Carbon disulphide in the spotlight: UV-dependent production and consumption processes in seawater and their impact on oceanic emissions

Carbon disulfide (CS2) is one of the most important precursors for atmospheric carbonyl sulphide (OCS), a climate relevant trace gas that can serve as a proxy to quantify terrestrial gross primary production. Currently, limited understanding of the production and consumption processes of CS2 in seawater preclude quantifying its marine emissions, which pose major uncertainties in the atmospheric budget of both OCS and CS2. Here we present controlled incubation experiments with natural dissolved organic matter (DOM) from three different oceanic locations, with and without UV light treatment. We show for the first time that in addition to its photochemical production, CS2 is also naturally degraded by UV light. CS2 is also produced in the dark: while the mechanism of this light independent production process is currently unknown, we show that dark production rates scale with the amount of organic sulphur present in DOM. Our results help to disentangle production and consumption processes of CS2 in seawater, in order to facilitate the interpretation of field measurements and ultimately enable modelling approaches.