Carbon Cycle Adapted in part from lectures by Dr. Gerardo Chin-Leo, TESC, and Dr. Richard Gammon, UW-Seattle 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

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Global Carbon Cycle Sabine et al. (2004) SCOPE Ocean sequester ~30% of fossil fuel CO 2 Human perturbations overlay large natural background C cycle Climate responses and feedbacks of ocean C sink not well known

Average Surface Water DIC Increase in 2000 ~ 1.2 µmol kg -1 yr -1 Under IPCC “Business as Usual”the pH of surface sea water drops by 0.4 pH units by CO 3 = in surface water drops by 54% from pre- industrial values Hatfield Seminar

Air Increase = 1.48 ± 0.05 µatm yr -1 ; Seawater Increase = 2.48 ± 0.28 µatm yr -1 Dore et al., (2003) Dore et al., (2003)

Feedback Loop Linking Glaciations, Atmospheric CO 2 and Phytoplankton C-burial Interglacial Period Small Ice Caps Large Exposed Continental Mass More Nutrients to the Sea From Land Erosion High Productivity High C-Burial Low CO 2 Cool Temperatures Ice Age Large Ice Caps Small Exposed Continental Mass Few Nutrients to the Sea From Land Erosion Low Productivity Low C-Burial High CO 2 Warm Temperatures

Atmospheric O 2 and the C Cycle

WOCE/JGOFS/OACES Global CO 2 Survey ~72,000 sample locations collected in the 1990s DIC ± 2 µmol kg -1 TA ± 4 µmol kg -1 Sabine et al (2004).

Because the ocean mixes slowly, half of the anthropogenic CO 2 stored in the oceans is found in the upper 10% of the ocean. Sabine et al. Science (2004) Global Anthropogenic CO 2 Inventory = 118±19 Pg C

Column inventory of anthropogenic CO 2 that has accumulated in the ocean between 1800 and 1994 (mol m -2 ) Mapped Inventory 106±17 Pg C + marginal seas 6± 6 Pg C + Arctic Ocean 6± 6 Pg C Total Inventory 118±19 Pg C Sabine et al. Science (2004)

Over the past 200 years, the ocean has been the only reservoir to consistently take up anthropogenic CO 2 from the atmosphere. Carbon Changes Between 1800 and 1994 Sabine et al. Science (2004)

Aragonite and Calcite Saturation Depths in the Global Oceans

From Riebesell et al. Nature (2001) Scanning electron micrographs of Emiliania huxleyi (left) and Geophyrocapsa oceanica (right) under conditions of 300 (top) and ppm (bottom) pCO 2 showing malformed coccospheres at the higher CO 2 levels Hatfield Seminar

Coccolithophores calcite Corals NOAA Forams Calcareous algae Nancy Sefton T. Tyrrel calcite High-Mg calcite aragonite 2004 Hatfield Seminar

Pteropods Clio pyramidata Victoria J. Fabry R. W. Gilmer and G. R. Harbison Cavolinia tridentata aragonite R. W. Gilmer and G. R. Harbison The effects of increased levels of CO 2 on the dissolution of Clio pyramidata shells after 4 and 48 hours of exposure Hatfield Seminar

From: R. Buddemeier

Isotope composition of carbonate sediments reveals the net production of O 2 Photosynthesis selects C 12 over C 13, thus organic material is depleted (isotopically lighter) in C 13 During times of increased net O 2 production, more organic C is buried, thus atmospheric and oceanic C becomes richer (isotopically heavier) in C 13 This enrichment of C 13 in the environment is reflected in carbonate sediments Assuming a constant total mass of C 13 and C 12, the faster the organic C is buried (more O 2 accumulates) the heavier (enriched C 13) the carbonates become

 13 C Isotope Signature Scale (Del)  C 13 in ‰ (C 13 / C 12 ) sample - (C 13 / C 12 ) standard = X 1000 (C 13 / C 12 ) standard Example: [( – )/ ]*1000 = 1.78 ( C 13 / C 12 ) 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 O 2 in the atmosphere There is evidence for the existence of forests dating back to ~360 mya. These forests need O 2 to exist There is evidence of forest fires ever since (charcoal in sediment) Forest fires cannot occur if O 2 < 13% If O 2 > 35% fires burn so fiercely that all forests would have disappeared Consequently, O 2 is believed to have remained in the range of 13-35% (current concentration is 21%)

13 C as an Indicator of Ancient CO 2 Levels 13 C is taken by plants slower than 12 C. Thus organic matter is depleted in 13 C compared to CO 2. However, when CO 2 concentrations are low, plants do not discriminate 13 C from 12 C as much as when CO 2 levels are high. Thus, the 13 C: 12 C ratio in organic matter under low CO 2 levels is higher (more 13 C relative to 12 C) than during times of high CO 2 levels (more 13 C relative to 12 C).

Use of 13 C in Ecology 13 C is fractionated (or discriminated) by physical processes (e.g evaporation/precipitation). There is less 13 C in atmospheric CO 2 than in dissolved CO 2 (bicarbonate) Consequently land plants are isotopically lighter than aquatic plants There is another fractionation of 13 C 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  - 13 C signatures.

Through condensation-evaporation, water gets isotopically “lighter” as it moves to higher latitudes. Polar ice is depleted in 18 O.

18 O indicates ancient ice volumes and temperatures Volume: Evaporation/precipitation and formation of polar ice excludes 18 O. During ice ages the concentration of 18 O in the oceans increases. Benthic foraminifera fossils show the 18 O: 16 O of ancient seawater Paleothermometer: the formation of CaCO 3 by foraminifera excludes 18 O as a function of temperature. Benthic foraminifera form shells under constant temperature thus their 18 O: 16 O reflects the isotope composition of the water. Planktonic foraminifera experience temperature fluctuations and these are recorded as changes in their 18 O: 16 O relative to benthic forms

Relationship Between 18 O Content and Temperature Water  18 O is derived from benthic (deep) foraminifera. Carbonate  18 O is derived from planktonic foraminifera

From: Introduction to Marine Biogeochemistry -Libes (1992)

Evidence that Increasing Atmospheric CO 2 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 14 C: 12 C in CO 2 by the input of “old” carbon from fossil fuel burning (Higher 14 C when lower solar magnetic activity shields Earth less from incoming cosmic rays)

Lower recent C 14 /C 12 from fossil fuel burning Evidence of anthropogenic source for greenhouse gases Little Ice Age: low solar magnetic activity throughout?

Solar magnetic activity and C 14 production Cosmic rays excite N 14 → decays to C 14 Solar max: magnetic solar wind sweeps away cosmic rays → less *N 14 → less C 14

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 CO 2 is the same, whether it comes from a Porsche or your lungs – anthropogenic CO 2 does no extra harm There’s 30 times as much natural CO 2 as man-made Water vapor is the dominant greenhouse gas, so why worry so much about CO 2 ? We can’t do anything about water vapor, so Kyoto targeting CO 2 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 CO 2 as they can – currently about half, increasingly less