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Scientific background & drivers (cont.)

Science drivers

The current assumption of a passive ocean biosphere in assessments of global change is not tenable; as hypothesised by the International Geosphere-Biosphere Programme (IGBP) Surface-Ocean Lower Atmosphere Study (SOLAS) and other programmes (Ecological Determinants of Ocean Carbon Cycling, EDOCC; Ocean Carbon Transport, Exchanges and Transformations, OCTET). For a warming Earth, with changing atmospheric and oceanic, circulation, thermal structure, albedo and ecosystem functioning, there is a need for precise data, globally, to constrain the fluxes of CO2 and other climatically active gases (Aiken et al., 1992; Lefevre et al., 1998; Lefevre et al., 2001; Kettle et al., 2001).  Ocean surface physics, biogeochemistry and coupled atmospheric properties, regulate the exchanges of heat, momentum, particles and gases at this boundary (Liss & Duce, 1997).  By reducing and constraining the errors in estimates of the marine C-cycle, the marine fraction of the global CO2 budget, the unconstrained terrestrial fraction and the total Earth CO2 budget will also be better quantified.

For important practical reasons, better knowledge of the air-sea flux of CO2 is needed to quantify the fluxes at sub-basin scales and sub-seasonal (monthly) time scales.  Both terrestrial and marine sinks for anthropogenic CO2 vary greatly from year to year (Rayner et al., 1999). As part of the post-Kyoto carbon accounting, changes in these natural sinks must be tracked and if possible predicted. Terrestrial carbon sinks at the continental scale can be tracked using regionally resolving atmospheric inverse models, but the results are reliable only if the intervening oceanic sinks are constrained independently (Gurney et al., 2002). Thus, improved estimates of oceanic fluxes will lead to better estimates of the land-atmosphere components of the global carbon cycle.

On decadal to centennial scales, we expect substantial changes in both marine and terrestrial components of the C-cycle in response to global change.  Current predictions range from the modest to near-catastrophic (Cox et al., 2000). In the marine realm, we expect that increasing CO2 concentrations, temperatures and an intensifying hydrological cycle will affect ocean circulation, ventilation and ecosystem structure.  Currently we have little knowledge of the impact of these changes on the capacity of the oceans to take up atmospheric CO2, and no methods to monitor the extent of their occurrence now or in the future.  EO data, combined with models and in-situ observations offer the best prospects of a quantitative solution.

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References

  • Aiken, J., Moore, G., Holligan, P., 1992. Remote sensing of ocean biology in relation to global climate change. Journal of Phycology, 28, 579-590.

  • Lefevre, N., Moore, G., Aiken, J., Watson, A., Cooper, D., Ling, R., 1998. Variability of pCO2 in the tropical Atlantic. Journal of Geophysical Research - Oceans, 103, 5623-34.

  • Lefevre, N., Aiken, J., Rutllant, J., Daneri, G., Lavender, S., Smyth, T., 2001. Observations of pCO2 in the coastal upwelling off Chile: spatial, temporal extrapolation using satellite data. Journal of Geophysical Research - Oceans, 107, art. no. 3055.

  • Kettle, A.J., Rhee, T.S., von Hobe, M., Poulton, A., Aiken, J., Andreae, M.O., 2001. Assessing the flux of different volatile sulfur gases. Journal of Geophysical Research, 106, 12193-209.

  • Liss, P.S. & Duce, R.A., 1997. The Sea Surface and Global Change. Cambridge University Press, 519pp.

  • Rayner, P.J., Enting, I.G., Francey, R.J., Langenfelds, R., 1999. Reconstructing the recent carbon cycle from atmospheric CO2, delta C-13 and O2/N2 observations. Tellus B, 51, 213-232.

  • Gurney, K.R., Law, R.M., Denning. A.S., et al., 2002. Towards robust regional estimates of sources and sinks using atmospheric transport models. Nature, 415, 626-630.

  • Cox, P.M., Betts, R.A., Jones, C.D., Spall, S.A., Totterdell, I.J., 2000. Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model. Nature, 408, 184-187.

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