Carbonate Chemistry, Carbon Cycle, and Its Sequestration in Aquatic System

Carbon is the universal currency used by biota to store and expend energy. Oceans act as a reservoir for almost 30% of the atmospheric carbon dioxide. The oceans store carbon in three forms: dissolved inorganic carbon (CO 2 , HCO 3 − , and CO 3 2− ), dissolved organic carbon (both small and large organic molecules), and particulate organic carbon (live organisms or fragments of dead plants and animals). They also store it in the form of black carbon (BC). Carbon keeps on exchanging between the aquatic and terrestrial ecosystems via atmosphere. Inorganic carbon is absorbed and released at the interface of the ocean's surface and surrounding air, through the process of diffusion. This exchange of inorganic carbon takes place only in the form of CO 2 , which forms carbonate when dissolved in seawater. The formation of carbonate allows oceans to take up and store a much larger amount of carbon than would be possible if dissolved CO 2 remained in that form. Carbon is also cycled through the ocean by the biological processes of photosynthesis, respiration, and decomposition of aquatic plants. The changes in the chemistry of the ocean due to acidification have a great impact on marine life as well as corals and foraminifera. Since the concentration of carbon dioxide has increased rapidly in the last few decades, it becomes crucial for us to fully understand the carbonate processes and the various source and sink of carbon in the aquatic system in order to mitigate the negative effects of global warming and climate change.