Paleolimnology of Lago Pichilaguna over the past ∼12,600 years based on a fine-resolution diatom record, northwestern Patagonia (41°S)

The Pacific sector of Northwestern Patagonia (NWP, 40°-44°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 closed-basin 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. •A diatom record from Lago Pichilaguna tracks southern westerly wind (SWW) activity since ∼12.6 cal ka BP.•Positive hydrologic balance prevailed between ∼12.6–11.4 cal ka BP and ∼5.7-0 cal ka BP under strong SWW.•A distinct negative hydrologic balance occurred between ∼11.4–6.9 cal ka BP under a SWW minimum.•Centennial-scale variability in SWW influence started at ∼5.7 cal ka BP and lingers until the present.•Terrestrial and aquatic ecosystems covaried in response to SWW variations since ∼12.6 cal ka BP.