The University of Hamburg is part of environmental studies in the INDEX Program, which was establishes by the BGR (Federal Institute of Geosciences and Natural Resources) in Hanover to explore Massive Sulphides with regard to a potential future deep sea mining. The INDEX license area is located in the oligotrophic subtropical gyre of the South Indian Ocean. The water samples were collected with a CTD water rosette during two ship cruises with R/V Merian in 2016 (MSM 59/2 "INDEX 2016-2"; November−December 2016) and R/V Sonne in 2017 (SO 259 "INDEX 2017"; August−October 2017) and were analysed for nutrients and stable isotopes of nitrate.