The role of differential DMSP production and community composition in predicting variability of global surface DMSP concentrations

Dimethylsulfoniopropionate (DMSP) is an important labile component of the marine dissolved organic matter pool that is produced by the majority of eukaryotic marine phytoplankton and by many prokaryotes. Despite decades of research, the contribution of different environmental drivers of DMSP production to regional and seasonal variability remains unknown. A synthesis of the current state-of-knowledge suggested that approximately half of confirmed DMSP producers are low producers (intracellular DMSP < 50 mM). Low DMSP producers (LoDPs; e.g., diatoms) were shown to strongly regulate intracellular DMSP concentrations (similar to 16-fold change) as a predictable function of nutrient stress. By comparison, high DMSP producers (HiDPs; e.g., coccolithophores) showed very little response (similar to 1.5-fold change). To assess the importance of differential DMSP production by low and high producers, DMSP concentrations were predicted for two time-series sites (a high- and low-productivity site) and for the global ocean by explicitly incorporating both community composition and mechanistic nutrient stress. Despite large, predictable intracellular DMSP changes, low producers contributed less than 5% to global DMSP. This indicates that, while variations in DMSP production by low producers could be important for predicting microbial interactions and low producer physiology, it is not necessary for predicting global DMSP concentrations. Our analysis suggests that community composition, particularly HiDP biomass, is the dominant driver of variability in in situ DMSP concentrations, even in low-productivity regions where high producers are typically the subdominant group. Accurate predictions of in situ DMSP concentrations require improved representation of subdominant community dynamics in ecosystem models and remote-sensing algorithms.