Browsing by Author "Villa-Martinez, R. P."

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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.