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NOCES - Northern Ocean-atmosphere Carbon Exchange Study

Summary information

Funding:FP5 - Research project
Total cost:2324197
Ec contribution:1582774
Start date:2002-04-01
End date:2005-03-31
Duration:36 months
Coordinator:James Orr (
Organisation:Commissariat a L’Energie Atomique – France
Regio:North Atlantic; North Sea
Keywords:Interannual-to-decadal variability of air-sea CO2 fluxes; northern hemisphere; impact on carbon budgets; models
Project name:NOCES - Northern Ocean-atmosphere Carbon Exchange Study
Project summary:Problems to be solved
Noces will set constraints on interannual-to-decadal variability of air-sea CO2 fluxes, particularly over the northern hemisphere. An understanding of this variability, associated uncertainties and the mechanisms which drive it will be used to i) Evaluate the ocean component of coupled carbon-climate models which predict future atmospheric CO2 and ii) Improve the skill of inverse atmospheric models to distinguish contributions of European, Asian, and North American terrestrial carbon sinks.

Therefore, NOCES will improve current understanding of the variability of air-sea CO2 fluxes and its impact on carbon budgets. Such will help ameliorate numerical models that are used to evaluate present and future carbon uptake over Europe and other regions of the Northern Hemisphere. Although the Kyoto Protocol is being negotiated internationally, credible carbon budgets have not been established. This must change if Europe is to verify commitments and be in a proper position during future negotiations. Credible carbon budgets are needed to make all nations accountable. Without accountability, atmospheric CO2 would be sure to rise far beyond acceptable levels.

Scientific objectives and approach
NOCES has three main objectives: i) To assess patterns and uncertainties of interannual-to-decadal variability of air-sea CO2 exchange by means of diagnostic ocean model comparison and data evaluation ii) To evaluate how different prognostic coupled carbon climate models perform for the ocean component on this most relevant time scale and iii) To improve constraints on the terrestrial carbon sink over Europe, using simulated air-sea CO2 fluxes and uncertainties as a priori estimates for inverse atmospheric models.

NOCES is original because i) It will be the first to make forced ocean carbon simulations of interdecadal variability, ii) It will do so with six diverse ocean models to provide uncertainty estimates and results that are not model specific, iii) It will elucidate the mechanisms responsible for this variability (using statistical correlation analysis, comparison with time series data and comparison with another ongoing mechanistic study), and iv) It will improve the a priori constraint for air-sea CO2 fluxes used by atmospheric inverse models and thus reduce uncertainties in terrestrial carbon uptake.
Project outputs:Scientific achievements
• Production of standard protocols with which ocean modellers are now able to make comparable simulations of inter-annual to decadal variability. The NOCES/OCMIP-3 protocol document has become a standard in the community.
• Production of a detailed multi-model output archive from the standard ocean model simulations made within NOCES. This legacy from NOCES will serve the community as a standard reference point for many years to come and will be more valuable due to efforts to improve the common protocol guidelines.
• Improved atmospheric inverse modelling approach.
• Improved method to evaluate the variability of air-sea CO2 fluxes from satellite information.
• Comparison of simulated inter-annual variability of air-sea CO2 fluxes from ocean models vs. atmospheric inverse models [Peylin et al., 2005].
• Improved understanding of what controls tropical Pacific carbon and radiocarbon [see NOCES publication Rodgers et al., 2004].
• Improved understanding of temporal trend in observed pCO2 in the North Atlantic [see NOCES publication Lefèvre et al., 2004].
• First evaluation of decadal variability of air-sea CO2 fluxes in the North Atlantic [see NOCES publication Raynaud et al., 2005].
• Better understanding of compensating regional variability of air-sea CO2 fluxes in the North Atlantic basin. The North Atlantic’s subtropical gyre was not the largest contributor to the overall, basin-wide variability, in contrast to previous suggestions. The subpolar gyre and the inter-gyre region (the transition area between the subpolar and subtropical gyres) also contribute to major multipolar anomalies at multiple frequencies: these tend to cancel one another out in terms of the basin-wide air-sea CO2 flux [see NOCES publication Raynaud et al., 2005].
• First accounting for time lag between inter-annual variability of air-sea CO2 fluxes and driving mechanisms [see NOCES publication Raynaud et al., 2005]. Statistical analysis within NOCES have shown that there is indeed a strong correlation between air-sea CO2 fluxes and the North Atlantic Oscillation (NAO), but only if one takes into account time lags (maximum r = 0.64 for lags between 1 and 3 years) [see NOCES publication Raynaud et al., 2005].
• Improved understanding of the effect of increasing atmospheric CO2 (the anthropogenic perturbation) on total variability. The effect is negligible at inter-annual time scales, whereas at the decadal (13-year) time scale, it increased variability by 30% [see NOCES publication Raynaud et al., 2005].
• Serendipitous discovery that during pre-industrial times there was probably a large ocean transport of about 0.8 Pg C yr−1 from the northern to the southern hemisphere, caused by iron limited primary productivity in the Southern Ocean [see NOCES publication Wetzel., 2004]. This finding resolves a long-standing enigma as to why all other ocean models (none of which featured iron limitation) could not simulate such a large inter-hemispheric ocean transport, as theorized based on supposed pre-industrial atmospheric CO2 gradients.
• Serendipitous discovery that high-latitude surface waters may become corrosive to CaCO3 minerals such as aragonite by the end of the century, a first in perhaps 25 million years [see NOCES publication Orr et al., 2005]. This would seriously threaten marine calcifying organisms such as cold-water corals and some plankton.
• Production of various other related scientific publications from NOCES (see activity reports from each of the work packages).

Socio-economic relevance and policy implications
NOCES addresses how improving our understanding in the variability of the air-sea CO2 flux in the Northern Hemisphere would (1) reduce uncertainties concerning uptake of atmospheric carbon by the terrestrial biosphere and (2) improve predictions of future atmospheric CO2. Both improvements are relevant to EU environmental policies, and in particular the Kyoto Protocol, by which EU Member States have agreed to reduce fossil carbon emissions.

The NOCES project built on the current EU investment in several recent or ongoing projects (e.g., CARBOEUROPE, CAVASSOO, PREDICATE) and has helped to set the stage for ocean, global carbon cycle and biogeochemistry research which was initiated within the 6th Framework Programme. NOCES must be carried out at the European level, i.e., its goals cannot be obtained from any of the Member States alone because it requires extensive model comparison and evaluation with a diverse group of models to provide interpretations that are not model specific.

Accomplishments during NOCES came more slowly than originally planned because it proved difficult to elaborate, refine, and agree on all the details necessary to make rigorous comparisons of model simulations of inter-annual variability. Nonetheless, the NOCES modelling groups persisted. This effort has provided an archive of standard model output from multiple models, which will serve as the de facto reference for this type of simulation for years to come.