Carbon CycleAdapted in part from lectures by Dr. Gerardo Chin-Leo, TESC

Chautauqua UWA-6, Dr. E.J. Zita

9-11 July 2007

Fire, Air, and Water: Effects of the Sun, Atmosphere, and Oceans in

Climate Change and Global Warming

Milankovitch Mechanism is not a complete explanation for glaciation cycles…

Evidence for carbon feedback contribution to long-term climate regulation

Feedback Loop Linking Glaciations, Atmospheric CO2 and Phytoplankton C-burial

Interglacial PeriodSmall Ice CapsLarge Exposed

Continental Mass

More Nutrients to the SeaFrom Land ErosionHigh Productivity

High C-Burial

Low CO2

Cool Temperatures

Ice AgeLarge Ice CapsSmall Exposed

Continental Mass

Few Nutrients to the SeaFrom Land Erosion

Low ProductivityLow C-Burial

High CO2

Warm Temperatures

Chemistry of Inorganic C in WaterCarbonate buffering and pH

• CO2 + H2O <---> H2CO3- (carbonic acid)

• H2CO3 <---> H+ + HCO2- (bicarbonate)

• HCO3- <---> H+ + CO32+ (carbonate)

Atmospheric O2 and the C Cycle

Isotope composition of carbonate sediments reveals the net production of O2

• Photosynthesis selects C12 over C13, thus organic material is depleted (isotopically lighter) in C13

• During times of increased net O2 production, more organic C is buried, thus atmospheric and oceanic C becomes richer (isotopically heavier) in C13

• This enrichment of C13 in the environment is reflected in carbonate sediments

• Assuming a constant total mass of C13 and C12, the faster the organic C is buried (more O2 accumulates) the heavier (enriched C13) the carbonates become

13C Isotope Signature Scale

(Del) C13 in ‰

(C13/ C12) sample - (C13/ C12) standard

= --------------------------------------------------- X 1000

(C13/ C12) standard

Example:

[(0.001125 – 0.001123)/0.001123]*1000 = 1.78

(C13/ C12) standard is the ratio in a standard sample of the fossil invertebrate Belemnitella americana (Cretaceous Peedee formation in South Carolina)

Evidence for the relative constancy of O2 in the atmosphere

• There is evidence for the existence of forests dating back to ~360 mya. These forests need O2 to exist

• There is evidence of forest fires ever since (charcoal in sediment)

• Forest fires cannot occur if O2 < 13%• If O2 > 35% fires burn so fiercely that all forests would

have disappeared• Consequently, O2 is believed to have remained in the

range of 13-35% (current concentration is 21%)

13C as an Indicator of Ancient CO2 Levels

• 13C is taken by plants slower than 12C. Thus organic matter is depleted in 13C compared to CO2.

• However, when CO2 concentrations are low, plants do not discriminate 13C from 12C as much as when CO2 levels are high. Thus, the 13C: 12C ratio in organic matter under low CO2 levels is higher (more 13C relative to 12C) than during times of high CO2 levels (more 13C relative to 12C) .

Use of 13C in Ecology

• 13C is fractionated (or discriminated) by physical processes (e.g evaporation/precipitation). There is less 13C in atmospheric CO2 than in dissolved CO2 (bicarbonate)

• Consequently land plants are isotopically lighter than aquatic plants

• There is another fractionation of 13C based on the photosynthetic metabolism of the plant (C3, C4 or CAM).

• Consequently organic matter from C3, C4 or CAM plants can be distinguished from each other based on their -13C signatures.

Through condensation-evaporation, water gets isotopically“lighter” as it moves to higher latitudes.

Polar ice is depleted in 18O.

18O indicates ancient ice volumes and temperatures

• Volume: Evaporation/precipitation and formation of polar ice excludes 18O. During ice ages the concentration of 18O in the oceans increases. Benthic foraminifera fossils show the 18O:16O of ancient seawater

• Paleothermometer: the formation of CaCO3 by foraminifera excludes 18O as a function of temperature.

• Benthic foraminifera form shells under constant temperature thus their 18O:16O reflects the isotope composition of the water. Planktonic foraminifera experience temperature fluctuations and these are recorded as changes in their 18O:16O relative to benthic forms

Relationship Between 18O Content and Temperature

Water 18O is derived from benthic (deep) foraminifera.

Carbonate 18O is derived from planktonic foraminifera

From: Introduction to Marine Biogeochemistry -Libes (1992)

Evidence that Increasing Atmospheric CO2 is Anthropogenic

• Increase consistent with onset and development of industrialization

• Magnitude and rate of increase consistent with magnitude and rates of fossil fuels consumption

• Suess effect: Lowering of 14C:12C in CO2 by the input of “old” carbon from fossil fuel burning

(Higher 14C when lower solar magnetic activity shields Earth less from incoming cosmic rays)

Lower recent C14 /C12 from fossil fuel burning

Evidence of anthropogenic source for greenhouse gases

Little Ice Age: low solar magnetic activity throughout?

Solar magnetic activity and C14 production

Cosmic rays excite N14 → decays to C14

Solar max: magnetic solar wind sweeps away cosmic rays → less *N14 → less C14

http://www.nuclearonline.org/newsletter/Oct05.htm

http://www.dsri.dk/~hsv/Noter/solsys99.html

Car & Driver: Global warming is natural

• Earth has been getting steadily warmer since the last ice age – a few more degrees would be nice

• All CO2 is the same, whether it comes from a Porsche or your lungs – anthropogenic CO2 does no extra harm

• There’s 30 times as much natural CO2 as man-made

• Water vapor is the dominant greenhouse gas, so why worry so much about CO2?

• We can’t do anything about water vapor, so Kyoto targeting CO2 is trivial.

Discuss and analyze these claims, given what we now know.

Inconvenient truth: accelerated GW is anthropogenic

Bad news: we can’t do anything about

• Milankovitch cycles

• Increasing solar luminosity

• Increasing solar magnetic activity

Good news:

• We CAN do something about anthropogenic emissions of greenhouse gases

• Oceans and plants will absorb as much CO2 as they can.