This special issue is dedicated to Heimo Nielsen and his pioneering scientific work on the stable isotope geochemistry of sulphur on different scales in time and space. Heimo Nielsen was born on 27th April 1920 in Glückstadt and grew up in Hamburg, Germany. He started working on sulphur isotopes in the early 1960s, when he directed the newly founded ‘Central Laboratory for the Geochemistry of Isotopes’ (in German: Zentrallabor für Geochemie Isotope) in Göttingen.
At that time, sulphur isotopes in earth sciences were still in their infancy. The precise measurement of stable isotope ratios was restricted to a small number of laboratories around the world, which were generally specialised in the analysis of one particular element. Heimo Nielsen was the first to measure sulphur isotopes in West Germany.
The papers presented in this special issue cover fundamental aspects of microbiological processes, from the cellular level up to the global sulphur cycle, demonstrating the importance of stable sulphur isotope techniques as tools in interdisciplinary biogeochemical studies. They represent a collection of research topics that have been influenced by Heimo Nielsen.