Browsing by Author "García B., Juan Luis"

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    10Be chronology of the Last Glacial Maximum and Termination in the Andes of central Chile: The record of the Universidad Glacier (34° S)
    (Elsevier Ltd., 2024) Fernández Navarro, Hans Andrés; García B., Juan Luis; Nussbaumer, Samuel U.; Tikhomirov, Dmitry; Pérez Mora, Francia Débora; Gartner Roer, Isabelle; Christl, Marcus; Egli, Markus
    Reconstructing mid-latitude glacier variations is a prerequisite for unveiling the interhemispheric climate linkages and atmospheric-ocean forcings that triggered those changes during the last glacial cycle. Nonetheless, the timing, magnitude, and structure of glacier fluctuations in the southern mid-latitudes remain incomplete. Here, we present a new Be-10 chronology of the Universidad Glacier in the Andes of central Chile (34 degrees S, 70 degrees W; similar to 2500 m a.s.l.) based on 21 cosmogenic-exposure ages of boulders on discrete moraine ridges defining former ice margins. Our findings include the mapping and dating of three moraines, UNI I, UNI II, and UNI III, located similar to 20 km, 15 km, and 10 km down-valley from the present-day glacier front, respectively. The Be-10 exposure ages of the UNI I moraine range from 135.9 +/- 7.1 to 51.4 +/- 2.7 ka (n = 3). The UNI II moraine gave a mean age of 18.0 +/- 0.9 (n = 15) and the UNI III moraine yielded a mean age of 13.9 +/- 0.8 ka (n = 3). The UNI I moraine implies the largest ice extent during a pre-Last Glacial Maximum (pre-LGM) period, including the penultimate glaciation. The UNI II is a moraine complex that represents cold and humid conditions in central Chile at the end of the LGM, which we attribute to the northward-shift of the Southern Westerly Winds (SWW). The UNI III moraine represents a return to glacial conditions interrupting the Termination, evidencing both a double-step deglacial trend observed through the southern middle and high latitudes at the end of the last ice age. The Andes at this subtropical latitude record a global signal of glacial and climate change.
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    14C and 10Be dated Late Holocene fluctuations of Patagonian glaciers in Torres del Paine (Chile, 51°S) and connections to Antarctic climate change
    (2020) García B., Juan Luis; Hall, B. L.; Kaplan, M. R.; Gomez, G. A.; De Pol Holz, R.; Garcia, V. J.; Schaefer, J. M.; Schwartz, R.
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    Accelerating Glacier Area Loss Across the Andes Since the Little Ice Age
    (John Wiley & Sons, 2024) Carrivick, Jonathan L.; Davies, Morwenna; Wilson, Ryan; Davies, Bethan J.; Gribbin, Tom; King, Owen; Rabatel, Antoine; García B., Juan Luis; Ely, Jeremy C.
    Andean glaciers are losing mass rapidly but a centennial-scale context to those rates is lacking. Here we show the extent of >5,500 glaciers during the Little Ice Age chronozone (LIA; c. 1,400 to c. 1,850) and compute an overall area change of -25% from then to year 2000 at an average rate of -36.5 km(2 )yr(-1) or -0.11% yr(-1). Glaciers in the Tropical Andes (Peru, Bolivia) have depleted the most; median -56% of LIA area, and the fastest; median -0.16% yr(-1). Up to 10 x acceleration in glacier area loss has occurred in Tropical mountain sub-regions comparing LIA to 2,000 rates to post-2000 rates. Regional climate controls inter-regional variability, whereas local factors affect intra-region glacier response time. Analyzing glacier area change by river basins and by protected areas leads us to suggest that conservation and environmental management strategies should be re-visited as proglacial areas expand.
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    Climate and coastal low-cloud dynamic in the hyperarid Atacama fog Desert and the geographic distribution of Tillandsia landbeckii (Bromeliaceae) dune ecosystems
    (Springer, 2021) García B., Juan Luis; Lobos Roco, Felipe Andres; Schween, Jan H.; Río López, Camilo del; Osses, Pablo; Vives Ansted, Raimundo José; Pezoa Jadue, Mariana Ignacia; Siegmund, Alexander; Latorre H., Claudio; Alfaro, Fernando; Koch, Marcus A.; Loehnert, Ulrich
    Despite the extensive area covered by the coastal Atacama fog Desert (18-32 degrees S), there is a lack of understanding of its most notorious characteristics, including fog water potential, frequency of fog presence, spatial fog gradients or fog effect in ecosystems, such as Tillandsia fields. Here we discuss new meteorological data for the foggiest season (July-August-September, JAS) in 2018 and 2019. Our meteorological stations lie between 750 and 1211 m a. s. l. at two sites within the Cordillera de la Costa in the hyperarid Atacama (20 degrees S): Cerro Oyarbide and Alto Patache. The data show steep spatial gradients together with rapid changes in the low atmosphere linked to the advection of contrasting coastal (humid and cold) and continental (dry and warm) air masses. One main implication is that fog presence and fog water yields tend to be negatively related to both distance to the coast and elevation. Strong afternoon SW winds advect moisture inland, which take the form of fog in only about 6% of the JAS at 1211 m a. s. l., but 65% at 750 m a. s. l. on the coastal cliff. Although sporadic, long lasting fog events embrace well-mixed marine boundary layer conditions and thick fog cloud between 750 and 1211 m a. s. l. These fog events are thought to be the main source of water for the Tillandsia ecosystems and relate their geographic distribution to the lowest fog water yields recorded. Future climate trends may leave fog-dependent Tillandsia even less exposed to the already infrequent fog resulting in rapid vegetation decline.
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    Evolución morfoestratigráfica de paleodunas y paleosuelos en la ensenada de Quintero, Región de Valparaíso, Chile
    (2021) Cabello Espínola, Misael; García B., Juan Luis; Pontificia Universidad Católica de Chile. Instituto de Geografía
    La preservación de los sedimentos eólicos confiere unos de los marcadores estratigráficos más completos del Cuaternario, como proxis de la circulación atmosférica pasada y actual, especialmente en zonas semiáridas. Es por ello que la ensenada de Quintero (32ºS) y las paleodunas y paleosuelos permiten determinar las condiciones paleoambientales de la costa de Chile central dentro del Pleistoceno superior. Este estudio ocurre en el sitio Ventanas II del complejo paleodunar del sector. Para determinar las características paleogeográficas y paleoambientales se identificaron las unidades morfoestructurales dentro de la ensenada. En base a descripción y muestreo se definieron las características granulométricas (Tamizado y Bouyoucos) así como el tipo de ambiente depositacional (estadística y Función Discriminante Lineal), y con la densidad aparente e Índice de desarrollo de suelo (IDS) se establecen las condiciones pedogenéticas. Como resultados cronológicos estimados se obtiene que la depositación sobre la terraza marina T1 comenzó en el Estadio Marino Isotópico (MIS) 5, hace 125 o 100 ka. En base a las características texturales se identificaron 13 unidades clasificadas en cuatro facies (F. arenosa dunar; F. arcillosa; F. arcillo limosa y F. arenosa de playa), de las cuales cinco corresponden a paleodunas donde evolucionaron 5 paleosuelos intercalados, bajo estas unidades se evidencia un cambio en la paleogeografía por la presencia de un posible paleo humedal sobre un depósito de playa que reflejan una cercanía a la línea de costa, por último sobre la terraza marina se infiere que evolucionó un paleosuelo. En cuanto a los paleosuelos evolucionados de las paleodunas presentan las mismas características pedogenéticas, reflejando que las condiciones paleoambientales fueron similares durante las fases de formación. Finalmente, una correlación permitió establecer edades relativas con las seis primeras unidades mostrando que estas evolucionaron dentro de los MIS 4, 3 y 2.
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    Geomorfología y geocronología (10-Be) de las fluctuaciones del Glaciar Universidad en los Andes chilenos subtropicales (34° S) desde el Último Máximo Glacial al presente: Implicancias paleoclimáticas
    (2023) Fernández Navarro, Hans Andrés; García B., Juan Luis; Pontificia Universidad Católica de Chile. Instituto de Geografía
    Los glaciares ubicados en los Andes de Chile central (30°—35° S) son altamente sensibles a los cambios del clima. Por lo cual, reconstruir la evolución de los glaciares a través de registros geológicos tales como morrenas, brinda una oportunidad para reconstruir las variaciones climáticas en distintas escalas de tiempo. En este trabajo se reconstruyó la evolución del Glaciar Universidad (34° 42' S, 70° 20' O) desde el Último Máximo Glacial al presente. Para aquello se confeccionó un mapeo geomorfológico a lo largo de los ~20 km del valle del Glaciar Universidad. El mapeo permitió identificar cuatro morrenas denominadas desde la más distal a la más proximal como UNI I–IV. Las morrenas se distribuyen entre los ~1100 y 2500 m.s.n.m. Complementariamente, se aplicó datación por exposición superficial (10-Be) en cuarenta y nueve bloques granodioríticos emplazados principalmente en la superficie de las morrenas. Tres bloques granodioríticos obtenidos desde la morrena UNI I brindaron edades de exposición pre-Último Máximo Glacial (51.4±2.7 a 135.9±7.1 ka; 1 ka= hace 1000 años). Catorce edades de exposición obtenidas desde la Morrena UNI II fluctuaron entre los 17.0±0.8 y 19.9±1.0 ka (promedio= 18.2±0.7 ka), lo que coincide con el Último Máximo Glacial. Desde la morrena UNI III se obtuvieron seis edades de exposición que variaron entre 9.7±0.5 y 14.4±1.1 ka (promedio=11.8±1.8 ka), lo que implica un reavance tardiglacial ocurrido entre la Última Terminación Glacial y comienzos del Holoceno. La morrena UNI IV es un complejo morrénico construido principalmente durante el último milenio. Veintiséis edades de exposición indicaron que el primer avance máximo del glaciar ocurrió entre el siglo 13 y 16, mientras que el segundo reavance máximo ocurrió durante la primera mitad del siglo 19. La dispersión de datos obtenidos desde la morrena UNI I no permite establecer relación alguna entre su periodo de construcción y un evento climático especifico. El principal factor climático que explica los avances glaciares que construyeron las morrenas UNI II y UNI III es la migración de los Vientos del Oeste (VO) hacia Chile central, el cual implicó el transporte de condiciones atmosféricas más húmedas y frías desde regiones subantárticas hacia latitudes subtropicales. De igual manera, el complejo morrénico UNI IV se construyó durante la migración de los VO hacia latitudes medias durante una fase negativa del Modo Anular del Sur (SAM), el que se extendió desde el año ~1400 al 1850 (año calendario). El último avance del Glaciar Universidad ocurrió a mediados del siglo 20, también en un periodo negativo del SAM. Después de ese último reavance el Glaciar Universidad solo ha tendido a decaer en respuesta a un clima más cálidos y seco.
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    Glacial to periglacial transition at the end of the last ice age in the subtropical semiarid Andes
    (Elsevier B.V., 2024) García B., Juan Luis; Carraha Molina, Javiera Paz; Fernández Navarro, Hans Andrés; Nussbaumer, Samuel U.; Pérez Mora, Francia Débora; Hidy, Alan J.; Gärtner-Roer, Isabelle; Haeberli, Wilfried
    Atmospheric warming and circulation reorganization at the end of the last ice age represent the most important climate change of the last 100,000 years and provide an opportunity to uncover how the southern subtropics cryosphere responded to strong changes in the global climate system. Extensive mapping and chronologic records on cryogenic landforms to better understand the association and interactions between glaciers and viscous creep of ice-rich permafrost landforms (rock glaciers) are widely missing in the region. In this paper, we reconstruct the geomorphic imprint of the Last Glacial Maximum (LGM) and the Termination I in the high Andes of the Río Limarí Basin (30–31°S) in the subtropical semiarid Andes of Chile. 74 new 10Be surface exposure dating ages constrain the timing of glaciation, deglaciation, and glacial to periglacial transition. Glacial advances occurred first by 41.2 ± 0.6 – 35.0 ± 0.5 ka during Marine Isotope Stage 3, but probably earlier also; then, a second advance occurred during the global LGM between 24.2 ± 0.4 and 18.6 ± 0.2 ka. Deglaciation by 17.6 ± 0.2 ka left extensive hummocky moraines on the main valleys. Characteristic patterns of furrows and ridges typical of rock glaciers and solifluction superimposed on the LGM hummocky moraine indicate ice-rich permafrost in glacial deposits likely between 15.5 ± 0.3 and 13.6 ± 0.3 ka. We propose that moraines deposited by LGM debris-covered glaciers served as a niche for strong seasonal frost and permafrost creep, which substantially modified the original landforms. Our results contribute to a better understanding of major transformations in an ice-rich high mountain area of the southern hemisphere where the interplay of temperature and precipitation changes drove glacial to periglacial transitions.
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    Late Pleistocene to Holocene glacial, periglacial, and paraglacial geomorphology of the upper Río Limarí basin (30-31° S) in the Andes of central Chile
    (Taylor & Francis Group, 2024) Carraha Molina, Javiera Paz; García B., Juan Luis; Nussbaumer, Samuel U.; Fernández Navarro, Hans Andrés; Gartner-Roer, Isabelle
    We present a field-based reconstruction of the geomorphology in the Subtropical Andean mountains of the Limari basin, semiarid central Chile (30-31 degrees S). Fieldwork campaigns and remote-sensing analysis served for detailed geomorphological mapping at four formerly glaciated valleys in the heads of the Combarbala and Rio Hurtado sub-basins. We identify a mosaic of glacial, periglacial, and paraglacial landforms. Glacial landforms include a massive dead-ice moraine complex, with thermokarst and debris-filled fractures suggesting former ice-cored moraine degradation. This landform is superimposed by transversal and arcuate ridges suggesting active-ice processes. Periglacial landforms such as rock glaciers, gelifluction, and protalus lobes occur in cirques and U-shaped valleys, but also on moraine deposits. Paraglacial processes are indicated by talus accumulation in those formerly glaciated slopes. The geomorphological imprint is evidence for the interaction and succession between glacial, periglacial, and paraglacial dynamics from the Late Pleistocene to the present.
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    Living at the dry limits: ecological genetics of Tillandsia landbeckii lomas in the Chilean Atacama Desert
    (2019) Koch, Marcus A.; Kleinpeter, Dorothea; Auer, Erik; Siegmund, Alexander; Río López, Camilo del; Osses Mc-Intyre, Pablo; García B., Juan Luis; Marzol, Maria V.; Zizka, Georg; Kiefer, Christiane
    The northern Chilean Atacama Desert is among those regions on Earth where life exists at its dry limits. There is almost zero rainfall in its core zone, and the only source of water is a spatio-temporally complex fog system along the Pacifc coast, which is reaching far into the hyperarid mainland. Hardly any vascular plants grow in these areas, and, thus, it is intriguing to be faced with a vegetation-type build-up by one single and highly specialized bromeliad species, Tillandsia landbeckii Phil., forming regular linear structures in a sloped landscape. We studied the genetic make-up of a population system extending an area of approximately 1500 km2 and demonstrated a fne-scale correlation of genetic diversity with spatial population structure and following an elevational gradient of approximately 150 m. Increase in genetic diversity is correlated with increased ftness as measured by fowering frequency, and evidence is provided that outbreeding is linked with a large-distance fying pollinator feeding occasionally as generalist on its fowers, but not using the plant as source for larvae feeding. Our data demonstrate that establishment of linear vegetation structure is in principle a process driven by clonal growth and propagation of ramets over short distances. However, optimal conditions (slope, elevation, fog occurrence) for linear growth pattern formation also increase sexual plant reproductive ftness, thus providing the reservoir for newly combined genetic variation and counteracting genetic uniformity. Our study highlights the Tillandsia vegetation, also called Tillandsia lomas, as unique and genetically diverse system, which is highly threatened by global climate change and disturbance of the coastal fog system.
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    Soil bacterial community structure of fog-dependent Tillandsia landbeckii dunes in the Atacama Desert
    (Springer, 2021) Alfaro, Fernando D.; Manzano, Marlene; Almiray, Cristian; García B., Juan Luis; Osses, Pablo; Río López, Camilo del; Vargas Vásquez, Constanza Giovanna; Latorre H., Claudio; Koch, Marcus A.; Siegmund, Alexander; Abades, Sebastian
    The interplay between plants and soil drives the structure and function of soil microbial communities. In water-limited environments where vascular plants are often absent and only specialized groups of rootless plants grow, this interaction could be mainly asymmetric, with plants supporting nutrients and resources via litter deposition. In this study, we use observational approaches to evaluate the impact of local distribution of Tillandsia landbeckii across elevation on soil bacterial community structure and composition in the Atacama Fog Desert. Tillandsia landbeckii is a plant without functional roots that develops on meter-scale sand dunes and depends mainly on marine fog that transports resources (water and nutrients) from the Pacific Ocean. Our data show that soil bacterial abundance, richness, and diversity were significantly higher beneath T. landbeckii plants relative to bare soils. However, these differences were not significant across T. landbeckii located at different elevations and with different input of marine fog. On the other hand, bacterial community composition was significantly different with T. landbeckii plants across elevations. Further, samples beneath T. landbeckii and bare soils showed significant differences in bacterial community composition. Around 99% of all operational taxonomic units (OTUs) were recorded exclusively beneath T. landbeckii, and only 1% of OTUs were observed in bare soils. These findings suggest that the presence of T. landbeckii promotes significant increases in bacterial abundance and diversity compared with bare soils, although we fail to demonstrate that local-scale changes in elevation can affect patterns of soil bacterial diversity and abundance beneath T. landbeckii.
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    Soil microbial abundance and activity across forefield glacier chronosequence in the Northern Patagonian Ice Field, Chile
    (2020) Alfaro, F. D.; Salazar Burrows, Alejandro Francisco; Banales Seguel, C.; García B., Juan Luis; Manzano, M.; Marquet, P. A. (Pablo A.); Ruz, K.; Gaxiola Alcantar, Aurora