The role of sediment resuspension in biogeochemical cycling across continental shelves

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The role of sediment resuspension in

biogeochemical cycling across

continental shelves

A modelling study of the Black Sea system

Arthur Capet,1,3_{Filip J. R. Meysman ,}2_{Karline Soetaert ,}2 and Marilaure Gr ´egoire3

1_{CNR, OGS, Trieste, Italy} 2_{NIOZ, Yerseke, The Netherlands}

3_{Oceanology Laboratory, University of Li `}_{ege, Belgium}

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Context

The Black Sea Objectives

Model(s)

Diagenetic variability

The role of sediments resuspension

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Northwestern shelf I <120 m

I Large freshwater and nutrient inputs Central basin

I 120 - 2000 m I Strong stratification

Objectives:

Resolve biogeochemical budgets across River-Shelf-Basin continuum.

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Northwestern shelf I <120 m

I Large freshwater and nutrient inputs Central basin

I 120 - 2000 m I Strong stratification

Objectives:

Resolve biogeochemical budgets across River-Shelf-Basin continuum.

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I Dunne et al., 2007 : 30% of NPP reach the sediments in region <50 m (18% for 50-200 m).

I Gr ´egoire and Friedrich, 2004: ∼ 50% of N inputs removed by benthic denitrification and burial.

→Importance of benthic-pelagic coupling to represent the shelf biogeochemistry

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I Benthic-dissolved fluxes are expensive measurements. I Few available data

I Large variability

Technical requirement: set up a bentic-pelagic coupled model resolving the variability of benthic solutes fluxes

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I Benthic-dissolved fluxes are expensive measurements. I Few available data I Large variability

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I Benthic-dissolved fluxes are expensive measurements. I Few available data I Large variability

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Context

Model(s)

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GHER 3D Hydrodynamic Model

Hydrostatic model, Double Sigma coordinates, Real time forcings (ECMWF)

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GHER 3D Biogeochemical Model

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Benthic-Pelagic coupling

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Benthic-Pelagic coupling

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Benthic-Pelagic coupling

τ = τcurrents+ τwaves τcurrents←(GHER model) τwaves←(WAM model, offline) Kandilarov and Stanev, 2012

τf: Critical stress for deposition and erosion of Sf_. τs: Critical stress for erosion of Ss_.

Deposition Resusp. Sf _{Resusp. S}s

τ < τf _τf _{< τ} _τs_{< τ}

P = (1 − τ

τf).wPOM.[POM] Pf = (ττf −1).Mef Ps= ( τ

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Context

Model(s)

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Context

Model(s)

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Bottom stress effects impact on

spatial variability

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Bottom stress effects impact on

spatial variability

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Bottom stress effects impact on

shelf budgets

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Bottom stress effects impact on

shelf budgets

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Bottom stress effects impact on

seasonal variability

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Bottom stress effects impact on

seasonal variability

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Bottom stress effects impact on

basin budgets

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Bottom stress effects impact on

basin budgets

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Bottom stress effects impact on

basin budgets

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Context

Model(s)

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Conclusions

I Considering sediment resuspension is necessary to reproduce the variability of benthic dissolved fluxes.

I The calibration of bottom stress effects at shelf scale ..

I .. is difficult AND bears large scale impacts,

I affects the biogeochemical “filtering” capacity of the shelf

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Conclusions

I Considering sediment resuspension is necessary to reproduce the variability of benthic dissolved fluxes. I The calibration of bottom stress effects at shelf scale ..

I affects the biogeochemical “filtering” capacity of the shelf

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Conclusions

I _{affects the biogeochemical “filtering” capacity of the shelf}

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Conclusions

I _{affects the biogeochemical “filtering” capacity of the shelf}

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What’s next ?

Big gaps in this study :

I Fixed roughness length

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