Please read the Paper by Graven (2016) - to be discussed 13.04 Link to the paper pdf here
13.04 The global carbon cycle - link to lecture notes here
Questions for class -- lecture will help in explaining details
1) How do we know that the CO2 accumulating in the atmosphere is coming mostly from burning fossil fuels?
2) What processes in oceans and on land remove excess CO2 out of the atmosphere?
3) How big are theses net C sinks compared to changes in emissions proposed in international climate agreements?
4) How might climate change alter ocean and land C sinks? (give one positive and one negative feedback as examples)
28.04 == NO CLASS (See Reading and questions for the methane cycle)
04.05 == NO CLASS (Reading for the methane cycle)
1) Name an important negative feedback between the rock cycle and atmospheric CO2 for inorganic C and organic C? How does it work?
2) Why do we think it is reasonable that the early atmosphere had relatively high atmospheric CO2 compared to today?
3) What happened to the CO2 that was initially in the atmosphere over geologic time? (The main source of CO2 on long timescales is volcanism. The main sinks are the rate of burial of organic matter and precipitation of calcium carbonate in the oceans. Have the ratios of these two burial mechanisms varied over time and how can we use isotopes to know? )
4) The model described in the paper is very complex – for a simplified form, take a look at the the online GEOCARB model - see: this link
Try the following:– set “Transition spike” to zero, and change the CO2 degassing rate from 1.5 to 11.5 x 1012 mole/year. How does atmospheric pCO2 vary? Does the ratio of weathering of C to organic C vary? What happens if you turn on plants (and why?)?
5) The earth has been cold enough for ice sheets to form on land only a few times in its history. We are currently in such an “icehouse” climate now. This is also accompanied by very low (in terms of earth’s history) CO2 concentrations. What is one explanation given for the low CO2 in the last millions of years?
1) What is some evidence for a lack of free O2 in the atmosphere before 2.2 Billion years ago?
2) How is the O2 cycle linked to the cycles of other elements like Sulfur and Iron (Fe)?
3) What information do we get from the speciation of trace elements (Molybdenum and Chromium?)
4) What is the ‘biological pump? And how have element distributions with ocean depth changed over time and with O2 availability>
5) What are the main processes controlling the atmospheric O2 levels over the past ~ 2 billion years?
6) Why is a certain amount of O2 thought to be necessary for the development of animals and plants?
1) In what ways does methane impact the earth system? (why is it important?)
How has the mixing ratio of methane changed over time?
2) What are the main natural sources and sinks of methane?\\ 3) How much of the methane produced in wetlands and sediments makes it to the atmosphere?
4) What is the ‘lifetime’ of methane in the atmosphere? \\ 5) What does the difference in methane mixing ratio between northern and southern hemispheres tell us about the evolution of sources and sinks over time?
6) How have humans altered the methane cycle? 7) What are the possible causes of the changes in methane accumulation in the atmosphere from the 1990s to 2000s to now and what lines of evidence are used to support arguments for ro against:
- changes in methane sink (OH) - changes in agricultural sources - changes in fossil sources
1) What are the major forms of delivery of Fe to the oceans? Why is the form of Fe delivery important?
2) How do sources of Fe in the oceans differ from coastal regions to the deep ocean regions far from continents?
3) How do soluble Fe concencentrations vary with depth in the ocean (what is a “nutrient-like’ profile?
4) What is a ‘limiting nutrient”? In what parts of the ocean is Fe thought to be a limiting nutrient?
5) How has Fe been proposed as a ‘geoengineering’ solution to global warming? (and why is it implicated in glacial to interglacial CO2 change in the atmosphere?)
6) Why is Fe limitation considered for the ocean but not for land?
P cycle questions:
1) What is the “Walker and Syers” model of how P varies with time of soil development?
2) How are the Fe and P cycles linked? Can dust be important in both cycles?
3) How have plants devised methods to increase their supply of P?
4) How have humans altered the global P cycle, and what is the major impact?
5 ) What is the major evidence that the P cycle has changed with time?
015.06 Stoichiometry of N and P
Reading: Imbalance in N an P
1) In your own words, how do you interpret the concept of element imbalance?
2) Given the current changes in the stoichiometry of N:P inputs to terrestrial ecosystems, what pattern can we expect in a resource-consumer plot?
3) What are potential consequences of not enough available P to supply the demand of terrestrial ecosystems under higher CO2 and N deposition?
4) Why is the conceptual framework of 'ecological stoichiometry' useful to study element imbalances in the Earth system?
5) What are potential strategies of living organisms to maintain a homeostatic stoichiometry in their internal bodies?
6) How would global biogeochemical cycles differ if all living organisms on Earth would have either a complete homeostatic or a 'you are what you eat' strategy?
22.06 The Nitrogen Cycle
Reading: The Evolution and Future of Earth’s Nitrogen Cycle