Late Holocene Environmental Changes in the Western Pampas of Argentina Recorded in Sediments from a Water-Filled Deflation Pan

ISABEL VILANOVA; KARSTEN SCHITTEK; MATHIAS GEILENKIRCHEN; WILFRIED SCHULZ

Tunuyán

Conferencia; 4th Southern Deserts Conference; 2014

Universidad Nacional de Cuyo

We present a multi-proxy record from Laguna Nassau (33° 57´S, 65° 21´W) in order to reconstruct paleoenvironmental and paleoclimatic variations in the Western Pampas for the last ca. 1100 years. The palynological, charcoal, and geochemical analyses reflect three principal environmental settings: (1) between ca. 1100-640 cal BP, dominant Typha stands settled in a shallow depression under moist conditions and marked the beginning of primary succession. The high charcoal accumulation rates (CHAR) suggest fire events with Typha litter biomass as fuel and semi-arid to arid conditions with dry phases and less frequent wet events. Variations in Fe are related to humic formation, whereas decreasing trends of Si can be related to erosion. (2) Between ca. 640-300 cal BP, oscillating Typha values suggest unstable water levels; peaks of Cyperaceae and increasing aquatic algae indicate water input, whereas oscillating CHAR reveal variable fire events. Opposing Fe and Si trends are related to biological activities in a deeper water body. These environmental conditions suggest higher climatic variability than before. (3) Between ca. 300-50 cal BP, higher Poaceae values suggest vegetation covering the surrounding dunes, increasing aquatics palynomorphs reflect deeper water level, and decreasing Typha coincides with a decrease in CHAR that suggests fewer fire events. The abrupt increase in Ca suggests the formation of carbonates. These environmental conditions reflect wet phases and less frequent dry events. Conditions from 1100 cal BP to ca. 700 cal BP are contemporaneous with the Medieval Climate Anomaly. At regional scale, it triggered dry and wet phases with different timing between eastern (humid) and western (dry) regions of the Pampean plain. The period between 300-50 cal BP is concurrent with the Little Ice Age, when Laguna Nassau records indicate a similar hydrological response to the northwestern region but behaves differently from the eastern and northeastern Pampean plain.