This study investigates the sulphur source of gypsum sulphate and dissolved groundwater sulphate in the Central Namib Desert, home to one of Africa's most extensive gypsum (CaSO 4 ร2H 2 O) accumulations. It investigates previously suggested sulphate precursors such as bedrock sulphides and decompositional marine biogenic H 2 S and studies the importance of other potential sources in order to determine the origin of gypsum and dissolved sulphate in the region. An attempt has been made to sample all possible sulphur sources, pathways and types of gypsum accumulations in the Central Namib Desert. We have subjected those samples to sulphur isotopic analyses and have compiled existing results. In addition, ionic ratios of Cl=SO 4 are used to determine the presence of non-sea-salt (NSS) sulphur in groundwater and to investigate processes affecting groundwater sulphate. In contrast to previous work, this study proposes that the sulphur cycle, and the formation of gypsum, in the Namib Desert appears to be dominated by the deposition of atmospheric sulphates of phytoplanktonic origin, part of the primary marine production of the Benguela upwelling cells. The aerosol sulphates are subjected to terrestrial storage within the gypsum deposits on the hyper-arid gravel plain and are traceable in groundwater including coastal sabkhas. The hypothesis of decompositional marine biogenic H 2 S or bedrock sulphide sources, as considered previously for the Namib Desert, cannot account for the widespread accumulation of gypsum in the region. The study area in the Central Namib Desert, between the Kuiseb and Omaruru rivers, features extensive gypsum accumulations in a ca. 50-70 km wide band, parallel to the shore. They consist of surficial or shallow pedogenic gypsum crusts in the desert pavement, hydromorphic playa or sabkha gypsum, as thin isolated pockets on bedrock ridges and as discrete masses of gypsum selenite along some faults. The sulphur isotopic values (ฮด 34 S โฐCDT) of these occurrences are between ฮด 34 S C13.0 and C18.8โฐ, with lower values in proximity to sulphuric ore bodies (ฮด 34 S C3.1 and C3.4โฐ). Damaran bedrock sulphides have a wide range from ฮด 34 S 4.1 to C13.8โฐ but seem to be significant sources on a local scale at the most. Dissolved sulphate at playas, sabkhas, springs, boreholes and ephemeral rivers have an overall range between ฮด 34 S C9.8 and C20.8โฐ. However, they do not show a systematic geographical trend. The Kalahari waters have lower values, between ฮด 34 S C5.9 and C12.3โฐ. Authigenic gypsum from submarine sediments in the upwelling zone of the Benguela Current between Oranjemund and Walvis Bay ranges between ฮด 34 S 34.6 to 4.6โฐ. A single dry atmospheric deposition sample produced a value of ฮด 34 S C15.9โฐ. These sulphur isotopic results, complemented by meteorological, hydrological and geological information, suggest that sulphate in the Namib Desert is mainly derived from NSS sulphur, in particular oxidation products of marine dimethyl sulphide CH 3 SCH 3 (DMS). The hyper-arid conditions prevailing along the Namibian coast since Miocene times favour the overall preservation of the sulphate minerals. However, sporadic and relatively wetter