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.

In a Carbon Cycle Data Assimilation System (CCDAS) one infers the values of the parameters controlling the function of a process model using various observations. One can then calculate quantities of interest from the optimized parameters and the model. One can also calculate the uncertainties on the parameters and propagate these to uncertainties of the calculated quantities. In Rayner et al. [2005] we assimilated atmospheric observations over two decades, into a terrestrial model and calculated fluxes over this period. Here we extend this work by calculating the response of the calibrated terrestrial biosphere to a GCM simulation of future climate. Using this combination we are able to comment on the fate of terrestrial carbon pools and fluxes under climate change, calculate the uncertainties of the response, and determine which parameters in the model are responsible for this uncertainty. We include an extra parameter that scales the climate change signal from the GCM projection. We thus extend the sensitivity and uncertainty analysis to include the climate sensitivity.

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.

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.

This paper examines two key feedbacks that operate between the terrestrial carbon cycle, atmospheric carbon dioxide (CO₂) and climate: the positive carbon cycle-climate feedback and the negative CO₂ fertilization feedback.  Both feedbacks affect strongly the growth rate of future atmospheric CO₂, and interact in such a way that the effect of one is notably modified in the absence of the other.

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).

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.

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.