This processed Conductivity, Temperature, Depth (CTD) data from Marion Island Relief Voyage on the SA Agulhas II Voyage 030 from 13 April to 28 April 2018. The Conductivity, Temperature, Depth (CTD) data is uncalibrated and not verified. The 2018 Marion Relief Voyage 030 offered the 6th opportunity to conduct multi-disciplinary, shipbased marine research focusing on links and interactions between air and sea, ocean physics, chemistry, biogeochemistry and biology, including microbial and planktic communities on board South Africa’s polar research and supply vessel MV SA Agulhas II en route to, and around, the sub-Antarctic Prince Edward archipelago. The overall aim was to continue contributing to an oceanographic observation and monitoring system directed by South African research institutions in support of South Africa’s needs – and where possible, in support of global requirements of inter alia the Global Oceans Observing System (GOOS), the Southern Ocean Observing System (SOOS), the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR), and the Agreement on the Conservation of Albatrosses and Petrels (ACAP). This dataset was processed using older standards which may not align with international best practices and the standards currently adhered to by the Department of Forestry, Fisheries and the Environment (DFFE). The Department is re-processing and replacing data to ensure everything has the same format and is of the same quality and datasets will be marked as obsoleted once that is done. As such the user assumes the entire risk related to the use of these data in its current state and format. DFFE disclaims all warranties of the data whether expressed or implied, including without limitation, any warranties of merchantability or fitness for a particular purpose. For any concerns regarding the data, the user may decide to liaise with the listed PIs who will share their insight on the data quality, where possible. It is also strongly recommended that the user liaises with the listed PIs regarding their proposed projects to mitigate against duplication of research efforts.