Xuyuan Ai^1,2, Anja S Studer³, Daniel Mikhail Sigman¹, Alfredo Martinez-Garcia², François Fripiat², Lena Thöle⁴, Elisabeth Michel⁵, Simone Moretti², Eri Amsler⁶, Antoine Thévenaz⁶, Sam Jaccard⁶ and Gerald H Haug², (1)Princeton University, Princeton, NJ, United States, (2)Max Planck Institute for Chemistry, Mainz, Germany, (3)University of Basel, Basel, Switzerland, (4)Utrecht University, Utrecht, Netherlands, (5)Laboratoire des Sciences du Climat et de l’Environnement, IPSL, Université Versailles‐St Quentin, CNRS, Gif sur Yvette, France, (6)University of Bern, Bern, Switzerland