This study demonstrated, through an ocean alkalinity enhancement (OAE) experiment using mesocosms, that higher pH levels can reduce the ratio of biogenic silica to particulate organic carbon in sinking particles by promoting the dissolution of diatom-derived silica in seawater. Higher pH conditions might also cause organic carbon produced by diatoms to be remineralized at shallower depths, thereby reducing its ocean residence time and weakening the biological carbon pump for sequestering atmospheric carbon dioxide. This study also provides valuable insights into the linkage between OAE and biogeochemical processes in the ocean.