Relating estimates of CaCO₃ production, export, and dissolution in the water column to measurements of CaCO₃ rain into sediment traps and dissolution on the sea floor: A revised global carbonate budget

Abstract

The global CaCO 3 budget is constrained by new estimates of standing stocks, fluxes through the water column, and dissolution in the water column and on the sea floor. Previous estimates of carbonate production and export are indistinguishable within a large range of values, 0.4–1.8 Gt PIC yr −1 . Globally, excess alkalinity (TA*) and water mass tracers indicate dissolution of 1.0 Gt PIC yr −1 between 200 and 1500 m, suggesting production and export must at least equal this amount. Most water column dissolution occurs at high latitudes, and alkalinity fluxes from outer shelf and upper slope sediments (100–1500 m) only support 5–10% of the TA* inventory. Below 2000 m, the sinking flux of PIC (0.6 Gt PIC yr −1 ) is consistent with the rate of sea floor dissolution (0.4 Gt PIC yr −1 ) plus burial (0.1 Gt PIC yr −1 ). This rain rate constrains the export value to >1.6 Gt PIC yr −1 . Satellite‐based estimates of standing stocks of CaCO 3 indicate a decrease equatorward, which is opposite in trend to sediment trap fluxes. This observation may be explained by an equatorward decrease in sinking particle dissolution, systematic changes in PIC residence time with latitude, or satellite retrieval problems. Globally averaged euphotic zone standing stock (5.4 mmol m −2 ) and export estimates indicate PIC residence times of 5–18 days.