Environmental change since the Late Pleistocene in the eastern Patagonian Andes (46.5º S): insights from geomorphology and lake sediments.

Understanding Earth-surface processes at the margins of former ice sheets is key to reconstruct past environmental variability and anticipate landscape responses to climate change. The Meseta Chile Chico (71.6º-72.0º W, 46.5º-46.8 º S), a volcanic plateau in the eastern Patagonian Andes, offers key insights into glacial, tectonic, and climatic interactions. This study integrates landform characterizations and lacustrine sediment records from this region, to reconstruct environmental change from the Late Pleistocene throughout the Holocene. Geomorphological evidence shows that the rugged topography of the Meseta Chile Chico developed through enhanced erosion driven by tectonic uplift and glacial isostatic rebound at least since the Late Pliocene. During the Last Glacial Maximum, its surrounding valleys were glaciated while the plateau surface was shaped by periglacial processes such as freeze-thaw cycles and nivation. After deglaciation, slope instability increased along plateau margins due to paraglacial debuttressing and regional base-level changes. Thereafter, these processes became increasingly influenced by Holocene climatic variability. A continuous sediment record from Laguna Meseta, a lake on the plateau, reflects ca. 10,000 years of postglacial environmental change. High lake productivity persisted, since 10,000 until 5500 cal yr BP, when a marked increase in detrital input, linked to enhanced runoff, coincided with the Mid-Holocene glacier advance, documented across Patagonia. Additional insights come from Laguna Vogt, a lake on the southwestern margin of Meseta Chile Chico, which provides a high-resolution record of the last ca. 1600 years. Its sediments show that runoff-driven detrital input remained dominant into the Late Holocene. In contrast, between 1300-1000 and 750-250 cal yr BP, runoff markedly decreased, while periods of high lake productivity alternated with flooding events. These instable conditions suggest shifts between wet-cold and dry-warm phases and marked the onset of seasonality. At ca. 250 al yr BP, allochthonous input increased again, consistent with the last glacial advance of the Holocene. These environmental reconstructions suggest that high runoff intensities were mainly driven by precipitation. Combined with low temperatures, these conditions led to neoglacial stages associated with latitudinal shifts and expansion of the Southern Hemisphere Westerly Winds (SWW), as indicated by former regional studies. This correlation suggests that Holocene climate at the eastern margin of the Patagonian Andes was primarily controlled by the SWW, while intervals of enhanced seasonality played a key role on multi-centennial timescales. Overall, this integrated reconstruction highlights the complex interplay among tectonic forces, glacial, periglacial and postglacial activity, and atmospheric circulation in central west Patagonia. It underscores the value of combining geomorphology and sediment proxies to understand long-term environmental change and improve predictions of how such dynamic landscapes may respond to future climate shifts.