Sea-ice thickness, draft, salinity, temperature, density, stable water isotope composition, and nutrient concentrations ([NO3]- + [NO2]; [NO2]; [NH4]+; [PO4]-; [Si(OH)4]) were measured during surveys at the main ice coring site (MCS), strength site, melt pond, and ridge site during the MOSAiC expedition (leg 5). The ice cores were extracted either with a 9-cm (Mark II) or 7.25-cm (Mark III) internal diameter ice corers (Kovacs Enterprise, US). This data set includes data from coring site visits performed from 31 August 2020 to 18 July 2020 at coring locations in the MOSAiC Central Observatory (CO3, Nicolaus et al., 2022). During each coring event, ice temperature was measured in situ from a separate temperature core, using Testo 720 thermometers in drill holes with a length of half-core-diameter at 5-cm vertical resolution. Ice bulk practical salinity was measured from melted core sections at 5-cm resolution using a YSI 30 conductivity meter. Ice density was measured using the hydrostatic weighing method (Pustogvar and Kulyakhtin, 2016) from a density core in the freezer laboratory onboard Polarstern at the temperature of –15°C. Relative volumes of brine and gas were estimated from ice salinity, temperature, and density using Cox and Weeks (1983) for cold ice and Leppäranta and Manninen (1988) for ice warmer than –2°C. Nutrient analyses were conducted shipboard or samples were frozen and analyzed at a shore-based lab. In either case, analyses were conducted colorimetrically using a Seal Analytical AA3 continuous flow auto analyzer (AACE Software, Version 7.09). Measurement of nutrients followed best practices adopted from GO-SHIP recommendations (Hydes et al., 2010; Becker et al., 2020).The data contains the event label (1), time (2), and global coordinates (3,4) of each coring measurement, coring site (5), and core type (6). Each core has its manually measured ice thickness (7), ice draft (8), and mean snow height (19). Each core section has the total length of its middle (9), top (10), and bottom (11) measured in situ. Each core section has the value of its practical salinity (12), as well as sea ice temperature (13) and ice density at the laboratory (14) and in situ (15) temperatures. Brine volume (16) fraction estimates are presented only for 0 to 60% fractions. Gas volume fraction estimates at the laboratory (17) and in situ (18) temperatures are also given only for brine volume fraction from 0 to 60%. Some core sections have stable water isotopic values (21, 22, 23) (Meyer et al., 2000), nitrate + nitrite (plus error and quality flag; 24, 25, 26), nitrite (27, 28, 29), ammonium (30, 31, 32), phosphate (33, 34, 35), silicate (36, 37, 38).The locations of the main sites are shown on the map. They include the main coring site co-located with 2020T85 buoy (https://doi.pangaea.de/10.1594/PANGAEA.958443), the strength site, the ridge site co-located with buoy DTC53 (https://doi.pangaea.de/10.1594/PANGAEA.962505), the Remote Sensing melt pond site co-located with buoy DTC52 (https://doi.pangaea.de/10.1594/PANGAEA.962496).Oxygen and hydrogen isotope analyses were carried out at the ISOLAB Facility at AWI Potsdam (https://hdl.handle.net/10013/sensor.ddc92f54-4c63-492d-81c7-696260694001) with mass spectrometers (DELTA-S Finnigan MAT, USA): https://hdl.handle.net/10013/sensor.af148dea-fe65-4c87-9744-50dc4c81f7c9 https://hdl.handle.net/10013/sensor.62e86761-9fae-4f12-9c10-9b245028ea4c employing the equilibration method (details in Meyer et al., 2000). δ18O and δD values were given in per mil (‰) vs. Vienna standard mean ocean water (V-SMOW) as the standard. The second order parameter d excess was computed according to: d excess = δD-8 δ18O (Dansgaard, 1964).