Variations in radiocarbon ages of various organic fractions in core sediments from Erhai Lake, SW China

Radiocarbon dating was performed for the extracted organic fractions (cellulose-rich and humic acid fractions of plant fragment; fulvic acid, humic acid and humin fractions of humus substance) and shell from core sediments of the Erhai Lake, SW China. The 14C dating results reveal that there are considerable differences, but there apparently is a humic acid ≤ humin < fulvic acid fraction sequence of 14C age increase. The variability in radiocarbon ages of organic fraction of lake sediment suggests that special caution is necessary when radiocarbon ages of bulk sediments are used. The linear correlation between 14C age of allochthonous terrestrial macrofossil (plant fragment and shell) and depth indicates roughly a constant sedimentation rate of ca. 0.7 mm yr–1 in central Erhai Lake since 4500 yr BP. The 14C ages of the autochthonous humic acid fraction are 210~4800 yr shift from “the true 14C age” obtained by interpolating the corresponding horizontal level to the above 14C age-depth correlation. Such age difference may be alternatively attributed to a uniform reservoir effect (most likely ca. 300 yr). The period with large 14C age shift synchronizes with the period of changes in δ13C and ARM intensity and ARM/susceptibility values.