land ocean coupling coupling riverine fluxes of nutrients to a global biogeochemical ocean general...
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Land Ocean CouplingCoupling riverine fluxes of nutrients to a Global
Biogeochemical Ocean General Circulation Model
WWW.BJERKNES.UIB.NO
Christophe Bernard, Christoph HeinzeGeophysical Institute, Bjerknes Center for Climate Research
University of Bergen
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• 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.
The HAMOCC5-MPIOM
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Application of the coastal segmentation : estimating natural silica fluxes to the coastal zone
Dürr and Meybeck, 2007
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
-> < 20 % of area responsible for >50% of natural silica yield
6,2 teramoles of silicon per year
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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.
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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
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With riverine silicate
Without riverine silicate
Computing the difference between the 2 runs
Riverine contribution to the Opal export
production
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Fate of riverine Si depends on the level of primary production.
Limiting nutrientAnnual photosynthesis
the computation of the photosynthesis is driven by the less available nutrient corrected by a multiplying factor.
XK
XtzIJPhyPhoto
POPhy
4
*)),((*
PFePN R
Fe
R
NOPOX
::
34 ,,min
Bernard et al. 2008, submitted
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Example of the Amazon contribution
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.
Bernard et al. 2008, submitted
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Continental margins in the model’s grid
• Defined as the 8% shallowest grid points
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Marge vs global ocean: the riverine nutrients
contribution Carbon
Silica
0.5 Gt C
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Relative contribution of riverine nutrients to the export production of Opal and C
All Nut No Nut No Si No Org No Part
No DIN No DIP
C
Si
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Marginal seas….
All Nut No Nut No Si No Org No Part
No DIN No DIP No C All DI form
0,09 Gt C
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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.