1. Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Uncertainties of model simulations of anthropogenic carbon uptake J. Segschneider, E Maier-Reimer, and K. Six Max-Planck-Institute for Meteorology, Hamburg, Germany EU FP6 IP 511176 (GOCE) CARBOOCEAN

2. Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. In CARBOOCEAN we want to reduce the range of uncertainty in estimates of carbon uptake which processes give rise to uncertainties? how exact is the representation of processes in our models? how well are parameters defined? Motivation:

3. Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Uncertainties which processes give rise to uncertainty? biological production and remineralization in a warming climate export production dust/iron input – other effects than iron supply? (e.g., N-fixation, ballast effect) CaCO 3 export and alkalinity pump: silicate depletion vs. acidification shifts in PFT abundance, physics vs. biogeochemistry? role of shelf seas (nutrient supply, river input) production of climate relevant gases (DMS, N 2 ?) climate feedback

4. Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Uncertainties how appropriate is the representation of processes in our models? photosynthesis and remineralization: simple, difficult to constrain for more complex schemes export production: simple (Martin curve) to more complex (aggregation schemes) dust/iron input: simple, more details emerging (like spatially varying solubility, deep water concentrations) CaCO 3 export and alkalinity pump: simple, diatoms/coccos distinguished, quantitatively little known about ecosystem during acidification role of shelf seas: emerging in global models climate relevant gases: emerging

5. Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Uncertainties HAMMOCC5.1 tunable parameters: chemistry: 62 parameters, most fairly well known, largest uncertainty from gas exchange? biology including export: 44 (including DMS), +16 from aggregation largest uncertainty from biology (grazing rates, growth rates, remineralization, settling velocity) sediment: 12 + 2 for erosion total: 138 …..+ physics! some are known from experiments, some determined by ‘’fit’’ to tracer distribution (hard constraint since well observed)

6. Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Uncertainties examples for tunable parameters: nutrient uptake: Redfield ratio (122C:16N:- 172O 2 :1P) known fairly exact but may be variable iron chemistry: solubility of iron, complexation, scavenging… ongoing research carbonate chemistry: solubility, reaction constants, …, mainly from experimental work in early 1970s, interaction with physics [T,S] biology: growth and grazing rates of phyto- and zooplankton, mortality, export (wide parameter range, mainly determined by fit to nutrient distribution and [less robust] fit to satellite chlorophyll, ongoing research - model resolution sensitive, MOC sensitive

7. Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Uncertainties how much do we depend on physical models? photosynthesis and remineralization: nutrient distribution (currents, mixing), temperature, solar radiation export production: vertical mixing, turbulence dust/iron input: atmospheric models of dry/wet deposition, aerosol chemistry CaCO 3 export and alkalinity pump: MOC, temperature, mixing role of shelf seas: representation of shelf processes gas exchange: wind field, ice cover, mixing

8. Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Uncertainties how to quantify (with regard to C ant )? multi model approach / inter comparison comparison with observations/observation based estimates of C ant parameter variations (like ensemble studies in atmospheric/climate research, expensive due to long equilibrium time constants, can take years) CFC/ 14 C simulations + comparison with observations

9. Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. GLODAP (Observed) 110 GtC MODEL 109 GtC 1994 anthropogenic CO 2 column inventory [mol/m 2 ] Model test: ‘historical’ uptake until 1994

10. Third annual CarboOcean meeting, 4.-7.December 2007, Bremen, Segschneider et al. Summary Uncertainties in the model integration to derive the initial state mean uncertainties in the projections (are the uncertainties constant in time)? Ideally we would like to have an assimilation system to estimate the current status and start model projections from there - this would also provide error bars for the period covered by observations and maybe beyond depending on the choice of the system