Earth Systems Science

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Earth Systems Science
THE CARBON CYCLE
The circulations of the atmosphere, hydrosphere,
and lithosphere were studied in previous
chapters. Here, we learn how nutrients are
recycled in the earth system. We focus on carbon
in particular due to its importance for
biological activity and for global climate.
Nutrients substances normally in the diet that
are essential to organisms.
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Earth Systems Science
THE CARBON CYCLE

1. carbon cycle dynamics
2. The short term terrestrial organic carbon cycle
3. The short term marine organic carbon cycle
4. The long term organic carbon cycle
5. The short term inorganic carbon cycle
   interaction with the biological pump
6. The long term inorganic carbon cycle the
   carbonate-silicate geochemical cycle

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THE CARBON CYCLE DYNAMICS
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THE CARBON CYCLE DYNAMICS
Reservoirs Locations, or types of regions, where
the substance you are tracking is stored. Value
of reservoir depends on the net flux
STELLA diagram of global C cycle used in our lab,
adapted Chameides and Perdue (1997)
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THE CARBON CYCLE DYNAMICS
The atmosphere A variety of processes are related
to flux into and out of the atmosphere. These
may vary seasonally, resulting in a seasonal
cycle in atmospheric carbon concentration. Steady
state same as dynamic equilibrium
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THE CARBON CYCLE DYNAMICS
Residence time, or response time, or e-folding
time Average amount of time that a substance
(e.g. atom of C) remains in a reservoir under
steady state conditions Residence time T
(reservoir size) / outflow rate or
(reservoir size) / inflow rate T(atm) 760
(Gt-C) / 60 (Gt-C/yr) 12.7 yr
T time in which a perturbed system will return
to 1/e, or 38, of original value
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THE CARBON CYCLE DYNAMICS
Residence time T is calculated at equilibrium
using total inflow or total outflow T
(reservoir size) / (total outflow)
(reservoir size) / (total inflow) (reservoir
size) / (flux_out_1 flux_out_2) (reservoir
size) / (flux_in_1 flux_in_2)
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THE CARBON CYCLE DYNAMICS
Rate constant r is calculated using the
individual flow r_in_1 flux_in_1 / reservoir
r_in_2 flux_in_2 / reservoirr_out_1 flux_o
ut_1 / reservoirr_out_2 flux_out_2 /
reservoir
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THE CARBON CYCLE DYNAMICS
Oxidized C that is combined with
oxygen examples CO2, CaCO3 Reduced C that is
not combined with oxygen, usually combined with
other carbon atoms (C-C), hydrogen (C-H), or
nitrogen (C-N) example organic carbon in
carbohydrates reduced substances tend to be
unstable in the presence of oxygen organic
matter decomposes, metals rust
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THE SHORT-TERM TERRESTRIAL ORGANIC CARBON CYCLE
Organic carbon associated with living organisms
contains C-C or C-H bonds Photosynthesis C is
removed from the atmosphere and incorporated into
carbohydrate molecule becomes organic. Primary
productivity amount of organic matter produced
by photosynthesis (per year, per area) Primary
producers (producers, autotrophs) organisms
that store solar energy in chemical bonds
(carbohydrates) for other organisms to
consume Respiration C is returned to the
atmosphere becomes inorganic Net primary
productivity (NPP) primary productivity -
respiration
Image Name North America NDVIImage Date March
1990-November 1990Image Source AVHRR
Mosaic http//edc.usgs.gov/products/landcover.html
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THE SHORT-TERM TERRESTRIAL ORGANIC CARBON CYCLE
Photosynthesis CO2 H20 ? CH20
02 (solar energy) Respiration CO2
H20 ? CH20 02 (release
energy)
Consumers (heterotrophs) organisms that can not
use solar energy directly, get their energy by
consuming primary producers
Image Name Global Greenness Image Date June
1992Image Source AVHRR NDVIhttp//edc.usgs.gov/
products/landcover.html
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THE SHORT-TERM TERRESTRIAL ORGANIC CARBON CYCLE
Steady stateflux in flux out
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THE SHORT-TERM TERRESTRIAL ORGANIC CARBON CYCLE
Where is the atmosphere in this model?
STELLA diagram of terrestrial forest C cycle
(adapted from Huggett, 1993)
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THE SHORT-TERM TERRESTRIAL ORGANIC CARBON CYCLE
aerobic biological process that uses oxygen for
metabolism aerobe an aerobic organism organism
whose metabolism is aerobic metabolism  The
chemical processes occurring within a living cell
or organism that are necessary for the
maintenance of life. In metabolism some
substances are broken down to yield energy for
vital processes while other substances, necessary
for life, are synthesized. (dictionary.com)
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THE SHORT-TERM TERRESTRIAL ORGANIC CARBON CYCLE
anaerobic biological process whose metabolism
uses no oxygen anaerobe an anaerobic organism
organism whose metabolism is anaerobic Methanogene
sis an anaerobic form of metabolism
Photosynthesis CO2 H20 ? CH20
02 (solar energy) Respiration CO2
H20 ? CH20 02 (release
energy)
Methanogenesis CO2 CH4 ? 2CH20
(release energy)
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THE SHORT-TERM MARINE ORGANIC CARBON CYCLE
Plankton organisms floating in water
photic zone mixed layer, upper 100m
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THE SHORT-TERM MARINE ORGANIC CARBON CYCLE
Plankton organisms floating in water
photic zone mixed layer, upper 100m
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THE SHORT-TERM MARINE ORGANIC CARBON CYCLE
The Biological Pump
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THE SHORT-TERM MARINE ORGANIC CARBON CYCLE
The Biological Pump
Nutrient Limitation
Organisms (i.e. plankton) require a variety of
nutrients to grow. These nutrients are obtained
from the ambient water. Nutrients are required in
certain ratios Redfield Ratios
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THE SHORT-TERM MARINE ORGANIC CARBON CYCLE
SEAWIFS Mean Chlorophyl September 97 - August
2000
http//seawifs.gsfc.nasa.gov/SEAWIFS/IMAGES/
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THE LONG-TERM ORGANIC CARBON CYCLE
On long time scales the processes that are part
of the short term cycle are approximately in
equilibrium. However, the slower processes
associated with geological processes become
important.
Reservoir value flux T
(Gt-C) (Gt-C/y) (y) atmosphere 760
60 12.7soil/sed. 1600 30
53.3sed. rock 1e07 0.05
2e08
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THE LONG-TERM ORGANIC CARBON CYCLE
Terrestrial as well as marine organic sediments
fill the ocean basins, get buried and lithify,
remain in sedimentary rocks until uplift and
weathering, or subduction.
This is sometimes referred to as a leak from
the short term organic C cycle because removal of
CO2 leaves one oxygen molecule (O2 ) in the
atmosphere CO2 H20 ? CH20 02
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THE LONG-TERM ORGANIC CARBON CYCLE
Fossil fuels are formed from the organic carbon
in sedimentary rocks. How does the burning of
fossil fuels affect this system diagram?
How does the deforestation affect this system
diagram?
What about reforestation?
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THE INORGANIC CARBON CYCLE
Sources and sinks of atmospheric carbon that do
not depend directly on biological activity
exist. source a reservoir from which the
atmosphere gains carbon sink a reservoir to
which the atmosphere loses carbon inorganic not
directly related to biological activity
Important reservoirs of inorganic carbonthe
atmosphere, the ocean, sedimentary rocks
Sedimentary rock carbon reservoirs consist mostly
oflimestone CaCO3dolomite CaMg(CO3)2 (older
sedimentary rocks)
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THE INORGANIC CARBON CYCLE
atm
mixed layer
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THE INORGANIC CARBON CYCLE
atm
mixed layer
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THE INORGANIC CARBON CYCLE
Atmosphere Ocean Carbon Exchange CO2 diffuses
between the atmosphere and the ocean Diffusion
the free or random movement of a substance from a
region in which it is highly concentrated into
one in which it is less concentrated. In gases
and liquids, it happens spontaneously at the
molecular level, and continues until the
concentration becomes uniform (Kemp, The
Environment Dictionary)
CO2 dissolves in water dissolve when two
substances go into solutionsolution a
homogeneous mixture formed when substances in
different states are combined together, and the
mixture takes on the state of one of the
components (Kemp, The Environment Dictionary)
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THE INORGANIC CARBON CYCLE
Atmosphere Ocean Carbon Exchange CO2 diffuses
between the atmosphere and the ocean The
direction and magnitude of diffusion depends on
the partial pressure of CO2 in the atmosphere,
the amount of CO2 in solution, the solubility of
CO2 in water, and on the rate constant of the
diffusion process partial pressure pressure of
one particular gas in the atmospheresolubility
the maximum amount of a substance that will
dissolve in a specified liquid (similar to
saturation in the atmosphere)rate constant
number representing speed with which diffusion
occurs
(CO2)g ?? (CO2)aq where ggas, aqaqueous
dissolved in water
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THE INORGANIC CARBON CYCLE
Chemistry of Inorganic Carbon in Water dissolved
CO2 generates carbonic acid CO2 H2O ??
H2CO3 this reaction can go either direction,
depending on the relative concentrations of
reactants and products. Reaction occurs until
chemical equilibrium is reached reactants left
hand side of equationproducts right hand side
of equationchemical equilibrium when relative
concentrations of reactants and products reach
the point where no net change in
concentrations occurs
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THE INORGANIC CARBON CYCLE
Chemistry of Inorganic Carbon in Water carbonic
acid generates hydrogen ions, bicarbonate ions,
carbonate ions H2CO3 ?? H HCO3-
(bicarbonate ion) HCO3- ?? H CO32-
(carbonate ion)
H concentration determines the pH of water pH
-logHwhere H is the concentration of
hydrogen ions.
These reactions tend towards chemical
equilibrium, depending on the concentrations of
bicarbonate and carbonate, the concentration of
the H ion (pH), and the temperature.
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THE INORGANIC CARBON CYCLE
Summary (CO2)g ?? (CO2)aq diffusion
ocean - atm. CO2 H2O ?? H2CO3 CO2 -
carbonic acid H2CO3 ?? H HCO3-
carbonic acid - bicarbonate HCO3- ?? H
CO32- bicarbonate - carbonate Interaction
with the biological pump CO2 H20 ??
CH20 02 photosynthesis/decomposition
Ca2 2HCO3- ?? CaCO3 H2CO3 calcium
carbonate shells Net Effect plankton remove CO2
from surface water, drawing more CO2 out of the
atmosphere. The organic material, and calcium
carbonate shells, eventually sink into the deep
ocean.
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THE INORGANIC CARBON CYCLEinteraction with the
biological pump
atm
Net effect drawdown of atm CO2!
mixed layer
blue inorganic chemistryred organic carbon
dioxide effectgreen organic carbonate effect
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THE INORGANIC CARBON CYCLEinteraction with the
biological pump
atm
Net effect drawdown of atm CO2!
mixed layer
blue inorganic chemistryred organic carbon
dioxide effectgreen organic carbonate effect
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THE INORGANIC CARBON CYCLEinteraction with the
biological pump
atm
mixed layer
Equilibrium values depend on pH and
temperature pH -logH Dissolved CO2
contributes to acidification
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THE INORGANIC CARBON CYCLEinteraction with the
biological pump
From weathering to deposition on the sea
floor Rain drops are slightly acidic to due atm
CO2 dissolving in them, resulting in carbonic
acid. Carbonate WeatheringCaCO3 H2CO3 ?
Ca2 2HCO3-calcium carbonic calcium
bicarbonatecarbonate acid ion
ion Silicate WeatheringCaSiO3
2H2CO3 ? Ca2 2HCO3- SiO2
H2Owollastonite carbonic calcium
bicarbonate silica water
acid ion ion
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THE INORGANIC CARBON CYCLEinteraction with the
biological pump
From weathering to deposition on the sea
floor These reactions provide the weathered
material that gets washed into the oceans and is
available for production of calcium carbonate and
silicate shells by plankton in the mixed
layer. As the plankton die, and the shells sink
into the deep ocean, they do not dissolve much at
first. The shallow and middle depths of the ocean
are saturated with respect to CaCO3 there is
little acidity to dissolve the shells. In deeper
parts of the ocean they do dissolve more, as
these waters often have higher concentrations of
dissolved CO2, and therefore carbonic acid, due
to the decomposition of organic matter.
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THE INORGANIC CARBON CYCLEinteraction with the
biological pump
From weathering to deposition on the sea
floor carbonate compensation depth (CCD) depth
below which the carbonate shells dissolve faster
than the rate of shells settling through the
water column.
Below the CCD, carbonate shells dissolve, no
carbonate is deposited on the ocean floor.
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THE INORGANIC CARBON CYCLEinteraction with the
biological pump
From weathering to deposition on the sea
floor The net result of weathering to deposition
is that some carbon is removed from the
atmosphere and ends up in calcium carbonate on
the ocean floor. Thus, weathering removes CO2
from the atmosphere and stores it in calcium
carbonate sediments. This is another CO2 leak
from the system. If there were no other source of
CO2 into the atmosphere, CO2 concentrations would
drop to zero in about a million years.
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THE INORGANIC CARBON CYCLEinteraction with the
biological pump
Summary of the cycle What process makes up for
the CO2 leakage from the atmosphere associated
with weathering?
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THE LONG TERM INORGANIC CARBON CYCLEThe
Carbonate-Silicate Geochemical Cycle
Net effect return of CO2 to the atm!
Carbonate metamorphismCaCO3 SiO2 ?
CaSiO3 CO2 calcite silica
wollastonite carbon
dioxide
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THE LONG TERM INORGANIC CARBON CYCLEThe
Carbonate-Silicate Geochemical Cycle
So, atmospheric CO2 loss by weathering is
compensated for by CO2 emissions associated with
plate tectonics (volcanic and mid-ocean ridge
emissions).