labs_title

Caldeira Lab Research:Ocean acidification and ocean carbon cycle

Evaluation of ocean model ventilation with CFC-11: comparison of 13 global ocean models

J.C. Dutay, J.L. Bullister, S.C. Doney, J.C. Orr, R. Najjar, K. Caldeira, J.M. Champin, 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.K. Matear, P. Monfray, G.K. Plattner, K. Sarmiento, R. Schlitzer, R. Slater I.J. Totterdell, M.F. Weirig, Y. Yamanaka & A. Yool

The abilities of thirteen ocean models to match observed distribution levels of CFC-11 in the ocean are compared. Since CFC-11 distribution can be used to determine ocean ventilation on a decadal time scale, this comparison is important to ascertain which models properly ventilate the ocean when predicting effects of long term CO2 uptake.


Dutay, J.-C., J.L. Bullister, S.C. Doney, J.C. Orr, R. Najjar, K. Caldeira, J.-M. Champin, 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, G.-K. Plattner, J. Sarmiento, R. Schlitzer, R. Slater, I.J. Totterdell, M.-F. Weirig, Y. Yamanaka, and A. Yool, Evaluation of ocean model ventilation with CFC-11: comparison of 13 global ocean models. Ocean Modeling 4, 89–120, 2002.

CFC-11 global inventory as predicted by various models: CFC-11 inventory is graphed above as a function of time for 13 different ocean models. The results show some disagreement but a generally similar trend.

Observed CFC-11 data compared to simulated data: Observed data (red line) is graphed compared to simulated data for CFC-11 inventory and penetration depth. Although it is difficult to extract exact values for each model here, a general trend of the models to underestimate inventory and penetration depth below 40 degrees latitude can be seen.

Abstract

We compared the 13 models participating in the Ocean Carbon Model Intercomparison 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 timescales relevant for anthropogenic CO2 uptake. We found a large range in the modeled global inventory, 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 globally 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.