The Fate of Ocean Alkalinity: Carbonate Formation and Reverse Weathering Reactions

The ocean’s buffering capacity, or alkalinity, regulates the amount of atmospheric CO₂ the ocean can sequester. Typically, it is assumed that the formation of carbonate minerals is the only sink for ocean alkalinity. However, in recent years, the formation of alumino-silicate phases in the seabed via reactions that consume alkalinity and produce CO₂ (reverse weathering) has been shown to be significant in the modern ocean and is thought to provide a control on the long-term C cycle. Evolutionary changes in the modes of carbonate production and the availability of certain seawater constituents are also important controls on CaCO₃ formation beyond the flux of alkalinity into the ocean. Here we explore the links between biogeochemical cycles, seawater chemistry, and alkalinity sinks.