Vegetation change during the last glacial-interglacial transition in the modern forest-steppe ecotone of Central Patagonia (~46° S).

CARMEN MIRANDA ; WILLIAM HENRÍQUEZ; PATRICIO MORENO; ISABEL VILANOVA; RODRIGO VILLA-MARTINEZ

Punta Arenas

Congreso; VIII Southern Connection Congress; 2016

Universidad de Magallanes

Very little is known about the timing and extent of Andean glaciers and the glacial/deglacial vegetation in the Aysén region of Central Chilean Patagonia (44°-49°S), a key sector of the southern mid-latitudes to understand the tempo, mode and forcing mechanisms of climate change during the last glacial-interglacial transition (LGIT). Here we present palynological results from Lago Unco (45°34´29.4´´S; 71°43?7.6´´W, 756 masl), a small closed-basin lake located in the modern forest-steppe ecotone, in direct association with moraines deposited by the Coyhaique-Balmaceda piedmont glacier lobe during the last glacial maximum (LGM). The Unco record contains multiple tephras, the lowermost of which are Ho and MENo with calendar ages of 17.8 ka. This tephra duplet is an excellent chronostratigraphic marker for the onset of the LGIT in this Andean sector of central Patagonia. The pollen record features predominance of herbs and shrubs characteristic of cold alpine environments and the Patagonian steppe between 12-18 ka, along with increasing Nothofagus and persistence of the hygrophilous, cold-resistant Gunnera, Drymis and the conifer Fitzroya/Pilgerodendron. This non-analogue assemblage suggests cold and hyperhumid conditions east of the Andes at the commencement of the LGIT. The early appearance of hygrophilous taxa (characteristic of the modern rainforest vegetation along the Pacific coast of Patagonia) in Lago Unco suggests that hygrophilous vegetation thrived along the eastern glacier margins during the LGM and may have been a source for the postglacial colonization of the Pacific coastal environments. Our results and interpretations challenge traditional paleoclimate and biogeographic inferences for this region during the LGIT.