Abstract

Glacier fluctuations in the Strait of Magellan tell of the climatic changes that affected southern latitudes at c. 53-55 degrees S during the Last Glacial Maximum (LGM) and Late-glacial/Holocene transition. Here we present a revised chronology based on cosmogenic isotope analysis, C-14 assays, amino acid racemisation and tephrochronology. We unpick the effect of bedrock-derived lignite which has affected many C-14 dates in the past and synthesise 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 Be-10 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 15500-11770 cal yrs Bp. This latter advance overlaps the Bolling-Allerod 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.