Paleoecology of the southern Chilean Lake District-Isla Grande de Chiloe during middle-late Llanquihue glaciation and deglaciation

Subantarctic Parkland and Subantarctic-North Patagonian Evergreen Forest, e mbracing >40,000 C-14 years of middle and late Llanquihue glaciation, are r econstructed from pollen contained in multiple interdrift deposits and core s of lake sediments. The subantarctic plant communities at low elevations h ave since been replaced by temperate Valdivian Evergreen Forest. Data in su pport of the vegetation reconstruction derive from close-interval sampling (>1400 pollen analysed stratigraphic levels) and high-resolution chronology (>200 AMS and conventional radiocarbon-dated horizons). Pollen sequences a re from 15 sites, eight of which are exposures and seven mires,located in r elation to lobes of piedmont glaciers that occupied Lago Llanquihue, Seno R eloncavi, Golfo de Ancud, and the east-central sector of Isla Grande de Chi loe at the northern limit of the Golfo Corcovado lobe. Recurring episodes of grass maxima representing Subantarctic Parkland,when grass and scrub became widespread among patches of southern beech (Nothofag us), bear a relationship to glacial advances. The implication of the maxima , prominent with advances at 22,400 and 14,800 C-14 yr sp during late Llanq uihue glaciation in marine oxygen-isotope Stage 2, is of successive interva ls of cold climate with summer temperatures estimated at 6-8 degrees C belo w the modem mean. The earliest recorded maximum at >50,000 C-14 yr sp is po ssibly during late Stage 4. At the time of middle Llanquihue glaciation in Stage 3,cool, humid interstades on Isla Grande de Chiloe with Subantarctic Evergreen Forest, which under progressive cooling after 47,000 C-14 yr sp w as increasingly replaced by parkland. During stepwise deglaciation, when tr ansitional beech woodland communities supplanting parkland became diversifi ed by formation of thermophilous North Patagonian Evergreen Forest, warming in the order of 5-6 degrees C was abrupt after 14,000 C-14 yr BP. Closed-c anopy North Patagonian Evergreen Forest was established by 12,500 C-14 yr s p. Later, after c. 12,000 until 10,000 C-14 yr sp, depending on location, f orest at low elevations became modified by expansion of a cold-tolerant ele ment indicative of less than or equal to 2-3 degrees C cooler climate. This stepwise climatic sequence is seen at all late-glacial sites. Cool, humid interstadial conditions, punctuated by cold stadial climate, ar e characteristic of the last >40,000 C-14 years of the Pleistocene at midla titude in the Southern Hemisphere. Pollen sequences from southern South Ame rica and terrestrial-marine records from the New Zealand-Tasmania sector ex press a broad measure of synchrony of vegetational/climatic change for mari ne oxygen-isotope Stages 2-3. The data, combined with the timing of glacial maxima in the Southern Andes, Southern Alps of New Zealand, and in the Nor thern Hemisphere, are indicative of synchronous, millennial-scale, midlatit ude climatic changes in the polar hemispheres.