[2] After his PhD Jansen was given a researcher position and charged with building up the National Laboratory for light stable isotope geochemistry at the University of Bergen, which was established in 1983.
[4] Jansen has published about 200 scientific papers on the relationship between ocean circulation and climate change with emphasis on the build-up and demise of ice sheets.
[5] Most of his studies are from the Arctic and sub-Arctic regions, but his work also encompasses oceans in the Southern Hemisphere and the tropics.
In 2014 Jansen received an ERC Synergy Grant (ice2ice) to work with three other principal investigators on abrupt climate change.
[10] Jansen is also co-director of the SapienCE Centre which is a Norwegian Centre of Excellence awarded by the Norwegian Research Council in 2017,[11] and hosted by the University of Bergen, integrating archaeology, climate science and cognitive and neurosciences in studies of the emergence of modern behaviour in Homo sapiens in Southern Africa 120,000–50,000 years ago.