EVALUATION OF OCEAN MODEL VENTILATION WITH CFC-11: COMPARISON OF 13 GLOBAL OCEAN MODELS

Reference
Dutay,J.-Cl., J. Bullister, S. Doney, J. C. Orr, R. G. Najjar, K. Caldeira, J.-M Campin, H. Drange, M. Follows, Y. Gao, N. Gruber, M. W. Hecht, A. Ishida, F. Joos, K. Lindsay, G. Madec, E. Maier-Reimer, J.C. Marshall, R.J. Matear, P. Monfray, A. Mouchet, G.-K. Plattner, J.L. Sarmiento, R. Schlitzer, R. Slater, I.J. Totterdell, M.-F. Weirig, Y. Yamanaka, A. Yool, Evaluation of ocean model ventilation with CFC-11: Comparison of 13 global ocean models, Ocean Modeling, 4, 89-120, 2002.

Abstract
We compared the 13 models participating in the Ocean Carbon Model Intercomparaison
Project (OCMIP) with regards to their skill in matching observed distributions of CFC-11.
This analysis characterizes the abilities of these models to ventilate the ocean on time scales
relevant for anthropogenic CO2 uptake. We found a large range in the modeled global
iinventory (±30%), mainly due to differences in ventilation from the high latitudes. In the
Southern Ocean, models differ particularly in the longitudinal distribution of the CFC uptake
in the intermediate water, whereas the latitudinal distribution is mainly controlled by the
subgrid-scale parameterization. Models with isopycnal diffusion and eddy induced velocity
parameterization produce more realistic intermediate water ventilation. Deep and bottom water
ventilation also varies substantially between the models. Models coupled to a sea-ice model
systematically provide more realistic AABW formation source region; however these same
models also largely overestimate AABW ventilation if no specific parameterization of brine
rejection during sea-ice formation is included. In the North Pacific Ocean, all models exhibit a
systematic large underestimation of the CFC uptake in the thermocline of the subtropical gyre,
while no systematic difference toward the observations is found in the subpolar gyre. In the
North Atlantic Ocean, the CFC uptake is globaly underestimated in subsurface. In the deep
ocean, all but the adjoint model, failed to produce the two recently ventilated branches
observed in the North Atlantic Deep Water (NADW). Furthermore, simulated transport in
the Deep Western Boundary Current (DWBC) is too sluggish in all but the isopycnal model,
where it is too rapid.

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