The data set includes the results of biogeochemical and sedimentary analyses on 4 sediment cores (69.5 cm - 113 cm) from two thermokarst lakes in Far East Siberia near the town of Chokurdakh. The analysis include lake depth measurements, linescan imaging, XRF scans, grainsize distribution, loss-on-ignition, porewater content, magnetic susceptibility, dissolved organic carbon (DOC) concentration, sediment density, stable carbon isotope measurements of DOC and soil organic carbon and radiocarbon ages.