Tendencias climáticas para los pastizales pampeanos durante el Pleistoceno tardío-Holoceno: estimaciones cuantitativas basadas en secuencias polínicas fósiles

Abstract

CLIMATIC TRENDS FOR THE PAMPA GRASSLANDS DURING THE LATE PLEISTOCENE-HOLOCENE: QUANTITATIVE ES- TIMATIONS BASED ON FOSSIL POLLEN SEQUENCES. Pollen-climate calibration models for mean annual temperature (Tan), annual precipitation (Pan) and precipitation efficiency (EP) are presented for the Pampa grasslands region (33o-41oS and 56o-67oW). The Pan and EP models were optimal (r2 boots =0,669 and 0,717; RMSEPboots= 16%) to apply Modern Analog Technique and to obtain late Pleistocene-Holocene quantitative climatic estimations ba- sed on fossil pollen from two alluvial sequences. In the central Pampa grasslands, Pan and EP values were 100 to 200 mm lower than present ones during the late Pleistocene (16000-12000 yr cal BP). During the Pleistocene- Holocene transition, early Holocene and late Holocene the values were similar to modern ones. In the southwest, Pan and EP values were c. 200 mm higher than present ones during the mid-Holocene (5500-3000 yr cal BP), and decreased during the late Holocene reaching similar modern values during the last 500 years cal. The climatic inferences agree with previous paleoclimatic interpretations that state dry to semiarid conditions during the la- te Pleistocene, and subhumid humid conditions during the Pleistocene-Holocene transition and early Holocene. However, there are discrepancies as from 5000 yr cal BP, probably related to the different sensitivity of the cli- mate proxy data. The NE-SW precipitation gradient during the last c. 5500 yr cal may have been steeper than at present. These estimations are the first quantitative climatic reconstructions for the Pampa grasslands region, and should be taken as trends until new reconstructions confirm them.