Description: Sediment core (gravity core) HH14-897-GC-MF was collected from Brepolen Bay, inner Hornsund, Svalbard (76°59.555' N; 016°24.313' E), from a water depth of 125 m, on 18.10.2014, during R/V Helmer Hanssen cruise. The total core length was 154 cm. The sampling site was located in a glacial bay formed after the termination of the Little Ice Age (Strzelecki et al., 2020; doi:10.1002/esp.4819). The dataset consists of gamma spectrometry measurements of excess 210Pb (calculated as a difference between the total 210Pb and the average of 214Pb and 214Bi) and 137Cs, total organic carbon (TOC) content, and delta 13C isotopic ratio of bulk organic matter. The data were obtained within a National Science Center (Poland) project: 'Impact of post-Little Ice Age glaciers retreat on sediment accumulation and carbon burial rates in subpolar fjords' and presented during conference presentations (e.g. Szczuciński et al. 2017). The excess 210Pb and 137Cs data were measured in the Institute of Geology at Adam Mickiewicz University in Poznań, Poland using a gamma detector Canberra BE3830, cooled with cryostat Cryo-Pulse®5 plus. The detector was placed in 10 cm thick lead shield walls and is equipped with a remote detector chamber option (RDC-6 inches) for low energy background reduction. The detector was commercially characterized by ISOCS (In-Situ Object Calibration Software) and LabSOCS (Laboratory Sourceless Object Calibration Software). Efficiencies for measured geometries were determined using LabSOCS code applying all corrections for sample geometry, matrix, and container type, and were verified with IAEA standards measurements. The results (spectra) were analyzed with Canberra GENIE-2000 v. 3.3 gamma spectrometry software and were presented with 2-sigma uncertainty ranges (Szczuciński, submitted). The age model was calculated using the serac package (Bruel and Sabatier, 2020; doi:10.1016/j.jenvrad.2020.106449), and verified with 137Cs depth profile, the time of glacier retreat from the coring site (Błaszczyk et al. 2013), and counting of likely annual laminations visible in X-ray scans. TOC concentrations were measured at the Department of Quaternary Geology and Palaeogeography of Adam Mickiewicz University in Poznań, Poland. The analyses were done with a Vario MAX CNS elemental analyzer (Elementar, Germany). To determine the organic carbon content, prior to the analyses, samples were treated with 1 molar hydrochloric acid (HCl) to remove carbonates. Each sample was analyzed in duplicate. Analytical control was performed using certified reference materials (BN225497, BN230229, BN230227). The recoveries of C determinations were 101.6 ± 4.2% (Woszczyk et al. 2021; doi:10.1016/j.orggeochem.2021.104209). The bulk C-isotope analysis of bulk organic matter was conducted in a joint-venture Goethe University and BIK-F stable isotopes lab, Frankfurt-Main, Germany. The measurements were performed with a Flash Elemental Analyser – 1112 linked to a Thermo-Finnigan Mat 253 gas source mass spectrometer. Carbonate was removed with 10% HCl. The system was calibrated using external standards related to international reference materials. Results are reported relative to PDB for δ13C. The reproducibility of two replicate analyses was usually in the range ±0.2‰.