Lacustrine records of the Little Ice Age in Southern South America

PIOVANO, E.; CIOCCALE, M.; ARIZTEGUI, D.; ZANOR, G.; CÓRDOBA, F.

San Carlos de Bariloche

Congreso; IV Congreso Latinoamericano de Sedimentología - XI Reunión Argentina de Sedimentología.; 2006

Asociación Argentina de Sedimentología

The Little Ice Age (LIA) was the most recent period with a global increase of glacier extensions with predominance- but not necessarily constant - cooling condition over broad areas. In a pioneer contribution, Villalba (1994) proposed a warm period from AD 1080 to 1250 and a subsequent long cold period in southern South America (SSA) in coincidence with the LIA in the Northern Hemisphere. The clear paucity of complete, and well-dated Paleoclimate archives covering the LIA across SSA has been a major difficulty for depicting the regional environmental variability during this interval. Although the precise timing of the LIA is still a matter of debate, our contribution is focused on the comparison of contrasting hydrological balances across SSA, southward the Tropic of Capricorn (23.5° S) up to ca. 52° S. We reviewed the most significant published limnogeological and historical records, blending both climate archives for enlarging the environmental reconstructions for this time-window. Paleoclimate records were selected throughout a wide geographical range and climate regimes: a) Pampean plains; b) Andean Altiplano and Puna; c) Central and Southern Chile; and d) Northern Andean Patagonia and Extra Andean Southern Patagonia. SSA climate archives show a complex pattern of timing and climate variability during the LIA. There is, however, a noticeable antiphased hydrological balance at both sides of the Arid Diagonal, which extends across Argentina from the Atlantic coast at ca. 40-42° S up to the eastern flank of the Central Andes at 25-27° S. Today, the southern portion of the Arid Diagonal corresponds to the interphase between two different and dominant atmospheric circulation systems: a) the northernmost influence of the Westerlies, with prevailing winter precipitation, and b) the southernmost influence of the subtropical low-level jet associated to the South America Monsoonal system, with prevailing summer precipitation. Numerous paleohydrological reconstructions -based on sedimentological, geochemical, and isotope proxiessuggest high lake levels and, hence, wet conditions during the LIA, southward and westward of the Diagonal Arida (i.e., Patagonia, central and southern Chile) as well as part of the Andean Altiplano and Puna. Conversely, this cold climate phase in the Pampean plains was represented by very low lake levels as the result of pervasive draught. The antiphased cold-wet vs. cold-dry hydrological conditions at different latitudes in SSA reveal that increased rainfall triggered by intensified Westerlies are synchronous with dry conditions resulting from a diminished monsoonal activity. Several forcing factors determine the increase or decrease of moisture transport from the tropics into the Pampean plains. Ongoing limnogeological studies in Salinas de Ambargasta (29° S - 64° W) and lagunas Mar Chiquita (30° S - 62° W), Melincué (33° S - 61°W) and Encadenadas del Oeste de Buenos Aires (37 °S - 62°W) may help to disentangle the mechanisms behind the most recent and past climate variability in the subtropics of South America.