Molecular tracers of human settlement and agricultural activity in sedimentary records

Lacustrine sediments constitute a highly informative environmental archive, due to the large number of biomarkers that can be used for paleoclimatic reconstructions over long time intervals, especially by using a multi-proxy approach. Some organic biomarkers can provide information on the history of human activities and their influence on past climate. The spread of agriculture and pastoralism, including forest clearance activities operated on a large scale through controlled fires, resulted in huge changes in land use, recorded in sedimentary archives. Biomarkers employed as tracers for biomass burning and human/livestock presence include levoglucosan and some specific faecal sterols [1], respectively. However, the complexity of the matrix and the presence of several possible interferences require high analytical performance and a considerable effort in sample preparation and method development. In this work, a Gas Chromatography – Mass Spectrometry (GC-MS) and Ionic Chromatography – Mass Spectrometry (IC-MS) method based on Accelerated Solvent Extraction (ASE) of lacustrine sediments was developed and validated. Extraction was performed using a DCM:MeOH 9:1 v/v mixture. Extracts underwent clean-up by means of 2 g SPE silica tubes, collecting two different fractions for faecal sterols and levoglucosan then subsequently analyzed with GC-MS and IC-MS [2], respectively. The method was applied to a 360 cm core retrieved from Lake Trasimeno (Italy), divided into 72 subsamples and covering the last 25 ky. Results were interpreted according to the age model and the available historical information.