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.

This research was carried out to estimate the winter fluxes of CO₂ and CH₄ by the concentration profile method (indirect) and the chamber method (direct) at black spruce forest soils of central Alaska during the winter 2004/5. The average winter fluxes of CO₂ and CH₄ by the indirect and direct methods were 0.24±0.06 (SE; standard error) and 0.21±0.06 gCO₂-C/m²/d, and 21.4±5.6 and 21.4±14 µgCH₄-C/m²/h, respectively.  The fluxes estimated by two methods are not a significant difference based on a one-way ANOVA with a 95% confidence level.  The winter CO₂ flux corresponds to 30% of the annual CO₂ emitted from Alaskan black spruce forest soils.  The average winter emissions of CO₂ and CH₄ were 49±13 gCO₂-C/m² and 4.5±3.0 mgCH₄-C/m², respectively.  This suggests that the winter emissions of CO₂ and CH₄ are an important part of the annual carbon budget in seasonally snow-covered terrain.

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.

Paleo-climate records in ice cores revealed high variability in temperature, atmospheric dust content and carbon dioxide. The longest CO₂ record from the Antarctic ice core of the Vostok station went back in time as far as about 410 kyr BP showing a switch of glacials and interglacials in all those parameters approximately every 100 kyr during the last four glacial cycles with CO₂ varying between 180-300 ppmv [Petit et al., 1999]. New measurements of dust and the isotopic temperature proxy deuterium of the EPICA Dome C (EDC) ice core covered the last 740 kyr, however, revealed glacial cycles of reduced temperature amplitude [EPICA community members, 2004]. These new archives offer the possibility to propose atmospheric CO₂ for the pre-Vostok time span as called for in the EPICA challenge [Wolff et al., 2004]. Here, we contribute to this challenge using a box model of the isotopic carbon cycle [Köhler et al., 2005] based on process understanding previously derived for Termination I. Our results show that major features of the Vostok period are reproduced while prior to Vostok our model predicts significantly smaller amplitudes in CO₂ variations.

The Amazon region represents a large stock of biomass as well as a potentially important sink for additional atmospheric CO₂. Climate change, land-use changes and their interaction present a risk to this role in the global carbon cycle. Both positive and negative feedbacks exist in the system that can lead to resilience but also to accelerated break-down of the carbon stocks and sinks. A set of linked projects will investigate elements of these processes in the coming years.

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.

The Southern Annular Mode (SAM) is the leading mode of intraseasonal to interannual variability over the entire Southern Hemisphere, yet the impact of the SAM on the Southern Ocean carbon cycle is largely unknown. We investigate the impact of the SAM on surface wind, sea surface temperature (SST), chlorophyll concentration, and sea ice concentration on the basis of 8-day averaged satellite observations.  We find that Southern Ocean circulation and biogeochemistry react quite sensitively to this mode of variability, potentially resulting in air-sea CO₂ flux anomalies. Since variations in atmospheric CO₂ congruent with the SAM are small, we hypothesize that the SAM produces anomalous air-sea fluxes of both natural and anthropogenic CO₂, which act to compensate each other. 

This study examines the potential for feedbacks between the carbon cycle, atmospheric carbon dioxide (CO₂) increases and climate change to affect the anthropogenic emissions that are required to stabilize future levels of CO₂ in the atmosphere. Using a coupled climate-carbon cycle model, I found that positive carbon cycle-climate feedbacks reduced allowable emissions by an amount that varied with the model’s climate sensitivity.  Emissions were further reduced if CO₂ fertilization was assumed to be inactive in the model, as this removed an otherwise important negative feedback on atmospheric CO₂.

A coupled Biogeochemistry-Ecosystem-Circulation (BEC) ocean model is used to examine the sensitivity of ocean biogeochemical cycling and air-sea CO₂ exchange to variations in mineral dust deposition from the atmosphere.  Mineral dust deposition estimates from four different climate regimes are used to force the ocean model.  Our estimated climate-induced changes in dust deposition to the oceans significantly modify phytoplankton community composition, and global-scale rates of nitrogen fixation, export production, and air-sea CO₂ flux.  Dust driven variations in air-sea CO₂ exchange exceeding 1 PgC/yr are of similar magnitude to present net oceanic anthropogenic uptake.  Dust deposition directly modifies rates of export production and CO₂ flux over large regions where iron is the primary growth-limiting nutrient.  Dust deposition also indirectly influences these rates by modifying the rates of nitrogen fixation in the tropics and subtropics where nitrogen is the primary limiting nutrient.  Initially the direct pathway dominates the ocean biogeochemical response to dust variations, but over multi-decadal timescales the indirect response may be equally important.  Our predicted decrease in mineral dust deposition over the next century would significantly slow oceanic uptake of CO₂ and act as a positive feedback mechanism for the ongoing global warming.