CR1.5

EDI
Glaciation and climate change in the Andean Cordillera

The Andean Cordillera is cryospherically diverse, with high mountain glaciation in the north and large temperate ice masses in the south. These ice masses are critical for water security, the prevalence of geohazards, and a potentially substantial contribution to global sea level. The climatic influences on these ice masses vary across the Cordillera, and are strongly affected by large scale ocean-atmospheric systems such as ENSO and the Southern Annular Mode.

South America is one of the few landmasses in the ocean-dominated Southern Hemisphere available for terrestrial environmental and climate reconstructions. Palaeoclimatic records suggest that Patagonia was sensitive to the Antarctic Cold Reversal and variations in the Southern Annular Mode, which drives changes in the Southern Westerly Winds. Changes in these winds affect both Patagonia and Antarctica today. Further north, the glaciers in Peru and Bolivia are receding rapidly, threatening water security in these latitudes. These glaciers are strongly affected by rising atmospheric air temperatures and changes in ENSO. The high climate sensitivity of these glaciers and icefields, as well as their large latitudinal transect across the Andes, renders them a useful barometer of changes in large-scale atmospheric circulation and palaeoclimate.

We invite interdisciplinary contributions that investigate climate and cryosphere interactions over a range of timescale. This session will bring together researchers working on contemporary mass balance and climatology in the Andean Cordillera, Quaternary palaeoclimatic reconstructions from proxy data (including from lakes, bogs, marine records, aeolian records, ice cores, etc.), (palaeo)climate modelling, and reconstructions of former, present and future ice extent and dynamics from field-based studies and numerical modelling. It will provide a forum in which researchers can contrast their data and shed light on Quaternary glaciations and their palaeoclimatic drivers in South America. We especially invite studies that use data-model comparisons to improve projections of future climate and ice mass behaviour in the Andean Cordillera.

Co-organized by CL4/GM7
Convener: Bethan Davies | Co-conveners: Jacob BendleECSECS, Neil Glasser
vPICO presentations
| Fri, 30 Apr, 15:30–17:00 (CEST)

vPICO presentations: Fri, 30 Apr

Chairpersons: Bethan Davies, Jacob Bendle, Neil Glasser
15:30–15:35
Patagonia & Southern Andes
15:35–15:37
|
EGU21-7633
|
ECS
Grace Skirrow, Rachel Smedley, Richard Chiverrell, and Janet Hooke

The eastern margin of the former Patagonian Ice Sheet was drained by large and dynamic river systems, which remain largely unstudied. New geomorphological mapping and luminescence chronology of the glacially-fed Rio Chubut reveal the preservation of large gravel outwash terraces up to 50 m above the modern river channel that previously acted as glacial spillways during the last glaciation. Also discovered is a gradual shift from a braided to a meandering planform between 12.3 ± 1.0 ka and 9.4 ± 0.8 ka, where the braided system experienced a decrease in energy and subsequent abandonment, transitioning into the meandering system that persists today. The coincidence of a new luminescence age from the innermost ice lobe in the Epuyen area (18.1 ± 2.2 ka), palaeoenvironmental records (Moreno et al. 2018, Whitlock et al. 2007, Iglesias et al. 2016) and the PATICE ice sheet reconstruction (Davies et al, 2020) suggest that the abandonment of the Rio Chubut braided planform was not a product of the river decoupling from the ice sheet. Alternatively, it was a response to the reduced water supply likely linked with the weakening and southward shift in the mid-latitude storm tracks and westerlies ~11.3 ka (Moreno et al. 2018). These findings contradict the widely reported process of planform change in glacially-fed river systems whereby a river decoupled from a glacier experiences a loss in sediment supply, which leads to incision and the river confining to a single channel. Here at the Rio Chubut, braiding is sustained in a paraglacial landscape for ~5 ka after the ice had retreated into the Andean mountains. A reduction in water supply related to precipitation changes in the early Holocene is identified as the key driver of planform change.

References

Davies, B.J., Darvill, C.M., Lovell, H., Bendle, J.M., Dowdeswell, J.A., Fabel, D., García, J.L., Geiger, A., Glasser, N.F., Gheorghiu, D.M. and Harrison, S., 2020. The evolution of the Patagonian Ice Sheet from 35 ka to the present day (PATICE). Earth-Science Reviews, p.103152.

Iglesias, V., Markgraf, V. and Whitlock, C., 2016. 17,000 years of vegetation, fire and climate change in the eastern foothills of the Andes (lat. 44 S). Palaeogeography, Palaeoclimatology, Palaeoecology, 457, pp.195-208.

Moreno, P.I., Videla, J., Valero-Garcés, B., Alloway, B.V. and Heusser, L.E., 2018. A continuous record of vegetation, fire-regime and climatic changes in northwestern Patagonia spanning the last 25,000 years. Quaternary Science Reviews, 198, pp.15-36.

Whitlock, C., Moreno, P.I. and Bartlein, P., 2007. Climatic controls of Holocene fire patterns in southern South America. Quaternary Research, 68(1), pp.28-36.

How to cite: Skirrow, G., Smedley, R., Chiverrell, R., and Hooke, J.: Environmental drivers of planform change in the glacially-fed Rio Chubut, Argentina (42°S), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7633, https://doi.org/10.5194/egusphere-egu21-7633, 2021.

15:37–15:39
|
EGU21-2820
Tancrede Leger, Andrew Hein, Robert Bingham, Ángel Rodes, and Derek Fabel

The former Patagonian Ice Sheet was the most extensive Quaternary ice sheet of the southern hemisphere outside of Antarctica. Against a background of Northern Hemisphere-dominated ice volumes, it is essential to document how the Patagonian Ice Sheet and its outlet glaciers fluctuated throughout the Quaternary. This information can help us investigate the climate forcing mechanisms responsible for ice sheet fluctuations and provide insight on the causes of Quaternary glacial cycles at the southern mid-latitudes. Patagonia is part of the only continental landmass that fully intersects the precipitation-bearing Southern Westerly Winds and is thus uniquely positioned to study past climatic fluctuations in the southern mid-latitudes. While Patagonian palaeoglaciological investigations have increased, there remains few published studies investigating glacial deposits from the north-eastern sector of the former ice sheet, between latitudes 41°S and 46°S. Palaeoglaciological reconstructions from this region are required to understand the timing of Pleistocene glacial expansion and retreat, and to understand the causes behind potential latitudinal asynchronies in glacial advances throughout Patagonia. Here, we reconstruct the glacial history and chronology of a previously unstudied region of north-eastern Patagonia that formerly hosted the Río Corcovado (43°S, 71°W) palaeo ice-lobe. Here we present a new set of cosmogenic 10Be exposure ages from presumed pre-LGM moraine boulder and glaciofluvial outwash surface cobble samples, establishing for the first time a comprehensive chronology for pre-LGM glacial margins of the Río Corcovado palaeo-glacier. This new dataset completes our effort to date the entire preserved moraine record of the Río Corcovado valley: which captures at least seven distinct Pleistocene glacial events. Our results allow answering questions on the timing of the maximum local ice extent of the last glacial cycle as well as older, pre-last glacial cycle glaciations, for which few robust glacier chronologies exist in the Southern Hemisphere. The most informative cosmogenic nuclide-derived glacial chronologies with the capacity to resolve questions on interhemispheric phasing of climate change require unambiguous dating of glacial margins spanning the entirety of the last glacial cycle and ideally earlier glacial cycles. Therefore, our findings have significant implications for understanding past climate fluctuations at the southern mid-latitudes, former Southern Westerly Winds behaviour and interhemispheric climate linkages throughout the Pleistocene. They also provide further evidence supporting the proposed latitudinal asynchrony in the timing of Patagonian Ice Sheet expansion during the last glacial cycle and enable novel glacio-geomorphological interpretations for the studied region.

How to cite: Leger, T., Hein, A., Bingham, R., Rodes, Á., and Fabel, D.: A detailed Pleistocene cosmogenic nuclide chronology of Patagonian Ice-Sheet expansions in north-eastern Patagonia (43°S), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2820, https://doi.org/10.5194/egusphere-egu21-2820, 2021.

15:39–15:41
|
EGU21-13184
|
ECS
Emma-Louise Cooper, Varyl Thorndycraft, Bethan Davies, Adrian Palmer, and Juan-Luis García

The former Patagonian Ice Sheet (PIS, 38 – 56°S) was one of the largest ice masses to develop in the Southern Hemisphere. Its formation was uniquely influenced by the Southern Westerly Winds (SWWs) colliding with the Andean Cordillera, generating a marked West-East precipitation gradient. Variability in the strength and position of the SWWs is thought to have played a significant role in ice sheet dynamics. In particular, understanding of the timing of palaeo-glacier fluctuations is required to elucidate the role of these regional climate drivers on ice retreat. However, in order to fully understand the structure and pace of deglacial ice fluctuations, detailed glacial geomorphological reconstructions must be completed.

During deglaciation, as the PIS retreated from local Last Glacial Maxima positions, large proglacial lakes formed east of the austral Andes, ice-dammed by the Andean Cordillera. In central-Patagonia (44 – 46°S) during the final stages of deglaciation, these ice-dammed lakes drained to the west, through the Andean Cordillera, opening new drainage corridors towards the Pacific Ocean. As a result, the floors of these valleys are now exposed subaerially, preserving a complex suite of glacial and glaciolacustrine landform assemblages. Moreover, as most of the region is now ice-free, excluding smaller mountain ice caps such as Queulat (44.4°S, ~2000 m a.s.l) more recent Holocene geomorphology has also been exposed. These landforms possess the potential to yield new insights into the style and manner of regional ice retreat, during the transition from large terrestrial ice-lobes, to smaller mountain glaciers and ice caps.

We mapped seven terrestrial palaeo-ice lobes of the PIS: the Río Pico (~44.2°S), Río Cisnes (~44.6°S), Lago Plata-Fontana (~44.8°S), Río El Toqui (~45°S), Lago Coyt/Río Ñirehuao (~45.3°S), Simpson/Paso Coyhaique (~45.5°S) and Balmaceda (~46°S) lobes. Mapping was then extended west, into the Andean Cordillera. Landforms were mapped using ESRI™ DigitalGlobe World (1-2 m) and Sentinel-2 (10 m) imagery, verified with field surveys. These new data build on previous work in the area. To date, over 60,000 ice-marginal, ice-contact, subglacial, glaciolacustrine and glaciofluvial landforms have been mapped across a ~70,000km2 area of the Andean Cordillera and adjacent valleys. When combined with robust geochronological reconstructions, these data possess the potential to inform on the role of the SWWs, versus local topography, and ice-marginal processes in regulating the structure and rate of regional deglaciation.

How to cite: Cooper, E.-L., Thorndycraft, V., Davies, B., Palmer, A., and García, J.-L.: The Glacial Geomorphology of central-Patagonia (44 – 46°S): glacier dynamics within and beyond the austral Andes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13184, https://doi.org/10.5194/egusphere-egu21-13184, 2021.

15:41–15:46
|
EGU21-10973
|
ECS
|
solicited
Claudio Bravo, Deniz Bozkurt, Andrew N. Ross, and Duncan J. Quincey

Patagonia (40°S-55°S) includes two large icefields, the Northern and Southern Patagonian Icefields (NPI and SPI). Most of the glaciers within these icefields are shrinking rapidly, raising concerns about their contribution to sea-level rise in the face of ongoing climatic change. This ice volume loss has led to rapid changes that remain imprinted on the Patagonia landscapes. In view of the local, regional and worldwide impacts of glacier retreat in Patagonia, an assessment of the potential future surface mass balance (SMB) and ice loss of the icefields, is critical. We seek to provide this assessment by modelling the SMB between 1976 and 2050 for both icefields, using regional climate model data (RegCM4.6) and a range of emission scenarios at a spatial resolution of 10 km. Additionally, using meteorological observations during strong drought conditions which occurred in Patagonia in 2016, key meteorological and glaciological characteristics are described, quantified and analysed in order to assess possible future conditions.

For the NPI, a reduction between 1.51 m w.e.  (RCP2.6) and 1.88 m w.e. (RCP8.5) was projected, suggesting that negative SMB will prevail well into future decades. For the SPI the projected reduction was within the range of 1.12 m w.e. (RCP2.6) to 1.45 m w.e. (RCP8.5), which implies positive SMB will dominate, albeit at a lower rate than the current observed. However, if it is assumed that the recent frontal ablation rates tend to continue into future decades, ice loss and sea-level contributions will increase for both Icefields. The trend towards lower SMB is explained by an increase in melt, and to a lesser extent by a reduction in snow accumulation.

Several mechanisms not accounted for our modelling approach could act as positive feedbacks in the magnitude of the ice loss. We summarise these feedbacks in a conceptual framework based on a combination of our own meteorological observations as well as on the recent research findings. This framework highlights the diversity of meteorological and glaciological conditions that can prevail even between nearby glaciers. Importantly, more frequent thermal inversion events and increased meltwater availability are likely to trigger ice dynamics changes and potential increases in ablation. Together, these plus other factors make the prediction of future glacier response and evolution in Patagonia a very complex and challenging task.

How to cite: Bravo, C., Bozkurt, D., Ross, A. N., and Quincey, D. J.: Projected increases in surface melt and ice loss and their potential feedbacks for the Northern and Southern Patagonian Icefields , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10973, https://doi.org/10.5194/egusphere-egu21-10973, 2021.

15:46–15:48
|
EGU21-6185
|
ECS
Matthias Troch, Sebastien Bertrand, Carina B. Lange, Paola Cardenas, Helge Arz, Ricardo De Pol-Holz, and Rolf Kilian

Our understanding of glacial isostatic rebound across Patagonia is highly limited, despite its importance to constrain past ice volume estimates and better comprehend relative sea-level variations. With this in mind, our research objective is to reconstruct the magnitude and rate of Late Glacial to Holocene glacial isostatic adjustment near the center of the former Patagonian Ice Sheet. We focus on Larenas Bay (48°S; 1.26 km2), which is connected to Baker Channel through a shallow (ca. 7.4 m) and narrow (ca. 150 m across) inlet, and hence has the potential to record periods of basin isolation and marine ingression. The paleoenvironmental evolution of the bay was investigated through a sedimentological analysis of a 9.2 m long, radiocarbon-dated, sediment core covering the last 16.8 cal. kyr BP. Salinity indicators, including diatom paleoecology, alkenone concentrations and CaCO3 content, were used to reconstruct the bay’s connectivity to the fjord. Results indicate that Larenas Bay was a marine environment before 16.5 cal. kyr BP and after 9.1 cal. kyr BP, but that it was disconnected from Baker Channel in-between. We infer that glacial isostatic adjustment outpaced global sea-level rise between 16.5 – 9.1 cal. kyr BP. During the Late Glacial - Holocene transition, the center of the former Patagonian Ice Sheet rose ca. 96 m, at an average rate of 1.30 cm/year. During the remainder of the Holocene, glacial isostatic adjustment continued (ca. 19.5 m), but at a slower average pace of 0.21 cm/year. Comparisons between multi-centennial variations in the salinity indicators and existing records of global sea-level rise suggest that the glacial isostatic adjustment rate fluctuated during these time intervals, in agreement with local glacier dynamics. More specifically, most of the glacial isostatic adjustment registered between 16.5 – 9.1 cal. kyr BP seems to have occurred before meltwater pulse 1A (14.5 – 14.0 kyr BP). Likewise, it appears that the highest Holocene glacial isostatic rebound rates occurred during the last 1.4 kyr, most likely in response to glacier recession from Neoglacial maxima. This implies a relatively rapid response of the local solid earth to ice unloading, which agrees with independent modelling studies investigating contemporary uplift. We conclude that the center of the former Patagonian Ice Sheet experienced a glacial isostatic adjustment of ca. 115 m over the last 16.5 kyr, and that >80% occurred during the Late Glacial and early Holocene.

How to cite: Troch, M., Bertrand, S., Lange, C. B., Cardenas, P., Arz, H., De Pol-Holz, R., and Kilian, R.: Glacial isostatic adjustment near the center of the former Patagonian Ice Sheet (48°S) during the last 16.5 kyr, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6185, https://doi.org/10.5194/egusphere-egu21-6185, 2021.

15:48–15:50
|
EGU21-10265
Andres Rivera, Francisca Bown, Andres Castillo, Jonathan Oberreuter, María Gabriela Lenzano, and Luis Lenzano

The Patagonian Icefields are among the biggest worldwide glaciers contributors to sea level rise. In spite of ongoing deglaciation in Patagonia, climatic models are estimating that the icefields surface mass balances during at least the last 4 decades has been neutral or even positive. The main mass losses are therefore, mainly related to frontal ablation, namely surface ablation, calving and subaquatic melting. These are the predominant factors in almost every single calving glacier in the region, especially among the eastern glaciers of the Southern Patagonia Icefield that are ending into deep lakes. The only and most remarkable exception to this trend on the eastern side of the SPI is the well-known stable and even advancing state of glaciar Perito Moreno. In spite of the relatively benign surface mass balances modelled for the last 4 decades, during the 2010’s several freshwater calving glaciers experienced strong retreats, and in some cases, the collapse of the whole ice fronts with losses mounting several square kilometers of ice in single events or during a series of huge calving events.   In order to study the glacier-lake interactions in the area, a collaborative research program was initiated in 2013 by Chilean and Argentinean scientists allowing the installation of a network of Automatic Weather Stations, fixed photographic cameras, water level pressure sensors and GPS stations at both sides of the international border. Since 2013 several field campaigns were conducted to the area including the survey of lake waters nearby several retreating glaciers. In most of the studied cases were detected very deep bathymetries (up to 600 m in places), and in some cases, a vertical structure of the lake water indicating a highly stratified condition that we estimate is responsible for very low subaquatic melting favoring the presence of glacier foots extending tens or even few hundreds of meters beyond the subaerial ice walls. The most remarkable recent collapses took place at glaciares O’Higgins and Viedma, whilst the rest or our studied glaciers (Chico, Upsala and Dickson) also experienced retreats with smaller rates. In this presentation we will show novel data collected in the main freshwater calving glaciers of the SPI and will discuss the local conditions explaining the recent glacier behavior.

How to cite: Rivera, A., Bown, F., Castillo, A., Oberreuter, J., Lenzano, M. G., and Lenzano, L.: Southern Patagonia Icefield freshwater calving glaciers recent collapses into deep lake waters , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10265, https://doi.org/10.5194/egusphere-egu21-10265, 2021.

15:50–15:52
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EGU21-4193
|
ECS
Loic Piret, Sebastien Bertrand, Nhut Nguyen, Jon Hawkings, Cristian Rodrigo, and Jemma Wadham

Glacial Lake Outburst Floods (GLOFs) are an increasing threat to Patagonian environments and communities. Here, we investigate the geomorphological and hydrological impact of a recent GLOF from Pascua River, which discharges at the head of Baker Fjord (Chile, 48°S). To do so, a sediment core was taken ~4 km offshore of the Pascua River mouth at a water depth of 248 m. The coring site is located on the flank of a submarine channel incised trough the subaquatic delta of Pascua River, 30 m above the bottom of the channel. The sediment physical and chemical properties were analysed at high resolution with X-ray CT, MSCL and XRF core scanning, in combination with lower resolution grain-size and bulk organic geochemistry measurements, and a core chronology was established using downcore variations in 137Cs activity. In addition, historical maps and satellite imagery of the past century were examined in combination with multibeam bathymetry of Baker Fjord to aid the interpretation of the sediment record.

Results show that the sediments are composed of two distinct units separated by a 5-cm thick event deposit dated 1945±9 CE. Below the event, the sediment consists of coarse silt and fine sand, likely representing sediment deposition from turbidity currents. Above it, it consists of very fine silts, likely representing settling from the surficial sediment plume. Historical evidence shows that the event deposit corresponds to a ~256 106 m3 GLOF from Bergues Lake, the proglacial lake of Lucia Glacier that discharges directly into Pascua River. Before 1945, historical information shows that Pascua River drained via two active river branches that were most likely connected to the two submarine channels visible in the bathymetry of the subaquatic delta. After 1945, only the western river branch appears active, which likely caused the abandonment of the eastern submarine channel near which the sediment core was taken. Therefore, we hypothesize that the 1945 Bergues Lake GLOF caused the abandonment of the eastern river branch and submarine channel, which explains the absence of coarse-grained sediments in our sediment record after 1945±9 CE.

This study provides the first report of a GLOF from the northeastern part of the Southern Patagonian Icefield, and it demonstrates that GLOFs can have long-term impacts on the hydrology of fjord-river systems.

How to cite: Piret, L., Bertrand, S., Nguyen, N., Hawkings, J., Rodrigo, C., and Wadham, J.: Long-lasting impacts of a glacial lake outburst flood on the hydrology of a fjord-river system (Pascua River, Chilean Patagonia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4193, https://doi.org/10.5194/egusphere-egu21-4193, 2021.

15:52–15:54
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EGU21-14687
Sebastien Bertrand, Elke Vandekerkhove, Dmitri Mauquoy, Dave McWethy, Brian Reid, Sarah Stammen, Krystyna Saunders, and Fernando Torrejon

Glacial Lake Outburst Floods (GLOFs) constitute a major hazard in periglacial environments. Despite a recent increase in the size and number of glacial lakes worldwide, there is only limited evidence that climate change is affecting GLOF frequency. In Patagonia, GLOFs are particularly common in the Baker River watershed (47°S), where 21 GLOFs occurred between 2008 and 2017 due to the drainage of Cachet 2 Lake into the Colonia River, a tributary of the Baker River. During these GLOFs, the increased discharge from the Colonia River blocks the regular flow of the Baker River, resulting in the inundation of the Valle Grande floodplain, which is located approximately 4 km upstream of the confluence. To assess the possible long-term relationship between GLOF frequency, glacier behavior, and climate variability, four sediment cores collected in the Valle Grande floodplain were analyzed. Their geophysical and sedimentological properties were examined, and radiocarbon-based age-depth models were constructed. All cores consist of dense, fine-grained, organic-poor material alternating with low-density organic-rich deposits. The percentage of lithogenic particles, which were most likely deposited during high-magnitude GLOFs, was used to reconstruct the flood history of the last 2.75 kyr. Results show increased flood activity between 2.57 and 2.17 cal kyr BP, and between 0.75 and 0 cal kyr BP. These two periods coincide with glacier advances during the Neoglaciation. Our results suggest that GLOFs are not a new phenomenon in the region. Although rapid glacier retreat is likely responsible for high GLOF frequency in the 21st century, high-magnitude GLOFs seem to occur more frequently when glaciers are larger and thicker.

How to cite: Bertrand, S., Vandekerkhove, E., Mauquoy, D., McWethy, D., Reid, B., Stammen, S., Saunders, K., and Torrejon, F.: Neoglacial increase in high-magnitude Glacial Lake Outburst Flood frequency (Baker River, Patagonia, 47°S), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14687, https://doi.org/10.5194/egusphere-egu21-14687, 2021.

Peru & Tropical Andes
15:54–15:56
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EGU21-12809
Guillaume Leduc, Etienne Legrain, Pierre-Henri Blard, and Julien Charreau

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 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 ~-1.5 °C.km-1 (20 sites). At higher latitude, in both hemispheres (Central Andes, 15°S – 35°S (8 sites); Sierra Nevada and San Bernardino mountains (40°N – 34°N) (6 sites), the LR was constant during the LGM. 

 Our results show that a drier climate during the LGM is systematically associated with a steeper LR. Modification of LR during 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 valid, this mechanism implies that tropical glaciers are more vulnerable 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: Leduc, G., Legrain, E., Blard, P.-H., and Charreau, J.: Moisture control on high-altitude cooling during the Last Glacial Maximum, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12809, https://doi.org/10.5194/egusphere-egu21-12809, 2021.

15:56–15:58
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EGU21-13819
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ECS
Hans Fernández, Juan-Luis García, Samuel U. Nussbaumer, Alessa Geiger, Isabelle Gärtner-Roer, Dmitry Tikhomirov, and Markus Egli

The geochronological and geomorphological reconstruction of glacier fluctuations is required to assess the timing and structure of climate changes of the last glacial cycle in the subtropical Andes of Chile. The scarcity of data in this region limits the knowledge related to the timing of glacial landscape changes during this long-term period. To provide a new framework to better understand the climate history of the semiarid Andes of Chile, we have reconstructed the glacial history of the Universidad glacier (34° S).

Our mapping shows the existence of four moraine belts (UNI I to UNI IV, from outer to inner) that are spatially unequally distributed along the 13 km of the valley between ~2500 and ~1400 m a.s.l. We applied 10Be cosmogenic surface exposure dating to 26 granodioritic boulders on moraines and determined the age of the associated glacial advances. UNI I moraine represents the distal glacier advance between 20.8±0.8 and 17.8±0.8 kyr ago (number of 10Be samples = 11). Other two significative glacier advances terminated one and four km up-valley from the UNI I moraine, respectively, formed 16.1±0.9 kyr (n=1) (UNI II) and 14.6±1 to 10±0.5 kyr ago (n=3) (UNI III). A sequence of six distinct and smaller moraine ridges has been identified in the proglacial area. They are part of last significative glacier advances labeled as UNI IV. The four distal ridges have been dated to between 645-150 years ago (n=11), while the most proximal moraines coincide with mid-20th century and 1997 aerial photographs.

The results indicate that the Universidad glacier advanced during the Last Glacial Maximum (LGM) (UNI I). Deglaciation was punctuated by glacier readvances during the Late Glacial when the UNI II and UNI III moraines were deposited. Finally, UNI IV moraine shows six glacier fluctuations developed between the 14th and 20th centuries.

Our data suggest that the glacier advances by the Universidad glacier were triggered by intensified southern westerly winds bringing colder and wetter conditions to subtropical latitudes in the SE Pacific. Moreover, our data indicate that more or less in-phase Late-Glacial advances along the tropical and extratropical Andes occurred. We discuss different climate forcings that explain these glacier changes. Finally, we illustrate the influence of the “Little Ice Age” in the Semiarid Andes.

How to cite: Fernández, H., García, J.-L., Nussbaumer, S. U., Geiger, A., Gärtner-Roer, I., Tikhomirov, D., and Egli, M.: Last Glacial Maximum to near present 10Be chronology of the Universidad glacier fluctuations in the Subtropical Chilean Andes (34° S): paleoclimate implications  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13819, https://doi.org/10.5194/egusphere-egu21-13819, 2021.

15:58–16:00
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EGU21-6795
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ECS
Lihan Del Rocio Hoyos Zarzosa, Ibeth Celia Rojas Macedo, Christian German Garcia Rojas, Luzmila Dávila Roller, and Pedro Tapia Ormeño

In areas located over 2000 m.a.s.l., the warm phase of ENSO (El Niño) is characterized by a decrease in precipitation and an increase in temperature which can reach values above the annual average, while in the cold phase of ENSO (La Niña), precipitation increases and temperature decreases compared to the annual average. In both cases ENSO has an influence on the glacier evolution of the Andes.

The objective of the present investigation is to determine the influence of ENSO in the Cordillera Blanca through satellite images (glacier coverage delimitation) and climatic proxy (ice core) in the Shallap and Artesonraju glaciers respectively for the hydrological years between 2009/2010 to 2018/2019.

The climate analysis in both glaciers showed higher annual temperatures and lower precipitation, revealing the influence of the 2015/2016 El Niño on the studied glaciers. There was a prominent reduction in glacier coverage in Shallap, which is supported by the ice core record extracted from Artesonraju, presenting an equivalent accumulated water decrease and an 18O enrichment for this period. These findings point out the influence of the 2015/2016 El Niño that significantly reduced the glacier coverage in both studied areas. On the other hand, the 2011/2012 La Niña event displayed the opposite effect, that is, colder temperatures, less glacier coverage reduction, an increase in the volume of accumulated water and an impoverishment of 18O.

Given the results, it can be affirmed that during an El Niño year the loss of glacier coverage is greater, causing less equivalent water accumulation and an enrichment of 18O; inversely for a La Niña year. These results support previous findings shown in research about glaciers in Peru.

How to cite: Hoyos Zarzosa, L. D. R., Rojas Macedo, I. C., Garcia Rojas, C. G., Dávila Roller, L., and Tapia Ormeño, P.: Influence of Enso in Perú's Cordillera Blanca Glaciers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6795, https://doi.org/10.5194/egusphere-egu21-6795, 2021.

16:00–16:02
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EGU21-7524
Catriona L. Fyffe, Emily Potter, Stefan Fugger, Andrew Orr, Simone Fatichi, Katy Medina, Robert Å. Hellström, Thomas E. Shaw, Maud Bernat, Alan Llacza, Gerardo Jacome, Caroline Aubry-Wake, Wolfgang Gurgiser, L. Baker Perry, Wilson Suarez, Duncan J. Quincey, Edwin Loarte, and Francesca Pellicciotti

Peruvian glaciers are important contributors to dry season runoff for agriculture and hydropower, but they are at risk of disappearing due to climate warming. Their energy balance and ablation characteristics have previously been studied only for individual glaciers, with no comparisons between regions. We applied the physically-based, energy balance melt component of the model Tethys-Chloris at five on-glacier meteorological stations: three in the Cordillera Blanca near Huaraz (with glaciers above ~4300 m a.s.l.), and two in the Cordillera Vilcanota east of Cusco (with glaciers above ~ 4800 m). The climate of these regions is strongly seasonal, with an austral summer wet season and winter dry season. 

Our results revealed that at most sites the energy available for melt is greatest in the wet season. This is a consequence of the dry season energy losses from the latent heat flux and net longwave radiation which counter-balance the high dry season net shortwave radiation, which otherwise dominates the energy balance. The sensible heat flux is a relatively small contributor to melt energy in both seasons. Comparison of the five sites suggests that there is more energy available for melt at a given elevation in the Cordillera Vilcanota compared to the Cordillera Blanca. At three of the sites the wet season snowpack was discontinuous, forming and melting within a daily to weekly timescale. Albedo and melt are thus highly variable in the wet season and closely related to the precipitation dynamics. At the highest site, in the accumulation zone of the Quelccaya Ice Cap, 81% of ablation was from sublimation. Sublimation was less important at the lower sites, but it reduces dry season melt. 

Correlation of the NOAA Oceanic El Niño Index (ONI) to the outputs of the two sites with the longest records revealed that the warmer wet season temperatures characteristic of a positive ONI were associated with a decreased albedo, greater net shortwave radiation, a more positive sensible heat flux and increased melt rates.  Air temperature and precipitation inputs were also perturbed at all five sites to understand their sensitivity to climate change. Enhanced mass loss was predicted with a static increase of 2°C or more, even with a +30% precipitation increase, with the lower elevation Cordillera Blanca sites at risk of the greatest mass loss due to warming.

How to cite: Fyffe, C. L., Potter, E., Fugger, S., Orr, A., Fatichi, S., Medina, K., Hellström, R. Å., Shaw, T. E., Bernat, M., Llacza, A., Jacome, G., Aubry-Wake, C., Gurgiser, W., Perry, L. B., Suarez, W., Quincey, D. J., Loarte, E., and Pellicciotti, F.: Quantifying the controls of Peruvian glacier response to climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7524, https://doi.org/10.5194/egusphere-egu21-7524, 2021.

16:02–16:04
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EGU21-7580
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ECS
Ethan Lee, Neil Ross, Andrew Henderson, Andrew Russell, Stewart Jamieson, and Derek Fabel

Palaeo-glaciological studies of former ice thickness and extent within the tropical Andes have tended to focus on locations where glaciers are currently present, or in high elevation locations where evidence exists of recently deglaciated cirques. Few studies have focussed on low elevation regions due to the presumption that glaciers could not have existed at such low altitudes within the tropics. A latitudinal ‘data gap’ exists between Ecuador and more central and southern Peru where evidence for former glaciation is abundant. To fill this gap we present rare evidence of past glaciation from the Las Huaringas region, northern Peru, located in a relatively low elevation massif (<3900 m).

Within Las Huaringas a large valley glacier existed, extending N-S ~12 km down valley to ~2900 m in elevation while glacial cirques existed exhibiting an E-W orientation on the western facing hillslope of the massif with pronounced moraine complexes and bedrock erosion. We used high-resolution remotely sensed imagery, a 30 m ALOS DEM, and preliminary field observations to identify and map an abundance of geomorphic evidence of glaciation. These include moraines at different stages of preservation and predominance, eroded bedrock surfaces, cirque landforms and overdeepened valleys to develop the first glacial geomorphological map of the region. We performed morphometric analysis (e.g. width, length, altitude, azimuth) of the mapped glacial landforms and cirques along with hypsometric analysis of the main valley of Laguna Shimbe, yielding a hypsometric maxima of 3250 m. Using the geomorphological map, we determine the former extent and thickness of palaeoglaciers in the area and use delineated glacial outlines of their furthest extent to reconstruct Equilibrium Line Altitudes (ELAs) of these ice masses using a combination of ELA estimation techniques.

Ongoing research aims to determine whether the palaeoglacial evidence is consistent with formation by valley glaciers or an icecap and whether the timing of the local Last Glacial Maximum (LGM) was synchronous with the global timing. A set of hypotheses for the timing and drivers of the reconstructed extent of former glaciers in the area will be presented. Our analysis confirms the presence of former glaciers in a low elevation and low latitude region of the tropical Andes. Our ongoing work aims to unveil the timing of the glacial events and the drivers of the glacial and climate history seen within this important region.

How to cite: Lee, E., Ross, N., Henderson, A., Russell, A., Jamieson, S., and Fabel, D.: Palaeoglaciation in the low latitude, low elevation tropical Andes, northern Peru, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7580, https://doi.org/10.5194/egusphere-egu21-7580, 2021.

16:04–16:06
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EGU21-8669
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ECS
Emily Potter, Andrew Orr, Catriona Fyffe, Duncan Quincey, Andrew Ross, Helen Burns, Robert Hellström, Katy Medina, Edwin Loarte, Alan Llacza, Gerardo Jacome, Scott Hosking, and Francesca Pellicciotti

The Peruvian Andes contain the vast majority of the world’s tropical glaciers. Warming temperatures due to climate change have caused a dramatic shrinking of these glaciers, posing a threat to water supplies. Two of the most heavily glacierised areas of Peru are the Cordillera Blanca,  which includes the Rio Santa River Basin to the north of Peru, and the Cordilleras Urubamba, Vilcabamba, and Vilcanota towards the south.

Due to the topographic and climatic complexity of the regions, spatial variations in precipitation and temperature are high, and spatially distributed high-resolution climate data can offer a crucial tool to understand those variations, in a way which is not possible from limited, individual ground stations. Here we present a new high-resolution climate dataset over both regions, created by bias-correcting Weather Research and Forecasting (WRF) model output at 4 km spatial resolution against observations. 

The spatial variation in precipitation differs over the two river basins. In the region of the Cordillera Blanca, precipitation mostly increases with elevation and distance upstream. Around the southern cordilleras, there are regions of greater precipitation near the mountains and glaciers which lie further downstream, but the high elevations of the cordillera Vilcanota, further upstream, are much drier. Analysis of the precipitation and temperature trends from 1980 to 2018 demonstrates a clear warming trend in both regions. The precipitation trends are less uniform, with the Rio Santa showing a general trend for increasing precipitation, but with a less clear trend over the higher, glacierised regions of the valley. Around the Cordilleras Urubamba, Vilcabamba and Vilcanota, there is no clear trend in precipitation over recent decades.

Using a range of CMIP5 models, the high-resolution precipitation and temperature datasets are statistically projected into the future, using quantile mapping. Future trends in precipitation and temperature are analysed over both regions, and the inter-model variability in the CMIP5 models is examined.

 

How to cite: Potter, E., Orr, A., Fyffe, C., Quincey, D., Ross, A., Burns, H., Hellström, R., Medina, K., Loarte, E., Llacza, A., Jacome, G., Hosking, S., and Pellicciotti, F.: Multi-decadal past and future temperature and precipitation trends in the Peruvian Andes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8669, https://doi.org/10.5194/egusphere-egu21-8669, 2021.

16:06–16:08
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EGU21-12241
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ECS
Joanne Wood, Stephan Harrison, Ryan Wilson, Neil Glasser, John Reynolds, Alejandro Diaz Moreno, Adam Emmer, Simon Cool, Juan Carlos Torres, Adriana Caballero, Harrinson Jara, Christian Yarleque, Enver Melgarejo, Hilbert Villafane, Julia Araujo, Efrain Turpo, and Tito Tinoco

Climate change is resulting in mass loss and the retreat of glaciers in the Andes, exposing steep valley sides, over-deepened valley bottoms, and creating glacial lakes behind moraine dams. Glacial Lake Outburst Floods (GLOFs) present the biggest risk posed by glacier recession in Peru. Understanding the characteristics of lakes that have failed in the past will provide an aid to identifying those lakes that might fail in the future and narrow down which lakes are of greatest interest for reducing the risks to local vulnerable populations. 

Using a newly created lake inventory for the Peruvian Andes (Wood et al., in review) and a comprehensive GLOF inventory (unpublished) we investigate lakes from which GLOFs have occurred in the past. This is to establish which physical components of the glacial lake systems are common to those lakes that have failed previously and which can be identified remotely, easily and objectively, in order to improve existing methods of hazard assessment.

How to cite: Wood, J., Harrison, S., Wilson, R., Glasser, N., Reynolds, J., Diaz Moreno, A., Emmer, A., Cool, S., Torres, J. C., Caballero, A., Jara, H., Yarleque, C., Melgarejo, E., Villafane, H., Araujo, J., Turpo, E., and Tinoco, T.: What’s in a lake? Glacial Lake Outburst Floods in the Peruvian Andes., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12241, https://doi.org/10.5194/egusphere-egu21-12241, 2021.

16:08–16:10
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EGU21-12951
Léo Martin, Pierre-Henri Blard, Jérôme Lavé, Vincent Jomelli, Maarten Lupker, Julien Charreau, and Thomas Condom

The climatic reorganizations that occurred in the Southern and Northern hemispheres during the last deglaciation are thought to have affected the continental tropical regions. However, the respective impact of North and Southern climatic changes in the Tropics are still poorly understood. In the Norhtern Tropical Andes, moraines records indicate that the Antarctic Cold Reversal (ACR, 14.3-12.9 ka BP) stage was more represented than the Younger Dryas (12.9-11.7 ka BP) (Jomelli et al., 2014). However, further South, in the Altiplano basin (Bolivia), two cold periods of the North Hemisphere (Heinrich Stadial 1a (16.5-14.5 ka) and Younger Dryas) are synchronous with (i) major advances or stillstands of paleo-glaciers and with (ii) the highstands of the giant palaeo-lakes Tauca and Coipasa (Martin et al., 2018). Therefore, additional geochronological records of paleoglaciers fluctuations are necessary to address the respective impacts of North and South Hemisphere on the glacial dynamics in the region.

We present new Cosmic Ray Exposure (CRE) ages from glacial landforms of the Bolivian Andes that extend pre-existing datasets for four different sites spreading from 16 to 21°S. We reconstruct the Equilibrium Line Altitudes (ELA) associated with each moraine with the AAR method and use them in an inverse algorithm that combines both the palaeo-glaciers and palaeo-lake budgets to derive temperature and precipitation reconstructions. Our temperature reconstruction (ΔT vs. Present) shows a consistent trend through the four glacial sites with a progressive warming from ΔT= -5°C (17 ka BP) to –2.5°C (15-14.5 ka BP, at the end of the Tauca highstand). This is followed by a return to colder conditions, around -4°C, during the ACR (15.5-12.9 ka BP). The Coipasa highstand is coeval with another warming trend followed by ΔT stabilization at the onset of the Holocene (circa 10 ka BP), around -3°C. Precipitation is mainly characterized by increases during the lake highstands, modulated by the distance from the glacial sites to the center of the paleolakes that are moisture sources (recycling processes).

These new results highlight the decorrelation of the glacier dynamics to the temperature signal in regions that are characterized by high precipitation variability. They also provide a theoretical frame to explain how both regional and global forcings can imprint the paleo-glacial records. Our results strongly suggest that during the last deglaciation (20 – 10 ka BP), in the Tropical Andes, atmospheric temperatures follow the Antarctic variability, while precipitation is driven by the changes occurring in the Northern Hemisphere.

References

Jomelli et al., Nature, 2014; Martin et al., Sc. Advances, 2018

How to cite: Martin, L., Blard, P.-H., Lavé, J., Jomelli, V., Lupker, M., Charreau, J., and Condom, T.: Antarctic-like temperature variations in the Tropical Andes recorded by glaciers and lake levels during the last deglaciation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12951, https://doi.org/10.5194/egusphere-egu21-12951, 2021.

16:10–17:00