Hydroclimatic variability during the last 2000 years in the southeast of Pampa plain (South America)

Abstract

The Medieval Climatic Anomaly (MCA) and the Little Ice Age (LIA) have been described as global temperature anomalies, though there is a scientific concern to estimate hydrological anomalies at these times and to know the nature of the transition between these events. In this contribution we present a hydroclimatic reconstruction for the last 2000 years using a pollen index derived from the relative abundance of Cyperaceae and Chenopodiaceae, from four shallow lakes located in the southeast of the Pampa plain. The hydroecological balance index suggests drier conditions than present between 50 BCE and 1500 CE, coeval with MCA. These conditions continue during MCA-LIA transition. A positive hydrological balance during LIA suggests similar or perhaps slightly more humid conditions than the present. This change is not completely synchronous with the proposed chronology for LIA, and hydroclimatic conditions appear to have varied considerably even among sites within the same climatic zone. During the last 100 years, the complexity of signals has not allowed disentangling climatic from anthropogenic factors affecting these aquatic ecosystems. The regional paleoclimatic synthesis allows proposing MCA as a homogeneous climatic event with generalized dry conditions, whereas LIA was more heterogeneous, with humid and dry conditions at different sites in the Pampa plain. The differences should not be interpreted as climatic discrepancies but rather as different expressions that may or may not be responding to the same climatic forcing.