Here are the bundled geochemical data of an 11-m-long sediment core EN21103 collected from Lake Ulu (63.34°N, 141.05°E) in the Oymyakon region (eastern Siberia) during the 'Yakutia 2021' expedition, which consists of five datasets.(1) Dataset 1. Radiocarbon dating performed on the total organic carbon content of 40 bulk sediments, measured at the MICADAS (Mini Carbon Dating System) Laboratory of AWI in Bremerhaven.(2) Dataset 2. Bacon age-depth model. This model was established based on the Bayesian method with a hiatus at 138 cm and calibrated using the IntCal20 dataset via the Bacon function in the R-package rbacon. A reservoir effect of approximately 351 ± 24 radiocarbon years has been determined by the dated surface sample (0−0.5 cm). We assumed a constant reservoir effect over time and therefore subtracted a value of 351 years from all radiocarbon ages.(3) Dataset 3. Element composition including total carbon (TC), total organic carbon (TOC), total inorganic carbon (TIC), and total nitrogen (TN), measured with a soli TOC cube (Elementar) and a rapid MAX N exceed (Elementar) at the Carbon and Nitrogen Laboratory of AWI in Potsdam. The minimum detectable concentration for natural sediment samples is 0.1% for both machines.(4) Dataset 4. Stable carbon isotopes of organic matter (d13C), measured with a Delta V Advantage Mass Spectrometer at the ISOLAB Facility of AWI in Potsdam. All isotopic values are reported in standard δ-notation in per mil (‰) relative to VPDB.(5) Dataset 5. X-ray fluorescence (XRF) scanning data, scanned with an AvaaTech XRF core scanner at AWI in Potsdam. All elements were measured at X-ray voltages of 10 kV and 30 kV and currents of 0.45 mA and 0.15 mA, respectively, with a step size of 0.5 cm and an exposure time of 10 s. The data are semiquantitative and provide relative fluctuations in the chemical element compositions as counts per second (cps).