Browsing by Author "Sagredo T., Esteban"
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- ItemAnatomía de las fluctuaciones glaciales en Patagonia norte durante la última terminación glacial(2020) Soteres García, Rodrigo León; Sagredo T., Esteban; Pontificia Universidad Católica de Chile. Instituto de GeografíaLa Última Terminación Glacial (18.000 – 11.700 años antes del presente) exhibe una secuencia sincrónica de cambios climáticos asimétricos en latitudes polares de ambos hemisferios. Sin embargo, la extensión espacial y la cronología de estas señales climáticas polares se encuentra aún poco conocida en latitudes medias del hemisferio sur. En este estudio presento cronologías basadas en 14C y 10Be de las geoformas glaciales originadas por los lóbulos glaciales Golfo de Corcovado (~42,5o S) y Lago Palena/General Vintter (~43,5o S), ambos ubicados en Patagonia norte, con el objeto de descifrar el comportamiento pasado de los glaciares de la región para clarificar la naturaleza de las divergencias climáticas polares y contribuir a discriminar los potenciales mecanismos tras los cambios climáticos asociados a la Última Terminación Glacial. Mis resultados indican que ambos lóbulos glaciales se comportaron de manera sincrónica con otros glaciares de Patagonia y Nueva Zelanda, replicando la secuencia de cambios climáticos observados en Antártica. Esta respuesta coordinada de la criósfera de latitudes medias del hemisferio sur coincide temporalmente con los desplazamientos latitudinales de los Vientos del Oeste Australes inferidos a partir de indicadores independientes, sugiriendo que los mecanismos atmosféricos jugaron un papel fundamental en la variabilidad climática durante el fin de la última glaciación.
- ItemEquilibrium line altitudes along the Andes during the Last millennium : paleoclimatic implications(2017) Sagredo T., Esteban; Lowell, Thomas V.; Kelly, Meredith A.; Rupper, Summer; Aravena, Juan Carlos; Ward, Dylan J.; Malone, Andrew G. O.
- ItemEvolution of Glacial Lake Cochrane During the Last Glacial Termination, Central Chilean Patagonia (∼47°S)(2022) Vásquez, Alicia; Flores-Aqueveque, Valentina; Sagredo T., Esteban; Hevia, Rodrigo; Villa-Martínez, Rodrigo; Moreno, Patricio; Antinao, José L.Vásquez, Alicia; Flores-Aqueveque, Valentina; Sagredo T., Esteban; Hevia, Rodrigo; Villa-Martínez, Rodrigo; Moreno, Patricio; Antinao, José L.Large ice-dammed lakes developed along the eastern margin of the Patagonian Ice Sheet (PIS) during the Last Glacial Termination (T1). Their spatial/temporal evolution, however, remains poorly constrained despite their importance for deciphering fluctuations of the shrinking PIS, isostatic adjustments, and climate forcing. Here we examine the distribution and age of shoreline features deposited or sculpted by Glacial Lake Cochrane (GLC) in the Lago Cochrane/Pueyrredón (LCP) basin, Central Patagonia, following recession of the LCP glacier lobe from its final Last Glacial Maximum (LGM) moraines. GLC drained initially toward the Atlantic Ocean and continuing ice shrinking opened new drainage routes allowing the discharge toward the Pacific Ocean. We identify five clusters of lake terraces, shorelines, and deltas between elevations ∼600–500 (N5), ∼470–400 (N4), ∼360–300 (N3), ∼230–220 (N2), and ∼180–170 masl (N1) throughout the LCP basin. The distribution of these clusters and associated glaciolacustrine deposits provide constraints for the evolving position of the damming glacier bodies. Elevation gradients within the landform clusters reveal glacio-isostatic adjustments that enable us to quantify the magnitude of deglacial rebound and construct isostatically corrected surfaces for the different phases in the evolution of GLC. Our chronology, based principally on radiocarbon dates from lake sediment cores and new OSL dating, suggests that these phases developed between ∼20.7–19.3 ka (N5), ∼19.3–14.8 ka (N4), ∼14.8–11.3 ka (N3), and shortly thereafter (N2 and N1). The N3 landforms are the most ubiquitous, well-preserved, and voluminous, attributes that resulted from a ∼3,500-year long period of glacial stability, enhanced sediment supply by peak precipitation regime, and profuse snow and ice melting during the most recent half of T1. This scenario differs from the cold and dry conditions that prevailed during the brief N5 phase and the moderate amount of precipitation during the N4 phase. We interpret the limited development of the N2 and N1 landforms as ephemeral stabilization events following the final and irreversible disappearance of GLC after N3. This event commenced shortly after the onset of an early Holocene westerly minimum at pan-Patagonian scale at ∼11.7 ka, contemporaneous with peak atmospheric and oceanic temperatures in the middle and high latitudes of the Southern Hemisphere.
- ItemGlacier and terrestrial ecosystem evolution in the Chilotan archipelago sector of northwestern Patagonia since the Last Glacial Termination(2022) Moreno, Patricio; Fercovic, E.I.; Soteres, R.L.; Ugalde, P.I.; Sagredo T., Esteban; Villa-Martínez, RodrigoWe examine the glacier, terrestrial ecosystem, and climate evolution since the Last Glacial Termination (T1) based on glacial sediments/landform assemblages and palynological data from the Chilotan archipelago (41°30′S-43°30′S), northwestern Patagonia. Deglacial warming drove recession of the Golfo Corcovado glacier lobe from the Last Glacial Maximum moraines in the interior of Isla Grande de Chiloé (IGC) before ∼17.8 ka, along with a rapid and irreversible trend toward arboreal dominance. Subsequent glacier stabilization led to deposition of the innermost moraines in eastern IGC and adjacent islands sometime between ∼17.5–16.9 ka, followed by an acceleration in glacial retreat that vacated the Chilotan Interior Sea in ∼200 years or less. Early successional cold-tolerant shade-intolerant trees prevailed during the initial stages of T1, followed by temperate rainforests dominated by thermophilous shade-tolerant species between ∼15–14.5 ka. A mixed forest with cold-tolerant hygrophilous conifers established between ∼14.5–12.6 ka, implying cooler climate and stronger Southern Westerly Wind (SWW) influence during the Antarctic Cold Reversal. Stand-replacing fires favored early successional shade-intolerant trees, shrubs, and herbs between ∼12.6–10.8 ka in response to milder temperatures and weaker SWW during Younger Dryas time. The early Holocene (∼10.8–7.5 ka) features a maximum in shade-intolerant thermophilous trees, absence of conifers, and peak fire activity, signaling a warm/dry interval with minimum SWW influence. Cooler/wetter conditions have prevailed over the last ∼7500 years driven by strong SWW influence. We conclude that Patagonian glaciers and terrestrial ecosystems responded simultaneously to climate changes at regional, hemispheric, and global scales multiple times since T1. We adhere to the concept that millennial-scale variations in the SWW linked the response of the hydro- bio and cryosphere across the southern mid- and high southern latitudes, and were teleconnected with northern hemisphere events through the atmospheric concentration of greenhouse gases, latitudinal shifts in the Intertropical convergence zone, and deep ocean circulation.
- ItemGlacier fluctuations in the northern Patagonian Andes (44°S) imply wind-modulated interhemispheric in-phase climate shifts during Termination 1(2022) Soteres García, Rodrigo León; Sagredo T., Esteban; Kaplan, Michael R.; Martini, Mateo A.; Moreno, Patricio I.; Reynhout, Scott A.; Schwartz, Roseanne; Schaefer, Joerg M.Soteres García, Rodrigo León; Sagredo T., Esteban; Kaplan, Michael R.; Martini, Mateo A.; Moreno, Patricio I.; Reynhout, Scott A.; Schwartz, Roseanne; Schaefer, Joerg M.The Last Glacial Termination (T1) featured major changes in global circulation systems that led to a shift from glacial to interglacial climate. While polar ice cores attest to an antiphased thermal pattern at millennial timescales, recent well-dated moraine records from both hemispheres suggest in-phase fluctuations in glaciers through T1, which is inconsistent with the bipolar see-saw paradigm. Here, we present a glacier chronology based on 30 new 10Be surface exposure ages from well-preserved moraines in the Lago Palena/General Vintter basin in northern Patagonia (~ 44°S). We find that the main glacier lobe underwent profound retreat after 19.7 ± 0.7 ka. This recessional trend led to the individualization of the Cerro Riñón glacier by ~ 16.3 ka, which underwent minor readvances at 15.9 ± 0.5 ka during Heinrich Stadial 1, during the Antarctic Cold Reversal with successive maxima at 13.5 ± 0.4, 13.1 ± 0.4, and 13.1 ± 0.5 ka, and a minor culmination at 12.5 ± 0.4 ka during Younger Dryas time. We conclude that fluctuations of Patagonian glaciers during T1 were controlled primarily by climate anomalies brought by shifts in the Southern Westerly Winds (SWW) locus. We posit that the global covariation of mountain glaciers during T1 was linked to variations in atmospheric CO2 (atmCO2) promoted by the interplay of the SWW-Southern Ocean system at millennial timescales.
- ItemHolocene glacier fluctuations in Patagonia are modulated by summer insolation intensity and paced by Southern Annular Mode-like variability(2019) Reynhout, S.A.; Sagredo T., Esteban; Kaplan, M.R.; Aravena, J.C.; Martini, M.A.; Moreno, P.I.; Rojas, M.; Schwartz, R.; Schaefer, J.M.
- ItemHolocene glacier history of northeastern Cordillera Darwin, southernmost South America (55°S)(2022) Reynhout, Scott A.; Kaplan, Michael R.; Sagredo T., Esteban; Aravena, Juan Carlos; Soteres García, Rodrigo León; Schwartz, Roseanne; Schaefer, Joerg M.Reynhout, Scott A.; Kaplan, Michael R.; Sagredo T., Esteban; Aravena, Juan Carlos; Soteres García, Rodrigo León; Schwartz, Roseanne; Schaefer, Joerg M.In the Cordillera Darwin, southernmost South America, we used 10Be and 14C dating, dendrochronology, and historical observations to reconstruct the glacial history of the Dalla Vedova valley from deglacial time to the present. After deglacial recession into northeastern Darwin and Dalla Vedova, by ~16 ka, evidence indicates a glacial advance at ~13 ka coeval with the Antarctic Cold Reversal. The next robustly dated glacial expansion occurred at 870 ± 60 calendar yr ago (approximately AD 1150), followed by less-extensive dendrochronologically constrained advances from shortly before AD 1836 to the mid-twentieth century. Our record is consistent with most studies within the Cordillera Darwin that show that the Holocene glacial maximum occurred during the last millennium. This pattern contrasts with the extensive early- and mid-Holocene glacier expansions farther north in Patagonia; furthermore, an advance at 870 ± 60 yr ago may suggest out-of-phase glacial advances occurred within the Cordillera Darwin relative to Patagonia. We speculate that a southward shift of westerlies and associated climate regimes toward the southernmost tip of the continent, about 900–800 yr ago, provides a mechanism by which some glaciers advanced in the Cordillera Darwin during what is generally considered a warm and dry period to the north in Patagonia.
- ItemHolocene History of Río Tranquilo Glacier, Monte San Lorenzo (47°S), Central Patagonia(2021) Sagredo T., Esteban; Reynhout, Scott A.; Kaplan, Michael R.; Aravena, Juan C.; Araya, Paola S.; Luckman, Brian H.; Schwartz, Roseanne; Schaefer, Joerg M. Sagredo T., Esteban; Reynhout, Scott A.; Kaplan, Michael R.; Aravena, Juan C.; Araya, Paola S.; Luckman, Brian H.; Schwartz, Roseanne; Schaefer, Joerg M.The causes underlying Holocene glacier fluctuations remain elusive, despite decades of research efforts. Cosmogenic nuclide dating has allowed systematic study and thus improved knowledge of glacier-climate dynamics during this time frame, in part by filling in geographical gaps in both hemispheres. Here we present a new comprehensive Holocene moraine chronology from Mt. San Lorenzo (47°S) in central Patagonia, Southern Hemisphere. Twenty-four new 10Be ages, together with three published ages, indicate that the Río Tranquilo glacier approached its Holocene maximum position sometime, or possibly on multiple occasions, between 9,860 ± 180 and 6,730 ± 130 years. This event(s) was followed by a sequence of slightly smaller advances at 5,750 ± 220, 4,290 ± 100 (?), 3,490 ± 140, 1,440 ± 60, between 670 ± 20 and 430 ± 20, and at 390 ± 10 years ago. The Tranquilo record documents centennial to millennial-scale glacier advances throughout the Holocene, and is consistent with recent glacier chronologies from central and southern Patagonia. This pattern correlates well with that of multiple moraine-building events with slightly decreasing net extent, as is observed at other sites in the Southern Hemisphere (i.e., Patagonia, New Zealand and Antarctic Peninsula) throughout the early, middle and late Holocene. This is in stark contrast to the typical Holocene mountain glacier pattern in the Northern Hemisphere, as documented in the European Alps, Scandinavia and Canada, where small glaciers in the early-to-mid Holocene gave way to more-extensive glacier advances during the late Holocene, culminating in the Little Ice Age expansion. We posit that this past asymmetry between the Southern and Northern hemisphere glacier patterns is due to natural forcing that has been recently overwhelmed by anthropogenic greenhouse gas driven warming, which is causing interhemispherically synchronized glacier retreat unprecedented during the Holocene.
- ItemHolocene tephrochronology around Cochrane (~47° S), southern Chile(2016) Stern, Charles R.; Moreno, Patricio I.; Henriquez, William I.; Villa Martinez, Rodrigo; Sagredo T., Esteban; Aravena, Juan Carlos; De Pol-Holz, Ricardo
- ItemLate glacial climate evolution in the Patagonian Andes (44–47° S) from alpine glacier modelling(2023) Muir, Ruby; Eaves, Shaun; Vargo, Lauren; Anderson, Brian; Mackintosh, Andrew; Sagredo T., Esteban; Soteres García, Rodrigo LeónMuir, Ruby; Eaves, Shaun; Vargo, Lauren; Anderson, Brian; Mackintosh, Andrew; Sagredo T., Esteban; Soteres García, Rodrigo LeónNumerical glacier models applied to moraine chronologies provide an opportunity to quantify past climate change. Here we apply a two-dimensional coupled mass balance – ice flow model to well-dated moraine sequences deposited by former alpine glaciers at two central Patagonian sites: Cerro Riñón (43.97°S, 71.64°W) and Río Tranquilo (47.50°S, 72.38°W), to reconstruct the local temperatures during both the Antarctic Cold Reversal (14.7–13 ka) and the Younger Dryas (12.9–11 ka). Modelled temperature anomalies during the Antarctic Cold Reversal are −2.6 ± 0.4 °C at 44°S, and −2.9 ± 0.6 °C at 47°S. At both locations this cold event is followed by temperature increases of +0.6–0.7 °C or precipitation reductions of c. 20% to drive glacier retreat to moraines deposited during Younger Dryas time. The consistent climatic anomalies between these two latitudes suggest this region of Patagonia was responding to a common climatic event. Further, the late-glacial temperature anomalies found here compare well to those determined by similar glacier modelling techniques in New Zealand, at 43–44° S. These results support a trans-Pacific response throughout the southern mid to high latitudes (43–47° S) during the ACR that is best explained by a northward expansion of the south westerly winds.
- ItemLate pleistocene glaciations of the arid subtropical Andes and new results from the Chajnantor Plateau, northern Chile(2015) Ward, Dylan J.; Cesta, Jason M.; Galewsky, Joseph; Sagredo T., Esteban
- ItemMid-latitude trans-Pacific reconstructions and comparisons of coupled glacial/interglacial climate cycles based on soil stratigraphy of cover-beds(2018) Alloway, B.; Almond, P.; Moreno, P.; Sagredo T., Esteban; Kaplan, M.; Kubik, P.; Tonkin, P.
- ItemModelled glacier equilibrium line altitudes during the mid-Holocene in the southern mid-latitudes(2015) Bravo, C .; Rojas, M.; Anderson, B. M.; Mackintosh, A. N.; Sagredo T., Esteban; Moreno, P. I.
- Item(Paleo)glacier studies in Patagonia over the past decades (1976–2020): A bibliometric perspective based on the Web of Science(2023) Soteres García, Rodrigo León; Riquelme, Fabián; Sagredo T., Esteban; Kaplan, MichaelSoteres García, Rodrigo León; Riquelme, Fabián; Sagredo T., Esteban; Kaplan, MichaelPatagonia features the most extensive glaciers of the Southern Hemisphere, excluding Antarctica, and a vast inventory of glacial landforms, so it is thought to have played a key role in (paleo)glacier studies since the late 19th century. However, no systematic attempts to characterize the specific research trends and the scientific community focused on Patagonian cryosphere have been conducted so far. To fill this gap, we analyzed the metadata associated to 305 articles compiled from the Web of Science database following a bibliometric approach covering the period between 1976 and 2020. Our results point to an irregular but net increase on the number of contributions on Patagonian (paleo)glaciers. Mass balance analyses based on satellite data of present-day glaciers and the reconstruction of past glacier activity by dating glacial landforms formed during the Last Glacial Termination, were the most addressed topics during the analyzed period. Patagonian (paleo)glacier studies are mostly published in generic Earth Sciences publications, followed by Quaternary and glaciological journals. Most of the studies were led by scientists from the United Kingdom, followed by Chile, Argentina and United States. In terms of collaborations, these studies can be divided into two main clusters, one composed by researchers from United States, Chile and Argentina institutions, and another mostly composed by British researchers. So far, the most prolific authors are nearly equally distributed in nationality, yet gender inclusion and international collaborations are still caveats that must be solved. Even though our query on the Web of Science missed highly influential (so-called) grey literature, such as local scientific journals and technical reports, the reviewed scientific literature unambiguously indicates that Patagonia is a privileged location for (paleo)glaciers studies worldwide and that it will continue offering vast opportunities to tackle critical questions related to global cryosphere and past-to-present climate changes.
- ItemReconstrucción climática del holoceno en Patagonia Noroeste mediante diatomeas(2023) Sepúlveda Zúñiga, Einer Alexander; Sagredo T., Esteban; Pontificia Universidad Católica de Chile. Instituto de GeografíaEl sector Pacífico de Patagonia Noroeste (PNO; 40°-44°S) se ha establecido como una región clave para descifrar los impactos de la variabilidad climática y las influencias humanas en los ecosistemas de latitudes medias del hemisferio sur (HS). Los Vientos del Oeste del Sur (SWW) constituyen el principal componente atmosférico que controla los patrones de precipitación en HS, existiendo una fuerte correlación positiva entre la intensidad del viento zonal y la precipitación local en este sector. Por esta razón, durante las últimas décadas, se han realizado diversos estudios paleoclimáticos en PNO que han inferido cambios en el equilibrio hidrológico atribuidos a variaciones de los SWW. No obstante, existen amplias discrepancias acerca de la evolución de los SWW durante el Holoceno en la vertiente pacífica de PNO. En virtud de su sensibilidad y especificidad, las diatomeas son ideales para examinar los cambios pasados en los ecosistemas acuáticos y descifrar los rangos de variabilidad bajo condiciones naturales e inducidas por el hombre. Hasta la fecha, sin embargo, muy pocos estudios basados en diatomeas han examinado en detalle la evolución ambiental durante el Holoceno en PNO. Aquí presento un nuevo registro de diatomeas de Lago Pichilaguna (41°S), un lago de cuenca cerrada y poca profundidad situado en las tierras bajas de la Región de los Lagos de Chile. Las variaciones en los ensambles de diatomeas más importantes sugieren cambios en el balance hídrico, la estratificación térmica y la mezcla de la columna de agua a escalas milenial y centenal. Entre ~12,6-11,5 ka, detecté el predominio de ensambles de diatomeas planctónicas relacionados con aguas templadas, oligotróficas y bajo nivel hídrico (e.g., Cyclotella distinguenda), lo que sugiere una influencia moderada de los SWW durante este periodo. A continuación, entre ~11,5-5,7 ka, observé un incremento en las especies planctónicas indicadoras de mayor estratificación térmica e incremento de nutrientes (e.g., Discostella stelligera). Este periodo fue interrumpido por intervalos dominados por ensambles ticoplanctónicos (grandes Aulacoseira spp.) relacionados con niveles de lago muy bajos y con una mayor mezcla en la columna de agua. Estas condiciones sugieren un mínimo en la influencia de los SWW. A partir de ~5,7 ka detecté una elevada inestabilidad climática, caracterizada por fluctuaciones de escala centenal, donde infiero periodos de mayor estratificación térmica entre ~5,1-4,2 ka; ~4-3,4 ka; ~3,2-3 ka; ~2,4-1,9 ka; ~1,6-1,1 ka; 1-0,9 ka; 0,6-0,3 ka, bajo una tendencia multimilenial frío/húmeda marcada por el predominio de ensambles perifíticos (pequeñas fragilarioides y pequeñas rafidias). Basado en lo anterior, infiero un fortalecimiento de los SWW con variaciones de escala centenal atribuibles a cambios en la intensidad y/o amplitud latitudinal de la influencia del SWW. Finalmente, a partir de los ~0,2 ka detecté los cambios más conspicuos en la composición de los ensambles de diatomeas del registro, marcados por una abrupta transición en la dominancia de las diatomeas perifíticas a las planctónicas, lo que sugiere el inicio de la fase más seca de los últimos milenios. Este periodo coincide con la quema deliberada del paisaje por parte de los colonos para la agricultura, la explotación del bosque nativo y el establecimiento de pastizales durante el siglo XIX en PNO. Mis resultados revelan que las perturbaciones humanas durante el período histórico sobrepasaron los rangos naturales de variabilidad y resiliencia de los ecosistemas acuáticos y terrestres durante el Holoceno, generando cambios abruptos en la biodiversidad, la composición de las especies y la estructura de las comunidades.
- ItemRefinement of the tephrostratigraphy straddling the northern Patagonian Andes (40–41°S): new tephra markers, reconciling different archives and ascertaining the timing of piedmont deglaciation(2022) Alloway, Brent V.; Pearce, Nicholas J.G.; Moreno, Patricio I.; Villarrosa, Gustavo; Jara, Ignacio A.; Henríquez, Carla A.; Sagredo T., Esteban; Ryan, Matthew T.; Outes, ValeriaWe describe the stratigraphy, age, geochemistry and correlation of tephra from west to east across the northern Patagonian Andes (c. 40–41°S) with a view to further refining the eruptive history of this region back to the onset of the Last Glacial Termination (~18 cal. ka). Eastwards across the Andes, rhyodacite to rhyolitic tephra markers of dominantly Puyehue-Cordón Caulle source are persistently recognised and provide a stratigraphic context for more numerously erupted intervening tephra of basalt to basaltic–andesite composition. Tephra from distal eruptive centres are also recognised. West of the Andean Cordillera, organic-rich cores from a small closed lake basin (Lago Pichilafquén) reveal an exceptional high-resolution record of lowland vegetation–climate change and eruptive activity spanning the last 15 400 years. Three new rhyodacite tephra (BT6-T1, -T2 and -T4) identified near the base of the Pichilafquén record, spanning 13.2 to 13.9 cal. ka bp, can be geochemically matched with correlatives in basal andic soil sequences closely overlying regolith and/or basement rock. The repetitiveness of this tephrostratigraphy across this Andean transect suggests near-synchronous tephra accretion and onset of up-building soil formation under more stable (revegetating) ground-surface conditions following rapid piedmont deglaciation on both sides of the Cordillera by at least ~14 cal. ka bp.
- ItemSensitivities of the equilibrium line altitude to temperature and precipitation changes along the Andes(2014) Sagredo T., Esteban; Rupper, Summer; Lowell, Thomas V.
- ItemStratigraphy, age and correlation of Lepué Tephra: a widespread c. 11 000 cal a BP marker horizon sourced from the Chaitén Sector of southern Chile(2017) Brent V. Alloway; Moreno, Patricio I.; Pearce, Nick J. G.; De Pol Holz, Ricardo; Henríquez, William I.; Pesce, Oscar H.; Sagredo T., Esteban; Villarosa, Gustavo; Outes, Valeria
- ItemThe glacial geomorphology of the Rio Corcovado, Rio Huemul and Lago Palena/General Vintter valleys, northeastern Patagonia (43 degrees S, 71 degrees W)(2020) Leger, T. P. M.; Hein, A. S.; Bingham, R. G.; Martini, M. A.; Soteres García, Rodrigo León; Sagredo T., Esteban; Martinez, O. A.
- ItemTrans-pacific glacial response to the Antarctic Cold Reversal in the southern mid-latitudes(2018) Sagredo T., Esteban; Kaplan, Michael R.; Araya, Paola S.; Lowell, Thomas V.; Aravena, Juan C.; Moreno, Patricio I.; Kelly, Meredith A.; Schaefer, Joerg M.