Ocean Carbon Sink Calculator

The global oceans absorb approximately 2.5–3 billion tonnes (Gt) of CO₂ per year, representing roughly 25–30% of all human CO₂ emissions annually. This makes the ocean the largest active carbon sink on Earth, playing a critical role in slowing the pace of climate change.

Key factors include sea surface temperature (colder water dissolves more CO₂), wind speed (higher winds increase gas exchange), atmospheric CO₂ concentration (a larger gradient drives more absorption), ocean circulation, salinity, and biological productivity (phytoplankton convert CO₂ into organic carbon). Regional differences also matter — polar oceans tend to absorb more than tropical ones.

CO₂ is more soluble in cold water than warm water, following Henry's Law of gas solubility. As oceans warm due to climate change, their capacity to absorb CO₂ decreases. This creates a concerning feedback loop: more CO₂ warms the planet, which warms the ocean, which reduces the ocean's ability to absorb CO₂, leaving more in the atmosphere.

The ocean carbon sink refers to the net transfer of CO₂ from the atmosphere into the ocean. It operates through two main mechanisms: the 'solubility pump' (CO₂ dissolves into seawater, especially in cold, dense polar waters that sink to the deep ocean) and the 'biological pump' (phytoplankton absorb CO₂ during photosynthesis, and when they die, carbon sinks to the deep sea). Together, these mechanisms have removed over 40% of all human CO₂ emissions since industrialization.

Yes — research indicates that while the absolute amount of CO₂ absorbed by oceans continues to rise with higher atmospheric concentrations, the efficiency of the sink (as a fraction of emissions) may be declining in some regions. Ocean warming, acidification, and changes in circulation patterns all affect long-term sink capacity. Some studies have found evidence of sink weakening in the Southern Ocean and North Atlantic.

When CO₂ dissolves in seawater, it forms carbonic acid, which lowers the ocean's pH — a process called ocean acidification. Since the Industrial Revolution, ocean pH has dropped from about 8.2 to 8.1, representing a 26% increase in acidity. This affects marine ecosystems, particularly shellfish and corals that need carbonate ions to build their shells, and may ultimately reduce the ocean's long-term biological carbon uptake capacity.

The calculator uses a gas transfer velocity approach based on the Wanninkhof piston velocity formula, which depends on wind speed and sea surface temperature. The CO₂ flux is estimated from the partial pressure difference between atmospheric CO₂ and ocean surface CO₂ (modulated by temperature and salinity), the gas transfer velocity, and the ocean surface area. Regional factors adjust the baseline absorption efficiency for different ocean types such as polar, tropical, coastal, or upwelling zones.

Wind speed drives turbulence at the ocean surface, which increases the rate of gas exchange between the atmosphere and the ocean. The relationship is roughly proportional to the square of wind speed — so doubling wind speed roughly quadruples the gas transfer velocity. This is why stormy, high-latitude oceans with strong winds tend to have much higher gas exchange rates than calm tropical waters.