TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 57 (No. 4), pp. 433-450, 2001

Sensitivity of CFCs and Anthropogenic CO2 Uptake in a North Pacific GCM to Mixing Parameterization and Surface Forcing

Akio Ishida1*, Kisaburo Nakata2, Shigeaki Aoki3, Hiroshi Kutsukake4, Michio J. Kishi5 and Masahisa Kubota2

1Kansai Environmental Engineering Center Co., Ltd., 1-3-5 Aduchi-cho, Chuo-ku, Osaka 541-0052, Japan
2School of Marine Science and Technology, Tokai University, Shimizu 424-8610, Japan
3Environmental Assessment Department, National Institute for Resources and Environment, Tsukuba 305-8569, Japan
4Institute of Environmental Information, Metocean Environment Inc., Yokohama 224-0025, Japan
5Graduate School of Fisheries Sciences, Hokkaido University, Hakodate 041-8611, Japan

(Received 27 October 1998; in revised form 20 October 2000; accepted 20 October 2000)

Abstract: Distributions and characteristics of water mass and chlorofluorocarbons (CFCs) in the North Pacific are investigated by using a General Circulation Model (GCM). The anthropogenic CO2 uptake by the ocean is estimated with velocity fields derived from the GCM experiments. The sensitivity of the uptake to different diffusion parameterizations and different surface forcing used in the GCM is investigated by conducting the three GCM experiments; the diffusive processes are parameterized by horizontal and vertical eddy diffusion which is used in many previous models (RUN1), parameterized by isopycnal diffusion (RUN2), and isopycnal diffusion and perpetual winter forcing for surface temperature and salinity (RUN3). Realistic features for water masses and CFCs can be simulated by the isopycnal diffusion models. The horizontal and vertical diffusion model fails to simulate the salinity minimum and realistic penetration of CFCs into the ocean. The depth of the salinity minimum layer is better simulated under the winter forcing. The results suggest that both isopycnal parameterization and winter forcing are crucial for the model water masses and CFCs simulations. The oceanic uptake of anthropogenic CO2 in RUN3 is about 19.8 GtC in 1990, which is larger by about 10% than that in RUN1 with horizontal and vertical diffusive parameterization. RUN3 well simulates the realistic water mass structure of the intermediate layer considered as a candidate of oceanic sink for anthropogenic CO2. The results suggest that the previous models with horizontal and vertical diffusive parameterization may give the oceanic uptake of anthropogenic CO2 underestimated.

*Corresponding author E-mail: ishidaa@jamstec.go.jp

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