Investigating air-sea interactions


Brief description and intermediate results

Our ACE project addresses interactions between the ocean and the atmosphere, which include in essence the transfer of water from the atmosphere to the ocean (precipitation in the form of rain and snow) and vice versa (evaporation). The difference between precipitation and evaporation is called the “freshwater flux” and is essential for ocean salinity and ocean circulations. In the Southern Ocean, only few measurements exist about precipitation and evaporation, and the meteorological conditions that drive these air-sea fluxes are not fully understood.

Scientists launched more than 100 atmospheric probes in the forme of huge balloons.

ACE therefore provided a unique opportunity to obtain valuable measurements of atmospheric conditions, atmospheric humidity, and air-sea interaction processes in the Southern Ocean. To this end, we performed continuous measurements of the stable water isotope composition of atmospheric vapour – these isotopes are seen as ideal tracers for better understanding the various processes that influence ocean evaporation and the formation of precipitation. In addition, we manually collected several hundreds of samples of rain and snow on the ship, and from surface waters on sub-Antarctic islands, and we probed the atmospheric conditions with about 100 balloons and, during precipitation events, with a small radar. Our instruments worked very reliably such that we now can analyse a long dataset of stable water isotopes and meteorological parameters.

The atmospheric probe rising to get data…

In a first case study, we looked at an event of strong ocean evaporation in the Ross Sea related to a cold air outbreak from Antarctica. The ship crossed this event and we could measure a clear isotope signal related to it. In parallel, a lot of work is involved in calibrating and postprocessing all measurements and analysing the liquid samples in the lab.


Principal Investigator (PI)

Heini Wernli

Institute for Atmospheric and Climate Science, ETH Zürich, Switzerland


Investigation of air-sea interaction in the Southern Ocean from stable water isotope measurements

Principal institution / country

  • EPFL (Switzerland)
  • University of Bergen (Norway)
  • Lund University (Sweden)