Ocean Biogeochemistry and Climate Feedbacks

Atmospheric levels of CO₂ and other greenhouse gases (CH₄ and N₂O) have increased substantially above preindustrial levels due to human activities. Carbon dioxide is continuously exchanged between the atmosphere and the ocean. Carbon dioxide entering the surface ocean immediately reacts with water to form bicarbonate (HCO₃^–) and carbonate (CO₃^2–) ions by means of the physical and the biological pump. These two pumps maintain a vertical gradient in CO₂ regulating the exchange of CO₂ between the atmosphere and the ocean. The strength of the solubility pump depends globally on the strength of the MOC, surface ocean temperature, salinity, stratification and ice cover. The efficiency of the biological pump depends on the fraction of photosynthesis exported from the surface ocean as sinking particles. Nowadays the oceans take ∼2.6 PgC/yr. However, models and observations suggest that, the rate of growth of this sink may have slowed down producind sever feedbacks on the climate system.

• Changes in CO₂ solubility:

CO₂ solubility is a function of the temperature, therefore as the ocean’stemperature increases the solubility of CO₂ decreases and consequently the uptake of the CO₂ is reduced.

• Changes in the ocean stratification:

Increased the sea surface temperatures (SST) and increased precipitation at high latitudes lead to an increase in the ocean’s surface stratification. This causes a shallower mixing layer and a reduction in the vertical exchange and transport of anthropogenic CO₂ to the deep ocean. The stratification reduces the supply of DIC and nutrients, which are needed for biological activity.

• Changes in the marine productivity:

Warming and other environmental changes (e.g. ocean acidification) can lead to further changes in marine productivity

• Changes in the ocean circulation:

On centennial time scales the ocean carbon sink may also be affected by climate-driven changes in the ocean circulation such as the slowing down of the Thermohaline Circulation

Using state of the art earth system model  (EC-Earth) and the experience on climate prediction gained in the Climate Prediction Group, the aim of the ocean biogeochemistry and climate feedbacks research line is to study the response of the ocean in a changing climate and their feedbacks.