1. Outline : Carbon cycling and organic matter biogeochemistry
Global carbon cycle - pools, sources, sinks and fluxes
pools of organic carbon - POC, DOC - vertical & horizontal segregation, vertical fluxes
Ocean productivity
Biological carbon pump
Preservation of organic carbon
Vertical flux of POM – sediment traps
Dissolved organic carbon (DOC)
Concentrations & distribution
Characterization of DOC pool - molecular size and reactivity
Sources and fates of POM & DOM
Age and long-term sinks for DOM

2. Operational pools of carbon in seawater
POM - particulate organic matter (includes not only carbon but also H, O, N, P, S etc)
DOM - dissolved organic matter (about 50% C by weight)
POC - particulate organic carbon (refers only to the carbon)
DOC - dissolved organic carbon
PIC – Particulate inorganic carbon (CaCO3)
DIC - dissolved inorganic carbon (all forms)
Organic nutrient pools
PON & POP (the pools of N & P that are bound in organic particles larger than the operational cut-off)
DON & DOP - (the pools of N & P that are bound in organic matter that passes through the operational cut-off filter)
All pools are operational! (depend on selected criteria for filtration)

3. 0.4-0.2 µm filtration cut-off
Organic particle size continuum
µm filtration cut-off

4. Organic carbon = Reduced carbon
Includes all carbon other than CO2, HCO3-, H2CO3, CO, CO32-, and carbonate minerals
Includes hydrocarbons CH4, CH3-CH3 etc & black carbon.
Nearly all reduced carbon is biogenic. However, some chemical/geochemical alteration of OM takes place, petroleum and natural gas formation being notable examples.
Because organic matter is mainly biogenic it typically contains not only reduced carbon but also some H, O, N, P and S etc.

5. Net export from surface 8-15
Global Carbon reservoirs and exchanges (Figure based on Libes; data from Table 11.1 in Emerson & Hedges)
pools in 1015 gC (boxes) fluxes in 1015 gC y-1 (arrows)
Atmospheric CO2 784
Terrestrial biota 600
River DIC 0.5
Exchange 90
Soil & detritus 1500
Net export from surface 8-15
Ocean DIC 38,000
Marine biota 1-2
Detrital POC 30
DOC 700
0.2
Sedimentary reservoirs are huge!
Organic sediments
10,000,000
Fossil fuels 3577
Limestone & dolomite
50,000,000

6. Most organic carbon in the sea is dissolved or colloidal.
Biomass pools are very small
 Operationally-dissolved 
Dissolved and Colloidal materials are operationally Dissolved

7. Based on Table 9.1 in Millero, 2006
Sources of organic matter to the open oceans
% of total
Primary production
Phytoplankton
Macrophytes
Rivers
Groundwater
Atmospheric input
Rivers are a small source of organic matter to open ocean!
Based on Table 9.1 in Millero, 2006

8. Ocean Net Primary Production in different trophic regimes Trophic zone
Mixed layer Chl a (μg L-1)
Net Primary Production
(1015 gC y-1)
% of Ocean NPP
Oligotrophic <
22.7
(<100 gC m-2 y-1)
Mesotrophic
56.5
( gC m-2 y-1)
Eutrophic >
18.7
( gC m-2 y-1)
Macrophytes
2.1
Total ocean production = 48.5
Total terrestrial production = 56.4
Total global production = 104.9

9. Global primary productivity pattern as deduced from satellite imagery
Behrenfeld et al Nature 444:
Considerations:
Depth distribution i.e. euphotic depth
Seasonal variations, esp. in polar regions
Interannual variations
Oceanic/oligotrophic areas– dominated by picoplankton < 2 μm
Upwelling, coastal & temperate areas have larger phytoplankton (> 2 μm) as major primary producers

10. Behrenfeld et al 2006. Nature 444:
Temporal changes in global average Chlorophyll anomaly and Net Primary Productivity (NPP) anomaly.
was a strong El Nino year which reduced NPP. Rapid recovery ensued, with slow decline thereafter.
Behrenfeld et al Nature 444:

11. The Biological Carbon Pump
Exporting carbon below the pycnocline
CO2 (g) 
CO2 (aq) + H2O <=> H2CO3 <=> H+ + HCO3- <=> H+ + CO32-
Air
Sea
Euphotic zone
Photosynthesis
calcification
Pycnocline
sinking
Upwelling of high DIC, high pCO2 water
POM
CaCO3
Some DOM
DIC & alkalinity
CaCO3-rich sediment above CCD
No preservation of CaCO3 below CCD
CO2
Deep Sea
respiration
spreading
Alkalinity
POM
CCD
Ridge crest
CaCO3 dissolution
Carbon burial & preservation as POM and CaCO3
Non-carbonate sediment
carbonates

12. Export Production
per year
Falkowski et al., Science 298:

13. POMflux(z) = POMflux (100)(z/100)-0.858
Flux of organic matter decreases exponentially with depth :
POMflux(z) = POMflux (100)(z/100)-0.858
Where POMflux(100) is the downward flux at the base of the euphotic zone (100 m), and POMflux(z) is the flux of organic carbon at depth (z) measured with sediment traps.
At 5000 meters, the flux is only 3.5% of that at the base of the euphotic zone!
Very little organic matter (POM) reaches the deep ocean – and what does reach the bottom is lower quality
Data for the figure of Bishop et al came from Martin et al. 1987
Vertical flux of POM is via dead phytoplankton, fecal pellets, molt shells, fragments, mucous feeding nets etc.

14. DOC export from surface ocean represents 8-18% of the total organic carbon export.
Modeled DOC downward flux
DOC/POC downward flux ratio
Hansell et al., 2010

15. Sediment traps - particle interceptors
Poison or preservative
Baffle to reduce hydrodynamic effects
Particle flux 
Base of euphotic zone m
500 m
Capture flux decreases exponentially with depth
1000 m
3000 m

16. Many different designs of sediment traps have been used
Time series traps - rotating cylinders within trap collect for certain period of time
1-1.5 meters
Large surface area trap for oceanic sampling

17. Diagram of an automated time-series sediment trap used in the Arabian Sea. A baffle at top keeps out large objects that would clog the funnel. The circular tray holds collection vials. On a preprogrammed schedule (every 5 days to 1 month), the instrument seals one vial and rotates the next one into place. Scientists retrieve the samples up to a year later to analyze the collected sediment. (courtesy Oceanus magazine, WHOI)

18. What results do you expect for POM captured in a sediment trap array deployed over a full oceanic depth profile?
Quantity of POM?
Quality of POM - C:N, specific biomolecules?, 14C-content?

19. Three sediment trap designs.
The original funnel design (moored trap) uses a large collection area to sample marine particulates that fall to great depths.
Surface waters produce enough sediment so that traps there don’t require funnels. Neutrally buoyant, drifting sediment traps catch falling material instead of letting it sweep past in the current. Drawings are not to scale.
Source:

20. Joaquim Goes and his team deploy simple sediment traps in the Southern Ocean

21. WHOI scientists Ken Buesseler and Jim Valdes with one of the neutrally buoyant sediment traps they helped design. The central cylinder controls buoyancy and houses a satellite transmitter. The other tubes collect sediment as the trap drifts in currents at a predetermined depth, then snap shut before the trap returns to the surface. (Tom Kleindinst, WHOI)

22. Significance of Organic Carbon Burial
Much of the present global carbon burial (preservation) is in marine environments
Little organic carbon preservation in terrestrial soils except for high latitude peats. Terrestrial burial of OM has been more significant in the geological past (i.e. Carboniferous coal deposits)
Significance of Organic Carbon Burial
Burial and preservation of biogenic (reduced) carbon in sedimentary reservoirs removes atmospheric CO2 and allows excess O2 to remain in the atmosphere.
Burial of organic matter removes some nutrient elements and trace elements.
Carbon burial leads to petroleum, organic rich shales, & natural gas

23. Percent of primary production accumulated in the sediments
The greater the overall sedimentation rate of particles, the greater the fraction of surface primary production delivered to sediments
Sediment accretion rate (cm per 1000 y)
0.1 1 10
100
1000
0.001
0.01
Percent of primary production accumulated in the sediments
Coastal areas – maximum of ~10%
y = x1.25
See Fig in Pilson for actual data graph
>5000 m depth
> m depth
>2000 m depth incl. Black Sea

24. Most burial nearshore on continental margins
Burial will be a small fraction of the carbon delivered to the sediments. Most will be respired to CO2 and diffuse back to water column.
Libes, Chapter 25

25. Reasons for high carbon burial on the continental margins:
high productivity - > high POM flux to benthos
high particle flux leading to faster burial rate - OM preservation tied directly to mineral surface area (see Keil et al. 94)
shallow depth - less organic matter degradation on descent
remineralization slower under anoxia - still a debatable issue.

26. Coastal waters can have much higher DOC
Dissolved organic carbon - the largest pool of organic matter in seawater
Measured by converting DOC into CO2 via:
Wet-chemical oxidation
High temperature catalytic combustion
UV-oxidation
Sealed tube combustion
DOC concentrations are µM in surface waters of the open ocean, and µ M at depth.
Coastal waters can have much higher DOC

27. Surface ocean (30 m) DOC concentrations
Dots are measured values, background color field is modeled
Hansell et al., 2010

28. Deep ocean (3000 m) DOC concentrations decrease along ocean conveyor (meridional overturning circulation)
Dots are measured values, background color field is modeled
NADW starts with about 46 µM DOC
The semi-labile fraction of DOC degrades during the long transit from North Atlantic to the Pacific. What is left (~34 M) is ultra-refractory since it survived the ~1000 y trip through the deep ocean. This DOC is present as background DOC in surface waters and has an average age of ~6000 years.
Hansell et al., 2010

29. DOC Concentration (µM)B C D
DOC Concentration (µM)
1000
2000
3000
4000
Depth (m) 10 20 30 40 50 60 70
Labile DOC; Small pool; τ = hours to days
Semi labile DOC; larger pool (25-30 µM) in sfc;
τ = weeks to months
Open ocean surface DOC concentration is about 70 µM. It is about 44 µM in the deep Sargasso and about 34 µM in the deep Pacific.
Ultra-refractory DOC; τ = >6000 y
Refractory DOC; τ = ~1000 years
After Benner, 2002

30. The average 14C age of deep DOC is 6000 years|!

31. DOC is generally conservative with salinity in estuaries
DOC (µM)
Salinity 36
400 75
Freshwater end-member
Implies terrestrial DOC delivery to ocean – but most is lost on shelf (see next slide)
In fact, some modification of riverine DOC takes place in estuaries, but conservative pattern still observed
Seawater end-member ~ µM

32. DOC concentration decreases away from shore
Much of the DOC delivery to ocean is lost on the shelf, close to shore

33. Constituents of DOM
High molecular weight >5000 Da (includes colloids)
proteins
polysaccharides (mucus, structural polymers)
nucleic acids
some humic substances
Medium Molecular weight Da
humic substances (refractory)
oligopeptides, oligonucleotides
lipids
pigments
Low molecular weight < 500 Da
monomers (sugars, amino acids, fatty acids)
osmolytes (DMSP, betaines, polyols)
toxins, pheromones and other specialty chemicals
See Chapter 22 in Libes for structures of organic compounds
Moderate lability
Mixed lability – some very refractory
High lability

34. Shift

35. Examples of some polysaccharides that might be part of a semi-labile, high molecular weight pool of DOM.
Pectin contains O-methoxy groups
Chitin is an amino sugar, i.e. it contains N

36. Depolymerization - Polymer hydrolysis
Conversion of high molecular weight DOM or POM into low molecular weight DOM
Carried out primarily by bacteria but really a
consortium of microbes.
Proteins -> free amino acids & peptides by proteases
Polysaccharides to monosaccharides by glucosidases, chitinases, cellulases
Peptides to amino acids by peptidases
RNA or DNA to nucleotides by nucleases

37. Origin of labile DOM in seawater
Exudates - Amino acids, sugars, some high molecular weight labile polysaccharides - rapidly consumed
Death or lysis of cells - rapid uptake by bacteria
Sloppy feeding - leaking of phytoplankton cell contents
Digestion - Digestor theory. Jumars, Penry et al. Zooplankton maximize their organic matter assimilation by maximizing throughput not by being highly efficient. This results in considerable release of DOC from fecal pellets and zooplankton.

38. Marine Snow. Agglomerated organic matter - amorphous aggregates
Enriched with bacteria and protozoans
possible low oxygen conditions
elevated nutrients
Still understudied.
Some species of phytoplankton release mucilage i.e. Phaeocycstis sp.
TEP - Transparent ExoPolymer. Is a form of marine snow
Marine Snow or aggregates caused by surface phenomenon. Enrichment of OM at surfaces of bubbles, waves convergence zones. You can make snow in the lab by rotating filtered water samples in bottle. Snow, and DOC make, sea foam.

39. Sea foam generated from Phaeocystis bloom in Dutch Wadden Sea
Phaeocystis globosa colony –cells embedded in mucous form spherical colony
Sea foam generated from Phaeocystis bloom in Dutch Wadden Sea

40. Blowing sea foam at Nags Head, North Carolina during Hurricane Sandy, October 2012
Nags Head, N.C.
High winds blow sea foam into the air as a person walks across Jeanette's Pier in Nags Head, N.C., Sunday, Oct. 28, 2012 as wind and rain from Hurricane Sandy move into the area. Governors from North Carolina, where steady rains were whipped by gusting winds Saturday night, to Connecticut declared states of emergency. Delaware ordered mandatory evacuations for coastal communities by 8 p.m. Sunday. (AP Photo/Gerry Broome)

41. What isn’t there may be most important!
Biogeochemists rule # 1
What isn’t there may be most important!
Substances with low concentrations may be especially important in biogeochemical fluxes - their concentrations are low because they are desirable molecules to microbes!
This axiom isn’t always true, but it often is

42. kloss Glycine (2 nM) production loss
Concentrations of most labile, low molecular weight organic compounds are low (typically in the 1-10 nM (10-9 – 10-8 Molar) range). Compare this to total DOC concentration in surface waters of about 75 µM C. But some LMW compounds have very fast turnover.
Glycine
(2 nM)
pseudo-steady
state conc.
production
loss
kloss
Pool size
Production = loss under steady state
Hypothetical example of amino acid turnover
k = 50 d-1
2 nM x 50 d-1 = 100 nM d-1
The flux of carbon through a particular compound is a function of: turnover (Conc. X Kloss ) and carbon content per molecule.
So for this example, 100 nM glycine d-1 x 2 mol C/mol glycine = 200 nM C d-1 flux through the glycine pool.
Thus, even substances with low concentrations can have high carbon fluxes if the turnover rate constant is large (fast turnover)
Glycine and DMSP dissolved pools may turn over times per day!

43. Carbon utilization efficiency affects trophic transfer and CO2/O2 dynamics
In terms of carbon
Carbon Assimilation Efficiency
Microbial Growth Efficiency (MGE)
Biomass Production (BP) = =
BP + Respiration
From the literature: MGE varies from 0.05 to 0.30 in different ocean waters (up to 0.52 in estuaries)
Microbial Carbon Demand = Microbial C Production
Microbial Growth Efficiency
These terms are often referred to as bacterial growth efficiency (BGE) and bacterial carbon demand (BCD) (until discovery of ocean Archaea complicated things)

44. Oligotrophic (from some recent studies)
eutrophic
Oligotrophic (from some recent studies)
Microbial Growth Efficiency = MGE = [Microb. Prod/(Microb. Prod + Respiration)]
See also del Giorgio et al L&O 56:1-16

45. Turnover of higher molecular weight material is relatively slow
Polysaccharide material (relatively labile) may turnover on time scales of days, and because of relatively large pool sizes (micromolar C), the mass flux can be large
Turnover of humic substances and other refractory material may be very long (years)
DOC in the deep sea is very refractory (14C-ages of years) - this explains its nearly uniform distribution (see Bauer, Williams and Druffel et al.)
Surface water DOC pool has average 14C age of ~1000 y - this DOC is composed of young (modern) carbon (14C age of +200 y) plus some of the old refractory material (14C age of ~6000 y)

46. How is this material ultimately removed from the ocean?
If 14C-age of deep DOC is ~6000 years, then this material has survived several ocean mixing cycles.
How is this material ultimately removed from the ocean?
Photochemical oxidation may be the key (Mopper and Kieber et al. 1991).
Photooxidation breaks down DOM into CO2 and smaller, often more labile molecules, thus returning it to biologically active pool of carbon (Kieber et al. Nature, 1989).
Hansell et al. (2009) also suggest particle adsorption (scavenging) in the deep see may remove some refractory carbon

47. Photochemical Blast Zone - some DOM oxidized
Photooxidation as a major sink for refractory DOM in the sea
Photochemical Blast Zone - some DOM oxidized
NADW formation. Labile DOM is utilized in relatively short time - leaving old refractory carbon to make another circuit
Upwelling of refractory, old DOM
Deep water transit (= 1000 y)
Little alteration of old, refractory carbon
This is a highly conceptualized diagram! Its not this simple!

48. Relative C:N ratios
Amino acids (AA’s) < protein < lipids < carbohydrates.
AA’s C:N 2-6 except for phenylalanine and tyrosine (C:N= 9)
POM concentration is generally high in the upper water column and euphotic zone. Very low at depth.
C:N of POM in surface ocean is generally similar to Redfield, i.e. 5-7
C:N of POM increase with depth (more labile N-containing compounds are removed in upper water column)

49. Molar ratios of C:N and C:P in marine plankton, DOM, and high molecular weight (HMW) DOM from the surface (<100 m) and deep (>1000 m) ocean.
From Benner, Chemical composition and reactivity of marine dissolved organic matter.
C:N
DOM has much higher C:N and C:P than plankton (Redfield)
Redfield
C:P

50. Humic substances in the sea
Complex, amorphous organic matter Gelbstoffe (colored DOM or CDOM) (contain many functional groups incl. aromatics)
Humic acids - insoluble at pH < 4
Fulvic acids - soluble at all pH’s
Humic acids + fulvic acids = humic substances
Significant terrestrial input of humic substances to the sea via rivers, but most is destroyed on continental shelves before reaching open ocean, probably via photooxidation. Only a small fraction (~1%) of oceanic DOC is terrestrially-derived, but up to 10% of humic substances might be terrestrial (based on lignin biomarkers and 13C-content)
Autocthonous humic substances - marine origin. Lack lignin moieties. Result from condensation of marine DOM - possibly via photoreactions

51. Soil humic acid showing amorphous structure and many functional groups
Ligand bound Fe
Adsorbed Al-Silicate clay
No two humic molecules will be the same

52. Role of sediment adsorption of organic matter in the carbon cycle (after Hedges and Keil, 1999)
Adsorption of organic compounds to inorganic sediment surfaces may play a role in organic carbon preservation
Can be labile compounds – just not bioavailable when stuck to sediment

53. Organic carbon (weight percent)
SA = Surface area of sediment particles
OC/SA = Organic carbon per unit surface area
Relatively constant amount of organic carbon per surface area
Keil and Hedges, Nature 370:549

54. Hedges & Keil, 1995

55. Organic matter desorbed from sediment particles is rapidly degraded
Age of the sediment layer from which Organic Matter was desorbed.
This material persisted for at least 460 years but when desorbed, it degraded in days. Therefore it is labile stuff – protected by adsorption
Hedges & Keil, 1995

56. More than monolayer equivalent
Less than monolayer equivalent
Percent of global organic carbon burial that occurs in different depositional environments. The largest fractions are Delta (44%) and Shelf (45%) indicating that 90% of global carbon burial occurs on ocean margins. The shading indicates where organic content is More, Less or Equivalent to monolayer absorption based on surface area of sediment particles. (after Keil & Hedges)

57. finish

58. Role of sediment adsorption of organic matter in the carbon cycle (after Hedges and Keil, 1999)
Adsorption of organic compounds to inorganic sediment surfaces may play a role in organic carbon preservation
Can be labile compounds – just not bioavailable when stuck to sediment

59. Low Mol Wt DOC
High Mol Wt DOC
Photo – Jeff Cornwell O2

60. From Davis and Benner, 2007

61. Reactivity of DOM vs. molecular size (after Amon and Benner, 1996)
Counterintuitive? Big molecules more reactive than small?
Applies to Bulk DOC – not to individual compounds
Many small molecules have VERY high reactivity e.g. amino acids, DMSP

62. Latitudinal variation of DOC in the deep ocean
Latitudinal variation of DOC in the deep ocean. The semi-labile fraction of DOC degrades during the long transit from North Atlantic to the Pacific. What is left (~34 M) is ultra-refractory since it survived the ~1000 y trip through the deep ocean. This DOC is present as background DOC in surface waters and has an average age of ~6000 years.
Hansell.

63. Larger pool of semi-labile DOC in surface water; τ = weeks
Small pool of very labile (easily degradable) DOC in surface waters; τ = hours to 1 day
Larger pool of semi-labile DOC in surface water; τ = weeks
Refractory DOC; τ = years
Ultra-refractory DOC; τ = >6000 y
Open ocean surface DOC concentration is about 70 µM. Its about 44 µM in the deep Sargasso and about 34 µM in the deep Pacific.

66. Hydrolyzing/fermenting cell
Under anoxic conditions it takes a consortium of organisms to degrade complex organic matter
Very high Mol Wt DOC
Fermentative cell
High Mol Wt DOC
Low Mol Wt DOC
Hydrolyzing/fermenting cell
Respiring cell
Low Mol Wt DOC

67. Different organic fractions degrade at different rates

68. Ocean productivity by province
% of Ocean Prod.
81%
18% 1%
These values for productivity are old and a low estimate! Other recent estimates of global ocean productivity (e.g. Martin et al. 1987) are closer to x 1015 gC/y. The distribution percentages, however will be similar to those shown here.

69. Hopkinson & Vallino. Nature 433: 2005

70. Seasonal cycle of DOC at the BATS station in the Sargasso Sea - Carlson et al 1994
Winter mixing homogenizes upper 200m & mixes down some DOC
Spring build up of DOC

72. Global Carbon Cycle Problem
Global CO2 release is known, but net increase in atmosphere is less than predicted
Where does this carbon go?
Some of the carbon can be accounted for by ocean uptake (see Quay et al.), but there is a missing sink of 0.7 GT. Terrestrial biomass (i.e. trees) might be missing sink.
0.7 GT of C is only 4% of net annual primary productivity on land and 3% of ocean carbon exchange with atmosphere, therefore it is hard to discern with accuracy. Ocean exchange in particular is difficult because of spatio-temporal shifts in carbon exchange.
The role of the oceans in Carbon exchange is being studied intensively!

73. G3 G2 G1

74. Carbon generally not considered limiting to primary productivity in the sea - plenty of bicarbonate or CO2 in seawater (DIC = ~2 mM). The ratio of C:N:P in surface seawater is 1000:16:1. Thus C not likely to be limiting to Primary Production.
However, the form of inorganic carbon available to phytoplankton does makes a difference. Phytoplankton take up predominantly the neutral species of DIC (CO2(aq) and H2CO3) so if pCO2 is low, phytoplankton can experience carbon limitation.
Some species may have “carbon concentrating mechanisms” to transport HCO3-.

75. Oceanic/oligotrophic areas– dominated by picoplankton < 2 μm
Upwelling, coastal & temperate areas have larger phytoplankton (> 2 μm) as major primary producers
Considerations:
Depth distribution i.e. euphotic depth
Seasonal & interannual variations
-seasonal variations

76. Deep DOC ~5900 years old
Deep DOC ~4100 years old

77. Fig. 2. Observed values of the total Corg rparticle surface area
loading of sediment in riverine, deltaic, nondeltaic continental
margin, and deep-sea environments sediments Mayer, 1994a,b;
Keil et al., Despite contributions of both terrestrial and
marine Corg , the particle surface area specific Corg load of deltaic
material is comparable to oligotrophic deep sea sites that are
essentially entirely marine Corg , indicating major loss from deltaic
sediments relative to all source material. Approximate terrestrial
and marine percentages ";15% for deltaic, shelf; ";5% for
deep-sea.are based on typical bulk sediment isotopic rangese.g.,
Showers and Angle, 1986; Emerson and Hedges, 1988; Bird et al.,
1995; Keil et al., The riverine and deep Pacific Corg
loading values represent simple averages of reported data "SD
indicated., deltaic and nondeltaic shelf values represent slopes of
Corg vs. particle surface area regressions"SE indicated.. The
asymptotic value of Corg rarea at depth in sediment is used at a
given site if a depth variation below the sediment–water interface
is evidentMayer, 1994a,b..

78. Polysaccharides & Proteins
Revised Molecular Size-Reactivity Continuum Model for Marine DOC (after Amon and Benner, 1996)
This modification of the figure presented in Amon and Benner, 1996, attempts to illustrate that a large fraction of the total DOC (quantity is indicated by the distance between the two curves) is high molecular weight material (>10,000 MW). The material >1,000 MW, represented by polysaccharides, is relatively labile (high reactivity) when compared with the low molecular weight material (refractory humics) near and just below 1,000 MW. Together these pools make up the bulk of the DOC concentration. On the low end of the size spectrum, most compounds are labile (amino acids etc.), but their concentrations are very low (together making only 1% of DOC) but their reactivity is VERY high.
High
Labile Monomers
- Amino acids
- DMSP
- sugars
Log Reactivity
Low
concentration
Labile
Polysaccharides & Proteins
Refractory humic
substances
quantity
Low
10000 MW
1000 MW
500 MW
0 MW
High
Low
Log Molecular Size
All scales are somewhat arbitrary, and should probably viewed as a log-type scale