Permafrost deposits preserve organic matter which is decomposed and potentially released as greenhouse gases (CO2 and CH4) during thermokarst processes and in particular thaw lake development. Younger near-surface and older organic matter from slumping and expanding lake shores are deposited in the lake basin and contribute to the lacustrine carbon cycle. Bioproductivity within the lakes complements carbon accumulation in lacustrine deposits and provides an additional source of young carbon and greenhouse gases. A set of lake sediment cores from Goldstream Valley in the discontinuous permafrost zone of Interior Alaska was studied for their origin of organic matter during the Holocene. With the aim to distinguish the provenance (terrestrial or aquatic) of carbon contributions to sediments over time, core samples were analyzed for their total organic carbon/total nitrogen ratio (C/N) as well as stable carbon isotopes. The case study of Goldstream Valley Lake, located in yedoma permafrost, indicates a dominance of aquatic plant material in the littoral zone with a mean C/N ratio as low as 8.7. Although a similar signal is found for sediments in the lake’s central basin, a clear shift to a terrestrial carbon signal (C/N of 22) is presumably indicating the trash layer of the initial lake phase. Further, ongoing organic matter decomposition in talik sediments proves to be crucial to assess the contribution of thaw lakes to future climate change by mobilizing Pleistocene soil carbon.