Underway seawater samples have been taken from underneath the research vessel Polarstern through a pipe installed on the ship. The valve had been open for about 2 minutes before collecting the samples to avoid possible contaminations. Water samples for measurement of stable water isotopes (δ18O, δD,) were collected in narrow-mouth low-density polyethylene 20- or 30-mL plastic bottles (VWR international LLC, Germany), sealed with Parafilm M and stored at +4 °C from the end of the expedition until the measurement. Average daily salinity values were extracted from dship portal (https://dship.awi.de/). 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).