Sediment Diagenesis. 1/61

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1 Sediment Diagenesis 1/61

2 Sequence of catabolic reactions In the presence of free O 2 : G (kj/mol) (1) Aerobic respiration: (CH 2 O) 106 (NH 3 ) 16 H 3 PO O 2 H 3 PO HNO CO H 2 O -475 In the absence of free O 2 : (1) Denitrification: (CH 2 O) 106 (NH 3 ) 16 H 3 PO HNO 3 H 3 PO N CO H 2 O -448 (1) Manganese reduction: (CH 2 O) 106 (NH 3 ) 16 H 3 PO MnO H + H 3 PO Mn NH CO H 2 O -349 (1) Iron reduction: (CH 2 O) 106 (NH 3 ) 16 H 3 PO Fe 2 O H + H 3 PO Fe NH CO H 2 O -114 (1) Sulfate reduction: (CH 2 O) 106 (NH 3 ) 16 H 3 PO SO 4 2 H 3 PO S NH CO H 2 O -77 In the absence of free and linked oxygen: (1) Fermentation/Disproportionation: (CH 2 O) 106 (NH 3 ) 16 H 3 PO 4 H 3 PO NH CO CH /61

3 Porewater evolution in a closed system in equilibrium with calcite Assumptions: 1) Initial solution equivalent to NA deep waters. 2) Closed system with excess organic matter. 3) Oxidants are limiting and each reaction proceeds to completion before the next oxidant is used. 4) System in equilibrium with calcite. As [Ca 2+ ] will not vary significantly until sulfate reduction proceeds, we will simply set [CO 3 2- ] as a constant value equal to K C */[Ca 2+ ]. Neglecting variations in borate alkalinity and changes in [H 2 CO 3* ]: ΔDIC = ΔΣCO 2 = Δ[HCO 3- ] + Δ[CO 3 2- ] ΔTA = ΔA c = Δ[HCO 3- ] + 2Δ[CO 3 2- ] Δ[CO 3 2- ] = ΔTA - ΔDIC 3/61

4 Oxic degradation If we omit N temporarily, CH 2 O will be oxidized as follows: (CH 2 O) O CO H 2 O ΔDIC = + 106, ΔTA = 0 but, since they must be equal upon calcite saturation (i.e., Δ[CO 3 2- ] = ΔTA ΔDIC = 0), one mole of CaCO 3 must dissolve for every mole of CO 2 produced according to: 106 CaCO CO H 2 O 106 Ca HCO 3 - (CH 2 O) O CaCO Ca HCO 3 - ΔDIC = ΔTA = +212 CaCO 3 dissolution. (NH 3 ) O 2 16 NO H 2 O + 16 H +, ΔDIC = 0, ΔTA = CaCO H + 16 Ca HCO 3 -. (NH 3 ) O CaCO 3 16 NO Ca HCO H 2 O ΔDIC = ΔTA = +16 CaCO 3 dissolution. Taking into consideration the dissociation of phosphoric acid: (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 )+ 138 O CaCO HCO NO Ca H 2 O + HPO 4 2- ΔDIC = ΔTA = +230 CaCO 3 dissolution. 4/61

5 Porewater evolution in a closed system A B C D E DIC, mm O 2, µm NO 3-, µm SRP, µm Mn 2+, µm Fe 2+, µm SO 4 2-, mm NH 4+, µm A Initial conditions B After oxygen reduction C After nitrate reduction D After MnO 2 (Mn(IV)) reduction E After FeOOH (Fe(III) reduction O 2 (µm) DIC (mm) SRP (µm) NO 3 - (µm) Mn 2+ (µm) Fe 2+ (µm) A Metabolic CO 2 production, µmoles B C D E 5/61

6 After oxygen has been consumed, nitrate reduction will start: NO 3- reduction (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 ) NO CaCO N HCO Ca 2+ + HPO H 2 O ΔDIC = ΔTA = CaCO 3 dissolution. After nitrate has been consumed, Mn(IV) reduction will start: Mn(IV) reduction (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 )+ 236 MnO Ca HCO CaCO Mn N 2 + HPO H 2 O ΔDIC = ΔTA = -258 CaCO 3 precipitation. After reactive Mn(IV) has been consumed, Fe(III) reduction will start: Fe(III) reduction (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 )+ 424 FeOOH Ca HCO CaCO Fe NH 4+ + HPO H 2 O ΔDIC = ΔTA = -650 CaCO 3 precipitation. 6a/61

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8 Porewater evolution in a closed system A B C D E DIC, mm O 2, µm NO 3-, µm SRP, µm Mn 2+, µm Fe 2+, µm SO 4 2-, mm NH 4+, µm A Initial conditions B After oxygen reduction C After nitrate reduction D After MnO 2 (Mn(IV)) reduction E After FeOOH (Fe(III) reduction O 2 (µm) DIC (mm) SRP (µm) NO 3 - (µm) Mn 2+ (µm) Fe 2+ (µm) A Metabolic CO 2 production, µmoles B C D E 7/61

9 Suboxic diagenesis From: Froelich et al. (1979) GCA, 43: /61

10 Sulfate reduction and fermentation After reactive Fe(III) has been consumed, sulfate reduction will start: SO 4 2- reduction (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 )+ 53 SO HCO HS NH 4+ + HPO H + Fe 2+ + HS - FeS(s) + H + 8 Fe(OH) HS H + 8 FeS(s) + SO H 2 O 8 Fe(OH) HS - + SO H + 8 FeS 2 (s) + 28 H 2 O After sulfate has been consumed, fermentative bacteria will take over: Fermentation/Disproportionation (CH 2 O) 106 (NH 3 ) 16 H 3 PO H 2 O 53 HCO NH CH 4 + HPO H + (but complex organic compounds cannot be utilized by methanogens, Chemolithotrophic methanogens: CO 2 + 4H 2 CH H 2 O Quasi-chemolithotrophic methanogens: 4HCOOH 4CO 2 + 4H 2 Methylothrophic methanogens: CH 3 COOH CH 4 + CO 2 9/61

11 Sulfate reduction 10/61

12 Sulfate reduction 11/61

13 Trace metal remobilization (idealized Mn diagenetic cycle) Flux = φ D s δc/δz D s = D 0 /(1 + n(1- φ)) n 3 for marine muds From: Froelich et al. (1979) GCA, 43: /61

14 Calypso piston corer 13/61

15 Calypso piston core on the R/V Marion Dufresne II 14/61

16 R/V Marion Dufresne II 15/61

17 R/V ALCIDE C. HORTH 16/61

18 R/V CORIOLIS II 17/61

19 Piston coring 18/61

20 Piston coring 19/61

21 Box coring 20/61

22 Box coring 22/61

23 Box-corer and recovered interface 23/61

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28 Trace metal remobilization (Mn diagenetic cycle in the LSLE) From: Katsev et al. (2007) Limnol. Oceanogr., 52: /61

29 Trace metal remobilization (Mn diagenetic cycle in the LSLE) Depth (cm) From: Lefort et al. (2012; Aquatic Geochemistry 18: ) 29/61

30 Trace metal remobilization (Fe diagenetic cycle in the LSLE) Depth (cm) From: Lefort et al. (Aquat. Geochem, 2012) 30/61

31 Trace metal remobilization (idealized Mn and Fe diagenetic cycle) IRON CONCENTRATION (FeOOH) S DEPTH (Fe 2+ ) AQ From: Froelich et al. (1979) GCA, 43: /61

32 Simplified diagenetic manganese cycle WATER Particulate Flux OXIC SEDIMENTS? Mn(II) + O 2 MnO 2 SUBOXIC SEDIMENTS Mn(II) MnO 2 (reactive) OM ANOXIC SEDIMENTS Mn(II)-carbonate + Mn(II) ads 2 cm SO CH 2 O H 2 S + 2HCO 3-32/61

33 Simplified diagenetic iron cycle WATER Particulate Flux OXIC SEDIMENTS X Fe(II) + O 2 FeO x SUBOXIC SEDIMENTS Fe(II) OM FeO x (reactive) ANOXIC SEDIMENTS Fe(II) + H 2 S FeS x 2 cm SO CH 2 O H 2 S + 2HCO 3-33/61

34 Multi-corer and undisturbed interface 34/61

35 Sediment incubations 35/61

36 Benthic fluxes Katsev, Sundby and Mucci (2007, Limnol. Oceanogr., 52(6): /61

37 Measuring porewater properties directly The core remains intact Low risk of contamination Spatial resolution is high In-situ measurements are possible Data are acquired in real time Multi-element capacity 37/61

38 Micro-electrode anodic stripping voltammetry Mn 2+ I - 38/61

39 -25 0 Simultaneous measurements of O 2, I -, Mn 2+, and Fe 2+ O 2 (Depth in mm) Depth (mm) Fe 2+ Mn 2+ I µm µm µm 39/61

40 From: Madison et al. (2013, Science 341: ) 40/61

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46 Fig. 2 Examples of oxygen distribution in sediments. The grey scales images were converted to false colour. (a) Control without organism (resolution: lm); (b) C. neritea (resolution: lm); (c and d) N. diversicolor (resolution: lm and lm); and ( e) N. virens (resolution: lm). Times after which the picture have been acquired are indicated. Taken from: Pischedda et al. (2008) Acta Biotheor. 56: /61

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48 Trace metal remobilization (As diagenetic cycle in the LSLE) Depth (cm) From: Lefort et al. (Aquat. Geochem., 2012) 48/61

49 Phosphate Diagenesis From: Sundby et al. (1992) Limnol. Oceanogr. 37: /61

50 Arsenic and Phosphate Diagenesis From: Mucci et al. (2000) Aquat. Geochem.6: /61

51 Arsenic and Phosphate Diagenesis From: Mucci et al. (2000) Aquat. Geochem. 6: /61

52 From: Mucci et al. (2000) Aquat. Geochem. 6: Arsenic Diagenesis

53 Arsenic Diagenesis WATER Particulate Flux + O 2, MnO 2 As(V) + Fe(II) + O 2 FeO x As(V) OXIC SEDIMENTS As(V) +Fe(II) OM FeO x (reactive) As(V) SUBOXIC SEDIMENTS As(III), As(V) + Fe(II) 2 cm H 2 S FeO x (refractory) As(V) SO CH 2 O H 2 S + 2HCO 3 - ANOXIC SEDIMENTS

54 Phosphate Diagenesis From: Mucci et al. (2000) Aquat. Geochem. 6:

55 The diagenetic equation δc i /δt = δci/δz (φ (D s + D B ) δci/δz) ω δci/δz + ΣR diffusion + advection + reactions where δci/δz is the concentration gradient of species i φ the porosity D s is the molecular diffusion coefficient D B is the bioturbation/biodiffusion coefficient ω is the sedimentation rate ΣR is the sum of the rates of all chemical reactions which affect the concentration of i, including redox, acid-base, adsorption and precipitation/dissolution reactions. At steady state, δc i /δt = 0

56 Diagenetic modeling

57 Diagenetic modeling (CH 2 O) X (NH 3 ) Y (H 3 PO 4 ) Z + X/2 SO 4 2- XHCO 3- + X/2 H 2 S + Y NH 3 + Z H 3 PO 4 δc n = γ n D m k (ωθ) -2 + (1 + K m ) δc m γ m D n k (ωθ) -2 + (1 + K n ) C n & C m are concentrations of n and m γ n & γ m are stroichiometric coefficients D n & D m are the molecular diffusivities k is the rate constant for the redox reaction ω is the sedimentation rate θ is the tortuosity K n & K m are the adsorption coefficients From: Boudreau, Canfield and Mucci (1992) Limnol. Oceanogr. 37:

58 Diagenetic modeling For species that do not adsorb strongly to solid particles and, given that D S k/ω 2 >>1 and assuming Redfield stoichiometry (i.e., x = 106, Y = 16, Z =1): δσh 2 S = - DSO 4 2- = vs δso 4 2- theo DΣH 2 S δσco 2 = 2 DΣH 2 S = 2.71 vs 2.67 δσh 2 S theo DΣCO 2 δσco 2 = 2 DSO 2-4 = vs δso 2-4 theo DΣCO 2 From: Boudreau, Canfield and Mucci (1992) Limnol. Oceanogr. 37:

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60 The fate of carbon in sediments From: Mucci et al. (2000) Deep-Sea Res. 47:

61 The fate of carbon in sediments From: Gehlen et al. (1999) GCA 63:

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