Before the Industrial Revolution, the ocean was a source of CO to the atmosphere balancing the impact of rock weathering and terrestrial particulate organic carbon; now it has become a sink for the excess atmospheric CO.  Carbon dioxide is absorbed from the atmosphere at the ocean's surface at an exchange rate which varies locally  but on average, the oceans have a net absorption of CO 2.2 Pg C per year. Because the solubility of carbon dioxide increases when temperature decreases, cold areas can contain more CO and still be in equilibrium with the atmosphere; In contrast, rising sea surface temperatures decrease the capacity of the oceans to take in carbon dioxide.  The North Atlantic and Nordic oceans have the highest carbon uptake per unit area in the world, and in the North Atlantic deep convection transports approximately 197 Tg per year of non-refractory carbon to depth.
A 2020 study found significantly higher net flux of carbon into the oceans compared to previous studies. The new study used satellite data to account for small temperature differences between the surface of the ocean and the depth of a few meters where the measurements are made.