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Late Pleistocene snowline fluctuations at Nevado Coropuna (15°S), southern Peruvian Andes
Abstract
Deposits preserved on peaks in the southern Peruvian Andes are evidence for past glacial fluctuations and, therefore, serve as a record of both the timing and magnitude of past climate change. Moraines corresponding to the last major expansion of ice on Nevado Coropuna date to 20-25 ka, during the last glacial maximum. We reconstructed the snowline at Coropuna for this period using a combined geomorphic-numeric approach to provide a first-order estimate of the magnitude of late-Pleistocene climate change. Our reconstructions show that snowline was approximately 550-770 m lower during the last glacial maximum than during the late Holocene maximum, which ended in the 19th century, and ∼750 m lower than today. While these values are similar to data from nearby Nevado Solimana, reconstructions from the neighbouring peak of Nevado Firura reveal a smaller snowline depression, suggesting the glacial response to climate forcing in the tropics is strongly influenced by non-climatic factors. These data constitute some of the first directly dated palaeo-snowline data from the arid tropics and suggest that the magnitude of the last glaciation in at least parts of the tropical Andes was similar to late-Pleistocene events at higher latitudes. Copyright © 2011 John Wiley & Sons, Ltd.
... Palaeotemperature and palaeoprecipitation can be reconstructed using a range of proxy records: palaeo-Equilibrium Line Altitudes (ELAs) from reconstructed glaciers (e.g., Porter, 2001), ice-cores (δ 18 O and 2 H) (e.g., Thompson et al., 1998), lake sediment cores (e.g., pollen and diatoms) (e.g., Stansell et al., 2014), and palaeoecological techniques (e.g., Chevalier et al., 2020). Temperature reconstructions from palaeo-ELA reconstructions have estimated the LLGM temperature of Peru to range between 6.4 and 2°C cooler than present (Rodbell, 1992;Ramage et al., 2005;Smith et al., 2005;Bromley et al., 2011a;Úbeda et al., 2018). The wide range in the estimated values is due to local controlling factors such as local topography, aspect, and relief. ...
... The ELA is the theoretical line where accumulation and ablation are equal (Benn et al., 2005) and has been frequently used as a proxy of the surrounding climate conditions of temperature and precipitation for the reconstruction of tropical Andean glaciers and climate (Porter, 2001;Bromley et al., 2011a;Martin et al., 2020). Although the ELA would not have been static for long periods of time due to the varying climate conditions, the reconstructed palaeo-ELA inferred in this study is assumed to be at its lowest potential elevation and thus represents the time the glaciers were at their most extensive (i.e., LLGM). ...
... Our lowest estimate of temperature cooling (i.e., 8.9°C) is consistent with other palaeo-ELA temperature reconstructions within the tropical Andes (see Supplementary Table 2) (Rodbell, 1992;Ramage et al., 2005;Smith et al., 2005;Bromley et al., 2011a;Úbeda et al., 2018). Temperature cooling estimates from valley glaciation locations that are considerably lower than those reported by our study, with Ramage et al. (2005) reporting a cooling of 2.5°C in Lake Junin, and Smith et al. (2005) estimating a cooling between 2°C and 4°C for the Lake Junin and Milluni and Zongo valleys. ...
Characterising glaciological change within the tropical Andes is important because tropical glaciers are sensitive to climate change. Our understanding of glacier dynamics and how tropical glaciers respond to global climate perturbations is poorly constrained. Studies of past glaciation in the tropical Andes have focused on locations where glaciers are still present or recently vacated cirques at high elevations. Few studies focused on lower elevation localities because it was assumed glaciers did not exist or were not as extensive. We present the first geomorphological evidence for past glaciations of the Lagunas de Las Huaringas, northern Peru, at elevations of 3,900–2,600 m a.s.l. Mapping was conducted using remotely-sensed optical imagery and a newly created high-resolution (∼2.5 m) digital elevation model (DEM). The area has abundant evidence for glaciation, including moraines, glacial cirques, hummocky terrain, glacial lineations and ice-sculpted bedrock. Two potential models for glaciation are hypothesised: 1) plateau-fed ice cap, or 2) valley glaciation. Assuming glaciers reached their maximum extent during the Local Last Glacial Maximum (LLGM), between 23.5 ± 0.5 and 21.2 ± 0.8 ka, the maximum reconstructed glacial area was 75.6 km². A mean equilibrium line altitude (ELA) of 3,422 ± 30 m was calculated, indicating an ELA change of −1,178 ± 10 m compared to modern snowline elevation. There is an east to west ELA elevation gradient, lower in the east and higher in the west, in-line with modern day transfer of moisture. Applying lapse rates between 5.5 and 7.5°C/km provides a LLGM temperature cooling of between 6.5–8.8°C compared to present. These values are comparable to upper estimates from other studies within the northern tropical Andes and from ice-core reconstructions. The mapping of glacial geomorphology within the Lagunas de las Huaringas, evidences, for the first time, extensive glaciation in a low elevation region of northern Peru, with implications for our understanding of past climate in the sub-tropics. Observations and reconstructions support a valley, rather than ice cap glaciation. Further work is required to constrain the timing of glaciations, with evidence of moraines younger than the LLGM up-valley of maximum glacier extents. Numerical modelling will also enable an understanding of the controls of glaciation within the region.
... Therefore, where precipitation is Moreover, the paleoclimatic reconstructions over the last glacial maximum in the Arid Tropical Andes are not homogenous either. The Coropuna ELA depression shows a~5 • C cooling regarding the current climate [37,47], if no changes in paleoprecipitation (∆ = 0%) are taken into account. Conversely, another work on Tunupa (~20 • S, Figure 1) during the Tauca highstand (~17-15 ka), found somewhat higher cooling (~6.5 • C) and higher precipitation (between ×1.6 and ×3.0) than in the present [8]. ...
... They deduced that the pre-CI moraines were older than the CI moraines, but they did not verify that hypothesis by absolute dating. In a later work, Bromley et al. [47] reconstructed the current ELAs and the paleoELAs around the Coropuna. On the northern slope they estimated an ELA of 5915 ± 44 m. ...
... On the northern slope they estimated an ELA of 5915 ± 44 m. Different paleoELAs were presented for the CI phase, depending on the calculation method or the THAR ratio used: Bromley et al. [47] used the paleoELA depression (~750 m) and the air temperature lapse ratio (ATLR) 7-6 • C/km, supposing that the past precipitation had been similar to the present one, to argue that the paleotemperature of the CI phase was~5.2-4.5 • C colder than nowadays. ...
This work investigates the timing, paleoclimatic framework and inter-hemispheric teleconnections inferred from the glaciers last maximum extension and the deglaciation onset in the Arid Tropical Andes. A study area was selected to the northeastward of the Nevado Coropuna, the volcano currently covered by the largest tropical glacier on Earth. The current glacier extent, the moraines deposited in the past and paleoglaciers at their maximum extension have been mapped. The present and past Equilibrium Line Altitudes (ELA and paleoELA) have been reconstructed and the chlorine-36 ages have been calculated, for preliminary absolute dating of glacial and volcanic processes. The paleoELA depression, the thermometers installed in the study area and the accumulation data previously published allowed development of paleotemperature and paleoprecipitation models. The Coropuna glaciers were in maximum extension (or glacial standstill) ~20-12 ka ago (and maybe earlier). This last maximum extension was contemporary to the Heinrich 2-1 and Younger Dryas events and the Tauca and Coipasa paleolake transgressions on Bolivian Altiplano. The maximum paleoELA depression (991 m) shows a colder (−6.4 • C) and moister climate with precipitation ×1.2-×2.8 higher than the present. The deglaciation onset in the Arid Tropical Andes was 15-11 ka ago, earlier in the most southern, arid, and low mountains and later in the northernmost, less arid, and higher mountains.
... En otro trabajo, Bromley et al. (2011a) reconstruyeron las ELAs actuales y las paleoELAs alrededor del Coropuna. En la vertiente norte estimaron una kinematic ELA=5915±44 m. ...
... En la vertiente norte estimaron una kinematic ELA=5915±44 m. También diferentes paleoELAs para el máximo avance CI, dependiendo del método de cálculo o el ratio THAR empleado: -PaleoELA MELM (Maximum Elevation of Lateral Moraines): 5167±59 m. -PaleoELAs THAR: 5116±91 m (THAR=0,25); 5116±89 m (THAR=0,28) y 5200±88 m (THAR=0,30); con un promedio 5144±89 m. Bromley et al. (2011a) relacionaron la depresión de la paleoELA (~750 m) y un gradiente térmico vertical de la temperatura del aire GVTa=7-6°C, considerando que la precipitación en el pasado era similar a la actual. De esa manera dedujeron que durante el máximo avance CI el clima debía haber sido 5.2-4.5°C ...
... -En otras montañas la máxima expansión temprana fue seguida por el retroceso de los glaciares y muchas edades de exposición proceden de morrenas de reavance. Lo mismo sucede para parte de las edades glaciales de Bromley et al. (2009);Bromley et al., (2011a) para el Nevado Coropuna. ...
ABSTRACT
The Nevado Coropuna is a volcanic complex covered by the most extensive glacier system in the tropics. It is in the arid Central Andes, where glaciers are more sensitive to precipitation than to temperature. In the northeast of the Coropuna, volcanism, geothermal heat and the presence of the altiplano influenced in the past evolution of the glaciers, hindering its understanding. This work is a preliminary analysis of that problem, by a 36 Cl age survey of maximum glacier extent, the beginning of deglaciation and the last volcanic eruption. Complementarily also was reconstructed the Equilibrium Line Altitude of present and past glaciers and the cooling respect to the current climate at the glaciers expansion. The results were compared to previous glacial ages, from Coropuna and other mountains in Central Andes, and paleoclimatic proxies of Altiplano humidity and temperature in both Earth hemispheres. The data suggest that the maximum expansion occurred 26-11 ka, in relation to wetter climate than present that maybe was driven by the boreal cooling during Last Glacial Maximum and the Heinrich and Young Dryas episodes.
RESUMEN
El Nevado Coropuna es un complejo volcánico cubierto por el sistema glaciar más extenso de los trópicos. Está en los Andes Centrales áridos, donde los glaciares son más sensibles a la precipitación que a la temperatura. Al noreste del Coropuna, el vulcanismo, el calor geotérmico y la presencia del altiplano influyeron en la evolución de los glaciares en el pasado, dificultando su comprensión. Este trabajo es un análisis preliminar de ese problema, realizando una prospección de edades 36 Cl de la máxima expansión glaciar, el comienzo de la deglaciación y la última erupción volcánica. Complementariamente se reconstruyeron las Equilibrium Line Altitudes de glaciares actuales y pasados y el enfriamiento del clima con respecto al presente durante la expansión glaciar. Los resultados se compararon con anteriores edades glaciales, del Coropuna y otras montañas de los Andes Centrales, y proxies paleoclimáticos de humedad en el Altiplano y temperatura en ambos hemisferios terrestres. Los datos sugieren que la máxima expansión glaciar sucedió hace ~26-11 ka, en relación con un clima más húmedo que el actual, que tal vez fue impulsado por el enfriamiento boreal durante el Last Glacial Maximum y los episodios Heinrich y Younger Dryas.
... Alcalá et al. (2011) reported an LLGM (local last glacial maximum) ELA in the Huayuray valley of 4980 m with AA (Area x Altitude) method. Bromley et al. (2011b) used the MELM (Maximum Elevation of Lateral Moraines) and THAR (Terminus Headwall Altitude Ratio) methods to calculate LLGM ELAs for the Pucuncho peaks. The results reported using the MELM method were an average of 4887 ± 77 m for the Western slope and 4745 ± 66 m for the South slope, the results using the THAR method (with ratio 0.28), were an average of 5059 ± 68 m for the West and 4728 ± 228 m for the South slope. ...
... In the Coropuna volcanic complex, research by Úbeda (2011) on the northeast and southeast slopes found that the ELA AABR on the SE slope was 5844 m in 2007, and modern ELAs calculated by Bromley et al. (2011b) show average results of 5850 ± 54 m for the West slope and 5580 ± 54 m for the South slope. For tropical glaciers, Kaser & osmaston (2002) consider the aaR (accumulation Area Ratio) value = 0.67 to be the most appropriate. ...
... ELa values are highest on north-flowing glaciers and lowest on south-flowing glaciers. The ELa aaBR for LLGM obtained in this present study was 4762 m, this result is close to those reported by Úbeda (2011) with the AABR method obtaining an ELA of 4951 m for the SE slope of Nevado Coropuna and Bromley et al. (2011b) with the MELM (Maximum Elevation of Lateral Moraines) and THAR (Terminus Headwall Altitude Ratio) methods for the calculation of LLGM ELAs for the Pucuncho peaks, reporting an average of 4887 ± 77 m for the Western slope and 4745 ± 66 m for the South slope (using the MELM method), and an average of 5059 ± 68 m for West and 4728 ± 228 for the South (using the THAR method with a ratio of 0.28). The results reported by Alcalá et al. (2011) for the LLGM ELA in the Huayuray valley is 4980 m with AA method and the result reported by Alcalá (2015) on HualcaHualca is 5006 m using the AABR method. ...
The main aim of this research was to reconstruct the LLGM (local last glacial maximum), 1955 and 2007 glacial phases on the South West slope of Nevado Coropuna to obtain valuable information on the changes that have occurred and analyze the glacier evolution. For this purpose the ELA (Equilibrium Line Altitude) indicator has been used as a reference, with the AABR (Area x Altitude Balance Ratio) method, based on the principle of weighting the mass balance according to the distance above or below the ELA of that area. An ELA of 4762 m was obtained for the LLGM, 5779 m for 1955 and 5850 m for 2007, implying a vertical shift of 1088 m from the LLGM to 2007 and of 71 m from 1955 to 2007. The total glaciated surface was reduced by 21.5% between 1955 and 2007 and the temperature shift from LLGM to 2007 was 9.13 °C (0.0091°C/m). The ice of glaciers makes them valuable for climate research, this method offers quantitative information and the analysis of this data may contribute to research into climate change and climatic trends for future predictions.
... In paleoenvironmental reconstructions, the northern and southern Andes were cooler, more humid, and more heavily forested than today (Clapperton 1993a, b;Dillehay 1989;Van der Hammen and Correal 2001). Glaciers in the central Andes were primarily at elevations >5000 masl; they were patchier and not nearly as extensive as glaciers in North America at the time (Bromley et al. 2009(Bromley et al. , 2011a(Bromley et al. , b, 2016Clapperton 1993a, b). For tropical latitudes of the Andes, the LGM is locally dated to ~26,000-17,000 BC, followed by rapid deglaciation ~17,000-13,000 BC, with a brief hiatus at ~14,100 BC , which dramatically ameliorated the long asserted glacial and environmental "barriers" to exploration and habitation of the high altitudes (Aldenderfer 2008). ...
... For tropical latitudes of the Andes, the LGM is locally dated to ~26,000-17,000 BC, followed by rapid deglaciation ~17,000-13,000 BC, with a brief hiatus at ~14,100 BC , which dramatically ameliorated the long asserted glacial and environmental "barriers" to exploration and habitation of the high altitudes (Aldenderfer 2008). Glacial melting persisted thereafter (Bromley et al. 2009(Bromley et al. , 2011a(Bromley et al. , b, 2016. ...
This paper summarizes the current archaeological, physiographic, demographic, molecular, and bioarchaeological understanding of the initial peopling and subsequent population dynamics of South America. Well-dated sites point to a colonization by relatively few broad-spectrum foragers from northeastern Asia between ~13,000 and 12,000 cal BC via the Panamanian Peninsula. By ~11,500–11,000 cal BC, a number of regional, specialized bifacial technologies were developed, with evidence for the seasonal scheduling of resources and the colonization of extreme environments. Restricted mobility, landscape modification, and the cultivation of domesticates were underway by ~8000 cal BC. The early migration routes followed by colonists resulted in a broad east-west population structure among ancient South Americans. Genetic, demographic, and skeletal morphological data indicate that a subsequent demographically driven dispersal into South America largely replaced preexisting central Andeans ~5000 BC, due to increased fertility associated with the shift to agriculture. Beyond the Andes, however, there is little evidence of impact of these later expansions on foragers and horticulturists of the Amazon and Southern Cone who were largely descended from Paleoindians and early Holocene populations.
... In paleoenvironmental reconstructions, the northern and southern Andes were cooler, more humid, and more heavily forested than today (Clapperton 1993a, b;Dillehay 1989;Van der Hammen and Correal 2001). Glaciers in the central Andes were primarily at elevations >5000 masl; they were patchier and not nearly as extensive as glaciers in North America at the time (Bromley et al. 2009(Bromley et al. , 2011a(Bromley et al. , b, 2016Clapperton 1993a, b). For tropical latitudes of the Andes, the LGM is locally dated to ~26,000-17,000 BC, followed by rapid deglaciation ~17,000-13,000 BC, with a brief hiatus at ~14,100 BC , which dramatically ameliorated the long asserted glacial and environmental "barriers" to exploration and habitation of the high altitudes (Aldenderfer 2008). ...
... For tropical latitudes of the Andes, the LGM is locally dated to ~26,000-17,000 BC, followed by rapid deglaciation ~17,000-13,000 BC, with a brief hiatus at ~14,100 BC , which dramatically ameliorated the long asserted glacial and environmental "barriers" to exploration and habitation of the high altitudes (Aldenderfer 2008). Glacial melting persisted thereafter (Bromley et al. 2009(Bromley et al. , 2011a(Bromley et al. , b, 2016. ...
... However, there is still a lack of consensus as to whether Central Andean glaciers responded uniformly to these short-lived episodes of intensified monsoonal moisture transport. Some studies have associated dated moraines with the YD (Glasser et al., 2009;Rodbell et al., 2009;Zech et al., 2010;Kelly et al., 2012;Martini et al., 2017), but this correlation can be difficult to demonstrate unambiguously when calculated ages have uncertainties of ~1 ka and the YD interval only lasted from 12.9 ka to 11.7 ka (Bromley et al., 2011;Ward et al., 2015). Jomelli et al. (2014) suggested that moraine ages may instead correlate with the slightly earlier Antarctic Cold Reversal (ACR; 14.7-13.0 ...
... Both the ACR and YD climate events have been invoked to explain the timings of glacier advances in the Andes, but their relative importance is disputed (Bromley et al., 2011;Jomelli et al., 2014;Ward et al., 2015). Few moraines have been dated to either the YD interval or the ACR interval with 5+ boulders or 6+ boulders (i.e., the greatest confidence; Fig. 9d-e). ...
Advances in cosmogenic nuclide exposure dating have made moraines valuable terrestrial recorders of palaeoclimate. A growing number of moraine chronologies reported from the Central Andes show that tropical glaciers responded sensitively to past changes in precipitation and temperature over timescales ranging from 10^3 to 10^5 years. However, the causes of past glaciation in the Central Andes remain uncertain. Explanations have invoked insolation-modulated variability in the strength of the South American Summer Monsoon, teleconnections with the North Atlantic Ocean, and/or cooling in the Southern Hemisphere. The driver for these past climate changes is difficult to identify, partly due to a lack of dated moraine records, especially in climatically sensitive areas of the southern Central Andes. Moreover, new constraints are needed on precisely where and when glaciers advanced. We use cosmogenic 10Be produced in situ to determine exposure ages for three generations of moraines at the Sierra de Aconquija, situated at 27°S on the eastern flank of the southern Central Andes. These moraines record glacier advances at approximately 22 ka and 40 ka, coincident with summer insolation maxima in the sub-tropics of the Southern Hemisphere, as well as at 12.5 ka and 13.5 ka during the Younger Dryas and the Antarctic Cold Reversal, respectively. We also identify minor glaciation during Bond Event 5, also known as the 8.2 ka event. These moraines register past climate changes with high fidelity, and currently constitute the southernmost dated record of glaciation on the eastern flank of the Central Andes. To contextualise these results, we compile 10Be data reported from 144 moraines in the eastern Central Andes that represent past glacier advances. We recalculate exposure ages from these data using an updated reference production rate, and we re-interpret the moraine ages by taking the oldest clustered boulder age (after the exclusion of outliers attributed to nuclide inheritance) as closest to the timing of glacier advance-an approach for which we provide empirical justification. This compilation reveals that Central Andean glaciers have responded to changes in temperature and precipitation. We identify cross-latitude advances in phase with insolation cycles, the last global glacial maximum, and episodes of strengthened monsoonal moisture transport including the Younger Dryas and Heinrich Stadials 1 and 2. Our results from the Sierra de Aconquija allow us to constrain the southerly limit of enhanced precipitation associated with Heinrich Stadials at ~25°S. More broadly, our findings demonstrate at both local and regional scales that moraines record past climate variability with a fine spatial and temporal resolution.
... However, there is still a lack of consensus as to whether Central Andean glaciers responded uniformly to these short-lived episodes of intensified monsoonal moisture transport. Some studies have associated dated moraines with the YD (Glasser et al., 2009;Rodbell et al., 2009;Zech et al., 2010;Kelly et al., 2012;Martini et al., 2017), but this correlation can be difficult to demonstrate unambiguously when calculated ages have uncertainties of~1 ka and the YD interval only lasted from 12.9 ka to 11.7 ka (Bromley et al., 2011;Ward et al., 2015). Jomelli et al. (2014) suggested that moraine ages may instead correlate with the slightly earlier Antarctic Cold Reversal (ACR; 14.7e13.0 ...
... Both the ACR and YD climate events have been invoked to explain the timings of glacier advances in the Andes, but their relative importance is disputed (Bromley et al., 2011;Jomelli et al., 2014;Ward et al., 2015). Few moraines have been dated to either the YD interval or the ACR interval with 5 þ boulders or 6 þ boulders (i.e., the greatest confidence; Fig. 9dee). ...
Advances in cosmogenic nuclide exposure dating have made moraines valuable terrestrial recorders of palaeoclimate. A growing number of moraine chronologies reported from the Central Andes show that tropical glaciers responded sensitively to past changes in precipitation and temperature over timescales ranging from 10^3 to 10^5 years. However, the causes of past glaciation in the Central Andes remain uncertain. Explanations have invoked insolation-modulated variability in the strength of the South American Summer Monsoon, teleconnections with the North Atlantic Ocean, and/or cooling in the Southern Hemisphere. The driver for these past climate changes is difficult to identify, partly due to a lack of dated moraine records, especially in climatically sensitive areas of the southern Central Andes. Moreover, new constraints are needed on precisely where and when glaciers advanced. We use cosmogenic 10 Be produced in situ to determine exposure ages for three generations of moraines at the Sierra de Aconquija, situated at 27° S on the eastern flank of the southern Central Andes. These moraines record glacier advances at approximately 22 ka and 40 ka, coincident with summer insolation maxima in the sub-tropics of the Southern Hemisphere, as well as at 12.5 ka and 13.5 ka during the Younger Dryas and the Antarctic Cold Reversal, respectively. We also identify minor glaciation during Bond Event 5, also known as the 8.2 ka event. These moraines register past climate changes with high fidelity, and currently constitute the southernmost dated record of glaciation on the eastern flank of the Central Andes. To contextualise these results, we compile 10 Be data reported from 144 moraines in the eastern Central Andes that represent past glacier advances. We recalculate exposure ages from these data using an updated reference production rate, and we re-interpret the moraine ages by taking the oldest clustered boulder age (after the exclusion of outliers attributed to nuclide inheritance) as closest to the timing of glacier advancedan approach for which we provide empirical justification. This compilation reveals that Central Andean glaciers have responded to changes in temperature and precipitation. We identify cross-latitude advances in phase with insolation cycles, the last global glacial maximum, and episodes of strengthened monsoonal moisture transport including the Younger Dryas and Heinrich Stadials 1 and 2. Our results from the Sierra de Aconquija allow us to constrain the southerly limit of enhanced precipitation associated with Heinrich Stadials at ~25°S. More broadly, our findings demonstrate at both local and regional scales that moraines record past climate variability with a fine spatial and temporal resolution.
... Though there is a great focus on these issues in polar regions, it is a global concern in other parts of the world including high-elevation mountainous parts of South America. In the Region of Arequipa, Coropuna is a 6,377 m high dormant stratovolcano, 150 km northwest of the city of Arequipa (Venturelli et al. 1978;Bromley et al. 2011). Based on our analyses of historic Keyhole and contemporary Sentinel satellite imagery, from May 1978 to May 2019, respectively, Coropuna total ice and snow cover decreased by ~12.7% from ~88 km 2 to ~77 km 2 . ...
Analysis of historic and contemporary high-resolution imagery can help to fill knowledge gaps in land cover and management history in locations where documentation is non-existent or records are difficult to access. Historic imagery dating back to the 1960s can be used to structure quantitative investigation and mapping of land use and land cover change across space and time to enhance earth science, policy, and social science research. Imagery can further inform municipal planning and implementation in areas of natural resource allocation, infrastructure, and hazard mitigation. For management and public education, historic imagery can help people to understand environmental processes and the impacts of human activity in the local environment. Here we emphasize the value of high-resolution historic satellite imagery from the Corona and Keyhole satellite programs to inform environmental research, public education, and environmental management. Within the Region of Arequipa in southern Peru we highlight examples of urban development, agricultural expansion, river channelization, and glacial retreat via comparison of historic and modern satellite imagery. By incorporating these types of historic imagery data in formats accessible to non-professionals, public engagement as well as research into human-environmental investigations will be greatly enhanced.
... Kenya (Mahaney, 1990). También este método fue utilizado por Bromley et al., (2011), por Úbeda (2011) y por Alcalá (2014) en los Andes Centrales de Perú. ...
La altitud de la línea de equilibrio de los glaciares nos indica en qué punto el glaciar está en equilibrio con el clima, en ese punto la cantidad de masa ganada es equivalente a la que se pierde. Es muy común la utilización de la altitud de la línea de equilibrio glaciar como indicador climático, por ello se hace necesario disponer del estado actual de los glaciares, o de su estado durante la época de cuando se quiere reconstruir el clima. Para obtener estos datos es necesario disponer de la superficie, e idealmente, del volumen de los glaciares. Para obtener estas delimitaciones se propone una metodología de trabajo que empieza por realización de esquemas geomorfológicos con el objetivo de poder deducir los límites alcanzados por el hielo en otras épocas y posteriormente proceder a su reconstrucción y al cálculo de las líneas de equilibrio glaciar. Este estudio presenta el estado del arte de las metodologías y los procedimientos utilizados en las últimas décadas para realizar reconstrucciones glaciares y calcular la altitud de las líneas de equilibrio glaciar.
... The evidence at Cuncaicha thus appears to demonstrate that suggested climatic and physiologic barriers to settlement of the high Andes (Aldenderfer 1999(Aldenderfer , 2006 have been overestimated and that hypoxia exerted no serious obstacle to seasonal residential settlement of the high Central Andes in the Terminal Pleistocene (Rademaker et al. 2014. Paleoenvironmental records near Cuncaicha (Bromley et al. 2009(Bromley et al. , 2011a(Bromley et al. , 2011b and throughout the broader Central Andean region (Placzek et al. 2006;Moreno et al. 2009;Blard et al. 2011;Baker and Fritz 2015) show that Terminal Pleistocene Andean occupations were coeval with a period of increasing temperatures and greater precipitation, which would have made the highlands attractive to forager populations. ...
We report new accelerator mass spectrometry (AMS) ages on faunal and human remains recovered from Cuncaicha shelter (4480 m elevation) in the high southern Peruvian Andes. Using a large number of precise radiometric ages available for the Cuncaicha sequence, we employ Bayesian modeling to determine how human burials relate to discrete episodes of site occupation. Hunter-gatherers used Cuncaicha rockshelter as a residential camp beginning in the Terminal Pleistocene, ~12,000 years ago. In the Early Holocene, the site additionally became a cemetery where hunter-gatherers, and later pastoralists, interred their dead. Episodes of occupation alternated with episodes of burial, indicating persistent human presence in the high-elevation Pucuncho Basin and the maintenance of symbolically special places. The chronological framework presented here is the foundation for our team's ongoing interdisciplinary investigations of exploration and settlement in the Andes, one of the key world regions where humans have adapted to high elevation.
En este capítulo, reportamos nuevas dataciones radiocarbónicas obtenidas usando acelerador de espectrometía de masas (AMS) de restos humanos y faunísticos recuperados en el abrigo de Cuncaicha (4480 m de altura), localizado en los Andes peruanos del sur. Utilizando un gran número de fechados disponibles para la secuencia de Cuncaicha, empleamos un modelo Bayesiano para determinar de qué manera se relacionan los entierros humanos con episodios discretos de ocupación del sitio. Los cazadores-recolectores usaron el abrigo de Cuncai-cha como un campamento residencial desde el Pleistoceno Tardío, hace aproxi-madamente 12,000 años. Durante el Holoceno Temprano, el sitio se convirtió ade-más en un cementerio donde cazadores-recolectores y, más tarde, pastores, sepultaban a sus difuntos. Los episodios de ocupación alternaron con episodios de enterramiento, indicando una presencia humana persistente en la elevada cuenca de Pucuncho, así como la preservación de lugares simbólicamente especiales. El marco cronológico presentado aquí forma la base de las investigaciones interdisciplinarias actuales de nuestro equipo sobre la exploración y colonización de los Andes, una de las regiones clave donde los humanos se adaptaron a altitudes extremas.
... En el sector SW del complejo volcánico Dornbusch (2002) estimo valores de 5558 m para la ELA actual y 4750 m para la paleoELA del LGM. En un trabajo más reciente y exhaustivo (Bromley et al., 2011a) estudiaron numerosos valles alrededor del Coropuna, sugiriendo entre 4663±232 y 5200±68 m para la actualidad, 5319±139 y 5757±52 m para el LLG y 4663±232 y 5200±88 m para el LLGM, dependiendo de la orientación de las vertientes. En otra publicación, Ubeda (2010) ha utilizado procedimientos estadísticos para reconstruir las ELAs y paleoELAs de dos docenas de valles de los sectores NE y SE del complejo volcánico. ...
... Interpreting the abrupt climate change in the tropical Andes Nevado Coropuna, Cordillera Ampato Herreros et al., 2009 Ice core records Ice core analysis showed the dependency of precipitation on easterly circulation from the tropical Atlantic and identified ENSO Nevado Coropuna, Nevado Solimana and Nevado Firura in the Cordillera Ampato Bromley et al., 2011 Geomorphic-numeric approach Snowline reconstruction during the Pleistocene Favier et al., 2004aFavier et al., , 2004b. Air temperature increases during El Niño and the glaciers in the inner tropics (more sensitive to temperature) undergo enhanced ablation. ...
In this review, we summarized the evolution of glacier monitoring in the tropical Andes during the last few decades, particularly after the development of remote sensing and photogrammetry. Advantages and limitations of glacier mapping, applied so far, in Venezuela, Colombia, Ecuador, Peru and Bolivia are discussed in detail. Glacier parameters such as the equilibrium line altitude, snowline and mass balance were given special attention in understanding the complex cryosphere-climate interactions, particularly using remote sensing techniques. Glaciers in the inner and the outer tropics were considered separately based on the precipitation and temperature conditions within a new framework. The applicability of various methods to use glacier records to understand and reconstruct the tropical Andean climate between the Last Glacial Maximum (11,700 years ago) and the present is also explored in this paper. Results from various studies published recently were analyzed and we tried to understand the differences in the magnitudes of glacier responses towards the climatic perturbations in the inner tropics and the outer tropics. Inner tropical glaciers, particularly those in Venezuela and Colombia near the January Intertropical Convergence Zone (ITCZ), are more vulnerable to increase in temperature. Surface energy balance experiments show that outer tropical glaciers respond to precipitation variability very rapidly in comparison with the temperature variability, particularly when moving towards the subtropics. We also analyzed the gradients in glacier response to climate change from the Pacific coast towards the Amazon Basin as well as with the elevation. Based on the current trends synthesised from recent studies, it is hypothesized that the glaciers in the inner tropics and the southern wet outer tropics will disappear first as a response to global warming whereas glaciers in the northern wet outer tropics and dry outer tropics show resistance to warming trends due to the occurrence of cold phases of El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) together. Mountain glaciers in Ecuador show less retreat in response to the warming trend, probably due to high altitudes (above 5750 m), in comparison to glaciers in Colombia and Venezuela. However, elevation-dependent warming (EDW) is a major concern in the tropical Andes. In a nutshell, smaller glaciers at lower altitudes in the inner tropics and the southern wet outer tropics near the Amazon Basin are disappearing faster than other glaciers in the tropical Andes.
... Termination 1 in the tropics was characterised by pronounced warming, a sharp decline in the cryosphere, and abrupt shifts in seasonal precipitation. On a first-order basis, tropical palaeosnowline reconstructions invoke LGMeHolocene warming of approximately 5 C at higher elevations (Porter, 2001;Blard et al., 2007;Hastenrath, 2009;Barrows et al., 2011;Bromley et al., 2011b), a scenario that is supported by the near-uniform (>5‰) deglacial shift in d 18 O in tropical and extra-tropical ice cores (Thompson et al., 2000). Moreover, a growing body of data indicates this warming was not restricted to high altitudes. ...
... into their settlement systems. In the absence of late-glacial environmental barriers (Bromley et al. 2009(Bromley et al. , 2011a(Bromley et al. , 2011bRademaker et al. 2014:469, Materials and Methods 5-7), successful and redundant (Binford 1980) use of these rich habitats would be predicated only on the acquisition of landscape knowledge needed for navigating and finding critical resources. Redundant residential use of Cuncaicha rockshelter (Rademaker et al. 2014, fig. 3) defines successful Paleoindian colonization of the high Andes. ...
... However, as first recognized by Mercer (1984) and more recently shown by 10 Be and 14 C chronologies of glacial landforms (e.g., Clark et al., 2009;Denton et al., 1999a;Lowell et al., 1995;Putnam et al., 2013), the maximum extent of mountain glaciers and ice sheets worldwide was achieved between ∼25 and ∼18 kyr ago ( Fig. 1; Clark et al., 2009). For example, during that time period, mountain glaciers in North America (Porter and Swanson, 1998), Europe (Monegato et al., 2007), Hawaii (Anslow et al., 2010), Africa (Kelly et al., 2014), the tropical Andes (Bromley et al., 2011(Bromley et al., , 2009, Papua New Guinea (Barrows et al., 2011), southern South America (Denton et al., 1999a(Denton et al., , 1999bKaplan et al., 2008), and New Zealand (Doughty et al., 2015;Putnam et al., 2013) had all stood at their maximum extents. Further, the LGM snowline lowering is similar across the globe. ...
It is generally accepted that the glacial drawdown of atmospheric CO2 content is the sole result of uptake by the ocean. Here we make a case that the reduction of planetary CO2 outgassing made a significant contribution. We propose that the ocean contribution to CO2 reduction closely followed Northern Hemisphere summer insolation and was superimposed on a ramp-like decline resulting from a reduction in the input of planetary CO2. We base this scenario on new records of δ13C and B to Ca ratio in cores from the upper and lower portions of the deep Atlantic. They demonstrate that the waxing and waning of the stratification of Atlantic deep water follows summer insolation. Our thoughts were driven by the observation that over the last 30 kyr the extent of mountain glaciation in both hemispheres appears to have tracked the atmosphere's CO2 content, suggesting that the connection between orbital cycles and land ice cover is via the ocean. Instead of a direct connection between ice extent and summer insolation, the tie is a modulation of the heat and fresh water budgets of the northern Atlantic. Changes in the boundary conditions lead to reorganizations of ocean circulation and, as a consequence, changes in CO2 storage in the ocean.
... Various studies focused on monitoring the changes in glaciated area, ice volume or ice thickness of the Nevado Coropuna using remote sensing and GIS techniques (Racoviteanu et al. 2007;Peduzzi et al. 2010;Ubeda 2011). There are previous studies on the snowline variations of the Nevado Coropuna and other glaciers in the central Andes during the late Pleistocene (Bromley et al. 2009(Bromley et al. , 2011. The effects of recent warming in the tropics on the Nevado Coropuna using ice core records was published recently by Herreros et al. (2009). ...
This research focuses on the recent variations in the annual snowline and the total glaciated area of the Nevado Coropuna in the Cordillera Ampato, Peru. Maximum snowline altitude towards the end of dry season is taken as a representative of the equilibrium line altitude of the year, which is an indirect measurement of the annual mass balance. We used Landsat and IRS LISS3 images during the last 30 years due to its better temporal coverage of the study site. It is found that there was a decrease of 26.92% of the glaciated area during 1986-2014. We calculated the anomalies in precipitation and temperature in this region and also tried to correlate the changes in glacier parameters with the combined influence of ENSO and PDO. It is concluded that the snowline of Nevado Coropuna has been fluctuated during ENSO and maximum fluctuations were observed when ENSO and PDO were in phase.
... In northern Perú, fluctuations in temperature are believed to have alternatively lowered and raised tree-lines, altered biogeographic distributions, and produced mixed associations (Bush 2002;Hillyer et al. 2009;Netherley 2011;Weng et al. 2006). The intensity of these effects during cold reversals (like the Younger Dryas) also influenced precipitation levels and available moisture (Bromley et al. 2011;Gosling et al. 2008;Vimeux 2009;Weng et al. 2006). These alternating pressures had differential impacts on the distributions of specific plant and animal species within different ecological settings (Bush 2002;Mayle et al 2009). ...
On Perú's North Coast, the earliest documented lithic traditions are collectively known as the El Palto Phase (~14,200-9,600 cal BP). This phase, which spans the Late Pleistocene to Early Holocene, contains evidence for several contemporary or overlapping traditions, including early unifacial assemblages, and the Fishtail and Paiján complexes. Recent study of El Palto phase sites in the lower Jequetepeque Valley focused on evaluating the relationships between these assemblages and the populations who manufactured them. The results from several long-term regional studies are considered with these analyses to provide a new synthesis regarding early settlement patterns and technological change in this region of the Central Andes.
... The project included creation of a digital database of archaeological radiocarbon data (Rademaker et al. 2013a), geochemical characterization of the Alca obsidian source (Rademaker et al. 2013b), quantitative geographic information systems (GIS) predictive modeling , region-level archaeological survey, geophysical surveys, test excavations, and systematic surface collections (Rademaker 2012;Sandweiss and Rademaker 2013), and AMS dating of the Cuncaicha rockshelter (4480 m elevation), the highest Pleistocene archaeological site yet discovered in the world (Rademaker et al. 2014). Concurrent with these archaeological investigations, Gordon Bromley led glacial geologic investigations of Nevados Coropuna, Solimana, and Firura ( Fig. 3) to construct local, high-resolution paleoclimate records (Bromley et al. 2009(Bromley et al. , 2011a(Bromley et al. , 2011bBromley 2010). ...
A synthetic understanding of the timing and migration routes involved in the initial human settlement of the Americas remains elusive. Although site-level investigations have provided a wealth of information on adaptations to specific ecological zones, fundamental information is lacking on landscape-scale patterns of mobility, settlement, and inter-site connections. Beginning with the source of exotic obsidian artifacts found at the Paleoindian coastal site Quebrada Jaguay in southern Peru, my research integrated a number of approaches to locate Paleoindian hunter-gatherer archaeological sites in the high Andes, with the ultimate objective of understanding early coast-highland links. This interdisciplinary work has demonstrated that despite colder temperatures, more extensive glaciers, and low-oxygen conditions, successful human colonization of the high-altitude Andes began ~12,400–12,000 years ago at the end of the last ice age. Investigation of linkages between early coastal and highland sites is ongoing.
... In the context of the Cuncaicha Paleoindian occupation, our interpretation of the Coropuna moraine record and other paleoclimate data from the southern Peruvian Andes is as follows. First, as indicated by glacier reconstructions (32,53), ice did not present a barrier to human migration and settlement of the Pucuncho Basin. Indeed, local glaciers did not encroach upon the plateau even at the height of the last ice age (~25-20 ka). ...
... Glaciers along the length of the Andes were confined to cirques and high alpine valleys (Rodbell and Seltzer, 2000;Smith et al., 2005;Hall et al., 2009). In the western cordillera of southern Peru, for example, the ice margin did not descend below w4700 m on Nevado Coropuna (Bromley et al., 2009(Bromley et al., , 2011a(Bromley et al., , 2011b. Moreover, if late-glacial cooling did indeed pre-date the YD interval, the high-elevation Peruvian Andes were already warming before the first people were settling both coastal and highland Peru. ...
We synthesize the available radiocarbon data from Peruvian archaeological sites for the Terminal Pleistocene through Middle Holocene. Compilation and calibration of this dataset provide a new opportunity to examine trends in archaeological site distributions and occupation intensity. We compare the spatial and temporal patterning of radiocarbon dated archaeological sites with paleoenvironmental information to discuss possible human-environment dynamics and to identify major taphonomic biases affecting the existing dataset. Further, we evaluate the history of radiocarbon dating of Terminal Pleistocene to Mid-Holocene archaeological sites in both coastal and highland settings to identify research biases affecting the record and suggest ways in which future research may address these deficiencies.
... In contrast to mountain regions in Eurasia and North America, the Andean environment lacks sufficient high-resolution paleotemperature records, since tree-ring chronologies are not available for sites at high elevations, due to climate as well as to intense human cutting and grazing (tree line at 3900 m ASL; Ellenberg, 1979). Most of the published paleoclimate studies conducted in the Western Cordillera have concerned chronology of moraine sequences and Pleistocene equilibrium line altitudes (e.g., Bromley et al., 2011;Dornbusch, 2002Dornbusch, , 2005Engel, 2001;Hastenrath, 1971;Smith et al., 2009;Úbeda et al., 2009). These proxies are incomplete recorders of glaciations and provide only fragmentary evidence of paleoenvironmental conditions. ...
Global climate variability is a well-documented fact; however, the human contribution to climate change is now being vigorously debated. Therefore, a better understanding of past natural climate variability may help to establish the actual anthropogenic contribution to the observed climatic trend. A variety of high-resolution proxies now exist for documenting climate variability that has occurred in the northern hemisphere over the last 10. ka. In contrast, high-resolution paleoclimate records are more limited for regions such as high altitudes in the Andes/South America. However, many regions of the Andes contain a rich, but as yet overlooked, paleoclimate archive in the form of thick peat deposited in situ by the Distichia plant. In our study, based on altitudinal transect from the Peruvian Andes, we found a statistically significant and strong relationship between the stable carbon isotope composition of Distichia and air temperature (R = 0.92 p < 0.01). We also confirmed good preservation of relative differences in the original stable carbon isotope composition in peat derived from this plant. Our calibration showed that a decrease of ~ 0.97 ± 0.23‰ in the stable carbon isotope composition of Distichia peat reflects a 1 °C increase in mean air temperature of the growing seasons. This relationship can be used as a new high-resolution proxy for reconstruction of paleotemperature variations over the past several thousand years in the Andes Mountains based on Distichia peat cores.
Within coastal Andean archaeology there is a growing emphasis on the roles of hydrology and hydrological knowledge in Andean strategies for water management, settlement, and land use. Hydrological methods can not only help reconstruct past water environments but also illuminate the influence of changing climates and conditions in the Andean highlands on coastal water flows. Through a case study of the Supe River basin in north-central coastal Peru, focusing on the period from 5000 to 3000 calibrated radiocarbon years before present (cal. BP), I review several hydrological methods useful for archaeological study. I then combine these to develop a paleohydrological model that provides a basis for comparing the hydrological effects of changing climates, environmental factors, and settlement and land use patterns. Recognizing the importance of Andean highland climates on coastal river flows, I begin by developing a paleoclimate synthesis for the Norte Chico region (i.e., the Fortaleza, Pativilca, Supe, and Huaura basins) from 6000 to 2000 cal. BP. There has been considerable paleoclimate research in both the highlands and the coast but only limited efforts to develop these records into a coherent narrative of basin-wide climate patterns. Through a review of 21 studies spanning the tropical Andes, the central Andean highlands, the Altiplano, and the Peruvian coast, I identify three millennial-scale periods defined by distinct climatic transitions affecting the highlands and/or the coast: 6000-4000 cal. BP, 4000-3200 cal. BP, and 3200-2000 cal. BP. I then apply paleohydrological methods, which are largely grounded in geospatial analysis in a geographic information system. The first method is drainage network modeling from a digital elevation model, which defines stream networks and catchments for a study area. The second method is delineation of hydrological response units (HRUs), which are areas that have similar hydrological dynamics. The HRU model uses climate-based parameters derived from the paleoclimate synthesis to create a spatial layer of climate regions and combines these with geological and soils layers to define discrete units of shared characteristics. Although both methods provide useful context on their own, I combine them through a qualitative assessment of hydrological dynamics within and between each of the HRUs, tracing their effects on surface and ground water flows from the highest elevations through inland valleys to the coast. This is the core of the paleohydrological model. The hydrological conditions suggested by the model provide a basis for considering how Supe Valley settlement patterns relate to intra-basin and temporal variations in water availability, access to water and irrigable land, and flood risk. The study period is characterized by intensified settlement and agriculture in the inland valleys of the Norte Chico region between 5000 and 4000 cal. BP followed by marked shifts in the fortunes of certain settlements with a long-term decline in activity. The analysis calls into question previous hypotheses regarding social organization in the Supe Valley, irrigation practices, and the contribution of environmental processes to the region’s decline and suggests directions for future research to clarify these developments.
Constraining the age of young lavas, which generally fall outside the effective range of traditional geochronology methods, remains a key challenge in volcanology, limiting the development of high-resolution eruption chronologies. We present an in situ cosmogenic ³He and ³⁶Cl surface-exposure chronology, alongside new minimum-limiting ¹⁴C ages, documenting young eruptions at five sites in the Western Cordillera, southern Peru. Four ³He-dated lavas on the Nevado Coropuna volcanic complex (hitherto thought to be dormant) indicate that the central dome cluster is young and potentially active; two Holocene lavas on the easternmost dome are the youngest directly dated lavas in Peru to date. East of Coropuna, lava domes and block-lava flows represent the most extensive output to date of Nevado Sabancaya, one of Peru’s most active volcanoes. Two ³He measurements confirm the Holocene age of these deposits and expand the chronology for one of the youngest major lava fields in Peru. ³⁶Cl surface-exposure ages from the Purupurini dome cluster and Nevado Casiri document middle-late-Holocene episodes of effusive activity, while basal ¹⁴C ages from a lava-dammed wetland constrain an effusive eruption at Mina Arcata, north of Coropuna, to the late-glacial period. These new data advance the recent Western Cordillera volcanic record whilst demonstrating both the considerable potential and fundamental limitations of cosmogenic surface-exposure methods for such applications.
This paper studies a glaciated area on this volcanic complex which is located on the limit between the andean Altiplano and the ramp reaching the Pacific Ocean coast. The report of 36C1 cosmogenic isotopes of 8 surface samples on moraine boulders show several local glacier maximum advances among 21 and 11 kyr, over Marine Isotope Stage MIS 2. Glacial data analysis suggests very interesting new paleoclimatic and geomorphologic interpretations, both in local and regional scales.
Study of human adaptation to extreme environments is important for understanding our cultural and genetic capacity for survival.
The Pucuncho Basin in the southern Peruvian Andes contains the highest-altitude Pleistocene archaeological sites yet identified
in the world, about 900 meters above confidently dated contemporary sites. The Pucuncho workshop site [4355 meters above sea
level (masl)] includes two fishtail projectile points, which date to about 12.8 to 11.5 thousand years ago (ka). Cuncaicha
rock shelter (4480 masl) has a robust, well-preserved, and well-dated occupation sequence spanning the past 12.4 thousand
years (ky), with 21 dates older than 11.5 ka. Our results demonstrate that despite cold temperatures and low-oxygen conditions,
hunter-gatherers colonized extreme high-altitude Andean environments in the Terminal Pleistocene, within about 2 ky of the
initial entry of humans to South America.
Currently-available evidence of 20th-century warming from glaciers and permafrost is briefly reviewed. The signals are clear and strong: warming of polar firn and permafrost, and mass losses of glaciers at lower latitudes, were most striking towards the middle of the century. The easily observable length-reduction of mountain glaciers confirms the global character of the evolution. A probably intermittent reversal of the trend was observed in places after about 1950.
Air photo and map interpretation and field work provide evidence of four Pleistocene cold phases in the Cordillera Ampato indicated by glacial moraines and rock glaciers. The oldest glaciation is associated with a snowline depression of ∼ 1000 m and is likely to belong to the Last Glaciation. The eastward rise of the Pleistocene Equilibrium Line Altitude (ELA) was smaller than for the present indicating moisture conditions at least similar to those at present. During the largest glaciation, the regional ELA was at ∼ 4400 m allowing for most areas above 4000 m to be covered by ice or at least by snow for most of the year forming a tropical high altitude cooling surface that probably covered the whole width of the Andes north of 16°S.
Himalayan Journal of Sciences Vol.2(4) Special Issue 2004 pp. 100-1
Quaternary deposits are described and discussed in relation to their origin and to the dating methods employed. At the end of the Liki Glaciation (~12 000yr BP), most valley glaciers halted during recession in the late glacial to build moraines in high valleys at ~4000m asl. Neoglaciation, which began ~1000yr BP, consisted of two advances - Tyndall (~900yr BP) and Lewis (~100yr BP). -from Author
The length of time τM over which a glacier responds to a prior change in climate is investigated with reference to the linearized theory of kinematic waves and to results from numerical models. We show the following: τM may in general be estimated by a volume time-scale describing the time required for a step change in mass balance to supply the volume difference between the initial and final steady states. We suggest that τM for mountain glaciers can be substantially less than the 102-103 years commonly considered to be theoretically expected. -from Authors
Climatically sensitive tropical ecosystems provide important information
that may help us to fill the gaps in our knowledge concerning the
evolution of rainforests during periods of full glaciation. Small
changes in precipitation in the Amazon Basin have immediate consequences
for the survival of the Andean cloud forest, because its dominant source
of moisture today is the Atlantic Ocean. A 40 k.y. lacustrine record
from the Eastern Cordillera in Bolivia in an endemic species rich and
ecologically threatened region shows a dry Last Glacial Maximum,
indicating a drastic decrease of the Amazonian moisture source. To
explain this aridity, we infer steep temperature gradients between the
pole and equator in both hemispheres that would have reduced
considerably the size and displacement of the Intertropical Convergence
Zone and the austral summer precipitation. This major change in water
supply induced a dramatic reduction in species diversity and suggests
that the Andean cloud forest did not provide refugia for tropical
lowland taxa during full glacial times.
The substantial lowering of tropical snowlines at the Last Glacial Maximum (LGM), circa 21 kya, is examined using a modified version of the single-cell tropical climate model of Betts and Ridgway [1989]. These authors concluded that it was difficult to reconcile the large depression of snowlines at the LGM with the small reduction in mean tropical sea-surface temperature (SST) of the Climate: Long-Range Investigation, Mapping, and Prediction (CLIMAP) reconstruction. Here, climatic implications of the snowline depression are compared, not with CLIMAP, but with temperature proxies (delta18O and Sr/Ca ratios in corals, noble gas concentrations in aquifers, alkenone and Mg/Ca ratios in deep-sea sediments and recent faunal reconstructions) whose LGM values have been interpreted as implying lower surface temperatures in the tropics. It proves difficult, in the framework of this model, to reconcile the coldest of the indicated paleotemperatures with the observed snowline depression, which by itself is found to be consistent with an SST reduction of ~3 K. A cooling of this magnitude corresponds most closely to recent warm-pool LGM sea-surface temperature estimates based on Mg/Ca paleothermometry. Discordance among the various proxy reconstructions may result, at least in part, from regional variations in surface temperature change at the LGM.
Ice cores that were recovered from the summit of Sajama mountain in Bolivia provide carbon-14-dated tropical records and extend to the Late Glacial State (LGS). Oxygen isotopic ratios of the ice decreased 5.4 per mil between the early Holocene and the Last Glacial Maximum, which is consistent with values from other ice cores. The abrupt onset and termination of a Younger Dryas-type event suggest atmospheric processes' as the probable drivers. Regional accumulation increased during the LGS, during deglaciation, and over the past 3000 years, which is concurrent with higher water levels in regional paleolakes. Unlike polar cores, Sajama glacial ice contains eight times less dust than the Holocene ice, which reflects wetter conditions and extensive snow cover. (Résumé d'auteur)
Based on detailed and publicly available data, a map of annual precipitation has been constructed. This map indicates for most of the area above 4000 m altitude precipitation exceeding 600 mm/yr, with many areas receiving even more than 800 mm/yr. These values exceed the precipitation data given in maps in the literature by 200-500 mm/yr and indicate considerably wetter conditions than have so far been assumed. However, the general pattern shown in previous precipitation maps was confirmed: high precipitation at the eastern edge of the Andes decreases towards the Pacific, and precipitation in the Western Cordillera decreases from north to south. A correlation between the annual river discharge of rivers flowing into the Pacific and records for the El Niño Southern Oscillation (ENSO) was found only for parts of the period 1926 to 1971, leaving the question of a direct influence of ENSO on the precipitation in the Western Cordillera of Southern Peru unanswered. From annual mean temperatures for thirty-five stations above 3000 m, the altitude of the 0°C isotherm above each station was calculated, locating it above 5000-5100 m in the Eastern Cordillera and below 4900-4800 m in the Western Cordillera. A snowline altitude map was constructed from data for the contour line altitude that halves the glacier area, representing the accumulation area ratio (AAR) of 0.5 for 931 glaciers from the Peruvian glacier inventory. It shows the lowest snowlines at 4900-5000 m in the Eastern Cordillera and the highest snowlines at 5600 m in the Western Cordillera, but it also indicates that the 5200 m and 5300 m snowline contours cross the Andes from the Eastern to the Western Cordillera, leading to similar snowline altitudes at the Nevado Sara Sara in the Western Cordillera as in parts of the Eastern Cordillera, despite lower amounts of annual precipitation. With the concept of a 'normalised snowline altitude' the influence of precipitation differences as a single factor on the snowline altitude can be demonstrated. Because the observed precipitation differences should lead to larger snowline altitude differences between the Eastern and Western Cordillera than seen in the snowline altitude map, a second factor has to be taken into consideration for the climatic interpretation of the snowline altitude that is able to compensate the decreasing precipitation. This factor is the altitude of the annual 0°C isotherm.
We investigated past climate variability and the zonal short and long-range transport of air masses in tropical South America using chemical, isotopic and palynological signals from a 42 m-long ice core recovered in 2003 from the saddle of the Nevado Coropuna, southern Peru (72°39´ W; 15°32´ S; 6080 m a.s.l.). We found that precipitation at this site depends mainly on the easterly circulation of air masses originated from the tropical Atlantic Ocean. Nevertheless, sporadic Pacific air masses arrivals, and strong cold waves coming from southern South America reach this altitude site. In spite of post-depositional effects, we were able to identify two strong ENSO (El Niño-Southern Oscillation) event signatures (1982-1983 and 1992) and the eruptive activity of the nearby Sabancaya volcano (1994).
Plateau icefields occur commonly in glacierized areas and not uncommonly in glaciated mountains. We report on a glacierized area of plateaux and valleys centred round the highest peak Jiehkkevárri (1833 m) in the maritime Lyngen Alps, North Norway. Some valley glaciers are fed by steep, narrow plateau glacier outlets and/or ice avalanching from the plateaux over precipitous cliffs. Plateaux must therefore be considered as "contributing areas", if they supply ice to valley systems below. Equilibrium line altitudes (ELAs) are calculated for the valley glaciers during the Little Ice Age (LIA), accounting for both input and no input of ice from plateaux above. The results show that ELAs may be at significantly higher altitudes when plateau/x are contributing ice mass. The response of plateau glaciers to climate amelioration since the end of the LIA is some-what different to that of valley glaciers, which appear to be retreating markedly. These findings have significant implications for the interpretation of moraine systems, glacier dynamics, the construction and reconstruction of present and former ELAs, and palaeo-climates in glacierized and glaciated mountain plateau areas.
We examine the validity of two methods for estimating glacier equilibrium-line altitudes (ELAs) from topographic maps. The ELA determined by contour inflection (the kinematic ELA) and the mean elevation of the glacier correlate extremely well with the ELA determined from mass-balance data (observed ELA). However, the range in glacier elevations above sea level is much larger than the variation in ELA, making this correlation unhelpful. The data were normalized and a reasonable correlation (r2 = 0.59) was found between observed and kinematic ELA. The average of the normalized kinematic ELAs was consistently located down-glacier from the observed ELA, consistent with theory.The normalized mean elevation of the glacier exhibited no correlation and suggests that the toe-headwall altitude ratio is not a good approximation for the ELA. Kinematic waves had no effect on the position of the kinematic ELA. Therefore, topographic maps of glacier surfaces can be used to infer the position of the ELA and provide a method for estimating past ELAs from historic topographic maps.
Cerro Charquini, Bolivia (Cordillera Real, 5392 m a.s.l.) was selected as a site to reconstruct glacier recession since the maximum of the Little Ice Age (LIA) in the central Andes. Five glaciers, located on differently exposed slopes, present comprehensive and well-preserved morainic systems attributed to former centuries. The moraines were dated by lichenometry and show a consistent organization on the different slopes. The past geometry of the glaciers was reconstructed using ground topography and aerophotogrammetry. Lichenometric dating shows that the LIA maximum occurred in the second half of the 17th century, after which the glaciers have receded nearly continuously. Over the last decades of the 20th century (1983–97), recession rates increased by a factor of four. On the northern and western slopes, glaciers receded more than on the southern and eastern slopes (by 78% % and 65% % of their LIA maximum area, respectively). The mean equilibrium-line altitude (ELA) rose by about 160 m between the LIA maximum and 1997. Recession rates were analysed in terms of climatic signal, suggesting that glacier recession since the LIA maximum was mainly due to a change in precipitation and that the 19th century may have been drier. For the 20th century, a temperature rise of about 0.68C appears to be the main cause of glacier recession. Recent climatic conditions from 1983 to 1997 correspond to a mass deficit of about 1.36 m w.e. a –1 . If such conditions persist, the small glaciers below 5300 m a.s.l. in the Cordillera Real should disappear completely in the near future.
Modern glaciers in the cordillera west and east of the plain of Laguna Junín northeast of Lima are confined to small summits and west-facing cirques. Snowline today is at about 4900 m on the west and 4800 m on the east. That these small glaciers were larger in the recent past is indicated by small moraines and by areas nearly bare of vegetation peripheral to the present glacier limits.
In the Pleistocene a mountain glacier complex covered most of the cordillera and spread to all but the center of the plain, thus damming Laguna Junín. Two phases of glaciation can be distinguished. The younger is marked by sharp moraines dotted with small depressions. The older has smooth landforms, no undrained depressions, and locally a thin cover of loess. Retreat from the younger moraines may not have commenced until about 12,000 years ago.
Maximum late-Pleistocene snowline depression is calculated at about 300 m in the western cordillera and 500 m in the eastern, on the basis of the elevation of small cirque lakes. Snowline depression of 300 m could be caused by a depression in mean annual temperature of only 2°C. Greater snowline depression on the east may reflect the southward shift of the tropical rain zone in the Amazonian lowlands, as a secondary effect of the vast Laurentide ice sheet of North America.
As on all Peruvian Cordilleras, the glaciers on the eastern slopes of the Cordillera Blanca extend to generally lower elevations than those on the western slopes. The mountain range of Santa Cruz–Pucahirca possesses the largest east–west extension within the Cordillera Blanca. A significant retreat of the glaciers between two quasi-stationary situations around 1930 and 1950 was reconstructed from air photographs. The derived ELAs as well as the ∆ELA1930–50 show spatial diversities. The pattern of the ELAs is caused by differences in both accumulation and effective global radiation. The change in ELAs1930–50 is partly due to a spatially uniform increase in air temperature. The remaining rise of the equilibrium line, which varies within different parts of the investigation area, has to be related to changes in precipitation and effective global radiation. Both correspond to changes in air humidity which is suggested to be an important factor for tropical glacier fluctuations. A model of superposed typical tropical circulation patterns of different scales and ELA–climate model-based approaches is presented.
The fiordlands south of Merchants Bay contain an extensive, well-preserved moraine record of a late Foxe advance of local valley glaciers. This has allowed accurate reconstruction of former glacier margins and computation of former equilibrium-line altitudes (ELAs) by a variety of methods. Statistical comparison of three methods (maximum lateral-moraine elevation, median elevation, and accumulation area ratio (AAR)) shows that different techniques can give different results for the same glaciers. Lateral moraines gave estimates that were too low, probably due to post-glacial erosion or to non-deposition. Median elevations and the AAR method produced statistically similar results but only for glaciers of simple geometry. The median-elevation method fails to take into account variations in valley morphology and glaciological parameters, and so is not reliable in all situations. The AAR method is supported by empirical evidence and is the best of the three methods for estimating former ELAs.
Analysis of trend surfaces of present and late Foxe ELAs shows changes in elevation and orientation through time due to changing environmental factors. Present ELAs are strongly influenced by local factors, southerly storm tracks, and warm maritime conditions. Paleo-ELAs do not show this influence, suggesting that Davis Strait may have been ice-covered during the late Foxe stade and that storm tracks were from the north.
Air photo and map interpretation and field work provide evidence of four Pleistocene cold phases in the Cordillera Ampato indicated by glacial moraines and rock glaciers. The oldest glaciation is associated with a snowline depression of similar to- 1000 m and is likely to belong to the Last Glaciation. The eastward rise of the Pleistocene Equilibrium Line Altitude (ELA) was smaller than for the present indicating moisture conditions at least similar to those at present. During the largest glaciation, the regional ELA was at similar to 4400 m allowing for most areas above 4000 in to be covered by ice or at least by snow for most of the year forming a tropical high altitude cooling surface that probably covered the whole width of the Andes north of 16degreesS.
Sediments deposited during various glacial stages in the Eduadorian Andes can be broadly differentiated on the basis of altitude, morphology, stratigraphy, degree of weathering and, in places, radiocarbon dating. Massive moraines commonly mark the maximal extent of the last (Wisconsin) glaciation, terminating at a mean altitude of c3600 m. Immediately within the end moraines three to four smaller moraines are clustered closely together, indicating subsequent stadial or readvance positions of the glaciers. Six radiocarbon dates from organic sediments interbedded with tills indicate that glaciers in Ecuador expanded after c33 000 BP and that the organic sediments had been accumulating since before c43 000 BP. The glaciers shrank from these limits during the last global maximal glaciation (at c18 000 BP) because of increased aridity, but fluctuations occurred before they finally receded sometime after c15 000 BP. -from Author
Kilimanjaro (5895m) is the highest mountain in Africa, with a present glacier cover of about 5 km2. During five former glaciations the glaciers extended to about 150 km2, leaving distinctive and well-preserved moraines in the case of the Main Glaciation (probably equivalent to Wurm, Devensian, Wisonsin). The extents of both present and past glaciers differed greatly on different aspects of the mountain, having a consistently asymmetric pattern related to the local weather system, so particular care is needed in the correlation and interpretation of moraines and the inferences drawn from them. The average best estimate of the difference between present and Main Glaciation ELAs is 850m. Using the local lapse rate of 7°C per 1000m altitude, this represents a crude temperature difference of 6.0°C. -from Author
The present snowline in the Peruvian Andes (5-17°S), rises from as low as 4.7±0.1km on the eastern (windward) to more than 5.3 ± 0.1km on the western (leeward) side of the central Andes. The effect of temperature on snowline altitude is isolated from the effect of precipition by subtracting the altitude of the mean annual 0°C isotherm from the altitude of the snowline. This difference, defined as the normalized snowline altitude, increases with decreasing precipitation.The lowest late Pleistocene snowline rose from east to west and ranged in altitude from 3.2 to 4.9 (±0.1) km. Both the present and lowest late Pleistocene snowlines indicate that moisture at both times was derived principally from tropical easterly winds. An east-west precipitation gradient steeper than present is inferred for the eastern slopes of the centralAndes from the steeper late Pleistocene snowline gradient. Mean annual temperatures were 10±1.9°C cooler that today at 3.52 km, as calculated from a late Pleistocene snowline as much as 1.4±0.2 km lower than today. Mean annual precipitation was 25 to 50% less than today along the eastern side, and more than 75% less on the western side of the central Andes. These estimates of lower temperature and decreased precipitation are more extreme than previous estimates. They imply that the amount of glacial-age cooling elsewhere, such as in western North America, may also have been underestimated by previous researchers because they did not adequately consider the effect of reduced ice-age precipitation on snowline lowering.
Laguna Junin is a large lake 675 km long but only 4 m deep, located in the grass-covered altiplano at an altitude of 4,100 m, northeast of Lima. Pollen analysis of a 30-m core indicates that from about 12 000 yr ago until some time after 3000 yr ago, about 30%; of the pollen was carried in by easterly winds from the east Andean forests, which today are at least 600 m lower in elevation. Contemporaneous pollen deposition in lakes on moraines of the last glaciation west of the Junin plain was dominated by local grassland types and had little contribution from this easterly source. At some time after 3000 yr ago (perhaps about 1200 yr ago), the pollen influx to Laguna Junin from this distant forest source greatly diminished, perhaps because of deforestation by increased human populations. Between about 12 000 and 24 000 yr ago in the Junin core, the sparse pollen concentration was dominated by grassland types, supplemented by Polylepis/Acaena, Alnus, and Compositae blown in from the sub-puna shrublands that may have occupied much of the east Andean slopes in place of the humid forest that occurs there today. The silty sediment in this section of the core is interpreted as outwash from piedmont glaciers that invaded the plain, especially from the cordillera to the west. These glaciers left a distinctive pattern of moraines and outwash fans, which served to dam the lake basin. An unconformity in the sediment covers the time from about 24 000 to 39 000 yr ago, when the lake was probably dry. Before this time, the silty sediment and the dominance of grassland and shrubland pollen types indicates an earlier interval of glaciation, recorded on the landscape by an older set of moraines and outwash fans, which initially dammed the lake basin. -Authors
Comparisons between lake level variations in the Uyuni-Coipasa basin and the glacial fluctuations in the Eastern Cordillera show that lakes and glaciers have simultaneously registered changes in precipitation. The strong lacustrine maximum (~13-12 14C ka BP) appeared 4-6000 years before the highest lake levels in North Africa. There is an abridged English version. -English summary
ELA reconstructions using the toe-to-headwall-altitude ratio method for paleoglaciers in the Cordilleras Blanca and Oriental, northern Peruvian Andes indicate that ELAs during the last glacial maximum (LGM; marine isotope stage 2)) were c.4300 m in the Cordillera Blanca, c.3900-3600 m on the west side of the Cordillera Oriental, and c.3200 m on the east (Amazon Basin) side of the Cordillera Oriental. Comparison with estimated modern ELAs and glaciation thresholds indicate that ELA depression ranged from c.700 m in the Cordillera Blanca to c.1200 m on the east side of the Cordillera Oriental. Palynological evidence for drier conditions during the LGM in the tropical Andes suggests that ELA depression of this amount involved a temperature reduction (>5-6°C) that greatly exceeded the tropical sea-surface temperature depression estimates of CLIMAP (<2°C). The west to east increase in ELA depression during the LGM indicates that the steep modern precipitation gradients may have been even steeper during the LGM. -from Author
Western Montana is ideally situated to have both its climate affected by the presence of Pleistocene ice sheets and those effects be apparent in its distribution of mountain glaciers. Paleoequilibrium line altitudes (paleoELAs) determined through a weighted average of cirque floor elevations, highest lateral moraines. and interpreted glacial extents define a complex pattern which reflects sources of moisture, directions of airflow, and sites of local convergence and divergence of airmasses. The regional trend of paleoELAs is parallel to that of present glacier ELAs but lies about 450 m lower. The parallelism suggests that the regional controls on moisture availability during late Pleistocene time were similar to those at present. Numerical reconstructions of precipitation required to maintain glaciers assuming a uniform regional 10°C summer temperature depression indicate a Pleistocene decrease in precipitation, relative to present, of about 25 cm H2O. -from Author
Modern glaciers in the cordillera west and east of the plain of Laguna Junín northeast of Lima are confined to small summits and west-facing cirques. Snowline today is at about 4900 m on the west and 4800 m on the east. That these small glaciers were larger in the recent past is indicated by small moraines and by areas nearly bare of vegetation peripheral to the present glacier limits. In the Pleistocene a mountain glacier complex covered most of the cordillera and spread to all but the center of the plain, thus damming Laguna Junín. Two phases of glaciation can be distinguished. The younger is marked by sharp moraines dotted with small depressions. The older has smooth landforms, no undrained depressions, and locally a thin cover of loess. Retreat from the younger moraines may not have commenced until about 12,000 years ago. Maximum late-Pleistocene snowline depression is calculated at about 300 m in the western cordillera and 500 m in the eastern, on the basis of the elevation of small cirque lakes. Snowline depression of 300 m could be caused by a depression in mean annual temperature of only 2°C. Greater snowline depression on the east may reflect the southward shift of the tropical rain zone in the Amazonian lowlands, as a secondary effect of the vast Laurentide ice sheet of North America.
A number of methods for determining the climatic snowline are briefly described. The firn line on glaciers will normally lie slightly lower than the climatic snowline; however, most previous methods for its determination are connected with observations on glaciers. From a study of the distribution of glaciers and the altitudes of surrounding mountain summits, it is possible to determine a critical height (the "glaciation limit") which has normally to be exceeded if glaciers should form. This height is approximately 100 metres above the climatic snowline. The glaciation limit was determined on a large number of topographic maps, the results plotted on a small-scale map, and contour lines were drawn showing its regional variation in southern British Columbia and Alberta. The source material and possible errors in the determinations are discussed. A comparison is made with different maps showing precipitation, continentality, land surface elevation, and the 1961 firn line altitude on glaciers. It is concluded that the height of the glaciation limit is inversely connected with the precipitation distribution.
The transient snowline can be easily defined on air photographs of glaciers having a reasonably even topography, and its height can then be determined from topographic maps of good quality. A study of an extensive air photograph cover made almost simultaneously in two selected regions in western Canada in August, 1966, has shown that neighbouring glaciers often exhibit equal or very similar transient snowline heights. Exceptions can be found for glaciers in extreme positions, but such deviations can be more or less subdued by the calculation of a mean height for several glaciers within small areas. A definite trend of higher transient snowline altitudes from southwest towards northeast was found within both regions, and this trend is demonstrated by isohypses drawn on maps. Comparisons were made with the height of the glaciation level which was similarly plotted on the maps (contours redrawn from Östrem 1966). Both the glaciation level and the height of the transient snowline can be thought of as invisible surfaces intersecting the landscape at various altitudes, the glaciation level normally being the highest. The two surfaces are tilted with the highest elevation in their northeastern parts. Continuing detailed mass balance investigations on 5 glaciers disposed along an east-west section across the Cordillera were introduced in this study by the determination of the "present" height of the equilibrium line, i.e. its altitude in a year of steady state conditions regarding the mass balance. When this eqilibrium line height was plotted on southwest-northeast profiles across the investigated regions it was found to be just above the transient snowline as of 22-24 August 1966. The conclusion is drawn that if simultaneous air photograph cover or high-resolution satellite imagery were made available throughout the summer melt season one could closely follow the mass balance variations during the summer and relatively easily extrapolate results from field studies on a few glaciers to almost all glaciers within the photographed region. When the transient snowline reaches positions higher than the present equilibrium line height (for a "balanced year") this indicates that the glaciers have a negative mass balance and extra amounts of melt water are yielded to rivers in glacierized basins.
Tropical glaciers are both highly sensitive indicators of global climate
and fresh water reservoirs in some fast developing regions. This book
gives a theoretical and practical analysis of tropical glaciology
including a useful definition of tropical glacier-climate regimes and an
analysis of the main glaciological variables. The Rwenzori and the
Cordillera Blanca are investigated as examples of tropical glacierized
mountains. The fluctuations of their glaciers since the end of the
Little Ice Age are reconstructed and the probable climatic reasons are
discussed. The evidence of great expansions of mountain glaciers
throughout the tropics on several occasions during the Quaternary are
summarized, examined and then applied and contrasted.
Advance and retreat of temperate glaciers is largely controlled by changes in temperature and precipitation, but the relative importance of these drivers is debated. Numerical modeling of a New Zealand glacier reveals that temperature is the dominant control on glacier length. We find that a glacial advance, dated to ca. 13,000 yr B.P., requires a cooling event of 3 4 °C. This mid-latitude Southern Hemisphere cooling is similar in magnitude to the Antarctic Cold Reversal in the Vostok ice core record and likely to be a response to the same climate signal.
Currently-available evidence of 20th-century warming from glaciers and permafrost is briefly reviewed. The signals are clear and strong: warming of polar firn and permafrost, and mass losses of glaciers at lower latitudes, were most striking towards the middle of the century. The easily observable length-reduction of mountain glaciers confirms the global character of the evolution. A probably intermittent reversal of the trend was observed in places after about 1950. -Author
As on all Peruvian cordilleras, the glaciers on the eastern slopes of the Cordillera Blanca extend to generally lower elevations than those on the western slopes. The mountain range of Santa Cruz-Pucahirca possesses the largest east-west extension within the Cordillera Blanca. A significant retreat of the glaciers between two quasi-stationary situations around 1930 and 1950 was reconstructed from air photographs. The derived ELAs as well as the ΔELA1930-50 show spatial diversities. The pattern of the ELAs is caused by differences in both accumulation and effective global radiation. The change in ELAs1930-50 is partly due to a spatially uniform increase in air temperature. The remaining rise of the equilibrium line, which varies within different parts of the investigation area, has to be related to changes in precipitation and effective global radiation. Both correspond to changes in air humidity which is suggested to be an important factor for tropical glacier fluctuations. A model of superposed typical tropical circulation patterns of different scales and ELA-climate model-based approaches is presented.
The fiordlands south of Merchants Bay contain an extensive, well-preserved moraine record of a late Foxe advance of local valley glaciers. This has allowed accurate reconstruction of former glacier margins and computation of former equilibrium-line altitudes (ELAs) by a variety of methods. Statistical comparison of three methods (maximum lateral-moraine elevation, median elevation, and accumulation area ratio (AAR)) shows that different techniques can give different results for the same glaciers. Lateral moraines gave estimates that were too low, probably due to post-glacial erosion or to non-deposition. Median elevations and the AAR method produced statistically similar results but only for glaciers of simple geometry. The median-elevation method fails to take into account variations in valley morphology and glaciological parameters, and so is not reliable in all situations. The AAR method is supported by empirical evidence and is the best of the three methods for estimating former ELAs.
Analysis of trend surfaces of present and late Foxe ELAs shows changes in elevation and orientation through time due to changing environmental factors. Present ELAs are strongly influenced by local factors, southerly storm tracks, and warm maritime conditions. Paleo-ELAs do not show this influence, suggesting that Davis Strait may have been ice-covered during the late Foxe stade and that storm tracks were from the north.
Large paleolakes (∼33,000-60,000 km2) that once occupied the high-altitude Poopo, Coipasa, and Uyuni Basins in southern Bolivia (18-22°S) provide evidence of major changes in low-latitude moisture. In these now-dry or oligosaline basins, extensive natural exposure reveals evidence for two deep-lake and several minor-lake cycles over the past 120 k.y. Fifty-three new U-Th and 87 new 14C dates provide a chronologic framework for changes in lake level. Deposits from the "Ouki" deep-lake cycle are extensively exposed in the Poopo Basin, but no deep lakes are apparent in the record between 98 and 18.1 ka. The Ouki lake cycle was ∼80 m deep, and nineteen U-Th dates place this deep-lake cycle between 120 and 98 ka. Shallow lakes were present in the terminal Uyuni Basin between 95 and 80 ka (Salinas lake cycle), at ca. 46 (Inca Huasi lake cycle), and between 24 and 20.5 ka (Sajsi lake cycle). The Tauca deep-lake cycle occurred between 18.1 and 14.1 ka, resulting in the deepest (∼140 m) and largest lake in the basin over the past 120 ka. Multiple 14C and U-Th dates constrain the highest stand of Lake Tauca along a topographically conspicuous shoreline between 16.4 and 14.1 ka. A probable post-Tauca lake cycle (the Coipasa) produced a ≤55-m-deep lake that is tentatively dated between 13 and 11 ka. We suggest that paleolakes on the Bolivian Altiplano expanded in response to increased moisture in the Amazon and enhanced transport of that moisture onto the Altiplano by strengthened trade winds or southward displacement of the Intertropical Convergence Zone (ITCZ). Pole-to-equator sea-surface temperature (SST) and atmospheric gradients may have influenced the position of the ITCZ, affecting moisture balance over the Altiplano and at other locations in the Amazon Basin. Links between the position of the ITCZ and the ca. 23 ka precessional solar cycle have been postulated. March insolation over the Altiplano is a relatively good fit to our lake record, but no single season or latitude of solar cycling has yet to emerge as the primary driver of climate over the entire Amazon Basin. Temperature may influence Altiplano lake levels indirectly, as potentially dry glacial periods in the Amazon Basin are linked to dry conditions on the Altiplano. Intensification of the trade winds associated with La Niña - like conditions currently brings increased precipitation on the Altiplano, and deep-lake development during the Tauca lake cycle coincided with apparently intense and persistent La Niña - like conditions in the central Pacific. This suggests that SST gradients in the Pacific are also a major influence on deep-lake development on the Altiplano.
Six methods for approximating late Pleistocene (Pinedale) equilibrium-line altitudes (ELAs) are compared for rapidity of data collection and error (RMSE) from first-order trend surfaces, using the Colorado Front Range. Trend surfaces computed from rapidly applied techniques, such as glaciation threshold, median altitude of small reconstructed glaciers, and altitude of lowest cirque floors have relatively high RMSEs (97-186 m) because they are subjectively derived and are based on small glaciers sensitive to microclimatic variability. Surfaces computed for accumulation-area ratios (AARs) and toe-to-headwall altitude ratios (THARs) of large reconstructed glaciers show that an AAR of 0.65 and a THAR of 0.40 have the lowest RMSEs (about 80 m) and provide the same mean ELA estimate (about 3160 m) as that of the more subjectively derived maximum altitudes of Pinedale lateral moraines (RMSE = 149 m). Second-order trend surfaces demonstrate low ELAs in the latitudinal center of the Front Range, perhaps due to higher winter accumulation there. The mountains do not presently reach the ELA for large glaciers, and small Front Range cirque glaciers are not comparable to small glaciers existing during Pinedale time. Therefore, Pleistocene ELA depression and consequent temperature depression cannot reliably be ascertained from the calculated ELA surfaces.
We have used cosmogenic dating (10Be) to identify moraines of the local last glacial maximum along two east-west transects in the tropical Andes: the Junin region of central Peru ( ˜11° S 76° W) and the Cordillera Real of western Bolivia ( ˜16.3° S 68.2° W). The 10Be ages from boulders on moraines in our study areas suggest that the local last glacial maximum occurred ca. 30,000 10Be yr BP (before the inferred peak of Northern Hemisphere glaciation at ca. 21,000 calendar yr BP) and that deglaciation was well underway by 20,000 10Be yr BP. Recessional moraines were deposited between about 20,000 and 15,000 10Be yr BP. Published 14C dates from the Cordillera Real indicate that glaciers were within their present limits by about 11,000 calendar yr BP. Asymmetry in the east-west glacial extent and amount of snowline depression was relatively minor in the Junin region, but was more pronounced in the Cordillera Real. In the Junin region, terminal moraines of the local last glacial maximum lie at ˜4150-4200 m on the east side of the cordillera and at ˜4250-4400 m on the west side. In the Cordillera Real, lateral moraines of the local last glacial maximum lie at ˜4600 m on the southwest side of the cordillera (Milluni Valley), while a late-glacial (ca. 12,000 10Be yr BP) terminal moraine lies at ˜3800 m on the northeast side of the cordillera (Zongo Valley). Snowline depression during the local last glacial maximum in the Andes was ˜200-600 m on both sides of the eastern cordillera in the Junin region and on the southwest (Altiplano) side of the Cordillera Real, but closer to ˜900-1000 m on the northeast side of the Cordillera Real. The asymmetry likely arose from differences in precipitation (which comes mainly from the east) and from variations in shading, amount of supraglacial material, and topography between the deeply incised eastern valleys and the relatively broad, shallow valleys descending to high-altitude plateau surfaces on the west sides.
A new paleolimnological dataset from Lake Pacucha (13 °S, 3095 m elevation) in the Peruvian Andes provides evidence of changes in lake level over the past 24,700 yr. A late-glacial highstand in lake level gave way to an early-Holocene lowstand. This transition appears to have paralleled precessional changes that would have reduced insolation during the wet-season. The occurrence of benthic/salt-tolerant diatoms and CaCO3 deposition suggest that the lake had lost much of its volume by c. 10,000 cal yr BP. Pronounced Holocene oscillations in lake level included a second phase of low lake level and heightened volatility lasting from c. 8300 to 5000 cal yr BP. While a polymictic lake formed at c. 5000 cal yr BP. These relatively wet conditions were interrupted by a series of drier events, the most pronounced of which occurred at c. 750 cal yr BP. Paleolimnological changes in the Holocene were more rapid than those of either the last glacial maximum or the deglacial period.
Paleoclimatic data are increasingly showing that abrupt change is present in wide regions of the globe. Here a mechanism for abrupt climate change with global implications is presented. Results from a tropical coupled ocean-atmosphere model show that, under certain orbital configurations of the past, variability associated with El Nino-Southern Oscillation (ENSO) physics can abruptly lock to the seasonal cycle for several centuries, producing a mean sea surface temperature (SST) change in the tropical Pacific that resembles a La Nina. It is suggested that this change in SST would have a global impact and that abrupt events such as the Younger Dryas may be the outcome of orbitally driven changes in the tropical Pacific.
Nineteen former valley glaciers were reconstructed for their Last Glacial Maximum (LGM) extents in the northern Uinta Mountains, Utah, U.S.A. Mean equilibrium-line altitudes (ELAs) calculated by four methods (accumulation-area ratio, toe-headwall altitude ratio, lateral moraines and cirque floors) range from 3050 to 3300 m a.s.l. Modern mean summer temperatures (Ts) at the ELAs range from 8.7° to 11.2°C, while modern winter precipitation (P) ranges from 354 to 590 mm snow water equivalent (SWE). Based on the difference in elevation of mean ELAs across the range, LGM P values must have ranged from 940 to 3040 mm SWE, assuming the modern summer lapse rate was the same during the LGM. A Ts depression of 5.5°C is required for these precipitation values to plot in the range of modern ELA values. The reconstructed increase in P at the western end of the range is 10 times the modern increase, reflecting the influence of pluvial Lake Bonneville. Assuming ELA depression (ΔELA) resulted from this P increase and a uniform 5.5°C Ts decrease, the regional LGM ΔELA was approximately 900 m.
A climate-glacier model was used to reconstruct Late-glacial climate conditions from two case-study glaciers at 18° and 22°S in the arid (sub)tropical western Andes of northern Chile. The model uses (i) the geometry of the Late-glacial maximum glaciation, (ii) modern diurnal and annual cycles, amplitudes and lapse rates of the climate, (iii) empirical-statistical sublimation, melt and accumulation models developed for this area, and (iv) dynamic ice flow through two known cross-sections for steady-state conditions. The model is validated with modern conditions and compares favorably with the glaciological features of today. The mass-balance model calculates the modern equilibrium-line altitude at 18deg; S as high as 5850 m (field data 5800 m), whereas no glaciers exist in the fully arid southern area at 22° S despite altitudes above 6000 m and continuous per- mafrost. For Late-glacial times, the model results suggest a substantial increase in tropical summer precipitation (ΔP = +840 (-50/+ 10) mm a -1for the northern test area; +1000 (-10/+ 30) mm a -1for the southern test area) and a moderate temperature depression (ΔT = 4.4 (-0.1/+ 0.2) °C at 18° S; -3.2 (±0.1) °C at 22°S). Extratropical frontal winter precipitation (June-September) was <15% of the total annual precipitation. A scenario with higher winter precipitation from the westerlies circulation belt does not yield a numerical solution which matches the observed geometry of the glaciers. Therefore, we conclude that an equatorward displacement of the westerlies must be discarded as a possible explanation for the late Pleistocene glaciation in the Andes of northern Chile.
Dating of past glaciation in New Zealand allows Quaternary climatic events to be identified in areas at a great distance from northern hemisphere ice sheets and associated climatic feedbacks. Moreover, climate reconstruction in New Zealand provides insight into the amount of climate change that occurred in the Southwest Pacific where zonal circulation is an important integrator of the climate signal. Boulder Lake is a relatively low-elevation cirque in a range of moderate-relief (similar to 1600 m) mountains in South Island of New Zealand, and it experienced cirque and valley glaciation during the Late Quaternary. Geomorphic mapping. (10)Be and (26)Al exposure. and luminescence dating provide evidence for glacial advances during the Last Glacial Cycle, specifically during Marine Isotope Stage 4 (MIS 4) and Marine Isotope Stage 2 (MIS 2). The MIS 4 advance was fractionally larger and is dated by a former ice-marginal lacustrine deposit (minimum age) with a basal Optically Stimulated Luminescence (OSL) sediment deposition age of 64.9 +/- 10 ka. Paired (10)Be and (26)Al constrain a slightly less extensive MIS 2 glacial advance to 18.2 +/- 1.0 and 17.8 +/- 0.9 ka, coincident with the Last Glacial Maximum (LGM). Glacial equilibrium-line altitudes during both MIS 4 and MIS 2 phases were similar to 960 in lower than the present. This corresponds to a cooling of 5-7 degrees C, taking possible precipitation variability into account. Our findings and a growing number of publications indicate that many temperate valley glaciers reacted differently to the major ice sheets during the Last Glacial Cycle, reaching their Maximum extent during MIS 4 rather than during peak global ice volume during MIS 2.
In the Cordillera Vilcanota and the vicinity of the Quelccaya ice cap, near lat 14°S in eastern Peru, the last glaciation culminated sometime between about 28,000 and 14,000 B.P. Alpine glaciers were then only about half as long as during an earlier glaciation of unknown date. A rather minor readvance of the Quelccaya ice cap was in progress about 11,500 B.P. and culminated about 11,000 B.P., some 500 to 800 yr before the Younger Dryas Stade in Europe. By 10,000 B.P., the Quelccaya ice cap was little if any larger than it is today, and it was smaller than it is today between about 2700 and 1600 B.P. Glacier fluctuations during the interval 10,000 to 3000 B.P. have not yet been determined. A ``Little Ice Age'' maximum culminated between 600 and 300 B.P. The relative importance of changes in temperature and precipitation in causing these glacier variations is uncertain.
ABSTRACT Paleoclimatic data are increasingly showing,that abrupt change is present in wide regions of the globe. Here a mechanism,for abrupt climate change,with global implications is presented. Results from a tropical coupled ocean‐atmosphere model show that, under certain orbital configurations of the past, variability associated with El Nin ˜o‐Southern Oscillation (ENSO) physics can abruptly lock to the seasonal cycle for several centuries, producing,a mean,sea surface temperature,(SST) change in the tropical Pacific that resembles a La Nin ˜a. It is suggested that this change in SST would have a global impact and that abrupt events such as the Younger Dryas may,be the outcome,of orbitally driven changes,in the tropical Pacific.
Equilibrium-line-altitude (ELA) reconstructions using the toe-to-headwall-altitude ratio method for paleoglaciers in the Cordilleras Blanca and Oriental, northern Peruvian Andes (7–10°S; 77°20′–77°35'W), indicate that ELAs during the last glacial maximum (LGM; marine isotope stage 2) were c. 4300 m in the Cordillera Blanca, c. 3900–3600 m on the west side of the Cordillera Oriental, and c. 3200 m on the east (Amazon Basin) side of the Cordillera Oriental. Comparison with estimated modern ELAs and glaciation thresholds indicate that ELA depression ranged from c. 700 m in the Cordillera Blanca to c. 1200 m on the east side of the Cordillera Oriental. This augments data from many mountain ranges in middle- and low-latitude regions that indicate that ELAs during the LGM were depressed by c. 1000 m. Published palynological evidence for drier conditions during the LGM in the tropical Andes suggests that ELA depression of this amount involved a temperature reduction (> 5–6°C) that greatly exceeded the tropical sea-surface temperature depression estimates of CLIMAP (< 2°C). The west to east increase in ELA depression during the LGM indicates that the steep modern precipitation gradients may have been even steeper during the LGM.
Glacial geological studies in tropical mountain areas of the Southern Hemisphere can be used to address two issues of late Pleistocene climate change: the global synchroneity of deglaciation and the magnitude of temperature reduction in the tropics. Radiocarbon dates from the Cordillera Real and from other areas in Perú and Bolivia suggest that late Pleistocene glaciation culminated between 14 000 and 12 000 yr BP, followed by rapid deglaciation. Because deglaciation was apparently synchronous with that in Northern Hemisphere regions, insolation change at high latitudes may not have been the only factor that produced global deglaciation at this time. Late Pleistocene glaciation in the Cordillera Real culminated when precipitation was 200 mm yr−1 higher and temperatures were 3.5° ±1.6°C lower than today; this produced an equilibrium-line altitude depression of about 300 ± 100 m on the western side of the cordillera. Prior to this, conditions were drier and probably at least as cold. However, the lack of moraines in the Cordillera Real dated to the Last Glacial Maximum (ca. 18000 yr BP) precludes using the equilibrium-line altitude method to quantitatively evaluate the discrepancy between warm sea-surface temperatures and cold terrestrial conditions reconstructed with other proxies for this time period.
Three Pleistocene glaciations and two Holocene Neoglacial advances occurred on volcano Ajusco in central Mexico. Lateral moraines of the oldest glaciation, the Marqués, above 3250 m are made of light-gray indurated till and are extensively modified by erosion. Below 3200 m the till is dark red, decomposed, and buried beneath volcanic colluvium and tephra. Very strongly to strongly developed soil profiles (Inceptisols) have formed in the Marqués till and in overlying colluvia and tephra. Large sharp-crested moraines of the second glaciation, the Santo Tomás, above 3300 m are composed of pale-brown firm till and are somewhat eroded by gullies. Below 3250 m the till is light reddish brown, cemented, and weathered. Less-strongly developed soil profiles (Inceptisols) have formed in the Santo Tomás till and in overlying colluvia and tephra. Narrow-crested moraines of yellowish-brown loose till of the third glaciation, the Albergue, are uneroded. Weakly developed soil profiles (Inceptisols) in the Albergue till have black ash in the upper horizon. Two small Neoglacial moraines of yellowish-brown bouldery till on the cirque floor of the largest valley support weakly developed soil profiles with only A and Cox horizons and no ash in the upper soil horizons. Radiocarbon dating of organic matter of the B horizons developed in tills, volcanic ash, and colluvial volcanic sand includes ages for both the soil-organic residue and the humic-acid fraction, with differences from 140 to 660 yr. The dating provides minimum ages of about 27,000 yr for the Marqués glaciation and about 25,000 yr for the Santo Tomás glaciation. Dates for the overlying tephra indicate a complex volcanic history for at least another 15,000 yr. Comparison of the Ajusco glacial sequence with that on Iztaccíhuatl to the east suggests that the Marqués and Santo Tomás glaciations may be equivalent to the Diamantes glaciation First and Second advances, the Albergue to the Alcalican glaciations, and the Neoglacial to the Ayolotepito advances.
2000. Ice-core palaeoclimate records in tropical South America since the Last Glacial Maximum. ABSTRACT: Ice-core records spanning the last 25 000 yr from the tropical Andes of South America are reviewed. These records from Quelccaya, Huascarán and Sajama present a high temporal resolution picture of both the Late Glacial Stage (LGS) and the Holocene climatic and environmental conditions in the South American Andes. Late Glacial Stage conditions at high elevations appear to have been cooler than today, although the magnitude of the inferred cooling differs with the particular proxy used (e.g. snowline depression, pollen, ice cores). Insoluble dust and anion concentrations in the ice cores reveal that LGS hydrological conditions in the tropics (9°S) were much drier than today, whereas in the subtropics (18°S) LGS conditions were much wetter. This probably reflects the migration of the tropical Hadley Cell in response to a different meridional temperature gradient. Low nitrate concentrations in the LGS ice from both Huascarán and Sajama suggest that the Amazon Basin forest cover may have been much less extensive. Discussed is the conundrum surrounding the use of 18 O as a palaeothermometer in the tropics, where temperatures exhibit little seasonal variation yet the ice-core records suggest that 18 O records temperature variations on decadal to millennial time-scales. Finally evidence is presented for a strong twentieth century warming.
The Andes of Ecuador, Peru and Bolivia host the majority of the world's tropical glaciers. In the tropical Andes, glaciers accumulate during the wet season (austral summer) and ablate year-round. Precipitation is delivered mainly by easterlies, and decreases both N–S and E–W. Chronological control for the timing of glacial advances in the tropical Andes varies. In Ecuador, six to seven advances have been identified; dating is based on radiocarbon ages. Timing of the local Last Glacial Maximum (LGM) and the existence of Younger Dryas advances remain controversial. In Peru, local variability in glaciation patterns is apparent. Surface exposure dating in the Cordillera Blanca and Junin Plain suggests that the local LGM may have been early ($30 ka), although uncertainties in age calculations remain; the local LGM was followed by a Lateglacial readvance/stillstand and preceded by larger glaciations. In contrast, preliminary data from an intervening massif indicate that the largest moraines are Lateglacial. Chronologies from Bolivia also suggest local variability. In leeward Milluni and San Francisco Valleys, local LGM moraines descend to $4300 m above sea level (a.s.l.), whereas in windward Zongo Valley Lateglacial moraines reach $3400 m a.s.l. Atlantic and Pacific sea surface temperatures, El Niñ o–Southern Oscillation and insolation changes all likely play roles in mediating tropical Andean glacial cycles.