Radiocarbon content and age 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). Radiocarbon (¹⁴C) content measurements were performed on 4 to 7 mg of sample on May 2022 using the Continuous Flow Accelerator Mass Spectrometry (CFAMS) system at the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility (Woods Hole Oceanographic Institution, Woods Hole, MA, USA). The ¹⁴C content was used to calculate ¹⁴C isotope ratios (D¹⁴C) and to reconstruct non-calibrated and calibrated ¹⁴C ages of plant debris isolated from the sediment fraction with a density lower than 1.8 g/cm3. Additionally, D¹⁴C values were used to calculate the ¹⁴C content of plant debris at time of sediment deposition (D¹⁴Ci) and the latter to obtain pre-depositional ¹⁴C ages. The dataset allowed to reconstruct the age of the terrestrial plant material when deposited at the coring site and identify its provenance from within the permafrost OC pool (sub-surface soil within 1 m depth vs deep soil) after remobilization. The average pre-depositional ¹⁴C age of plant debris was ultimately used to model methane emissions from relatively young permafrost organic carbon during the late deglaciation (ca. 10 to 15 cal. kyr BP).