This video explains the principles of working in a clean room with marine samples. These methods are used to analyse the distribution of trace elements and their isotopes in the ocean, which is the aim of the GEOTRACES project for improving our understanding of the ocean (https://www.youtube.com/watch?v=IGUt4OZL2Z8 ). The GEOTRACES project (www.geotraces.org ) is a global research collaboration, endorsed by the Scientific Committee on Oceanic Research (SCOR). This is the third of three videos produced at the Alfred Wegener Institute (AWI), supported by the Volkswagen Stiftung as part of the GEOTRACES summer school 2022 (W. Geibert/ C. Hanfland, AWI and eventfive GmbH).