Das Projekt "Modellierung des biogeochemischen Kohlenstoff-Zyklus" wird vom Umweltbundesamt gefördert und von Universität Bern, Physikalisches Institut, Abteilung für Klima- und Umweltphysik durchgeführt. Parallel to the glacial-interglacial climatic variations, the atmospheric concentrations of carbon dioxide changed. Via the greenhouse effect, CO2 and other trace gases habe played an important role as climate forcing factors. The large changes in the climate-CO2 system connected with the ice-age cycles are one of the most fascinating and challenging problems of current climate research. The CO2 variations are probably linked to rearrangements of the large-scale ocean circulation, but the details of the mechanisms involved are not clear. We propose to develop a carbon cycle model of intermediate complexity between simple box models and 3-dimensional ocean circulation models. This shall be accomplished in the following steps: 1) Inclusion of the biogeochemical cycle of carbon and associated elements (nutrients, oxygen) into the 2-D dynamical ocean model, developed at the Institut d'Astronomie et de Geophysique at Louvain-La-Neuve, Belgium. 2) Validation of the 2-D ocean model by comparing calculated with observed distributions. 3) Study the sensitivity of the concentration and isotopic composition of atmospheric CO2 to changes in marine biology, ocean circulation, temperature etc. 4) Identification of the causes of glacial-interglacial CO2 variations by comparing model results with paleo-observations from deep-sea sediments and polar ice cores.