Browsing by Author "Moreno, Patricio I."
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- ItemA 15,400-year long record of vegetation, fire-regime, and climate changes from the northern Patagonian Andes(2019) Jara, Ignacio A.; Moreno, Patricio I.; Alloway, Brent V.; Newnham, Rewi M.Paleoecological studies from the northern Patagonian Andes (40-44 degrees S) have identified past changes in vegetation, fire regimes and paleoclimate since the last glaciation, including variations in strength and position of the Southern Westerly Winds (SWW). The extent to which records west and east of the Andes provide a congruent paleoclimatic history, however, has not been explored in detail in the literature. Physical and biological contrasts are evident between these regions today and are to be expected in paleoclimate reconstructions. In this context, we present pollen and charcoal records from sediment cores collected in Lago Espejo, a small closed-basin lake located in the core sector of the northern Patagonian Andes that spans uninterrupted the last similar to 15,400 years. Following glacier withdrawal, the vegetation surrounding Lago Espejo features scattered Nothofagus woodlands, including relatively thermophilous rainforest trees between similar to 15,400 and 14,400 cal yr BP. The disappearance of these trees and an abrupt rise in Nothofagus at similar to 14,400 cal yr BP mark the establishment of closed-canopy forests during the Antarctic Cold Reversal, followed by increases in the cold-tolerant hygrophilous conifer Podocarpus nubigena during the Younger Dryas (similar to 12,700-11,500 cal yr BP). The Holocene vegetation consists of Nothofagus-dominated forests with modest variation in composition and structure until the present, attesting to the resilience of these forest communities to climate change and natural disturbance regimes. Rapid deforestation, anthropogenic fires and the establishment of artificial meadows with exotic herbs introduced by Europeans at similar to 150 cal yr BP, triggered a rapid, large-magnitude landscape transformation unprecedented in the last 14,000 years. The timing and structure of vegetation changes revealed by the Lago Espejo record suggest that changes in the SWW were the main driver of vegetation and fire regimes in the Andes of northern Patagonia over the last 15,400 years. Comparison between multiple reconstructions from northern Patagonia reveals overall coherent vegetation and fire regime changes in the western and Andean sectors, and a spatially variable and more divergent behaviour in sites located further east. This spatial patter is akin to the present-day correlation between precipitation and SWW in this region. (C) 2019 Elsevier Ltd. All rights reserved.
- ItemEnvironmental evolution of western Tierra del Fuego (∼54°S) since ice-free conditions and its zonal/hemispheric implications(2023) Moreno, Patricio I.; Lambert, Fabrice; Hernández, Loreto; Villa Martínez, Rodrigo P.By virtue of its position adjacent to the Drake Passage, Tierra del Fuego in South America allows examining the vegetation and environmental history of the southernmost continental landmass outside Antarctica, and the evolution of the Southern Westerly Winds-Southern Ocean (SWW–SO) coupled system since the Last Glacial Maximum (LGM). For that purpose, we studied sediment cores from Lago Charquito, a small closed-basin lake in central-west Tierra del Fuego with a continuous lacustrine record since ~17.3 ka. Ice-free conditions at the site imply a ~70 km retreat of the Bahía Inútil glacier lobe from its LGM position during a ~800-year interval, a trend that continued until its disappearance ~100 km upstream from L. Charquito, ~800 years later. Our palynological data show an open landscape dominated by cold-tolerant shrubs and herbs between ~17.3–12.9 ka, with increases in precipitation of SWW origin at ~16.3 ka, ~14.7 ka, between ~8.7–7.6 ka, and after ~6.8 ka. Warming at ~12.9 ka initiated an abrupt afforestation trend that stalled during the early Holocene (~12–8.7 ka) owing to a precipitation decline and wildfires, and later resumed in response to invigorated SWW. We hypothesize that sparse Nothofagus tree populations inhabited the periphery of the Patagonian Ice Sheet (PIS) during the LGM and migrated toward the Andes contemporaneous with glacier recession as temperature rose during the Last Glacial Termination (T1). We posit that besides establishing topographic and climatic barriers for land biota, the PIS enabled the connectivity of cold-tolerant hygrophilous plant populations along a humid fringe adjacent to its land-based perimeter, despite the presumably dry conditions downwind from the eastern PIS margin. Our results suggest that southward shifts or expansion of the SWW toward or beyond Tierra del Fuego enhanced upwelling and ventilation of deep waters in the SO, northward shifts or weakening had the opposite effect. We observe that the time evolution of atmospheric CO2 concentrations, high-latitude air and sea-surface temperatures, and sea level during T1 fall short in explaining the timing and abruptness of the Bahía Inútil glacier lobe collapse, and quite possibly multiple other glacier lobes from the PIS.
- ItemFreshwater diatom evidence for Southern Westerly Wind evolution since-18 ka in northwestern Patagonia(2023) Diaz, Carolina; Moreno, Patricio I.; Villacis, Leonardo A.; Sepulveda-Zuniga, Einer A.; Maidana, Nora I.We report a fossil diatom record from small closed-basin Lago Lepue ' (43 degrees S) to examine past changes in freshwater ecosystems and hydrologic balance in northwestern Patagonia since-18 ka. The record starts with abundant staurosiroids and the heavily silicified Aulacoseira granulata suggesting deep turbulent mixing during a low lake level stand between -18-16.4 ka. A. distans increased shortly after-16.4 ka and achieved maximum abundance between-15.4-13.6 ka, while A. granulata disappeared at-15.8 ka and A. alpigena rose at-14.9 ka to its maximum between-13-12 ka. We infer turbulent, cold, and circumneutral to slightly acid lake conditions contemporaneous with a steady lake level rise that started at-16.4 ka and culminated between-13-12 ka. These trends reversed between-11-7.8 ka with the dominance of Discostella stelligera and staurosiroids, suggesting warmer lake conditions and shallower mixing. Subsequent changes include increases of A. distans with D. stelligera between-7.8-5.8 ka, dominance of the former between-5.8-3.3 ka, a rapid increase in A. perglabra at-3.3 ka, and ensuing diversification of benthic acidophilous species. We infer a rapid lake-level decline between-11-7.8 ka, with subsequent rising pulses at-7.8 ka and-5.8 ka, a multimillennial-scale lake acidification trend, and overall high lake levels with centennial-scale reversals between-6-0 ka. Coherent variations in terrestrial and aquatic ecosystem changes recorded in the same core suggest negative hydrologic balance between-18-16.4 ka and-11-7.8 ka, positive balance between-14.9-12 ka and-6-0 ka, with transitional conditions in the interim, overprinted by millennial-scale changes and enhanced variability since-6 ka. Covariation with paleoclimate records at regional, pan-Patagonian, and hemispheric scale suggests millennial to centennial-scale variability superimposed upon a multi-millennial pacing of Southern Westerly Wind evolution since-18 ka.
- 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 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
- ItemNew perspectives on ice forcing in continental arc magma plumbing systems(2024) Singer, Brad S.; Moreno-Yaeger, Pablo; Townsend, Meredith; Huber, Christian; Cuzzone, Joshua; Edwards, Benjamin R.; Romero, Matias; Orellana-Salazar, Yasmeen; Marcott, Shaun A.; Breunig, Rachel E.; Ferrier, Ken L.; Scholz, Kathryn; Coonin, Allie N.; Alloway, Brent V.; Tremblay, Marissa M.; Stevens, Sally; Fustos-Toribio, Ivo; Moreno, Patricio I.; Vera, Franco; Amigo, AlvaroDetermining how and why eruptive outputs are modulated by the loading and unloading of ice is key to understanding whether ongoing and accelerating deglaciation across mid- to high-latitudes will impact future activity at many volcanoes. Here, we address two central questions. First, does decompression of the upper crust during rapid thinning of ice sheets propel increases in eruption rates? Second, does surface loading during ice sheet growth, followed by rapid unloading during deglaciation, promote changes in magma storage conditions and compositions within the underlying magma plumbing systems? To provide new perspectives on these questions, we address the mechanics and dynamics of ice sheet-arc magma plumbing system interactions at a regional-to-local scale within the Andean Southern Volcanic Zone. Here, piedmont glacier lobes, forming the northernmost extension of the Patagonian ice sheet, have enveloped dozens of large, active, composite volcanoes as these glaciers reached local thicknesses of nearly 2 km during the local Last Glacial Maximum (LGM) between similar to 35 and 18 ka, before retreating rapidly between 18 and 15 ka. Our multi-faceted review features a synthesis of existing and new field observations, laboratory measurements, and numerical simulations. Advances in Ar-40/Ar-39 radioisotopic and He-3 surface exposure geochronology, in conjunction with geologic mapping, facilitate reconstructions of volcanic eruptive histories spanning the last glacial-deglacial cycle and in places provide constraints on the thickness of ice at specific time slices. The magnitude and geometry of the glacial loading and unloading is captured in a climate model-driven numerical simulation that reveals spatial and temporal heterogeneities in the configuration of the northernmost Patagonian ice sheet retreat. Geological observations including dated moraine complexes, dated lava-ice contact features, and glacial erratic boulders at high altitude on volcano slopes, are consistent with this model. Deep valleys imply intense localized erosion on volcano flanks, and deposited sediment in nearby floodplains implies narrow regions of rapid sediment deposition. These observations, in conjunction with dated lava flows, provide constraints on rates and patterns of crustal loading and unloading by sediment redistribution.
- 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.
- 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 last two glacial cycles in central Patagonia: A precise record from the Nirehuao glacier lobe(2023) Peltier, Carly; Kaplan, Michael R.; Sagredo, Esteban A.; Moreno, Patricio I.; Araos, Jose; Birkel, Sean D.; Villa-Martinez, Rodrigo; Schwartz, Roseanne; Reynhout, Scott A.; Schaefer, Joerg M.Milankovitch orbital parameters control cycles of insolation, a primary pacer of long term changes in climate, but exactly how insolation signals are transmitted around the globe in the climate system is unclear. In order to address the fundamental questions of when and how ice age climates begin and end, how fast glaciers retreated during the last deglaciation, and how glaciers behaved before anthropogenic influence, we need robust glacial chronologies. The timing of local glacial maxima beyond the last glacial cycle, however, has remained largely unconstrained due to moraine degradation over time, limiting our ability to fully explore these questions. By developing a detailed geomorphic surficial map and targeting relatively tall, ridge-top boulders, we have constructed a new, precise 10Be chronology of glacial maxima of the Nirehuao glacier lobe (45 degrees S) for the last two glacial cycles. We report one of the first directly dated records of a MIS 6 glacier advance in Patagonia, which formed a major set of moraines by at least 153 +/- 5.1 ka, with a stillstand or smaller readvance by 137 +/- 4.2 ka, corresponding to the two coldest and dustiest periods of MIS 6 in Antarctica. The next largest advance occurred at 23.6 +/- 0.9 ka, at the end of peak Southern Hemisphere MIS 2 cooling. Retreat of the glacier commenced by similar to 18.5 cal ka BP when lakes in a tributary valley just to the southwest became ice-free. Overall we find that advances of the Nirehuao glacier lobe occur when winter sea ice around Antarctica is expansive and both obliquity and eccentricity are at their minima. (c) 2022 Published by Elsevier Ltd.
- 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.
- ItemVegetation, disturbance, and climate history since the onset of ice-free conditions in the Lago Rosselot sector of Chiloe continental (44°S), northwestern Patagonia(2021) Moreno, Patricio I.; Videla, Javiera; Kaffman, Maria Jose; Henriquez, Carla A.; Sagredo, Esteban A.; Jara-Arancio, Paola; Alloway, Brent V.We present results from Lago Negro, a small closed-basin lake adjacent to Lago Rosselot, to examine the vegetation and environmental history of an insufficiently studied sector of Chiloe Continental (41 degrees 30'-44 degrees S) in northwestern Patagonia. Lake sediment cores from Lago Negro reveal 27 tephra deposited since similar to 12.7 ka, including two prominent rhyodacite tephra marker beds erupted from Volcan Melimoyu, and a stratified basal clastic unit we attribute to meltwater discharge from an ice tongue that originated from Monte Queulat and covered Lago Rosselot during its expanded position, presumably Antarctic Cold Reversal in age. The pollen record shows closed-canopy North Patagonian rainforests since similar to 12.7 ka, with variations in species composition and structure that suggest dynamic responses of the vegetation to past environmental changes. Vegetation responses to climate in the Lago Negro record were modulated, sometimes interrupted, by high magnitude and frequent disturbance regimes, most notably during maxima in explosive volcanic activity (similar to 9.5-7.2 ka and similar to 3.6-1.6 ka) and heightened fire activity.