The dataset describes a 5 m long sediment core taken from beneath thermokarst lake Goltsovoye Lake on the Bykovsky Peninsula, northeastern Siberia. Core location: N 71.74530 E 129.30243.The data represent biogeochemical parameters of sediment core PG2420. Biogeochemical analyses include total organic carbon (TOC) content and stable carbon isotopes (δ13C). δ13C was measured for samples with TOC > 0.1 wt %. The data also include radiocarbon measurements. Calibrated and rounded calibrated ages are presented. Calibrations were performed according to Stuiver et al. (2017) using CALIB 7.1 software and the IntCal13 calibration curve.To all data, the vertical position in the sediment core is given in cm (midth of sample) measured from the ice surface on top of the lake. Depth from ice surface to sediment surface was 510 cm.