The ocean carbon pool: a vital component of the global carbon cycle

The global carbon cycle is an integral part of the Earth System. Of the land, atmosphere, and ocean components of the global carbon cycle that exchange carbon on the timescales of decades to centuries, the ocean contains more than 90% of carbon. The ocean carbon pool represents a critical component of the Earth's carbon cycle, playing a pivotal role in regulating atmospheric carbon dioxide (CO2) levels and influencing climate dynamics. The exponential increase of total anthropogenic CO2 emissions in the industrial era implies the ocean's uptake has increased exponentially, reaching 2.5 ± 0.6 Pg C yr-1 for 2009-2018. Without the ocean and land sinks, atmospheric CO2 levels would be close to 600 ppm. The ocean carbon pool comprises dissolved inorganic carbon (DIC), organic carbon, and particulate organic matter, collectively responsible for the sequestration and release of carbon into the atmosphere. Phytoplankton, the microscopic marine plants, play a fundamental role in the oceanic carbon cycle by photosynthesizing and fixing atmospheric CO2 into organic matter. This organic matter can be transferred to the deep ocean through the biological pump, further contributing to the storage of carbon in the form of sinking particles. The bulk of the global ocean margin represents a carbon sink of ~0.1-0.2 Pg C. Oceanic processes, such as ocean circulation and upwelling, help redistribute carbon from surface waters to the deep ocean. The solubility pump, which is driven by changes in temperature and salinity, also affects the solubility of CO2 in seawater. These natural processes work to mitigate the increase in atmospheric CO2 concentrations and help regulate global temperatures