Role of carbonate burial in Blue Carbon budgets

Calcium carbonates (CaCO(3)) often accumulate in mangrove and seagrass sediments. As CaCO(3) production emits CO(2), there is concern that this may partially offset the role of Blue Carbon ecosystems as CO(2) sinks through the burial of organic carbon (C(org)). A global collection of data on inorganic carbon burial rates (C(inorg), 12% of CaCO(3) mass) revealed global rates of 0.8 TgC(inorg) yr(−1) and 15–62 TgC(inorg) yr(−1) in mangrove and seagrass ecosystems, respectively. In seagrass, CaCO(3) burial may correspond to an offset of 30% of the net CO(2) sequestration. However, a mass balance assessment highlights that the C(inorg) burial is mainly supported by inputs from adjacent ecosystems rather than by local calcification, and that Blue Carbon ecosystems are sites of net CaCO(3) dissolution. Hence, CaCO(3) burial in Blue Carbon ecosystems contribute to seabed elevation and therefore buffers sea-level rise, without undermining their role as CO(2) sinks.