It is investigated how abrupt changes in the North Atlantic (NA) thermohaline circulation (THC) affect the terrestrial carbon cycle. The Lund-Potsdam-Jena Dynamic Global Vegetation Model is forced with climate perturbations from freshwater experiments with the ECBILT-CLIO ocean-atmosphere model. A reorganization of the marine carbon cycle is not addressed. Modeled NA THC collapsed and recovered after about a millennium in response to prescribed freshwater forcing. The initial cooling of several Kelvin over Eurasia causes a reduction of extant boreal and temperate forests and a decrease in carbon storage in high northern latitudes, whereas improved growing conditions and slower soil decomposition rates lead to enhanced storage in mid-latitudes. The magnitude and evolution of global terrestrial carbon storage in response to abrupt THC changes depends sensitively on the initial climate conditions. These were varied using results from time slice simulations with the Hadley climate model for different periods over the past 21,000 years. Terrestrial storage varies between -67 and +50 PgC for the range of experiments with different initial conditions. Simulated peak-to-peak differences in atmospheric CO₂ and d¹³C are 6 and 18 ppmv for glacial and early Holocene conditions. Simulated changes in d¹³C are between 0.18 and 0.30 permil. The small CO₂ changes modelled for glacial conditions are compatible with available evidence from marine studies and the ice core CO₂ record. The latter shows CO₂ variations of up to 20 ppmv broadly in parallel with the Antarctic warm events A1 to A4.

The terrestrial ecosystem carbon cycle model, Sim-CYCLE, was combined with the CCSR/NIES/FRCGC AGCM5.7b (including a land surface model: MATSIRO). That coupled model shows a reasonable distribution of the LAI, NPP and other carbon storages after the 1000yrs spin-up run. This presentation introduces the preliminary results of the coupled run in 20th century.

Here we use the severe heat and drought event in Europe from summer 2003 as a natural experiment to study the impact of a climatic extreme event on ecosystem physiology and its feedback to the atmosphere. The combination of continuous eddy covariance and tree growth measurements at two nearby located deciduous forests showed a large reduction in carbon uptake during the drought (-30%) and a strong carry-over effect into the next year. Both forests, however, responded differently, although climatic forcing was almost identical. Species composition and site condition of the ecosystems seemed to play a major role in the ecosystems response to the drought.

Measurements of the isotopic composition of carbon dioxide were performed on EPICA Dome C ice on 76 different depth levels covering the last 40’000 years. The time resolution is in the order of 500 years for the last 18’000 years. For each depth level at least two determinations were obtained. The d¹³C signals show different trends during the last 18000 years that are anti-parallel to the CO₂ concentration evolution as measured on the same ice core. However millennial scale deviations from these trends are observed for at least three time periods. The robustness and significance of these deviations are investigated by Monte Carlo simulations performed with different subsets of the measurements. The decreases of carbon isotopes could be connected with observed step-like increases of the CO₂ concentration. Furthermore, a similar evolution as for stable carbon isotopes is visible for detrended radiocarbon. We will discuss potential mechanisms responsible for the trends as well as for the millennial scale deviations in carbon-13, including changes in the thermohaline circulation as well as potential influences of a changing ¹⁷O-¹⁸O relationship.

Using a coupled 3D hydrodynamic-biogeochemical model system for the Northwest-European shelf we simulated the years 1993-96, which exhibit an extremely strong transition from a NAOI-high to a NAOI-low regime. The induced temperature-shift had two consequences for the carbon budget of the North Sea: Firstly it increased the CO₂ solubility and secondly it destabilized the water column in spring 1996. The latter effect was the precondition for mixing events which brought new nitrogen for primary production into the upper layer. Consequently the air-sea flux was 540 Gmol C a^-1 in 1996, the NAOI-low year, and it was 203 Gmol C a^-1 in 1995, the year with the highest NAOI.

A Time Dependent Inverse (TDI) model is used to estimate CO₂ fluxes for 64 regions of the globe from atmospheric data in the period January 1988–December 2001. These estimated are then used for understanding interannual variability in fluxes and simulating the CO₂ concentrations at various sites. The NIES/FRCGC transport model driven by interannually varying meteorology is used in both part of the analysis. Estimated atmospheric CO₂ concentrations agree closely with those observed at various sites globally.

The Amazon region of South America plays a significant role in global cycles of water, energy and carbon, yet it is also one of the most challenging biogeographical areas of the world to model correctly. Numerous global climate models have problems with anomalous die-back of the Amazon rain forest variously attributed to inadequate representation of rainfall, faulty soil moisture dynamics or an inability to correctly simulate the drought tolerance of the vegetation. Such misrepresentation of the Amazon in global climate models can cause larger than observed excursions of the global carbon cycle. This poster explores soil moisture and drought stress for Amazonia with the Simple Biosphere Model (SiB3) and possible reasons and solutions to the rain-forest die back problem, which should lead to more reasonable estimates of carbon fluxes at the ecosystem scale.

Increasing ocean stratification associated with global warming has been posited to serve as a positive feedback on global warming, reducing the oceanic uptake of anthropogenic carbon dioxide. We suggest that a poleward shift of westerly winds combined with future increases in atmospheric carbon dioxide may drive an increase in the CO₂ uptake in the Southern Ocean, representing a negative feedback on atmospheric anthropogenic CO₂.

The mixing ratios of atmospheric CO₂ were observed at the summit of Mt. Fuji by using a system for continuous measurements during September 2002-February 2003 and May 2003-May 2004. The observed CO₂ variations at Mt. Fuji showed a seasonal cycle of the background level with a maximum around April and a minimum around August. A lot of episodic events with a large enhancement of CO₂ were found, and the episodic enhancements of CO₂ at Mt. Fuji were well associated with increased CO peaks observed at the same time. The enhancement ratios of CO to CO₂ mixing ratios (ΔCO/ΔCO₂) mainly showed lower values of less than 0.03 due to urban/industrial sources, while relatively higher ΔCO/ΔCO₂ ratios up to 0.08 were also found for the episodic events due to the biomass burning emissions. Three-dimensional transport model simulations of CO suggested that the major contributions for the increased events at Mt. Fuji were from China (~50%) and the other major regions were Southeast Asia and South Asia (~10%).