PALEOENVIRONMENTS AND PALEOCLIMATES IN TIERRA-DEL-FUEGO AND SOUTHERNMOST PATAGONIA, SOUTH-AMERICA

A continuous paleoclimatic history for the past 14,000 years is presen ted based on palynological records from south of latitude 50-degrees-S in South America. Prior to 12,500 yr B.P. dry Empetrum heathlands, no t mesic tundra, dominated throughout the high southern latitudes, indi cating high winds, annual precipitation of less than 300 mm, and freez ing temperatures year-round. After 12,500 yr B.P. steppe replaced the heathlands, suggesting decrease in wind intensity, increase in effecti ve moisture, and increase in temperatures. When forests expanded at 90 00 yr B.P. along the rainward side, and at 8000 yr B.P. in the rainsha dow side of the Andes, precipitation reached Holocene levels. Judging from the greater openness of the early Holocene forests, including tho se in the rainward part of the region precipitation levels probably ra nged between 500 and 800 mm, comparable to those from today's forest/s teppe transition. After a pronounced mid-Holocene dry event, the late Holocene forests appeared more closed than the early Holocene forests, suggesting greater effective moisture, probably related to cooler tem peratures. The high latitude paleoclimatic history differs from that o f lower latitudes as far as the actual amplitude of change and the cli matic signal is concerned. Low moisture levels prior to 12,500 yr B.P. between latitudes 45-degrees and 55-degrees-S suggest that the wester ly stormtracks responsible for precipitation patterns in southern Sout h America may have been located year-round closer to the equator than today. The precipitation increase at 12,500 yr B.P. that extended only as far south as 50-degrees-S, indicates that the stormtracks had shif ted poleward, but did not reach Tierra del Fuego. By 9000 yr B.P. the stormtracks had shifted to the high southern latitudes, but the large seasonal latitudinal shift comparable to the modem situation - equator wards in winter and polewards in summer - did not develop until after 4500 yr B.P.