Simulations of storage of anthropogenic carbon dioxide in the North Pacific using an ocean general circulation model

There is a large uncertainty of how much anthropogenic CO2 has been and will be taken up by the ocean. The North Pacific is normally considered a small sink of anthropogenic CO2. Recently, some researchers have proposed that the North Pacific may take up more anthropogenic CO2 than thought previously. Here we explore this issue with a basin-wide OGCM of the North Pacific. The sensitivities of ocean circulation and the redistribution of dissolved anthropogenic CO2 in the North Pacific to the values of some mixing parameters are examined. The increase of isopycnal diffusivity generally leads to improvement of distributions of water masses. Larger isopycnal diffusivity produces larger CO2 uptake in the subpolar region but smaller CO2 uptake in the tropical region. Increasing thickness diffusivity reduces CO2 uptake in both the subpolar and subtropical regions, and also reduces the inventory of CO2 in the western subtropical region. Both smaller isopycnal and thickness diffusivities result in a large net transport of CO2 from the North Pacific to the South Pacific. Simulated results show that the North Pacific has taken up about 23 GtC of excess carbon dioxide released by human activities between 1800 and 1997. The averaged uptake rate in the North Pacific during 1990–1997 is 0.40 GtC/year. Our model estimates the largest air–sea fluxes along the western boundary around 42°N, 150°E and in the equatorial Pacific. Our simulated inventories slightly overestimate data-based estimates in the eastern North Pacific, but exhibit less penetration of anthropogenic carbon dioxide in the western North Pacific.