Last Glacial Maximum Equilibrium Line Altitudes Research Articles

LGM Glaciations in the Northeastern Anatolian Mountains: New Insights

Barhal Valley belongs to the Çoruh Valley System in the Kaçkar Mountains of northeastern Anatolia. This 13 km long valley is located to the south of the main weather divide and to the east of Mt. Kaçkar, with the highest peak of the mountain range being 3932 m. Today, source of an average yearly precipitation of 2000 mm of moisture is the Black Sea, situated approximately 40 km to the north of the study site. Glaciers of the Last Glacial Maximum (LGM) descended directly from Mt. Kaçkar and reached an altitude of ca. 1850 m a.s.l. (above sea level). In this study, we are exploring whether the position of Barhal Valley to the south of the main weather divide and its east–west orientation have an influence on the existence and expansion of paleoglaciers. Here, we present 32 new cosmogenic 36Cl dates on erratic boulders from the Çoruh Valley System. We reconstructed three geomorphologically well-contained glacier advances in the Barhal Valley, namely at 34.0 ± 2.3 ka, 22.2 ± 2.6 ka, and 18.3 ± 1.7 ka within the time window of the global LGM. Field evidence shows that the glacier of the 18.3 ± 1.7 ka advance disappeared rapidly and that by the latest time, at 15.6 ± 1.8 ka, the upper cirques were ice-free. No evidence for Lateglacial glacier fluctuations was found, and the Neoglacial activity is restricted to the cirques with rock glaciers. A range of 2700 to 3000 m for the Equilibrium Line Altitude (ELA) at the LGM was reported based on modeling of the glacial morphology. We determined that the most likely position of the LGM ELA in the Çoruh Valley System was at 2900 m a.s.l. We suggest an alternative moisture source to the direct transport from the Black Sea for the ice accumulation in the Eastern Black See Mountains. The shift of the Polar Front and of the Siberian High Pressure System to the south during the LGM resulted in the domination of easterly airflow to the Caucasus and Kaçkar Mountains with moisture from expanded lakes in central–western Siberia and from the enlarged Aral- and Caspian Seas.

Late Pleistocene glacial advances, equilibrium-line altitude changes and paleoclimate in the Jakupica Mts (North Macedonia)

In the Jakupica Mts a plateau glacier was reconstructed (max. area ∼45 km2, max thickness: ∼260 m). The study area comprises six formerly glaciated valleys, five of which were fed by the plateau glacier and one had an independent cirque when local glaciation reached its maximum ice extent (MIE). The equilibrium line altitude (ELA) of the most extended glacial phase was at 2075+37/-25 m asl. The 10Be cosmic ray exposure (CRE) age of this phase was estimated at 19.3+1.7/-1.3 ka, conformable with the Last Glacial Maximum (LGM). CRE ages from the next moraine generation placed the first phase of deglaciation to 18.2+1.0/-3.0 ka. The samples from the moraine of the penultimate deglaciation phase provided CRE ages with large scatter and biased towards old ages, which is probably the result of inherited cosmogenic nuclide concentrations within the rock.Glacio-climatological modelling was performed for the MIE, which has a well-established LGM age. The degree-day model was used to calculate the amount of accumulation required to sustain the glaciological equilibrium assuming a certain temperature drop at the ELA. The degree-day model constrained by the pollen-based July paleo-temperature reconstructions yielded an annual total melt at the LGM ELA comparable to or slightly higher than the current mean annual precipitation at the same elevation. These wetter LGM conditions inferred from the paleo-glaciological evidence in Jakupica Mts suggest an enhanced moisture advection in the region.

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.

Reconstruction and paleoclimatic significance of late Quaternary glaciers in the Tararua Range, North Island, New Zealand

Reconstructed mountain glaciers are routinely used as a proxy for climate in the search for evidence of interhemispheric climate fluctuations during the Quaternary. In New Zealand, valley glaciers at the Last Glacial Maximum (LGM) extended from an ice sheet centred on New Zealand's Southern Alps to below present-day sea level. In contrast, evidence of LGM glacial activity on the North Island is rare. Here, a glacioclimatic reconstruction is presented of two former glaciers in the Tararua Range (41°S) in the southern North Island. At Mt. Aston, an isolated cirque basin contains landform evidence of a marginal niche glacier. At Park Valley, the lateral moraine of a larger cirque glacier has yielded published cosmogenic isotope ages. The paleoglacier reconstruction shows that paleoequilibrium line altitudes increased northwards across New Zealand during the local LGM. Hence, at this latitude only topography >1200 m above present day sea-level was of sufficient elevation to allow small glaciers to form. The Mt Aston glacier covered only 0.18 km2 with an equilibrium line altitude (ELA) of c. 1287 m above present sea level. A mean ELA glacier thickness of c. 25 m gives a basal shear stress at the ELA of c. 100 kPa−1, with a mean summer (December, January, February, DJF) temperature at the ELA of no lower than 5.5 °C below present, below which precipitation would have been insufficient to support the reconstructed glacier. Implied LGM paleo-temperatures from both the ELA reconstruction and the glaciological reconstruction broadly accord with other paleo-temperature proxies from the North Island. Park Valley glacier covered c. 0.45 km2 with an ELA of c. 1270 m and a mean ELA basal shear stress of 65 kPa. Its balance discharge was 9 × greater than at Mt Aston. It appears to have been glaciologically viable across a wide range of paleotemperatures: thus, the more marginal glacier is a more useful paleoclimatic indicator because it places a maximum limit on LGM temperature depression, which the larger glacier does not. ELAs of both glaciers closely approximate the regional LGM ELA trend surface. The paleo-glacier reconstructions imply that together with temperature driving LGM paleo-ELA depression, changes in south-westerly airflow over New Zealand, bringing moisture-laden but cool air, maximized snowfall and minimised winter melt. The corollary is that patterns of Quaternary glacier fluctuations may be interpreted as responses, at least in-part, to precipitation-driven changes, and secondly, North Island glaciation was probably more extensive than previously assumed.

Cosmogenic 10Be surface exposure dating and glacier reconstruction for the Last Glacial Maximum in the Quemuqu Valley, western Nyainqentanglha Mountains, south Tibet

ABSTRACTThe nature and timing of glaciations enable inferences to be made about glacial climates. However, the paucity of reliable glacial chronologies impedes a full understanding of the Last Glacial Maximum (LGM) climate in the western Nyainqentanglha Mountains, south Tibet. In this study, we investigated the LGM glacial history in the Quemuqu Valley, western Nyainqentanglha, using 10Be surface exposure dating. We used a physically based glacier model to reconstruct the LGM glacial surfaces, and estimated the LGM equilibrium‐line‐altitude (ELA) using integrated methods. Combined with previously published 10Be exposure ages from the western Nyainqentanglha, ten 10Be exposure ages imply a relatively restricted glacial extent in the LGM but extensive growth in the early last glacial. The modeled LGM glaciers had ice areas of ∼36.3 km2, 3.21 km3 in volume and 89 m m in average thickness in the Quemuqu Valley. The reconstructed LGM ELAs have values of 5463–5583 m asl, with a depression of ∼244–364 m. By combining the reconstructed ELAs with an equation deduced from glacier mass balance, we concluded that the temperature dropped by ∼2.6–4.6 °C in the LGM relative to the present, with 30–70% lower precipitation than the present. Global cooling induced the LGM glacial advance in the western Nyainqentanglha despite decreased precipitation.

Last glacial maximum climate based on cosmogenic 10Be exposure ages and glacier modeling for the head of Tashkurgan Valley, northwest Tibetan Plateau

Fully understanding the timing and climate of Last Glacial Maximum (LGM) is still lack in the head of the Tashkurgan Valley, northwest Tibetan Plateau (TP). The recent improvements in cosmogenic 10Be exposure dating and glacier modeling present an opportunity to estimate the LGM climatic conditions. In the paper, we investigated the moraines and used the 10Be exposure dating on the moraine boulders to constrain the timing of the LGM, the Kuzigun glacial stage in the head of the Tashkurgan Valley. Then, we used a coupled mass-balance and ice-flow model to quantify the paleoclimate from past glacier extents constrained by mapped and dated Kuzigun glacial moraines in the area. We showed that the glaciers terminated at an elevation of 4100–4200 m asl during the Kuzigun glacial stage and the glacial stage occurred during or slightly before 15–23 ka, corresponding to the timing of the global LGM. The modeled mass balances indicated that present-day equilibrium line altitude (ELA) ranges from 5150 to 5250 m asl, and LGM ELA is between 4550 and 4600 m asl in the area, suggesting an ELA lowering of ∼600 m during the LGM. Model results suggested that the temperature during the LGM in the head of the Tashkurgan Valley is 5–8 °C colder than today, considering a 30–70% reduction in precipitation compared to today. The paleoclimate estimates are generally consistence with previous studies that showed the LGM climate was colder and drier than today on the TP.

Last Glacial Maximum climate inferences from integrated reconstruction of glacier equilibrium-line altitude for the head of the Urumqi River, Tianshan Mountains

The relationship between climate and glacial equilibrium-line altitude (ELA) during the Last Glacial Maximum (LGM) has recently received considerable interest. However, in the headwaters of Urumqi River in northwest China, a systematic reconstruction for the paleo-ELAs had not been completed to permit regional and large-scale paleoclimate inferences. Recent improvements in dating and understanding of glacial extents provide the possibility to use glacial reconstruction to infer the paleoclimate. To improve the ability to obtain paleoclimate information, the ELAs during the local LGM (MIS2–3) and modern time (1998–2004) were constructed by using an integrated method. The regional tectonic uplift is considered when calculating the LGM ELAs in order to improve their precision and thus obtain a better estimate of the paleoclimate. The estimated ELA values were input into a robust equation to derive the forcing paleoclimatic conditions. During the local LGM in the study area, the ELA was between 3420 and 3560 m a.s.l., 493–633 m lower than modern ELA. Considering energy and mass balance in the equation to account for the ELA decrease, during the LGM, the temperature decreased by 5.42–6.30 °C and the precipitation was ∼30% compared to the present.

Small valley glaciers and the effectiveness of the glacial buzzsaw in the northern Basin and Range, USA

The glacial buzzsaw hypothesis suggests that efficient erosion limits topographic elevations in extensively glaciated orogens. Studies to date have largely focussed on regions where large glaciers (tens of kilometres long) have been active. In light of recent studies emphasising the importance of lateral glacial erosion in lowering peaks and ridgelines, we examine the effectiveness of small glaciers in limiting topography under both relatively slow and rapid rock uplift conditions. Four ranges in the northern Basin and Range, Idaho, Montana, and Wyoming, USA, were chosen for this analysis. Estimates of maximum Pleistocene slip rates along normal faults bounding the Beaverhead–Bitterroot Mountains (~ 0.14 mm y − 1 ), Lemhi Range (~ 0.3 mm y − 1 ) and Lost River Range (~ 0.3 mm y − 1 ) are an order of magnitude lower than those on the Teton Fault (~ 2 mm y − 1 ). We compare the distribution of glacial erosion (estimated from cirque floor elevations and last glacial maximum (LGM) equilibrium line altitude (ELA) reconstructions) and fault slip rate with three metrics of topography in each range: the along-strike maximum elevation swath profile, hypsometry, and slope-elevation profiles. In the slowly uplifting Beaverhead–Bitterroot Mountains, and Lemhi and Lost River Ranges, trends in maximum elevation parallel ELAs, independent of variations in fault slip rate. Maximum elevations are offset ~ 500 m from LGM ELAs in the Lost River Range, Lemhi Range, and northern Beaverhead–Bitterroot Mountains, and by ~ 350 m in the southern Beaverhead–Bitterroot Mountains, where glacial extents were less. The offset between maximum topography and mean Quaternary ELAs, inferred from cirque floor elevations, is ~ 350 m in the Lost River and Lemhi Ranges, and 200–250 m in the Beaverhead–Bitterroot Mountains. Additionally, slope-elevation profiles are flattened and hypsometry profiles show a peak in surface areas close to the ELA in the Lemhi Range and Beaverhead–Bitterroot Mountains, suggesting that small glaciers efficiently limit topography. The situation in the Lost River Range is less clear as a glacial signature is not apparent in either slope-elevation profiles or the hypsometry. In the rapidly uplifting Teton Range, the distribution of ELAs appears superficially to correspond to maximum topography, hypsometry, and slope-elevations profiles, with regression lines on maximum elevations offset by ~ 700 and ~ 350 m from the LGM and mean Quaternary ELA respectively. However, Grand Teton and Mt. Moran represent high-elevation “Teflon Peaks” that appear impervious to glacial erosion, formed in the hard crystalline bedrock at the core of the range. Glacier size and drainage density, rock uplift rate, and bedrock lithology are all important considerations when assessing the ability of glaciers to limit mountain range topography. In the northern Basin and Range, it is only under exceptional circumstances in the Teton Range that small glaciers appear to be incapable of imposing a fully efficient glacial buzzsaw, emphasising that high peaks represent an important caveat to the glacial buzzsaw hypothesis.

Late Pleistocene climate inferred from the reconstruction of the Taylor River glacier complex, southern Sawatch Range, Colorado

Ice surface topography of a late Pleistocene glacier complex, herein named the Taylor River Glacier Complex (TRGC), was reconstructed on the basis of detailed mapping of glacial landforms combined with analyses of aerial photos and topographic maps. During the last glacial maximum (LGM), the TRGC covered an area of 215 km 2 and consisted of five valley or outlet glaciers that were nourished by accumulation in cirques basins and/or upland ice fields. Equilibrium-line altitudes (ELAs) for the glaciers of the TRGC were estimated using the accumulation-area ratio method, assuming that ratio to be 0.65 ± 0.05. ELAs thus derived ranged from about 3275 to 3400 m, with a mean of 3340 ± 60 m. A degree-day model (DDM) was used to infer the climatic significance of the LGM ELA. With no appreciable differences in precipitation with respect to modern climate, the ELA implies that mean summer temperatures during the LGM were ∼7.6 °C cooler than today. The DDM was also used to determine the temperatures required to maintain steady-state mass balances for each of the reconstructed glaciers. The required reductions in summer temperature vary little about a mean of 7.1 °C. The sensitivity of these results to slight (± 25%) changes assumed for LGM precipitation are less than ± 0.5 °C. Even under an LGM climate in which precipitation is assumed to be substantially different (± 50%) than the present, mean summer temperatures must be on the order of 7.0 to 8.5 °C lower to depress equilibrium lines to LGM altitudes. The greater sensitivity of the ELA to changes in temperature suggests that glaciation in the region was driven more by decreases in summer temperature rather than increases in precipitation.

Reconstruction of glacier equilibrium‐line altitudes for the Last Glacial Maximum on the High Plain of Bogotá, Eastern Cordillera, Colombia: climatic and topographic implications

AbstractThe High Plain of Bogotá in the Andes of Colombia provides an exceptionally detailed record of glaciation. A two‐stage Last Glacial Maximum (LGM) is noted in Bogotá; the older stage (max) presents an opportunity to reconstruct individual valley glaciers and explore spatial patterns. Well‐mapped geomorphic features on topographic base maps permit the reconstruction of 23 palaeoglacier surfaces. Glacier extent varies across the region, with lower altitudes reached farther to the east. Equilibrium line altitudes (ELAs) are reconstructed using the area–altitude balance ratio (AABR) method, with BRs in three groups reflecting the W–E gradient in glacier extent and selected by minimising variation from group means. Average LGM ELA for all palaeoglaciers is 3488 m with a standard deviation of 182 m. The average lowering in ELA from LGM to modern of ca. 1300 m is best explained by a considerable drop in temperature. Significant intra‐regional variance in LGM ELA can be ascribed to topography and its influence on precipitation and/or glacier form, with lower headwall elevations being correlated to larger accumulation areas. Copyright © 2005 John Wiley & Sons, Ltd.

An evaluation of snowline data across New Guinea during the last major glaciation, and area-based glacier snowlines in the Mt. Jaya region of Papua, Indonesia, during the Last Glacial Maximum

Geomorphological mapping and lake-core data from Mt. Jaya, western New Guinea, show that Last Glacial Maximum (LGM) glaciation was less extensive than previously thought. Average equilibrium line altitudes (ELAs), calculated using the area–altitude-balance ratio method, for minimum and maximum ice configurations were 4050±49 and 4000±56 m a.s.l., respectively. This is about 600 m below the ELA of the Mt. Jaya glaciers in 1971–73 and ca 400 m higher than values previously quoted for LGM ELAs in this area. A reappraisal of the evidence used to reconstruct the ELA of glaciers across New Guinea suggests that published chronologies are not sufficient to demonstrate that reported ELAs fall within the LGM window of 21,000±2 yr BP. Furthermore, the published information only constrains the altitude of the ELAs between 3400 and 3800 m a.s.l., not including uncertainty in topography. A simple mass and energy-balance model indicates that an ELA depression of 500 m (i.e., the observed change at Mt. Jaya after adjustment for sea-level change) could be accomplished with 2.5–3 °C of cooling provided precipitation was reduced by 35% and lapse rate changed. This cooling is less than the 6–8 °C cooling inferred from LGM pollen.

Last Glacial Maximum equilibrium line altitudes in the circum-Caribbean (Mexico, Guatemala, Costa Rica, Colombia, and Venezuela)

Equilibrium line altitude (ELA) estimates for Last Glacial Maximum (LGM) paleoglaciers in Mexico, Guatemala, Costa Rica, Colombia, and Venezuela were determined using the accumulation area balance ratio (AABR), accumulation area ratio (AAR), toe-to-headwall altitude ratio (THAR), and the maximum altitude of lateral moraine (MALM) methods. LGM glacial expansions are chronologically constrained in Mexico, the Mérida Andes of Venezuela, the mountains around Bogotá, Colombia, and the Ruíz-Tolima massif, Colombia. Undated glacial sites are tentatively correlated to dated sites on the basis of similar moraine morphology and weathering characteristics. LGM ELAs are 3400–3950 m in central Mexico, 3544 m for Guatemala, 3477±13 m for Costa Rica, 4104±197 m for the Sierra Nevada de Santa Marta, Colombia, 3480 m for the Ruíz-Tolima region of Colombia, 3345±130 m for the mountains around Bogotá, Colombia, 4151±181 m for the Sierra Nevada de Cocuy, Colombia, and 3576±163 m for the Mérida Andes of Venezuela. As the modern ELA and/or 0 °C isotherm is found at 4900±200 m, LGM ELA depression in the circum-Caribbean region was between 500 and 1625 m.

Tropical climate at the last glacial maximum inferred from glacier mass-balance modeling.

Model-derived equilibrium line altitudes (ELAs) of former tropical glaciers support arguments, based on other paleoclimate data, for both the magnitude and spatial pattern of terrestrial cooling in the tropics at the last glacial maximum (LGM). Relative to the present, LGM ELAs were maintained by air temperatures that were 3.5 degrees to 6.6 degrees C lower and precipitation that ranged from 63% wetter in Hawaii to 25% drier on Mt. Kenya, Africa. Our results imply the need for a approximately 3 degrees C cooling of LGM sea surface temperatures in the western Pacific warm pool. Sensitivity tests suggest that LGM ELAs could have persisted until 16,000 years before the present in the Peruvian Andes and on Papua, New Guinea.