BiogeochemicaBiogeochemical Cyclesl Cycles

Carbon CycleCarbon Cycle

AnnouncementsAnnouncements

• Midterm is WED.• Review materials: are posted on

website.

• Review session: in sections this week

* reminder: Bring your books to section.

Announcements:Announcements:

Midterm: • You will need pink scantron & #2 pencil

• You will not need a calculator

• People with accommodations please see me at break

““Biogeochemical Biogeochemical Cycles”?Cycles”?

Biogeochemical cycles: The interlinked cycling of matter

(and energy) between geosphere and biosphere.

““Biogeochemical Biogeochemical Cycles”?Cycles”?

“Only in recent decades have scientists begun to fathom the extremely complex interplay of biological, geological and chemical processes by which materials and energy are exchanged and reused at the Earth's surface. These intermeshed processes, known as biogeochemical cycles, operate on timescales of microseconds to eons and occur within domains that range in size from a living cell to the entire atmosphere-ocean system.”

“ Driven by solar or geothermal energy, these cycles are concentrated at interfaces where living organisms catalyze chemical reactions…”

Biogeochemical CyclesBiogeochemical Cycles

The flow of matter & ways in which it is recycled

Sedimentation and burial

0.05

Weathering

0.05

Maybe a better Maybe a better

picturepicture: : understand understand biogeospherbiogeosphere as a e as a

systemsystem

““Biogeochemical Biogeochemical Cycles”?Cycles”?

Three interlocking elements:1) Chemistry 2) Biology3) Geological or atmospheric processes (e.g.

weathering, sedimentation, dust transport etc)

1) The Basics 1) The Basics

What is “organic” carbon?

C-C-C CH2-CH2-CH2

?

1) The Basics 1) The Basics

Life (biosphere) transforms and recycles carbon

Inorganic matter(oxidized carbon)

CO2

Organic matter(reduced carbon)

CHO

Organic Matter • Based on reduced

carbon (C-H)

• Carbohydrates (sugars and starches - CHO)

• Fats and Oils (CH)• Proteins (contain N

too)

Inorganic Matter

1)Oxidized carbon COx

2) Macro Nutrients– Nitrogen– Phosphorus– Sulfur– Potassium

3) Trace Nutrients– ie, Iron, Cobalt,

Selenium, etc.

Matter: Matter: Building Blocks of Building Blocks of LifeLife

• 1) Autotrophs (plants): Fixation of elements into “organic matter”

• 2) Heterotrophs: return elements to geosphere via breakdown of organic matter

Inorganic matter(oxidized carbon)

CO2

Organic matter(reduced carbon)

CHO

autotrophs

heterotrophs

Carbon & nutrients Captured by Carbon & nutrients Captured by AutotrophsAutotrophs

• Autotrophs get carbon & nutrients from environment in inorganic form

• (ie nitrogen as NO2, Phosphorous as PO4)

Figure 6.1

PRIMARY PRODUCERSPRIMARY PRODUCERS

• autotrophs or green plants

• use energy from the sun to turn nutrients into organic compounds:

PHOTOSYNTHESISCO2 + H2O ==> CH2O +

O2

carbon dioxide + water becomes organic tissue + oxygen

What controls this process? What controls this process?

First: actually, there’s more happening:CO2 + PO4 + NO3 + H2O ==> CH2O,P,N + O2

carbon dioxide + phosphate + nitrate + water becomes organic tissue + oxygen

OrganicMatt

er

• Carbohydrates • Fats and Oils

Proteins • Pigments, etc

Inorganic

Carbon (Co2)

• Macro Nutrients– Nitrogen– Phosphorus– Sulfur– Potassium

• Trace Nutrients

Think of all living things : aThink of all living things : a basic basic “recipe”“recipe”

x

y

z

Typically, it’s the thing you are Typically, it’s the thing you are short of.. short of..

• “Limiting Nutrient”–Liebig’s law of the minimum: growth rate of plants is determined by the least abundant nutrient relative to the needs of the plant

HeterotrophsHeterotrophs

• Heterotrophs or Consumers: get their energy from their food

• Cannot “fix carbon” = make organic compounds from only inorganic nutrients

DECOMPOSERS DECOMPOSERS (“remineralization”)(“remineralization”)

• Also Heterotrophs - such as fungi and bacteria

• Convert organic molecules to inorganic nutrients, usually using oxygen

RESPIRATION CH2O + O2 ==> CO2 +

H2O Organic tissue + oxygen becomes carbon dioxide

+ water

DECOMPOSERS DECOMPOSERS (“remineralization”)(“remineralization”)

• Heterotrophs such as fungi and bacteria

Again, there’s more happening:CH2O,P,N + O2 ==> CO2 + PO4 + NO3 + H2O

organic tissue + oxygen becomes carbon dioxide + phosphate + nitrate + water

The Basic Carbon Cycle The Basic Carbon Cycle (short (short term)term)

*CO2 from the atmosphere is fixed into organic matter

•Organics Matter (OM) is stored, transported

•Ultimately it is respired- back to CO2…

CO2

OM

OM OM

CO2

Problem: How to be Problem: How to be quantitativequantitative??

Understand biogeochemical system so can make predictions?

(ie, a perturbation will do..what..? )

2) BOX MODELS2) BOX MODELS

• The basic modeling tool used to study biogeochemical systems

• Goal: Parameterize a system as reservoirs and fluxes

• A simple box model of “reservoirs” of carbon- (approximately to scale..)

• What about fluxes?

Terrestrial Marine

Plant

Litter

Biota

Soil

Humus

Biota

DOC

Sedimentary OC

ILKRESVR

ATM CO2

Example:Example: “ “Pools” & Fluxes of Pools” & Fluxes of Carbon in Atmosphere and OceanCarbon in Atmosphere and Ocean

Atmospheric CO = 750 (+3.4/yr)

Land Biota

Soil Humus 1600Marine Biota

3

Soil Litter 70

570

DOC

Kerogen = 15,000,000

50

preservation

60

2

net marineprimary

production

net terrestrialprimary

production

litter

fall

700

organic

particlerain46

0.15uplife and

weathering

Recent Sedimentary OC 1000

river DOC

river POC

Con

tine

nt Oce

an

ILKRSFLX

15

50

0.250.15

Units of 10 gC Fluxes are per year

0.15

DIC: 37,000

Sedimentation and burial

0.05

Weathering

0.05

““Pools and Pools and fluxes”fluxes”

working of the working of the whole system whole system depends on depends on

1) 1) sizesize of of reservoirsreservoirs

2) 2) rates rates of of transfertransfer

Sedimentation and burial

0.05

Weathering

0.05

Key additional Key additional concept: concept:

Is the system in Is the system in equilibrium?equilibrium? =“steady =“steady state”state”

Box Box ModelModel

Box represents a RESERVOIRAmount of substance in reservoir is INVENTORYArrow represents a FLOW or FLUX

IF in STEADY - STATEINVENTORY remains CONSTANTFLUX IN = FLUX OUT

FLUX IN FLUX OUT

Box Box ModelModel

Box represents a RESERVOIRAmount of substance in reservoir is INVENTORYArrow represents a FLOW or FLUX

RESIDENCE TIME = INVENTORY / FLUX= average time one molecule spends in reservoir

WHY IS RESIDENCE TIME IMPORTANT? Tells 1) how long it would take to significantly affect

the INVENTORY if the FLUX IN or OUT is altered 2) how quickly will something can change.

(Start seeing changes in inventory ~half of a residence time)

FLUX IN FLUX OUT

Residence Time ConceptResidence Time Concept

Residence time = Inventory / Flux

“Inventory” = mass (g)“flux” = mass/ time ( g/ yr)

Residence time = (g ) / (g/yr)

= yr (time)

Residence TimeResidence Time

Inventory (total amount in ocean)

Total Fluxes Out

Residence time =

Inventory / Flux

= The average amount of time one atom of constituent spends in ocean

Also = Approx. amount of time it takes for the concentration of a constituent to significantly change

Total Fluxes InAmount / time

=

Residence time ExampleResidence time Example

My assistant will now My assistant will now conceptually demonstrate:conceptually demonstrate:

Baxter The Dog.Baxter The Dog.

Note Relative Hair Length:Note Relative Hair Length:

Long Hair or Short Hair?

““Fur Inventory”: (?)Fur Inventory”: (?)

Would you thus estimate the total amount (“inventory”) of Dog-Hair to be on Baxter:

a) relatively LARGE b) Relatively SMALL

(vs other dogs)

What about Bax-Fur “Residence What about Bax-Fur “Residence time”?time”?

IF you guessed that the inventory of Baxter-fur is relatively SMALL…

•What would you GUESS the residence time is (short or long)?

•What other information would you need to really find out?

Recall: Recall:

Residence time = Inventory / FLUX

•How can we measure FLUX?

1 Month Yield from Electronic 1 Month Yield from Electronic Hair Isolation/ concentration Hair Isolation/ concentration Device:Device:

* ~ 3lbs total mass !!!

~90 % Dog Hair!!!~90 % Dog Hair!!!

FLUX is HIGH !!FLUX is HIGH !!

Mass: 3 lbs * 90% = 2.7 LB Dog Hair.

2.7 lbs* 0.45 (Kilo/ Lb) = 1.22 Kilos * 1000 (g/Kg)

= 1222 grams Dog Hair!!

if FLUX = mass/timeif FLUX = mass/time

Mass: = 1222 grams Dog Hair Experiment TIME: 30 days

FLUX = 40 grams/Day!!

(That, my friends, is a LOT of dog hair.)

Key Concept:Key Concept:

Inventory and Flux are NOT necessarily related!

Ie: If you know inventory- tells you NOTHING about flux (and vice versa)

*can easily have very small inventory- BUT high flux(or small flux, but Huge inventory..)

So: So: can we get a can we get a real number for real number for Bax-fur residence Bax-fur residence time?time?

What would we need?

1. ASSUME STEADY STATE

Can we get a number for Can we get a number for residence time?residence time?

2. Need a Good estimate for Hair INVENTORY in g’s..but how..

Real Example: Real Example: What is res time of water in ocean?What is res time of water in ocean?

RESERVOIR is the OCEANINVENTORY is 1350 X 106 km3

FLUX IN (river flow from continents into ocean)FLUX OUT (evaporation and transport of water to continents)

FLUX IN FLUX OUT

RESIDENCE TIME OF WATER IN OCEANS: Average t ime it takes for runoff to

replace total ocean volume:

inventory 1350 X 106 km3 = _______ _______________ 34,000 years

flux 0.0 40 X 106 km3/year

What about water in atmosphere?What about water in atmosphere?RESERVOIR is the ATMOSPHEREINVENTORY is 0.013 X 106 km3

FLUX IN (evaporation of water from Earth’s surface)FLUX OUT (precipitation)

FLUX IN FLUX OUT

RESIDENCE TIME OF WATER IN ATMOS PHERE: Average t ime water vapor remains in atmosphere before raining out

inventory 0.01 3 X 106 km3 = _______ = ____ ___________ 11 days

flux 0.425 X 10 6 km3/year

The Atmospheric Carbon Reservoir

In the absence of fossil fuel burning and other human activities,the atmospheric carbon reservoir would be in steady state..

inventory = _______ = ____ ___________ 12 Years

flux

760 Gton

60 Gton/Yr

RESIDENCE TIME in Atmosphere GAS (years)

H2O ~ 0.025 *

CO2 ~ 10 **

O2 ~ 1,000 **

N2 ~ 10,000,000 **

* w.r.t. evaporation/precipitation ** w.r.t. terrestrial biosphere photosynthsis/respiration

RESIDENCE TIME = INVENTORY / FLUX

Fluxes are due to evaporation and precipitationFluxes are due to photosynthesis and respiration

3) FOCUS on 3) FOCUS on MODERN MODERN CARBON CARBON CYCLE CYCLE

Biogeochem. Cycle where Biogeochem. Cycle where Carbon is Carbon is “currency”“currency”

• Carbon cycle” most commonly studied biogeochemical cycle

• “Currency” (=what you are modeling in fluxes and reservoirs) is CARBON

• Q: Why carbon?

“Cartoon” of overall carbon cycle

Fig. 6.6

Biota Carbon Balance: Gross primary production (GPP) (carbon flux in)Respiration + Death (carbon flux out)

NET primary production (NPP) = (GPP - Respir) (120 - 60 = 60 Pg/yr)

Biota Balance

Fig. 6.6

ATMOSPHERE (a reservoir NOT in steady-state)Fluxes in: 0.1 + 5.3 + 2.0 + 4 + 60 + 55 + 88 = 7.4 + 207 = 214.4 Pg/yearFluxes out: 120 + 90 = 210 Pg/year (Fluxes in > Fluxes out by ~ 4 Pg/yr)

Atmospheric reservoir of C is growing ~ 4 Pg/year!Human emissions: ~7.4 ± 1.0 Pg/year.

If 4 Pg/year is accumulating in the atmosphere, where are the other 3.4 ± 1.0 Pg/year going?

Atmosphere: not in balance!

•We emit about 7.4 ± 1.0 Pg/yr

• We measure atmosphere gaining 4.0 Pg/yr

• Calculation 3.4 ± 1.0 Pg/yr missing from the atmosphere

Fig. 6.6

BIOTA & SOILSReservoir size: 2000Flux in: 120Flux out: 4+60+55 = 119120 - 119 = 1 Pg/yr BIOTA & SOILS are gaining ~ 1 Pg/yr

Is it going into Biota? Some..

Fig. 6.6

OCEANReservoir size: 38000Flux in: 90Flux out: 88+0.2=88.290 - 88.2 = 1.8 Pg/yrOCEAN is gaining 1.8 Pg/yr

Is it going into Ocean?.. A lot more!

Sources & Sinks of Anthropogenic Sources & Sinks of Anthropogenic carboncarbon

BIOTA & SOILSFlux in: 120Flux out: 4+60+55 = 119Net SINK: 1 Pg/yr

OCEANFlux in: 90Flux out: 88+0.2 = 88.2Net SINK: 1.8 Pg/yr

Human SOURCES: 7.4 ± 1.0 Pg/yrMeasured Atmospheric increase: 4.0 Pg/yrCALCULTED Carbon SINKS: 3.4 ± 1.0 Pg/yrMeasured carbon SINKS: 2.8 Pg/yr

Calculated and Measured SINKS are equal within error

SOURCE: where atmospheric carbon is coming fromSINK: where atmospheric carbon is going

Ocean currently taking up ~ 2x more Ocean currently taking up ~ 2x more than land..than land..

• Ocean currently takes up ~ 2x more than land.. But also..

• Ocean uptake each year is 50% what’s going into the atmosphere.

our problems would be MUCH MUCH worse if ocean uptake slowed down.. Much better if speeded up..

Key to understand ocean C uptake mechanisms!

4) Some FEEDBACKS in C-4) Some FEEDBACKS in C-

CYCLECYCLE

1. CO2 fertilization: higher CO2 1. CO2 fertilization: higher CO2 causes faster plant growth, more causes faster plant growth, more carbon uptake carbon uptake

Fossil Fuel use increase

CO2 increases

Plant growth increases

CO2 decreases

(-)

2. warming also causes faster 2. warming also causes faster plant growth, more carbon uptake plant growth, more carbon uptake

Fossil Fuel use

CO2 increases

Global warming

Plant growth increases

CO2 decreases

Fixed Nitrogen*

Plant growth increases

CO2 decreases

3. Nitrogen fertilization: faster 3. Nitrogen fertilization: faster plant growth, more carbon uptake plant growth, more carbon uptake

* Via fertilizer production

Fossil Fuel use

CO2 increases

Global warming

Decay increases

CO2 increases

5. BUT: warming causes faster 5. BUT: warming causes faster decay, decay, carbon releasecarbon release

Fossil Fuel use

CO2 increases

Global warming

Decay increases

Nutrients increase

Plant growth increases

CO2 decreases

4. BUT faster decay, also means 4. BUT faster decay, also means more nutrients for plant growth, more nutrients for plant growth, carbon uptakecarbon uptake

Overall: to understand Overall: to understand system- must explore, system- must explore,

parameterize & parameterize & test test all all feedbacks.. feedbacks..

Create enormous super-Create enormous super-

computer models..computer models..

EndEnd

Next : Next : Focus on Ocean’s Focus on Ocean’s Role in Atm CO2 Role in Atm CO2 regulationregulation

Sources & Sinks of Anthropogenic Sources & Sinks of Anthropogenic carboncarbon

BIOTA & SOILSFlux in: 120Flux out: 4+60+55 = 119Net SINK: 1 Pg/yr

OCEANFlux in: 90Flux out: 88+0.3 = 88.3Net SINK: 1.7 Pg/yr

Human SOURCES: 7.4 ± 1.0 Pg/yearAtmospheric increase: 4.0 Pg/yearCarbon SINKS: 3.4 ± 1.0 Pg/year

SOURCE: where carbon is coming fromSINK: where carbon is going

Two Mechanisms for ocean to take up carbon:1. Increase in ‘biological pump’2. Increase in carbon dissolving in ocean (“buffering”), causes ocean

acidification!

“BIOLOGICAL PUMP”:-primary producers use inorganic nutrients and carbon to form organic matter-organic matter is exported out of surface ocean into deep ocean -carbon is stored in deep ocean for 100’s of years

“OCEAN BUFFERING”CO2 + CO3

2- + H2O ==> 2 HCO3--

Surface versus Deep Dissolved Surface versus Deep Dissolved NutrientsNutrients

• Surface Ocean (light in upper ~100 m)– Photosynthesis dominates– carbon/nutrient concentrations are LOW

• Organic particles formed in surface ocean fall into deep ocean (exporting nutrients out of surface)

• Deep Ocean (dark below ~100 m)– Respiration of organic particles– carbon/nutrient concentrations are HIGH

CO2 + PO4 + NO3 + H2O CH2O,P,N + O2

photosynthesis

respiration

0

500

1000

1500

2000

2500

3000

350050 100 150 200 250 300 350

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Depth

(mbs

f)

PO4 (µmol/kg)

O2 (µmol/kg)

O2

PO4

1 mole = 6.023 X 1023 molecules molecular mass = grams/moleµmol/kg = 1 x 10-6 moles per kg

O2 PO4

At surface: Photosynthesis

Uses PO4 Produces O2

Photosynthesis

Falling Particles of Dead Organic Matter

Respiration

Uses O

2

Prod

uces

PO

4

Dissolved Inorganic Carbon in the Ocean

High dissolved Carbon in the Surface

Higher dissolved Carbon in the Sub-surface

WHY ISN’T CARBONIN THE SURFACE USED UP?

Two Mechanisms for ocean to take up carbon:1. Increase in ‘biological pump’2. Increase in carbon dissolving in ocean (“buffering”), causes ocean

acidification!

“BIOLOGICAL PUMP”:-primary producers use inorganic nutrients and carbon to form organic matter-organic matter is exported out of surface ocean into deep ocean -carbon is stored in deep ocean for 100’s of years

“OCEAN BUFFERING”CO2 + CO3

2- + H2O ==> 2 HCO3--

Regions with HIGH Nitrogen, but LOW biological production(where biological growth is limited by IRON)IRON FERTILIZATION: An idea for increasing the biological pump in regions that are iron-limited.

END END

Box model review Box model review

OCEAN

Land (via rivers)

hydrothermal

atmosphere Ocean Salt is in “Steady State”

Chemistry of ocean is not changing

Input fluxes = Output fluxesOR

Sources = Sinks

Sediments

““Greening” of the Greening” of the plantetplantet

Quiz QuestionsQuiz Questions

Question #1Question #1

• Autotrophs– A. only need sunlight to grow– B. get their nutrients from eating

complex organic molecules– C. get their nutrients from inorganic

compounds – D. need all the elements found on

earth

Question #2Question #2

• Heterotrophs– A. only need sunlight to grow– B. get their nutrients from eating

complex organic molecules– C. get their nutrients from inorganic

compounds – D. need all the elements found on

earth

Question #3Question #3

The residence time of a constituent in a reservoir is approximately equal to the amount of time:

A. it takes to fill the reservoir with input fluxesB. it takes to empty the reservoir with output fluxesC. it takes to significantly alter the inventory of the

reservoirD. all of the aboveToday’s fluxes of carbon into and out of various

reservoirs indicates that the Global Carbon Cycle is:A.Well-balanced and in steady-stateB.Imbalanced and not in steady-stateC.About to achieve steady-state soon

Question #4Question #4

Question #5Question #5

Which of these are currently causing the flux of carbon INTO the biosphere to increase:

A. more CO2 is slowing plant growthB. more nitrogen is increasing plant growthC. global warming causes more respiration and

release of CO2 from soilsD. global warming is slowing plant growth

NOT USED SLIDESNOT USED SLIDES

Carbon Dioxide (was Carbon Dioxide (was mixed in biogeochem mixed in biogeochem cycle section- no cycle section- no explanation text)explanation text)