The Carbon Cycle-1:
A general overview
For Friday
1) Will meet in EMS A333 after all
* Thereafter, on Fridays will be in IGPP conf.
Room (EMS C332.)
2) Bring to turn in : three questions. (at least)
1) Grad: science questions- larger picture.
2) Undergrad- can do above, but can also do
questions about ANYTHING- definitions,
background, anything that seemed important
that you did not understand.
What is the “C” cycle?
A quantitative, world-scale view of :
•
•
•
*chemical forms of carbonaceous materials
* reservoirs of carbonaceous materials
* rates of transfer and chemical transformations,
* the processes involved (both chemical and physical).
•
•
IN SUM:
•
RESERVOIRS - FORMS - PROCESSES - RATES
C-Cycle =
The C cycle: Why study it?
1) As a backdrop for understanding
constraints on natural processes
For example:
* photosynthesis and respiration (balance affects
atmospheric O2)
* Available energy/matter for biological processes.
* Air/sea exchange (how fast gases pass in and out of
the ocean)
* Weathering and crustal outgassing (balance affects
atmospheric CO2 Mixtures
2) To assess potential environmental responses to
anthropogenic activities
For example:
* Fossil fuel burning = oxidation of C & reservoir transfer.
* de/re - forestation & agricultural effects = changes terrestrial
storage of carbon in humus & Biomass
* Affects pathways and fates of pollutants: organic carbon
affects gaseous, solid and liquid pollutants ( eg: effects of
“humics” and other organics )
* Basis for other important cycles: N, O and S cycles closely
Linked to C cycle
Background: Why the big deal about
“C”?
First: C is abundant :
A major part of all matter in universe
The Top
10
Elemental
abundance in
universe
Abundant
Elements in the
Universe
( Heiserman, 1992)
Element
Abundance
measured relative to silicon
Hydrogen
40,000
Helium
3,100
Oxygen
22
Neon
8.6
Nitrogen
6.6
Carbon
3.5
Silicon
1
Magnesium
0.91
Iron
0.6
Sulfur
0.38
But Note: Oxygen is far, far more
abundant
Approximate
% by weight
Oxygen
46.6
Silicon
27.7
Aluminum
8.1
Iron
5.0
Calcium
3.6
Sodium
2.8
Potassium
2.6
Magnesium
2.1
All others
1.5
Element
Carbon in crust: 0.96 %
Given the abundance of
oxygen, it should not be
surprising that without
life, almost all carbon
would be oxidized.
Leads to Basic division of C cycle:
Within this abundant supply, carbon exists in the environment
exists in as either:
Organic = reduced (unstable, comes only from biology)
Inorganic = oxidized quantitatively the main form- in
mainly in rocks & gasses(~stable = fate of all Carbon without biology)
Oxidized carbon
(thermodynamically stable)
Typically involves multiple bonds to oxygen e.g. C≡O,
O=C=O, H2CO3).
a) Main oxidized form ATM = CO2 = major green
house gas & climate regulator.
b) Main oxidized form in waters watersHxC0x =
major buffer system, source of C for aquatic
photosynthesis
c) Main Form in Sedimentary Rocks (Earths Crust)
are Buried Carbonates. (Marine Sedimentary rocks)
Reduced Carbon
C-H(x)
a) H= reductant.
b) C-H bond is high energy bond, thus unstable.
c) BUT since most C-H comes from biology, most
reduced carbon = Organic carbon, thus more
complex. Essentially all contains C-C bonds, and
Oxygen.
thus: “CHO”= common shorthand for organic
matter
Useful fact:
OM = ~ 50% C by wt.
As backbone of all organic molecules C is the major, and
relatively constant (typically 50  10%) elemental
constituent of nonliving organic matter (NOM)
 Total Carbon = good Proxy for total OM
The Atmospheric Connection
Modern bulk composition of Atm:
(Originally out-gassed from planet, modified by life)
*Major oxidant for
heterotrophy*Atm. conc. has been
maintained in fairly strict
balance for eons-
N2
78%
O2
21 %
CO2 0.03 %
*Major raw material for 1
prod.
*Major Greenhouse gas/
center of debate on
anthropogenic climate change
The Atmospheric Connection-II
Organic carbon cycle is intimately tied to planet’s free-oxygen
(the inorganic carbon cycle also, but not as directly)
C-oxidized
Every C has at least
2 Oxygens
Carbon-reduced
Every C has <1
oxygen
The Atmospheric Connection
Atm O2
“Buried” CHO
(today =ocean seds)
“A carbon paved is an oxygen saved!”
Basic problem of C-Cycle modeling:
Box models
Sources
C Reservoir
w /composition
X, Y, Z…..
Sinks
Recall:
 = Q /(dQ/dt) = mean residence time
= pool size / flux in or flux out (at steady
state)
Q = Concentration or pool size
Example: Long-Term C-Cycle Box Model
(more on this later)
CO2?
B-
A closer look at some main
components, in four parts:
Part 1: C Reservoirs & Sizes
Part 2-Transfer rates
Part 3- Composition & Mechanism
Part 4- Briefly: What’s in the boxes?
Part 1 of Puzzle: C Reservoirs
ATM CO2
Te rre s tria l
Ma rine
Biota
Biota
DOC
Pla nt
Litte r
DIC
Soil
Humus
Not to scale..
Se dime nta ry OC
ILKRESVR
First Question: How (and why) do you
define a given “Reservoir”?
(sometimes obvious..sometimes not)
Basic Idea = What is Function in an
environment (or in the larger C-Cycle)?
 “Function” tied to physical “Form” of the
carbon.
Example: What is DOM?
(what is POM? What is “Humus”?)
Te rre s tria l
Ma rine
Biota
Biota
DOC
Pla nt
Litte r
Soil
Humus
Se dime nta ry OC
ILKRESVR
Example: Size Continuum of OC in Natural
Water
Colloidal
Particulate
Dissolved
1. What
is the recovery of “bulk sample?”
Zooplankton
EG: DOM, POM,
Colloid
analysis:
Protists
Active Transport
Organisms
Phytoplankton
Bacteria
Substrates
Biodegradation
Microgels
Gels
Nanogels
Marine DOM
DOM
Polymer Physics
Methods
100,000
Microscopic
10,000
Molecular Biology Chromatographic
1000
100
10
Size, nanometers
1
1000
0.1
100
0.01
10
~Mol Wt
 The size range of "organic entities" (particulate and dissolved) in
(Seawater DOM)
the ocean, including nanogels and microgesl. From an as- yet undeclined JH Proposal (with Pedro
Verdugo et al.).
Example: Why (& how) do you put POM and
DOM in different boxes?
Individual
molecules
10 A
0.1
Colloids, clays
1 nM
10
100
Larger aggregations
1 uM
10
OM “SIZE” in ocean water column is a
continuum
(not two boxes)
100
“Function” varies, but depends on what you
are most interested in:
Can be directly
taken up across
a cell wall
Must be
hydrolyzed
Individual
molecules
10 A
0.1
Colloids, clays
1 nM
10
100
Doesn’t
Sink
(advected!)
Larger aggregations
1 uM
10
100
Sinks (will become seds)
In practice: a definition is selected is also
based on other practical considerations:
combination of Methods, interests & history
Individual
molecules
10 A
0.1
Colloids, clays
1 nM
10
100
Larger aggregations
1 uM
SIZE
"DOM" "POM"
10
100
“Operational definitions”= organic
reservoir or “material” defined mostly by the
method (operations) used to collect it.
Eg: “DOM” = that material which does not pass a GFF filter.
“Sinking POM”: that material which a sediment trap catches
“Humic material” that HMW organic which precipitates at PH=2
“Kerogen”- reduced C left over after extensive organic extractions
The Lesson: when considering organic data for a give OM reservoirMust always consider what the operational definition is, and
How relevant this is to your actual interest!
Next Question: How do you figure out
Total carbon in an “operational”
reservoir?
•For Inorganic C: typically relatively easy
•For organics, tougher:
•Goal: Total Organic Carbon. (Which recall is ~ 50% by
mass of total Organic matter.) However: almost never
measured directly as organics, Because:
1)Tightly co-mingled w/ inorganic matter: Cannot easily
separate Inorganic from organic ( organic = inorganic
associations typically very tight-esp clays, biological tests)
2) Direct compound analysis does not work: too many
compounds, very difficult matrixes.
3) Inorganic carbon often large fraction of total.
Total C-Measurement
 Usual Measurement : by sequential
conversion to CO2.
1) Remove in-organics via acid treatment
2) Combust organics via very high temps ( 1000 +)
Review of Main Reservoirs:
Sedimentary Rocks
(all data in1018 gC)
Inorganic
carbonates
60,000
Organic
kerogen
15,000
coal
15
petroleum in reservoirs
1
Active (surficial) Pools
Inorganic
marine DIC
soil carbonate
atmospheric CO2
Organic
land biota
plant litter
soil humus (top 1 m)
marine biota
seawwater DOC
marine sediments (1 m)
38
1.1
0.75
0.57
0.07
1.6
0.003
0.70
1.0
“Active” vs. “Inactive” Reservoirs:
Somewhat subjective,
but basically linked to
residence time of a
carbon pool
*active reservoirs have
fairly short residence
times*Appreciably affected
by biological processes
Sedimentary Rocks
(all data in1018 gC)
Inorganic
carbonates
60,000
Organic
kerogen
15,000
coal
15
petroleum in reservoirs
1
Active (surficial) Pools
Inorganic
marine DIC
soil carbonate
atmospheric CO2
Organic
land biota
plant litter
soil humus (top 1 m)
marine biota
seawwater DOC
marine sediments (1 m)
38
1.1
0.75
0.57
0.07
1.6
0.003
0.70
1.0
Main “Active” C Reservoirs
ATM CO2
Te rre s tria l
Atmosphere CO2: 0.75 x 1018
Ma rine
Biota
Terr.
Biota: 0.57 x 1018
Soil humus: 1.5 x 1018
Plant Litter: .07 x 1018
Ocean DOC: 0.7 x 1018
Marine S .Seds: 1 x 1018
(marine Biota/POC: 0.003 x 1018)
Biota
DOC
Pla nt
Litte r
Soil
Humus
Se dime nta ry OC
Recent additions:
Petroleum: ~1 x 1018
Coal: ~15 x 1018
ILKRESVR
Review of main observations
1. 99.8% of all crustal C is in rocks and inactive on
millennial time scales.
2. fossil fuels are  0.1% of all kerogen, but ~ 20 x
atmospheric CO2atm.
aside: relatively tiny petroleum reservoir, therefore oil
will all be burnt relataviely soon. Lots more (~15x)
coal in beds than petroleum in economic reserves.
3. most of all active C is in seawater DIC (largely as
bicarbonate).
7. CO2atm/DIC  1/50.
Review of Main Observations-2
* Most organic matter in active pools is dead.
* About 2/3rds of total active organic matter is stored on land.
* Largest active organic matter reservoir is in soils as humus.
** Several Organic Active Reservoirs that are similar in size to
total ATM CO2:
ATM CO2 ~reservoir is ~ equal to each of these
other pools:
Ocean DOC , Ocean Surface Sed OC , Soil
carbonate, and < 50% soil Humus
Even small changes in preservation/degradation
balance in any of these major OM pools could
have LARGE consequences for ATM CO2
balance.
 Major interest in understanding composition &
cycling of “small” rapidly cycling pools!
Part II: Transformations/ Rates
ATM CO2
Te rre s tria l
Ma rine
Biota
Biota
DOC
Pla nt
Litte r
DIC
Soil
Humus
Se dime nta ry OC
Not to scale..
ILKRESVR
Q: What are the rates of major transfers?
How do you measure these rates?
1. Directly: measure OC amounts, and direct fluxes
Eg:
* Biota ==> Seds. How much OC in sediment trap?
* Terrestrial ==> marine: How much C in river water?
Transformations/ Rates
2. In-Directly: Measure “age” of a pool = turnover time.
Eg:
* DOC in ocean ==> 14C “AGE” = 4000-6000 yrs.
Therefore: assumed flux = pool size/ avg age
Major transfer rates: in 10E15 G/ YR
A tm ospheric CO 2= 750 (+3.4/yr)
net m arine
prim ary
net terrestrial
prim ary
production
50
50
production
60
570
Soil Litter 70
Soil H um us 1600
river D O C
river PO C
0 .2 5
0 .1 5
M arine Biota
3
4
6
uplife and
0.15
DOC
700
w eathering
0 .1 5
K erogen = 15,000,000
15
U nits of 10 gC
particle
rain
Ocean
Continent
litterfall
L and Biota
organic
preservation
Recent Sedim entary O C 1000
Fluxes are per year
ILKRSFLX
Fluxes : Some Observations
* The BIG fluxes are RAPID cycles: biological production &
respiration.
* These are essentially in complete balance.
thus: the fate of 99+ % of ALL OM is respiration!
* Among preserved pools- DOM and SOIL humus are LARGEST
fluxes- but are assumed to be “holding reservoirs”- ie
intermediate term cycling..
*Long-Term preservation fluxes: Sed burial &uplift
remineralization: Fluxes are small, but pools are HUGE.
These are ASSUMED to be in balance- but no one knows exactly
how..
III: For Organics: Composition
(Why do we care?)
Composition
Mechanism
Why Composition Matters:
An Example From Earth History
Atm O2 over last 550 MY ( Berner 1998)
Recall: 02 is linked to directly to OC cycle:
(“an C paved = O saved”)
WHAT does this plot say about OC CYCLE over deep time?
Recall: 02 is linked to directly to OC cycle:
(“an C paved = O saved”)
Carboniferous/ Permian period- Land Plants
(lignin, other structures evolve- MORE OC buried?
Recall: 02 is linked to directly to OC cycle:
(“an C paved = O saved”)
Back in Balance- but why? Fungi evolve to degrade lignin?
High O2 levels lead to frequent global wildfires?
PART IV: So what’s in each
box? (very brief tour)
Te rre s tria l
Ma rine
Biota
Biota
DOC
Pla nt
Litte r
•Formation pathways
•Degradation Pathways
•Likely residence times
Soil
Humus
Chemical identity gives you
main clues to:
Se dime nta ry OC
ILKRESVR
The Biota Box (starting stuff..)
Te rre s tria l
Ma rine
Biota
Biota
Terrestrial:
•Cellulose
•Lignin
(proteins, carbos, some lipids)
DOC
Pla nt
Litte r
Soil
Humus
Se dime nta ry OC
ILKRESVR
Marine:
•Proteins
• Carbos
* Some lipids
Terrestrial: Soil Humus
Te rre s tria l
Ma rine
Biota
Biota
Terrestrial Humus:
•Humic/Fulvic acids
• = “Geomolecules”
( + minor proteins, carbos, lipids)
DOC
Pla nt
Litte r
Soil
Humus
Se dime nta ry OC
ILKRESVR
“Humic/ Fulvic Acids”
Soil humus: “all nonliving, amorphous
(not recognizable) soil organic matter”
Operational Definitions:
Humic acid  soluble in base
(pH ~13) and insoluble in acid
(pH ~2
fulvic acid  soluble in base
(pH ~13) and soluble in acid
(pH ~2)
humin  insoluble in base
(pH ~13)
Ocean: DOM box
Te rre s tria l
Ma rine
Biota
Biota
DOC
Pla nt
Litte r
Soil
Humus
Ocean DOM- An illustrative
example of effect of knowing
composition.
* Traditionally thought to be also
similar to terrestrial humus
Se dime nta ry OC
ILKRESVR
•Now know: not at all true.
•Mostly Carbos
•Some proteins
•CRAM? (Whole new class of
unknown molecules?)
aliphatic/highly acid groups
•Sources and structures…???
The DOM Pardigm shift
Te rre s tria l
Ma rine
Biota
Biota
DOC
Pla nt
Litte r
Pre-1990’s: research into abiotic
degredation/ condensation
mechanisms.
Soil
Humus
Current: Research into
*biological factors (eg refractory
cell wall polymers)
Se dime nta ry OC
ILKRESVR
*Abiotic protection ideas (eg
polymer gels, lipidic colloids)
OCEAN: Sediments
Te rre s tria l
Ma rine
Biota
Biota
Ocean Sediments:
•Depends on
Age/Condition/location
DOC
Pla nt
Litte r
Soil
Humus
Se dime nta ry OC
• Largely thought to be similar
to terrestrial humus
ILKRESVR
But In reality… maybe not…
 Surfaces / clay protection
may be key…
“Kerogen: OM in Sedimentary
Rocks
Also “Operationally” defined:
• =“non-extractable” organic
matter in ancient rocks
• assumed to be “cooked”
• Think: ~ plastic in brick
•Some quantiative observations:
•* 1/5 of carbons in rocks is
organic (largely kerogen).
Te rre s tria l
Ma rine
Biota
Biota
DOC
Plant
Litter
S oil
Humus
S e dime ntary OC
ILKRESVR
•* fossil fuels are  0.1% of all
kerogen, but ~ 20 x
atmospheric CO2atm.
Reiteration of an important point:
Atm ospheric CO 2= 750 (+3.4/yr)
net m arine
prim ary
net terrestrial
prim ary
production
50
50
production
litterfall
Land Biota
60
570
Soil L itter 70
Soil H um us 1600
river D O C
river PO C
0 .2 5
0 .1 5
M arine Biota
3
4
uplife and
0.15
DOC
700
w eathering
0 .1 5
Kerogen = 15,000,000
15
U nits of 10 gC
particle
rain
Ocean
Continent
6
organic
preservation
R ecent Sedim entary O C 1000
Fluxes are per year
IL KRSFLX
 MINOR differences effect MOST of the controls!
ie: as above, The fate of almost ALL active Pools is to be
recycled
so: its very SMALL differences in reactivity (or rate),
which control sizes of OM pools!
Thought Experiment:
Atm ospheric CO 2= 750 (+3.4/yr)
net m arine
prim ary
net terrestrial
prim ary
production
50
50
production
litterfall
Land Biota
60
570
Soil L itter 70
Soil H um us 1600
river D O C
river PO C
0 .2 5
0 .1 5
M arine Biota
3
4
uplife and
0.15
DOC
700
w eathering
0 .1 5
Kerogen = 15,000,000
15
U nits of 10 gC
particle
rain
Ocean
Continent
6
organic
preservation
R ecent Sedim entary O C 1000
Fluxes are per year
IL KRSFLX
 What might happen to the Carbon Cycle if:
* A new species of Alga evolved with cell-wall polymer 10%
more resistant to oxic degredation?
END