Highly Variable Freshwater Reservoir Offsets Found along the Upper Lena Watershed, Cis-Baikal, Southeast Siberia

Abstract

A program of paired dating of human and faunal remains on a sample of 11 prehistoric (Mesolithic/Neolithic to Early Bronze Age) graves in the Upper Lena basin, southeast Siberia, was initiated to investigate the freshwater reservoir effect (FRE). The results show the presence of a substantial but highly variable offset, ranging from 255 to 1010 ¹⁴C yr. In contrast to previous studies centered on Lake Baikal and the Angara River, human stable nitrogen isotope values show little or no correlation with the radiocarbon offset, despite the clear trophic differences seen in δ¹⁵N between terrestrial and aquatic sources of protein in the region’s isotope ecology. However, stable carbon isotope measurements show a moderate negative correlation of some predictive value (r = –0.70, p = 0.016, df = 10). Two different regression equations have been calculated, the first using human δ¹³C values for the entire data set (r² = 0.49) and the second, using both δ¹³C and δ¹⁵N values, limited to the Early Bronze Age of the southern Upper Lena (r² = 0.84, p = 0.030, df = 5). The source of the old carbon in the Upper Lena River system is not clear. While the river flows over carbonate bedrock and is moderately alkaline, we suggest that old terrestrial carbon entering the riverine foodweb through bank erosion and other processes is a more likely candidate for the majority of the ¹⁴C offset.

DOI: 10.2458/azu_rc.57.18458