Freshwater diatom evidence for Southern Westerly Wind evolution since-18 ka in northwestern Patagonia
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Date
2023
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Abstract
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.
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Freshwater diatoms, Patagonia, Southern westerly winds, Last glacial termination, Holocene, Hydrologic balance, Millennial and centennial-scale variability