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Biogeochemical OGCM, PISCES series, with particle dynamics

Development/validation of a biogeochemical ocean general circulation model –PISCES is a biogeochemical model which simulates the marine biological productivity and describes the biogeochemical cycles of carbon and the main nutrients (P, N, Si, Fe) in the ocean. In 2004, a stable release of the model became available to the community on the OPA website (hhtp://

Model developments within ORFOIS essentially consisted in improving the description of biogeochemical fluxes below the euphotic zone and in adding a sediment model (Heinze et al. 1999).

Thanks to the large database of sediment traps and sediment composition put together, the ORFOIS project enabled us to test / validate the new developments.

Model studies focused on:

- Particle fluxes in the mesopelgaic: sensitivity experiments and validation. We have tested the parameterisations / parameters of some of the processes represented in the PISCES standard version by carrying out sensitivity experiments. We have found that many of the processes (sinking speed, aggregation, flux feeding) introduced in the model have the ability to substantially modify deep fluxes. In particular, the way we parameterise flux feeding on particles has been found to be very sensitive. While the flux feeding intensity strongly modulates particle fluxes in the intermediate and deep water column, it has only little impact on surface ocean productivity.

- Iron fertilization experiments. Example of experiment: patchy Fe additions. Patchy Fe additions were performed at various locations of the three main Fe limited regions to mimic the small-scale in-situ fertilization experiments. Except in the sub-arctic Pacific, the model broadly reproduces the main observed features of the biological response to the supply of iron (increased in total chlorophyll, diatoms relative abundance, export production and decreased pCO2).

In the Southern Ocean, the magnitude and the timing of the response display large variations between the different sites. The major controlling factors are the background iron and silicate concentrations, the physical environnement and the timing relative to the growing season. We show in particular a strong correlation between the maximum of the chlorophyll response and the depth of the mixed layer at the fertilized point.

- Global warming experiment: PISCES was coupled to the IPSL climate coupled model (IPSL-CM4). A global warming experiment was carried out from 1xCO2 (pre-industrial state) to 4xCO2, with a 1% per year increase in atmospheric pCO2. The objective was to investigate how global warming may affect the surface ecosystem, uptake of carbon from the atmosphere, recycling and export of carbon from the euphotic zone and re-mineralisation of carbon in the water column.

Reported by

CEN Saclay, L'Orme des Merisiers, Bât. 701
91191 Gif-sur-Yvette
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