Origin of organic matter in the Lake Cheko (Central Siberia, Russia)

Total Organic Carbon (TOC), Total Nitrogen (TN), d13C and d15N analyses were performed on 5 sediment cores collected within Lake Cheko, a small basin 9 km NW of the Tunguska Event (TE) epicentre (Central Siberia, Russia), during the field work carried out in 1999. The aim was to shed light on the origin of organic matter (OM) deposited within the lake and to contribute to reconstruct recent paleolimnological history and environmental evolution of the lake itself and its catchment. OM analyses were performed on 1-2 cm slices all along the core records. Total concentrations ranges between 0,2 and 8,6% d.w. for TOC and 0,02 and 0,67% d.w. for TN. C/N ratio ranges between 7,6 and 17,9, whereasd13C shows values ranging between -29,73 and -26,47%o and d15N between 0,09 and 3,32%o. Two main differences among the study cores are amount, and composition of organic matter along the sedimentary record allowing us to distinguish different units. In particular, macrorelains, C/N >10 and very negative d13C values compatible with C3-type Land plants (boreal forest) were interpreted as the results of high energy transport events such as seasonal floods or slope failures, whereas low C/N values should correspond to OM produced within the lake basin by autochthonous organisms. Cross-analysis of obtained data allowed us to reconstruct the recent paleolimnological evolution of the basin that responds in different ways according to periodic events such as seasonal floods and winter stasis, as well as extraordinary events such as fire in the taiga.