Equilibrium Line Altitude Lowering Research Articles

Reconstruction of Palaeoglacier in the Qugaqie valley in Nyainqêntanglha Range

Reconstruction of palaeoglacier is important for understanding the mechanism of palaeo-climatic change and predicting water resource in Tibet. The climate and water resource are sensitive to global change in western Nyainqêntanglha Range. However, the data of how glacier changed in its area and equilibrium line, particularly its volume are still in paucity. In this study, we generated the palaeoglacier landform map by field investigation and 3S (RS, GPS and GIS) technology, reconstructed the palaeoglaciers surface by glacial landforms and glacier model, accordingly estimated the ice volume and equilibrium line altitude (ELA), and then discussed the palaeo-climate during the last glacial maximum (LGM) in the Qugaqie valley. During the LGM, the Qugaqie glacier was about 18.5 km long and 102.1 m thick in average. It covered an area of 59.1 km2 and had a volume of 6.05 km3, which were 8.34 times of the area and 18.33 times of the ice volume of the modern glacier. The 75.3% of Qugaqie valley was covered by glacier. The palaeo-ELA was 5405∼5496 m with a depression of 400 to 300 m, which confirms Shi Yafeng’s point that an even global ELA lowering value of about 1000 m didn’t virtually exist.

Glacier sensitivity to equilibrium line altitude and reconstruction for the Last Glacial cycle: glacier modeling in the Payuwang Valley, western Nyaiqentanggulha Shan, Tibetan Plateau

Glaciers respond sensitively to climate change and paleoclimate conditions can be inferred from the geomorphic evidence by reconstructing equilibrium line altitude (ELA) and by modeling glacier mass balance and ice flow. However, such work has not been extensively carried out on the vast Tibetan Plateau, and thus the knowledge of glacier sensitivity to paleoclimate change and paleoglacier volume is still lacking on the plateau. Recent improvements in understanding glacial extent and chronology in the Payuwang Valley, southern Tibetan Plateau, present an opportunity to estimate the paleoclimate conditions during the Last Glacial cycle. Using a coupled mass-balance and ice-flow model, this study tests the glacier sensitivity to ELA change in the Payuwang Valley. By fitting modeled glaciers to the corresponding moraine positions, we reconstruct glacier extents probably occurred at oxygen isotope stage 3 (MIS 3) and Last Glacial Maximum (LGM) in the valley and infer the related climate conditions that could have supported these glacier advances. The glacier sensitivity tests indicate that in the Payuwang Valley, the glaciers responded to centennial-scale shifts in climate. With ELAs below 5600m asl, the tributary glaciers coalesce into the main valley and expand rapidly there. The model results also show that the Payuwang Valley contained ice volumes of ~1.58×109m3 and ~1.23×109m3 with ELA lowering values of 370m and 340m in the MIS 3 and LGM glacial advances, respectively. By examining other independent paleoclimatic reconstructions, we conclude that during the MIS 3 glacier advance, the temperature was only 1.5°C lower or even 0.2°C higher than the period of 2005–2008 with precipitation 40–100% higher than the 2005–2008 amount; and during the LGM glacier advance, the temperature was 3.3–4.4°C lower than the period of 2005–2008 with the precipitation 30–70% lower than the 2005–2008 amount. These estimates add to the knowledge of better understanding the relationship between glacier dynamic and climatic change on the Tibetan Plateau.

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.

Spatial patterns of Holocene glacier advance and retreat in Central Asia

Glaciers in the southern Himalayas advanced in the early Holocene despite an increase in incoming summer solar insolation at the top of the atmosphere. These glacier advances are in contrast to the smaller alpine glaciers in the western and northern regions of Central Asia. Two different glacier mass-balance models are used to reconcile this Holocene glacier history with climate by quantifying the change in equilibrium-line altitudes (ELA) for simulated changes in Holocene climate. Both ELA models clearly show that the lowering of ELAs in the southern Himalayas is largely due to a decrease in summer temperatures, and that an increase in monsoonal precipitation accounts for less than 30% of the total ELA changes. The decrease in summer temperatures is a dynamic response to the changes in solar insolation, resulting in both a decrease in incoming shortwave radiation at the surface due to an increase in cloudiness and an increase in evaporative cooling. In the western and northern zones of Central Asia, both ELA models show a rise in ELAs in response to a general increase in summer temperatures. This increase in temperatures in the more northern regions is a direct radiative response to the increase in summer solar insolation.

Last glacial maximum equilibrium-line altitude and paleo-temperature reconstructions for the Cordillera de Mérida, Venezuelan Andes

The pattern and magnitude of glacier equilibrium-line altitude (ELA) lowerings in the tropics during the last glacial maximum (LGM) are topics of current debate. In the northern tropics, paleo-ELA data are particularly limited, inhibiting the ability to make regional and large-scale paleoclimatic inferences. To improve these records, nine paleo-glaciers in the Venezuelan Andes were reconstructed based on field observations, aerial photographs, satellite imagery and high-resolution digital topographic data. Paleo-glacier equilibrium-line altitudes (ELAs) were estimated using the accumulation-area ratio (AAR) and the area-altitude balance ratio (AABR) methods. During the local LGM in Venezuela (∼ 22,750 to 19,960 cal yr BP), ELAs were ∼ 850 to 1420 m lower than present. Local LGM temperatures were are at least 8.8 ± 2°C cooler than today based on a combined energy and mass-balance equation to account for an ELA lowering. This is greater than estimates using an atmospheric lapse rate calculation, which yields a value of 6.4 ± 1°C cooler. The paleo-glacial data from the Venezuelan Andes support other published records that indicate the northern tropics experienced a greater ELA lowering and possibly a greater cooling than the Southern Hemisphere tropics during the LGM.

A modelling reconstruction of the last glacial maximum ice sheet and its deglaciation in the vicinity of the northern patagonian icefield, south america

ABSTRACT. A time‐dependent model is used to investigate the interaction between climate, extent and fluctuations of Patagonian ice sheet between 45° and 48°S during the last glacial maximum (LGM) and its subsequent deglaciation. The model is applied at 2 km resolution and enables ice thickness, lithospheric response and ice deformation and sliding to interact freely and is perturbed from present day by relative changes in sea level and equilibrium line altitude (ELA). Experiments implemented to identify an LGM configuration compatible with the available empirical record, indicate that a stepped ELA lowering of 750 to 950 m is required over 15000 years to bracket the Fenix I‐V suite of moraines at Lago Buenos Aires. However, 900 m of ELA lowering yields an ice sheet which best matches the Fenix V moraine (c. 23000 a BP) and Caldenius’ reconstructed LGM limit for the entire modelled area. This optimum LGM experiment yields a highly dynamic, low aspect ice sheet, with a mean ice thickness of c. 1130 m drained by numerous large ice streams to the western, seaward margin and two large, fast‐flowing outlet lobes to the east. Forcing this scenario into deglaciation using a re‐scaled Vostok ice core record results in an ice sheet that slowly shrinks by 25% to c. 14500 a bp, after which it experiences a rapid collapse, loosing some 85% of its volume in c. 800 years. Its margins stabilize during the Antarctic Cold Reversal after which it shrinks to near present‐day limits by 11 000 a bp.

Constraints on ice‐sheet thickness over Tibet during the last 40 000 years

AbstractThe Late Quaternary glaciation of Tibet has received considerable attention in the last few decades due to its influence on the regional climate, especially the Asian summer monsoon. Recently, however, it has been argued that the Tibetan ice sheet also might have played an important role in initiating global‐scale palaeoclimatic changes. Controversy, however, exists on the nature of Late Quaternary ice cover over Tibet due largely to the subjectivity in the interpretation of the sparse and complex geomorphological evidence. We have examined this problem in the light of δ 18O data (a temperature proxy) of ice cores‐from the Dunde ice cap on the northern flank of Tibet. Considering only the gross features in the Dunde ice‐core isotopic data, we have interpreted a temperature decrease of 4°–6°C and consequent lowering of equilibrium line altitude (ELA) in the range 700–850 m during the last glacial stage (LGS). This could have caused depression of the snow line below the mean altitutde of the Tibetan plateau, resulting in an areally extensive but marginally thick ice cover. However, if one also considers the possibility that precipitation on the Tibetan plateau during LGS may have been significantly lower than at present, the ELA depression would be much less than that estimated by considering the temperature effect alone.

Younger dryas and holocene glacier fluctuations and equilibrium-line altitude variations in the Jostedalsbre region, western Norway

Reconstructed Younger Dryas (11000-10000 y BP) valley- and cirque glaciers west of the Jostedalsbre ice cap suggest an equilibrium-line altitude (ELA) depression of 450±50 m compared to the present level. The mid-Preboreal (9500±200 y BP) deglaciation was characterized by vertical wastage, indicating that the ELA was above the summit plateaus. During the Erdalen event (9100±200 y BP) marginal moraines were formed up to 1 km beyond the Little Ice Age (LIA) moraines which lie in front of the present valley outlet glaciers of the Jostedalsbre ice cap. The average ELA lowering during this event is calculated to 325 m below the modern level. Lithostratigraphic and paleobotanical studies show that the Hypsithermal (ca. 8000-6000 y BP) ELA was about 450 m higher than at present. As a result, Jostedalsbreen probably disappeared entirely during that period. The glacier reformed about 5300 y BP. The ELA intersected the modern mean equilibrium line altitude five times from ca. 2600 y BP to the present. The outlet valley glaciers reached their maximum Neoglacial extent during the LIA in the mid-18th century, when the ELA was depressed 100–150 m below the present level.

The age and origin of Neoglacial moraines in Jotunheimen, southern Norway: new evidence from weathering‐based data

This paper considers the controversial issue of the existence of pre‐‘Little Ice Age’ Neoglacial moraines in southern Norway. Schmidt hammer rebound values are combined with measures of boulder roundness and weathering rind thickness in an attempt to isolate moraines that include weathered boulders. A critical approach is used in distinguishing sites where boulders have weathered in situ from those where previously weathered clasts have been incorporated into relatively young moraines. The results confirm that possible pre‐‘Little Ice Age’ Neoglacial moraines seem to be restricted to small, high‐altitude glaciers in eastern Jotunheimen. It is concluded that at these glaciers a particularly large response to a short‐lived earlier Holocene climatic event is more likely to explain the survival of such moraines than a particularly subdued response to the climatic deterioration of the ‘Little Ice Age’. More refined dating techniques are required to determine the age of formation of the anomalous moraines, but before the palaeoclimatic significance of such dates can be assessed, a critical test is required to establish whether the moraines mark former ice‐front positions, and therefore reflect lowering of equilibrium line altitudes, or whether they have been displaced forwards by later and more extensive glacier advances.

Mass Balance of “Vesper” Glacier, Washington, U.S.A.

AbstractDuring 1974–75 glaciologic and geologic studies were conducted on a small (0.17 km2) avalanche-nourished glacier in the North Cascade Range of Washington. The approximate equilibrium-line altitude (ELA) for this ice body, informally called “Vesper” glacier, lies at 1475 m, some 300 m below the regional ELA value. Estimated annual accumulation was 6 100±675 mm during the two years of study; 15 to 30% of this flux resulted from avalanche and wind–transported snow. Average annual ablation during the period was 5 350 mm, giving a total net balance of + 1 600 mm for the two-year study period. “Vesper” glacier persists well below the regional snow-line because of excessive local precipitation, substantial avalanche contributions, and a favourable north-facing aspect.Neoglacial moraines indicate that maximum ELA lowering in this period was approximately 165 m and occurred prior to a.d. 1670. Minor re-advances occurred during the nineteenth century. These reconnaissance measurements are consistent with the sparse geologic data reported from other glaciers in the Cascade Range. While the relationship between regional lowering of snow-line and avalanche activity is uncertain at present, these data suggest that avalanche-nourished glaciers provide a useful record of climatic fluctuations.

Mass Balance of “Vesper” Glacier, Washington, U.S.A.

AbstractDuring 1974–75 glaciologic and geologic studies were conducted on a small (0.17 km2) avalanche-nourished glacier in the North Cascade Range of Washington. The approximate equilibrium-line altitude (ELA) for this ice body, informally called “Vesper” glacier, lies at 1475 m, some 300 m below the regional ELA value. Estimated annual accumulation was 6 100±675 mm during the two years of study; 15 to 30% of this flux resulted from avalanche and wind–transported snow. Average annual ablation during the period was 5 350 mm, giving a total net balance of + 1 600 mm for the two-year study period. “Vesper” glacier persists well below the regional snow-line because of excessive local precipitation, substantial avalanche contributions, and a favourable north-facing aspect.Neoglacial moraines indicate that maximum ELA lowering in this period was approximately 165 m and occurred prior to a.d. 1670. Minor re-advances occurred during the nineteenth century. These reconnaissance measurements are consistent with the sparse geologic data reported from other glaciers in the Cascade Range. While the relationship between regional lowering of snow-line and avalanche activity is uncertain at present, these data suggest that avalanche-nourished glaciers provide a useful record of climatic fluctuations.