Abstract

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.