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ORFOIS Résumé de rapport

Project ID: EVK2-CT-2001-00100
Financé au titre de: FP5-EESD
Pays: Denmark

BOGCM HAMOCC runs, global warming

The physical ocean model fields driving the biogeochemical module HAMOOC5 were computed under anomaly forcing using the ECHAM3/OPIC results from the GHG experiment (Roeckner et al., 1999). Changes in the ocean carbon uptake due to an increased atmospheric CO2-concentration were determined from being integrated with the HAMOCC5 model. The atmospheric CO2-concentration was prescribed in the period 1860-2050 according to the IS92a-scenario. This IS92a implies a "business-as-usual" scenario resulting in a rapid increase in the atmospheric CO2-level such that the pCO2 level has reached 519ppm by 2050.

The carbon uptake experiments were started from a 1200-year spin-up of the physical model. The nutrients, oxygen and biomasses were started from a 650-year integration. Initial conditions for total CO2 and alkalinity were obtained by starting integration from present day total CO2 and alkalinity fields (gridded results from the GLODAP project, R. Key et al., 2004). The gridded data of total CO2 and alkalinity was interpolated onto the HAMOCC5 grid for each vertical level, in the same way as the two-dimensional ECHAM4/OPYC3 forcing fields were interpolated.

Finally, the fields were linearly interpolated onto the depth levels in the HAMOCC5 grid. The GLODAP data only covers the ocean up to 64 N. North of this latitude the total CO2 and alkalinity was estimated from linear relationships to salinity. These relations were determined from total CO2, alkalinity and salinity measured in the Nordic seas. Initially the model was integrated with an atmospheric pCO2 = 280ppm to obtain a DIC-field in equilibrium with pre-industrial conditions. The HAMOCC5 IS92a-experiment presented in this report is from a 35 year spin-up with a pCO2 = 280ppm.

This implies that the upper ocean has not equilibrated to the pCO2 = 280ppm. Therefore the first century of the integration is not representative for the ocean uptake in this period, and in the final part of the integration only the time dependent trends are representative for the oceanic carbon uptake. The surface alkalinity field is relaxed toward the observed field in a way similar to the relaxation performed on the surface salinity. The CO2 air-sea gas exchange depends on the fractional ice-cover. The initial conditions for the IS92a were not equilibrated with the pre-industrial conditions. However, a longer 100-year integration was made with an atmospheric pCO2 level of 280. This solution was closer to equilibrium than the solution used for the initial conditions.


Joergen BENDTSEN, (senior scientist)
Tél.: +49-40-41173233
Fax: +49-40-41173298