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Scientific background & drivers (cont.)

CASIX approach

Estimating CO₂ fluxes globally, requires continuous data, which ships and buoys alone can not provide. EO data are the only global sources and CASIX will exploit these in concert with in situ data and models.  Studies of the oceans and shelf seas use diverse EO sensors and need to develop new algorithms for precise interpretations of EO data (Doerffer et al., 1999).  New EO methods can address flux uncertainties, as already demonstrated for hydrological fluxes (Jost et al., 2002).  A CASIX goal is to deliver precise, quality-assured EO data for use in models addressing uncertainties of Earth system science.

One CASIX approach will use EO and in situ data to derive improved parameterisations of the air-sea gas fluxes, including analysis of the importance of processes not presently considered in predictions of future oceanic carbon uptake.  We will consider the complex cycling of carbon in the shelf seas, the impact of white-capping and the role of surface films in inhibiting air-sea gas exchange. 

A second CASIX approach will develop methods for data assimilation of carbon and ecosystem variables into 3-D ocean circulation models, using EO colour data to interpolate the oceanic ecosystem between sparse in situ measurements.  This will provide coherent, self-consistent and time evolving maps of the pCO₂ distributions, and using the improved CASIX parameterisations, accurate maps air-sea fluxes of CO₂.  The different processes of carbon uptake in shelf seas and the open ocean will be handled in separate models, with careful attention to the links between these at the shelf edge. 

CASIX will use the new models and archived EO data to produce a 10-year climatology of air-sea gas fluxes, primarily CO₂, over the North Atlantic and where possible the globe.  Analysis of these and comparison with climatologies derived from a less comprehensive approach, will provide the knowledge needed to parameterise gas fluxes more robustly in global climate models. 

Finally, remote sensing of atmospheric concentrations of CO₂ will be available from SCIAMACHY.  CASIX will both utilise and evaluate these measurements.

The initial focus of CASIX is on CO₂ and the ocean Carbon cycle, which should improve our understanding of air-sea interactions and fluxes in general.  As CASIX evolves, the contributions of other gases will be explored where there are good models of the biogeochemical pathways for production and release (e.g. DMS).

Geographical Area of Interest

The issues of climate change are global and the scales of study that are required to address this problem are basin-wide at the minimum.  The shelf seas are an important component of the global ocean, representing approx. 10% of the ocean area but contributing much of the biological production, and are crucial for accurate quantification of CO₂ and other gas fluxes in global budgets. As only a few measurements exist globally it is unknown if the shelf seas are a net source or sink of CO₂. The initial focus of CASIX is on the North Atlantic and the adjacent European shelf seas. The CASIX team has internationally recognised expertise in both of these areas. Over the longer term, CASIX will move towards providing global estimates.

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References

• Doerffer, R., Sorensen, K., Aiken, J., 1999. MERIS: Potential for Coastal Zone Applications. International Journal of Remote Sensing, 20, 1809-18.

• Jost, V., Bakan, S., Fennig, K., 2002. HOAPS - A new satellite-derived freshwater flux climatology. Meteorologische Zeitschrift, 11, 61-70.

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