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Land Ocean Coupling

Land Ocean Coupling. WWW.BJERKNES.UIB.NO. Coupling riverine fluxes of nutrients to a Global Biogeochemical Ocean General Circulation Model. Christophe Bernard, Christoph Heinze Geophysical Institute, Bjerknes Center for Climate Research University of Bergen. The HAMOCC5-MPIOM.

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Land Ocean Coupling

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  1. Land Ocean Coupling WWW.BJERKNES.UIB.NO Coupling riverine fluxes of nutrients to a Global Biogeochemical Ocean General Circulation Model Christophe Bernard, Christoph Heinze Geophysical Institute, Bjerknes Center for Climate Research University of Bergen

  2. The HAMOCC5-MPIOM • NPZD model with colimitation of Nutrients such as N, P,Si,Fe • orthogonal curvilinear C-grid with a formal resolution of 3◦ • 20 km in the Arctic and about 350 km in the Tropics • 40 vertical levels with level thickness increasing with depth • North pole is located over Greenland and the other over Antarctica.

  3. Relative silica flux Global mean silica yield 3.3 t SiO2 km-2 yr-1 Hyperactive Very active Active Sub-active Hypo-active Inactive ‘Dead’ 10 5 2 0.5 0.2 0.1 0.01 Application of the coastal segmentation : estimating natural silica fluxes to the coastal zone Dürr and Meybeck, 2007 6,2 teramoles of silicon per year -> < 20 % of area responsible for >50% of natural silica yield

  4. The riverine inputs • Figure 1. Integrated annual flux of silica as added in the model grid, according to the 129 coastal segments from the COSCAT approach. Riverine silica inputs are given in megamoles Si per year.

  5. The coupling • Flux computed at each time step: 10 times a day • It includes : Si, DIN, DIP, DON,DOP,PP,PN and POC • Homogeneous along the coastal segment • Constant over time

  6. With riverine silicate Computing the difference between the 2 runs Without riverine silicate Riverine contribution to the Opal export production

  7. Fate of riverine Si depends on the level of primary production. Bernard et al. 2008, submitted Annual photosynthesis Limiting nutrient the computation of the photosynthesis is driven by the less available nutrient corrected by a multiplying factor.

  8. Example of the Amazon contribution Bernard et al. 2008, submitted Figure 4. The seasonal cycle of nutrient limitation (element equivalent phosphorous) in the Amazon plume, (lower panels) with (left) and without (right) riverine silica inputs. Opal and calcium carbonate export (F opal and F calcarb) at 10m depth in response to photosynthesis (upper panels). Nutrient limitation is expressed as the concentration adjusted to the necessary stoichiometric concentration of nitrogen and iron relative to phosphate. The limitation of photosynthesis is driven by the lowest concentration equivalent phosphate (iron, nitrate or phosphate). Opal and calcium carbonate competition is driven by the silica concentration.

  9. Continental margins in the model’s grid • Defined as the 8% shallowest grid points

  10. Marge vs global ocean: the riverine nutrients contribution Carbon 0.5 Gt C Silica

  11. Relative contribution of riverine nutrients to the export production of Opal and C C Si All Nut No Nut No Si No Org No Part No DIN No DIP

  12. Marginal seas…. 0,09 Gt C All Nut No Nut No Si No Org No Part No DIN No DIP No C All DI form

  13. To summarise… and conclude. • Human activity (urban development, land use, damming) changes the river load of nutrients to the ocean(decreased Si, increased N and P). • Changes in the riverine inputs of nutrients do have an impact on a global scale. • Marginal seas are more sensitive to river load changes. • Eutrophication leads to a larger burial of Opal on the continental shelf.

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