The cumulative ocean uptake during the period from 1850 to 1998 is estimated to be 120 ± 50PgC - that is, about 30% of anthropogenic emission has been taken up in the ocean.
The fraction of anthropogenic CO2 that is taken up in the ocean declines with increasing CO2 concentration in the atmosphere. Increasing atmospheric CO2 concentration maintains the atmosphere-ocean difference in partial pressure of CO2 that causes net uptake of carbon by the ocean. However, increasing DIC reduces the buffer capacity of the carbonate system, and thus weakens the capacity of the oceanic uptake.
The capacity of the ocean uptake is also sensitive to the rate of increase of atmospheric CO2. The uptake is limited with the rate of mixing between deep water and surface water, and hence the lower the growth rate of atmospheric CO2, the higher the rate of CO2 sequestration.
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