Depositional processes of varved sediments from proglacial Lago Frías since 1800 CE (North Patagonian Andes, Argentina)

The glacierized Valle Frías in Northern Patagonia is one of the best‐studied valleys in South America and includes varved sediments from Lago Frías. We complement this lacustrine record with a high‐resolution documentation of varve counts and their composition. Geochemical and grain size analyses support their interpretation as proglacial varves attributed to over‐ and interflows resulting from snow‐ and glacier melt. Integration of radiometric, tephra and historic ages with microfacies analyses and semi‐automatic varve counting utilizing high‐resolution images obtained by computed tomography provides a calendar‐year chronology consisting of an upper (1960–2019 CE) and a floating lower varve chronology (1803–1893 CE). Intercalated between both varved sections are two event layers: a tephra resulting from the eruption of Volcán Calbuco (1893 CE) directly followed by an erosive mass‐wasting deposit associated with the Great Chilean Earthquake (1960 CE). Statistical comparison of varve‐thickness measurements with instrumental temperature data and dendroclimatological summer‐temperature reconstruction on an annual basis indicates only a weak temperature control on varve thickness. However, analysis of decadal means documents that the occurrence of thicker varves in the 21st century coincides with warmer summers.