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 wil l be taken up by the ocean. The North Pacific is normally considered a smal l sink of anthropogenic CO2. Recently, some researchers have proposed that the North Pacific may take up more anthropogenic CO2 than thought previousl y. 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 paramet ers 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 i n both the subpolar and subtropical regions, and also reduces the inventory of CO2 in the western subtropical region. Both smaller isopycnal and thick ness diffusivities result in a large net transport of CO2 from the North Pa cific to the South Pacific. Simulated results show that the North Pacific h as taken up about 23 GtC of excess carbon dioxide released by human activit ies between 1800 and 1997. The averaged uptake rate in the North Pacific du ring 1990-1997 is 0.40 GtC/year. Our model estimates the largest air-sea fl uxes along the western boundary around 42 degreesN, 150 degreesE and in the equatorial Pacific. Our simulated inventories slightly overestimate data-b ased estimates in the eastern North Pacific, but exhibit less penetration o f anthropogenic carbon dioxide in the western North Pacific. (C) 2000 Elsev ier Science B.V. All rights reserved.