Reconstruction of the environmental conditions for the past 2,000 years in the Perico River basin (NW Argentina) based on fossil pollen records

Abstract

In this paper we aim to reconstruct seasonal humid conditions of the past 2,000 years based on fossil pollen records from high altitude sites (> 3,000 m a.s.l.) in NW Argentina. Palaeoenvironmental studies were conducted in two wetlands located in the upper basin of the Perico River (Jujuy province, Argentina). To assess the seasonal characteristics for different climatic periods, we used the pollen index log10 P/A to describe summer conditions, where P/A stands for the ratio between the percentages of Poaceae (P) and Asteraceae (A). To interpret winter conditions we used log10 T/A index. T/A is the ratio between the sum of percentages of transported pollen coming from Andean forest (T) and the percentage of Asteraceae (A). The prevalence of Poaceae pollen during certain time periods provides indirect information about soil moisture indicating rainy summers related to an intensified activity of the South American Monsoon System (SAMS). In contrast, periods with predominance of Asteraceae pollen suggest drier summers as a consequence of a reduction in SAMS activity. Structural changes from grassland to mixed steppe occurred at a multi-centennial scale, mainly driven by rainfall variability. The analysis of the log10T/A index enabled us to reconstruct the frequency of the mountain-valley breeze and indirectly to infer the winter precipitation. Periods with a high input of tree pollen (> 20%) indicate high breeze frequency and consequently less winter precipitation and vice versa. We applied this reconstruction approach to characterize the seasonal humidity conditions during the Medieval Climate Anomaly, Little Ice Age and Current Warm Period in the study region.