Atmospheric pCO2 is set to a large degree by the oceanic carbon pumps,a combination of biological, physical and chemical processes which lead to the enrichment of inorganic carbon in the deep ocean.

This thesis analyzes in depth the factors that affect the strength of the oceanic carbon pumps and how they impact the air-sea balance of CO2 and oceanic biological production. We show that the strength of the carbon pumps depends strongly on the large scale circulation, on the concentration of preformed nutrients in high latitudes and on the rate of gas exchange. Through their effect on the large scale circulation and Southern Ocean convective overturning, diapycnal mixing has a large impact on the carbon pumps while isopycnal mixing has a small impact. The emphasis in on trying to understand the behavior of the soft tissue pump, the single most important pump for changes in the air-sea carbon balance.

Nutrients are present in the ocean in two separate forms: preformed and remineralized. The net preformed nutrient concentration of the deep ocean is a function of the relative contributions of Antarctic Bottom Water and North Atlantic Deep Water to the deep and the initial preformed nutrient concentration of these source waters.
I show that changes in oceanic circulation and depletion of high latitude nutrients impact strongly the deep ocean preformed concentration, forcing remineralized nutrients to change in such a way as to conserve the total nutrient pool.
In turn, the amount of remineralization in the ocean is primarily responsible for setting the soft tissue pump strength and the oceanic uptake of CO2. Therefore, the soft tissue pump strength and CO2 sequestration in the deep ocean are controlled almost completely by the factors that control preformed nutrients.

In agreement with previous studies I show that the Southern Ocean is crucial in controlling the atmosphere-ocean balance of carbon dioxide as well as global biological production. The large-scale pattern of circulation in the Southern Ocean involves upwelling of deep water, some of which flows to the south to sink as bottom water, and some of which flows to the north to form intermediate and mode waters.

This work shows that the air-sea balance of carbon dioxide is controlled primarily by the biological pump and circulation in the deep-water
formation (Antarctic) region, whereas global biological productivity is controlled
primarily by the biological pump and circulation in the intermediate and mode water formation (Subantarctic) region. This implies that it may be possible for climate change or human intervention to modify one of these without greatly altering the other.

Specific locations of active deep water formation and convective exchange such as the Weddell Sea rather than the entire Antarctic surface are shown to be most relevant for the air-sea carbon balance. Finally, the thesis examines the impact of different factors (diapycnal mixing, rate of biological uptake, seasonality, rate of gas exchange) on the relationship between atmospheric pCO2 and biological production.