Glacier Equilibrium Line Research Articles

Climate Model Simulations of the Effects of Orbital Parameters on Glacier Equilibrium Line Altitude

AbstractThe effects of obliquity and precession on conditions favorable for Northern Hemisphere glaciation are explored using an energy balance and mass balance model of equilibrium line altitude (ELA), the height on a glacier where accumulation and ablation are in balance annually. Climate forcing for the ELA model is obtained from idealized single‐forcing orbital simulations with two atm‐ocean general circulation models, Geophysical Fluid Dynamics Laboratory (GFDL) CM2.1 and National Center for Atmospheric Research (NCAR) Community Earth System Model version 1.2. Over Scandinavia and Baffin Island, the respective locations in which the Scandinavian and Laurentide ice sheets are thought to have originated, low obliquity and perihelion at the boreal winter solstice are associated with lower ELA values, as would be expected from the orbital theory of the ice ages. Linear reconstructions of ELA variations over the past 800 kyr indicate that precession dominated ELA variations in Scandinavia and Baffin Island in the GFDL model, and in Scandinavia in the NCAR model. Obliquity and precession played equal roles in Baffin Island in the NCAR model. A decomposition of the ELA responses finds that the effects of ablation on ELA are much larger than the effects of precipitation. Overall, the findings of this study point to precession being a more important factor in glacial inception than obliquity, which contrasts with previous findings in which obliquity had a slightly larger effect on positive degree days (PDDs), a simple metric for ablation. This is likely due to differences in seasonality of melt from the ELA model and PDDs.

Equilibrium line altitudes of alpine glaciers in Alaska suggest Last Glacial Maximum summer temperature was 2–5 °C lower than during the pre-industrial

Abstract. The lack of continental ice sheets in Alaska during the Last Glacial Maximum (LGM; 26–19 ka) has long been attributed to extensive aridity in the western Arctic. More recently, climate model outputs, a few isolated paleoclimate studies, and global paleoclimate synthesis products show mild summer temperature depressions in Alaska compared to much of the high northern latitudes. This suggests the importance of limited summer temperature depressions in controlling the relatively limited glacier growth during the LGM. To explore this further, we present a new statewide map of LGM alpine glacier equilibrium line altitudes (ELAs), LGM ΔELAs (LGM ELA anomalies relative to the Little Ice Age, LIA), and ΔELA-based estimates of temperature depressions across Alaska to assess paleoclimate conditions. We reconstructed paleoglacier surfaces in ArcGIS to calculate ELAs using an accumulation area ratio (AAR) of 0.58 and an area–altitude balance ratio (AABR) of 1.56. We calculated LGM ELAs (n= 480) in glaciated massifs in the state, excluding areas in southern Alaska that were covered by the Cordilleran Ice Sheet. The data show a trend of increasing ELAs from the southwest to the northeast during both the LGM and the LIA, indicating a consistent southern Bering Sea and northernmost Pacific Ocean precipitation source. Our LGM–LIA ΔELAs from the Alaska Range, supported with limited LGM–LIA ΔELAs from the Brooks Range and the Kigluaik Mountains, average to −355 ± 176 m. This value is much greater than the global LGM average of ca. −1000 m. Using a range of atmospheric lapse rates, LGM–LIA ΔELAs in Alaska translate to summer cooling of < 2–5 ∘C. Our results are consistent with a growing number of local climate proxy reconstructions and global data assimilation syntheses that indicate mild summer temperature across Beringia during the LGM. Limited LGM summer temperature depressions could be explained by the influence of Northern Hemisphere ice sheets on atmospheric circulation.

10Be exposure ages and paleoenvironmental significance of rock glaciers in the Western Tatra Mts., Western Carpathians

Relict rock glaciers are well-preserved features of high-elevated valleys in the Western Tatra Mts., Western Carpathians, but their chronology remained poorly constrained with numerical dating methods. We present the first robust set of 10Be exposure ages for eight rock glaciers with front elevation of 1376–1819 m asl. The results suggest that the rock glaciers stabilized throughout the Weichselian Lateglacial from ∼16.5 ka to 11 ka. This timing is consistent with the period of rock glacier stabilization in European mountain regions, but it extends the age span previously determined for rock glaciers in the Tatra Mts. There are differences between north- and south-facing valleys in the elevation and time of the stabilization of the rock glaciers, which were probably caused by contrasts in potential incoming solar radiation that affected the retreat of former glaciers and the subsequent formation of the rock glaciers. The initiation altitude of ∼1610 and ∼1830 m asl determined for the oldest and youngest dated rock glaciers is generally consistent with previous estimates of the glacier equilibrium line altitude during the Greenland Stadials 2.1 and 1, respectively. However, the lower limit of the rock glaciers is well above regional paleopermafrost features from the same periods, which suggests that rock glaciers may underestimate past permafrost extents and temperature declines disputing their regional validity for paleoenvironmental reconstructions.

On the Shift of Glacier Equilibrium Line Altitude (ELA) under the Changing Climate

Presently available information on the glacier equilibrium line altitude (ELA) is being collected and examined. The historical course of the world’s longest ELA series of 107 years at the Claridenfirn is reviewed together with climatic elements. Further, the changes in ELAs of 70 glaciers the world over are investigated, and a linear plane model for the speed of the ELA shift is proposed as a function of the changing rates of summer temperature and winter mass balance. The four glaciers in Europe, which diverge most from the plane, are investigated in detail. The cause of the divergence is likely due to be the change in solar global radiation. Although a precise quantification of the role of radiation is not possible at this stage for the entire world, the role of solar radiation is investigated for these glaciers. Globally viewed, ten, or 15% of the 70 investigated glaciers, are expected to lose their accumulation areas within the next ten years. Half of all studied glaciers will follow the same fate by the end of this century under the present climatic conditions. If climate change is accelerated, the disappearance of glaciers will occur sooner than presented in this study.

The West Kunlun Glacier Anomaly and Its Response to Climate Forcing during 2002–2020

Research into glacial mass change in West Kunlun (WK) has been sufficient, but most of the existing studies were based on geodetic methods, which are not suitable for specific health state analyses of each glacier. In this paper, we utilize Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery, applying the continuity equation to obtain altitudinal specific mass balance (SMB) for 615 glaciers (>2 km2) during 2002–2011, 2011–2020, and 2002–2020 to research glacial health and its response to climatic forcing. The results show dissimilar glacier SMB patterns between 2002–2011 (0.10 ± 0.14 m w.e. a−1), 2011–2020 (–0.12 ± 0.14 m w.e. a−1) and 2002–2020 (−0.01 ± 0.07 m w.e. a−1). Additionally, the glacier equilibrium line altitude (ELA) in WK was 5788 m, 5744 m, and 5786 m, respectively, and the corresponding accumulation area ratios (AARs) were 0.59, 0.62, and 0.58, during 2002–2011, 2011–2020, and 2002–2020, respectively. Regarding glacier response, compared with the ordinary-least-square (OLS) model, the artificial neural network (ANN) model revealed a respectively less and more sensitive glacier SMB response to extreme negative and positive summer skin temperatures. In addition, the ANN model indicated that the glacier ELA was less sensitive when the integrated water vapor transport (IVT) change exceeded 0.7 kg m−1s−1. Moreover, compared with IVT (−121.57 m/kg m−1s−1), glacier ELA shifts were chiefly dominated by summer skin temperature (+154.66 m/℃) in the last two decades. From 2002–2011 and 2011–2020, glacier SMB was more susceptible to summer skin temperature (−0.38 m w.e./℃ and −0.16 m w.e./℃, respectively), while during 2002–2020, it was more influenced by IVT (0.45 m w.e./kg m−1s−1). In contrast with eastern WK, glaciers in western WK were healthier, although mitigation measures are still needed to safeguard glacier health and prevent possible natural hazards in this region. Finally, we believe that the inconsistent change between glacier SMB and ELAs from 2002–2020 was connected with ice rheology and that the combined effects of skin temperature and IVT can explain the WK glacier anomaly.

Spatiotemporal Variability in the Glacier Snowline Altitude across High Mountain Asia and Potential Driving Factors

The glacier snowline altitude (SLA) at the end of the melt season is an indicator of the glacier equilibrium line altitude and can be used to estimate glacier mass balance and reconstruct past climate. This study analyzes the spatiotemporal variability in glacier SLA across High Mountain Asia, including the Altai Mountains, Karakoram Mountains, Western Himalayas, Gongga Mountains, Tian Shan, and Nyainqentanglha Mountains, over the past 30 years (1989–2019) to better elucidate the state of these mountain glaciers. Remote-sensing data are processed to delineate the glacier SLA across these mountainous regions, and nearby weather station data are incorporated to determine the potential relationships between SLA and temperature/precipitation. The mean SLAs across the Altai and Karakoram mountains ranged from 2860 ± 169 m to 3200 ± 152 m and from 5120 ± 159 m to 5320 ± 240 m, respectively, with both regions experiencing an average increase of up to 137 m over the past 30 years. Furthermore, the mean glacier SLAs across the Western Himalayas and Gongga Mountains increased by 190–282 m over the past 30 years, with both regions experiencing large fluctuations. In particular, the mean glacier SLA across the Western Himalayas varied from 4910 ± 190 m in 1989 to 5380 ± 164 m in 2000, and that across the Gongga Mountains varied from 4960 ± 70 m in 1989 to 5330 ± 100 m in 2012. Correlation analyses between glacier SLA and temperature/precipitation suggest that temperature is the primary factor influencing glacier SLA across these High Mountain Asia glaciers. There is a broad increase in glacier SLA from the Altai Mountains to the Karakoram Mountains, with a decrease in glacier SLA with decreasing latitude across the Himalayas; the maximum SLA occurs near the northern slopes of the Western Himalayas. The glacier SLA is lower on the eastern side of the Tibetan Plateau and exhibits a longitudinal distribution pattern. These results are expected to provide useful information for evaluating the state of High Mountain Asia glaciers, as well as their response and feedback to climate change.

A first-order flexible ELA model based on geomorphic constraints

Alpine glaciers, with their valuable combination of highly sensitive response to climate and near-global extent, are powerful tools for investigating previous and present climate changes. They also represent critical water resources for areas around the globe, with the potential for far-reaching effects in a warming world. Advancements to understand and model glacial changes and the variables influencing them are therefore paramount. Many glacier models fall into one of two endmembers: either highly complex transient models requiring careful tuning of multiple parameters to individual glaciers, or basic empirical correlations of glacier area and length with few considerations for local and regional variations in characteristics. Here we detail a physical steady-state model for alpine glaciers relating directly to glacier mass balance (via the equilibrium line altitude) while retaining the simplicity of other morphology methods, and simultaneously including error estimates. We provide custom MATLAB functions as a user-friendly and generally-applicable method to estimate glacier equilibrium line altitudes from only a limited number of glacier bed topography and glacier width measurements. As a test of the model’s efficacy, we compare the model results for present-day glaciers in the Swiss Alps with previously published estimates of equilibrium line altitudes and intermediate model outputs.•The method estimates glacier equilibrium line altitudes from a limited set of bed topography measurements and constraints on glacier width.•The method is based on continuity equations, reducing the need for empirical coefficients tuned with measured data.•The method uses Monte Carlo sampling and bootstrapping to generate uncertainty bounds on the equilibrium line altitude estimates.

Numerical Reconstruction of Three Holocene Glacial Events in Qiangyong Valley, Southern Tibetan Plateau and Their Implication for Holocene Climate Changes

The dating of well-preserved Holocene moraines in the Qiangyong Valley, southern Tibetan Plateau (TP), offers great potential for reconstructing Holocene glacier extents and examining climate changes in the region. Guided by Holocene moraine features, this study used Geographic Information System (GIS) model tools to reconstruct paleo-glacier surfaces and glacier equilibrium line altitude (ELA) depressions for three Holocene glacial stages in the valley. The GIS-based models showed that the Qiangyong Valley contained ice volumes of 8.1 × 108, 6.2 × 108, and 4.6 × 108 m3 during the early Holocene, Neoglacial, and Little Ice Age (LIA) glacial stages, and that the ELA was decreased by ~230 ± 25, ~210 ± 25, and ~165 ± 25 m, respectively, compared to modern conditions. Furthermore, the summer temperatures were estimated to be 1.56–1.79, 1.37–1.64, and 1.29–1.32 °C cooler than present to support the three Holocene glacier extents, based on the evidence that the respective precipitation increased by 20–98, 13–109, and 0.9–11 mm relative to the present, which were derived from the lacustrine pollen data for the southern TP. By comparison, this study found that the amplitudes of the ELA-based summer temperature depressions were much larger than the pollen-based counterparts for the three glacial stages, although the two proxies both showed increasing trends in the reconstructed summer temperatures.

Bayesian geomorphology

SummaryThe rapidly growing amount and diversity of data are confronting us more than ever with the need to make informed predictions under uncertainty. The adverse impacts of climate change and natural hazards also motivate our search for reliable predictions. The range of statistical techniques that geomorphologists use to tackle this challenge has been growing, but rarely involves Bayesian methods. Instead, many geomorphic models rely on estimated averages that largely miss out on the variability of form and process. Yet seemingly fixed estimates of channel heads, sediment rating curves or glacier equilibrium lines, for example, are all prone to uncertainties. Neighbouring scientific disciplines such as physics, hydrology or ecology have readily embraced Bayesian methods to fully capture and better explain such uncertainties, as the necessary computational tools have advanced greatly. The aim of this article is to introduce the Bayesian toolkit to scientists concerned with Earth surface processes and landforms, and to show how geomorphic models might benefit from probabilistic concepts. I briefly review the use of Bayesian reasoning in geomorphology, and outline the corresponding variants of regression and classification in several worked examples. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

Late Quaternary glacier equilibrium line altitudes (ELA) in the mountains of Iran

Climate change in the late Quaternary period led to the displacement of the equilibrium line altitudes (ELAs) of glaciers in the mountainous regions of Iran. Considering the extent of Iran in different latitudes and its terrains, the effect of the direction of terrains and latitudes on the formation of a glacier and hence on the ELAs cannot be ignored. In order to estimate ELAs of the Quaternary and investigate the effect of the above-mentioned factors on the difference of the ELAs (∆ELAs), the Quaternary glacier cirques were identified in different parts of Iran’s terrains. The ELA is estimated using cirque-floor altitude and terminus-to-head altitude ratio (THAR) methods. The results indicate that in general, estimation of ELA using AAR is more consistent with cirque-floor altitude in Iran’s terrains. The maximum estimated Quaternary ELA is 3098 m in the southern part of Central Iran, and the minimum ELA is 2033 m in Talesh Mountains in Alborz terrain. The ∆ELA of Iran’s terrains is 1065 m. This elevation varied from 2030 to 3100 m.

Latest Pleistocene glacier advances and post-Younger Dryas rock glacier stabilization in the Mt. Kriváň group, High Tatra Mountains, Slovakia

The timing of glacier disappearance and rock glacier stabilization in the highest massifs of the Carpathians is still poorly documented. In this paper, we establish the extent and chronology of the final stages of glaciation and timing of stabilization of the uppermost rock glaciers in the Tatra Mountains, which are the highest (2654 m a.s.l.), northernmost (N 49°12′), and coldest range in the Carpathians. On the base of morphostratigraphic principles, Schmidt Hammer tests and glacier equilibrium line altitude (ELA) estimation, we assigned moraines and rock glaciers in the Mt. Kriváň massif (SW part of High Tatras) to a threefold stratigraphic sequence with glacial stages/advances from older to younger: Popradské pleso (Pp), Suchá važecká I (Sv I) and Suchá važecká II (Sv II). Landforms attributed to two younger advances, Sv I and Sv II, were sampled for the purpose of cosmogenic 10Be surface exposure dating. Our data show that Pp and Sv I glacial advances occurred during the Oldest Dryas climatic downturn. The younger advance (Sv I) occurred just before the Bølling-Allerød (B/A) warming at 14.9 ± 0.4 ka, at this time small glaciers occupied lower glacial cirques in the study area. The youngest Sv II advance was characterized by rock glaciers and small debris-covered glaciers confined to the highest cirques. The mean exposure age of four relict rock glaciers of this stage is 11.1 ± 0.9 ka but individual rock glacier mean ages spanned between 11.8 and 10.4 ka. Our research results show that the youngest moraines and rock glaciers in the Tatra Mountains were formed during the Younger Dryas (YD), but the final permafrost melting and rock glacier stabilization period was delayed until the early Holocene, but no later than 10.4 ka. In high elevation cirque bottoms (up to 2120 m a.s.l.), the YD glaciers and rock glaciers readvanced across land which was ice-free as early as 14.8–14.2 ka. Thus, it is likely that during the B/A interphase, glaciers completely disappeared in the Tatra Mountains. The YD was the last period of glacial/periglacial activity in the massif. As we investigated one of the highest-situated rock glaciers in the Tatras (up to 2220 m a.s.l.), we conclude that all rock glaciers in this massif are relict landforms which developed in response to severe Lateglacial climate conditions. The Lateglacial climate of the Tatra Mountains is discussed herein on the basis of glacier equilibrium line altitude (ELA) estimation and the vertical distribution of rock glacier belts. We argue that paleoclimate significance of the presented geomorphological record may match paleobotanical proxy reconstructions and the results of climate simulations, but only if the impact of enhanced temperature seasonality on glacier mass balance and rock glacier activity is taken into account.

Glacier extent and climate in the Maritime Alps during the Younger Dryas

This study focuses on an Egesen-stadial moraine located at 1906–1920 m asl in the NE Maritime Alps, Europe. Three moraine boulders are dated, via cosmogenic isotope analyses, to 12,490 ± 1120, 12,260 ± 1220 and 13,840 ± 1240 yr, an age compatible with the Younger Dryas cooling event. The reconstructed glacier that deposited the moraine has an equilibrium line altitude of 2349 ± 5 m asl, calculated with an Accumulation Area Balance Ratio of 1.6. The result is very similar to the equilibrium line altitude of another reconstructed glacier that deposited a moraine also dated to Younger Dryas, in the SW Maritime Alps. The similarity suggests comparable climatic conditions across the region during the cooling event. The Younger Dryas palaeoprecipitation is 1549 ± 26 mm/yr, calculated using the empirical law that links precipitation and temperature at a glacier equilibrium line altitude, with palaeotemperatures obtained from nearby palynological and chironomids studies. The palaeoprecipitation is similar to the present, thus indicating non-arid conditions during the Younger Dryas. This is probably due to the Maritime Alps peculiar position, at the crossroads between air masses from the Mediterranean and the North Atlantic, the latter displaced by the southward migration of the polar front. The equilibrium line altitude interval defined by the two reconstructed glaciers, is used to model the extent of another 66 potential Younger Dryas glaciers in the region. Each modelled glacier is reconstructed by iteratively changing the position of its front until the reconstructed glacier has an ELA that falls within the interval. The result, which is checked against geomorphological evidence, shows that glaciers covered 83.74 km2 during the Younger Dryas, with a volume of 5.39 km3. All valley heads were occupied by ice, except for the Maddalena/Larche Pass (1999 m asl), an ideal site for future archaeological, palaeoecological and palaeozoological studies.

Key indicators of Arctic climate change: 1971–2017

Key observational indicators of climate change in the Arctic, most spanning a 47 year period (1971–2017) demonstrate fundamental changes among nine key elements of the Arctic system. We find that, coherent with increasing air temperature, there is an intensification of the hydrological cycle, evident from increases in humidity, precipitation, river discharge, glacier equilibrium line altitude and land ice wastage. Downward trends continue in sea ice thickness (and extent) and spring snow cover extent and duration, while near-surface permafrost continues to warm. Several of the climate indicators exhibit a significant statistical correlation with air temperature or precipitation, reinforcing the notion that increasing air temperatures and precipitation are drivers of major changes in various components of the Arctic system. To progress beyond a presentation of the Arctic physical climate changes, we find a correspondence between air temperature and biophysical indicators such as tundra biomass and identify numerous biophysical disruptions with cascading effects throughout the trophic levels. These include: increased delivery of organic matter and nutrients to Arctic near‐coastal zones; condensed flowering and pollination plant species periods; timing mismatch between plant flowering and pollinators; increased plant vulnerability to insect disturbance; increased shrub biomass; increased ignition of wildfires; increased growing season CO2 uptake, with counterbalancing increases in shoulder season and winter CO2 emissions; increased carbon cycling, regulated by local hydrology and permafrost thaw; conversion between terrestrial and aquatic ecosystems; and shifting animal distribution and demographics. The Arctic biophysical system is now clearly trending away from its 20th Century state and into an unprecedented state, with implications not only within but beyond the Arctic. The indicator time series of this study are freely downloadable at AMAP.no.

A multi-model analysis of glacier equilibrium line altitudes in western China during the last glacial maximum

Based on numerical experiments undertaken with nine climate models, the glacier equilibrium line altitudes (ELAs) in western China during the last glacial maximum (LGM) are investigated to deepen our understanding of the surface environment on the Tibetan Plateau. Relative to the preindustrial period, the summer surface air temperatures decrease by 4–8°C while the annual precipitation decreases by an average of 25% across the Tibetan Plateau during the LGM. Under the joint effects of reductions in summer temperature and annual precipitation, the LGM ELAs in western China are lowered by magnitudes that vary with regions. The ELAs in the southern margin and northwestern Tibetan Plateau decline by approximately 1100 m; the central hinterland, by 650–800 m; and the eastern part, by 550–800 m, with a downward trend from southwest to northeast. The reduction in ELAs is no more than 650 m in the Tian Shan Mountains within China and approximately 500–600 m in the Qilian Mountains and Altai Mountains. The high-resolution models to reproduce the low values of no more than 500 m in ELA reductions in the central Tibetan Plateau, which are consistent with the proxy records from glacier remains. The accumulation zones of the Tibetan Plateau glaciers are mainly located in the marginal mountains during the LGM and have areas 2–5 times larger than those of the modern glaciers but still do not reach the central part.

Climate on the equilibrium line altitudes of glaciers: theoretical background behind Ahlmann'sP/Tdiagram

ABSTRACTThe climatic condition that prevails at a glacier equilibrium line altitude (ELA) is often parameterized in terms of summer air temperature (T) and annual precipitation (P). This simple parameterization was initially proposed by Hans W:son Ahlmann. The physical background of the relationship betweenPandTon the equilibrium line, however, has been left unexplained since Ahlmann first questioned the mathematical form of the relationship. This relationship can be explained when the thermal and hydrological processes of the ELA formation are investigated. The present authors studied the energy exchange processes that prevail on the ELA during the melt season. The inclusion of solar radiation brings Ahlmann's hypothesis closer to energy balance, and improves hisP/Tdiagram. By comparing the observed fluxes from the polar through the mid-latitude to the equatorial glaciers, it was found that these glaciers in different climatic regions share important similarities at the ELA. Further, it was found that the classicP/Tcurve originally proposed by Ahlmann in the early 20th century is a concise expression of the conservation principle of energy and mass at the ELA of glaciers, and takes the form of a polynomial of the fourth order.

Deglaciation of the North Cascade Range, Washington and British Columbia, from the Last Glacial Maximum to the Holocene

Glacial retreat from the North Cascade Range after the Last Glacial Maximum (LGM) at approximately 21 ka until the end of the Pleistocene at 11.6 ka was complex and included both continental and alpine glaciers. Alpine valley glaciers reached their maximum extent before 21.4 ka, then underwent a punctuated retreat to valley heads. In the south, beyond the reach of ice sheet glaciation, several end moraines were deposited after the LGM. Moraines marking a re-advance of alpine glaciers to <5 km below modern glaciers were deposited from 13.7 to 11.6 ka.The Cordilleran Ice Sheet flowed south from near 52° north latitude in British Columbia into the North Cascades. At its maximum size the ice sheet covered more than 500 km2 and had a surface elevation of 2200 m in upper Skagit valley. Deglaciation commenced about 16 ka by frontal retreat of ice flanking the mountains. Surface lowering eventually exposed regional hydrologic divides and stranded ice masses more than 1000 m thick in valleys. Isolated fragments of the ice sheet disintegrated rapidly from 14.5 to 13.5 ka, with the pattern of deglaciation in each valley controlled by valley orientation, topography, and climate. Like alpine glaciers to the south, retreat of the ice sheet remnants was slowed by millennial scale climate fluctuations that produced at least one large recessional moraine, and multiple lateral moraines and kame terraces from elevations of 200-1400 m in most valleys. Large volumes of glacial meltwater flowed through the North Cascades and was concentrated in the Skagit and Methow rivers. Outburst floods from deep proglacial lakes spilled across divides and down steep canyons, depositing coarse gravel terraces and alluvial fans at valley junctions.Climate at the LGM was characterized by a mean summer temperature 6 to 7 ºC cooler than today, and 40% lower mean annual precipitation. Persistence of this climate for thousands of years before the LGM caused a 750-1000 m decrease in alpine glacier equilibrium line altitudes (ELA). In the southern North Cascades at 16 ka, glacial ELAs were 500-700 m lower than today, and during advances from 13.7 to 11.6 ka alpine glacier ELAs were 200-400 m lower.

Rock glacier development in the Northern Calcareous Alps at the Pleistocene-Holocene boundary

Relict rock glaciers provide information on past discontinuous permafrost and former mean annual air temperatures. A lack of records showing former permafrost distribution along the northern Alpine fringe prompted the investigation and numerical dating of a belt of relict rock glaciers in the Karwendel Mountains of the Northern Calcareous Austrian Alps. In two neighbouring cirques that were still glaciated during the early Younger Dryas, eleven 36Cl exposure ages from boulder surfaces were obtained. The ages imply the onset of rock glacier activity around ~12.3ka with subsequent stabilization and permafrost melt out no later than ~10.1ka. Hence, rock glacier formation coincided with glacier retreat in the cirques around the mid-Younger Dryas and continued into the early Holocene. As permafrost induced features, the rock glacier termini indicate the local past lower limit of discontinuous permafrost in open cirque floors at ~2000masl, which is around 400m lower than during the mid-twentieth century at comparable locations in the Karwendel Mountains. Thus, a mean annual air temperature reduction of ~−2.6 to −3.8°C relative to the mid-twentieth century is inferred. Based on a minimum glacier equilibrium line altitude in the cirques, a summer temperature reduction of less than −2.6 to −1.8°C is shown, suggesting an increased seasonality at the time of rock glacier activity.

Modelled glacier equilibrium line altitudes during the mid-Holocene in the southern mid-latitudes

Abstract. Glacier behaviour during the mid-Holocene (MH, 6000 years BP) in the Southern Hemisphere provides observational data to constrain our understanding of the origin and propagation of palaeoclimate signals. In this study we examine the climatic forcing of glacier response in the MH by evaluating modelled glacier equilibrium line altitudes (ELAs) and climatic conditions during the MH compared with pre-industrial time (PI, year 1750). We focus on the middle latitudes of the Southern Hemisphere, specifically Patagonia and the South Island of New Zealand. Climate conditions for the MH were obtained from PMIP2 model simulations, which in turn were used to force a simple glacier mass balance model to simulate changes in ELA. In Patagonia, the models simulate colder conditions during the MH in austral summer (−0.2 °C), autumn (−0.5 °C), and winter (−0.4), and warmer temperatures (0.2 °C) during spring. In the Southern Alps the models show colder MH conditions in autumn (−0.7 °C) and winter (−0.4 °C), warmer conditions in spring (0.3 °C), and no significant change in summer temperature. Precipitation does not show significant changes but exhibits a seasonal shift, with less precipitation from April to September and more precipitation from October to April during the MH in both regions. The mass balance model simulates a climatic ELA that is 15–33 m lower during the MH compared with PI conditions. We suggest that the main causes of this difference are driven mainly by colder temperatures associated with the MH simulation. Differences in temperature have a dual effect on glacier mass balance: (i) less energy is available for ablation during summer and early autumn and (ii) lower temperatures cause more precipitation to fall as snow rather than rain in late autumn and winter, resulting in more accumulation and higher surface albedo. For these reasons, we postulate that the modelled ELA changes, although small, may help to explain larger glacier extents observed by 6000 years BP in South America and New Zealand.

Decadal‐scale changes of the ödenwinkelkees, central austria, suggest increasing control of topography and evolution towards steady state

Small mountain glaciers have short mass balance response times to climate change and are consequently very important for short‐term contributions to sea level. However, a distinct research and knowledge gap exists between (1) wider regional studies that produce overview patterns and trends in glacier changes, and (2) in situ local scale studies that emphasise spatial heterogeneity and complexity in glacier responses to climate. This study of a small glacier in central Austria presents a spatiotemporally detailed analysis of changes in glacier geometry and changes in glaciological behaviour. It integrates geomorphological surveys, historical maps, aerial photographs, airborne LiDAR data, ground‐based differential global positioning surveys and Ground Penetrating Radar surveys to produce three‐dimensional glacier geometry at 13 time increments spanning from 1850 to 2013. Glacier length, area and volume parameters all generally showed reductions with time. The glacier equilibrium line altitude increased by 90 m between 1850 and 2008. Calculations of the mean bed shear stress rapidly approaching less than 100 kPA, of the volume–area ratio fast approaching 1.458, and comparison of the geometric reconstructions with a 1D theoretical model could together be interpreted to suggest evolution of the glacier geometry towards steady state. If the present linear trend in declining ice volume continues, then the Ödenwinkelkees will disappear by the year 2040, but we conceptualise that non‐linear effects of bed overdeepenings on ice dynamics, of supraglacial debris cover on the surface energy balance, and of local topographically driven controls, namely wind‐redistributed snow deposition, avalanching and solar shading, will become proportionally more important factors in the glacier net balance.

Little Ice Age climate reconstruction from ensemble reanalysis of Alpine glacier fluctuations

Abstract. Mountain glaciers sample a combination of climate fields – temperature, precipitation and radiation – by accumulation and melting of ice. Flow dynamics acts as a transfer function that maps volume changes to a length response of the glacier terminus. Long histories of terminus positions have been assembled for several glaciers in the Alps. Here I analyze terminus position histories from an ensemble of seven glaciers in the Alps with a macroscopic model of glacier dynamics to derive a history of glacier equilibrium line altitude (ELA) for the time span 400–2010 C.E. The resulting climatic reconstruction depends only on records of glacier variations. The reconstructed ELA history is similar to recent reconstructions of Alpine summer temperature and Atlantic Multidecadal Oscillation (AMO) index, but bears little resemblance to reconstructed precipitation variations. Most reconstructed low-ELA periods coincide with large explosive volcano eruptions, hinting at a direct effect of volcanic radiative cooling on mass balance. The glacier advances during the LIA, and the retreat after 1860, can thus be mainly attributed to temperature and volcanic radiative cooling.