Biogeochemical modelling of upper ocean sulfur dynamics and its impact on cloud forming aerosols

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The solar radiation dose in the oceanic upper mixed layer (SRD) is now recognized as a key climatic factor influencing global dimethylsulfide (DMS) dynamics and its seasonal patterns. DMS is believed to cool the Earth’s radiative budget by affecting the formation and properties of tropospheric clouds over the ocean. A positive correlation between DMS and SRD suggests a natural feedback mechanism between the oceanic biosphere and climate, potentially mitigating anthropogenic global warming through a shallower mixed layer depth (MLD) and increased SRD, DMS concentrations, and emissions. Using two globally-derived DMS diagnostic models, we analyzed the response of the DMS-producing pelagic ocean to a projected 50% increase in atmospheric CO2, comparing it to an unperturbed control run. Our findings indicate a slight global increase in surface DMS concentrations, particularly in summer. However, this increase (1.2% globally) is minimal compared to the radiative forcing from rising greenhouse gases. This contrasts sharply with the significant seasonal variability of DMS (1000-2000% summer-to-winter ratio). We propose that the 'plankton - DMS - clouds - Earth albedo feedback' hypothesis may be less effective as a long-term climate regulator than as a seasonal mechanism that modulates solar radiation exposure to the Earth’s biosphere.