Displays

Thick supraglacial debris covers the ablation areas of many large Himalayan glaciers, particularly those in the Everest region where debris is typically several metres thick. Sustained mass loss from these high-elevation debris-covered glaciers is causing supraglacial debris layers to expand and thicken. However, at the same time, regional satellite observations have demonstrated that debris-covered glaciers in High Mountain Asia are currently losing mass at the same rate as clean-ice glaciers. This greater than expected mass loss—sometimes referred to as the “debris-cover anomaly”—could be due to surface processes that locally enhance ablation, including the formation and decay of ice cliffs and supraglacial ponds.

We tested the hypothesis that the presence of ice cliffs and supraglacial ponds is responsible for the rapid decay of debris-covered Himalayan glaciers, using a numerical glacier model that includes the feedbacks between debris transport, mass balance and ice flow. We show that parameterising differential ablation processes in our higher-order ice flow model of Khumbu Glacier in Nepal does increase glacier-wide mass loss, but is not sufficient to match the observed glacier surface elevation change between 1984 and 2015 CE. Additional mass balance forcing is required to simulate the remaining mass balance change, which may represent the impact of rising air temperatures on englacial and supraglacial hydrology or englacial ice temperatures. Under a moderate future warming scenario (RCP4.5), Khumbu Glacier is projected to lose 59% of ice volume by 2100 CE, and 94% by 2200 CE accompanied by a dynamic shutdown that causes the death of this iconic glacier by 2160 CE.

How to cite: Rowan, A., Egholm, D., Quincey, D., Hubbard, B., Miles, E., Miles, K., and King, O.: Accelerating recent mass loss from debris-covered Khumbu Glacier in Nepal, and projected response to climate change by 2200 CE, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20189, https://doi.org/10.5194/egusphere-egu2020-20189, 2020.

The equilibrium line altitudes (ELAs) of past cirque glaciers are used to obtain quantitative palaeoclimatic information from Alpine environments. The dimensions of these glaciers, and therefore their ELAs, are partly reconstructed from ice-free glacial cirques. However, in order to derive palaeoclimatic data for a particular time period, studies typically gloss-over the fact that cirques are time-transgressive landforms, shaped over multiple glacial cycles. In this study, we test the time-transgressive nature of cirque formation and assess the validity of using cirques as indicators of climate during individual glacial periods. To achieve this, we reconstruct glaciers and obtain palaeo ELAs from ∼4000 cirques across Norway and Sweden. The cirques are mapped in GIS, and the GlaRe tool is used to reconstruct glacier outlines before palaeo ELAs are estimated. The population of cirques is analysed to investigate whether sub-divisions can be made on the basis of floor altitude, aspect, and links to known palaeoclimatic patterns. In all, this study allows us to test the usefulness of cirques as indicators of palaeoclimate during specific time periods.  

How to cite: Oien, R., Spagnolo, M., Rea, B., Barr, I., Bingham, R. G., and Jansen, J.: Analysing palaeo cirque glacier equilibrium line altitudes as indicators of palaeoclimate across Scandinavia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16981, https://doi.org/10.5194/egusphere-egu2020-16981, 2020.

Subglacial carbonate deposits have been exposed on the lee sides of small protuberances on a bare polished and striated limestone bedrock surface in the immediate vicinity of the retreating Triglav Glacier in southeastern Alps. They are fluted and furrowed crust-like deposits generally around 5 mm thick and characterized by brownish, greyish or yellowish colour. The deposits are generally around 0.5 cm in thickness and internally laminated. They offer a unique opportunity to gain additional knowledge of the past glacier’s behaviour and consequently the characteristics of the past climate which is essential to understand and predict future changes. Currently, the known extent and behaviour of the Triglav Glacier spans from the present to the Little Ice Age, the cool-climate anomaly between the Late Middle Ages and the mid-19th century, and is based on geomorphological remnants, historical records, and systematic monitoring. However, the preliminary uranium-thorium (U-Th) ages of the subglacial carbonates yielded considerably old ages: 23.62 ka ± 0.78 ka, 18.45 ka ± 0.70 ka and 12.72 ka ± 0.28 ka; the results indicate that these subglacial carbonate dates fall within the Last Glacial Maximum (LGM) and the Younger Dryas (YD).

The Triglav Glacier has generally been viewed as relict of the LIA, with discontinuous presence due to the Holocene Climatic Optimum, a period of high insolation and generally warmer climate between 11,000 and 5,000 years BP. Present chemical denudation rates of carbonate rocks in Alpine and temperate climate vary from ca. 0.009 to 0.140 mm/year. Taking the low and high extreme values for, e.g., 6 ka during the Holocene Climatic Optimum, the denudation in the Triglav area would be between 54 and 840 mm, so the exposed 5 mm thick subglacial carbonate would have already been denuded if exposed in the past. In addition, carbonate surfaces in periglacial areas are additionally exposed to frost weathering, promoting disintegration of depositional features. And lastly, glaciers cause pronounced erosion and in case of just a short-term retreat beyond the subglacial carbonates, the re-advance of the glacier would likely abrade the deposits. Therefore, had the subglacial carbonate deposits been exposed in the past, they should have been eroded by chemical denudation, frost weathering, or erosion at the onset of individual Holocene glacial expansion episodes, such as the LIA. May the presence of subglacial carbonates dated to the LGM and the YD at the Triglav Glacier suggest the continuous existence of the glacier throughout all but the latest Holocene?

How to cite: Lipar, M., Martín Pérez, A., Tičar, J., Pavšek, M., Gabrovec, M., Hrvatin, M., Komac, B., Zorn, M., Zupan Hajna, N., Zhao, J., Drysdale, R., and Ferk, M.: Recently exposed subglacial carbonate deposits at the retreating Triglav Glacier, Slovenia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21664, https://doi.org/10.5194/egusphere-egu2020-21664, 2020.

The deglaciation of the Italian Central Alps is still discussed and not well known, especially when we consider the Late Pleistocene-Early Holocene. This study will use different fraction of the iron content of paleo-spodosols to date the time of the deglaciation of three areas in the Central Italian Alps (Gavia, Stelvio and Val Viola). Relying on a first soil distribution analysis and on geomorphological evidences, we opened and described 24 soil pits and from each A and B horizon we collected at least 1 kg of sample to do some basic soil physical analysis: granulometry, water content, pH and loss on ignition. The oxalate extractable iron fraction and the dithionite extractable iron fraction have been determined with standard lab procedures, the total iron content has been determined using a SEM/EDX analysis. We calculated the Iron Crystallinity Ratio, defined as the difference between the dithionite extractable iron fraction and the oxalate extractable iron fraction, normalized on the total iron content. The Iron Crystallinity Ratio gives us a relative age of the soil formation: using data from radiocarbon dating and from cosmogenic dating, we calibrated the Iron Crystallinity Ratio with absolute ages. With the obtained functions, which showed a good fitting, we calculated ages between 15809 years and 5490 years in the Gavia area, between 11760 years and 7237 years in the Stelvio area and between 14668 years and 7096 years in the Val Viola area.

How to cite: Longhi, A. and Guglielmin, M.: Iron Chemical Analysis of Spodosols to Date Last Pleistocene-Holocene. The Example of the Italian Central Alps., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1450, https://doi.org/10.5194/egusphere-egu2020-1450, 2020.

Mountain glaciers are useful quantitative paleoclimate proxies because of their mass-balance being sensitive to both temperature and precipitation. Paleoglacial reconstructions in the Alps, together with other paleoclimate proxies^[1], suggest a shift in Alpine atmospheric circulation during the Last Glacial Maximum (LGM), with a change from northerly (Atlantic) to south-westerly (Mediterranean) moisture advection^[2]. However, the post-LGM reorganization of the atmospheric circulation system in terms of both amplitude and timing remains elusive, as well as the resulting glacier response in the Alps^[3,4].

This study focuses on Aosta Valley and its tributaries (SW Alps, Italy). Few chronological constraints are available for the post-LGM glacial history of the region, mainly related to the Ivrea Amphitheatre (terminal extent of Pleistocene glaciations)^[5] and the Mont-Blanc massif^[6]. We aim to quantify the potential variability in glacier responses for the different massif catchments of Aosta Valley, our working hypothesis being that they have distinct geomorphic (e.g. hypsometry) and climatic conditions (e.g. aspect, moisture sources). Following a detailed geomorphological mapping of glacial landforms and deposits, we sampled moraine boulders and glacially-polished bedrock for in-situ ¹⁰Be surface exposure dating in 3 main massifs: Mont-Blanc (Courmayeur), Matterhorn (Valpelline) and Gran Paradiso (Val di Cogne and Valsavarenche). In addition, we also investigated the confluence between Aosta Valley and Gran Paradiso valleys (Saint Pierre area). Morphometric analyses were conducted to investigate the possible influence of local factors (e.g. hypsometry and aspect) on glacier fluctuations, before isolating a climatic signal from our paleoglacial reconstructions.

Our ¹⁰Be chronology and boulder provenance results testify that glaciers from Mont-Blanc were lastly occupying the Aosta Valley in Saint Pierre at ca. 15 ka, while Gran Paradiso glaciers had already retreated within tributary valleys. In the upper Aosta Valley, Mont-Blanc glaciers retreat is marked by at least^[7] two Late-glacial stages nearby Courmayeur at ca. 14 and 11 ka. Bedrock deglaciation profiles in Valpelline (SW of Matterhorn) record an onset of ice-thinning at ca. 14 ka, well after glacier retreat from the Ivrea Amphitheatre (20-24 ka)^[5]. This result agrees with other studies from high Alpine passes^[9], supporting the idea that glaciers thinning within the high Alps clearly postdated the rapid post-LGM deglaciation in the foreland. Final deglaciation of Valpelline occurred at ca. 10-11 ka (Younger Dryas), roughly synchronous with the final glacier retreat in Courmayeur. Additional ¹⁰Be samples from the Gran Paradiso valleys are under process to further assess potential spatial variability in post-LGM glacier fluctuations between the main northern and southern massifs. Finally, paleoglacial reconstructions and geochronology constraints will be included in ice numerical simulations to test the potential influence of precipitation changes on glacier retreat within the Aosta Valley.

References

^[1]Heiri, O. et al., 2014, Quaternary Science Reviews.

^[2]Florineth, D. & Schlüchter, C., 2000, Quaternary Research.

^[3]Luetscher, M. et al., 2015, Nature Communications.

^[4]Monegato, G. et al., 2017, Scientific reports.

^[5]Gianotti, F. et al., 2015, Alpine and Mediterranean Quaternary.

^[6]Wirsig, C. et al., 2016, Quaternary Science Reviews.

^[7]Porter, S. & Orombelli, G., 1982, Boreas.

^[8]Ivy-ochs, S., 2015, Cuadernos de Investigación Geográfica.

^[9]Hippe, K. et al., 2014, Quaternary Geochronology.

How to cite: Serra, E., Valla, P. G., Gribenski, N., Magrani, F., Carcaillet, J., and Deline, P.: Post-LGM glacial history of Aosta Valley (western Italian Alps) and implications for Alpine paleo-atmospheric circulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10157, https://doi.org/10.5194/egusphere-egu2020-10157, 2020.

Several studies applied numerical age determination methods to examine glacial phases of the central Balkan Peninsula. However, the resulting conflicting datasets require further discussion. This study provides ¹⁰Be Cosmic Ray Exposure (CRE) ages of a succession of glacial landforms in the Jablanica and Jakupica Mts (North Macedonia), aiming at a better understanding of Late Pleistocene glacier development in the area.

In the Jablanica Mt. (~41.25° N; Crn Kamen, 2257 m a.s.l.) six glacial stages were identified (Temovski et al., 2018). The CRE ages of five glacial stages (from the second oldest to the youngest) range from 16.8^+0.8/_-0.5 ka to 13.0^+0.4/_-0.9 ka. Accordingly, the most extensive glaciation in the Jablanica Mt. occurred before ~17 ka (Ruszkiczay et al., 2020).

Based on the accumulation area balance ratios (AABR) of the reconstructed glaciers, their mean equilibrium line altitudes (ELAs) were estimated. The average ELA of the glaciers was 1792±18 m a.s.l. during the largest ice extent, and 2096±18 m a.s.l. during the last phase of the deglaciation.

Independent reconstructions of key climatic drivers of glaciological mass balance suggest that glacial re-advances during the deglaciation in the Jablanica Mt. were associated to cool summer temperatures before ~15 ka. The last glacial stillstand may result from a modest drop in summer temperature coupled with increased winter snow accumulation. In the study area no geomorphological evidence for glacier advance after ~13.0^+0.4/_-0.9 ka could be found. Relying on independent climate proxies we propose that (i) the last glacier advance occurred no later than ~13 ka, and (ii) the glaciers were withdrawing during the Younger Dryas when low temperatures were combined with dry winters.

In the Jakupica Mt. (~41.7° N, Solunska Glava, 2540 m a.s.l.) a large plateau glacier was reconstructed. The study area comprised six eastward facing, formerly glaciated valleys. Cirque floor elevations range from ~2180 m a.s.l. at Salakova Valley, to between ~2115 and ~2210 m a.s.l. on the carbonate plateau. The lowest mapped moraines are descending down to 1550-1700 m a.s.l. Due to the large plateau ice and the complicated system of confluences, glacier reconstructions using semi-automated GIS tools are problematic. Four to six deglaciation phases were reconstructed, and a preliminary estimation of the ELAs based on the maximum elevation of the lowermost lateral moraines leads to ELA values of 1800±50 m a.s.l. for the most extended phase. Multiple CRE ages for the subsequent glacial stages are also being acquired for Jakupica Mts.

This research was supported by the NKFIH FK124807 and GINOP-2.3.2-15-2016-00009 projects, by the INSU/CNRS and the ANR through the program “EQUIPEX Investissement d’Avenir” and IRD and by the Radiate Transnational Access 19001688-ST.

Ruszkiczay-Rüdiger Zs., Kern Z, Temovski M, Madarász B, Milevski I, Braucher R, ASTER Team (2020) Last deglaciation in the central Balkan Peninsula: Geochronological evidence from Jablanica Mt (North Macedonia). Geomorphology 351: 106985

Temovski M, Madarász B, Kern Z, Milevski I, Ruszkiczay-Rüdiger Zs. (2018) Glacial geomorphology and preliminary glacier reconstruction in the Jablanica Mountain, Macedonia, Central Balkan Peninsula. Geosciences 8(7): 270

How to cite: Ruszkiczay-Rüdiger, Z., Kern, Z., Temovski, M., Madarász, B., Milevski, I., Braucher, R., Lachner, J., Steier, P., and Team, A.: Last deglaciation in the central Balkan Peninsula: geochronological evidence from the Jablanica and Jakupica Mts (North Macedonia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8126, https://doi.org/10.5194/egusphere-egu2020-8126, 2020.

Reconstructing the spatial and temporal variabilities of the vertical atmospheric temperature gradient (lapse rate, LR) is key to predict the evolution of glaciers in a changing climate. Variations in this parameter may indeed amplify or mitigate the future warming at high elevation, implying contrasted impacts on the stability of glaciers. Several regional studies suggested that the tropical LR was steeper than today during the last glacial maximum (LGM) (Loomis et al., 2017; Blard et al., 2007), while another study concluded that the LGM lapse rate was similar than today (Tripati et al., 2014).

Here we combine published LGM sea surface temperatures (SSTs) data and LGM moraines dated by cosmogenic nuclides to reconstruct the lapse rate along the American Cordillera. To do so, we combined paleo-Equilibrium Line Altitudes (ELAs) of glaciers with independent precipitation proxies to derive high latitude atmospheric temperatures. The whole dataset includes 34 paleo-glaciated sites along a North-South transect in the American Cordillera, ranging in latitude from 40°N to 36°S. Our reconstruction indicates that the lapse rate (LR) was steeper than today in the tropical American Cordillera (20°N – 11°S). The average ΔLR (LGM – Modern) for this Tropical Andes region (20°N – 11°S) is ~-2 °C.km^-1 (20 sites). At higher latitude, in both hemispheres, the LR was constant or decreased during the LGM. More precisely, this ΔLR change in the Central Andes (15°S – 35°S) is between 0 and 1°C.km^-1 (8 sites), while it is ~1 °C.km^-1 in Sierra Nevada and San Bernardino mountains (40°N – 34°N) (6 sites).

 Our results show that a drier climate during the LGM is systematically associated with a steeper LR. Modification of LR during the LGM was already observed from other tropical regions, in Hawaii-Central Pacific (Blard et al 2007), and in Eastern Africa (Loomis et al., 2017). Similarly, in these regions, precipitation did not increase during the LGM. With this multi-site exhaustive synthesis, we make a case that drier Tropical LGM conditions induce a steeper LR. This corresponds to an amplification of cooling at high altitude during the LGM. These results highlight the necessity to consider LR variations in modelling future climate. In a warmer and wetter Earth, temperature increase may be amplified at high elevation, due to smoother LR. If true, this mechanism indicates that tropical glaciers are more threatened by climate change than predicted by current climate modelling.

References

Blard, P.-H., Lavé, J., Pik, R., Wagnon, P., & Bourlès, D. (2007). Persistence of full glacial conditions in the central Pacific until 15,000 years ago. Nature, 449(7162), 591.

Loomis, S. E., Russell, J. M., Verschuren, D., Morrill, C., De Cort, G., Damsté, J. S. S., … & Kelly, M. A. (2017). The tropical lapse rate steepened during the Last Glacial Maximum. Science advances, 3(1), e1600815.

Tripati, A. K., Sahany, S., Pittman, D., Eagle, R. A., Neelin, J. D., Mitchell, J. L., & Beaufort, L. (2014). Modern and glacial tropical snowlines controlled by sea surface temperature and atmospheric mixing. Nature Geoscience, 7(3), 205.

How to cite: Blard, P.-H., Legrain, E., and Charreau, J.: Amplification of high-altitude temperature changes in the American Cordillera driven by precipitation during the Last Glacial Maximum, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19512, https://doi.org/10.5194/egusphere-egu2020-19512, 2020.

Glacier ice cores from mid latitude are capable of retaining essential information on past climate and anthropic activities at high time resolution. However, Alpine glaciers are also highly sensitive to the current atmospheric warming, which is seriously compromising the quality of the signal preserved in the ice and threatens the very persistence of these ice bodies.

In this context, we present new chronological and palynological results from a 46 m deep ice core extracted from the Adamello glacier in the locality Pian di Neve (3100 m a.s.l.). The glacier is situated in northern Italy and it is the most extened (16,3 km²) and deepest (257 m) glacier of the Southern European Alps. Ice core chronological results obtained from Cs-137, Pb- 210 isotopic analyses, black carbon and pollen annual layer counting will be discussed in the frame of the effects of the ongoing climate warming on Alpine glaciers. Furthermore, we will discuss the palynological data gained from the ice in terms of vegetation changes driven by the combined effect of intensive human activities and alarming climate change in the post World War II period.

How to cite: Festi, D., Jenk, T., Schwikowski, M., Maggi, V., and Oeggl, K.: The effects of climate warming inferred from an Adamello Glacier (Italy) ice core, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10786, https://doi.org/10.5194/egusphere-egu2020-10786, 2020.

The Aneto is the largest glacier of the Pyrenees, is located on the Maladeta Massif (Central Pyrenees), close to the highest point of the range, the Aneto peak (42° 37' 52 N, 0° 39' 24 E; 3,404 m a.s.l.). This glacier is 675 meters long, occupy an area of 48.64 ha and their maximum altitude is 3,269 meters. The glacier front ends at 3,029 m a.s.l. and its mean slope is 23.6°, reaching a maximum of 56° in some parts. The main aim of this research is to present a detailed volumetric reconstruction of the glacier since the LIA and analyze their retreat. Based on morphological features, the extent of the glacier has been reconstructed for different periods (LIA, 1957, 2000, 2006, 2015 and 2017) and their ice volume, maximum ice thickness and ELAs has been calculated. To delimitate the glacier extension during the LIA, the moraines have been mapped by using photo interpretation techniques. For the recent phases digital aerial photographs and satellite images have been used. To estimate the topography of the glacier we used a simple steady-state model that assumes a perfectly plastic ice rheology, reconstructing the theoretical ice profiles and obtaining the extent of the glaciers. Later, to reconstruct the ice surface we calculated longitudinal profiles, with these reconstructed profiles a digital elevation model was created and combined with the bedrock topography in order to obtain the ice thickness at each phase. This bedrock topography was obtained by combining the glacier topography with a 3D model of the glacier obtained with geo-radar (ERHIN program, Government of Aragon).

This study reveals a great retreat of the Aneto Glacier since the LIA. The length of the glacier has been reduced from 1,970 m during the LIA to 675 m in 2017, and its tongue has retreated from 2,385 to 3,029 m a.s.l. during the same period. Regarding the area, it has been reduced from 245 ha during the LIA to 48.64 ha in 2017. During this period, the ELA has increased from 2,925 to 3,140 m a.s.l. The glacier volume has been reduced from 82.57 x10⁶ m³ to 3.48 x10⁶ m³, and the maximum ice thickness from 95 m to 27m. These data reveals a huge retreat of the glacier since the LIA, furthermore, this retreat has been more accelerated since the 50's.

Research funded by PYRENEEND project (10.18258/11352)

How to cite: Campos, N., Alcalá, J., Watson, C. S., Grima, N., Kougkoulos, I., and Quesada, A.: Unraveling the retreat of the Aneto Glacier (Pyrenees, Spain) since the Little Ice Age, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1027, https://doi.org/10.5194/egusphere-egu2020-1027, 2020.

The Little Ice Age (LIA) occurred between CE 1250 and 1850 and is considered a period of moderate cold conditions, especially recorded in the northern hemisphere. Numerous recent studies provide robust evidence of glacier advances worldwide during the LIA and a dramatic retreat since then. These studies combined investigation of moraine records, paintings, topographical and glaciological measurements as well as multitemporal aerial and terrestrial photographs and satellite images. For instance, post-LIA glaciers retreat amounts ~60 % in the Alps (Paul et al., 2020), ~88 % in the Pyrenees (Rico et al., 2016) and 89 % in the Bolivian Andes (Ramírez et al., 2001). However, there is scarce knowledge in Mexico about the glacier changes since the LIA. The reconstructions are limited to the Iztaccíhualt volcano where Schneider et al. (2008) established a glacier retreat of 95 %.

Here, we reconstruct the glacier evolution since the LIA to CE 2015 of the Mexican highest ice-capped volcano: Pico de Orizaba (19° 01´ N, 97° 16´W, 5,675 m a.s.l.). Due to Pico de Orizaba is in the outer Tropic, the most plausible scenario is a glacier evolution similar to the Bolivian Andes and especially to the Iztaccíhualt volcano. To carry out this research, we mapped the glacier area during the LIA, based on moraine record, and the area during 1945, 1958, 1971, 1988, 1994, 2003 and 2015 using a previous map elaborated by Palacios and Vázquez-Selem (1996), aerial orthophotographs and satellite images. The geographical mapping and the calculus of area, minimum altitude and volume of the glacier were generated with the software ArcGIS 10.2.2. The results show that glacier area retreated 92% between the LIA (8.8 km²) and 2015 (0.67 km²), being a drastic glacier loss in agreement with the Bolivian Andes and Iztaccíhualt. Therefore, mexican glaciers have experienced the major shrunk since LIA that implies a highly sensitive reaction to global warming.

This research was supported by the Project UNAM-DGAPA-PAPIIT grant IA105318.

References

Palacios, D., Vázquez-Selem, L. 1996. Geomorphic effects of the retreat of Jamapa glacier, Pico de Orizaba volcano (Mexico). Geografiska Annaler, Series A, Physical Geography 78, 19-34.

Paul F., Rastner P., Azzoni R.S., Diolaiuti G., Fugazza D., Le Bris R., Nemec J., Rabatel A., Ramusovic M., Schwaizer G., and Smiraglia C. 2020. Glacier shrinkage in the Alps continues unabated as revealed by a new glacier inventory from Sentinel-2 https://doi.org/10.5194/essd-2019-213.

Ramírez, E., Francou, B., Ribstein, P., Descloitres, M., Guérin, R., Mendoza, J., Gallaire, R., Pouyaud, B., Jordan, E. 2001. Small glaciers disappearing in the tropical Andes: a case study in Bolivia: Glaciar Chacaltaya (16° S). Journal of Glaciology 47 (157), 187-194.

Rico I., Izagirre E., Serrano E., López-Moreno J.I., 2016. Current glacier area in the Pyrenees : an updated assessment 2016. Pirineos 172, doi: http://dx.doi.org/10.3989/Pirineos.2017.172004.

Schneider, D., Delgado-Granados, H., Huggel, C., Kääb, A. 2008. Assessing lahars from ice-capped volcanoes using ASTER satellite data, the SRTM DTM and two different flow models: case study on Iztaccíhuatl (Central Mexico). Natural Hazards and Earth System Sciences 8, 559-571.

How to cite: Alcalá Reygosa, J., Campos, N., Le Roy, M., Kozhikkodan Veettil, B., and Emmer, A.: Drastic glacier retreat at Pico de Orizaba (19º N, Mexico) since the Little Ice Age, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10863, https://doi.org/10.5194/egusphere-egu2020-10863, 2020.

Glaciers are important indicators of climate change and observations worldwide document increasing rates of mountain glacier recession. Here we present ~200 years of change in mountain glacier extent in northern Troms and western Finnmark. This was achieved through: (1) mapping recent (post-1980s) changes in ice extent from remotely sensed data and (2) lichenometric dating and mapping of major moraine systems within a sub-set of the main study area (the Rotsund Valley). Lichenometric dating reveals that the Little Ice Age (LIA) maximum occurred as early as AD 1814 (±41 years), which is before the early-20th century LIA maximum proposed on the nearby Lyngen Peninsula, but younger than the LIA maximum limits in southern and central Norway (ca. AD 1740-50). Between LIA maximum and AD 1989, the reconstructed glaciers (n = 15) shrank by 3.9 km² (39%), with those that shrank by >50% fronted by proglacial lakes. Between AD 1989 and 2018, the total area of glaciers within the study area (n = 219 in AD 1989) shrank by ~35 km². Very small glaciers (<0.5 km² in AD 1989) show the highest relative rates of shrinkage, and 90% of mapped glaciers within the study area are <0.5 km² as of AD 2018.

How to cite: Leigh, J., Stokes, C., Evans, D., Carr, R., and Andreassen, L.: ‘Little Ice Age’ maxima and glacier retreat in northern Troms and western Finnmark, northern Norway, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3905, https://doi.org/10.5194/egusphere-egu2020-3905, 2020.

The investigation of Holocene glacier chronologies has been recognised as a key element of research on mountain glaciations in the light of current global change. They can be utilised as high-resolution palaeoclimatic archives for the immediate and more distant geological past. During the past few decades considerable progress has been achieved, in particular due to substantial improvements of the ability to accurately date glacial landforms such as terminal moraines essential for reconstructing past glacier margins and subsequent analysis in the context of glacier advance/retreat periods. The Southern Alps of New Zealand are among the few suitable study sites for the investigation of Holocene glacier chronologies in the mid-latitudinal Southern Hemisphere that consequently have drawn attention.

Since early studies of Holocene glacier chronologies in the mid-20th century, mapping of the investigated glacier forelands has been an integrated part of almost all scientific approaches regardless of the individual dating methods that may have been applied. These mapping attempts serve the identification and positioning of certain glacial or glaciofluvial landforms subsequently allowing the reconstruction of former glacier margins. They frequently also provide information about the location of sample sites for the various dating techniques applied. If detailed geomorphological mapping schemes are in use, such maps additionally support the interpretation of any chronological data by identifying the genetic origin of any landform investigated, thus enabling to link the latter to different dynamic stages of the glacier. Additionally, such maps may highlight related uncertainties such as postdepositional disturbance or potentially unclear morphodynamic relationships to the glacier's behaviour.

Reviewing recent publications it seems, however, that some appraisal of such detailed geomorphological mapping is often traded-off against the impressive progress with up-to-date dating techniques and high-resolution digital elevation models or satellite/aerial imagery. Unfortunately, the latter do neither qualify as geomorphological maps per se or fully serve the abovementioned purposes. The widespread applied common GIS software has, furthermore, limitations with respect to its graphic capabilities and unintentionally entails negligence of established and well-suited signatures or mapping schemes.

A detailed geomorphological map of the glacier foreland of Mueller Glacier, Southern Alps/New Zealand is presented as a case study. It follows an established geomorphological mapping scheme ("GMK 25") that has been adequately modified to fit both purpose and selected scale. Despite several glacier chronological studies have been conducted on this glacier foreland and the site is considered as a regional key site for related research, this map constitutes the first of its kind. The detailed geomorphological map is utilised to assess discrepancies among existing chronologies by reviewing the morphometric properties and genetic origin of those landforms that have been dated. It reveals that potential postdepositional modification of some landforms investigated had not been appropriately considered with certain previous studies. As a result, the evidence of few glacier advances needs to be classified as weak.  

Summarising, detailed geomorphological mapping is still essential for the study of Holocene glacier chronologies and should not lose its prominent position or even disappear.

How to cite: Winkler, S.: Potential of detailed geomorphological mapping for the study of Holocene glacier chronologies: Mueller Glacier, Southern Alps/New Zealand, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1482, https://doi.org/10.5194/egusphere-egu2020-1482, 2020.

The glacier equilibrium line altitude (ELA) represents the elevation on the glacier surface at which the amount of mass gained (via precipitation, avalanching and windblown snow, equals the amount of ice lost (via ablation and sublimation, over the mass balance year. The ELA can be measured on modern glaciers or calculated for reconstructed, former glaciers. Despite its simple definition, the ELA represents an incredibly powerful, quantitative expression of the relationship between glaciers and climate. As a glacier responds dynamically to climate, so does the ELA. Precipitation at the glacier ELA has been empirically linked to ablation season temperature. Thus, the reconstruction of former glacier geometries and their ELAs leads to the quantification of palaeoclimate.

In recent years, the concept of an “average Quaternary ELA” (or “mean Quaternary ELA”) has become popular because of the role it might play in relation to the glacial buzzsaw hypothesis, i.e. the idea that glacial erosion could offset mountain uplift and therefore control and limit the growth of mountains. Attempts to determine the average Quaternary ELA have been undertaken, leading to some interesting conclusions. For example, it has been argued that the floor altitudes of glacial cirques can be used as a measure of average Quaternary ELA, therefore implying that average Quaternary mountain glaciers expansion was confined to the topmost portion of alpine valleys.

Time has passed from these initial attempts to determine the average Quaternary ELA and more palaeoclimatic and palaeoglaciological data have become available, so it is appropriate to reconsider these calculations and perhaps question the validity of such a concept. To do so, we revisit how the idea of an average Quaternary ELA developed and what such a parameter would really mean. We do so in light of a new quantitative study on the average ELA relative to both a single glacial cycle and multiple glaciations experienced during the past   ̴2.6 million years, i.e. the Quaternary. Collectively, this new study presents a very different perspective than previously suggested.

How to cite: Spagnolo, M., Rea, B., and Barr, I.: The (mis)conception of an average Quaternary equilibrium line altitude, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4167, https://doi.org/10.5194/egusphere-egu2020-4167, 2020.

Ice aprons are small but ubiquitous ice masses in high alpine ranges such as the Mont Blanc massif. Mainly present on its north faces above 3200 m a.s.l., they are a condition for practice of the so-called "traditional" mountaineering (now on the Intangible Cultural Heritage UNESCO list) and an indicator of the presence of permafrost in the bedrock. Most often thin (<10 m), these ice aprons are very sensitive to increasing air temperatures while their evolution during the recent decades suggests many coming disappearances in the short term and, consequently, a change in the permafrost thermal regime and a related increase in the rockfall occurrence.

Very few studied, ice aprons however represent an important glacial inheritance. We suggest that ice aprons are made up of very old ice, likely the oldest surface one in the Alps. In the north face of the Mont Blanc du Tacul (4248 m a.s.l.) for example, following the disappearance of the upper layers due to the increased occurrence of summer heatwaves, the ice on the present surface formed c. 2700 ago years (cold phase of Göschener I), against probably 200-300 years for the ice at the front of the Mer de Glace, the largest glacier in the French Alps. We present the ice ages acquired from five ice aprons on rock walls of the Mont Blanc massif together with ice ages from two glacier tongues of the massif (Mer de Glace and Miage Glacier).

How to cite: Ravanel, L., Preunkert, S., Guillet, G., Kaushik, S., Magnin, F., and Deline, P.: Ice aprons on steep North faces: oldest surface ice in the Alps?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11062, https://doi.org/10.5194/egusphere-egu2020-11062, 2020.

Modern systematic studies on the record of the Alpine Lateglacial (~ 19 – 11.7 ka) are missing for the Eastern Alps east of the Hohe Tauern mountain range. In order to fill this gap, a study has been started in the Niedere Tauern mountain range, which reaches 2862 m in altitude and comprises crystalline rocks. The recently non-glaciated mountain range is famous for a glacially shaped morphology with a series of cirques. During the Last Glacial Maximum (LGM), it was part of the transection glacier complex, which covered the western and central parts of the Eastern Alps. Thus, the conditions for studying the glacial chronology after the LGM are excellent.

In recent decades, three phases of glacier advances from cirques or higher altitude valleys have been distinguished within the Alpine Lateglacial, i.e. phase of ice-decay (immediately after the breakdown of the large valley glaciers like the Enns glacier), Gschnitz Stadial (correlated with the Heinrich 1 ice rafting event) and Egesen Stadial (marking the beginning of the Younger Dryas). A first step for additional paleogeographic, geochronological and palaeoglaciological studies in the Niedere Tauern is the identification and characterisation of the legacy of these three glacial phases within the Großsölk valley.

In this paper, we deal with the Egesen Stadial. New fieldwork reveals geomorphological and sedimentological evidence for glacier advances in three cirques in the Großsölk valley. Peaks bounding these east facing cirques are at 2400-2600 m altitude. The cirques contain lateral and end moraine ridges surrounding small tongue-shaped lake basins. These up to 5 m high ridges consist of boulder-bearing sandy to gravelly diamicts, which are interpreted to have formed during discrete phases of glacier stabilisation. The observed features in the three cirques allow us to interpret the following, from south to north:

1) A glacier at Lake Schimpelsee that extended down to 1930 m and which deposited three sharp crested end-moraines and one marginal moraine ridges during three stabilisation phases.
2) A similar glacier at Grünsee that extended down to 1920 m and underwent two stabilisation phases. An end moraine ridge is not observable, because in the suspected position there is a lake today. Evidence for the second stabilisation phase is partly overprinted by a relict rock glacier.
3) At Weißensee, large angular boulders along smoothed ridges testify to a debris-covered glacier in this area, which extended to 2000 m a.s.l.

Considering the altitude of the catchment area, the eastward facing orientation, the altitude of the maximum extent of the ancient glaciers as well as the geomorphologically constrained multiphase glacier retreat, we associate these glacier advances with the Egesen Stadial. Future radionuclide work will provide better age constraints for the Großsölk valley, extending knowledge of the Würmian Lateglacial to less investigated eastern parts of Austria.

How to cite: Griesmeier, G. E. U., Reitner, J. M., and Le Heron, D. P.: How extensive was the Younger Dryas glacier advance in Austria? New insights from the Großsölk Valley, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19645, https://doi.org/10.5194/egusphere-egu2020-19645, 2020.

The onset of Pleistocene glaciations in the European Alps represented a significant change in the palaeoenvironmental settings of this mountain range. The stratigraphy of the event was described in the subsoil of the Po Plain (Muttoni et al., 2003; Scardia et al., 2012) and is marked by a regional unconformity (namely “Red unconformity”, Muttoni et al., 2003) at 870 ka, in the final part of the Matuyama chron. Elsewhere, in the Alpine end-moraine systems the record of early stages of glaciations is scarce and cryptic. Spots of glacigenic deposits with reverse magnetic polarity were recognized only in the Ivrea (Carraro et al., 1991) and Garda (Cremaschi, 1987; Scardia et al., 2015) end-moraine systems, while deposits related to (peri)glacial environment were recorded along the Lombardian foothills (Scardia et al., 2010). The updated record of the Garda system shows the geometry of a late Matuyama glacier overrunning the piedmont plain with comparable size in respect to the LGM (Monegato et al., 2017). This indicates a fully glaciated Adige-Sarca catchment, one of the largest of the Alps, suggesting that the Alpine Ice Sheet reached one of its waxing climax during a late Matuyama cold stage (MIS20 or MIS22).

References

Carraro et al. 1991, Boll. Museo Reg. Sc. Nat. Torino 9, 99-117.

Cremaschi 1987, Edizioni Unicopli, 306 pp.

Monegato et al. 2017, Scientific Reports 7, 2078.

Muttoni et al. 2003, Geology 31, 989-992.

Scardia et al. 2010, Quaternary Science Reviews 29, 832-846.

Scardia et al. 2012, Tectonics 31, TC6004.

Scardia et al. 2015, GSA Bulletin 127, 113-130.

How to cite: Monegato, G. and Scardia, G.: The late Matuyama glaciation in the southern European Alps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3426, https://doi.org/10.5194/egusphere-egu2020-3426, 2020.

Chronological evidence from the southern part of the Alps (Monegato et al. 2017) indicates an earlier last glacial maximum of the Alpine glaciers relative to the Eurasian Ice Sheet maximum extent. This asynchronicity is probably due to the expansion of the North American Ice Sheet causing a southward shift of the North Atlantic jet stream and the establishment of a meridional atmospheric circulation over Europe (Luetscher et al. 2015). The advection of humid air masses from the Mediterranean Sea caused the Alpine glaciers to reach their maximum extent prior to the Eurasian ice sheet. Hence, the ice cap of the southern Black Forest must have been in a lee position with respect to the Alpine glaciers. This suggests that the last glacial maximum in the Black Forest was out of phase with the Alps. Since the lack of chronological data from the southern Black Forest prevents this hypothesis to be tested, a glacier chronology is crucially needed. As a first step towards such a framework, glacial landforms in the southern Black Forest are mapped based on both the analysis of highresolution LiDAR (Light detecting and ranging) data and its derivates as well as field mapping. Geomorphological mapping of a key site resulted in the identification of 18 ice-marginal positions in a single valley, whereby a significant number of moraines has been mapped for the first time. These findings reinforce the idea of a dynamic Lateglacial in the southern Black Forest interrupted by multiple periods of moraine stabilisation. Additional geomorphological and sedimentological investigations will be carried out to provide a solid base for the application of up-to-date geochronological methods (¹⁰Be exposure dating of boulders on moraines and optically stimulated luminescence dating) with particular emphasis on supposed last local glacial maximum moraines. Geomorphological, sedimentological and geochronological evidence will then be combined for palaeoglacier modelling. The determination of equilibrium line altitudes will ultimately enable the determination of palaeo-precipitation and –temperature during the last local glacial maximum and the subsequent Lateglacial. This palaeoclimatic reconstruction will be supported by data from the lake Bergsee record (southernmost Black Forest) spanning the 45-14.7 ka period (Duprat-Oualid et al. 2017).

References

Duprat-Oualid F., Rius D., Bégeot C., Magny M., Millet L., Wulf S., Appelt O. 2017. Vegetation response to abrupt climate changes in Western Europe from 45 to 14.7 k cal a BP: the Bergsee lacustrine record (Black Forest, Germany). J. Quaternary Sci. 32, 1008-1021.

Luetscher M., Boch R., Sodemann H., Spötl C., Cheng H., Edwards R.L., Frisia S., Hof F., Müller W. 2015. North Atlantic storm track changes during the Last Glacial Maximum recorded by Alpine speleothems. Nat. Commun. 6, 6344.

Monegato G., Scardia G., Hajdas I., Rizzini F., Piccin A. 2017. The Alpine LGM in the boreal ice-sheets game. Sci. Rep-UK 7, 2078.

How to cite: Hofmann, F. M., McCreary, W., and Preusser, F.: Was the last glaciation of the Black Forest (southern Germany) synchronous with the Alpine glaciation?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-136, https://doi.org/10.5194/egusphere-egu2020-136, 2020.

The Šumava/Bayerischer Wald mountains are located to the north of the eastern Alps, at the borders of present-day Austria, Bavaria and the Czech Republic. The Šumava/Bayerischer Wald belong to the Variscan mountain ranges of central Europe; these ranges hosted mountain glaciers at the times when the region of central Europe formed a broad unglaciated corridor between the glaciated Alps and the southern margin of the Fennoscandian Ice Sheet. While the region was home to some of the early studies into Pleistocene glaciations in the 19^th century, there is still uncertainty both about the maximum extent of Pleistocene glaciation and its chronology. With the availability of high-resolution digital elevation data it is now possible to map the geomorphological traces of glaciation better than before.

We mapped glacial geomorphology from high-resolution digital elevation data for the entire mountain range. We newly find evidence of glacial erosion outside of the well-developed and earlier studied glacial cirques. Widespread traces of glacial erosion in the relatively low-relief, high-elevated central portion of the range indicate that the maximum Pleistocene extent of glaciation might have taken the form of an icefield. The scarcity of glacial depositional landforms beyond the well-developed glacial cirques (the moraines of which have earlier been dated to Marine Isotope Stage 2) may indicate that the icefield existed during one or more of the earlier cold stages of the Pleistocene and most of the depositional landforms formed by those glaciations have since been denudated. Quantitative geochronology would have the potential to correlate the occurrence of the inferred icefield in the Šumava/Bayerischer Wald mountains with the glaciations of the eastern Alps.

How to cite: Margold, M. and Krause, D.: Geomorphological evidence of icefield-style glaciation in the Šumava/Bayerischer Wald mountains, Central Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8450, https://doi.org/10.5194/egusphere-egu2020-8450, 2020.

During the last Pleistocene glaciation, dozens of mountain ranges in the Great Basin of the western United States were glaciated and numerous valleys were occupied by pluvial lakes. This unique setting provides an opportunity to reconstruct regional-scale climate change during the last glacial-interglacial transition based on a well-documented record of lacustrine deposits and moraines. Chronologies of water-level changes in pluvial lakes throughout the Great Basin have been developed through decades of effort chiefly involving radiocarbon dating of fossil material recovered from paleoshorelines and sediment cores. Glacial chronologies have been developed more recently through cosmogenic nuclide exposure dating of glacial features in mountains of the northern Great Basin. Here, we resolve the relative timing of mountain glacial maxima and pluvial lake highstands based on an analysis of these chronologies. The moraine record displays evidence of two intervals of near-maximum glacier length, one represented by terminal moraines with cosmogenic nuclide exposure ages 22-19 ka, and another represented by downvalley recessional moraines with exposure ages 18-16 ka. The earlier maximum corresponds to the latter part of the global Last Glacial Maximum, during which lake highstands occurred in the southern Great Basin, whereas many lakes in the northern Great Basin were below their highstand levels. The climate in the northern Great Basin during this interval was apparently cold enough to drive glaciers to their maximum extents but too dry for the expansion of lakes, in contrast to the southern Great Basin where conditions were wetter. The latter glacial maximum was synchronous with lake highstands across much of the Great Basin and to the early part of Heinrich Stadial 1, which featured persistent cooling and shifting precipitation patterns in western North America. Most lake highstands occurred at this time, although some lakes in the extreme northwestern Great Basin reached highstands somewhat later. Widespread lake highstands during the interval 18-16 ka combined with near-maximum glacier lengths suggests a cool and wet climate favoring both glacial and lacustrine maxima, despite rising atmospheric greenhouse gases and summer insolation. Nearly all downvalley moraines in the Great Basin were abandoned by 16 ka, whereas many lakes persisted until 15 ka or later. This pattern suggests a climatic shift at ca. 16 ka to conditions favoring lakes but not glaciers. By the time of the last lake highstands, glaciers had diminished greatly in length and were generally confined to cirques.

How to cite: Laabs, B. and Munroe, J.: Relative timing of mountain glacial maxima and pluvial lake highstands in the Great Basin, western United States, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11051, https://doi.org/10.5194/egusphere-egu2020-11051, 2020.

The timing and extent of mountain glaciation during the Late Pleistocene shows considerable variability around the world. Identifying the nature and timing of glaciation is important for understanding landscape evolution and changing climatic conditions (precipitation and temperature). In the Balkans, glaciers were actually larger during the Middle Pleistocene when large ice caps formed in several mountain ranges including the Dinaric Alps, Montenegro, and the Pindus Mountains, Greece. Glaciations younger than Marine Isotope Stage 6 were characterised by smaller ice masses with glaciers mainly restricted to the highest mountains. The behaviour of Late Pleistocene glaciers in this region influenced the timing of sediment and meltwater delivery to river systems; the migration of modern humans across Europe; and the dynamics of biological refugia. However, dating control is limited for Late Pleistocene glaciers in the Balkans.

Here we report new in-situ ³⁶Cl terrestrial cosmogenic nuclide exposure ages from moraine boulders sampled in the Velika Kalica valley, in the Durmitor massif, Montenegro. This valley was targeted because it contains the Debeli Namet glacier - the last remaining glacier in Montenegro. We have sampled 25 limestone boulders from 5 moraines situated down-valley of the current glacier at altitudes between 1650–2000 m. AgCl targets for ³⁶Cl assay were prepared at The University of Manchester and ³⁶Cl concentrations were measured on the SIRIUS 6MV accelerator at the Centre for Accelerator Science at the Australian Nuclear Science and Technology Organisation. At the last local glacial maximum, the Debeli Namet glacier extended almost 3 km beyond its current position. These ³⁶Cl analyses are part of a wider regional Mediterranean study, totalling >50 new exposure ages, which also includes Mount Tymphi in the Pindus Mountains, NW Greece. The project will address both a significant spatial and temporal gap in Mediterranean glacial chronologies by targeting the hitherto undated Late Pleistocene glacial record. The work in Montenegro will also shed light on the nature of Holocene glaciation in the Balkans.

How to cite: Allard, J., Hughes, P., Woodward, J., Fink, D., Simon, K., Wilcken, K., and Tomkins, M.: Late Pleistocene glacial chronologies in the Balkans: new 36Cl exposure-age dating from Montenegro and Greece, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9744, https://doi.org/10.5194/egusphere-egu2020-9744, 2020.

Reasons for restricted and non-uniform glaciation over High-Mountain Asia (HMA) during last glacial maximum (LGM) have been intensively studied but remain elusive. Using a 1-km-resolution ice-sheet model, we show glaciers across HMA exhibit high region-variability in glaciation. Glaciers in western and southern HMA are the most sensitive to climate change and those in the interior are the least sensitive. Our model broadly reproduces the restricted glaciation across HMA during LGM, although it overestimates the extent of glaciation over western and southern HMA as compared with reconstructions. Modelled decreases in precipitation hampers glacier growth over northern HMA, while insufficient cooling hampers glacier advance over eastern HMA for LGM. Both reduced precipitation and insufficient cooling inhibit large-scale glaciation over inner HMA. Moreover, climatic conditions conducive to glaciation across the entire HMA include a reduction in temperature of ~10ºC and an increase in precipitation, unlikely to have occurred during any Quaternary glacial maximum.

Moreover, based on a transient climate-ice sheet simulation, we demonstrate that the glacier extent shrinks rapidly after the LGM and reaches the minimum around ~8‒7 ka, followed by a slight long-term advancing trend afterwards. Our results suggest a dominant role of summer temperature in controlling the overall trend of glacier response, with precipitation generally modulating the extent of glaciation. However, the timing and extent of glaciation varies across the Himalayan-Tibetan orogen on millennial timescale, especially between the monsoon-influenced southern and westerly-influenced western parts, further confirming previous speculations. 

How to cite: Yan, Q.: Evolution of glaciation over High-Mountain Asia since the last glacial maximum, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2288, https://doi.org/10.5194/egusphere-egu2020-2288, 2020.

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.

How to cite: Blomdin, R., Stroeven, A. P., Harbor, J. M., Hättestrand, C., Heyman, J., and Gribenski, N.: Quantification of long-term and time-integrated glaciation patterns in Central Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21574, https://doi.org/10.5194/egusphere-egu2020-21574, 2020.