Seawater samples have been taken from the station Ocean City on the main MOSAiC ice floe on legs 1, 2, and 3. Water samples for measurement of stable water isotopes (δ18O, δD) were collected in 50-mL glass screw-cap narrow-neck vials (VWR international LLC, Germany), sealed with Parafilm M and stored at +4 °C from the end of the expedition until the measurement. 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).