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].

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.

Monthly time series of atmospheric carbon dioxide (CO₂), the relative amount of carbon-13 in CO₂ (¹³C), hydrogen (H₂) carbon monoxide (CO), and methane (CH₄) are examined and related to each other and to an index of the status of ENSO. Making use of simple 12-month running mean and difference filters isolates the year-to-year variability in the concentrations and apparent sources of these constituents.

An idealized general circulation model is constructed of the ocean’s deep circulation and CO₂ system that reproduces the main features of glacial-interglacial CO₂ cycles, including the tight correlation between atmospheric CO₂ and Antarctic temperatures, the lead of Antarctic temperatures over CO₂ at terminations, and the shift of the ocean’s ¹³C minimum from the North Pacific to the Atlantic sector of the Southern Ocean. The model is based on a new idea about the nature of the glacial-interglacial cycles in which the driving force is independent of the orbital forcing and is not in the ocean. The key to glacial-interglacial transitions, we claim, is a relationship between the mid-latitude westerly winds, atmospheric CO₂, and the mean state of the atmosphere. Cold glacial climates seem to have equatorward-shifted westerlies, which allow more respired CO₂ to accumulate in the deep ocean. Warm climates like the present have poleward-shifted westerlies that flush respired CO₂ out of the deep ocean.

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%).

Increased winter temperatures associated with the observed positive trend in the winter Arctic Oscillation can partially explain trends towards earlier spring leafout in the northern hemisphere.  Increased spring drawdown associated with earlier leafout, coupled with increased winter respiration due to warmer temperatures, indicate the trend in the winter Arctic Oscillation can help explain observed increases in the seasonal amplitude of atmospheric CO₂ concentration.

In recent years attention has focused on the role of terrestrial biosphere dynamics in the climate system, and the possibility of large land-atmosphere carbon cycle feedbacks under human-induced future climate warming. During the 1990s rapid development of Dynamic Global Vegetation Models (DGVMs) led a growing community to soon recognize the need for model evaluation and intercomparison. In Cramer et al. 2000 six DGVMs were run using identical forcing data based on the HadCM2 GCM climatology (1860-2100) and the IS92a emission scenario.

In this study we evaluate the individual and combined impacts of CO₂, climate and Ozone on future terrestrial carbon storage using the computationally efficient GCM analogue model coupled to the MOSES/TRIFFID land surface carbon cycle model. Ozone is modelled to have a significant detrimental effect on future plant productivity and hence terrestrial carbon storage, opposing the enhanced production and terrestrial carbon storage associated with elevated atmospheric CO₂ concentrations.

Atmospheric deposition of mineral dust aerosols supplies the essential nutrient of iron to the ocean.  However, only the readily soluble iron is available to biological uptake while the insoluble iron precipitates to the ocean bottom.  Here we present a global model simulation of Aeolian iron input to the ocean, considering hematite dissolution in mineral dust aerosols catalyzed by nitric and sulfuric acids.  Our model suggests that atmospheric deposition of soluble iron to the oceans is much larger than previous model results in high nitrate low chlorophyll (HNLC) regions.