Browsing by Author "Garcia, Juan-Luis"

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    A composite 10Be, IR-50 and 14C chronology of the pre-Last Glacial Maximum (LGM) full ice extent of the western Patagonian Ice Sheet on the Isla de Chiloe, south Chile (42° S)
    (2021) Garcia, Juan-Luis; Luthgens, Christopher; Vega, Rodrigo M.; Rodes, Angel; Hein, Andrew S.; Binnie, Steven A.
    Unanswered questions about the glacier and climate history preceding the global Last Glacial Maximum (LGM) in the southern temperate latitudes remain. The Marine Isotope Stage (MIS) 3 is normally understood as a global interstadial period; nonetheless its climate was punctuated by conspicuous variability, and its signature has not been resolved beyond the polar realms. In this paper, we compile a Be-10 depth profile, single grain infrared (IR) stimulated luminescence dating and C-14 samples to derive a new glacier record for the principal outwash plain complex, deposited by the western Patagonian Ice Sheet (PIS) during the last glacial period (Llanquihue Glaciation) on the Isla de Chiloe, southern Chile (42 degrees S). In this region, the Golfo de Corcovado Ice Lobe left a distinct geomorphic and stratigraphic imprint, suitable for reconstructing former ice dynamics and timing of past climate change. Our data indicate that maximum glaciation occurred by 57.8 +/- 4.7 ka without reaching the Pacific Ocean coast. Ice readavanced and buttressed against the eastern side of the Cordillera de la Costa again by 26.0 +/- 2.9 ka. Our data further support the notion of a large ice extent during parts of the MIS 3 in Patagonia and New Zealand but appear to contradict near contemporaneous interstadial evidence in the southern midlatitudes, including Chiloe. We propose that the PIS expanded to its full-glacial Llanquihue moraines, recording a rapid response of southern mountain glaciers to the millennial-scale climate stadials that punctuated the MIS 3 at the poles and elsewhere.
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    De-icing landsystem model for the Universidad Glacier (34° S) in the Central Andes of Chile during the past ∼660 years
    (2022) Fernandez, Hans; Garcia, Juan-Luis; Nussbaumer, Samuel U.; Janine Geiger, Alessa; Gartner-Roer, Isabelle; Perez, Francia; Tikhomirov, Dmitry; Christl, Marcus; Egli, Markus
    Reconstructing latest Holocene (< 1000 years) glacial landscape development in the Central Andes of Chile (30-35 degrees S) is key for understanding the response of the cryosphere during periods of negative glacier mass balance, such as the current one. The excellently preserved glacial landscape produced during the latest ice advance and retreat cycle is of particular interest for examining the detailed response of glaciers to deglaciation. To establish a conceptual model of glacier behavior under warm and dry climatic conditions, we reconstructed and dated the recent glacial history of the Universidad Glacier (34 degrees S) through detailed geomorphological mapping and Be-10 cosmogenic surface exposure dating. Our mapping describes a landsystem that spans from the current ice front to similar to 3 km down-valley, where a mosaic of glacial landforms includes mounded relief; sinkholes; debris -filled stripes; moraine belts; flutings; and a prominent basal till plain. Our Be-10 ages suggest that the Universidad Glacier has fluctuated in its forefield since the 13th - 15th centuries CE. We propose that the glacier evolved from a clean glacier to a debris-covered glacier, to an ice-cored moraine, and finally, to a massive dead-ice topography. This deglacial evolution intermittent and potentially reset by multiple standstills and/or re-advances during the overall retreat. The implication is that phases of active ice were followed by stagnation associated with progressive melting of dead ice under the supraglacial debris layer. Similar geomorphic features and processes are recorded in the present-day Universidad Glacier ablation zone, denoting a recurrent reconditioning over time analogous to the glacier's evolution during the latest Holocene.(C) 2022 Elsevier B.V. All rights reserved.
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    Fluctuations of the Universidad Glacier in the Andes of central Chile (34? S) during the latest Holocene derived from a 10Be moraine chronology
    (2023) Fernandez-Navarro, Hans; Garcia, Juan-Luis; Nussbaumer, Samuel U.; Tikhomirov, Dmitry; Perez, Francia; Gartner-Roer, Isabelle; Christl, Marcus; Egli, Markus
    The reconstruction of glacier fluctuations during the latest Holocene (<1000 years) is necessary for understanding the climate context preceding the warmer conditions of the 20th and 21st centuries. The glacier records in the Andes of central Chile are suitably located to track former latitudinal changes of the Southern Westerly Winds (SSW), which are mostly unknown at this middle latitude region. Here, we present a reconstruction of the glacial fluctuations using Terrestrial Cosmogenic Nuclides (10Be) dating of boulders resting on moraines and other glacial landforms that make up the moraine complex in the forefield of the Universidad Glacier (34 degrees S). This massive and chaotic-looking moraine was built during the latest Holocene ice advances and subsequent decay of the Universidad Glacier to its present position. Geomorphological mapping and 10Be surface exposure ages (n = 20) show that the Universidad Glacier advanced at least twice to nearly the same maximum extent, first by the 13th to 16th centuries and then by the early to the mid-19th century. Since then, eight moraine ridges denote a rather active and gradual ice demise. We interpret the glacier advances as a response to an equatorward shift of the SWW linked to a long-term negative phase of the Southern Annular Mode (SAM), which embraced net humid and cold atmospheric conditions in central Chile between the 13th century and the mid-19th century. Our glacier chronology is comparable to others from Patagonia and New Zealand, altogether exposing the culmination of the latest Holocene glacial maximum by the mid-19th century, before overall ice decay in a global warming world, with accelerated ice loss since the mid-20th century. (c) 2022 Elsevier Ltd. All rights reserved.
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    Glacial geomorphology of the former Patagonian Ice Sheet (44-46 °S)
    (2021) Cooper, Emma-Louise; Thorndycraft, Varyl R.; Davies, Bethan J.; Palmer, Adrian P.; Garcia, Juan-Luis
    We map the glacial geomorphology of the former Patagonian Ice Sheet between 44 degrees S and 46 degrees S. Building on previous work, our map covers a similar to 50,000 km(2) region of west-central Patagonia. The study area includes the eastward-flowing Rio Pico, Rio Caceres, Rio Cisnes, Lago Plata-Fontana, El Toqui, Lago Coyt/Rio Nirehuao, Simpson/Paso Coyhaique, and Balmaceda palaeo-outlet glaciers, adjacent valleys, and the Andean Cordillera. The inventory contains >70,000 individual landforms mapped from remotely-sensed imagery and field surveys. Mapping was classified into ice-marginal (e.g. moraine ridges, trimlines), subglacial (e.g. glacial lineations, flutes), glaciolacustrine (e.g. palaeolake shorelines, perched deltas), glaciofluvial (e.g. proglacial outwash plains, meltwater channels), and non-glacial (e.g. palaeochannels, landslides or slumps) landform groups. The new map will inform future interpretations of regional glacier dynamics, and the development of robust geochronological datasets that test the timing of glaciation and deglaciation.
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    Resolving the paradox of conflicting glacial chronologies: Reconstructing the pattern of deglaciation of the Magellan cordilleran ice dome (53-54°S) during the last glacial - interglacial transition
    (2024) Mcculloch, Robert D.; Bentley, Michael J.; Fabel, Derek; Fernandez-Navarro, Hans; Garcia, Juan-Luis; Hein, Andrew S.; Huynh, Carla; Jamieson, Stewart S. R.; Lira, Maria-Paz; Luethgens, Christopher; Nield, Grace A.; Roman, Manuel San; Tisdall, Eileen W.
    Raised shorelines and associated lacustrine sediments in the central Estrecho de Magallanes (Strait of Magellan) have been interpreted as products of cordilleran glaciers impounding a large proglacial lake and preventing drainage to the South Pacific and Southern Ocean during the Late glacial between c. 15.0 and 12.0 cal ka BP. However, a growing body of glacial geological evidence points towards an earlier retreat of the Magellan cordilleran ice dome, insufficient to dam lakes at that time. We critically re-evaluate the extant evidence for the c. 15.0-12.0 cal ka BP lake, here named 'Lago Kawesqar', and provide further sedimentological and chronological evidence for its existence. We also provide new cosmogenic surface nuclide dating of erratic and bedrock samples collected from extensive field campaigns that confirm the rapid and widespread retreat of the Magellan ice fields to the inner fjords of the Fuegian archipelago by c. 16.0 ka. To resolve the apparent paradox between these two lines of evidence we propose that glacial isostatic adjustment led to a topographic barrier to lake drainage rather than an ice dam. We use Glacial Isostatic Adjustment modelling to demonstrate that rapid isostatic recovery following the early deglaciation after c. 17.0 cal ka BP likely led to elevation of the present shallow south-western coastal margin of the Fuegian archipelago. Final drainage of Lago Kawesqar was probably caused by neotectonic subsidence of the same margin along the boundary of the South American - Scotia tectonic plates at c. 12.0 cal ka BP.
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    Spatial analysis of paleoclimate variations based on proxy records in the south-central Andes (18°-35° S) from 32 to 4 ka
    (2023) Orellana, Hector; Latorre, Claudio; Garcia, Juan-Luis; Lambert, Fabrice
    The long-term climate dynamics of the central Andes are part of an ongoing international research effort to reconstruct past climatic variations and sensitivity to different regional and global drivers during the last 50,000 years. The large number of diverse records, however, makes it difficult to compare results without an integrated spatial analysis that considers the nature of the record and whether they are integrating environmental conditions across a large basin (i.e., a lake record) or at a very local scale (such as a rodent midden). We compiled 92 records from the southern sector of the central Andes (SCA, 18 & DEG;- 35 & DEG;S). Recalibrated records were further compared by converting the original author's interpretation into a scale of relative moisture anomalies (compared to the present) that ranges from -2 (very dry) to very wet (+2). Moisture anomaly maps were generated for intervals at 4, 6, 9.5,14, 17, 21 and 32 ka BP (103 calibrated 14C years before present) using records within a 5% age uncertainty. Our compilations show a surprising degree of agreement in the extent and magnitude of past climate changes during late Pleis-tocene, but less spatial agreement during the Holocene. The TRACE21 transient climate model shows similar results, with better agreement during the Pleistocene compared to the Holocene. Our analyses not only reveal discrepancies between proxy record interpretations at sites from the same region but show which regions in the SCA require more study. & COPY; 2023 Elsevier Ltd. All rights reserved.
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    The Last Glacial Maximum and Deglacial History of the Seno Skyring Ice Lobe (52°S), Southern Patagonia
    (2022) Lira, Maria-Paz; Garcia, Juan-Luis; Bentley, Michael J.; Jamieson, Stewart S. R.; Darvill, Christopher M.; Hein, Andrew S.; Fernandez, Hans; Rodes, Angel; Fabel, Derek; Smedley, Rachel K.; Binnie, Steven A.
    There are still many uncertainties about the climatic forcing that drove the glacier fluctuations of the Patagonian Ice Sheet (PIS, 38-55 degrees S) during the last glacial period. A key source of uncertainty is the asynchrony of ice lobe fluctuations between the northern, central, and southern PIS. To fully understand the regional trends requires careful mapping and extensive geochronological studies. This paper presents geomorphological and geochronological reconstructions of the glacial and deglacial landforms formed during the last glacial period at the Seno Skyring lobe, southernmost Patagonia (52 degrees S, 71 degrees W). We present a detailed geomorphological map, where we identify two moraine systems. The outer and older is named Laguna Blanca (LB) and the inner Rio Verde (RV). The LB moraines were built subaerially, whereas parts of the RV were deposited subaqueously under the palaeo lake Laguna Blanca, which developed during deglaciation. We conducted surface exposure Be-10 dating methods on boulder samples collected from LB and RV glacial margins. The moraine LB III and LB IV formed at 26.3 +/- 2.3 ka (n = 5) and 24.3 +/- 0.9 ka (n = 3), respectively. For the inner RV moraine, we obtained an age of 18.7 +/- 1.5 ka (n = 6). For the palaeo Laguna Blanca evolution, we performed Be-10 exposure ages on shoreline berms and optically stimulated luminesce dating to constrain the lake levels, and Be-10 depth profile dating on an outwash deposit formed by a partial lake drainage event, which occurred at 22 +/- 3 ka. For the RV moraine deglaciation, we performed radiocarbon dating of basal sediments in a peat bog, which indicates that the glacier retreated from the terminal RV moraine by at least c. 16.4 cal kyr BP. Our moraine geochronology shows an asynchrony in the maximum extents and a different pattern of ice advances between neighbouring lobes in southern Patagonia. We speculate that this may be due, at least in part, to the interaction between topography and the precipitation carried by the southern westerly wind belt. However, we found broad synchrony of glacial readvances contemporaneous with the RV moraine.
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    Vegetation, glacier, and climate changes before the global last glacial maximum in the Isla Grande de Chiloe, southern Chile (42° S)
    (2022) Gomez, Gabriel A.; Garcia, Juan-Luis; Villagran, Carolina; Luethgens, Christopher; Abarzua, Ana M.
    Climatic and vegetation features of the mid-latitudes of the Southern Hemisphere before the global Last Glacial Maximum (gLGM) are still a matter of discussion. The signatures of Marine Isotope Stage (MIS) 3 show strong variability at the poles that has not yet been resolved at lower latitudes. This work discusses one of the first terrestrial records that reflects the vegetation, glacier, and climate conditions in southern South America during this period. The stratigraphic, palynological, and geomorphological features of the Punta Pihuio, Rio Huicha, Punta Pirquen and Punta Detico sites (41-42 degrees S) on the Isla Grande de Chiloe (southern Chile) are described and discussed. Glacially sourced sediment intercalated with peat soils constrained by single-grain feldspar (SGIR50) luminescence and radiocarbon (C-14) dating show that the Late MIS 5 and the MIS 3 were periods of high environmental variability at these locations. Pollen records from peat layers indicate an open forest with conifers, Nothofagus and thermophilic elements, such as Myrtaceae, representing interstadial conditions that were abruptly interrupted by glacial expansions during stadials. High variability between arboreal and herbaceous taxa is also interpreted as environmental instability. Moreover, we show that the Patagonian Ice Sheet (PIS) reached full glacial extent during Early to Middle MIS 3, as is also observed in other Southern Hemisphere glacier records on both sides of the Pacific Ocean. Our data support that millennial-to multi-millennial-scale climate changes characterized the pre-gLGM not only at the poles, but also at the southern mid-latitudes. (C) 2021 Elsevier Ltd. All rights reserved.