The datasets include raw and corrected measurements of mercury in sediment samples from core DEEP 5045-1 extracted from Lake Ohrid in 2013, as part of the ICDP-funded project: Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO). Lake Ohrid (41° 02′ N, 20° 43′ E) is a tectonic lake situated 693 m above sea level in south-east Europe. The ~447 m-long sedimentary succession extracted from the DEEP (central) site provides a continuous record of hemipelagic sediment accumulation since ~1360 ka, with age control provided by combining tephrochronological data from 16 Ar/Ar dated tephra layers, magnetostratigraphic data, and orbital-tuning of peaks in total organic carbon. Paine et al. (2024) analysed sedimentary Hg concentrations in the top 36 m of the DEEP 5045-1 sediment succession. Here, this dataset is extended to cover the full 447 m succession, with Hg measurements taken for 640 powdered bulk sediment samples between 36 and ~447 m composite depth at a sampling resolution of 64 cm (or an average of ~2000 years). Total Hg concentrations (HgT) were measured using a RA-915+ Portable Mercury Analyzer with PYRO-915+ Pyrolyser, Lumex (Bin et al., 2001) at the University of Oxford. In Lake Ohrid, endogenic calcite (CaCO3{~}) accounts for up to >80% of the total sediment carbonate mass with small contributions from biogenic and detrital terrigenous calcium carbonate. Such a high and variable carbonate content creates a high risk of Hg fluxes to the sediment being diluted, and the variability results in a positive correlation to other diluted phases (TOC, TS, quartz, clay minerals), when this effect is not suitably accounted for. Also included are details for each standard sample analyzed in conjunction with the DEEP 5045-1 samples, in order to calibrate the instrument, and thus calculate integrated Hg concentration values.

Age (ka): Age ascribed to each sample, given in kiloyears before present (ka). Ages follow the chronology published in Wagner et al. (2019): which combines tephrochronological data from 16 39Ar/40Ar dated tephra layers, magnetostratigraphic data, and orbital-tuning of peaks in total organic carbon. The final age model was calculated using Bacon 2.2, considering broadly uniform sedimentation rates at the DEEP core site. The average errors for specific depths averaged ±5.5 kyr (95% confidence), with a maximum uncertainty of ±10.7 kyr. The resulting chronology suggests that the upper 447.12 m of the DEEP site record continuously covers the past 1.35 million years. (Wagner et al., 2019)HgT: Total Hg in the bulk sediments of DEEP 5045-1. Measured using the RA-915 Portable Mercury Analyzer with PYRO-915 Pyrolyzer, Lumex at the University of Oxford. (Paine et al., 2026; Paine et al., 2024; Bin et al.,2001)HgAR: Total sedimentary Hg accumulation relative to background, given in ng cm−2 yr−1. This calculation uses values of dry bulk density (DBD), which were calculated immediately after sampling from volumetrically sampled aliquots at the University of Cologne by Francke et al. (2016), and values for sedimentation rate (SR) given by Wagner et al. (2019). Values for HgAR are calculated with respect to the median age estimate for each sample. (Paine et al., 2026; Paine et al., 2024); Wagner et al., 2019; Francke et al., 2016).HgT-CFB: The carbonate-free concentration/abundance of Hg in the samples of DEEP 5045-1, calculated by (and presented in) Paine et al. (2026). This calculation uses values for CaCO3 (see below) calculated from total inorganic carbon (TIC) values published in Wagner et al. (2019). (Paine et al., 2026; Wagner et al., 2019; Lacey et al., 2016).Carbonate: The concentration of carbonate carbonate (CaCO3) measured in each DEEP 5045-1 sample given as a weight percentage (%), and calculated from total inorganic carbon (TIC) values published in Wagner et al. (2019), using a mass ratio of 8.33. Inorganic carbon compounds in the Lake Ohrid sediment archive are dominated by calcite with minor amounts of siderite (FeCO3) present during periods of overall low TIC. Hence, here it is assumed that all TIC is in CaCO3 in DEEP 5045-1. (Wagner et al., 2019).