Numerical study of weathering fluxes at the catchment scale in a boreal watershed: a coupled thermo-hydro-geochemical mechanistic approach.

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Numerical study of weathering fluxes at the catchment scale in a boreal watershed: a coupled

thermo-hydro-geochemical mechanistic approach.

L. Orgogozo, Y. Godderis, O. Pokrovsky, J. Viers, D. Labat, A Prokushkin, B Dupré

To cite this version:

L. Orgogozo, Y. Godderis, O. Pokrovsky, J. Viers, D. Labat, et al.. Numerical study of weathering fluxes at the catchment scale in a boreal watershed: a coupled thermo-hydro-geochemical mechanistic approach.. Goldschmidt Conference 2011, Aug 2011, Prague, Czech Republic. �hal-01882522�

Numerical study of weathering fluxes at the catchment scale in a boreal watershed: a coupled thermo-hydro-geochemical mechanistic approach.

Numerical study of weathering fluxes at the catchment scale in a boreal watershed: a coupled thermo-hydro-geochemical mechanistic approach.

Context : study of the element fluxes in permafrost catchments of central Siberia in the frame work of the GDRI CAR WET SIB.

Perspectives : assesment of the processes which govern weathering at the boreal catchment scales with continu permafrost, assesment of the effect of global warming on these processes

L. Orgogozo ^1* , Y. Goddéris ¹ , O.S. Pokrovsky ¹ , J. Viers ¹ , D. Labat ¹ , A.S. Prokushkin ² and B. Dupré ¹

1

GET, 31400, Toulouse, France (*correspondence: laurent.orgogozo@get.obs-mip.fr)

2

V.N. Sukachev Institute of Forest, SB RAS, Akademgorodok, Russia

N

(south aspected)

S

(north aspected)

Snow Permafrost Organic layer River Taliks

HEAT FLUXES : WINTER

(October – beginning of May)

geothermal flux

heat conduction

solar radiation solar radiation

heat co

nduction

Heat flux

N

(south aspected)

S

(north aspected)

geothermal flux

heat co

nduction and ad

vection heat conduction

HEAT FLUXES : SPRINGFLOOD

(end of May – June)

solar radiation solar radiation

N

(south aspected)

S

(north aspected)

geothermal flux

solar radiation solar radiation

heat co

nduction and ad

vection heat conduction and advection

HEAT FLUXES : SUMMER

(July-September)

N

(south aspected)

S

(north aspected)

Snow Permafrost Organic layer River Taliks

WATER FLUXES : WINTER

(October – beginning of May; ~ 5-10 % of total annual discharge)

deep brines

snow sublimation snow sublimation

snow fall

snow fall snow fall snow fall

snow sublimation snow s

ublimation

Snow flux Water flux

N

(south aspected)

S

(north aspected)

WATER FLUXES : SPRINGFLOOD

(end of May – June; ~60-65 % of total annual discharge)

rain fall rain fall

evapotr anspira tion

deep brines

Sno wpa ck m elt + Run off Suprap

ermafro st flow (ac tive lay er melt + in filtratio n) Snowp

ack me

lt + Run off

N

(south aspected)

S

(north aspected)

WATER FLUXES : SUMMER

(July-September; ~30% of total annual discharge)

rain fall rain fall

evapotr anspira tion

deep brines

Sup rape rma fros t flow (ac tive laye r

mel t + i nfilt ratio n) Run off

Run off (major rain ev ents)

evap otra nsp irati on

Qualitative thermo-hydrological model for the catchments of the Kochechum River and the Nizhniya Tunguska River (according to Pokrovsky et al., 2005, 2006, Prokushkin et al., 2007, Bagard et al., 2011)

Q

_SA1

, C

_SA1

Q

_SA2

, C

_SA2

Q

_NA1

, C

_NA1

Q

_NA2

, C

_NA2

Q

_R

, C

_R

Q

_talik

, C

_talik

P

_rain

, P

_Snow

, ETP

_SA

, SUB

_SA

, W

_SA

P

_rain

, P

_Snow

, ETP

_NA

, SUB

_NA

, W

_NA

W

_geothermal

W

_geothermal

•

Coupled Richards equation and Heat

equation

• WITCH model

• Biomass impact : forcing

• Weekly time step

• Multiannual simulations

SOUTH ASPECTED SLOPES NORTH ASPECTED SLOPES

Active layer

Water input to the river Active layer

A mechanistic approach to set up a quantitative modelling of water, energy and elements fluxes in the catchments of the Kochechum River and the Nizhniya Tunguska River

•

Coupled Richards equation and Heat

equation

• WITCH model

• Biomass impact : forcing

• Weekly time step

• Multiannual simulations

River Permafrost

Taliks

Organic layer

Snow flux Water flux

Active layer

Heat flux

Conceptual diagram of the proposed modeling approach Example of data on witch the model will

be build up (Bagard et al., 2011)

• Testing the completeness of the qualitative

scenario of thermo-hydrological functionning by quantitative modelling

• Once calibrated and validated for present climatic conditions, the model will be used to assess the impact of variation of climatic conditions on

weathering fluxes

• This semi-mechanistic approach will be the basis of a 3D fully mechanistic approach of weathering processes at the scale of a small catchment

(Kulingadakan)

Expected results

(i) Weathering of continental silicated rocks is considered to be one of the main sinks of atmospheric carbon (Berner, 1992).

(ii) Basalyic outcrops account for about 30% of this flux (Dupré et al., 2003).

(iii) The observed global warming, at least partly due to anthropogenic carbon, seems to be particularly strong in boreal areas (e.g. IPCC 1998).

(iv) Global Warming is strongly suspected to induce a thawing of boreal

permafrosts (decrease of the permafrost extension and increase of active layer thickness) even if these points are still a matter of debate (e.g.

Serreze et al. 2000, Frauenfeld et al. 2007).

(v) Positive feedbacks are expected between global warming and permafrost thawing (e.g. Zimov et al. 2005, Khvorostyanov et al. 2008)

(vi) Putorana Plateau, is an ideal place for studying weathering of boreal basaltic areas (e.g. Pokrovsky et al., 2005)

(i) The thermo-hydrological state of a soil exerts a strong control on its weathering and thus on the associated atmosperic CO

₂

consumption (e.g. Beaulieu et al., 2010).

(ii) There is strong coupling between hydrological and thermal

processes in permafrost areas : snow melt, phase changes of the water of the active layer, … Occurrences of advective heat transport have even been reported in surficial permafrost during spring flood (e.g. Hinkel et al 1997).

(iii) Otherwise, current large scale modeling of the CO

₂

cycle in boreal areas have high sensitivities (e.g. Khvorostyanov et al., 2008 part II).

(iv) Performing modeling studies of elements cycles at smaller scales would allow to get stronger constraints on the processes at stake.

(v) Indeed, the need of developing such mechanistic modelling tools is now recognize (e.g. Frampton et al, 2011).

So we aim to build up a mechanistic modelling of thermo-hydro- geochemical processes at work in the weathering of the Kochechum river and the Nizhniya Tunguska River, on the basis of the data

hydro-geochemical data avalaible in the GDRI CAR WET SIB.

Hinkel et al. 1997 : Monitoring of

temperature profil along depth during springflood period in permafrost areas (Alaska and Arctic Canada) :

highlighting of advective heat transport Beaulieu et al. 2010 : One can see a dependance of weathering flux to

hydrological (run off, computed) and thermal conditions (annual mean temperture, measured, 1982-1990) of the considered areas (22 sites with silicated outcrops around the world).

Putorana Plateau rivers have been studied for years in order to constraint weathering processes, and a qualitative model of thermo-

hydrological processes at work have been develloped on the basis of the quantitative geochemical field measurements (e.g. Pokrovsky et al. 2005, 2006, Prokushkin et al. 2007, Bagard et al. 2011)

Problematic