Spreading olivine powder in seawater to enhance alkalinity through weathering reactions has been proposed as a potential solution to control atmospheric CO₂ concentration by modeling studies. However, experimental evidence of the impact of olivine dissolution on the seawater carbonate system as well as the ecosystem is rare. In this study, an olivine addition experiment was conducted to investigate variation in the seawater carbonate system, bacterial diversity and community composition in the surface and bottom seawater of a representative marine ranch area in the Muping, Yantai. The results show that the addition of olivine resulted in a significant increase of pH, TA, DIC, and a decrease in pCO₂ in both surface and bottom seawater incubations. The changes of the carbonate system in bottom seawater incubation were higher than those in the surface seawater, indicating low pH environment might favor the olivine dissolution. The composition of the particle-attached microbial community was affected by the application of olivine. The relative abundance of biofilm-forming microbes in particle-attached fraction increased after the addition of olivine, while no significant variation in the free-living bacterial community was observed. Our study suggests that olivine addition would affect the seawater carbonate system dramatically and might reshape the bacterial community structure, especially in particle-attached microenvironments.