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 NO HPO H H 2 O Elemental ratios of OM, and reaction stoichiometry, are central to this approach.

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

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

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)

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

Short deployments of floating arrays of sediment traps

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

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

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

Primary production roughly constant offshore Attenuation increased offshore

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

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

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.

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

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 NO HPO H H 2 O C 106 H 263 O 110 N 16 P H:C = 2.48 O:C = 1 (pure carbohydrate)

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

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

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

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

Use potential temperature to account for mixing

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

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

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

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

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

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

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

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

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

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

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

Lignin composition – terrestrial vascular plants gymnosperm angiosperm non-woodywoody

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?

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

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?

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