WG 2: Biogeochemistry
Dr. Victor Brovkin
MPI for Meteorology, Bundesstr. 53, 20146 Hamburg
Dr. Tatiana Ilyina
MPI for Meteorology, Bundesstr. 53, 20146 Hamburg
Dr. Peter Köhler
Alfred-Wegener-Institut (AWI) Helmholz-Zentrum für Polar- und Meeresforschung, Am Alten Hafen 26, 27568 Bremerhaven
1. Alfred-Wegener-Institut (AWI) Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven
2. Institut für Biogeochemie und Meereschemie der Universität Hamburg (UHH), Hamburg
3. Institut für Geowissenschaften der Universität Kiel (CAU), Kiel
4. MARUM - Zentrum für Marine Umweltwissenschaften der Universität Bremen, Bremen
5. Max-Planck-Institut für Chemie (MPI-C), Mainz
6. Max-Planck-Institut für Meteorologie (MPI-M), Hamburg
7. Potsdam-Institut für Klimafolgenforschung (PIK) e. V., Potsdam
Ice cores provide compelling evidence that glacial-interglacial changes in climate and greenhouse gases are tightly coupled. The long-term goal of WG2 in PalMod is to understand processes controlling this coupling and to quantify feedbacks between biogeochemistry and climate during glacial cycles using Earth System Models. In the 2nd phase, the main challenge for WG2 is to apply project ESMs for fully-coupled interactive climate-carbon cycle simulations through the last deglaciation (21 to 6 ka). Such simulations were never done before with full-scale ESMs. In addition to deglaciation runs, WG2 will also perform millennial-scale ESM simulations to analyze the carbon and CH4 cycle variability during abrupt climate events in MIS-3 and to compare them with available data together with WG3. To prepare fully-coupled interactive climate-biogeochemistry simulations through the last glacial cycle in the 3rd phase, first simulations of the glacial inception (125-110 ka) with prescribed atmospheric CO2 concentration for physics but prognostic CO2 concentration in biogeochemistry will be performed in cooperation with WG1.
Our general strategy is to use the model ensemble developed in phase 1: AWI-ESM, CESM, MPI-ESM. The principal feature of the global carbon cycle is that it strongly depends on the physical climate components: atmospheric and ocean circulations, as well as the cryosphere. Therefore, setting up the biogeochemical components (land vegetation and carbon cycle, ocean biogeochemistry) for transient simulations will be done in close interaction with WG1 packages 1.1 to 1.3. Every ESM team will prepare biogeochemistry models for the transient runs in coupled setup, when changes in land and ocean carbon fluxes simultaneously influence atmospheric CO2 concentration and, consequently, climate. A particular challenge in the 2nd phase is to couple land and ocean biogeochemical exchange in shelf regions induced by sea-level changes in co-operation with the CC.2 theme. Experiments with the two orders-of-magnitude faster EMIC CLIMBER-X will serve as a guideline for transient simulations with ESMs.
Workflow in WG2 is structured along biogeochemical components, and three WG2 packages are focused on the marine carbon cycle, terrestrial and shelf processes, and the CH4 cycle.
WP2.1 Marine Carbon Cycle
Principal Investigators: P. Köhler (AWI), T. Ilyina (MPI-M), B. Schneider (CAU), A. Paul (MARUM)
Setting up biogeochemical simulations with prognostic atmospheric CO2 concentration in all three ESMs is a first task for WP2.1. This work includes adjustment of initial inventories, a coupling of land- ocean carbon exchanges due to sea level changes, as well as accounting for weathering fluxes and volcanic outgassing. Simulations done together with WP1.1 will be evaluated against available data estimates and additional sensitivity simulations will be performed. Carbon isotopes will help to identify which changes in the physical system agree with reconstructions. Here, 14C can and will also be used in simulations without interactive carbon cycle, as done before (Butzin et al., 2012), while for 13C isotopic fractionation during photosynthesis needs to be considered and therefore an interactive carbon cycle is necessary.
WP2.2 Land and Shelf Processes
Principal Investigators: A. Ganopolski (PIK), M. Claussen (MPI-M), J. Hartmann (Uni HH)
This work package takes care of biogeochemical processes on land and exposed shelves. Vegetation, desert, and land carbon dynamics during deglaciation, inception, and MIS3 will be quantified using MPI-ESM in co-operation with WG1. It will be also be utilized for AWI-ESM, and compared with available pollen data synthesized in WG3. The carbon exchange between land and ocean components on exposed shelves will be done together with CC.1. Weathering on exposed shelves will be reconstructed and -included in simulations with prognostic CO2 concentrations. WG2 will also use the EMIC, CLIMBER-X, as a fast 3-D ocean model prototype to test hypotheses on processes behind deglacial CO2 rise and CO2 decrease during glacial inception.
WP2.3 Methane Cycle
Principal Investigators: T. Kleinen (MPI-M), B. Steil (MPI-C)
The main challenge in the CH4 work package is to simulate atmospheric CH4 concentrations in a concert between terrestrial CH4 emissions (mostly from wetlands) and the atmospheric methane sink using the MPI-ESM model asynchronously coupled to the atmospheric chemistry model EMAC. We will investigate CH4 dynamics during the deglaciation, glacial inception, and MIS3. A number of hypotheses will be tested using available CH4 data and the atmospheric isotopic composition of different chemical tracers. Abrupt changes in atmospheric CH4 concentrations during abrupt climate events in MIS3 will be addressed together with WP1.3.
While results during phase 1 do not indicate any major risks from the CH4 modelling itself, CH4 emissions are critically dependent on correct terrestrial C pools and fluxes (i.e. atmospheric CO2 concentrations). In case these cannot be provided by WPs 2.1 and 2.2, the fall back option of driving the model with prescribed CO2 will be required.