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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
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
POC -
(about 50% C by weight)
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)
Organic particle size continuum
0.4-0.2 µm
filtration
cut-off
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.
Global Carbon reservoirs and exchanges (Figure based on Libes; data from Table
11.1 in Emerson & Hedges)
pools in 1015 gC (boxes)
Terrestrial
biota 600
fluxes in 1015 gC y-1 (arrows)
Atmospheric CO2 784
River DIC 0.5
Exchange
90
Soil & detritus 1500
Net export
from surface
8-15
Marine biota 1-2
Ocean DIC 38,000
Detrital POC 30
0.2
Sedimentary
reservoirs are
huge!
Organic sediments
10,000,000
Fossil fuels 3577
DOC 700
Limestone & dolomite
50,000,000
•Most organic carbon in the sea is dissolved or colloidal.
•Biomass pools are very small
Relative partitioning of organic
carbon in the ocean
Dissolved
Colloidal
Detritus (POM)
Phytoplankton
Zooplankton
Bacteria
Dissolved and Colloidal materials
are operationally Dissolved
Sources of organic matter to the open oceans
% of total
Primary production
Phytoplankton
84.4
Macrophytes
6.2
Rivers
3.65
Groundwater
0.3
Atmospheric input
5.45
Rivers are a small source of organic matter to open ocean!
Based on Table 9.1 in Millero, 2006
Ocean Net Primary Production in different trophic regimes
Trophic zone
Oligotrophic
Mixed layer
Chl a (μg L-1)
Net Primary
Production
(1015 gC y-1)
% of
Ocean
NPP
< 0.1
11.0
22.7
Mesotrophic
-2 -1
0.1 -1.0
27.4
56.5
Eutrophic
> 1.0
9.1
18.7
-
1.0
2.1
(<100 gC
m-2
y-1)
(100-300 gC m y )
(300-500 gC
m-2
y-1)
Macrophytes
Total ocean production = 48.5
Total terrestrial production = 56.4
Total global production = 104.9
Global primary productivity pattern as
deduced from satellite imagery
Behrenfeld et al 2006. Nature 444:
Considerations:
Oceanic/oligotrophic areas– dominated by picoplankton < 2 μm • Depth distribution i.e. euphotic depth
• Seasonal variations, esp. in polar
Upwelling, coastal & temperate areas have larger
regions
phytoplankton (> 2 μm) as major primary producers
• Interannual variations
Temporal changes in
global average
Chlorophyll anomaly
and Net Primary
Productivity (NPP)
anomaly.
1997-98 was a strong El
Nino year which reduced
NPP. Rapid recovery
ensued, with slow decline
thereafter.
Behrenfeld et al 2006. Nature 444:
The Biological Carbon Pump
Exporting carbon below the pycnocline
Air
Sea
CO2 (g)

CO2 (aq) + H2O <=> H2CO3 <=> H+ + HCO3- <=> H+ + CO32calcification
Photosynthesis
Pycnocline
sinking
Upwelling of
high DIC,
high pCO2
water
Euphotic zone
POM
CaCO3
Some DOM
DIC & alkalinity
No preservation
of CaCO3 below
CCD
CO2
respiration
Alkalinity
CCD
CaCO3 dissolution
Non-carbonate sediment
carbonates
POM
Deep Sea
spreading
Ridge crest
Carbon burial &
preservation as POM
and CaCO3
CaCO3-rich
sediment above
CCD
Export
Production
per year
Falkowski et al., 1998.
Science 298:
Flux of organic matter decreases
exponentially with depth :
POM flux as % of flux at 100 m
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.
0
40
60
80
-1000
-2000
-3000
-4000
-5000
-6000
Very little organic matter (POM)
reaches the deep ocean – and what
does reach the bottom is lower
quality
20
0
Depth (m)
POMflux(z) =
POM flux vs depth based on
equation of Bishop (1989)
At 5000 meters,
the flux is only
3.5% of that at
the base of the
euphotic zone!
-7000
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.
100
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
Sediment traps - particle interceptors
Baffle to reduce
hydrodynamic effects
Particle flux 
Base of euphotic zone 100-200 m
500 m
1000 m
Poison or
preservative
3000 m
Capture flux
decreases
exponentially
with depth
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
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)
http://www.whoi.edu/instruments/gallery.do?mainid=19737&iid=10286
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?,
content?
14C-
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:
http://www.whoi.edu/instru
ments/gallery.do?mainid=1
9735&iid=10286
Joaquim Goes
and his team
deploy simple
sediment traps
in the Southern
Ocean
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)
http://www.whoi.edu/instrume
nts/gallery.do?mainid=19750
&iid=10286
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
The greater the overall sedimentation rate of particles, the greater
the fraction of surface primary production delivered to sediments
Percent of primary production
accumulated in the sediments
100
10
Coastal
areas –
maximum
of ~10%
y = 0.028 x1.25
1
0.1
>5000 m depth
>2-5000 m depth
0.01
0.001
0.1
>2000 m depth
incl. Black Sea
1
10
100
Sediment accretion rate (cm per 1000 y)
1000
See Fig.
11.5 in
Pilson for
actual
data
graph
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
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.
-
Dissolved organic carbon - the largest
pool of organic matter in seawater
Measured by converting DOC into
CO2 via:
Vertical profile of DOC
concentrations in the ocean
DOC (micromolar)
• Wet-chemical oxidation
0
0
• High temperature catalytic
combustion
• Sealed tube combustion
DOC concentrations are
70-100 µM in surface
waters of the open ocean,
and 35-50 µ M at depth.
Coastal waters can have much higher DOC
-1000
Depth (m)
• UV-oxidation
-500
-1500
-2000
-2500
-3000
20
40
60
80
100
Surface ocean (30 m) DOC concentrations
Dots are measured values, background color field is modeled
Hansell et al., 2010
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
DOC Concentration (µM)
0
10
20
30
0
A
B
60
70
C
D
Semi labile
DOC; larger
pool (25-30
µM) in sfc;
τ = weeks to
months
1000
Depth (m)
50
40
Labile DOC;
Small pool;
τ = hours to
days
2000
3000
4000
Ultrarefractory
DOC; τ =
>6000 y
Open ocean surface
DOC concentration
is about 70 µM. It is
Refractory
about 44 µM in the
DOC; τ =
deep Sargasso and
~1000 years
about 34 µM in the
deep Pacific.
After Benner, 2002
The average 14C age of deep DOC is 6000 years|!
DOC is generally conservative with salinity in estuaries
400
Implies
terrestrial DOC
delivery to ocean
– but most is
lost on shelf (see
next slide)
Freshwater end-member
DOC
(µM)
75
Seawater
end-member
~80-100 µM
0
0
Salinity
36
In fact, some
modification of
riverine DOC
takes place in
estuaries, but
conservative
pattern still
observed
DOC
concentration
decreases
away from
shore
Much of the DOC
delivery to ocean is
lost on the shelf,
close to shore
Constituents of DOM
Moderate
lability
Mixed
lability –
some very
refractory
High
lability
See Chapter 22 in Libes for
structures of organic compounds
High molecular weight >5000 Da (includes colloids)
• proteins
• polysaccharides (mucus, structural polymers)
• nucleic acids
• some humic substances
Medium Molecular weight 500-5000 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
Shift
Examples of
some
polysaccharides
that might be
part of a semilabile, high
molecular weight
pool of DOM.
Pectin contains O-methoxy groups
Chitin is an amino sugar,
i.e. it contains N
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
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.
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.
Phaeocystis
globosa colony
–cells
embedded in
mucous form
spherical
colony
http://www.microscopy-uk.org.uk/mag/artapr01/foam.html
http://www.ifremer.fr/delec-en/projets/efflores%20phyto/phaeocystis/phaeocys.htm
Sea foam generated from
Phaeocystis bloom in Dutch
Wadden Sea
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)
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
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.
Pool size
production
Glycine
(2 nM)
pseudo-steady
state conc.
kloss
loss
k = 50 d-1
Hypothetical example of amino acid turnover
Production
= loss under
steady state
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 10-50 times per day!
Carbon utilization efficiency affects trophic
transfer and CO2/O2 dynamics
In terms of carbon
Carbon
Biomass Production (BP)
Microbial Growth
= Assimilation
=
Efficiency (MGE)
BP + Respiration
Efficiency
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)
eutrophic
Oligotrophic (from some recent studies)
Microbial Growth Efficiency = MGE = [Microb. Prod/(Microb. Prod + Respiration)]
See also del Giorgio et al 2011. L&O 56:1-16
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
4000-6000 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)
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
Photooxidation as a major
sink for refractory DOM
in the sea
Photochemical Blast Zone - some DOM oxidized
Upwelling of
refractory,
old DOM
NADW formation.
Labile DOM is
utilized in
relatively short
time - leaving old
refractory carbon
to make another
circuit
Deep water transit (= 1000 y)
Little alteration of old, refractory carbon
This is a highly conceptualized diagram! Its not this simple!
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 Ncontaining compounds are removed in upper water
column)
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, 2002. Chemical
composition and reactivity of
marine dissolved organic
matter.
C:N
Redfield
C:P
DOM has
much
higher
C:N and
C:P than
plankton
(Redfield)
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
Soil humic acid showing amorphous structure and many functional
groups
Ligand bound Fe
Adsorbed
AlSilicate
clay
No two humic molecules will be the same
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
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, 1994. Nature 370:549
Hedges & Keil, 1995
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
Monolayer
equivalent
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)
finish
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
O2
Low Mol Wt DOC
Photo – Jeff Cornwell
High Mol
Wt DOC
From Davis and Benner, 2007
Molecular size
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
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.
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
Ultrarefractory
DOC; τ =
>6000 y
Refractory
DOC; τ =
1000 years
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.
Under anoxic conditions it takes a
consortium of organisms to degrade
complex organic matter
Low Mol
Wt DOC
Very high
Mol Wt
DOC
High
Mol Wt
DOC
Respiring cell
Low
Mol Wt
DOC
Different organic fractions degrade at different rates
Ocean productivity by province
Province
Area
(106 km2)
% of
ocean
Mean
productivity
(gC m-2 y-1
Open ocean
326
90
Coastal zone
36
0.36
Upwelling
areas
Total
% of
Ocean
Prod.
50
Total
Production
(1015 gC y-1)
16.3
9.9
100
3.6
18%
0.1
300
0.108
1%
81%
20
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 40-50 x 1015 gC/y. The
distribution percentages, however will be similar to those shown here.
Hopkinson &
Vallino. Nature
433: 2005
Seasonal cycle of DOC at the BATS station in the Sargasso Sea - Carlson et al 1994
Spring
build up
of DOC
Winter mixing
homogenizes
upper 200m &
mixes down
some DOC
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 spatiotemporal shifts in carbon exchange.
The role of the oceans in Carbon exchange is being
studied intensively!
G3
G2
G1
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-.
Oceanic/oligotrophic areas– dominated by picoplankton < 2 μm
Considerations:
Upwelling, coastal & temperate areas have larger phytoplankton (> • Depth distribution i.e. euphotic
depth
2 μm) as major primary producers
-seasonal variations
Deep DOC ~5900 years old
Deep DOC ~4100 years old
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., 1997.. 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., 1997.. 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..
Revised Molecular Size-Reactivity Continuum
Model for Marine DOC (after Amon and Benner, 1996)
High
Log Reactivity
Labile Monomers
- Amino acids
- DMSP
- sugars
Low
concentration
Labile
Polysaccharides &
Proteins
Refractory humic
substances
quantity
Low
10000 MW
High
1000 MW
500 MW
Log Molecular Size
All scales are somewhat arbitrary, and should probably viewed as a log-type scale
0 MW
Low
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.