The marine cycle of calcium carbonate (CaCO3
) influences the distribution of CO2
between atmosphere and ocean, and thereby climate. We constrain export of biogenic CaCO3
(globally: 0.72–1.05 Gt C yr−1
) and dissolution within the water column (~ 80 %) in a novel Monte Carlo set-up with the Bern3D model based on alkalinity data. Whether CaCO3
dissolves in the upper ocean remains unresolved. We recommend using constant (saturation-independent) dissolution rates in Earth system models.