Model studies on the response of the terrestrial carbon cycle to climate change and variability

• Main Author: Scholze, M.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Hamburg 2003
• Subjects: ice core
• Online Access: http://hdl.handle.net/11858/00-001M-0000-0012-0198-9; http://hdl.handle.net/11858/00-001M-0000-0012-0197-B

The first part of this thesis describes the further development of a dynamic global vegetation model, LPJ, and its application to selected scientific questions. LPJ has been extended to include isotopic fractionation of 13C at the leaf level during assimilation and includes a full isotopic terrestrial carbon cycle. Hence, it simulates the isotopic signature of the heterotrophic respiration fluxes. The model thus allows a quantitative analysis of the net biosphere exchange of CO2 and 13CO2 with the atmosphere as a function of changes in climate, land cover, atmospheric CO2, and the isotope ratio of CO2. The extended version of LPJ has been used to study the response of the global vegetation distribution to an abrupt climate change event (Younger Dryas) and the thereby incurred changes in the terrestrial carbon pools and fluxes and their isotopic 13C/12ratio. Climate data from a 850-year-long coupled ocean-atmosphere general circulation model (ECHAM3/LSG) is used for these simulations. The comparison of the modelled vegetation distribution and shifts during this idealized Younger Dryas event with reconstructed vegetation maps for North America and Europe based on pollen records shows a reasonable agreement. The impact of the terrestrial carbon release during the Younger Dryas on the atmospheric CO2 and δ 13C is analyzed using a simplified ocean model and compared to ice core measurements. In the standard case the simulation exhibits a significant change in global total terrestrial carbon stocks of about 180 Pg C leading to an atmospheric CO2 increase of approx. 28 ppmv as a consequence of the climate change event. The robustness of the terrestrial signal during the Younger Dryas is studied by several sensitivity experiments concerning the initial values of the carbon pool sizes as well as the CO2 fertilization effect and the temperature dependency of the carbon decomposition rates. The resulting increase of atmospheric CO2 concentrations for the cold event varies between 16 to 33 ppmv among the different ...