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Abstract This study presents a comparative analysis of the radiocarbon dates obtained on paired samples of various organic materials extracted from a lake sediment core. AMS radiocarbon dating of bulk sediment, chironomid capsules, and Trapa seeds was conducted to assess whether systematic offsets exist in the dates obtained on material that are commonly used to develop chronological frameworks for lake-based paleoenvironmental research. The findings reveal significant discrepancies between 14 C dates obtained on bulk sediment, chironomid capsules, and on the Trapa seeds used to develop a previously published age-depth model for a sediment core recovered from Deoria Tal, Garhwal Himalaya, India. The systematic offset between the bulk sediment, and to a lesser extent chironomid remains, and the Trapa seeds is attributed to the integration of allochthonous carbon in the bulk sediment, leading to older apparent ages. The 3.6‰ shift in the δ 13 C value of the bulk sediment at 252 cm is inferred to reflect an increase in the contribution of C4 plant matter to the lake. The increase in enriched δ 13 C organic matter, coincident with the increasing offset between the dates obtained on bulk sediment and chironomids, and those obtained on the Trapa seeds, between 800 and 400 cal BP, was likely driven by anthropogenic land use changes, as evidenced by the four-fold increase in Cerealia-type pollen during this interval. This study underscores the necessity of selecting appropriate materials for radiocarbon dating to ensure accurate chronological reconstruction and highlights the potential of using chironomids remains to develop robust radiocarbon chronologies for lake sediment records.
Rimal et al. (Tue,) studied this question.
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