An Upper Pleistocene macroflora indicates warm and dry climate during an interglacial in central Brazil

Abstract

This study is the first report of the fossil macroflora of the Paleolagoa Seca, an Upper Quaternary fossil locality of lacustrine origin in central Brazil. Here we present an analysis of well-preserved fossil leaves collected from an argillite level dated at ca. 43,000 cal yr BP and discuss the paleoclimatic implications of this record. We reconstructed paleotemperature and paleoprecipitation using Leaf Margin Analysis (LMA) and Leaf Area Analysis (LAA), respectively, and used mineralogical (XRD and IR) and palynological analyses of the fossiliferous level to assess a complete picture of the past landscape. To test the ability of LMA and LAA models available for Southern Hemisphere to correctly predict Mean Annual Temperature (MAT) and Mean Annual Precipitation (MAP) for the Paleolagoa Seca, we applied several calibration models to the leaf dataset of a modern Cerrado forest and then compared predictions with modern climate data. Six LMA calibration models presented consistent MAT results and all four LAA calibration models provided satisfactory estimations of the modern MAP. The botanical identification of the fossil leaves and the pollen record indicated a mosaic of open savanna, dry forests and gallery forest around the Paleolagoa Seca. The reconstructed MAP for the Paleolagoa Seca ranged between 647 and 948 mm depending on the LAA equation, which is at least 500 mm lower than the current MAP. The reconstructed Mean Annual Temperature (MAT) ranged between 22.6 and 26.3 °C, indicating a higher-than-present MAT, which we relate to a combination of high summer insolation and low humidity. Comparison with other local fossil macrofloras, including from nearby localities, and with other paleoclimatic records suggests that the observed dry conditions at Paleolagoa Seca were related to interhemispheric climate forcing and to a weakening of the South American Summer Monsoon (SASM).