Organic carbon content, stable carbon isotope ratios, and lignin phenol fingerprint of terrestrial material deposited at the paleo-delta of the Lena River at the transition to the Preboreal

The dataset was used to reconstruct the release of permafrost organic carbon from the watershed of the Lena River (Russia) between 11.1 and 11.7 calibrated thousand years Before Present (cal. kyr BP, Present = 1950 AD) and to model potential methane emissions from this carbon source. Data were obtained analyzing plant debris isolated from the low density fraction (<1.8 g/cm3) of muddy sediments from the Piston Core 23 (PC23). The sediment core was retrieved in July 2014 in the mid/outer-shelf of the Laptev Sea shelf (76° 10' 15.6''N; 129° 20' 13.2''E, water depth of 56 m) during Leg 1 of the SWERUS-C3 expedition (Swedish-Russian-U.S. Arctic Ocean – Investigation of Climate-Cryosphere-Carbon interactions). Measurement of total organic carbon (TOC) and stable (d¹³C) carbon isotopes were performed on 0.3 to 0.7 mg of samples on February 2022 using a Thermo DeltaQ isotope-ratio mass spectrometer (IRMS) coupled to a Thermo Flash 2000 Elemental Analyzer via a ConFlo IV interface at the at the Institute of Polar Sciences from the National Research Council of Italy (Bologna Section, Italy). The methodology for sample preparation followed Nieuwenhuize et al. (1994). Data on biomarkers (lignin phenols) were obtained extracting 2 to 3 mg of samples using a Microwave Accelerated Reaction System (MARS) 5 from CEM and following the methodology from Goñi & Montgomery (2000). The extracts were analysed using a Agilent 7890A gas chromatograph (GC) coupled to an Agilent 5975C mass spectrometer to identify and quantify the compounds of interest. Biomarkers extraction and analyses were carried out on March 2022 in the organic chemistry laboratories of the Ente Nazionale Idrocarburi (ENI)-National Research Council (CNR) of Italy Joint Research Center "Aldo Pontremoli" (Lecce, Italy). Stable isotope ratios and biomarkers were used to gain insights on the main vegetation source of the plant debris and (biomarkers only) to investigate the degradation state of the terrestrial material.