Browsing by Author "Villacis, L. A."

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    A freshwater diatom perspective on the evolution of the southern westerlies for the past-14,000 years in southwestern Patagonia
    (2023) Villacis, L. A.; Moreno, P. I.; Vilanova, I.; Henriquez, C. A.; Henriquez, W. I.; Villa-Martinez, R. P.; Sepulveda-Zuniga, E. A.; Maidana, N. I.
    Conflicting, even opposite interpretations on the evolution of the Southern Westerly Winds (SWW) are evident in paleoenvironmental records from southwestern Patagonia since the last ice age. These di-vergences call for new approaches utilizing different, ideally independent indicators of paleoenvir-onmental/paleoclimatic change from sensitive sites in climatically relevant locations. Here we present a multidecadally resolved diatom record from Lago Cipreses (51 degrees S), a small closed-basin lake located in a bedrock depression along the eastern foothills of the southern Patagonian Andes. The hydrological balance evolution of this isolated lake affords a direct tie with SWW intensity in a mountainous sector where zonal wind strength and local precipitation are highly correlated. We detect cold-tolerant diatoms (small fragilarioids) between-14-11.9 cal. ka BP followed by a shift to planktonic assemblages (Discostella pseudostelligera, Aulacoseira spp.) under warmer Holocene conditions. Diatom assemblages indicative of stratified water-column conditions (Discostella pseudostelligera, Achnanthidium aff tepidaricola, Achnan-thidium sieminskae) reached their maximum stability between-9.1-7.4 cal. ka BP. Stronger water-column mixing is evident by an abrupt species turnover to Aulacoseira spp. between-7.4-3.1 cal. ka BP, super-imposed on centennial-scale alternations between assemblages since-6.1 cal. ka BP. Cold-tolerant di-atoms resurge at-3.1 cal. ka BP and persist until the present. Our record offers assemblage-based evidence we interpret as sub-centennial to multimillennial scale changes in hydroclimate indicative of: (i) strong SWW influence between-14-11.9 cal. ka BP, (ii) a transition between-11.9-11.3 cal. ka BP to weak SWW influence between-11.3-6.5 cal. ka BP, with a SWW minimum between-9.1-7.4 cal. ka BP, and (iii) strong SWW influence since-6.5 cal. ka BP, with a Holocene SWW maximum since-3.1 cal. ka BP. We posit that enhanced hydroclimate variability since-6.1 cal. ka BP attests to the onset of Southern Annular Mode-like changes at centennial-to sub-centennial timescales. We detect a remarkably coherent and synchronous response of terrestrial and aquatic ecosystems at local scale since-14 cal. ka BP, highlighting the overriding importance of variations in SWW influence in terrestrial and aquatic envi-ronments at multiple timescales.(c) 2022 Elsevier Ltd. All rights reserved.
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    Development of a temperate rainforest zonation on the Pacific slopes of the North Patagonian Andes since-18 ka
    (2024) Moreno, P. I.; Alloway, B. V.; Valenzuela, M.; Villacis, L. A.; Villa-Martinez, R. P.
    Few studies along the western slopes of the Andes in Northwestern Patagonia (NWP: 40 degrees-44 degrees S) allow examining vegetation development through environmental gradients in latitude and elevation along a time continuum since the Last Glacial Termination (T1, -18-11 ka). This complete biostratigraphic context is necessary for assessing the sequence, timing, rates, and direction of compositional/structural changes of the former vegetation, and for deciphering their environmental drivers. Here we report palynological results from two NWP sites spaced -22 km apart on the western Andean slopes, Caleta Puelche roadside section located near sea level and Lago Reflejos at mid elevations (-800 m a.s.l.) and assess their continuous records since local ice-free conditions against other NWP sites. We find that cold-tolerant early successional trees dominated the initial stages of vegetation development in the Seno Reloncav & iacute; lowlands (-18-17 ka), followed by thermophilous shade-tolerant North Patagonian rainforest (NPRF) trees, which achieved their maxima between -17 and 15 ka at low-elevations. A spread of cold- and shade-tolerant hygrophilous NPRF conifers ensued (-14.8-13 ka) reaching similar magnitude at lowand mid-elevations, interrupted by increases in trees favored by canopy fragmentation linked to fire and explosive volcanism (-13-11 ka). Thermophilous, shade-intolerant, summer-drought tolerant Valdivian rainforest (VRF) trees increased and achieved maxima between -10 and 8 ka, most notably in the lowlands, coeval with peak abundance of the NPRF conifers Fitzroya/Pilgerodendron and Podocarpus nubigena in mid-elevation Lago Reflejos, contemporaneous with their virtual disappearance near sea level. Widespread increases in coldtolerant hygrophilous NPRF trees occurred after -8 ka, followed by mixing of NPRF and VRF elements in the lowlands after -6.3 ka with centennial-scale alternations. Inter-site and regional coherences of our findings suggest that variations in Southern Westerly Wind influence, along with disturbance regimes of natural and human origin, have driven the composition, structure, dynamics, and zonation of temperate rainforests in NWP since T1. We observe that Lago Reflejos features the highest abundance of Fitzroya cupressoides at regional scale since -12 ka, attesting to the importance of mid-elevation Andean environments for the persistence of these highly valued trees in the context of postglacial climate evolution, shifts in fire regimes, volcanic, and human disturbance in NWP.
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    Paleolimnology of Lago Pichilaguna over the past 12,600 years based on a fine-resolution diatom record, northwestern Patagonia (41°S)
    (2024) Sepúlveda-Zúñiga, E. A.; Villacis, L. A.; Maidana, N. I.; Sagredo T., Esteban; Moreno, P. I.
    The Pacific sector of Northwestern Patagonia (NWP, 40 degrees-44 degrees S) is key for examining the interaction between climate variability, explosive volcanism, and human influences on southern mid-latitude ecosystems. A limited number of studies in this region, however, have focused on aquatic ecosystem and hydrologic balance (HB) changes throughout the Holocene. Here we report a fossil diatom record from Lago Pichilaguna, a small closedbasin lake located in the lowlands of the Chilean Lake District, that reveals prominent changes in species composition and functional groups since 12.6 cal ka BP. We interpret positive HB between 12.6-11.4 cal ka BP and from 5.7 cal ka BP until recent that alternate with negative HB between 11.4-6.9 cal ka BP. We observe centennial-scale fluctuations since 5.7 cal ka BP that culminate with a negative HB phase over the past 270 years. Coherent responses in terrestrial and aquatic ecosystems recorded in the Lago Pichilaguna sediments underscore the influence of variations in the Southern Westerly Winds in NWP from multimillennial to centennial timescales since 12.6 cal ka BP. These inferences replicate the timing and direction of changes from previous studies at regional, pan-Patagonian, and zonal scales. The magnitude and rapidity of changes in diatom assemblages that started at 0.2 cal ka BP exceeds the ranges of local natural variability since 12.6 cal ka BP. This abrupt change is associated with a negative HB phase at centennial timescale, deposition of a tephra layer, and large-scale disturbance by Chilean/European settlers.