Water samples for stable isotopes were collected untreated in 10 mL HDPE vials, sealed tightly, stored in the dark at 4°C. Measurements were conducted at the laboratory facility for stable isotopes at AWI Potsdam using a Finnigan MAT Delta-S mass spectrometer equipped with equilibration units for the online determination of hydrogen and oxygen isotopic composition. The data is given as δD and δ18O values, which is the per mille difference to standard V-SMOW. The deuterium excess (d-excess) is calculated by: d-excess=δD-8.*δ18O. The measurement accuracy for hydrogen and oxygen isotopes was better than ±0.8%¸ and ±0.1%, respectively (Meyer et al., 2000; doi:10.1080/10256010008032939).

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