Shelf-vs. dissolution-generated alkalinity above the chemical lysocline

Processes that increase alkalinity in the upper water column facilitate the sequestration of anthropogenic CO2. Conventional wisdom has it that most alkalinity is generated by the dissolution of calcium carbonate and that this process chiefly occurs only at great depths in the oceans. This is because most surface waters are supersaturated with respect to both calcite and aragonite; hence, calcium carbonate does not dissolve. As a result, it is widely held that most alkalinity is released into the deep oceans and that it does not enhance the ability of the oceans to absorb anthropogenic CO2 at the air–sea interface. However, such anaerobic processes as sulfate reduction in the sediments on the continental shelves do generate alkalinity that is unrelated to the dissolution of calcium carbonate. In fact, shelf-generated alkalinity may almost be as important as that generated by dissolution in the open oceans above the chemical lysocline. Globally, the former amounts to 16–31×1012 mol/yr.