Near-surface atmospheric vapour and oceanic surface water isotopic compositions calibrated data from POLARSTERN cruises, 2015-2017

Here, we present a new isotopic dataset of near-surface water vapour and oceanic surface water continuously surveyed from the Polarstern research vessel during a period of two years from 2015-06-29 to 2017-07-01. The dataset covers areas spanning from the North Pole to the coasts of Antarctica in the Atlantic sector. Water vapour observations have been measured continuously on-board using a Cavity Ring-Down Spectrometer from a 29 m elevation above the sea level. The oceanic water has been sampled on a daily basis and later analyzed for water isotopic composition at the Alfred Wegener Institut laboratory in Potsdam, Germany. These observations contribute to better understand the creation of the first water vapour isotopic signal during oceanic evaporation. They reveal that the vapour deuterium excess within the atmospheric boundary layer is not modulated by wind speed, contrary to the commonly used theory, but controlled by relative humidity and sea surface temperature only. In sea ice covered regions, the sublimation of deposited snow on sea ice is also revealed as a key process controlling the local water vapour isotopic composition