3 LATE QUATERNARY POLLEN DIAGRAMS FROM SOUTHERN PATAGONIA AND THEIR PALEOECOLOGICAL IMPLICATIONS

Diagrams of fossil pollen in three deposits postdating glacial recession of the last ice age provide an account of late-glacial and Holocene vegetation and palaeoclimate in Southern Patagonia. Sites are mires, located along the Estrecho de Magallanes at Punta Arenas (53 degrees 09'S, 70 degrees 57'W) and Puerto del Hambre (53 degrees 36'S, 70 degrees 55'W), and an intermittent lake, some 300 km to the north, at Torres del Paine (50 degrees 59'S, 72 degrees 40'W). Chronostratigraphy is controlled by 20 radiocarbon dates, the oldest site (Puerto del Hambre) covering close to 16 000 years. Charcoal from the sites and carbonate (Torres del Paine), as well as tephra layers and an instance of marine incursion (Puerto del Hambre), supply additional data of interpretive value. Accompanying the fossil pollen records is a reference survey of modern pollen fallout from 43 surface sample localities. Late-glacial vegetation during deglaciation consisted mostly of tundra, dominated by communities of Empetrum, Acaena, Gunnera, and Tubuliflorae (Compositae), under a relatively cold, dry climate. Nothofagus, although present in numbers initially at Puerto del Hambre, did not expand until the close of the late-glacial; at Punta Arenas, expansion of Nothofagus was episodic, occurring during apparent warmer intervals of the last three millennia of steppe-tundra. Holocene vegetation is depicted at first as a patchwork of Nothofagus woodland and steppe subject to climate of relative warmth and limited moisture, except at Torres del Paine, where moisture levels were apparently higher than at sites to the south. Closed Nothofagus forest communities, subsequently, are best developed in the late Holocene under a climate with generally cooler, wetter parameters. Fire, believed to be caused mostly by Palaeoindians, has had an important role in shaping vegetation sequences in the Holocene. Formidable, however, in the development of vegetation are the latitudinal displacements/variable intensities of atmospheric conditions caused by shifting storm tracks of the Southern Westerlies.