Transcom 3 inversion intercomparison: Model mean results for the estimation of seasonal carbon sources and sinks

Abstract

[1] The TransCom 3 experiment was begun to explore the estimation of carbon sources and sinks via the inversion of simulated tracer transport. We build upon previous TransCom work by presenting the seasonal inverse results which provide estimates of carbon flux for 11 land and 11 ocean regions using 12 atmospheric transport models. The monthly fluxes represent the mean seasonal cycle for the 1992 to 1996 time period. The spread among the model results is larger than the average of their estimated flux uncertainty in the northern extratropics and vice versa in the tropical regions. In the northern land regions, the model spread is largest during the growing season. Compared to a seasonally balanced biosphere prior flux generated by the CASA model, we find significant changes to the carbon exchange in the European region with greater growing season net uptake which persists into the fall months. Both Boreal North America and Boreal Asia show lessened net uptake at the onset of the growing season with Boreal Asia also exhibiting greater peak growing season net uptake. Temperate Asia shows a dramatic springward shift in the peak timing of growing season net uptake relative to the neutral CASA flux while Temperate North America exhibits a broad flattening of the seasonal cycle. In most of the ocean regions, the inverse fluxes exhibit much greater seasonality than that implied by the DpCO 2 derived fluxes though this may be due, in part, to misallocation of adjacent land flux. In the Southern Ocean, the austral spring and fall exhibits much less carbon uptake than implied by DpCO 2 derived fluxes. Sensitivity testing indicates that the inverse estimates are not overly influenced by the prior flux choices. Considerable agreement exists between the model mean, annual mean results of this study and that of the previously published TransCom annual mean inversion. The differences that do exist are in poorly constrained regions and tend to exhibit compensatory fluxes in order to match the global mass constraint. The differences between the estimated fluxes and the prior model over the northern land regions could be due to the prior model respiration response to temperature. Significant phase differences, such as that in the Temperate Asia region, may be due to the limited observations for that region. Finally, differences in the boreal land regions between the prior model and the estimated fluxes may be a reflection of the timing of spring thaw and an imbalance in respiration versus photosynthesis.

Systematic assessment of terrestrial biogeochemistry in coupled climate–carbon models

“…The different spatial patterns in the two models are mostly unconstrained by existing observations and further highlight the need for future FACE The observations are from Globalview (Masarie & Tans, 1995). The model estimates were obtained using model fluxes from experiment 1.4 and monthly impulse response functions from the TRANSCOM experiment (Gurney et al, 2004). The TRANSCOM multimodel mean estimate is shown for each case.…”

“…To compare with the Globalview observations, we combined CASA 0 and CN surface CO 2 fluxes with monthly atmospheric impulse functions from the Atmospheric Tracer Transport Model Intercomparison Project (TRANSCOM) phase 3 level 2 experiments (Gurney et al, 2004) to construct simulated annual cycles of atmospheric CO 2 . Using techniques applied in interannual inversions, the response functions were used to fill a matrix (the H matrix defined in Baker et al, 2006).…”

Sources of variations in total column carbon dioxide

“…On yearly timescales, not all CO 2 emitted to the atmosphere by fossil fuel burning remains airborne: approximately 40-50% is taken up by natural oceanic or terrestrial sinks (Le Quéré et al, 2009). Inference of the strength and location of these natural sinks is the focus of many inverse studies (Gurney et al, 2002(Gurney et al, , 2004.…”

“…Inverse modeling represents one approach for estimating regional and global carbon fluxes from gradients in the observed concentration (or mixing ratio) of CO 2 , [CO 2 ] (Gurney et al, 2002(Gurney et al, , 2004.…”

Variability of oceanic carbon cycle in the North Pacific from seasonal to decadal scales

“…Future climate depends largely on the evolution of atmospheric CO 2 levels. As one of the major CO 2 reservoirs, the ocean has mitigated this rising CO 2 by taking up nearly one-third of anthropogenic CO 2 emissions at a rate of about 1.5-2.0 Pg C yr 21 [Battle et al, 2000;Sarmiento et al, 2000;Keeling and Garcia, 2002;Takahashi et al, 2002;Gurney et al, 2004;Sabine et al, 2004a;Gruber et al, 2009]. As a consequence, oceanic uptake of anthropogenic CO 2 can lead to ocean acidification, which reduces ocean pH value, lowers calcium carbonate saturation state, changes seawater chemical speciation, and further alters ocean biogeochemical cycle [Doney et al, 2009a].…”