Culmination and demise of the Northern Patagonian Ice Sheet (43°S) during the last glacial-interglacial transition

Deciphering the timing and regional extent of abrupt climate events during the last glacial cycle is critical for identifying causes and mechanisms responsible for large magnitude climate events. Previous studies in the Chilean Lake District and northern Isla Grande de Chiloé (40°-42°S) have provided key insights regarding the sequence of climate events, and their interhemispheric linkages during the Last Glacial Maximum (LGM: 30 - 18 ka; ka: thousands of years BP). Substantially less detailed information, however, is available about the sequence of glacial fluctuations during the last glacial termination (=T1) (T1: 18 - 11.5 ka), one of the largest climate changes since 600 ka. The existing information for this region suggested that the ice sheet retreated near the headwalls in the Andes prior to 16.7 ka, suggesting an abrupt and uninterrupted glacial collapse of piedmont glacier lobes from Northwestern Patagonia (NWP) following the LGM. Here, we present new glacial geomorphic maps and radiocarbon dates from Golfo Corcovado, an insufficiently studied lowland sector of NWP ( 42°S - 43°S) during T1. Our data suggest that the Golfo Corcovado ice lobe (i) abandoned its LGM position at 17.8 ka, then (ii) stabilized between 20-35 km from its maximum position until 16.8 ka, forming the Castro ice-dammed lake ( 100 m asl). Finally, (iii) the Golfo Corcovado ice lobe withdrew abruptly draining the Castro ice-dammed lake and retreating another 70 km deep into the Andes at 16.7 ka. Additionally, we have evidence from a small valley glacier, a tributary of the Palena ice lobe (43°S), that the ice front readvanced at 13.6 ka, during the Antarctic Cold Reversal. We explore potential mechanisms responsible for the observed glacial fluctuations by comparing our glacial chronology with paleoclimate records from the region.