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We use isoprene and related field measurements from three different ocean data sets together with remotely sensed satellite data to model global marine isoprene emissions. We show that using monthly mean satellite-derived chl a concentrations to parameterize isoprene with a constant chl a normalized isoprene production rate underpredicts the measured oceanic isoprene concentration by a mean factor of 19±12. Improving the model by using phytoplankton functional type dependent production values and by decreasing the bacterial degradation rate of isoprene in the water column results in only a slight underestimation (factor 1.7±1.2). We calculate global isoprene emissions of 0.21TgC for 2014 using this improved model, which is twice the value calculated using the original model. Nonetheless, the sea-to-air fluxes have to be at least 1 order of magnitude higher to account for measured atmospheric isoprene mixing ratios. These findings suggest that there is at least one missing oceanic source of isoprene and, possibly, other unknown factors in the ocean or atmosphere influencing the atmospheric values. The discrepancy between calculated fluxes and atmospheric observations must be reconciled in order to fully understand the importance of marine-derived isoprene as a precursor to remote marine boundary layer particle formation.

Carbon disulfide (CS2) has recently gained attention as an important precursor for the atmospheric trace gas carbonyl sulfide (OCS), which delivers sulfur to the stratospheric sulfur layer and impacts the radiative budget of the Earth. CS2 is naturally produced in the ocean and emitted to the atmosphere. However, the magnitude of its marine emissions is only poorly constrained due to lacking understanding of its production and consumption processes. Here, we present incubation experiments with and without UV light treatment and provide evidence for a previously not considered UV‐light‐driven degradation process of CS2 in seawater, following first‐order kinetics. In addition to its already known photochemical production process, CS2 production is found in the dark, depending on the amount of dissolved organic sulfur present in seawater. We provide novel production and consumption rates of CS2 in seawater that pave the way toward mechanistically quantifying marine emissions of this important trace gas. Plain Language Summary: The gas carbon disulfide (CS2) impacts the climate system of our planet as a precursor for sulfate aerosols. CS2 is naturally produced in the ocean, but how much marine CS2 is emitted to the atmosphere is not well known. In our study, we have experimentally derived production and degradation rates of CS2 in seawater and found processes that have previously not been considered: CS2 is degraded by UV radiation in seawater, and is produced in the absence of light. This dark production increases with the amount of dissolved organic sulfur in the water. Our results help to understand the production and degradation of CS2 in seawater, which is needed to quantify its emissions to the atmosphere. Key Points: Carbon disulfide in seawater is degraded by UV light at time scales of daysCarbon disulfide is produced in seawater without UV light at rates comparable to photochemical productionCarbon disulfide dark production is limited by dissolved organic sulfur [ABSTRACT FROM AUTHOR]