Porewater <i>δ</i><sup>13</sup>C<sub>DOC</sub> indicates variable extent of degradation in different talik layers of coastal Alaskan thermokarst lakes

Abstract. Thermokarst lakes play an important role in permafrost environments by warming and insulating the underlying permafrost. As a result, thaw bulbs of unfrozen ground (taliks) are formed. Since these taliks remain perennially thawed, they zones increased degradation where microbial activity geochemical processes can lead to greenhouse gas emissions from thermokarst lakes. It is not well understood though what extent organic carbon (OC) different talik layers below affected degradation. Here, we present two transects short sediment cores on Arctic Coastal Plain Alaska. Based their physiochemical properties, main were identified. A “lake sediment” identified at top with low density, sand, silicon content but high porosity. Underneath, “taberite” (former soil) density rich sand lower porosity Loss ignition (LOI) measurements show that matter (OM) lake 28±3 wt % (1σ, n=23) considerably higher than taberite soil 8±6 n=35), dissolved (DOC) leaches both concentrations: 40±14 mg L−1 n=22) 60±14 n=20). Stable isotope analysis porewater DOC (δ13CDOC) showed relatively wide range values −30.74 ‰ −27.11 mean -28.57±0.92 n=21) sediment, compared narrow −27.58 −26.76 -27.59±0.83 (one outlier ‰). The opposite was observed (SOC), δ13CSOC −29.15 −27.72 (-28.56±0.36 ‰, 1σ, comparison wider −25.55 (-26.84±0.81 n=21). δ13CDOC soil, narrower comparative δ13CSOC, along δ13C-shift indicates stable fractionation due ongoing sediment. Increased OC relative most likely explanation for differences values. be sources Arctic, it better understand degree individual as indicator potential release, especially, predicted coming decades will increase number (horizontal vertical) taliks.