A GLACIAL GEOCHRONOLOGIC RECORD OF ICE RETREAT IN BAHÍA PENHOAT, CHILE: IMPLICATIONS FOR THE LAST ICE-AGE TERMINATION IN SOUTH AMERICA

What causes ice-age terminations? The longstanding view is that global climate conditions are controlled by the local intensity of summertime insolation in the high-latitude northern hemisphere. Thus, ice ages, including their terminations, should occur asynchronously between the northern and southern hemispheres. However, this hypothesis cannot account for evidence of synchronous global climate shifts. A new hypothesis (the Zealandia Switch) invokes shifting of the Southern Hemisphere Westerlies as a means of driving globally synchronous ice-age terminations. Here, we present preliminary glacial geochronologic data from Bahía Penhoat (55°S, 69°W), Chile, to test the Zealandia Switch and other hypotheses of the cause of the last termination in the Southern Hemisphere. There are few highly-resolved glacial records south of 50°S spanning the most recent termination, making this new record key to tracking past climate changes at hemispheric and global scales. To carry out this work, we use ¹⁰Be surface exposure dating techniques, along with UAV-derived geomorphological mapping. In addition, we compare the results with glacial geologic data previously collected in South America and New Zealand, as well as with records of the westerly winds and atmospheric carbon dioxide variations to assess the driving mechanisms of the last termination.

Bahía Penhoat lies within Isla Hoste, south of Cordillera Darwin ice field. We have identified through satellite imagery, field observation, and drone work, a series of well-defined moraines that show a comprehensive structure of the last termination in the region. Glaciers in this area are controlled heavily by the Southern Hemisphere Westerlies; therefore, understanding their geomorphic record reflects westerly wind behavior in the Southern Hemisphere. Through regional and global comparison to other glacial extent records, we will better understand the climate drivers of ice ages and their terminations.