Carbonic anhydrase (CA) has been shown to promote calcite dissolution (Liu, 2001, https://doi.org/10.1111/j.1755-6724.2001.tb00531.x; Subhas et al., 2017, https://doi.org/10.1073/pnas.1703604114), and understanding the catalytic mechanism will facilitate our understanding of the oceanic alkalinity cycle. We use atomic force microscopy (AFM) to directly observe calcite dissolution in CA‐bearing solution. CA is found to etch the calcite surface only when in extreme proximity (~1 nm) to the mineral. Subsequently, the CA‐induced etch pits create step edges that serve as active dissolution sites. The possible catalytic mechanism is through the adsorption of CA on the calcite surface, followed by proton transfer from the CA catalytic center to the calcite surface during CO2 hydration. This study shows that the accessibility of CA to particulate inorganic carbon (PIC) in the ocean is critical in properly estimating oceanic CaCO3 and alkalinity cycles
