In ice cores as well as ice-wedges, a message about past temperature variations is conserved in the ice, formed from the snow falls whose isotopic compositions vary with the temperature. However, deciphering these past temperature variations is not always straightforward, as the temperature is not the only parameter which can have an imprint on the isotopic composition of the ice.

A better understanding of the mechanisms affecting water isotopic composition, such as the changes in origin of the moisture, can be obtained from present-day observations and contribute to the interpretation of such paleoclimate archives.

Many studies use water isotopes in complex atmospheric models to refine the analysis of paleoclimatic data. The same models are also used for future climate projections, a domain where large uncertainties are still linked to the prediction of the water cycle and the changes in precipitation patterns. Water isotopes can be useful to benchmark such models and contribute to their improvement.

According to a commonly cited, 40-year-old theory (Merlivat and Jouzel, 1979), the meteorological conditions under which the oceanic evaporation takes place leave their fingerprint in the isotopic composition of the vapor. Using a Picarro L2140-i Isotope and Gas Concentration Analyzer on-board  their research vessel, researchers were able to test this theory for the first time in the field under a large range of climatic conditions. The researchers were able to continuously record the water vapor isotopic composition (δ18O and δ2H) directly above the ocean surface, over all latitudes in the Atlantic sector, from the North Pole to the coast of Antarctica. Their observations yielded some surprising results.