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Coupled ocean-sediment model REcoM/MEDUSA
Ying Ye, Guy Munhoven, Christoph Völker„ Martin Butzin, Peter Köhler
Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research
17 December 2019, Bremen
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Why a sediment model?
I fluxes between ocean and sedimentparticularly important for more realisticparameterisation of iron source
I sediment accumulation → lithosphereI and long-term climate impact through
weathering
Heinze et al. 1999, Glob. Biogeochem. Cycles
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Composition of sediment and processes regulating fluxes
Boudreau, 1996, Diagenetic Models and their Implementation
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Reactions in sediment
Sarmiento & Gruber 2006
Microbial remineralization of organic matter →typical sequence of redox zones (different electron acceptors):
I oxic remineralization
I denitrification
I Fe/Mn reduction
I Sulfur reduction ...
Dissolution of CaCO3: depends on local pH, TAlk, DIC,pressure, dominant CaCO3 form
Dissolution of biogenic opal depends on lokal Si(OH)4
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REcoM uncoupled with MEDUSAI sinking flux of POC, PON, calcite, opal and lithogenic particles into benthic layerI release of dissolved components: proportional to microbial degradation of POM in
benthic layer and dissolution of calcite and opal
Hauck et al. 2014
I calcite dissolution independent of ΩI bottom water O2 and different redox processes not involvedI no permanent burial
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MEDUSA = layered sediment model
A 1-dimensional sediment column definedat each horizontal grid point
I diffusive boundary layer on top (optional)
I reactive layer, with prescribed porosityprofile and bioturbation depth
I consolidated sediment for recording oldstates (optional)
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Components and reactions considered
Solids POM (particulate organic matter)CaCO3 (calcite only, no aragonite)SiO2 (diatom frustules)lithogenic particles
Solutes carbonate systemNO−
3 , Si(OH)4, O2
Reactions oxic remineralizationdenitrificationCaCO3 and SiO2 dissolutiondissolved chemical equilibria
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Interaction between sediment and water column
REcoM → Medusa
I bottom water T, S, p
I bottom DIC, TAlk, O2, NO−3 , Si(OH)4
I sinking fluxes: CaCO3, SiO2, POC, PON, dust
Medusa → REcoM
I diffusive fluxes: DIC, TAlk, O2, NO−3 , Si(OH)4
To close the system
I permanent burial of CaCO3 and SiO2→ terrestrial input (e.g. riverine)
I denitrification and PON burial→ nitrogen fixation/atmospheric N input
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Coupled run
I at time step 0, MEDUSA first calculating until equilibrium
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First results: CaCO3
left: Seiter et al. 2004, right: REcoM/Medusa
I mainly distributed in Atlantic,Indian Ocean and part of South Pacific
I lower fraction in dust regions
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First results: opal
left: Seiter et al 2004, right: REcoM/Medusa
I mainly in high latitudes and equatorial Pacific
I data: also elevated in Indian Ocean
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First results: particulate organic matter
left: Seiter et al 2004, right: REcoM/Medusa
I model: too high in coastal regions and too low in open ocean
I sinking and remineralisation in water column? degradation in sediment?
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First results: oxygen utilization in sediment
left: Jahnke 1996, right: REcoM/MEDUSA
I high in coastal regions
I data: higher in open ocean e.g. Atlantic and equatorial Pacific →sinking?
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First results: oxygen utilization in sediment
left: Jahnke 1996, right: REcoM (increased sinking)
I clear change in high latitudes, EP and small change in northern IOI nutrients and DIC in water column also affected → NPPI sediment model provides additional constraints and requires more tests
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Next steps
I Further analysis of the first simulation, e.g. comparing with uncoupled model runI other components and processes, e.g. C isotopes and Fe, balancing denitrification
and burialI validation for present-day and then LGM and transition runI coupling with FESOM
Thanks for your attention!
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Next steps
I Further analysis of the first simulation, e.g. comparing with uncoupled model runI other components and processes, e.g. C isotopes and Fe, balancing denitrification
and burialI validation for present-day and then LGM and transition runI coupling with FESOM
Thanks for your attention!
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