1. Pore water oxygen profiles and benthic oxygen fluxes
(CH2O)106(NH3)16(H3PO4) + 138O2 =>
106HCO NO3- + HPO H+ + 16H2O
Integrated oxygen consumption => oxygen flux
organic C decomposition (oxic) + reoxidation of
reduced species (metals, sulfide)
gradient at sediment-water interface,
or fit profiles of oxygen or nitrate

2. O2 penetration depth
influence use of other electron acceptors
understand controls on C org preservation
interpret downcore % C org variations
predict profile and rate of CO2 release
“metabolic” carbonate dissolution
Comparisons:
benthic flux chamber : sediment trap (OM lability)
pore water : benthic flux chamber (bioirrigation)

3. What controls the O2 penetration depth?

5. Suggests that oxygen penetration depth is controlled by [O2]bw and O2 flux (in turn driven by OM flux)

6. Found a good relationship between predicted O2 penetration depth (bottom water oxygen and oxygen flux) and observed OPD
Cai and Sayles, 1996

7. The relationship breaks down at higher penetration depths; non-constant decomposition rate?

8. Simple model provides a way to predict response of processes linked to OPD – OM preservation and benthic denitrification – to changes in [O2]bw and surface ocean productivity (C flux, or O2 flux)

9. Martin and Sayles (2004) – test ability to predict OPD in cases where porosity is a function of depth, and over a range of [O2]bw and ko

10. Observed porosity (fn z)
in situ microelectrode O2 profiles in western North Atlantic. Rates estimated by fitting the data with a diagenetic model
Observed porosity (fn z)
Fitting the profiles, found that a constant O2 consumption rate (ko) was adequate for most sites
Martin and Sayles, 2004

11. Porosity is a significant factor
Good agreement with predicted dependence on [O2]bw and O2 consumption rate

12. The Cai and Sayles OPD - [O2]bw - O2 flux relationship is confirmed in the more-general (variable f) case.
(OPD increases with [O2]bw , decreases with O2 flux)

14. Oxygen evidence of the lability (reaction rate) of sediment OM – how tight is the link between OM input (sediment trap OM flux) and benthic decomposition?

15. Laboratory evidence of a range in lability for marine OM – plankton decomposition experiments.
Westrich and Berner, 1984

16. Sayles, Martin, and Deuser, 1994
Sediment trap carbon flux and benthic oxygen demand off Bermuda.
Long-term trap deployment, and a series of month-long BFC experiments
Sayles, Martin, and Deuser, 1994

17. Sediment trap carbon flux and Observed benthic oxygen demand (circles) compared with trap flux and model-predicted oxygen demand for slow (0.2/y) and fast (5/y) decomposition rates.
Observations more consistent with slow rates.

18. Contrast Sayles et al. Bermuda results (slow ko, lack of tight linkage between C flux and O2 demand) with results of Smith et al. off California.
Strong linkage off CA implies faster decomposition rates (5 to 10 / yr).

22. Relative importance of diffusion and bio-irrigation to oxygen uptake in continental margin sediments
Pore water profiles and benthic flux chamber deployments on the California margin
Reimers et al., 1992

23. Pore water oxygen from in situ microelectrodes
Pore water oxygen from in situ microelectrodes. Low bottom water oxygen in OMZ; oxygen penetration of millimeters at all these shallow sites.
oxygen respiration (CH2O)106(NH3)16(H3PO4) + 138O2 =>
106HCO NO3- + HPO H+ + 16H2O

24. Linear gradient estimates from steepest part of each profile.
Deeper sites, with higher bottom water oxygen and deeper oxygen penetration.
Linear gradient estimates from steepest part of each profile.
Reimers et al.

25. Benthic flux chamber results; short (1-2 day) deployments at these high-flux, low O2 sites.
Jahnke et al.

27. Reasonable agreement between O2 profiles (diffusive transport) and BFC results (total transport); no obvious pattern to the differences.

28. Archer and Devol – WA margin

29. Microelectrode oxygen profiles

30. Benthic flux chamber O2

32. Bioirrigation in high OM flux, high [O2]bw settings
Total oxygen uptake substantially higher than diffusive uptake at the high oxygen (shelf) sites of Archer and Devol.
Bioirrigation in high OM flux, high [O2]bw settings

34. A depth transect in the western Atlantic
A depth transect in the western Atlantic. Shallowest site (250 m) in the O2 minimum (165 mM), and also characterized by coarse, low-porosity sediment.
Martin and Sayles, 2004

35. Multiple in situ microelectrode O2 profiles at each site
Multiple in situ microelectrode O2 profiles at each site. Rates estimated by fitting the data with a diagenetic model (not the “steepest slope” approach of Reimers et al.)
O2 penetration 1 – 3 cm
Martin and Sayles, 2004

36. Production and consumption rates of nitrate and ammonia also obtained by fitting the data with a diagenetic model. The ammonia flux reflects OM oxidation by sulfate and iron reduction.

38. O2 respiration dominates more strongly than on CA margin
Martin and Sayles, 2004
O2 respiration dominates more strongly than on CA margin
O2: – 82 %
NO3- : – 6 %
SO42- + Fe: 13 – 20 %
O2: %
NO3- : %
SO42- + Fe: 7 %

47. Two-point gradient estimates at steepest part of profile.
Steep nitrate gradients reflect rapid, shallow denitrification.
nitrate reduction (CH2O)106(NH3)16(H3PO4) NO3- =>
13.6CO HCO N2 + HPO H2O

48. Mn2+ (open) and Fe2+ (filled) gradients (and MnOx and FeOx reduction rates) estimated from fits to upper part of each profile.

49. Reimers et al., Mn2+ decrease? No Mn2+? Fe2+ decrease?
MnO2 reduction (CH2O)106(NH3)16(H3PO4) + 236MnO H+ => 236Mn HCO3- + 8N2 + HPO H2O
Fe2O3 reduction (CH2O)106(NH3)16(H3PO4) + 212Fe2O H+ => Fe HCO NH4+ + HPO H2O
Fe2+ decrease?

50. The ammonia flux (corrected for Fe reduction) reflects sulfate reduction.
sulfate reduction (CH2O)106(NH3)16(H3PO4) + 53SO4-2 =>
106HCO NH4+ + HPO HS- + 39H+

51. The oxygen fluxes are corrected for NH3, Mn2+ and Fe2+ oxidation