Stable water isotopes of sea ice at Main Coring Site (MCS) during MOSAiC expedition

Sea ice cores were collected from the Biogeochemistry (BGC) team at different stations located on the main ice floe of MOSAiC expedition. Flat sea ice on the floe was categorized into three types based on the age: sea ice which grew during the same winter referred to as First-Year-Ice (FYI); sea ice which had survived one or more summer melting periods referred to as Second-Year-Ice (SYI). Sea ice cores were collected using a Kovacs Mark II 9 cm diameter corer. The core was extracted and placed in an aluminum holder equipped with a metric ruler. Using a standard Kovacs ice thickness gauge, the freeboard was taken and the length of the core was measured. The snow on top of the sea ice was brushed off the top of the cores to minimize the snow affecting the ice surface. Onboard RV Polarstern, the cores were cut in 10 cm sections using a handsaw at 4° C (leg 1) or an electric saw at -20° C (legs 2 and 3). Each section was transferred into a gas-tight TedlarTM bag. The closed bags were carefully degassed with a vacuum pump (NKF Neuberger, type N035). Melting occurred within 12 to 15 hours in a water bath in the dark. After shaking the melted ice within the TedlarTM bags, discrete sampling started by first rising the melt water carefully through a Tygon tube connected with the opened valves of the gas tide bags and then into prepared sample vials. Here we present the data from samples collected at Main Core Site (MCS) at the Dark Sector (DS). 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).