-wide erosion rates from the central and northern Tibetan Plateau derived using in-situ produced 10 Be concentrations of river sediments. Basin-wide erosion rates from the central plateau range from 10.1 ± 0.9 to 36.8 ± 3.2 mm / kyr , slightly higher than published local erosion rates measured from bedrock surfaces. These values indicate that long-term downwearing of plateau surfaces proceeds at low rates and that the landscape is demonstrably stable in the central plateau. In contrast, basin-wide erosion rates from the Kunlun Shan on the northern Tibetan Plateau range from 19.9 ± 1.7 to 163.2 ± 15.9 mm / kyr . Although the erosion rates of many of these basins are much higher than the rates from the central plateau, they are lower than published basin-wide erosion rates from other mountains fringing the Tibetan Plateau, probably because the basins in the Kunlun Shan include both areas of low-relief plateau surface and high-relief mountain catchments and may also result from retarded fluvial sediment transport in an arid climate. Significantly higher basin-wide erosion rates derived from the Tibetan Plateau margin, compared to the central plateau, reflect a relatively stable plateau surface that is being dissected at its margins by active fluvial erosion.

Geologic mapping in Yukon Territory, Canada, over the past 100 years has revealed a consistent pattern of diminishing Cordilleran Ice Sheet (CIS) extent during successively younger glaciations. Although this pattern is generally accepted, there is still much uncertainty about the number of glaciations, their ages, and the dynamics of the different lobes that constituted the digitate ice sheet margin, their subglacial thermal regimes, and ice thicknesses. We address uncertainties in the timing of glaciation using cosmogenic nuclide exposure dating at key localities that straddle several major lobes of the CIS in west-central Yukon Territory. Differences in exposure duration within what are thought to be the same map units are perhaps due to inheritance (older than expected), but more likely result from postglacial shielding (younger than expected) or surface erosion. Despite a significant spread in exposure durations on moraines and within map units, and tending to rely on longest exposure durations on moraines due to postglacial degradation and shielding, our results indicate that the McConnell glacial advance occurred during Marine Oxygen Isotope Stage (MIS) 2, judging from oldest minimum apparent exposure ages of 15.7 ± 1.5 and 17.7 ± 1.6 ka, a Gladstone glacial advance occurred before 51.8 ± 4.7 ka (MIS 4) and Reid glacial advances before 79.8 ± 7.3 and 82.8 ± 7.5 ka (consistent with MIS 6). Traces of even older glacial advances predate 100 ka (107.5 ± 9.9–154.3 ± 14.2 ka).

The glacial geomorphology of the Tian Shan has been mapped, with the study area covering almost 638,000km(2). The map, designed to be printed at A0 size due to the elongated shape of the mountain range, is presented at a scale of 1:1,100,000. Five glacial landform categories are presented; glacial valleys, marginal moraines, glacial lineations, hummocky terrain and meltwater channels. These landform categories were mapped using the Shuttle Radar Topography Mission (SRTM) digital elevation model (90m resolution), Landsat 7 ETM+ satellite imagery (30m resolution), and images contained in Google Earth. The mapped landforms were created by glaciers that were restricted to mountain areas and their immediate surroundings. AuthorCount:5

Reconstructing the paleoglaciation of the Tibetan Plateau is critical to understanding linkages between regional climate changes and global climate changes, and here we focus on the glacial history ...

The Liard Lobe formed a part of the northeastern sector of the Cordilleran Ice Sheet and drained ice from accumulation areas in the Selwyn, Pelly, Cassiar and Skeena mountains. This study reconstru ...

Glacial geomorphological mapping from satellite imagery and field investigations provide the basis for a reconstructionof the extent and style of glaciation of the Shaluli Shan, a mountainous area ...

Third Nordic Workshop on Cosmogenic Nuclide Techniques; Stockholm, Sweden, 8–10 June 2016

Published version, source at http://doi.org/10.1016/j.quascirev.2016.10.009. License CC BY-NC-ND 4.0. The Eurasian ice-sheet complex (EISC) was the third largest ice mass during the Last Glacial Maximum (LGM), after the Antarctic and North American ice sheets. Despite its global significance, a comprehensive account of its evolution from independent nucleation centres to its maximum extent is conspicuously lacking. Here, a first-order, thermomechanical model, robustly constrained by empirical evidence, is used to investigate the dynamics of the EISC throughout its build-up to its maximum configuration. The ice flow model is coupled to a reference climate and applied at 10 km spatial resolution across a domain that includes the three main spreading centres of the Celtic, Fennoscandian and Barents Sea ice sheets. The model is forced with the NGRIP palaeo-isotope curve from 37 ka BP onwards and model skill is assessed against collated flowsets, marginal moraines, exposure ages and relative sea-level history. The evolution of the EISC to its LGM configuration was complex and asynchronous; the western, maritime margins of the Fennoscandian and Celtic ice sheets responded rapidly and advanced across their continental shelves by 29 ka BP, yet the maximum aerial extent (5.48 × 106 km2) and volume (7.18 × 106 km3) of the ice complex was attained some 6 ka later at c. 22.7 ka BP. This maximum stand was short-lived as the North Sea and Atlantic margins were already in retreat whilst eastern margins were still advancing up until c. 20 ka BP. High rates of basal erosion are modelled beneath ice streams and outlet glaciers draining the Celtic and Fennoscandian ice sheets with extensive preservation elsewhere due to frozen subglacial conditions, including much of the Barents and Kara seas. Here, and elsewhere across the Norwegian shelf and North Sea, high pressure subglacial conditions would have promoted localised gas hydrate formation.

Deglaciation chronologies for some sectors of former ice sheets are relatively poorly constrained because of the paucity of features or materials traditionally used to constrain the timing of deglaciation. In areas without good deglaciation varve chronologies and/or without widespread occurrence of material that indicates the start of earliest organic radiocarbon accumulations suitable for radiocarbon dating, typically only general patterns and chronologies of deglaciation have been deduced. However, mid-latitude ice sheets that had warm-based conditions close to their margins often produced distinctive deglaciation landform assemblages, including eskers, deltas, meltwater channels and aligned lineation systems. Because these features were formed or significantly altered during the last glaciation, boulder or bedrock samples from them have the potential to yield reliable deglaciation ages using terrestrial cosmogenic nuclides (TCN) for exposure age dating. Here we present the results of a methodological study designed to examine the consistency of TCN-based deglaciation ages from a range of deglaciation landforms at a site in northern Norway. The strong coherence between exposure ages across several landforms indicates great potential for using TCN techniques on features such as eskers, deltas and meltwater channels to enhance the temporal resolution of ice-sheet deglaciation chronologies over a range of spatial scales.

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 ( ...

The Tibetan Plateau is a topographic feature of extraordinary dimension and has an important impact on regional and global climate. However, the glacial history of the Tibetan Plateau is more poorly constrained than that of most other formerly glaciated regions such as in North America and Eurasia. On the basis of some field evidence it has been hypothesized that the Tibetan Plateau was covered by an ice sheet during the Last Glacial Maximum (LGM). Abundant field- and chronological evidence for a predominance of local valley glaciation during the past 300,000 calendar years (that is, 300 ka), coupled to an absence of glacial landforms and sediments in extensive areas of the plateau, now refute this concept. This, furthermore, calls into question previous ice sheet modeling attempts which generally arrive at ice volumes considerably larger than allowed for by field evidence. Surprisingly, the robustness of such numerical ice sheet model results has not been widely queried, despite potentially important climate ramifications. We simulated the growth and decay of ice on the Tibetan Plateau during the last 125 ka in response to a large ensemble of climate forcings (90 members) derived from Global Circulation Models (GCMs), using a similar 3D thermomechanical ice sheet model as employed in previous studies. The numerical results include as extreme end members as an ice-free Tibetan Plateau and a plateau-scale ice sheet comparable, in volume, to the contemporary Greenland ice sheet. We further demonstrate that numerical simulations that acceptably conform to published reconstructions of Quaternary ice extent on the Tibetan Plateau cannot be achieved with the employed stand-alone ice sheet model when merely forced by paleoclimates derived from currently available GCMs. Progress is, however, expected if future investigations employ ice sheet models with higher resolution, bidirectional ice sheet-atmosphere feedbacks, improved treatment of the surface mass balance, and regional climate data and climate reconstructions.

Please click here to download the map associated with this article. The Cordilleran Ice Sheet (CIS), which grew and melted repeatedly across the mountain ranges of westernmost Canada during the late Cenozoic, has imprinted its legacy in the form of glacial landforms, such as meltwater landforms. However, despite their abundance, a coherent effort to map meltwater landforms has been lacking. Here, we present a first regional geomorphological map of glacial meltwater landforms of central British Columbia. Series of well-developed meltwater channels occur at higher elevations on the Interior Plateau, in marginal ranges east of the Coast Mountains, in the Skeena and Omineca mountains, and, in much lower abundances, in the Rocky Mountains. Single-ridged eskers, that in direction are consistent with the regional ice flow direction from glacial lineations, occur in elevated areas of the Interior Plateau. Multiple-ridged larger eskers and esker complexes are, on the other hand, confined to the main topog...

The glacial geomorphology of the central Tibetan Plateau was mapped over 285,000 km2. Here we present a map covering 135,000 km2 at a scale of 1:660,000. The glacial geomorphology was mapped using 15 and 30 m resolution Landsat 7 ETM+ satellite imagery, a 90 m resolution SRTM digital elevation model, and satellite and aerial images displayed in Google Earth. Four landform categories were discernible and mapped; glacial valleys, marginal moraines, glacial lineations, and hummocky terrain. The mapped landforms indicate multiple glacial advances of valley and piedmont glaciers. The mapped landform record lends no support to individual ice centres having coalesced to form a plateau-wide ice sheet.

Jansson, K. N., Stroeven, A. P., Alm, G., Dahlgren, K. I. T., Glasser, N. F., Goodfellow, B. W. (2011). Using a GIS filtering approach to replicate patterns of glacial erosion. Earth Surface Processes and Landforms, 36, (3), 408-418.

The last glacial maximum (LGM) outline and subsequent retreat pattern (21e7 kyr) of North Americanice sheets are reasonably well established. However, the evolution of the ice sheets during their build-upphase towards the LGM between 115 and 21 kyr has remained elusive, making it difficult to verifynumerical ice sheet models for this important time interval. In this paper we outline the pre-LGM icesheet evolution of the Laurentide and Cordilleran ice sheets by using glacial geological and geomorphologicalrecords to make a first-order reconstruction of ice sheet extent and flow pattern. We mappedthe entire area covered by the Laurentide and Cordilleran ice sheets in Landsat MSS images andapproximately 40% of this area in higher resolution Landsat ETMþ images. Mapping in aerial photographsadded further detail primarily in Quebec-Labrador, the Cordilleran region, and on Baffin Island.Our analysis includes the recognition of approximately 500 relative-age relationships from crosscuttinglineations. Together with previously published striae and till fabric data, these are used as the basis forrelative-age assignments of regional flow patterns. For the reconstruction of the most probable ice sheetevolution sequence we employ a stepwise inversion scheme with a clearly defined strategy for delineatingcoherent landforms swarms (reflecting flow direction and configuration), and linking these topreviously published constraints on relative and absolute chronology. Our results reveal that icedispersalcentres in Keewatin and Quebec were dynamically independent for most of pre-LGM time andthat a massive Quebec dispersal centre, rivalling the LGM in extent, existed at times when the SW sectorof the ice sheet had not yet developed. The oldest flow system in eastern Quebec-Labrador (Atlanticswarm had an ice divide closer to the Labrador coast than later configurations). A northern Keewatin-Central Arctic Ice Sheet existed prior to the LGM, but is poorly chronologically constrained. There is alsoevidence for older and more easterly Cordilleran Ice Sheet divide locations than those that prevailedduring the Late Wisconsinan. In terms of ice sheet build-up dynamics, it appears that “residual” ice capsafter warming phases may have played an important role. In particular, the location and size of remnantice masses at the end of major interstadials, i.e. OIS 5c and 5a, must have been critical for subsequentbuild-up patterns, because such remnant “uplands” may have fostered much more rapid ice sheetgrowth than what would have occurred on a fully deglaciated terrain. The ice-sheet configuration duringstadials would also be governed largely by the additional topography that such “residual” ice constitutesbecause of inherent mass balance-topography feedbacks.

Key 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- ...

The weathering and origin of an autochthonous blockfield in the northern Swedish mountains were investigatedthrough an examination of fine matrix and clasts from two pits excavated across ridge-top ...