Reference no: EM133192274 , Length: Word count: 4 Pages

Assignment Problem 1: There are 760 Gtons of carbon atoms in the form CO2 in the atmosphere. Every year, 60 Gtons of carbon are "fixed" into plants by the process photosynthesis.

Question:

a. How many years would it take to remove all of the CO2 from the atmosphere if photosynthesis were to continue to fix carbon dioxide at a rate of 60 Gtons yr-1?

b. Plants also respire and, when they die, they decompose. This process also occurs at a rate of 60 Gton yr-1. If photosynthesis were somehow to be shut off, how long would it take to produce 760 Gtons of carbon in the form of CO2 in the atmosphere (i.e., now long would it take to produce 760 Gtons, which would cause CO2 in the atmosphere to double)?

c. We determined that fossil fuel consumption and deforestation (mainly "slash and burn" agricultural practices) produces 3.3 Gtons yr-1 of carbon. This represents an additional source of CO2 to the atmosphere such that removal by photosynthesis is not perfectly balanced by reemission of CO2 to the atmosphere by respiration and decay.

How long will it take to double the present amount of CO2 (i.e., add an additional 760 Gtons) if humans continue to produce this additional 3.3 Gtons yr-1?

Assignment Problem 2: There is an enormous amount of organic ("fixed") carbon buried in sediments - about 10,000,000 Gtons (or 107 Gtons). Some of this is in the form of fossil fuels (mainly coal). Plate tectonics slowly buries carbon in sediments at the bottom of the ocean at a rate of 0.05 Gton yr-1.

a. Assuming this rate of burial has remained constant, how long did it take to produce the amount of organic carbon that is currently buried in sediments?

b. It is believed that extractable fossil fuels represent about 0.2% of all of the organic carbon buried in sediments, or about 20,000 Gtons. Humans are presently burning fossil fuels at the rate of 7.6 Gton yr-1. At this rate, how long would it take to use up all of the extractable fossil fuels buried in sediments?

c. If all of these 'fuels' were to be burned and emitted to the atmosphere as CO2, how much CO2 would there be in the atmosphere? (Don't forget the current amount of carbon in the atmosphere - 760 Gtons.)

d. Convert the value in 2c above to ppm using the relationship 1 GtonC = 0.45 ppm CO2. Recall that in the movie "Crude: The Incredible Journey of Oil", we learned that if atmospheric abundances of CO2 reach 1200-1400 parts per million the polar ice caps will likely melt and deep water formation will cease, leading to an oceanic anoxic event.

Is the amount of CO2 you determined in Part 2c more or less than the amount necessary to trigger an oceanic anoxic event?

Assignment Problem 3: Photosynthesis in the oceans takes up ("uptake") 90 Gtons yr-1 of carbon from the atmosphere and respiration and decay ("rerelease") return 88 Gtons yr-1 of carbon back to the atmosphere.

a. Assuming the imbalance between uptake and rerelease remains the same over long periods of time, how long would it take to remove the excess 20,000 Gtons of organic carbon in the deep ocean? Note - we call the process of transporting organic carbon from the surface of the ocean to the deep ocean the biological pump.

b. If the oceans become anoxic, release of carbon back to the atmosphere ceases (i.e., the 88 Gtons yr-1 of rerelease essentially drops to zero). If this were to occur, how long would it take to remove the excess 20,000 Gton of CO2 from the atmosphere in return it to the deep ocean (i.e. how long would it take to remove 20,000 Gtons of carbon from the atmosphere)? We can consider this the shortest time possible to restore balance back to the organic carbon cycle.