Chronology of the last glaciation in central Strait of Magellan and Bahia Inutil, southernmost South America

Abstract

Glacier fluctuations in the Strait of Magellan tell of the climatic changes that affected southern latitudes at c. 53–55°S during the Last Glacial Maximum (LGM) and Late-glacial/Holocene transition. Here we present a revised chronology based on cosmogenic isotope analysis, amino acid racemisation and tephrochronology. We unpick the effect of bedrock-derived lignite which has affected many new and revised dates that constrain five glacier advances (A to E). Advance A is prior to the LGM. LGM is represented by Advance B that reached and largely formed the arcuate peninsula Juan Mazia. Carbon-14 and 10Be dating show it occurred after 31 250 cal yrs BP and culminated at 25 200–23 100 cal yrs BP and was then followed by the slightly less extensive advance C sometime before 22 400–20 300 cal yrs BP. This pattern of an early maximum is found elsewhere in South America and more widely. Stage D, considerably less extensive, culminated sometime before 17 700–17 600 cal yrs BP and was followed by rapid and widespread glacier retreat. Advance E, which dammed a lake, spanned 15 500–11 770 cal yrs BP overlaps the Bølling–Allerød interstadials and the glacier retreat occurs during the peak of the Younger Dryas stadial in the northern hemisphere. However, the stage E advance coincides with the Antarctic Cold Reversal (c. 14 800–12 700 cal yrs BP) and may indicate that some millennial-scale climatic fluctuations in the Late-glacial period are out of phase between the northern and southern hemispheres.