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

T he 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.