1. Pore water profiles of reactants or products can be a sensitive way to estimate OM decomposition rates. Oxic respiration (assuming Redfield ratio): (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 ) + 138O 2 => 106HCO 3 - + 16NO 3 - + HPO 4 -2 + 124H + + 16H 2 O Elemental ratios of OM, and reaction stoichiometry, are central to this approach.

2. Today: - OM flux estimates from sediment traps. -OM composition estimates from plankton, water column, and trap data. - Importance of terrestrial OM (biomarker and 13C data). Thursday: - Electron acceptors for OM oxidation (order of use, relative importance) - Pore water oxygen profiles and benthic oxygen fluxes

3. Particle fluxes in the North Atlantic Bloom Experiment Moored sediment trap array, year- long deployments 1. OM flux estimates from sediment traps

4. Short (1 cup) offset in total mass fluxes w. depth => fast sinking (50 – 200 m/d) Implies packaging / ballasting Strong seasonality in total mass flux Total flux increases with depth (1-2 km)

5. Strong seasonality in biogenic fluxes (note mass units, not moles of C) CaCO 3 flux increases with depth @ 48N (trapping efficiency)

6. Short deployments of floating arrays of sediment traps

7. Dramatic attenuation of the POC flux with depth at each site Fluxes decrease moving offshore Derived similar curves for C, N, P, and O 2 demand -O 2 :P and –O 2 :C > Redfield

8. Lee et al. (1998) JGOFS Arabian Sea Process Study

9. 14 C Pri. Prod. 234 Th scavenging model Moored traps %C x Holocene sed rate Strong attenuation Different methods reflect different time scales

10. Primary production roughly constant offshore Attenuation increased offshore

11. 14 C Pri. Prod. Shallow drifting traps 234 Th scavenging model Moored traps (one yr, one cup) %C x Holocene sed rate 2. OM composition

13. All compound classes show attenuation; amounts differ Wakeham et al., 1997

14. Little fractionation between compound classes as first 90+ percent of OM flux is consumed (from plankton through 105 m); the residual (deep traps, sediments) is largely uncharacteized.

15. Empirical groupings of biochemicals by “behavior”: I.Selective degradation II.Mid-depth maximum III.Enriched in surface seds IV.Most resistant

16. Redfield ratio (C:H:N in plankton tow; -O 2 assumed): (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 ) + 138O 2 => 106HCO 3 - + 16NO 3 - + HPO 4 -2 + 124H + + 16H 2 O C 106 H 263 O 110 N 16 P H:C = 2.48 O:C = 1 (pure carbohydrate)

17. Anderson used typical elemental ratios of compound classes to predict OM composition: C 106 H 175 O 42 N 16 P + 150O 2 => 106CO 2 + 16HNO 3 + H 3 PO 4 + 78H 2 O H:C = 1.65 O:C = 0.4

18. Takahashi et al., 1985 Estimate C:N:P:-O 2 regeneration ratios from thermocline nutrient chemistry

19. Observed slopes reflect decomposition + mixing O 2 :P = -138 O 2 :P = -100

20. O 2 :P = -252 O 2 :P = -551

21. Use potential temperature to account for mixing

22. 138 172

23. Anderson and Sarmiento – Similar approach, -O 2 :P ~ 170

24. Hedges et al. 2002 13 C NMR on 5 plankton tow samples; model the proportions of 3 components – protein, carbohydrate, lipid

25. Hedges et al., -O 2 :P ~ 154 “Redfield” stoichiometry probably overestimates the oxidation state of OM, and thus overestimates the C org oxidation rate associated with a given oxygen flux

26. 3. Contribution of terrestrial OM? C:N ~ 106:16 ~ 6.6 (N:C ~ 0.15) C:N 10 80 Keil et al., 1994  13 C mar ~ -20 o/oo, terr ~ -27o/oo

27. Deines, 1980 C3 CAM Marine plankton “all” terrestrial plants C4 Grasses, corn, spartina

28. Rau et al. CO 2 availability (pCO 2, growth rate) (Goericke et al.) Plankton  13 C

29. Prahl et al. – Biomarkers on WA margin River sediments, shelf and slope sediments

30. n-alkanes (plant waxes) cutin Total lignin- derived phenols Ratio refractory biomarkers to TOC in river sediments Assumptions?

31. Estimate “end member” isotopic composition Extrapolated marine 13 C River seds

32. % terrestrial Shelf ~ 60% Slope ~ 30% Basin ~ 15%

33. Goni et al. – lignin, bulk  13 C, biomarker  13 C, bulk 14 C Impact of C4 plants on  13 C(terrestrial) and on interpretation of bulk sediment  13 C

34. Lignin composition – terrestrial vascular plants gymnosperm angiosperm non-woodywoody

35. Hedges and Parker, Goni et al. Bulk  13 C near -20 o/oo by 100 m Total lignin near 0 by 100 m Evidence of little terrestrial organic matter in marine sediments?

36. Lignin ratios imply lignin degradation. But can marine microbes degrade lignin?

37. Lignin-predicted  13 C of C3-C4 terrestrial mixture matches observed bulk  13 C of -20 o/oo Measure the  13 C of lignin (known terrestrial) in marine sediments, and use to estimate C3:C4 ratio of all terrestrial OM. Is this correct? Is it widespread?

38. Today: - OM flux estimates from sediment traps. -OM composition estimates from plankton, water column, and trap data. - Importance of terrestrial OM (biomarker and 13C data). Thursday: - Electron acceptors for OM oxidation (order of use, relative importance) - Pore water oxygen profiles and benthic oxygen fluxes