Introduction to carbon
Why are we talking about carbon?
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What is the link with the project?
What will you learn?
Know the different resevoirs of carbon and how the carbon cycle works.
Know the anthropogenic causes of the disruption of the carbon cycle.
The competences developed are :
systemic thinking
critical thinking
What is carbon?
Définition :
“Carbon : the building block of life. You may have heard this sentence, but have you fully considered what it really means? All living things are made of elements, the most abundant of which are, oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. Of these, carbon is the best at joining with other elements to form compounds necessary for life, such as sugars, starches, fats, and proteins. Together, all these forms of carbon account for approximately half of the total dry mass of living things.”
 | Carbon atom model, diamond and graphite (Sundqvist, 2021) |
Figure : Phase diagram of carbon taken from
Reminder : Earth’s Layers
Carbon Reservoirs
The concept of reservoir
Carbon reservoirs
 | The global carbon-cycle showing the different reservoirs for carbon and the exchanges between reservoirs in GT (109) . The arrows represent natural processes of carbon transfer between atmosphere and earth. |
Reservoir 1 : Atmosphere
Reservoir 2 : Ocean
2⁄3 of the Earth’s surface.
store and transporte heat.
making the atmosphere warm and moist.
enable life to flourish in the sea and on land.
CO2 (aqueous),
H2CO3 (carbonic acid),
HCO3− (bicarbonate ion),
CO32− (carbonate ion).
DIC = [CO2(aq)] + [H2CO3] + [HCO3−]+ [CO32−]
Reservoir 3: Solid carbonates or carbonates rock
Calcite or calcium carbonate, CaCO3
 | Photographs of typical seep carbonate rocks. |
 | Layers of sedimentary rock in Makhtesh Ramon |
Xi, Shichuan, Xin Zhang, Zengfeng Du, Lianfu Li, Bing Wang, Zhendong Luan, Chao Lian, et Jun Yan. 2018. « Laser Raman Detection of Authigenic Carbonates from Cold Seeps at the Formosa Ridge and East of the Pear River Mouth Basin in the South China Sea ». Journal of Asian Earth Sciences 168 (décembre) : 207‐24. https://doi.org/10.1016/j.jseaes.2018.01.023
Reservoir 4: Biomass (oceanic and continental)
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Graphical representation of the global biomass distribution by taxa.
Bar-On, Yinon M., Rob Phillips, et Ron Milo. 2018. « The Biomass Distribution on Earth ». Proceedings of the National Academy of Sciences 115 (25): 6506‐11. https://doi.org/10.1073/pnas.1711842115.
Reservoir 5 : Soil
 | 950 GtC is inorganic carbon. |
 | Credit: Antonio Jordán (distributed via imaggeo.egu.eu) 1500 Gt is organic carbon. |
 | Dignac, Marie-France, Delphine Derrien, Pierre Barr , S bastien Barot, Lauric C cillon, Claire Chenu, Tiphaine Chevallier, et al. 2017. Increasing Soil Carbon Storage: Mechanisms, Effects of Agricultural Practices and Proxies. A Review . Agronomy for Sustainable Development 37 (2) : 14. https://doi.org/10.1007/s13593-017-0421-2. Organic matter turnover (EN) = renouvellement de la matière organique (FR) shoots (EN) = pousses (FR) |
 | Figure : Soil carbon (C) cycle through the microbial loop. Carbon dioxide (CO2) in the atmosphere is fixed by plants (or autotrophic microorganisms) and added to soil through processes such as ❶ root exudation of low-molecular weight simple carbon compounds, or deposition of leaf and root litter leading to accumulation of complex plant polysaccharides. ❷ Through these processes, carbon is made bioavailable to the microbial metabolic “factory” and subsequently is either ❸ respired to the atmosphere or ❹ enters the stable carbon pool as microbial necromass. The exact balance of carbon efflux versus persistence is a function of several factors, including aboveground plant community composition and root exudate profiles, environmental variables, and collective microbial phenotypes [i.e., the metaphenome (19)]. Naylor, Dan, Natalie Sadler, Arunima Bhattacharjee, Emily B. Graham, Christopher R. Anderton, Ryan McClure, Mary Lipton, Kirsten S. Hofmockel, et Janet K. Jansson. 2020. « Soil Microbiomes Under Climate Change and Implications for Carbon Cycling ». Annual Review of Environment and Resources 45 (1): 29‐59. https://doi.org/10.1146/annurev-environ-012320-082720. |
Reservoir 6 : Kerogen
 | Figure. Photomicrograph of kerogen. This is the sapropelic Kimmeridge Coal (Upper Jurassic) from Dorset, UK. Cross-sections of bivalves are ubiquitous, and carbonized plant detritus is also visible. Reproduced with permission from Selley RC (2000) Applied Sedimentology, 2nd edn. London: Academic Press. |
 | Structure of a vanadium porphyrin compound (left) extracted from petroleum by Alfred E. Treibs, father of organic geochemistry. The close structural similarity of this molecule and chlorophyll a (right) helped establish that petroleum was derived from plants |
Kvenvolden, Keith A. 2006. « Organic Geochemistry – A Retrospective of Its First 70 Years ». Organic Geochemistry 37 (1): 1‑11. https://doi.org/10.1016/j.orggeochem.2005.09.001.
Reservoir 7 : Mantle
Carbon cycle
Short cycle
Carbon cycle : Short cycle part 1
SHORT CYCLE
Hydrosphere - atmosphere exchanges
Dissolution of atmospheric CO2 in the ocean and degassing of CO2 from the ocean to the atmosphere
Exchange of 300 GT of CO2 per year ;
Residence time = quantity of the element in the reservoir / sum of the flows of contribution in the reservoir.
Video to watch :
Henry's Law and Gas Solubility Explained https://www.youtube.com/watch?v=9JtTpPEesOk
At constant temperature and saturation, the partial pressure in the vapor phase of a volatile solute is proportional to the mole fraction of that body in the liquid solution.
So the higher the temperature, the less CO2 is soluble, and the more carbon is redistributed to the atmosphere.
For a given amount of carbon in the ocean+atmosphere, the amount of CO2 in the atmosphere increases if the temperature increases.
CO2 control : CO2 balance in the hydrosphere
DIC = [CO2(aq)] + [H2CO3] + [HCO3−]+ [CO32−]
Carbon cycle : Short cycle part 2
Diversion and leakage in the hydrosphere-atmosphere physical exchanges
There is a diversion of carbon flux from the atmosphere to the ocean through the weathering of rocks.
To know more about weathering of rocks : https://www.youtube.com/watch?v=sk B_A2sfBcY
There is a leakage of carbon from the hydrosphere to the lithosphere : the formation of carbonates.
Calcium carbonate solubility
 | Ω > 1 Precipitation Ω = 1 Equilibrium Ω < 1 Dissolution Modern Sea Surface Ω ≈ 2-5 Sea surface is supersaturated with respect to CaCO3, but calcium carbonates are not constantly precipitating. |
To precipitate calcium carbonate :
 | Woosley, Ryan J. 2018. « Carbonate Compensation Depth ». In Encyclopedia of Geochemistry, édit par William M. White, 204‑5. Encyclopedia of Earth Sciences Series. Cham: Springer International Publishing. https://doi.org/10.1007/978-3-319-39312-4_85. |
Carbon cycle : Short cycle part 3
Photosynthesis and respiration
From atmosphere to biomasse continental and oceanic
 | Photosynthesis 440 Gt of CO2 per year, shared equally between the oceans and the continents. |
From biomass to atmosphere
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Aerobic respiration chemical reaction :
Carbon cycle : Short cycle part 4
Organic carbon leakage to lithosphere :kerogen formation
 | Figure : Organic carbon cycle with the flow of kerogen (black solid lines) and the flow of biospheric carbon (green solid lines) showing both the fixation of atmospheric CO2 by terrestrial and marine primary productivity. The combined flux of reworked kerogen and biospheric carbon into ocean sediments constitutes total organic carbon burial entering the endogenous kerogen pool (Galy et al., 2015; Hedges and Oades, 1997). |
Conclusion of the short cycle
Long cycle
Long carbon cycle
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Berner, Robert A. 2003. « The Long-Term Carbon Cycle, Fossil Fuels and Atmospheric Composition ». Nature 426 (6964): 323‐26. https://doi.org/10.1038/nature02131. |
 | CO2 + CaSiO3 <->CaCO3 + SiO2 Contact Metamorphism Vs. Regional Metamorphism https://www.geologypage.com/ |
Trap rock forming a characteristic pavement, Giant's Causeway, Northern Ireland (left)
Three Devil's Grade in mid-Moses Coulee , USA (right)
Anthropogenic activities and carbon cycle
Disruption of the carbon cycle-causes
Observation of disruption of the carbon cycle
 | “Recent increases in global averaged temperature over the last decade already appear to be outside the normal variability of temperature changes for the last thousand years. A number of different analyses strongly suggest that this temperature increase is resulting from the increasing atmospheric concentrations of greenhouse gases, thus lending credence to the concerns about much larger changes in climate being predicted for the coming decades.” (Wuebbles, 2001) |
Source of the disruption
« Human-related emissions from fossil fuel use have been estimated as far back as 1751. Before 1863, emissions did not exceed 0.1 GtC/year. However, by 1995 they had reached 6.5 GtC/year, giving an average emission growth rate slightly greater than 3% per year over the last two and a half centuries. Recent growth rates have been significantly lower, at 1.8% per year between 1970 and 1995. Emissions were initially dominated by coal. Since 1985, liquids have been the main source of emissions despite their lower carbon intensity. The regional pattern of emissions has also changed. Once dominated by Europe and North America, developing nations are providing an increasing share of emissions. »
« Physical processes and feedbacks caused by land-use change, that may have an impact on the climate, include changes in albedo and surface roughness, and the exchange between land and atmosphere of water vapour and greenhouse gases [see section 4, chapter 7]. [...] Land-use change may also affect the climate system through biological processes and feedbacks involving the terrestrial vegetation, which may lead to changes in the sources and sinks of carbon in its various forms [see chapter 3)]. »
(IPCC, 2001)
Disruption of the carbon cycle-environmental issues
Consequences on the Earth System
Figure: Schematic representation of negative (a: regulating effect on the system) and positive (b: runaway effect on the system) feedback loops. An arrow with a "+" indicates a positive correlation between the two variables, and an arrow with a "-" indicates a negative correlation. |  |
Feedback loops
Feedback loop 1 |  |
Feedback loop 2 |  |
Feedback loop 6 |  |
Feedback loop 6 : focus biodiversity
Climate change = main cause of biodiversity loss
Preserving biodiversity = mitigating climate change
/!\ technological solutions to mitigate climate change can have negative impacts on biodiversity
Same causes: our socio-economic way of life
Anthropocene Atlas, Gemenne
Interesting source : https://ipbes.net/sites/default/files/2021-06/20210609_workshop_report_embargo_3pm_CEST_10_june_0.pdf
Disruption of the carbon cycle-social issues
Social impacts
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El-Hinnawi (1985): |  |
Définition : Climate Refugees
1951 Refugee Convention: refugee = from political persecution (UN)
“Climate Change Displaced People” : people whose habitat is threatened or is already at risk of being extinguished due to climatic change (Hodgkinson et al., 2009)
“Climate refugees” or “forced climate migrants”
Britannica, The Editors of Encyclopaedia. "Darfur". Encyclopedia Britannica, Invalid Date, https://www.britannica.com/place/Darfur. Accessed 15 September 2021.
The complex ethnic distinctions in Darfur are perhaps less important than the contrast between agriculturalists and pastoralists. The relationship between the two is governed by competition for land and water resources, which can be affected by short- and long-term climate change (whether random, cyclical or greenhouse-induced), both in terms of absolute availability and geographical extent of the resources. Jeffrey Mazo (2009) Chapter Three : Darfur : The First Modern Climate-ChangeConflict, The Adelphi Papers, 49:409, 73-86, DOI: 10.1080/19445571003755538 |  |
Définition : Armed Conflicts
3 elements (Sakaguchi, 2017):
There are correlation between climate change and
violence but no robust conclusion.
There are weak empirical support to the link between climate change and violence
Methodologies used in the different students have an impact on results
« Migration is generally considered to be the intermediate stage which links environmental degradation and disasters to conflict (Homer Dixon, 1991 and 1994) »
(Assessing the Impact of Climate Change on Migration and Conflict, Raleigh)
Conclusion
Scheffran, 2012 based on Scheffran, 2009