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. 

Temporal and spatial distributions of the δ¹⁸O value of atmospheric CO₂ (dC_a) can be used to constrain regional ecosystem carbon exchanges and linkages between carbon and water cycling. However, our understanding of the substantial observed temporal and spatial variability in dC_a is limited. Among many contributing factors, seasonal and inter-annual variations in climate are likely to be important. In this study we investigate the impact of dry climatic conditions on the ecosystem-atmosphere C¹⁸OO isoflux.

We conducted this study in the U.S. Southern Great Plains using five-year monthly-averaged precipitation δ¹⁸O values (δ_p) from the National Atmospheric Deposition Program (NADP) network, Mesonet meteorological forcing, and MODIS-derived NDVI and land-cover characterization. These data are used to force the isotope ecosystem model ISOLSM [Riley et al., 2002; Riley et al., 2003] at 10 km resolution across the region for relatively drier (2003) and wetter (2004) years. The model has been calibrated and tested in the dominant herbaceous vegetation types in the region [Biraud et al., this issue].

We have developed a multiple element (C, N, P, Si, Ca, Fe) biogeochemical model of marine ecology that includes small, large and diazotrophic phytoplankton as well as explicit ballast-driven sinking and remineralization of detrital organic matter and cycling of dissolved organic matter. Phytoplankton growth is described through a new formulation including co-limitation by N, P, Si, Fe and light to reproduce broad observational trends.  Phytoplankton grazing is described through different power laws in the closure terms for small and large phytoplankton to reproduce observed augmentation of large phytoplankton with increasing production. Detritus production is assumed to be a temperature dependent fraction of small and large phytoplankton. This model has been imbedded in a 1-degree; global ice/ocean general circulation model (MOM4) forced by a 43-year atmospheric reanalysis forcing from the Common Ocean Reference Experiments (CORE) program to quantify the relationship between food web structure, biogeochemical cycles and the atmospheric CO₂ signature on inter-annual timescales. Novel aspects in the model structure are described, the impact of the formulation of ecosystem structure on biogeochemical cycling are discussed, and results of the atmospheric reanalysis forcing experiment presented. Of particular interest are the dynamical roles played by equatorial ENSO variability and polar sea ice dynamics on air-sea CO₂ fluxes.

Various patterns of large-scale climate variability have exhibited trends over the past few decades. These patterns of variability are known to have contributed substantially to recent trends in, for example, surface temperatures and precipitation. However, it is less clear to what extent the climate impacts of these patterns extend to the carbon cycle. Here we summarize the observed relationships between monthly and daily mean variations in concentrations of atmospheric carbon dioxide and the dominant pattern of variability in the extratropical circulations, the so-called Northern and Southern Hemisphere Annular Modes. The observed relationships are compared with results derived from surface flux estimates from the Atmospheric Tracer Transport Model Intercomparison Project (TransCom).

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.