A method for estimating paleotemperatures from pollen assemblages applied to the quantification of the Early Holocene warming in Central Brazil

Abstract

This study presents a method for the quantification of paleotemperatures from pollen records based on the predominant leaf margin trait of the genera represented in the pollen assemblages. The method presented here uses the well-known and widely used relationship between leaf margin and mean annual temperature, which is commonly applied to macrofloras to reconstruct paleotemperatures. Here, genera occurring in the arboreal vegetation of Central Brazil were analyzed respective to the presence or absence of species bearing toothed leaves. Using floristic surveys, a correlation between the proportion of genera without toothed species and the mean annual temperature was investigated. A positive linear correlation between these two variables was found for forest sites, but not for the arboreal savannas. The equation derived from the linear regression between the two variables - proportion of genera without toothed species and mean annual temperature (MAT) - was applied to pollen assemblages collected on forest sites. The equation was used to calculate estimated MATs for surface samples in order to test the validity of its application to pollen assemblages. The equation was then applied to fossil records to estimate paleoMATs for two Brazilian sites located respectively at 15.5° and 28° of latitude, during the Pleistocene-Holocene transition (between 13.6 and 10 kyr cal BP). While MAT increases of around 3 °C were found for the higher latitude site, no significant differences between final Pleistocene and early Holocene MATs were found for the near-equatorial site.