H. C. Steen-Larsen’s main scientific expertise is associated with the use of water stable isotopes 1) to understand the physical processes of the atmospheric hydrological cycle, and 2) to use ice core water isotope records to deduce past climatic variations.  

　　During the first years of his academic career H. C. Steen-Larsen was involved in the international deep ice core-drilling project in North-West Greenland – NEEM (2008-2012): He was in charge of the surface isotope program with the purpose of understanding the processes creating the isotopic fingerprint in the snow. H. C. Steen-Larsen deployed in 2009 a water vapor isotope cavity-ring-down-spectrometer on top of the Greenland Ice Sheet thereby becoming the first to carry out this type of measurements in the Arctic. To improve the understanding of the atmospheric hydrological cycle H. C. Steen-Larsen initiated a network of water vapor isotope analyzers in the North Atlantic to measure both in the source region (Bermuda) and in the advection region (Iceland). He presented here, to date, the longest calibrated continuous water vapor isotope record of both isotopes (d18O and dD) and second-order parameter (d-excess).