global carbon cycle. why study the c cycle? key element of life – so fundamental –fossil fuel...

Global Carbon Cycle

Why study the C cycle?

• Key element of life – so fundamental– Fossil fuel burning and global warming

• Perturbation by humans (atm CO2)

• Complex cycle – long & short term cycles; organic and inorganic components

• Geological processes operating over millions of years• Biological processes operating on annual time scales• Interactions between long and short term cycles

“short”-term

“long”-term

anthropogenic

Fig. 8-3

Combined Inventories

Atmosphere 770 Gt CTerr. Systems ~2400 Gt COceans ~39,000 Gt CSed. Rocks 50,000,000 Gt C

Major Inventories1.Majority of C tied up in rock cycles – large reservoirs with long residence times2.Reservoirs active on short time scales are ocean, atm, & land3.Large exchange fluxes to and from atm – atm has short residence time (3 yr); small net fluxes due to biology (most PP is respired)4.Problem with adding fossil fuel CO2 to atm – transferring C from long term geologic reservoir to a short term reservoir – may affect short term feedback control mechanisms

Atmospheric CO2

Kerogen Land Plants

Soil humus

Humification

Sedimentary Rocks

Uplift of sedimentary

rocks

Particle Rain

Oceans

Recent Sediments

POC

POC Deposition

Carbon Burial

CO2

Marine primary prod.

Benthic Fluxes

Air-Sea ExchangeTerrestrial primary production and respiration

River transport

Respiration

50

0.1

50.3

59.6 - 59.7

60

0.1

CO2

remineralization

Upwelling

Physical weathering

0.4

A model – little transfer of biological C to ocean (from land) or sediments (from water)

Atmosphere

• Most C in atm as CO2

– Some methane and CO

• Atm CO2 shows rapid increase in recent time

– Beginning with Industrial Revolution

• See seasonal variations in recent increase– Uptake in Spring due to plant growth (N hemisphere)

– Release in fall from net respiration

Figs. 1-2 and 1-3

Northern hemisphere-More land-More terrestrial prod

300

320

340

360

380

400

1975 1980 1985 1990 1995 2000 2005

Year

CO

2 (

pp

m)

South Pole

Barrow, AK

Southern amplitude is lowerSeasonality offset by 6 mos.

Northern hemisphere has more extensive seasonal forestsClose tracking between N & S hemispheres

Prior to humans, the system showed natural variability(50 – 80 ppm glacial-interglacial)

Smaller Holocene changes

Glacial

Interglacial

Holocene changes

• Recent high resolution ice core

• Natural variability in Holocene is second order change when compared with glacial-interglacial excursions and anthropogenic increase

• Allows us to think about a nearly constant pre-industrial interglacial CO2 level of ~280 ppm

Recent increases in Atm CO2

• Some due to land use changes (pre-industrial)– Deforestation – two-fold problem

• Decrease PS uptake of CO2

• Burn the wood - charcoaling

• Mainly due to fossil fuel burning (post-industrial)

• Deforestation in tropics may be partially balanced by N hemisphere forest expansion/regrowth

AtmosphereEmissions(5.5 PgC/yr)

Atmos. increase(3.3 PgC/yr)

Ocean uptake (2 PgC/yr)

Land use change (1.7 PgC/yr)Residual terrestrial sink (1.9 PgC/yr)

IPCC – Intergovernmental Panel on Climate Change

Atmosphere

Surface Ocean

Deep Ocean

Sediments

CO2 CO2CO2

∆pCO2 > 0(primarily upwelling regions)

∆pCO2 < 0(primarily high latitudes)

CO2 + CO32- + H2O 2HCO3

-

Upwellingand vertical mixing

Sinking particulateorganic matter(“biological pump”)

CO2 + H2O Organic Matter + O2

CO2 + CO32- + H2O 2HCO3

-


Ca2+ + 2HCO32- CaCO3 + CO2 + H2O

CO2

HCO3-

Bottom water formation (high latitudes)(“solubility pump”)



Oceans are largest “active” reservoir in the carbon cycle – primarily DIC

Oceans

• Link the “active” or short-term cycles with long-term geological cycles – sink for fossil fuel CO2

• Ocean processes– Biological cycle– Weathering reactions and long term controls

– Atm CO2 riverine bicarb neutralized in ocean returned to atm or buried in seds

• Processes that remove CO2 from atm– Gas exchange – equilibration of sfc ocean with atm– Biological pump– Bottom water formation

Gas exchange• If CO2 were a simple gas, ocean could only take up

~3% of fossil fuel input• Acid-base chemistry enhances ocean uptake• Remember carbonate buffering system?

– CO32- + H2O + CO2 2 HCO3

-

– Buffering rxn drives CO2 to bicarb

• Surface waters reach equilibrium with atm in about 1 year– Can keep pace with human activity– But surface ocean too small to have capacity to remove it all

Biological Pump• PP and calcite ppt consume DIC• Removed from surface ocean via particle flux• Through interactions with carbonate system, this lowers

partial pressure (pCO2) in surface ocean which enhances gas exchange (pCO2< 0)

• Transports CO2 to deep ocean in the form of OM or calcite shells

• Limitations of biological pump– Availability of other nutrients (N, P, Fe)

– More CO2 doesn’t necessarily lead to more PP

Bottom water formation

• Removes CO2 by physical movement of water away from surface

• Solubility pump

• CO2 is more soluble in cold water

Intermediate and deep water

• Can add CO2 through oxidation of OM

• Calcite dissolution – excess CO2 from OM oxidation reacts with sinking calcite

Upwelling

• Intermediate waters are enriched in DIC– Mixing with deep waters, OM oxidation &

calcite dissolution, yields some CO2 increase

• Upwelling results in excess pCO2 in surface waters (pCO2 > 0)

– Oceans outgas CO2

– High productivity upwelling can still be net CO2 sinks

Global oceanic C sources and sinksfor atm C - reflect upwelling and deep water formationand high productivity

IPCC calculations

• Integrate data on ocean flux data

• Calculation attempts to assess short-term sinks for excess atm CO2 due to anthropogenic activities

Time scales of ocean C cyle• Ocean processes slow relative to rate of fossil fuel burning• Bottom water circulation on timescales of 100’s of years so

equilibration with atm is slow• Deep sea seds equilibrate with atm on timescales of 1000’s of

years – where the bulk of the ocean’s neutralizing capacity resides

• Oceans respond too slowly to take up all excess CO2 – so atm CO2 is increasing

• But, oceans have helped! Oceans have taken up 1/3 to ½ of added CO2

Atmosphere

Surface Ocean

Deep Ocean

Sediments

CO2 CO2CO2



∆pCO2 > 0(North Pacific and upwelling regions)

∆pCO2 < 0(primarily high latitudes)

CO2 + CO32- + H2O 2HCO3

-

Upwellingand vertical mixing

Sinking particulateorganic matter(“biological pump”)


CO2 + CO32- + H2O 2HCO3

-



CO2

HCO3-

Bottom waterformation (high latitudes)

Equilibration time ~1 yr

Equilibration time ~500-1000 yr

Equilibration time ~103-104 yr

Terrestrial systems• Variety of reservoirs that turnover on different timescales

– Soil humus – altered remains of plants

– Land plant biomass

– Methane – source of atm methane

• Terrestrial PP ~ = to Marine PP

• Terrestrial systems store excess CO2 differently – humus versus bicarb

• Imp for understanding system responses to increasing CO2. Increasing CO2:– might increase PP (neg feedback)

– might increase rates of decomposition (pos feedback)

Atmospheric CO2

Kerogen Land Plants

Soil humus

Humification

Sedimentary Rocks

Uplift of sedimentary

rocks

Particle Rain

Oceans

Recent Sediments

POC

POC Deposition

Carbon Burial

CO2


Benthic Fluxes

Physical weathering

Air-Sea ExchangeTerrestrial primary production and respiration

River transport

Respiration

50

0.4

0.1

50.3

59.6 - 59.7

60

0.1

CO2

remineralization

Upwelling

Comparable terrestrial & marine PP

negative feedback(temperature and CO2 fertilization)

positive feedback(temperature enhancement of soil respiration)

Terrestrial system responses to rising CO2 and global warming

Controls on atm CO2

• Break down overall cycle to components

• Look at effects on particular components

Atmospheric CO2

Kerogen Land Plants

Soil humus

Humification

Sedimentary Rocks

Uplift ofsedimentary

rocks

Particle Rain

Oceans

Recent Sediments

POC

POC Deposition

Carbon Burial

CO2


Benthic Fluxes

Physicalweathering

Air-Sea ExchangeTerrestrial primaryproduction and respiration

River transport

Respiration50

0.4

0.1

50.3

59.6 - 59.760

0.1

CO2

remineralization

Upwelling

Short-term biological cycle• Years to decades• Does not include calcite ppt/dissolution• Does not include anthropogenic inputs• PS versus respiration nearly balanced – little loss• Some transport of org C from land to oceans

– Most gets oxidized in the ocean

• Small amount of marine OM buried in seds– Leaves behind some O2 in atm

• Short-term cycles process a lot of CO2

- 30-50% of atm CO2 consumed per year

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Organic matter

O2 Netproductivity

CO2



Organic matter

O2 Netproductivity

CO2

CO2

O2Uplift and kerogenoxidation



Organic matter

O2 Netproductivity

CO2

CO2

O2Uplift and kerogenoxidation

CO2 H2O CH2OO2

Long term org C cycles

• Millions of years

• Components include: OM in sediments, fossil fuels, atm O2 versus CO2

• Burial of OM from Short-term cycle– Inc P and T; most ends up as kerogen,

– Some winds up in fossil fuels (oil, coal)

– OM in shale is largest reservoir on earth (long )

• Removal balanced by kerogen oxidation/weathering

• Affects atm O2

– Net burial leaves O2 in the atm

2Fe2O3 16Ca2 16HCO3 8SO4

2 4FeS2 16CaCO3 8H2O15O2

CO2 H2O CH2OO2

Produced by bacterial sulfate reduction - linked to carbon oxidation

Also linked to pyrite burial/oxidation which requires OMas an intermediate to catalyze the sulfate reduction

O2 in atm controlled by a balance between pyrite and OM burial in seds and later oxidation on landWithout this balance atm O2 would increase to 150% of presentLevels and depletion of atm CO2 in < 10,000 years (see text)

Long-term inorg C cycle• 100’s of millions of years

• Balance between weathering and plate tectonics– Weathering silicate rocks consumes CO2, transferred to the

ocean as bicarb, removal of bicarb by organisms & calcite, burial in seds, subduction, vulcanism (also affects other cations – Ca, Mg, Na)

• Cycle is a balance between weathering (takes up CO2) and tectonics (releases CO2)

• Plate tectonics – more vigorous then more CO2 release

• Climate sensitivity (weathering)

CO2 removalBicarbonate transport

CaCO3 ppt.

CaCO3

Figs. 8-17

(“regenerates” CO2)(“regenerates” CO2)

Short-term

Long term (organic)

Long term (inorganic/tectonic)

Onset of modern plate tectonics “turns this on”

“adds” back CO2

Link with short term C cycleIn surface oceans

Increase in surface temperature due to increase in solar luminosityDrop in CO2 by increased weathering at higher tempDecrease greenhouse – increase ppt of carbonates?

Bob Berner’s calculations of changes in CO2 over the Phanerozoic


“Hot” houses


“Hot” houses

“Ice” houses

Fig. 8-18

Effect of humans• Pre-industrial

– Steady state on decadal to century timescales

– Ocean a net source of CO2

• Neutralizes river bicarb and oxidation of OM from rivers

– Burial of org C• That which escaped oxidation and marine OM

• Humans– Oceans a sink for CO2

– Increase sediment and nutrient load to rivers/ocean

– Eutrophication, hypoxia, denitrification

Fig. 10-16 A portion of the biogeochemical cycles of inorganic carbon (Cing) and organic carbon (Corg), nutrient N and P, and suspended solids (SS) in the land–ocean system. (a) Geological, long-term system; (b) one possible situation today. In (b), the fluxes of organic and inorganic carbon and suspended solids to the seafloor are increased over their pristine geological values in (a). These increases are due to human activities. Notice the net heterotrophic nature of the ocean giving rise to a net flux of carbon dioxide to the atmosphere prior to human interference in the carbon cycle. Now more carbon dioxide enters the ocean because of the burning of fossil fuels and deforestation practices (see Chapter 12). Fluxes are in millions of tons of C, N, P, and suspended solids per year. (After Wollast and Mackenzie, 1989.)

Corg (terr.)400

Cing

400

CO2

oxidation

rxn. (1)

Cing

140

360 200

All fluxes are millions of tons of C per year

The Ocean

100 (net; approx.50,000 (r) - 50,100(pp))

Riverine inputs

Ca2 2HCO3 CaCO3 CO2 H2Orxn. (1)

200

460 (net)

Burial in sediments

Corg (marine +terr)

Fossil fuel burning

• Transferring large amounts of CO2 from rock cycle to atm with no equivalent rapid uptake mechanisms!– Ocean uptake limited by the biological pump (nuts)

– Uptake by terr. systems not rapid enough

– Accumulates in atm

• How does increase affect climate?– Depends on time scales of increase in atm conc versus time

scales of changes in earth’s heat balance (via its circulatory system)

– Positive and negative feedback responses

N and P Cycles

Global nitrogen reservoirs, fluxes and turnover times. Major reservoirs are underlined, pool sizes and fluxes are given in Tg (1012 g) N and Tg N yr-1. Turnover times (reservoir divided by largest flux to or from reservoir ) are in parentheses.

80 y-1

Atmosphere

120 (NF) 98 (DN)

Land

172 (DN)121 (NF)

27 (RT)Oceans

The Pre-Industrial N Cycle (fluxes = Tg N/yr)(1860’s numbers from Galloway et al., 2004)

Global sea level

Shelf denitrification

Area of continental shelves

Oceanic fixed-Ninventory

Oceanic primaryproductivity

Atmospheric CO2

Greenhouse effect Ice volume

(+)

Fig. 14-13 The iron fertilization hypothesis for the intensification of the biological pump during glaciations.

Stimulates N-fixation

Atmosphere

Terrestrial Ecosystems

Aquatic Ecosystems

Human Activities Groundwater Effects

Surface waterEffects

CoastalEffects

StratosphericEffects

EnergyProduction

PM &VisibilityEffects

OzoneEffects

Agroecosystem EffectsNHx

FoodProduction

NOx

NOx

Crop Animal

People (Food; Fiber)

Soil

NO3

The Nitrogen Cascade

NH3

--Indicates denitrification potential

Norg

Forests &Grassland

Soil

OceanEffects

N2O

GHEffects

N2O

Anthro. N fixation = 140 Tg N/yr

Retained in soils or denitrified

≈ 100 yr)

- 41- 8.5

- 9 -3.461.9 Tg N/yr

3.4 x (14 to 32) = 50-110~80 Tg N/yr missing ?

NOx emissions contribute to OH, which defines the oxidizing capacity of the atmosphere

NOx emissions are responsible for tens of thousands of excess-deaths per year in the United States

O3 and N2O contribute to atmospheric warming

N2O emissions contribute to stratospheric O3 depletion

Nr and the Atmosphere

• Surface water acidification– Tens of thousands of lakes and

streams

– Biodiversity losses

• As reductions in SO2 emissions continue, Nr deposition becomes more important.

Nr and Freshwater Ecosystems

Nr and Coastal Ecosystems• Increased algal productivity

• Shifts in community structure

• Harmful algal blooms

• Degradation of seagrass and algal beds

• Formation of nuisance algal mats

• Coral reef destruction

• Increased oxygen demand and hypoxia

• Increased nitrous oxide (greenhouse gas)

Sybil Seitzinger, 2003

There are significant effectsof Nr accumulation within each

reservoir

These effects are linked temporallyand biogeochemically in the

Nitrogen Cascade

Atmosphere


Aquatic Ecosystems

Human Activities


FoodProduction

Crop Animal


Soil


Norg

Galloway et al., 2003a

Atmosphere


Aquatic Ecosystems



CoastalEffects



FoodProduction

Crop Animal


Soil


NH3

Norg

Forests &Grassland

Soil

OceanEffects


Atmosphere


Aquatic Ecosystems



CoastalEffects



FoodProduction

Crop Animal


Soil

NO3


NH3

Norg

Forests &Grassland

Soil

OceanEffects


Atmosphere


Aquatic Ecosystems



CoastalEffects

EnergyProduction


OzoneEffects


FoodProduction

NOx

NOx

Crop Animal


Soil

NO3


NH3

Norg

Forests &Grassland

Soil

OceanEffects


Atmosphere


Aquatic Ecosystems



CoastalEffects

EnergyProduction


OzoneEffects


FoodProduction

NOx

NOx

Crop Animal


Soil

NO3


NH3


Norg

Forests &Grassland

Soil

OceanEffects

Atmosphere


Aquatic Ecosystems



CoastalEffects

StratosphericEffects

EnergyProduction


OzoneEffects


FoodProduction

NOx

NOx

Crop Animal


Soil

NO3


NH3


Norg

Forests &Grassland

Soil

OceanEffects

N2O

GHEffects

N2O

Ind. N fix.

PopulationCrop N fix.

Total react. N

Fossil fuel N F

Fig. 10-16 A portion of the biogeochemical cycles of inorganic carbon (Cing) and organic carbon (Corg), nutrient N and P, and suspended solids (SS) in the land–ocean system. (a) Geological, long-term system; (b) one possible situation today. In (b), the fluxes of organic and inorganic carbon and suspended solids to the seafloor are increased over their pristine geological values in (a). These increases are due to human activities. Notice the net heterotrophic nature of the ocean giving rise to a net flux of carbon dioxide to the atmosphere prior to human interference in the carbon cycle. Now more carbon dioxide enters the ocean because of the burning of fossil fuels and deforestation practices (see Chapter 12). Fluxes are in millions of tons of C, N, P, and suspended solids per year. (After Wollast and Mackenzie, 1989.)

Sulfur cycle

• N is the limiting nutrient in most temperate and polar ecosystems

• Nr deposition increases and then decreases forest and grassland productivity

• Nr additions probably decrease biodiversity across the entire range of deposition

Nr and Terrestrial Ecosystems

Sulfate

Pyrite burial

Pyrite uplift and weathering

Hydrothermal uptake



CO2 H2O CH2OO2

H2S

SO2

H2S

Sulfate

SO2

DMS

H2S

SO2 SO2

SO2

DMS

Sulfate

H2S

Ash and debris from volcanic eruptions

William Turner, “The fighting Téméraire tugged to her last berth to be broken up” (Tambora)

Edvard Munch “The Scream” (possibly inspired by Krakatoa)

Clouds Temp.

Cloud condensationnuclei

DMS Plankton

(+)

(+)

? (+/-)

(+)

(neg. feedback; reflectivity)

The CLAW Hypothesis

Fig. 14-18

Fig. 14-19

global carbon cycle. why study the c cycle? key element of life – so fundamental –fossil fuel...

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