Impact of oceanic circulation on biological carbon storage in the 1 ocean and atmospheric p CO

We use both theory and ocean biogeochemistry models to examine the role 3 of the soft-tissue biological pump in controlling atmospheric CO2. We demonstrate that 4 atmospheric CO2 can be simply related to the amount of inorganic carbon stored in the 5 ocean by the soft tissue pump, which we term (OCSsoft). OCSsoft is linearly related 6 to the inventory of remineralized nutrientwhich in turn is just the total nutrient in7 ventory minus the preformed nutrient inventory. In a system where total nutrient is con8 served, atmospheric CO2 can thus be simply related to the global inventory of preformed 9 nutrient. Previous model simulations have explored how changes in the surface concen10 tration of nutrients in deepwater formation regions change the global preformed nutri11 ent inventory. We show that changes in physical forcing such as winds, vertical mixing, 12 and lateral mixing can shift the balance of deepwater formation between the North At13 lantic (where preformed nutrients are low) and the Southern Ocean (where they are high). 14 Such changes in physical forcing can thus drive large changes in atmospheric CO2, even 15 with minimal changes in surface nutrient concentration. If Southern Ocean deepwater 16 formation strengthens, the preformed nutrient inventory and thus atmospheric CO2 in17 crease. An important consequence of these new insights is that the relationship between 18 surface nutrient concentrations, biological export production and atmospheric CO2 is more 19 complex than previously predicted. Contrary to conventional wisdom, we show that OCSsoft 20 can increase and atmospheric CO2 decrease, while surface nutrients show minimal change 21 and export production decreases. 22